Maximal Neighbor Similarity Reveals Real Communities in Networks

PubMed Central

Žalik, Krista Rizman

2015-01-01

An important problem in the analysis of network data is the detection of groups of densely interconnected nodes also called modules or communities. Community structure reveals functions and organizations of networks. Currently used algorithms for community detection in large-scale real-world networks are computationally expensive or require a priori information such as the number or sizes of communities or are not able to give the same resulting partition in multiple runs. In this paper we investigate a simple and fast algorithm that uses the network structure alone and requires neither optimization of pre-defined objective function nor information about number of communities. We propose a bottom up community detection algorithm in which starting from communities consisting of adjacent pairs of nodes and their maximal similar neighbors we find real communities. We show that the overall advantage of the proposed algorithm compared to the other community detection algorithms is its simple nature, low computational cost and its very high accuracy in detection communities of different sizes also in networks with blurred modularity structure consisting of poorly separated communities. All communities identified by the proposed method for facebook network and E-Coli transcriptional regulatory network have strong structural and functional coherence. PMID:26680448

Mesozooplankton respiration and community structure in a seamount region of the eastern South Pacific

NASA Astrophysics Data System (ADS)

Frederick, Leissing; Escribano, Ruben; Morales, Carmen E.; Hormazabal, Samuel; Medellín-Mora, Johanna

2018-05-01

Seamounts in the Juan Fernandez Ridge, as well as in other seamount regions in the eastern South Pacific and in the world oceans, remain poorly studied ecosystems in terms of structure and functioning. Here, community respiration by epipelagic mesozooplankton in three seamounts of the Juan Fernandez Ridge, including the O`Higgins Seamount close to the coastal upwelling zone and two oceanic seamounts near the Juan Fernandez Archipelago ( 33°S-78°W), was assessed. Oxygen consumption by mixed assemblages was estimated using continuous measurements of dissolved oxygen concentration under controlled temperature during onboard, short-term incubations (2-4 h). Mesozooplankton composition was analyzed with a ZooScan device and expressed in terms of community normalized size spectra, and taxa and size diversity (Shannon-Wiener index). Carbon-specific community respiration rates in the upper 100 m layer were in the range of 0.3-1.9 mg O2 m-2 d-1, indicating that up to 3.1% of the mesozooplankton biomass can be respired on a daily basis. The mesozooplankton community was dominated by small-size copepods but the proportions of small copepods, large copepods, and gelatinous zooplankton (mostly salps) changed between the seamounts, in association with modifications in taxa composition, size diversity, and the slope of the size spectrum. Community respiration was significantly correlated to these community descriptors, suggesting the composition of the pelagic community has a direct impact on the total amount of respired-C. Connectivity between the coastal upwelling zone and the Juan Fernandez Ridge region mediated by mesoscale activity, interacting with the seamounts, is suggested as a most important process in controlling zooplankton community structure and in turn community metabolism.

Bacterial density and community structure associated with aggregate size fractions of soil-feeding termite mounds.

PubMed

Fall, S; Nazaret, S; Chotte, J L; Brauman, A

2004-08-01

The building and foraging activities of termites are known to modify soil characteristics such as the heterogeneity. In tropical savannas the impact of the activity of soil-feeding termites ( Cubitermes niokoloensis) has been shown to affect the properties of the soil at the aggregate level by creating new soil microenvironments (aggregate size fractions) [13]. These changes were investigated in greater depth by looking at the microbial density (AODC) and the genetic structure (automated rRNA intergenic spacer analysis: ARISA) of the communities in the different aggregate size fractions (i.e., coarse sand, fine sand, coarse silt, fine silt, and dispersible clays) separated from compartments (internal and external wall) of three Cubitermes niokoloensis mounds. The bacterial density of the mounds was significantly higher (1.5 to 3 times) than that of the surrounding soil. Within the aggregate size fractions, the termite building activity resulted in a significant increase in bacterial density within the coarser fractions (>20 mum). Multivariate analysis of the ARISA profiles revealed that the bacterial genetic structures of unfractionated soil and soil aggregate size fractions of the three mounds was noticeably different from the savanna soil used as a reference. Moreover, the microbial community associated with the different microenvironments in the three termite mounds revealed three distinct clusters formed by the aggregate size fractions of each mound. Except for the 2-20 mum fraction, these results suggest that the mound microbial genetic structure is more dependent upon microbial pool affiliation (the termite mound) than on the soil location (aggregate size fraction). The causes of the specificity of the microbial community structure of termite mound aggregate size fractions are discussed.

Community response of zooplankton to oceanographic changes (2002-2012) in the central/southern upwelling system of Chile

NASA Astrophysics Data System (ADS)

Medellín-Mora, Johanna; Escribano, Ruben; Schneider, Wolfgang

2016-03-01

A 10-year time series (2002-2012) at Station 18 off central/southern Chile allowed us to study variations in zooplankton along with interannual variability and trends in oceanographic conditions. We used an automated analysis program (ZooImage) to assess changes in the mesozooplankton size structure and the composition of the taxa throughout the entire community. Oceanographic conditions changed over the decade: the water column became less stratified, more saline, and colder; the mixed layer deepened; and the oxygen minimum zone became shallower during the second half of the time series (2008-2012) in comparison with the first period (2002-2007). Both the size structure and composition of the zooplankton were significantly associated with oceanographic changes. Taxonomic and size diversity of the zooplankton community increased to the more recent period. For the second period, small sized copepods (<1 mm) decreased in abundance, being replaced by larger sized (>1.5 mm) and medium size copepods (1-1.5 mm), whereas euphausiids, decapod larvae, appendicularian and ostracods increased their abundance during the second period. These findings indicated that the zooplankton community structure in this eastern boundary ecosystem was strongly influenced by variability of the upwelling process. Thus, climate-induced forcing of upwelling trends can alter the zooplankton community in this highly productive region with potential consequences for the ecosystem food web.

Temperature-dependent body size effects determine population responses to climate warming.

PubMed

Lindmark, Max; Huss, Magnus; Ohlberger, Jan; Gårdmark, Anna

2018-02-01

Current understanding of animal population responses to rising temperatures is based on the assumption that biological rates such as metabolism, which governs fundamental ecological processes, scale independently with body size and temperature, despite empirical evidence for interactive effects. Here, we investigate the consequences of interactive temperature- and size scaling of vital rates for the dynamics of populations experiencing warming using a stage-structured consumer-resource model. We show that interactive scaling alters population and stage-specific responses to rising temperatures, such that warming can induce shifts in population regulation and stage-structure, influence community structure and govern population responses to mortality. Analysing experimental data for 20 fish species, we found size-temperature interactions in intraspecific scaling of metabolic rate to be common. Given the evidence for size-temperature interactions and the ubiquity of size structure in animal populations, we argue that accounting for size-specific temperature effects is pivotal for understanding how warming affects animal populations and communities. © 2017 The Authors. Ecology Letters published by CNRS and John Wiley & Sons Ltd.

Habitat structure and body size distributions: Cross-ecosystem comparison for taxa with determinate and indeterminate growth

USGS Publications Warehouse

Nash, Kirsty L.; Allen, Craig R.; Barichievy, Chris; Nystrom, Magnus; Sundstrom, Shana M.; Graham, Nicholas A.J.

2014-01-01

Habitat structure across multiple spatial and temporal scales has been proposed as a key driver of body size distributions for associated communities. Thus, understanding the relationship between habitat and body size is fundamental to developing predictions regarding the influence of habitat change on animal communities. Much of the work assessing the relationship between habitat structure and body size distributions has focused on terrestrial taxa with determinate growth, and has primarily analysed discontinuities (gaps) in the distribution of species mean sizes (species size relationships or SSRs). The suitability of this approach for taxa with indeterminate growth has yet to be determined. We provide a cross-ecosystem comparison of bird (determinate growth) and fish (indeterminate growth) body mass distributions using four independent data sets. We evaluate three size distribution indices: SSRs, species size–density relationships (SSDRs) and individual size–density relationships (ISDRs), and two types of analysis: looking for either discontinuities or abundance patterns and multi-modality in the distributions. To assess the respective suitability of these three indices and two analytical approaches for understanding habitat–size relationships in different ecosystems, we compare their ability to differentiate bird or fish communities found within contrasting habitat conditions. All three indices of body size distribution are useful for examining the relationship between cross-scale patterns of habitat structure and size for species with determinate growth, such as birds. In contrast, for species with indeterminate growth such as fish, the relationship between habitat structure and body size may be masked when using mean summary metrics, and thus individual-level data (ISDRs) are more useful. Furthermore, ISDRs, which have traditionally been used to study aquatic systems, present a potentially useful common currency for comparing body size distributions across terrestrial and aquatic ecosystems.

Think Locally, Act Locally: The Detection of Small, Medium-Sized, and Large Communities in Large Networks

PubMed Central

Jeub, Lucas G. S.; Balachandran, Prakash; Porter, Mason A.; Mucha, Peter J.; Mahoney, Michael W.

2016-01-01

It is common in the study of networks to investigate intermediate-sized (or “meso-scale”) features to try to gain an understanding of network structure and function. For example, numerous algorithms have been developed to try to identify “communities,” which are typically construed as sets of nodes with denser connections internally than with the remainder of a network. In this paper, we adopt a complementary perspective that “communities” are associated with bottlenecks of locally-biased dynamical processes that begin at seed sets of nodes, and we employ several different community-identification procedures (using diffusion-based and geodesic-based dynamics) to investigate community quality as a function of community size. Using several empirical and synthetic networks, we identify several distinct scenarios for “size-resolved community structure” that can arise in real (and realistic) networks: (i) the best small groups of nodes can be better than the best large groups (for a given formulation of the idea of a good community); (ii) the best small groups can have a quality that is comparable to the best medium-sized and large groups; and (iii) the best small groups of nodes can be worse than the best large groups. As we discuss in detail, which of these three cases holds for a given network can make an enormous difference when investigating and making claims about network community structure, and it is important to take this into account to obtain reliable downstream conclusions. Depending on which scenario holds, one may or may not be able to successfully identify “good” communities in a given network (and good communities might not even exist for a given community quality measure), the manner in which different small communities fit together to form meso-scale network structures can be very different, and processes such as viral propagation and information diffusion can exhibit very different dynamics. In addition, our results suggest that, for many large realistic networks, the output of locally-biased methods that focus on communities that are centered around a given seed node might have better conceptual grounding and greater practical utility than the output of global community-detection methods. They also illustrate subtler structural properties that are important to consider in the development of better benchmark networks to test methods for community detection. PMID:25679670

From individuals to populations to communities: a dynamic energy budget model of marine ecosystem size-spectrum including life history diversity.

PubMed

Maury, Olivier; Poggiale, Jean-Christophe

2013-05-07

Individual metabolism, predator-prey relationships, and the role of biodiversity are major factors underlying the dynamics of food webs and their response to environmental variability. Despite their crucial, complementary and interacting influences, they are usually not considered simultaneously in current marine ecosystem models. In an attempt to fill this gap and determine if these factors and their interaction are sufficient to allow realistic community structure and dynamics to emerge, we formulate a mathematical model of the size-structured dynamics of marine communities which integrates mechanistically individual, population and community levels. The model represents the transfer of energy generated in both time and size by an infinite number of interacting fish species spanning from very small to very large species. It is based on standard individual level assumptions of the Dynamic Energy Budget theory (DEB) as well as important ecological processes such as opportunistic size-based predation and competition for food. Resting on the inter-specific body-size scaling relationships of the DEB theory, the diversity of life-history traits (i.e. biodiversity) is explicitly integrated. The stationary solutions of the model as well as the transient solutions arising when environmental signals (e.g. variability of primary production and temperature) propagate through the ecosystem are studied using numerical simulations. It is shown that in the absence of density-dependent feedback processes, the model exhibits unstable oscillations. Density-dependent schooling probability and schooling-dependent predatory and disease mortalities are proposed to be important stabilizing factors allowing stationary solutions to be reached. At the community level, the shape and slope of the obtained quasi-linear stationary spectrum matches well with empirical studies. When oscillations of primary production are simulated, the model predicts that the variability propagates along the spectrum in a given frequency-dependent size range before decreasing for larger sizes. At the species level, the simulations show that small and large species dominate the community successively (small species being more abundant at small sizes and large species being more abundant at large sizes) and that the total biomass of a species decreases with its maximal size which again corroborates empirical studies. Our results indicate that the simultaneous consideration of individual growth and reproduction, size-structured trophic interactions, the diversity of life-history traits and a density-dependent stabilizing process allow realistic community structure and dynamics to emerge without any arbitrary prescription. As a logical consequence of our model construction and a basis for future studies, we define the function Φ as the relative contribution of each species to the total biomass of the ecosystem, for any given size. We argue that this function is a measure of the functional role of biodiversity characterizing the impact of the structure of the community (its species composition) on its function (the relative proportions of losses, dissipation and biological work). Copyright © 2013 Elsevier Ltd. All rights reserved.

Fish communities in coastal freshwater ecosystems: the role of the physical and chemical setting.

PubMed

Arend, Kristin K; Bain, Mark B

2008-12-29

We explored how embayment watershed inputs, morphometry, and hydrology influence fish community structure among eight embayments located along the southeastern shoreline of Lake Ontario, New York, USA. Embayments differed in surface area and depth, varied in their connections to Lake Ontario and their watersheds, and drained watersheds representing a gradient of agricultural to forested land use. We related various physicochemical factors, including total phosphorus load, embayment area, and submerged vegetation, to differences in fish species diversity and community relative abundance, biomass, and size structure both among and within embayments. Yellow perch (Perca flavescens) and centrarchids numerically dominated most embayment fish communities. Biomass was dominated by piscivorous fishes including brown bullhead (Ameiurus nebulosus), bowfin (Amia calva), and northern pike (Esox lucius). Phosphorus loading influenced relative biomass, but not species diversity or relative abundance. Fish relative abundance differed among embayments; within embayments, fish abundance at individual sampling stations increased significantly with submerged vegetative cover. Relative biomass differed among embayments and was positively related to total phophorus loading and embayment area. Fish community size structure, based on size spectra analysis, differed among embayments, with the frequency of smaller-bodied fishes positively related to percent vegetation. The importance of total phosphorus loading and vegetation in structuring fish communities has implications for anthropogenic impacts to embayment fish communities through activities such as farming and residential development, reduction of cultural eutrophication, and shoreline development and maintenance.

Size structuring and allometric scaling relationships in coral reef fishes.

PubMed

Dunic, Jillian C; Baum, Julia K

2017-05-01

Temperate marine fish communities are often size-structured, with predators consuming increasingly larger prey and feeding at higher trophic levels as they grow. Gape limitation and ontogenetic diet shifts are key mechanisms by which size structuring arises in these communities. Little is known, however, about size structuring in coral reef fishes. Here, we aimed to advance understanding of size structuring in coral reef food webs by examining the evidence for these mechanisms in two groups of reef predators. Given the diversity of feeding modes amongst coral reef fishes, we also compared gape size-body size allometric relationships across functional groups to determine whether they are reliable indicators of size structuring. We used gut content analysis and quantile regressions of predator size-prey size relationships to test for evidence of gape limitation and ontogenetic niche shifts in reef piscivores (n = 13 species) and benthic invertivores (n = 3 species). We then estimated gape size-body size allometric scaling coefficients for 21 different species from four functional groups, including herbivores/detritivores, which are not expected to be gape-limited. We found evidence of both mechanisms for size structuring in coral reef piscivores, with maximum prey size scaling positively with predator body size, and ontogenetic diet shifts including prey type and expansion of prey size. There was, however, little evidence of size structuring in benthic invertivores. Across species and functional groups, absolute and relative gape sizes were largest in piscivores as expected, but gape size-body size scaling relationships were not indicative of size structuring. Instead, relative gape sizes and mouth morphologies may be better indicators. Our results provide evidence that coral reef piscivores are size-structured and that gape limitation and ontogenetic niche shifts are the mechanisms from which this structure arises. Although gape allometry was not indicative of size structuring, it may have implications for ecosystem function: positively allometric gape size-body size scaling relationships in herbivores/detritivores suggests that loss of large-bodied individuals of these species will have a disproportionately negative impact on reef grazing pressure. © 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.

Size Matters: Assessing Optimum Soil Sample Size for Fungal and Bacterial Community Structure Analyses Using High Throughput Sequencing of rRNA Gene Amplicons

PubMed Central

Penton, C. Ryan; Gupta, Vadakattu V. S. R.; Yu, Julian; Tiedje, James M.

2016-01-01

We examined the effect of different soil sample sizes obtained from an agricultural field, under a single cropping system uniform in soil properties and aboveground crop responses, on bacterial and fungal community structure and microbial diversity indices. DNA extracted from soil sample sizes of 0.25, 1, 5, and 10 g using MoBIO kits and from 10 and 100 g sizes using a bead-beating method (SARDI) were used as templates for high-throughput sequencing of 16S and 28S rRNA gene amplicons for bacteria and fungi, respectively, on the Illumina MiSeq and Roche 454 platforms. Sample size significantly affected overall bacterial and fungal community structure, replicate dispersion and the number of operational taxonomic units (OTUs) retrieved. Richness, evenness and diversity were also significantly affected. The largest diversity estimates were always associated with the 10 g MoBIO extractions with a corresponding reduction in replicate dispersion. For the fungal data, smaller MoBIO extractions identified more unclassified Eukaryota incertae sedis and unclassified glomeromycota while the SARDI method retrieved more abundant OTUs containing unclassified Pleosporales and the fungal genera Alternaria and Cercophora. Overall, these findings indicate that a 10 g soil DNA extraction is most suitable for both soil bacterial and fungal communities for retrieving optimal diversity while still capturing rarer taxa in concert with decreasing replicate variation. PMID:27313569

Deterministic assembly of land snail communities according to species size and diet.

PubMed

Schamp, Brandon; Horsák, Michal; Hájek, Michal

2010-07-01

1. We investigated whether coexisting snail species in 145 treeless fen communities in the Western Carpathian Mountains differed more in size and diet than would be expected by chance, as predicted for traits commonly associated with competition and differential resource acquisition under limiting similarity theory. 2. Contrary to expectations, coexisting snail species were no more different in body size than expected by chance under a null model. However, variation in body size played a significant role in structuring snail communities: coexisting snail species were significantly more similar with respect to body size. 3. We developed two new test statistics to expand our investigation of limiting similarity to include diet, a nominal trait. We tested whether communities of snails were characterized by a greater richness of diet, and whether different diets were represented more or less evenly within communities. Communities of snails were significantly less evenly distributed than expected by chance, with detritivores being over-represented relative to predatory strategies. 4. We also examined the effect of water pH and conductivity, herbaceous cover, and bryophyte and vascular plant richness, on these trends by examining how the effect size of our tests varied across these gradients. Convergence in species size increased with increasing habitat pH. Specifically, smaller snail species were over-represented in fen communities in general, and this effect was accentuated in increasingly calcareous fens. 5. Theory predicts that traits related strongly to environmental conditions are more likely to be convergent. Our findings support this suggestion, as small snail species have an advantage in tolerating freezing conditions over winter when refuges are limited. 6. These results add to the growing body of literature demonstrating that variation in body size and diet play a strong role in structuring communities, although frequently in ways not predicted by limiting similarity theory. Finally, our results increase our understanding of how species are assembled non-randomly into communities with respect to important traits.

Interlinking backscatter, grain size and benthic community structure

NASA Astrophysics Data System (ADS)

McGonigle, Chris; Collier, Jenny S.

2014-06-01

The relationship between acoustic backscatter, sediment grain size and benthic community structure is examined using three different quantitative methods, covering image- and angular response-based approaches. Multibeam time-series backscatter (300 kHz) data acquired in 2008 off the coast of East Anglia (UK) are compared with grain size properties, macrofaunal abundance and biomass from 130 Hamon and 16 Clamshell grab samples. Three predictive methods are used: 1) image-based (mean backscatter intensity); 2) angular response-based (predicted mean grain size), and 3) image-based (1st principal component and classification) from Quester Tangent Corporation Multiview software. Relationships between grain size and backscatter are explored using linear regression. Differences in grain size and benthic community structure between acoustically defined groups are examined using ANOVA and PERMANOVA+. Results for the Hamon grab stations indicate significant correlations between measured mean grain size and mean backscatter intensity, angular response predicted mean grain size, and 1st principal component of QTC analysis (all p < 0.001). Results for the Clamshell grab for two of the methods have stronger positive correlations; mean backscatter intensity (r2 = 0.619; p < 0.001) and angular response predicted mean grain size (r2 = 0.692; p < 0.001). ANOVA reveals significant differences in mean grain size (Hamon) within acoustic groups for all methods: mean backscatter (p < 0.001), angular response predicted grain size (p < 0.001), and QTC class (p = 0.009). Mean grain size (Clamshell) shows a significant difference between groups for mean backscatter (p = 0.001); other methods were not significant. PERMANOVA for the Hamon abundance shows benthic community structure was significantly different between acoustic groups for all methods (p ≤ 0.001). Overall these results show considerable promise in that more than 60% of the variance in the mean grain size of the Clamshell grab samples can be explained by mean backscatter or acoustically-predicted grain size. These results show that there is significant predictive capacity for sediment characteristics from multibeam backscatter and that these acoustic classifications can have ecological validity.

Linking phytoplankton community metabolism to the individual size distribution.

PubMed

Padfield, Daniel; Buckling, Angus; Warfield, Ruth; Lowe, Chris; Yvon-Durocher, Gabriel

2018-05-25

Quantifying variation in ecosystem metabolism is critical to predicting the impacts of environmental change on the carbon cycle. We used a metabolic scaling framework to investigate how body size and temperature influence phytoplankton community metabolism. We tested this framework using phytoplankton sampled from an outdoor mesocosm experiment, where communities had been either experimentally warmed (+ 4 °C) for 10 years or left at ambient temperature. Warmed and ambient phytoplankton communities differed substantially in their taxonomic composition and size structure. Despite this, the response of primary production and community respiration to long- and short-term warming could be estimated using a model that accounted for the size- and temperature dependence of individual metabolism, and the community abundance-body size distribution. This work demonstrates that the key metabolic fluxes that determine the carbon balance of planktonic ecosystems can be approximated using metabolic scaling theory, with knowledge of the individual size distribution and environmental temperature. © 2018 The Authors. Ecology Letters published by CNRS and John Wiley & Sons Ltd.

Fish communities in coastal freshwater ecosystems: the role of the physical and chemical setting

PubMed Central

Arend, Kristin K; Bain, Mark B

2008-01-01

Background We explored how embayment watershed inputs, morphometry, and hydrology influence fish community structure among eight embayments located along the southeastern shoreline of Lake Ontario, New York, USA. Embayments differed in surface area and depth, varied in their connections to Lake Ontario and their watersheds, and drained watersheds representing a gradient of agricultural to forested land use. Results We related various physicochemical factors, including total phosphorus load, embayment area, and submerged vegetation, to differences in fish species diversity and community relative abundance, biomass, and size structure both among and within embayments. Yellow perch (Perca flavescens) and centrarchids numerically dominated most embayment fish communities. Biomass was dominated by piscivorous fishes including brown bullhead (Ameiurus nebulosus), bowfin (Amia calva), and northern pike (Esox lucius). Phosphorus loading influenced relative biomass, but not species diversity or relative abundance. Fish relative abundance differed among embayments; within embayments, fish abundance at individual sampling stations increased significantly with submerged vegetative cover. Relative biomass differed among embayments and was positively related to total phophorus loading and embayment area. Fish community size structure, based on size spectra analysis, differed among embayments, with the frequency of smaller-bodied fishes positively related to percent vegetation. Conclusion The importance of total phosphorus loading and vegetation in structuring fish communities has implications for anthropogenic impacts to embayment fish communities through activities such as farming and residential development, reduction of cultural eutrophication, and shoreline development and maintenance. PMID:19114002

Cascading failures in complex networks with community structure

NASA Astrophysics Data System (ADS)

Lin, Guoqiang; di, Zengru; Fan, Ying

2014-12-01

Much empirical evidence shows that when attacked with cascading failures, scale-free or even random networks tend to collapse more extensively when the initially deleted node has higher betweenness. Meanwhile, in networks with strong community structure, high-betweenness nodes tend to be bridge nodes that link different communities, and the removal of such nodes will reduce only the connections among communities, leaving the networks fairly stable. Understanding what will affect cascading failures and how to protect or attack networks with strong community structure is therefore of interest. In this paper, we have constructed scale-free Community Networks (SFCN) and Random Community Networks (RCN). We applied these networks, along with the Lancichinett-Fortunato-Radicchi (LFR) benchmark, to the cascading-failure scenario to explore their vulnerability to attack and the relationship between cascading failures and the degree distribution and community structure of a network. The numerical results show that when the networks are of a power-law distribution, a stronger community structure will result in the failure of fewer nodes. In addition, the initial removal of the node with the highest betweenness will not lead to the worst cascading, i.e. the largest avalanche size. The Betweenness Overflow (BOF), an index that we developed, is an effective indicator of this tendency. The RCN, however, display a different result. In addition, the avalanche size of each node can be adopted as an index to evaluate the importance of the node.

COMPARISONS OF ZOOPLANKTON COMMUNITY SIZE STRUCTURE IN THE GREAT LAKES

EPA Science Inventory

Zooplankton mean-size and size-spectra distribution potentially reflect the condition of trophic interactions and ecosystem health because they are affected by both resource availability and planktivore pressure. We assessed zooplankton mean-size and size-spectra using an optical...

Size Matters: Assessing Optimum Soil Sample Size for Fungal and Bacterial Community Structure Analyses Using High Throughput Sequencing of rRNA Gene Amplicons

DOE PAGES

Penton, C. Ryan; Gupta, Vadakattu V. S. R.; Yu, Julian; ...

2016-06-02

We examined the effect of different soil sample sizes obtained from an agricultural field, under a single cropping system uniform in soil properties and aboveground crop responses, on bacterial and fungal community structure and microbial diversity indices. DNA extracted from soil sample sizes of 0.25, 1, 5, and 10 g using MoBIO kits and from 10 and 100 g sizes using a bead-beating method (SARDI) were used as templates for high-throughput sequencing of 16S and 28S rRNA gene amplicons for bacteria and fungi, respectively, on the Illumina MiSeq and Roche 454 platforms. Sample size significantly affected overall bacterial and fungalmore » community structure, replicate dispersion and the number of operational taxonomic units (OTUs) retrieved. Richness, evenness and diversity were also significantly affected. The largest diversity estimates were always associated with the 10 g MoBIO extractions with a corresponding reduction in replicate dispersion. For the fungal data, smaller MoBIO extractions identified more unclassified Eukaryota incertae sedis and unclassified glomeromycota while the SARDI method retrieved more abundant OTUs containing unclassified Pleosporales and the fungal genera Alternaria and Cercophora. Overall, these findings indicate that a 10 g soil DNA extraction is most suitable for both soil bacterial and fungal communities for retrieving optimal diversity while still capturing rarer taxa in concert with decreasing replicate variation.« less

Size Matters: Assessing Optimum Soil Sample Size for Fungal and Bacterial Community Structure Analyses Using High Throughput Sequencing of rRNA Gene Amplicons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Penton, C. Ryan; Gupta, Vadakattu V. S. R.; Yu, Julian

We examined the effect of different soil sample sizes obtained from an agricultural field, under a single cropping system uniform in soil properties and aboveground crop responses, on bacterial and fungal community structure and microbial diversity indices. DNA extracted from soil sample sizes of 0.25, 1, 5, and 10 g using MoBIO kits and from 10 and 100 g sizes using a bead-beating method (SARDI) were used as templates for high-throughput sequencing of 16S and 28S rRNA gene amplicons for bacteria and fungi, respectively, on the Illumina MiSeq and Roche 454 platforms. Sample size significantly affected overall bacterial and fungalmore » community structure, replicate dispersion and the number of operational taxonomic units (OTUs) retrieved. Richness, evenness and diversity were also significantly affected. The largest diversity estimates were always associated with the 10 g MoBIO extractions with a corresponding reduction in replicate dispersion. For the fungal data, smaller MoBIO extractions identified more unclassified Eukaryota incertae sedis and unclassified glomeromycota while the SARDI method retrieved more abundant OTUs containing unclassified Pleosporales and the fungal genera Alternaria and Cercophora. Overall, these findings indicate that a 10 g soil DNA extraction is most suitable for both soil bacterial and fungal communities for retrieving optimal diversity while still capturing rarer taxa in concert with decreasing replicate variation.« less

Temperature-Correlated Changes in Phytoplankton Community Structure Are Restricted to Polar Waters.

PubMed

Ward, Ben A

2015-01-01

Globally distributed observations of size-fractionated chlorophyll a and temperature were used to incorporate temperature dependence into an existing semi-empirical model of phytoplankton community size structure. The additional temperature-dependent term significantly increased the model's ability to both reproduce and predict observations of chlorophyll a size-fractionation at temperatures below 2°C. The most notable improvements were in the smallest (picoplankton) size-class, for which overall model fit was more than doubled, and predictive skill was increased by approximately 40%. The model was subsequently applied to generate global maps for three phytoplankton size classes, on the basis of satellite-derived estimates of surface chlorophyll a and sea surface temperature. Polar waters were associated with marked decline in the chlorophyll a biomass of the smallest cells, relative to lower latitude waters of equivalent total chlorophyll a. In the same regions a complementary increase was seen in the chlorophyll a biomass of larger size classes. These findings suggest that a warming and stratifying ocean will see a poleward expansion of the habitat range of the smallest phytoplankton, with the possible displacement of some larger groups that currently dominate. There was no evidence of a strong temperature dependence in tropical or sub-tropical regions, suggesting that future direct temperature effects on community structure at lower latitudes may be small.

Predicting the consequences of species loss using size-structured biodiversity approaches.

PubMed

Brose, Ulrich; Blanchard, Julia L; Eklöf, Anna; Galiana, Nuria; Hartvig, Martin; R Hirt, Myriam; Kalinkat, Gregor; Nordström, Marie C; O'Gorman, Eoin J; Rall, Björn C; Schneider, Florian D; Thébault, Elisa; Jacob, Ute

2017-05-01

Understanding the consequences of species loss in complex ecological communities is one of the great challenges in current biodiversity research. For a long time, this topic has been addressed by traditional biodiversity experiments. Most of these approaches treat species as trait-free, taxonomic units characterizing communities only by species number without accounting for species traits. However, extinctions do not occur at random as there is a clear correlation between extinction risk and species traits. In this review, we assume that large species will be most threatened by extinction and use novel allometric and size-spectrum concepts that include body mass as a primary species trait at the levels of populations and individuals, respectively, to re-assess three classic debates on the relationships between biodiversity and (i) food-web structural complexity, (ii) community dynamic stability, and (iii) ecosystem functioning. Contrasting current expectations, size-structured approaches suggest that the loss of large species, that typically exploit most resource species, may lead to future food webs that are less interwoven and more structured by chains of interactions and compartments. The disruption of natural body-mass distributions maintaining food-web stability may trigger avalanches of secondary extinctions and strong trophic cascades with expected knock-on effects on the functionality of the ecosystems. Therefore, we argue that it is crucial to take into account body size as a species trait when analysing the consequences of biodiversity loss for natural ecosystems. Applying size-structured approaches provides an integrative ecological concept that enables a better understanding of each species' unique role across communities and the causes and consequences of biodiversity loss. © 2016 Cambridge Philosophical Society.

Influence of ocean acidification on plankton community structure during a winter-to-summer succession: An imaging approach indicates that copepods can benefit from elevated CO2 via indirect food web effects

PubMed Central

Taucher, Jan; Haunost, Mathias; Boxhammer, Tim; Bach, Lennart T.; Algueró-Muñiz, María; Riebesell, Ulf

2017-01-01

Plankton communities play a key role in the marine food web and are expected to be highly sensitive to ongoing environmental change. Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. These changes–summarized by the term ocean acidification (OA)–can significantly affect the physiology of planktonic organisms. However, studies on the response of entire plankton communities to OA, which also include indirect effects via food-web interactions, are still relatively rare. Thus, it is presently unclear how OA could affect the functioning of entire ecosystems and biogeochemical element cycles. In this study, we report from a long-term in situ mesocosm experiment, where we investigated the response of natural plankton communities in temperate waters (Gullmarfjord, Sweden) to elevated CO2 concentrations and OA as expected for the end of the century (~760 μatm pCO2). Based on a plankton-imaging approach, we examined size structure, community composition and food web characteristics of the whole plankton assemblage, ranging from picoplankton to mesozooplankton, during an entire winter-to-summer succession. The plankton imaging system revealed pronounced temporal changes in the size structure of the copepod community over the course of the plankton bloom. The observed shift towards smaller individuals resulted in an overall decrease of copepod biomass by 25%, despite increasing numerical abundances. Furthermore, we observed distinct effects of elevated CO2 on biomass and size structure of the entire plankton community. Notably, the biomass of copepods, dominated by Pseudocalanus acuspes, displayed a tendency towards elevated biomass by up to 30–40% under simulated ocean acidification. This effect was significant for certain copepod size classes and was most likely driven by CO2-stimulated responses of primary producers and a complex interplay of trophic interactions that allowed this CO2 effect to propagate up the food web. Such OA-induced shifts in plankton community structure could have far-reaching consequences for food-web interactions, biomass transfer to higher trophic levels and biogeochemical cycling of marine ecosystems. PMID:28178268

Ocean acidification reduces transfer of essential biomolecules in a natural plankton community

PubMed Central

Bermúdez, J. Rafael; Riebesell, Ulf; Larsen, Aud; Winder, Monika

2016-01-01

Ocean acidification (OA), a process of increasing seawater acidity caused by the uptake of anthropogenic carbon dioxide (CO2) by the ocean, is expected to change surface ocean pH to levels unprecedented for millions of years, affecting marine food web structures and trophic interactions. Using an in situ mesocosm approach we investigated effects of OA on community composition and trophic transfer of essential fatty acids (FA) in a natural plankton assemblage. Elevated pCO2 favored the smallest phytoplankton size class in terms of biomass, primarily picoeukaryotes, at the expense of chlorophyta and haptophyta in the nano-plankton size range. This shift in community composition and size structure was accompanied by a decline in the proportion of polyunsaturated FA (PUFA) to total FA content in the nano- and picophytoplankton size fractions. This decline was mirrored in a continuing reduction in the relative PUFA content of the dominant copepod, Calanus finmarchicus, which primarily fed on the nano-size class. Our results demonstrate that a shift in phytoplankton community composition and biochemical composition in response to rising CO2 can affect the transfer of essential compounds to higher trophic levels, which rely on their prey as a source for essential macromolecules. PMID:27324057

Body size distributions signal a regime shift in a lake ecosystem

USGS Publications Warehouse

Spanbauer, Trisha; Allen, Craig R.; Angeler, David G.; Eason, Tarsha; Fritz, Sherilyn C.; Garmestani, Ahjond S.; Nash, Kirsty L.; Stone, Jeffery R.; Stow, Craig A.; Sundstrom, Shana M.

2016-01-01

Communities of organisms, from mammals to microorganisms, have discontinuous distributions of body size. This pattern of size structuring is a conservative trait of community organization and is a product of processes that occur at multiple spatial and temporal scales. In this study, we assessed whether body size patterns serve as an indicator of a threshold between alternative regimes. Over the past 7000 years, the biological communities of Foy Lake (Montana, USA) have undergone a major regime shift owing to climate change. We used a palaeoecological record of diatom communities to estimate diatom sizes, and then analysed the discontinuous distribution of organism sizes over time. We used Bayesian classification and regression tree models to determine that all time intervals exhibited aggregations of sizes separated by gaps in the distribution and found a significant change in diatom body size distributions approximately 150 years before the identified ecosystem regime shift. We suggest that discontinuity analysis is a useful addition to the suite of tools for the detection of early warning signals of regime shifts.

Attack tolerance of correlated time-varying social networks with well-defined communities

NASA Astrophysics Data System (ADS)

Sur, Souvik; Ganguly, Niloy; Mukherjee, Animesh

2015-02-01

In this paper, we investigate the efficiency and the robustness of information transmission for real-world social networks, modeled as time-varying instances, under targeted attack in shorter time spans. We observe that these quantities are markedly higher than that of the randomized versions of the considered networks. An important factor that drives this efficiency or robustness is the presence of short-time correlations across the network instances which we quantify by a novel metric the-edge emergence factor, denoted as ξ. We find that standard targeted attacks are not effective in collapsing this network structure. Remarkably, if the hourly community structures of the temporal network instances are attacked with the largest size community attacked first, the second largest next and so on, the network soon collapses. This behavior, we show is an outcome of the fact that the edge emergence factor bears a strong positive correlation with the size ordered community structures.

Organizational Structure in Multi-Campus Community Junior Colleges/Districts.

ERIC Educational Resources Information Center

Chang, Nai-Kwang

The administrative structures and functions of multi-campus colleges/districts of the same size as the Community College of Denver (CCD) were investigated to determine the positive and negative aspects of multi-campus colleges vs. separate independent colleges and of centralization vs. decentralization of 38 administrative functions. A survey of…

The annual planktonic protist community structure in an ice-free high Arctic fjord (Adventfjorden, West Spitsbergen)

NASA Astrophysics Data System (ADS)

Kubiszyn, A. M.; Wiktor, J. M.; Wiktor, J. M.; Griffiths, C.; Kristiansen, S.; Gabrielsen, T. M.

2017-05-01

We investigated the size and trophic structure of the annual planktonic protist community structure in the ice-free Adventfjorden in relation to environmental factors. Our high-resolution (weekly to monthly) study was conducted in 2012, when warm Atlantic water was advected into the fjord in winter and summer. We observed a distinct seasonality in the protist communities. The winter protist community was characterised by extremely low levels of protist abundance and biomass (primarily Dinophyceae, Ciliophora and Bacillariophyceae) in a homogenous water column. In the second half of April, the total protist abundance and biomass rapidly increased, thus initiating the spring bloom in a still well-mixed water column. The spring bloom was initially dominated by the prymnesiophyte Phaeocystis pouchetii and Bacillariophyceae (primarily from the genera Thalassiosira, Fragilariopsis and Chaetoceros) and was later strictly dominated by Phaeocystis colonies. When the bloom terminated in mid-June, the community shifted towards flagellates (Dinophyceae, Ciliophora, Cryptophyceae and nanoflagellates 3-7 μm in size) in a stratified, nutrient-depleted water column. Decreases in the light intensity decreased the protist abundance and biomass, and the fall community (Dinophyceae, Cryptophyceae and Bacillariophyceae) was followed by the winter community.

Trait-based assembly and phylogenetic structure in northeast Pacific rockfish assemblages.

PubMed

Ingram, Travis; Shurin, Jonathan B

2009-09-01

If natural communities are assembled according to deterministic rules, coexisting species will represent a nonrandom subset of the potential species pool. We tested for signatures of assembly rules in the distribution of species' traits in Pacific rockfish (Sebastes spp.) assemblages. We used morphology, dietary niche (estimated with stable nitrogen isotopes), and distribution data to identify traits that relate to local-scale resource use (the alpha-niche) and to environmental gradients (the beta-niche). We showed that gill raker morphology was related to trophic position (an alpha-niche axis), while relative eye size was associated with depth habitat (a beta-niche axis). We therefore hypothesized that, within assemblages of coexisting rockfish species, the gill raker trait would be overdispersed (evenly spaced) due to limiting similarity, while relative eye size would be clustered due to environmental filtering. We examined the evolutionary relatedness of coexisting species to ask whether phylogenetic community structure and trait distributions gave similar indications about the roles of assembly processes. We tested the trait distributions and phylogenetic structure of 30 published rockfish assemblages against a null model of random community assembly. As predicted, the gill raker trait tended to be more evenly spaced than expected by chance, as did overall body size, while relative eye size was more clustered than expected. Phylogenetic community structure appeared to reflect historical dispersal and speciation and did not provide consistent support for assembly rules. Our results indicate that rockfish community assembly is nonrandom with regard to species' traits and show how distinguishing traits related to the alpha- and beta-niches and incorporating functional morphology can provide for powerful tests of assembly rules.

Habitat selection by breeding waterbirds at ponds with size-structured fish populations

NASA Astrophysics Data System (ADS)

Kloskowski, Janusz; Nieoczym, Marek; Polak, Marcin; Pitucha, Piotr

2010-07-01

Fish may significantly affect habitat use by birds, either as their prey or as competitors. Fish communities are often distinctly size-structured, but the consequences for waterbird assemblages remain poorly understood. We examined the effects of size structure of common carp ( Cyprinus carpio) cohorts together with other biotic and abiotic pond characteristics on the distribution of breeding waterbirds in a seminatural system of monocultured ponds, where three fish age classes were separately stocked. Fish age corresponded to a distinct fish size gradient. Fish age and total biomass, macroinvertebrate and amphibian abundance, and emergent vegetation best explained the differences in bird density between ponds. Abundance of animal prey other than fish (aquatic macroinvertebrates and larval amphibians) decreased with increasing carp age in the ponds. Densities of ducks and smaller grebes were strongly negatively associated with fish age/size gradient. The largest of the grebes, the piscivorous great crested grebe ( Podiceps cristatus), was the only species that preferred ponds with medium-sized fish and was positively associated with total fish biomass. Habitat selection by bitterns and most rallids was instead strongly influenced by the relative amount of emergent vegetation cover in the ponds. Our results show that fish size structure may be an important cue for breeding habitat choice and a factor affording an opportunity for niche diversification in avian communities.

Bacterial community structure in atmospheric particulate matters of different sizes during the haze days in Xi'an, China.

PubMed

Lu, Rui; Li, Yanpeng; Li, Wanxin; Xie, Zhengsheng; Fan, Chunlan; Liu, Pengxia; Deng, Shunxi

2018-05-09

Serious air pollution events have frequently occurred in China associated with the acceleration of urbanization and industrialization in recent years. Exposure to atmospheric particulate matter (PM) of high concentration can lead to adverse effects on human health. Airborne bacteria are important constituents of microbial aerosols and contain lots of pathogens. However, variations in bacterial community structure in atmospheric PM of different sizes (PM 2.5 , PM 10 and TSP) have not yet been explored. In this study, PM samples of different sizes were collected during the hazy days from Jul.2016 to Apr.2017 to determine bacterial diversity and community structure. Samples from soils and leaf surfaces were also collected to determine potential sources of bacterial aerosols. High-throughput sequencing technology was used generate bacterial community profiles, where we determined their diversity and abundances in the samples. Results showed that the dominant bacterial community structures in PM 2.5 , PM 10 and TSP were strongly similar. Compared with non-haze days, the relative abundances of most bacterial pathogens on the haze days did not increase. Meanwhile, temperature, O 3 and NO 2 had more significant effects on bacterial community than the other environmental factors. Source tracking analysis indicated that the airborne bacteria might be not from local environment. It may come from the entire city or other regions by long distance airflow transport. Results of this study improved our understanding of the influence of bioaerosols on human health and the potential sources of airborne microbes. Copyright © 2018 Elsevier B.V. All rights reserved.

Effects of reclamation years on composition and diversity of soil bacterial communities in Northwest China.

PubMed

Cheng, Zhibo; Zhang, Fenghua; Gale, William Jeffrey; Wang, Weichao; Sang, Wen; Yang, Haichang

2018-01-01

The objective of this study was to evaluate bacterial community structure and diversity in soil aggregate fractions when salinized farmland was reclaimed after >27 years of abandonment and then farmed again for 1, 5, 10, and 15 years. Illumina MiSeq high-throughput sequencing was performed to characterize the soil bacterial communities in 5 aggregate size classes in each treatment. The results indicated that reclamation significantly increased macro-aggregation (>0.25 mm), as well as soil organic C, available N, and available P. The 10-year field had the largest proportion (93.9%) of soil in the macro-aggregate size classes (i.e., >0.25 mm) and the highest soil electrical conductivity. The 5 most dominant phyla in the soil samples were Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria, and Bacteroidetes. The phylogenetic diversity, Chao1, and Shannon indices increased after the abandoned land was reclaimed for farming, reaching maximums in the 15-year field. Among aggregate size classes, the 1-0.25 mm aggregates generally had the highest phylogenetic diversity, Chao1, and Shannon indices. Soil organic C and soil electrical conductivity were the main environmental factors affecting the soil bacterial communities. The composition and structure of the bacterial communities also varied significantly depending on soil aggregate size and time since reclamation.

Helminth parasite communities of allopatric populations of the frog Leptodactylus podicipinus from Pantanal, Brazil.

PubMed

Campião, K M; da Silva, R J; Ferreira, V L

2014-03-01

Several factors may influence the structure of parasite communities in amphibian hosts. In this study, we describe the helminth parasites of three allopatric populations of the frog Leptodactylus podicipinus and test whether host size and sex were determinants of the structure and composition of the helminth communities. One hundred and twenty-three anurans were collected from three different study sites within the Pantanal wetlands and surveyed for helminth parasites. We found 14 helminth taxa: 7 species of nematodes, 4 species of trematodes, 1 species of cestodes, 1 species of acanthocephalan and one unidentified cyst. Host sex and size did not cause significant differences in helminth abundance or richness. The structure of helminth communities from the three study sites varied in terms of species composition, abundance and diversity. Six out of 14 helminth taxa were found in the three localities. Among those, the nematodes Cosmocerca podicipinus and Rhabdias sp., the trematode Catadiscus propinquus and the helminth cyst showed significant differences in mean abundances. We suggest that such differences found among the three component communities are driven by biotic and abiotic factors operating locally. Moreover, these differences stress the importance of local conditions, such as hydrologic characteristics and landscape composition, on helminth community structure.

Is the impact of eutrophication on phytoplankton diversity dependent on lake volume/ecosystem size?

USGS Publications Warehouse

Baho, Didier L.; Drakare, Stina; Johnson, Richard K.; Allen, Craig R.; Angeler, David G.

2017-01-01

Research focusing on biodiversity responses to the interactions of ecosystem size and anthropogenic stressors are based mainly on correlative gradient studies, and may therefore confound size-stress relationships due to spatial context and differences in local habitat features across ecosystems. We investigated how local factors related to anthropogenic stressors (e.g.,eutrophication) interact with ecosystem size to influence species diversity. In this study, constructed lake mesocosms (with two contrasting volumes: 1020 (shallow mesocosms) and 2150 (deep mesocosms) litres) were used to simulate ecosystems of different size and manipulated nutrient levels to simulate mesotrophic and hypertrophic conditions. Using a factorial design, we assessed how the interaction between ecosystem size and nutrients influences phytoplankton diversity. We assessed community metrics (richness, diversity, evenness and total biovolumes) and multivariate community structure over a growing season (May to early November 2011). Different community structures were found between deep and shallow mescosoms with nutrient enrichment: Cyanobacteria dominated in the deep and Charophyta in the shallow mesocosms. In contrast, phytoplankton communities were more similar to each other in the low nutrient treatments; only Chlorophyta had generally a higher biovolume in the shallow compared to the deep mesocosms. These results suggest that ecosystem size is not only a determinant of species diversity, but that it can mediate the influence of anthropogenic effects on biodiversity. Such interactions increase the uncertainty of global change outcomes, and should therefore not be ignored in risk/impact assessment and management.

Dullgren extraction of soil mites (Acarina): Effect of refrigeration time on extraction efficiency

Treesearch

Michelle B. Lakly; D.A. Crossley

2000-01-01

Soil microarthropods constitute one of the most species rich communities in . forest ecosystems (Crossley & Blair, 1991). The effects of soil fauna in these systems on decomposition rates, nutrient regeneration and soil structure have been well documented; however, dependable estimates of population size and community structure largely depend upon adequate sampling...

Variations in the Summer Phytoplankton Community Structure in Atlantic sub-Arctic and Arctic Waters

NASA Astrophysics Data System (ADS)

Small, A.; Hughes, C.; Bouman, H. A.

2016-02-01

Shifts in phytoplankton community structure serve not only as indicators of environmental change but also have implications for food-web interactions and biogeochemical cycles. The community structure of marine phytoplankton in sub-Arctic and Arctic waters was examined using 159 samples collected in the summer of 2013 along a latitudinal gradient spanning from 61.1 to 83.1 degrees N along the east coast of Greenland. Accessory pigment concentrations were used to infer information about the phytoplankton taxa present using CHEMTAX (CHEMical TAXonomy), an iterative MATLAB subroutine. The main algal classes found within the study region were diatoms, dinoflagellates, haptophytes, chlorophytes, cryptophytes and prasinophytes. Diatoms were present at nearly all stations and depths and were large contributors to the total pigment biomass for both ice and open water stations. Deeper samples were mainly dominated by diatoms and haptophytes. Surface sample communities were characterised by mixed assemblages, including dinoflagellates and chlorophytes although diatoms and haptophytes still comprised a significant portion of the pigment biomass. The differences in community structure were investigated in relation to the environmental conditions through multivariate statistical analysis (cluster and principle component analyses) in order to understand the factors influencing the spatial distribution of the various algal classes. Diagnostic pigment indices were also used to calculate the concentration of Chl-a attributed to three size classes (picophytoplankton 0.2-2µm, nanophytoplankton 2-20µm and microphytoplankton >20µm). These data were compared to a similar dataset from the same cruise where size fractionated Chl-a was separated by sequential filtration and quantified by fluorometric analysis. Size-fractionated Chl-a as measured directly by sequential filtration suggested a primarily mixed community across the study region. In contrast pigment based analysis suggested a strong dominance of larger cells and also resulted in the complete absence of picoplankton in some samples. These results suggest that diagnostic pigment indices may not be an accurate method of determining size classes in this region.

Is the community of fish gill parasites structured in a Neotropical floodplain?

PubMed

Bellay, Sybelle; Takemoto, Ricardo Massato; Oliveira, Edson Fontes

2012-03-01

Sixty-one specimens of the piranha Serrasalmus marginatus Valenciennes, 1837 were analyzed, aiming at assessing the community structure of their gill parasites. The samples were collected in lagoons of the Paraná, Ivinheima and Baia Subsystems within the Upper Paraná River Floodplain (Brazil). Host size and sex had little or no influence on the abundance and prevalence of parasites. The organization of the gill parasite infracommunities of S. marginatus was significantly non-random according to null models and ordination analyses. In general, parasite infrapopulations were not affected by interspecific associations or host characteristics (e.g. size, sex), what highlights the importance of local habitat characteristics to community organization of gill parasites of S. marginatus in the Upper Paraná River Floodplain.

Size really does matter: effects of filter fractionation on microbial community structure in a model oxygen minimum zone.

NASA Astrophysics Data System (ADS)

Torres Beltran, M.

2016-02-01

The Scientific Committee on Oceanographic Research (SCOR) Working Group 144 "Microbial Community Responses to Ocean Deoxygenation" workshop held in Vancouver, British Columbia in July 2014 had the primary objective of kick-starting the establishment of a minimal core of technologies, techniques and standard operating procedures (SOPs) to enable compatible process rate and multi-molecular data (DNA, RNA and protein) collection in marine oxygen minimum zones (OMZs) and other oxygen starved waters. Experimental activities conducted in Saanich Inlet, a seasonally anoxic fjord on Vancouver Island British Columbia, were designed to compare and cross-calibrate in situ sampling devices (McLane PPS system) with conventional bottle sampling and incubation methods. Bottle effects on microbial community composition, and activity were tested using different filter combinations and sample volumes to compare PPS/IPS (0.4 µm) versus Sterivex (0.22 µm) filtration methods with and without prefilters (2.7 µm). Resulting biomass was processed for small subunit ribosomal RNA gene sequencing across all three domains of life on the 454 platform followed by downstream community structure analyses. Significant community shifts occurred within and between filter fractions for in situ versus on-ship processed samples. For instance, the relative abundance of several bacterial phyla including Bacteroidetes, Delta and Gammaproteobacteria decreased five-fold on-ship when compared to in situ filtration. Similarly, experimental mesocosms showed similar community structure and activity to in situ filtered samples indicating the need to cross-calibrate incubations to constrain bottle effects. In addition, alpha and beta diversity significantly changed as function of filter size and volume, as well as the operational taxonomic units identified using indicator species analysis for each filter size. Our results provide statistical support that microbial community structure is systematically biased by filter fraction methods and highlight the need for establishing compatible techniques among researchers that facilitate comparative and reproducible science for the whole community.

Contrasting responses of bacterial and fungal communities to aggregate-size fractions and long-term fertilizations in soils of northeastern China.

PubMed

Liao, Hao; Zhang, Yuchen; Zuo, Qinyan; Du, Binbin; Chen, Wenli; Wei, Dan; Huang, Qiaoyun

2018-04-20

Soils, with non-uniform distribution of nutrients across different aggregate-size fractions, provide spatially heterogeneous microhabitats for microorganisms. However, very limited information is available on microbial distributions and their response to fertilizations across aggregate-size fractions in agricultural soils. Here, we examined the structures of bacterial and fungal communities across different aggregate-size fractions (2000-250 μm, 250-53 μm and <53 μm) in response to 35-years organic and/or chemical fertilization regimes in the soil of northeastern China by phospholipid fatty acid (PLFA) and high throughput sequencing (HTS) technology. Our results show that larger fractions (>53 μm), especially 250-53 μm aggregates, which contain more soil C and N, are associated with greater microbial biomass and higher fungi/bacteria ratio. We firstly reported the fungal community composition in different aggregate-size fractions by HTS technology and found more Ascomycota but less Zygomycota in larger fractions with higher C content across all fertilization regimes. Fertilization and aggregate-size fractions significantly affect the compositions of bacterial and fungal communities although their effects are different. The bacterial community is mainly driven by fertilization, especially chemical fertilizers, and is closely related to the shifts of soil P (phosphorus). The fungal community is preferentially impacted by different aggregate-size fractions and is more associated with the changes of soil C and N. The distinct responses of microbial communities suggest different mechanisms controlling the assembly of soil bacterial and fungal communities at aggregate scale. The investigations of both bacterial and fungal communities could provide a better understanding on nutrient cycling across aggregate-size fractions. Copyright © 2018. Published by Elsevier B.V.

Urban ecological stewardship: understanding the structure, function and network of community-based urban land management

Treesearch

Erika s. Svendsen; Lindsay K. Campbell

2008-01-01

Urban environmental stewardship activities are on the rise in cities throughout the Northeast. Groups participating in stewardship activities range in age, size, and geography and represent an increasingly complex and dynamic arrangement of civil society, government and business sectors. To better understand the structure, function and network of these community-based...

The role of community structure on the nature of explosive synchronization.

PubMed

Lotfi, Nastaran; Rodrigues, Francisco A; Darooneh, Amir Hossein

2018-03-01

In this paper, we analyze explosive synchronization in networks with a community structure. The results of our study indicate that the mesoscopic structure of the networks could affect the synchronization of coupled oscillators. With the variation of three parameters, the degree probability distribution exponent, the community size probability distribution exponent, and the mixing parameter, we could have a fast or slow phase transition. Besides, in some cases, we could have communities which are synchronized inside but not with other communities and vice versa. We also show that there is a limit in these mesoscopic structures which suppresses the transition from the second-order phase transition and results in explosive synchronization. This could be considered as a tuning parameter changing the transition of the system from the second order to the first order.

Diversity and patterns of interaction of an anuran-parasite network in a neotropical wetland.

PubMed

Campião, K M; Ribas, A; Tavares, L E R

2015-12-01

We describe the diversity and structure of a host-parasite network of 11 anuran species and their helminth parasites in the Pantanal wetland, Brazil. Specifically, we investigate how the heterogeneous use of space by hosts changes parasite community diversity, and how the local pool of parasites exploits sympatric host species of different habits. We examined 229 anuran specimens, interacting with 32 helminth parasite taxa. Mixed effect models indicated the influence of anuran body size, but not habit, as a determinant of parasite species richness. Variation in parasite taxonomic diversity, however, was not significantly correlated with host size or habit. Parasite community composition was not correlated with host phylogeny, indicating no strong effect of the evolutionary relationships among anurans on the similarities in their parasite communities. Host-parasite network showed a nested and non-modular pattern of interaction, which is probably a result of the low host specificity observed for most helminths in this study. Overall, we found host body size was important in determining parasite community richness, whereas low parasite specificity was important to network structure.

Rebuilding fish communities: the ghost of fisheries past and the virtue of patience.

PubMed

Collie, Jeremy; Rochet, Marie-Joëlle; Bell, Richard

2013-03-01

The ecosystem approach to management requires the status of individual species to be considered in a community context. We conducted a comparative ecosystem analysis of the Georges Bank and North Sea fish communities to determine the extent to which biological diversity is restored when fishing pressure is reduced. First, fishing mortality estimates were combined to quantify the community-level intensity and selectivity of fishing pressure. Second, standardized bottom-trawl survey data were used to investigate the temporal trends in community metrics. Third, a size-based, multispecies model (LeMans) was simulated to test the response of community metrics to both hypothetical and observed changes in fishing pressure in the two communities. These temperate North Atlantic fish communities have much in common, including a history of overfishing. In recent decades fishing pressure has been reduced, and some species have started to rebuild. The Georges Bank fishery has been more selective, and fishing pressure was reduced sooner. The two communities have similar levels of size diversity and biomass per unit area, but fundamentally different community structure. The North Sea is dominated by smaller species and has lower evenness than Georges Bank. These fundamental differences in community structure are not explained by recent fishing patterns. The multispecies model was able to predict the observed changes in community metrics better on Georges Bank, where rebuilding is more apparent than in the North Sea. Model simulations predicted hysteresis in rebuilding community metrics toward their unfished levels, particularly in the North Sea. Species in the community rebuild at different rates, with smaller prey species outpacing their large predators and overshooting their pre-exploitation abundances. This indirect effect of predator release delays the rebuilding of community structure and biodiversity. Therefore community rebuilding is not just the sum of single-species rebuilding plans. Management strategies that account for interspecific interactions will be needed to restore biodiversity and community structure.

Phytoplankton community structure is influenced by seabird guano enrichment in the Southern Ocean

NASA Astrophysics Data System (ADS)

Shatova, O. A.; Wing, S. R.; Hoffmann, L. J.; Wing, L. C.; Gault-Ringold, M.

2017-05-01

Phytoplankton biomass, productivity and community structure are strongly influenced by differences in nutrient concentrations among oceanographic water masses. Changes in community composition, particularly in the distribution of cell sizes, can result in dramatic changes in the energetics of pelagic food webs and ecosystem function in terms of biogeochemical cycling and carbon sequestration. Here we examine responses of natural phytoplankton communities from four major water masses in the Southern Ocean to enrichment from seabird guano, a concentrated source of bioactive metals (Mn, Fe, Co, Ni, Cu, Zn) and macronutrients (N, P), in a series of incubation experiments. Phytoplankton communities from sub-tropical water, modified sub-tropical water from the Snares Island wake, sub-Antarctic water and Antarctic water from the Ross Sea, each showed dramatic changes in community structure following additions of seabird guano. We observed particularly high growth of prymnesiophytes in response to the guano-derived nutrients within sub-Antarctic and sub-tropical frontal zones, resulting in communities dominated by larger cell sizes than in control incubations. Community changes within treatments enriched with guano were distinct, and in most cases more extensive, than those observed for treatments with additions of macronutrients (N, P) or iron (Fe) alone. These results provide the first empirical evidence that seabird guano enrichment can drive significant changes in the structure and composition of natural phytoplankton communities. Our findings have important implications for understanding the consequences of accumulation of bioactive metals and macronutrients within food webs and the role of seabirds as nutrient vectors within the Southern Ocean ecosystem.

GAP SIZE AND SUCCESSIONAL PROCESSES IN SOUTHERN APPALACHIAN FORESTS

EPA Science Inventory

We used clearcut logging in establishing four replicated sizes of canopy openings (0.016, 0.08, 0.4, and 2.0 ha) in a southern Appalachian hardwood forest in 1981 to examine the long-term effects of disturbance size on plant community structure, biomass accumulation, aboveground ...

Biogeography and body size shuffling of aquatic salamander communities on a shifting refuge

PubMed Central

Bonett, Ronald M.; Trujano-Alvarez, Ana Lilia; Williams, Michael J.; Timpe, Elizabeth K.

2013-01-01

Freshwater habitats of coastal plains are refugia for many divergent vertebrate lineages, yet these environments are highly vulnerable to sea-level fluctuations, which suggest that resident communities have endured dynamic histories. Using the fossil record and a multi-locus nuclear phylogeny, we examine divergence times, biogeography, body size evolution and patterns of community assembly of aquatic salamanders from North American coastal plains since the Late Cretaceous. At least five salamander families occurred on the extensive Western Interior Coastal Plain (WICP), which existed from the Late Cretaceous through the Eocene. Four of these families subsequently colonized the emergent Southeastern Coastal Plain (SECP) by the Early Oligocene to Late Miocene. Three families ultimately survived and underwent extensive body size evolution in situ on the SECP. This included at least two major size reversals in recent taxa that are convergent with confamilial WICP ancestors. Dynamics of the coastal plain, major lineage extinctions and frequent extreme changes in body size have resulted in significant shuffling of the size structure of aquatic salamander communities on this shifting refuge since the Cretaceous. PMID:23466988

Soil properties impacting denitrifier community size, structure, and activity in New Zealand dairy-grazed pasture

NASA Astrophysics Data System (ADS)

Jha, Neha; Saggar, Surinder; Giltrap, Donna; Tillman, Russ; Deslippe, Julie

2017-09-01

Denitrification is an anaerobic respiration process that is the primary contributor of the nitrous oxide (N2O) produced from grassland soils. Our objective was to gain insight into the relationships between denitrifier community size, structure, and activity for a range of pasture soils. We collected 10 dairy pasture soils with contrasting soil textures, drainage classes, management strategies (effluent irrigation or non-irrigation), and geographic locations in New Zealand, and measured their physicochemical characteristics. We measured denitrifier abundance by quantitative polymerase chain reaction (qPCR) and assessed denitrifier diversity and community structure by terminal restriction fragment length polymorphism (T-RFLP) of the nitrite reductase (nirS, nirK) and N2O reductase (nosZ) genes. We quantified denitrifier enzyme activity (DEA) using an acetylene inhibition technique. We investigated whether varied soil conditions lead to different denitrifier communities in soils, and if so, whether they are associated with different denitrification activities and are likely to generate different N2O emissions. Differences in the physicochemical characteristics of the soils were driven mainly by soil mineralogy and the management practices of the farms. We found that nirS and nirK communities were strongly structured along gradients of soil water and phosphorus (P) contents. By contrast, the size and structure of the nosZ community was unrelated to any of the measured soil characteristics. In soils with high water content, the richnesses and abundances of nirS, nirK, and nosZ genes were all significantly positively correlated with DEA. Our data suggest that management strategies to limit N2O emissions through denitrification are likely to be most important for dairy farms on fertile or allophanic soils during wetter periods. Finally, our data suggest that new techniques that would selectively target nirS denitrifiers may be the most effective for limiting N2O emissions through denitrification across a wide range of soil types.

Experimental whole-stream warming alters community size structure.

PubMed

Nelson, Daniel; Benstead, Jonathan P; Huryn, Alexander D; Cross, Wyatt F; Hood, James M; Johnson, Philip W; Junker, James R; Gíslason, Gísli M; Ólafsson, Jón S

2017-07-01

How ecological communities respond to predicted increases in temperature will determine the extent to which Earth's biodiversity and ecosystem functioning can be maintained into a warmer future. Warming is predicted to alter the structure of natural communities, but robust tests of such predictions require appropriate large-scale manipulations of intact, natural habitat that is open to dispersal processes via exchange with regional species pools. Here, we report results of a two-year whole-stream warming experiment that shifted invertebrate assemblage structure via unanticipated mechanisms, while still conforming to community-level metabolic theory. While warming by 3.8 °C decreased invertebrate abundance in the experimental stream by 60% relative to a reference stream, total invertebrate biomass was unchanged. Associated shifts in invertebrate assemblage structure were driven by the arrival of new taxa and a higher proportion of large, warm-adapted species (i.e., snails and predatory dipterans) relative to small-bodied, cold-adapted taxa (e.g., chironomids and oligochaetes). Experimental warming consequently shifted assemblage size spectra in ways that were unexpected, but consistent with thermal optima of taxa in the regional species pool. Higher temperatures increased community-level energy demand, which was presumably satisfied by higher primary production after warming. Our experiment demonstrates how warming reassembles communities within the constraints of energy supply via regional exchange of species that differ in thermal physiological traits. Similar responses will likely mediate impacts of anthropogenic warming on biodiversity and ecosystem function across all ecological communities. © 2016 John Wiley & Sons Ltd.

A geostatistical analysis of small-scale spatial variability in bacterial abundance and community structure in salt marsh creek bank sediments

NASA Technical Reports Server (NTRS)

Franklin, Rima B.; Blum, Linda K.; McComb, Alison C.; Mills, Aaron L.

2002-01-01

Small-scale variations in bacterial abundance and community structure were examined in salt marsh sediments from Virginia's eastern shore. Samples were collected at 5 cm intervals (horizontally) along a 50 cm elevation gradient, over a 215 cm horizontal transect. For each sample, bacterial abundance was determined using acridine orange direct counts and community structure was analyzed using randomly amplified polymorphic DNA fingerprinting of whole-community DNA extracts. A geostatistical analysis was used to determine the degree of spatial autocorrelation among the samples, for each variable and each direction (horizontal and vertical). The proportion of variance in bacterial abundance that could be accounted for by the spatial model was quite high (vertical: 60%, horizontal: 73%); significant autocorrelation was found among samples separated by 25 cm in the vertical direction and up to 115 cm horizontally. In contrast, most of the variability in community structure was not accounted for by simply considering the spatial separation of samples (vertical: 11%, horizontal: 22%), and must reflect variability from other parameters (e.g., variation at other spatial scales, experimental error, or environmental heterogeneity). Microbial community patch size based upon overall similarity in community structure varied between 17 cm (vertical) and 35 cm (horizontal). Overall, variability due to horizontal position (distance from the creek bank) was much smaller than that due to vertical position (elevation) for both community properties assayed. This suggests that processes more correlated with elevation (e.g., drainage and redox potential) vary at a smaller scale (therefore producing smaller patch sizes) than processes controlled by distance from the creek bank. c2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Trophic diversity, size and biomass spectrum of Bay of Bengal nematodes: A study case on depth and latitudinal patterns

NASA Astrophysics Data System (ADS)

Ansari, Kapuli Gani Mohamed Thameemul; Lyla, Somasundharanair; Khan, Syed Ajmal; Bhadury, Punyasloke

2017-09-01

Depth and latitudinal patterns of nematode functional attributes were investigated from 35 stations of Bay of Bengal (BoB) continental shelf. We aim to address whether depth and latitudinal variations can modify nematode community structure and their functional attributes (trophic diversity, size and biomass spectra). Global trend of depth and latitudinal related variations have also been noticed from BoB shelf in terms of nematode abundance and species richness, albeit heterogeneity patterns were encountered in functional attributes. Index of trophic diversity values revealed higher trophic diversity across the BoB shelf and suggested variety of food resource availability. However, downstream analysis of trophic status showed depth and latitude specific patterns but not reflected in terms of size and biomass spectrum. The peaks at different positions clearly visualized heterogeneity in distribution patterns for both size and biomass spectrum and also there was evidence of availability of diversified food resources. Nematode biomass spectra (NBS) constructed for nematode communities showed shift in peak biomass values towards lower to moderate size classes particularly in shallower depth but did not get reflected in latitudes. However, Chennai and Parangipettai transects demonstrated shift in peak biomass values towards higher biomass classes explaining the representation of higher nematode abundance. Our findings concluded that depth and latitudes are physical variables; they may not directly affect nematode community structure and functional attributes but they might influence the other factors such as food availability, sediment deposition and settlement rate. Our observations suggest that the local factors (seasonal character) of phytodetrital food flux can be very important for shaping the nematode community structure and success of nematode functional heterogeneity patterns across the Bay of Bengal shelf.

Effect of copper sulphate treatment on natural phytoplanktonic communities.

PubMed

Le Jeune, Anne-Hélène; Charpin, Marie; Deluchat, Véronique; Briand, Jean-François; Lenain, Jean-François; Baudu, Michel; Amblard, Christian

2006-12-01

Copper sulphate treatment is widely used as a global and empirical method to remove or control phytoplankton blooms without precise description of the impact on phytoplanktonic populations. The effects of two copper sulphate treatments on natural phytoplanktonic communities sampled in the spring and summer seasons, were assessed by indoor mesocosm experiments. The initial copper-complexing capacity of each water sample was evaluated before each treatment. The copper concentrations applied were 80 microg l(-1) and 160 microg l(-1) of copper, below and above the water complexation capacity, respectively. The phytoplanktonic biomass recovered within a few days after treatment. The highest copper concentration, which generated a highly toxic environment, caused a global decrease in phytoplankton diversity, and led to the development and dominance of nanophytoplanktonic Chlorophyceae. In mesocosms treated with 80 microg l(-1) of copper, the effect on phytoplanktonic community size-class structure and composition was dependent on seasonal variation. This could be related to differences in community composition, and thus to species sensitivity to copper and to differences in copper bioavailability between spring and summer. Both treatments significantly affected cyanobacterial biomass and caused changes in the size-class structure and composition of phytoplanktonic communities which may imply modifications of the ecosystem structure and function.

Plasma asymmetric dimethylarginine, L-arginine and left ventricular structure and function in a community-based sample.

PubMed

Lieb, Wolfgang; Benndorf, Ralf A; Benjamin, Emelia J; Sullivan, Lisa M; Maas, Renke; Xanthakis, Vanessa; Schwedhelm, Edzard; Aragam, Jayashri; Schulze, Friedrich; Böger, Rainer H; Vasan, Ramachandran S

2009-05-01

Increasing evidence indicates that cardiac structure and function are modulated by the nitric oxide (NO) system. Elevated plasma concentrations of asymmetric dimethylarginine (ADMA; a competitive inhibitor of NO synthase) have been reported in patients with end-stage renal disease. It is unclear if circulating ADMA and L-arginine levels are related to cardiac structure and function in the general population. We related plasma ADMA and L-arginine (the amino acid precursor of NO) to echocardiographic left ventricular (LV) mass, left atrial (LA) size and fractional shortening (FS) using multivariable linear regression analyses in 1919 Framingham Offspring Study participants (mean age 57 years, 58% women). Overall, neither ADMA or L-arginine, nor their ratio was associated with LV mass, LA size and FS in multivariable models (p>0.10 for all). However, we observed effect modification by obesity of the relations of ADMA and LA size (p for interaction p=0.04): ADMA was positively related to LA size in obese individuals (adjusted-p=0.0004 for trend across ADMA quartiles) but not in non-obese people. In our large community-based sample, plasma ADMA and l-arginine concentrations were not related to cardiac structure or function. The observation of positive relations of LA size and ADMA in obese individuals warrants confirmation.

Microbial community responses in forest mineral soil to compaction, organic matter removal, and vegetation control

Treesearch

Matt D. Busse; Samual E. Beattie; Robert F. Powers; Felipe G. Sanchez; Allan E. Tiarks

2006-01-01

We tested three disturbance hypotheses in young conifer plantations: H1: soil compaction and removal of surface organic matter produces sustained changes in microbial community size, activity, and structure in mineral soil; H2: microbial community characteristics in mineral soil are linked to the recovery of plant diversity...

Are the Most Plastic Species the Most Abundant Ones? An Assessment Using a Fish Assemblage

PubMed Central

Vidal, Nicolás; Zaldúa, Natalia; D'Anatro, Alejandro; Naya, Daniel E.

2014-01-01

Few studies have evaluated phenotypic plasticity at the community level, considering, for example, plastic responses in an entire species assemblage. In addition, none of these studies have addressed the relationship between phenotypic plasticity and community structure. Within this context, here we assessed the magnitude of seasonal changes in digestive traits (seasonal flexibility), and of changes during short-term fasting (flexibility during fasting), occurring in an entire fish assemblage, comprising ten species, four trophic levels, and a 37-fold range in body mass. In addition, we analyzed the relationship between estimates of digestive flexibility and three basic assemblage structure attributes, i.e., species trophic position, body size, and relative abundance. We found that: (1) Seasonal digestive flexibility was not related with species trophic position or with body size; (2) Digestive flexibility during fasting tended to be inversely correlated with body size, as expected from scaling relationships; (3) Digestive flexibility, both seasonal and during fasting, was positively correlated with species relative abundance. In conclusion, the present study identified two trends in digestive flexibility in relation to assemblage structure, which represents an encouraging departure point in the search of general patterns in phenotypic plasticity at the local community scale. PMID:24651865

Physical processes dominate in shaping invertebrate assemblages in reef-associated sediments of an exposed Hawaiian coast

USGS Publications Warehouse

DeFelice, R.C.; Parrish, J.D.

2001-01-01

The invertebrate assemblages in sediments bordering exposed fringing reefs at Hanalei Bay, Kauai, Hawaii, were examined during July to September 1994. Densities of invertebrate animals larger than 0.5 mm in sediments of the bay ranged from counts of 10 260 m-2 in the fine carbonate sands of the central bay to 870 m-2 in the habitat dominated by terrigenous silt near the reef edge close to the Hanalei river mouth. Similar sediment types supported broadly similar infaunal communities. Within the primarily carbonate sediments, mean grain size and wave exposure appear to have an important influence on the community. Taxonomic richness, number of individuals, and diversity showed significant negative relationships with exposure to wave energy (as estimated by sand ripple wavelength). The number of individuals was also significantly correlated with mean grain size. Overall, polychaetes and small crustaceans were numerically dominant among the major taxonomic groups investigated. Macrophagous and microphagous polychaetes had significant, but opposite, associations with grain size. In addition, microphagous polychaetes were significantly negatively correlated with wave exposure. No habitat variable measured could explain the variation in percent composition of crustaceans or echinoderms in the sedimentary habitats. The percentage of gastropods in the community was significantly negatively correlated with grain size, grain-size standard deviation and exposure, and positively with percent organic carbon. Bivalves were significantly positively associated with depth and grain size. These strong relationships imply that, in Hanalei Bay, physical processes are especially important in influencing assemblage structure, and that community structure and composition vary continuously along environmental gradients.

Biodiversity conservation in an anthropized landscape: Trees, not patch size drive, bird community composition in a low-input agro-ecosystem.

PubMed

Mellink, Eric; Riojas-López, Mónica E; Cárdenas-García, Melinda

2017-01-01

One of the most typical agro-ecosystems in the Llanos de Ojuelos, a semi-arid region of central Mexico, is that of fruit-production orchards of nopales (prickly pear cacti). This perennial habitat with complex vertical structure provides refuge and food for at least 112 species of birds throughout the year. Nopal orchards vary in their internal structure, size and shrub/tree composition, yet these factors have unknown effects on the animals that use them. To further understand the conservation potential of this agro-ecosystem, we evaluated the effects of patch-size and the presence of trees on bird community composition, as well as several habitat variables, through an information-theoretical modelling approach. Community composition was obtained through a year of census transects in 12 orchards. The presence of trees in the orchards was the major driver of bird communities followed by seasonality; bird communities are independent of patch size, except for small orchard patches that benefit black-chin sparrows, which are considered a sensitive species. At least 55 species of six trophic guilds (insectivores, granivores, carnivores, nectivores, omnivores, and frugivores) used the orchards. Orchards provide adequate habitat and food resources for several sensitive species of resident and migratory sparrows. The attributes that make orchards important for birds: trees, shrubs, herb seeds, and open patches can be managed to maintain native biodiversity in highly anthropized regions with an urgent need to find convergence between production and biological conservation.

Biodiversity conservation in an anthropized landscape: Trees, not patch size drive, bird community composition in a low-input agro-ecosystem

PubMed Central

Mellink, Eric; Cárdenas-García, Melinda

2017-01-01

One of the most typical agro-ecosystems in the Llanos de Ojuelos, a semi-arid region of central Mexico, is that of fruit-production orchards of nopales (prickly pear cacti). This perennial habitat with complex vertical structure provides refuge and food for at least 112 species of birds throughout the year. Nopal orchards vary in their internal structure, size and shrub/tree composition, yet these factors have unknown effects on the animals that use them. To further understand the conservation potential of this agro-ecosystem, we evaluated the effects of patch-size and the presence of trees on bird community composition, as well as several habitat variables, through an information-theoretical modelling approach. Community composition was obtained through a year of census transects in 12 orchards. The presence of trees in the orchards was the major driver of bird communities followed by seasonality; bird communities are independent of patch size, except for small orchard patches that benefit black-chin sparrows, which are considered a sensitive species. At least 55 species of six trophic guilds (insectivores, granivores, carnivores, nectivores, omnivores, and frugivores) used the orchards. Orchards provide adequate habitat and food resources for several sensitive species of resident and migratory sparrows. The attributes that make orchards important for birds: trees, shrubs, herb seeds, and open patches can be managed to maintain native biodiversity in highly anthropized regions with an urgent need to find convergence between production and biological conservation. PMID:28686608

Analysing taxonomic structures and local ecological processes in temperate forests in North Eastern China.

PubMed

Fan, Chunyu; Tan, Lingzhao; Zhang, Chunyu; Zhao, Xiuhai; von Gadow, Klaus

2017-10-30

One of the core issues of forest community ecology is the exploration of how ecological processes affect community structure. The relative importance of different processes is still under debate. This study addresses four questions: (1) how is the taxonomic structure of a forest community affected by spatial scale? (2) does the taxonomic structure reveal effects of local processes such as environmental filtering, dispersal limitation or interspecific competition at a local scale? (3) does the effect of local processes on the taxonomic structure vary with the spatial scale? (4) does the analysis based on taxonomic structures provide similar insights when compared with the use of phylogenetic information? Based on the data collected in two large forest observational field studies, the taxonomic structures of the plant communities were analyzed at different sampling scales using taxonomic ratios (number of genera/number of species, number of families/number of species), and the relationship between the number of higher taxa and the number of species. Two random null models were used and the "standardized effect size" (SES) of taxonomic ratios was calculated, to assess possible differences between the observed and simulated taxonomic structures, which may be caused by specific ecological processes. We further applied a phylogeny-based method to compare results with those of the taxonomic approach. As expected, the taxonomic ratios decline with increasing grain size. The quantitative relationship between genera/families and species, described by a linearized power function, showed a good fit. With the exception of the family-species relationship in the Jiaohe study area, the exponents of the genus/family-species relationships did not show any scale dependent effects. The taxonomic ratios of the observed communities had significantly lower values than those of the simulated random community under the test of two null models at almost all scales. Null Model 2 which considered the spatial dispersion of species generated a taxonomic structure which proved to be more consistent with that in the observed community. As sampling sizes increased from 20 m × 20 m to 50 m × 50 m, the magnitudes of SESs of taxonomic ratios increased. Based on the phylogenetic analysis, we found that the Jiaohe plot was phylogenetically clustered at almost all scales. We detected significant phylogenetically overdispersion at the 20 m × 20 m and 30 m × 30 m scales in the Liangshui plot. The results suggest that the effect of abiotic filtering is greater than the effects of interspecific competition in shaping the local community at almost all scales. Local processes influence the taxonomic structures, but their combined effects vary with the spatial scale. The taxonomic approach provides similar insights as the phylogenetic approach, especially when we applied a more conservative null model. Analysing taxonomic structure may be a useful tool for communities where well-resolved phylogenetic data are not available.

A hybrid spectral representation of phytoplankton growth and zooplankton response: The ''control rod'' model of plankton interaction

NASA Astrophysics Data System (ADS)

Armstrong, Robert A.

2003-11-01

Phytoplankton species interact through competition for light and nutrients; they also interact through grazers they hold in common. Both interactions are expected to be size-dependent: smaller phytoplankton species will be at an advantage when nutrients are scarce due to surface/volume considerations, while species that are similar in size are more likely to be consumed by grazers held in common than are species that differ greatly in size. While phytoplankton competition for nutrients and light has been extensively characterized, size-based interaction through shared grazers has not been represented systematically. The latter situation is particularly unfortunate because small changes in community structure can give rise to large changes in ecosystem dynamics and, in inverse modeling, to large changes in estimated parameter values. A simple, systematic way to represent phytoplankton interaction through shared grazers, one resistant to unintended idiosyncrasy of model construction yet capable of representing scientifically justifiable idiosyncrasy, would aid greatly in the modeling process. Here I develop a model structure that allows systematic representation of plankton interaction. In this model, the zooplankton community is represented as a continuous size spectrum, while phytoplankton species can be represented individually. The mechanistic basis of the model is a shift in the zooplankton community from carnivory to omnivory to herbivory as phytoplankton density increases. I discuss two limiting approximations in some detail, and fit both to data from the IronEx II experiment. The first limiting case represents a community with no grazer-based interaction among phytoplankton species; this approximation illuminates the general structure of the model. In particular, the zooplankton spectrum can be viewed as the analog of a control rod in a nuclear reactor, which prevents (or fails to prevent) an exponential bloom of phytoplankton. A second, more complex limiting case allows more general interaction of phytoplankton species along a size axis. This latter case would be suitable for describing competition among species with distinct biogeochemical roles, or between species that cause harmful algal blooms and those that do not. The model structure as a whole is therefore simple enough to guide thinking, yet detailed enough to allow quantitative prediction.

Vulnerability of coral reef fisheries to a loss of structural complexity.

PubMed

Rogers, Alice; Blanchard, Julia L; Mumby, Peter J

2014-05-05

Coral reefs face a diverse array of threats, from eutrophication and overfishing to climate change. As live corals are lost and their skeletons eroded, the structural complexity of reefs declines. This may have important consequences for the survival and growth of reef fish because complex habitats mediate predator-prey interactions [1, 2] and influence competition [3-5] through the provision of prey refugia. A positive correlation exists between structural complexity and reef fish abundance and diversity in both temperate and tropical ecosystems [6-10]. However, it is not clear how the diversity of available refugia interacts with individual predator-prey relationships to explain emergent properties at the community scale. Furthermore, we do not yet have the ability to predict how habitat loss might affect the productivity of whole reef communities and the fisheries they support. Using data from an unfished reserve in The Bahamas, we find that structural complexity is associated not only with increased fish biomass and abundance, but also with nonlinearities in the size spectra of fish, implying disproportionately high abundances of certain size classes. By developing a size spectrum food web model that links the vulnerability of prey to predation with the structural complexity of a reef, we show that these nonlinearities can be explained by size-structured prey refugia that reduce mortality rates and alter growth rates in different parts of the size spectrum. Fitting the model with data from a structurally complex habitat, we predict that a loss of complexity could cause more than a 3-fold reduction in fishery productivity. Copyright © 2014 Elsevier Ltd. All rights reserved.

How Community Has Shaped the Protein Data Bank

PubMed Central

Berman, Helen M.; Kleywegt, Gerard J.; Nakamura, Haruki; Markley, John L.

2015-01-01

Following several years of community discussion, the Protein Data Bank (PDB) was established in 1971 as a public repository for the coordinates of three-dimensional models of biological macromolecules. Since then, the number, size, and complexity of structural models have continued to grow, reflecting the productivity of structural biology. Managed by the Worldwide PDB organization, the PDB has been able to meet increasing demands for the quantity of structural information and of quality. In addition to providing unrestricted access to structural information, the PDB also works to promote data standards and to raise the profile of structural biology with broader audiences. In this perspective, we describe the history of PDB and the many ways in which the community continues to shape the archive. PMID:24010707

Among-Population Variation in Microbial Community Structure in the Floral Nectar of the Bee-Pollinated Forest Herb Pulmonaria officinalis L

PubMed Central

Jacquemyn, Hans; Lenaerts, Marijke; Brys, Rein; Willems, Kris; Honnay, Olivier; Lievens, Bart

2013-01-01

Background Microbial communities in floral nectar have been shown to be characterized by low levels of species diversity, yet little is known about among-plant population variation in microbial community composition. Methodology/Principal Findings We investigated the microbial community structure (yeasts and bacteria) in floral nectar of ten fragmented populations of the bee-pollinated forest herb Pulmonaria officinalis. We also explored possible relationships between plant population size and microbial diversity in nectar, and related microbial community composition to the distance separating plant populations. Culturable bacteria and yeasts occurring in the floral nectar of a total of 100 plant individuals were isolated and identified by partially sequencing the 16S rRNA gene and D1/D2 domains of the 26S rRNA gene, respectively. A total of 9 and 11 yeast and 28 and 39 bacterial OTUs was found, taking into account a 3% (OTU0.03) and 1% sequence dissimilarity cut-off (OTU0.01). OTU richness at the plant population level (i.e. the number of OTUs per population) was low for yeasts (mean: 1.7, range: 0–4 OTUs0.01/0.03 per population), whereas on average 6.9 (range: 2–13) OTUs0.03 and 7.9 (range 2–16) OTUs0.01 per population were found for bacteria. Both for yeasts and bacteria, OTU richness was not significantly related to plant population size. Similarity in community composition among populations was low (average Jaccard index: 0.14), and did not decline with increasing distance between populations. Conclusions/Significance We found low similarity in microbial community structure among populations, suggesting that the assembly of nectar microbiota is to a large extent context-dependent. Although the precise factors that affect variation in microbial community structure in floral nectar require further study, our results indicate that both local and regional processes may contribute to among-population variation in microbial community structure in nectar. PMID:23536759

Among-population variation in microbial community structure in the floral nectar of the bee-pollinated forest herb Pulmonaria officinalis L.

PubMed

Jacquemyn, Hans; Lenaerts, Marijke; Brys, Rein; Willems, Kris; Honnay, Olivier; Lievens, Bart

2013-01-01

Microbial communities in floral nectar have been shown to be characterized by low levels of species diversity, yet little is known about among-plant population variation in microbial community composition. We investigated the microbial community structure (yeasts and bacteria) in floral nectar of ten fragmented populations of the bee-pollinated forest herb Pulmonaria officinalis. We also explored possible relationships between plant population size and microbial diversity in nectar, and related microbial community composition to the distance separating plant populations. Culturable bacteria and yeasts occurring in the floral nectar of a total of 100 plant individuals were isolated and identified by partially sequencing the 16S rRNA gene and D1/D2 domains of the 26S rRNA gene, respectively. A total of 9 and 11 yeast and 28 and 39 bacterial OTUs was found, taking into account a 3% (OTU0.03) and 1% sequence dissimilarity cut-off (OTU0.01). OTU richness at the plant population level (i.e. the number of OTUs per population) was low for yeasts (mean: 1.7, range: 0-4 OTUs0.01/0.03 per population), whereas on average 6.9 (range: 2-13) OTUs0.03 and 7.9 (range 2-16) OTUs0.01 per population were found for bacteria. Both for yeasts and bacteria, OTU richness was not significantly related to plant population size. Similarity in community composition among populations was low (average Jaccard index: 0.14), and did not decline with increasing distance between populations. We found low similarity in microbial community structure among populations, suggesting that the assembly of nectar microbiota is to a large extent context-dependent. Although the precise factors that affect variation in microbial community structure in floral nectar require further study, our results indicate that both local and regional processes may contribute to among-population variation in microbial community structure in nectar.

Biophysical controls on cluster dynamics and architectural differentiation of microbial biofilms in contrasting flow environments

PubMed Central

Hödl, Iris; Mari, Lorenzo; Bertuzzo, Enrico; Suweis, Samir; Besemer, Katharina; Rinaldo, Andrea; Battin, Tom J

2014-01-01

Ecology, with a traditional focus on plants and animals, seeks to understand the mechanisms underlying structure and dynamics of communities. In microbial ecology, the focus is changing from planktonic communities to attached biofilms that dominate microbial life in numerous systems. Therefore, interest in the structure and function of biofilms is on the rise. Biofilms can form reproducible physical structures (i.e. architecture) at the millimetre-scale, which are central to their functioning. However, the spatial dynamics of the clusters conferring physical structure to biofilms remains often elusive. By experimenting with complex microbial communities forming biofilms in contrasting hydrodynamic microenvironments in stream mesocosms, we show that morphogenesis results in ‘ripple-like’ and ‘star-like’ architectures – as they have also been reported from monospecies bacterial biofilms, for instance. To explore the potential contribution of demographic processes to these architectures, we propose a size-structured population model to simulate the dynamics of biofilm growth and cluster size distribution. Our findings establish that basic physical and demographic processes are key forces that shape apparently universal biofilm architectures as they occur in diverse microbial but also in single-species bacterial biofilms. PMID:23879839

Exceptional body sizes but typical trophic structure in a Pleistocene food web.

PubMed

Segura, Angel M; Fariña, Richard A; Arim, Matías

2016-05-01

In this study, we focused on the exceptionally large mammals inhabiting the Americas during the Quaternary period and the paramount role of body size in species ecology. We evaluated two main features of Pleistocene food webs: the relationship between body size and (i) trophic position and (ii) vulnerability to predation. Despite the large range of species sizes, we found a hump-shaped relationship between trophic position and body size. We also found a negative trend in species vulnerability similar to that observed in modern faunas. The largest species lived near the boundary of energetic constraints, such that any shift in resource availability could drive these species to extinction. Our results reinforce several features of megafauna ecology: (i) the negative relationship between trophic position and body size implies that large-sized species were particularly vulnerable to changes in energetic support; (ii) living close to energetic imbalance could favour the incorporation of additional energy sources, for example, a transition from a herbivorous to a scavenging diet in the largest species (e.g. Megatherium) and (iii) the interactions and structure of Quaternary megafauna communities were shaped by similar forces to those shaping modern fauna communities. © 2016 The Author(s).

Size matters: The contribution of mega-infauna to the food webs and ecosystem services of an Oregon estuary - ESA

EPA Science Inventory

Background/Questions/Methods Large-bodied invertebrates (bivalves, polychaetes, burrowing shrimps) are common to infaunal communities of NE Pacific estuaries, but their contribution to estuarine community structure, function and ecosystem services is poorly understood because ...

Plasma asymmetric dimethylarginine, L-arginine and Left Ventricular Structure and Function in a Community-based Sample

PubMed Central

Lieb, Wolfgang; Benndorf, Ralf A.; Benjamin, Emelia J.; Sullivan, Lisa M.; Maas, Renke; Xanthakis, Vanessa; Schwedhelm, Edzard; Aragam, Jayashri; Schulze, Friedrich; Böger, Rainer H.; Vasan, Ramachandran S.

2009-01-01

Objective Increasing evidence indicates that cardiac structure and function are modulated by the nitric oxide (NO) system. Elevated plasma concentrations of asymmetric dimethylarginine (ADMA; a competitive inhibitor of NO synthase) have been reported in patients with end-stage renal disease. It is unclear if circulating ADMA and L-arginine levels are related to cardiac structure and function in the general population. Methods We related plasma ADMA and L-Arginine (the amino acid precursor of NO) to echocardiographic left ventricular (LV) mass, left atrial (LA) size and fractional shortening (FS) using multivariable linear regression analyses in 1,919 Framingham Offspring Study participants (mean age 57 years, 58 % women). Results Overall, neither ADMA or L-arginine, nor their ratio was associated with LV mass, LA size and FS in multivariable models (p>0.10 for all). However, we observed effect modification by obesity of the relations of ADMA and LA size (p for interaction p=0.04): ADMA was positively related to LA size in obese individuals (adjusted-p=0.0004 for trend across ADMA quartiles) but not in non-obese people. Conclusion In our large community-based sample, plasma ADMA and L-arginine concentrations were not related to cardiac structure or function. The observation of positive relations of LA size and ADMA in obese individuals warrants confirmation. PMID:18829028

Professional Development through Faculty Learning Communities

ERIC Educational Resources Information Center

Glowacki-Dudka, Michelle; Brown, Michael P.

2007-01-01

Faculty learning communities (FLC) provide opportunities for professional development and personal growth within university settings. Some FLC are structured; others are unstructured. Faculty at a mid-sized Midwestern state university were asked a series of close- and open-ended questions that examined the reasons for and benefits from their…

How community has shaped the Protein Data Bank.

PubMed

Berman, Helen M; Kleywegt, Gerard J; Nakamura, Haruki; Markley, John L

2013-09-03

Following several years of community discussion, the Protein Data Bank (PDB) was established in 1971 as a public repository for the coordinates of three-dimensional models of biological macromolecules. Since then, the number, size, and complexity of structural models have continued to grow, reflecting the productivity of structural biology. Managed by the Worldwide PDB organization, the PDB has been able to meet increasing demands for the quantity of structural information and of quality. In addition to providing unrestricted access to structural information, the PDB also works to promote data standards and to raise the profile of structural biology with broader audiences. In this perspective, we describe the history of PDB and the many ways in which the community continues to shape the archive. Copyright © 2013 Elsevier Ltd. All rights reserved.

Impact of dilution on microbial community structure and functional potential: comparison of numerical simulations and batch culture experiments

NASA Technical Reports Server (NTRS)

Franklin, R. B.; Garland, J. L.; Bolster, C. H.; Mills, A. L.

2001-01-01

A series of microcosm experiments was performed using serial dilutions of a sewage microbial community to inoculate a set of batch cultures in sterile sewage. After inoculation, the dilution-defined communities were allowed to regrow for several days and a number of community attributes were measured in the regrown assemblages. Based upon a set of numerical simulations, community structure was expected to differ along the dilution gradient; the greatest differences in structure were anticipated between the undiluted-low-dilution communities and the communities regrown from the very dilute (more than 10(-4)) inocula. Furthermore, some differences were expected among the lower-dilution treatments (e.g., between undiluted and 10(-1)) depending upon the evenness of the original community. In general, each of the procedures used to examine the experimental community structures separated the communities into at least two, often three, distinct groups. The groupings were consistent with the simulated dilution of a mixture of organisms with a very uneven distribution. Significant differences in community structure were detected with genetic (amplified fragment length polymorphism and terminal restriction fragment length polymorphism), physiological (community level physiological profiling), and culture-based (colony morphology on R2A agar) measurements. Along with differences in community structure, differences in community size (acridine orange direct counting), composition (ratio of sewage medium counts to R2A counts, monitoring of each colony morphology across the treatments), and metabolic redundancy (i.e., generalist versus specialist) were also observed, suggesting that the differences in structure and diversity of communities maintained in the same environment can be manifested as differences in community organization and function.

Mesoherbivores affect grasshopper communities in a megaherbivore-dominated South African savannah.

PubMed

van der Plas, Fons; Olff, Han

2014-06-01

African savannahs are among the few places on earth where diverse communities of mega- and meso-sized ungulate grazers dominate ecosystem functioning. Less conspicuous, but even more diverse, are the communities of herbivorous insects such as grasshoppers, which share the same food. Various studies investigated the community assembly of these groups separately, but it is poorly known how ungulate communities shape grasshopper communities. Here, we investigated how ungulate species of different body size alter grasshopper communities in a South African savannah. White rhino is the most abundant vertebrate herbivore in our study site. Other common mesoherbivores include buffalo, zebra and impala. We hypothesized that white rhinos would have greater impact than mesoherbivores on grasshopper communities. Using 10-year-old exclosures, at eight sites we compared the effects of ungulates on grasshopper communities in three nested treatments: (i) unfenced plots ('control plots') with all vertebrate herbivores present, (ii) plots with a low cable fence, excluding white rhino ('megaherbivore exclosures'), and (iii) plots with tall fences, excluding all herbivores larger than rodents ('complete ungulate exclosures'). In each plot, we collected data of vegetation structure, grass and grasshopper community composition. Complete ungulate exclosures contained 30% taller vegetation than megaherbivore exclosures and they were dominated by different grass and grasshopper species. Grasshoppers in complete ungulate exclosures were on average 3.5 mm longer than grasshoppers in megaherbivore exclosures, possibly due to changes in plant communities or vegetation structure. We conclude that surprisingly, in this megaherbivore hotspot, mesoherbivores, instead of megaherbivores, most strongly affect grasshopper communities.

[Effects of bamboo charcoal on the growth of Trifolium repens and soil bacterial community structure].

PubMed

Li, Song-Hao; He, Dong-Hua; Shen, Qiu-Lan; Xu, Qiu-Fang

2014-08-01

The effects of addition rates (0, 3% and 9%) and particle sizes (0.05, 0.05-1.0 and 1.0-2.0 mm) of bamboo charcoal on the growth of Trifolium repens and soil microbial community structure were investigated. The results showed that bamboo charcoal addition greatly promoted the early growth of T. repens, with the 9% charcoal addition rate being slightly better than the 3% charcoal addition rate. The effects of different particle sizes of bamboo charcoal on the growth of T. repens were not different significantly. Growth promotion declined with time during 120 days after sowing, and disappeared completely after 5 months. DGGE analysis of the bacterial 16S rDNA V3 fragment indicated that bamboo charcoal altered the soil bacterial community structure. The amount and Shannon diversity index of bacteria in the bamboo charcoal addition treatments increased compared with CK. The quantitative analysis showed that the amount of bacteria in the treatment with bamboo charcoal of fine particle (D < 0.05 mm) at the 9% addition rate was significantly higher than in the other treatments. The fine bamboo charcoal had a great effect on soil bacteria amount compared with the charcoal of other sizes at the same addition rate.

A nonuniform popularity-similarity optimization (nPSO) model to efficiently generate realistic complex networks with communities

NASA Astrophysics Data System (ADS)

Muscoloni, Alessandro; Vittorio Cannistraci, Carlo

2018-05-01

The investigation of the hidden metric space behind complex network topologies is a fervid topic in current network science and the hyperbolic space is one of the most studied, because it seems associated to the structural organization of many real complex systems. The popularity-similarity-optimization (PSO) model simulates how random geometric graphs grow in the hyperbolic space, generating realistic networks with clustering, small-worldness, scale-freeness and rich-clubness. However, it misses to reproduce an important feature of real complex networks, which is the community organization. The geometrical-preferential-attachment (GPA) model was recently developed in order to confer to the PSO also a soft community structure, which is obtained by forcing different angular regions of the hyperbolic disk to have a variable level of attractiveness. However, the number and size of the communities cannot be explicitly controlled in the GPA, which is a clear limitation for real applications. Here, we introduce the nonuniform PSO (nPSO) model. Differently from GPA, the nPSO generates synthetic networks in the hyperbolic space where heterogeneous angular node attractiveness is forced by sampling the angular coordinates from a tailored nonuniform probability distribution (for instance a mixture of Gaussians). The nPSO differs from GPA in other three aspects: it allows one to explicitly fix the number and size of communities; it allows one to tune their mixing property by means of the network temperature; it is efficient to generate networks with high clustering. Several tests on the detectability of the community structure in nPSO synthetic networks and wide investigations on their structural properties confirm that the nPSO is a valid and efficient model to generate realistic complex networks with communities.

Household demographic determinants of Ebola epidemic risk.

PubMed

Adams, Ben

2016-03-07

A salient characteristic of Ebola, and some other infectious diseases such as Tuberculosis, is intense transmission among small groups of cohabitants and relatively limited indiscriminate transmission in the wider population. Here we consider a mathematical model for an Ebola epidemic in a population structured into households of equal size. We show that household size, a fundamental demographic unit, is a critical factor that determines the vulnerability of a community to epidemics, and the effort required to control them. Our analysis is based on the household reproduction number, but we also consider the basic reproduction number, intrinsic growth rate and final epidemic size. We show that, when other epidemiological parameters are kept the same, all of these quantifications of epidemic growth and size are increased by larger households and more intense within-household transmission. We go on to model epidemic control by case detection and isolation followed by household quarantine. We show that, if household quarantine is ineffective, the critical probability with which cases must be detected to halt an epidemic increases significantly with each increment in household size and may be a very challenging target for communities composed of large households. Effective quarantine may, however, mitigate the detrimental impact of large household sizes. We conclude that communities composed of large households are fundamentally more vulnerable to epidemics of infectious diseases primarily transmitted by close contact, and any assessment of control strategies for these epidemics should take into account the demographic structure of the population. Copyright © 2015 Elsevier Ltd. All rights reserved.

Size matters: The contribution of mega-infauna to the food webs and ecosystem services of an Oregon estuary - 9-30-12

EPA Science Inventory

Large-bodied invertebrates (bivalves, polychaetes, burrowing shrimps) are common to infaunal communities of NE Pacific estuaries, but their contribution to estuarine community structure, function and ecosystem services is poorly understood because they are difficult to sample and...

Patterns of rare and abundant marine microbial eukaryotes.

PubMed

Logares, Ramiro; Audic, Stéphane; Bass, David; Bittner, Lucie; Boutte, Christophe; Christen, Richard; Claverie, Jean-Michel; Decelle, Johan; Dolan, John R; Dunthorn, Micah; Edvardsen, Bente; Gobet, Angélique; Kooistra, Wiebe H C F; Mahé, Frédéric; Not, Fabrice; Ogata, Hiroyuki; Pawlowski, Jan; Pernice, Massimo C; Romac, Sarah; Shalchian-Tabrizi, Kamran; Simon, Nathalie; Stoeck, Thorsten; Santini, Sébastien; Siano, Raffaele; Wincker, Patrick; Zingone, Adriana; Richards, Thomas A; de Vargas, Colomban; Massana, Ramon

2014-04-14

Biological communities are normally composed of a few abundant and many rare species. This pattern is particularly prominent in microbial communities, in which most constituent taxa are usually extremely rare. Although abundant and rare subcommunities may present intrinsic characteristics that could be crucial for understanding community dynamics and ecosystem functioning, microbiologists normally do not differentiate between them. Here, we investigate abundant and rare subcommunities of marine microbial eukaryotes, a crucial group of organisms that remains among the least-explored biodiversity components of the biosphere. We surveyed surface waters of six separate coastal locations in Europe, independently considering the picoplankton, nanoplankton, and microplankton/mesoplankton organismal size fractions. Deep Illumina sequencing of the 18S rRNA indicated that the abundant regional community was mostly structured by organismal size fraction, whereas the rare regional community was mainly structured by geographic origin. However, some abundant and rare taxa presented similar biogeography, pointing to spatiotemporal structure in the rare microeukaryote biosphere. Abundant and rare subcommunities presented regular proportions across samples, indicating similar species-abundance distributions despite taxonomic compositional variation. Several taxa were abundant in one location and rare in other locations, suggesting large oscillations in abundance. The substantial amount of metabolically active lineages found in the rare biosphere suggests that this subcommunity constitutes a diversity reservoir that can respond rapidly to environmental change. We propose that marine planktonic microeukaryote assemblages incorporate dynamic and metabolically active abundant and rare subcommunities, with contrasting structuring patterns but fairly regular proportions, across space and time. Copyright © 2014 Elsevier Ltd. All rights reserved.

Repeated parallel evolution reveals limiting similarity in subterranean diving beetles.

PubMed

Vergnon, Remi; Leijs, Remko; van Nes, Egbert H; Scheffer, Marten

2013-07-01

The theory of limiting similarity predicts that co-occurring species must be sufficiently different to coexist. Although this idea is a staple of community ecology, convincing empirical evidence has been scarce. Here we examine 34 subterranean beetle communities in arid inland Australia that share the same habitat type but have evolved in complete isolation over the past 5 million years. Although these communities come from a range of phylogenetic origins, we find that they have almost invariably evolved to share a similar size structure. The relative positions of coexisting species on the body size axis were significantly more regular across communities than would be expected by chance, with a size ratio, on average, of 1.6 between coexisting species. By contrast, species' absolute body sizes varied substantially from one community to the next. This suggests that self-organized spacing according to limiting-similarity theory, as opposed to evolution toward preexisting fixed niches, shaped the communities. Using a model starting from random sets of founder species, we demonstrate that the patterns are indeed consistent with evolutionary self-organization. For less isolated habitats, the same model predicts the coexistence of multiple species in each regularly spaced functional group. Limiting similarity, therefore, may also be compatible with the coexistence of many redundant species.

Small Schools, Real Gains.

ERIC Educational Resources Information Center

Wasley, Patricia A.; Lear, Richard J.

2001-01-01

Small school size (fewer than 400 students) makes possible success-enhancing structures and practices: strong, ongoing student/adult and home/school relationships; flat organizational structure; concentration on a few goals; ongoing, site-specific professional development; a respectful culture; and community engagement. Implementation barriers are…

Using community-level metrics to monitor the effects of marine protected areas on biodiversity.

PubMed

Soykan, Candan U; Lewison, Rebecca L

2015-06-01

Marine protected areas (MPAs) are used to protect species, communities, and their associated habitats, among other goals. Measuring MPA efficacy can be challenging, however, particularly when considering responses at the community level. We gathered 36 abundance and 14 biomass data sets on fish assemblages and used meta-analysis to evaluate the ability of 22 distinct community diversity metrics to detect differences in community structure between MPAs and nearby control sites. We also considered the effects of 6 covariates-MPA size and age, MPA size and age interaction, latitude, total species richness, and level of protection-on each metric. Some common metrics, such as species richness and Shannon diversity, did not differ consistently between MPA and control sites, whereas other metrics, such as total abundance and biomass, were consistently different across studies. Metric responses derived from the biomass data sets were more consistent than those based on the abundance data sets, suggesting that community-level biomass differs more predictably than abundance between MPA and control sites. Covariate analyses indicated that level of protection, latitude, MPA size, and the interaction between MPA size and age affect metric performance. These results highlight a handful of metrics, several of which are little known, that could be used to meet the increasing demand for community-level indicators of MPA effectiveness. © 2015 Society for Conservation Biology.

Phytoplankton community structure and dynamics in the North Atlantic subtropical gyre

NASA Astrophysics Data System (ADS)

Cáceres, Carlos; Rivera, Antonella; González, Sonia; Anadón, Ricardo

2017-02-01

Phytoplankton fuel epipelagic ecosystems and affect global biogeochemical cycles. Nevertheless, there is still a lack of quantitative information about the factors that determine both phytoplankton community structure and dynamics, particularly in subtropical gyres. Here, we estimated size fractionated phytoplankton growth (μ) and microzooplankton grazing rates (m) along a transect in the subtropical North Atlantic, from the island of Hispaniola to the Iberian Peninsula, by conducting dilution experiments and fitting mixed models. We also examined the relationship between nutrient availability and the differences in both phytoplankton community structure and size fractionated phytoplankton growth rates at two spatial scales (i.e. subtropical gyre and within-province spatial scale). Our results revealed high values for both phytoplankton growth and microzooplankton grazing rates. Phytoplankton growth (0.00-1.19 d-1) displayed higher variability among stations, biogeochemical provinces and size fractions than the microzooplankton grazing rate (0.32-0.74 d-1). Differences in phytoplankton community structure were associated with dissolved inorganic nitrogen (0.72-5.85 μM; R2 = 0.19) and squared Brunt-Väisälä frequency (R2 = 0.21) at the whole gyre scale. Conversely, the differences in phytoplankton growth rate showed a weak relationship with those properties (R2 ⩽ 0.05) at that scale, but a stronger relationship at the within province scale (R2 ⩾ 0.07). These results support the idea that phytoplankton grow at high rates in oligotrophic subtropical gyres, this is likely due to the selection of phytoplankton groups with functional traits suited to exploit low nutrient availability. Thus, shedding new, multi-scale knowledge on the commonly misunderstood "ocean deserts".

How mammalian predation contributes to tropical tree community structure.

PubMed

Paine, C E Timothy; Beck, Harald; Terborgh, John

2016-12-01

The recruitment of seedlings from seeds is the key demographic transition for rain forest trees. Though tropical forest mammals are known to consume many seeds, their effects on tree community structure remain little known. To evaluate their effects, we monitored 8,000 seeds of 24 tree species using exclosure cages that were selectively permeable to three size classes of mammals for up to 4.4 years. Small and medium-bodied mammals removed many more seeds than did large mammals, and they alone generated beta diversity and negative density dependence, whereas all mammals reduced diversity and shaped local species composition. Thus, small and medium-bodied mammals more strongly contributed to community structure and promoted species coexistence than did large mammals. Given that seedling recruitment is seed limited for most species, alterations to the composition of the community of mammalian seed predators is expected to have long-term consequences for tree community structure in tropical forests. © 2016 by the Ecological Society of America.

Prey dispersal rate affects prey species composition and trait diversity in response to multiple predators in metacommunities.

PubMed

Howeth, Jennifer G; Leibold, Mathew A

2010-09-01

1. Recent studies indicate that large-scale spatial processes can alter local community structuring mechanisms to determine local and regional assemblages of predators and their prey. In metacommunities, this may occur when the functional diversity represented in the regional predator species pool interacts with the rate of prey dispersal among local communities to affect prey species diversity and trait composition at multiple scales. 2. Here, we test for effects of prey dispersal rate and spatially and temporally heterogeneous predation from functionally dissimilar predators on prey structure in pond mesocosm metacommunities. An experimental metacommunity consisted of three pond mesocosm communities supporting two differentially size-selective invertebrate predators and their zooplankton prey. In each metacommunity, two communities maintained constant predation and supported either Gyrinus sp. (Coleoptera) or Notonecta ungulata (Hemiptera) predators generating a spatial prey refuge while the third community supported alternating predation from Gyrinus sp. and N. ungulata generating a temporal prey refuge. Mesocosm metacommunities were connected at either low (0.7% day(-1)) or high (10% day(-1)) planktonic prey dispersal. The diversity, composition and body size of zooplankton prey were measured at local and regional (metacommunity) scales. 3. Metacommunities experiencing the low prey dispersal rate supported the greatest regional prey species diversity (H') and evenness (J'). Neither dispersal rate nor predation regime affected local prey diversity or evenness. The spatial prey refuge at low dispersal maintained the largest difference in species composition and body size diversity between communities under Gyrinus and Notonecta predation, suggesting that species sorting was operating at the low dispersal rate. There was no effect of dispersal rate on species diversity or body size distribution in the temporal prey refuge. 4. The frequency distribution, but not the range, of prey body sizes within communities depended upon prey dispersal rate and predator identity. Taken together, these results demonstrate that prey dispersal rate can moderate the strength of predation to influence prey species diversity and the local frequency distribution of prey traits in metacommunities supporting ecologically different predators.

Size, time, and asynchrony matter: the species-area relationship for parasites of freshwater fishes.

PubMed

Zelmer, Derek A

2014-10-01

The tendency to attribute species-area relationships to "island biogeography" effectively bypasses the examination of specific mechanisms that act to structure parasite communities. Positive covariation between fish size and infrapopulation richness should not be examined within the typical extinction-based paradigm, but rather should be addressed from the standpoint of differences in colonization potential among individual hosts. Although most mechanisms producing the aforementioned pattern constitute some variation of passive sampling, the deterministic aspects of the accumulation of parasite individuals by fish hosts makes untenable the suggestion that infracommunities of freshwater fishes are stochastic assemblages. At the component community level, application of extinction-dependent mechanisms might be appropriate, given sufficient time for colonization, but these structuring forces likely act indirectly through their effects on the host community to increase the probability of parasite persistence. At all levels, the passive sampling hypothesis is a relevant null model. The tendency for mechanisms that produce species-area relationships to produce nested subset patterns means that for most systems, the passive sampling hypothesis can be addressed through the application of appropriate null models of nested subset structure.

Habitat degradation and fishing effects on the size structure of coral reef fish communities.

PubMed

Wilson, S K; Fisher, R; Pratchett, M S; Graham, N A J; Dulvy, N K; Turner, R A; Cakacaka, A; Polunin, N V C

2010-03-01

Overfishing and habitat degradation through climate change pose the greatest threats to sustainability of marine resources on coral reefs. We examined how changes in fishing pressure and benthic habitat composition influenced the size spectra of island-scale reef fish communities in Lau, Fiji. Between 2000 and 2006 fishing pressure declined in the Lau Islands due to declining human populations and reduced demand for fresh fish. At the same time, coral cover declined and fine-scale architectural complexity eroded due to coral bleaching and outbreaks of crown-of-thorns starfish, Acanthaster planci. We examined the size distribution of reef fish communities using size spectra analysis, the linearized relationship between abundance and body size class. Spatial variation in fishing pressure accounted for 31% of the variation in the slope of the size spectra in 2000, higher fishing pressure being associated with a steeper slope, which is indicative of fewer large-bodied fish and/or more small-bodied fish. Conversely, in 2006 spatial variation in habitat explained 53% of the variation in the size spectra slopes, and the relationship with fishing pressure was much weaker (approximately 12% of variation) than in 2000. Reduced cover of corals and lower structural complexity was associated with less steep size spectra slopes, primarily due to reduced abundance of fish < 20 cm. Habitat degradation will compound effects of fishing on coral reefs as increased fishing reduces large-bodied target species, while habitat loss results in fewer small-bodied juveniles and prey that replenish stocks and provide dietary resources for predatory target species. Effective management of reef resources therefore depends on both reducing fishing pressure and maintaining processes that encourage rapid recovery of coral habitat.

Comorbidity and ventricular and vascular structure and function in heart failure with preserved ejection fraction: a community-based study.

PubMed

Mohammed, Selma F; Borlaug, Barry A; Roger, Véronique L; Mirzoyev, Sultan A; Rodeheffer, Richard J; Chirinos, Julio A; Redfield, Margaret M

2012-11-01

Patients with heart failure and preserved ejection fraction (HFpEF) display increased adiposity and multiple comorbidities, factors that in themselves may influence cardiovascular structure and function. This has sparked debate as to whether HFpEF represents a distinct disease or an amalgamation of comorbidities. We hypothesized that fundamental cardiovascular structural and functional alterations are characteristic of HFpEF, even after accounting for body size and comorbidities. Comorbidity-adjusted cardiovascular structural and functional parameters scaled to independently generated and age-appropriate allometric powers were compared in community-based cohorts of HFpEF patients (n=386) and age/sex-matched healthy n=193 and hypertensive, n=386 controls. Within HFpEF patients, body size and concomitant comorbidity-adjusted cardiovascular structural and functional parameters and survival were compared in those with and without individual comorbidities. Among HFpEF patients, comorbidities (obesity, anemia, diabetes mellitus, and renal dysfunction) were each associated with unique clinical, structural, functional, and prognostic profiles. However, after accounting for age, sex, body size, and comorbidities, greater concentric hypertrophy, atrial enlargement and systolic, diastolic, and vascular dysfunction were consistently observed in HFpEF compared with age/sex-matched normotensive and hypertensive. Comorbidities influence ventricular-vascular properties and outcomes in HFpEF, yet fundamental disease-specific changes in cardiovascular structure and function underlie this disorder. These data support the search for mechanistically targeted therapies in this disease.

Size- and food-dependent growth drives patterns of competitive dominance along productivity gradients.

PubMed

Huss, Magnus; Gårdmark, Anna; Van Leeuwen, Anieke; de Roos, André M

2012-04-01

Patterns of coexistence among competing species exhibiting size- and food-dependent growth remain largely unexplored. Here we studied mechanisms behind coexistence and shifts in competitive dominance in a size-structured fish guild, representing sprat and herring stocks in the Baltic Sea, using a physiologically structured model of competing populations. The influence of degree of resource overlap and the possibility of undergoing ontogenetic diet shifts were studied as functions of zooplankton and zoobenthos productivity. By imposing different size-dependent mortalities, we could study the outcome of competition under contrasting environmental regimes representing poor and favorable growth conditions. We found that the identity of the dominant species shifted between low and high productivity. Adding a herring-exclusive benthos resource only provided a competitive advantage over sprat when size-dependent mortality was high enough to allow for rapid growth in the zooplankton niche. Hence, the importance of a bottom-up effect of varying productivity was dependent on a strong top-down effect. Although herring could depress shared resources to lower levels than could sprat and also could access an exclusive resource, the smaller size at maturation of sprat allowed it to coexist with herring and, in some cases, exclude it. Our model system, characterized by interactions among size cohorts, allowed for consumer coexistence even at full resource overlap at intermediate productivities when size-dependent mortality was low. Observed shifts in community patterns were crucially dependent on the explicit consideration of size- and food-dependent growth. Accordingly, we argue that accounting for food-dependent growth and size-dependent interactions is necessary to better predict changes in community structure and dynamics following changes in major ecosystem drivers such as resource productivity and mortality, which are fundamental for our ability to manage exploitation of living resources in, e.g., fisheries.

Feedbacks Between Soil Structure and Microbial Activities in Soil

NASA Astrophysics Data System (ADS)

Bailey, V. L.; Smith, A. P.; Fansler, S.; Varga, T.; Kemner, K. M.; McCue, L. A.

2017-12-01

Soil structure provides the physical framework for soil microbial habitats. The connectivity and size distribution of soil pores controls the microbial access to nutrient resources for growth and metabolism. Thus, a crucial component of soil research is how a soil's three-dimensional structure and organization influences its biological potential on a multitude of spatial and temporal scales. In an effort to understand microbial processes at scale more consistent with a microbial community, we have used soil aggregates as discrete units of soil microbial habitats. Our research has shown that mean pore diameter (x-ray computed tomography) of soil aggregates varies with the aggregate diameter itself. Analyzing both the bacterial composition (16S) and enzyme activities of individual aggregates showed significant differences in the relative abundances of key members the microbial communities associated with high enzyme activities compared to those with low activities, even though we observed no differences in the size of the biomass, nor in the overall richness or diversity of these communities. We hypothesize that resources and substrates have stimulated key populations in the aggregates identified as highly active, and as such, we conducted further research that explored how such key populations (i.e. fungal or bacterial dominated populations) alter pathways of C accumulation in aggregate size domains and microbial C utilization. Fungi support and stabilize soil structure through both physical and chemical effects of their hyphal networks. In contrast, bacterial-dominated communities are purported to facilitate micro- and fine aggregate stabilization. Here we quantify the direct effects fungal versus bacterial dominated communities on aggregate formation (both the rate of aggregation and the quality, quantity and distribution of SOC contained within aggregates). A quantitative understanding of the different mechanisms through which fungi or bacteria shape aggregate formation could alter how we currently treat our predictions of soil biogeochemistry. Current predictions are largely site- or biome-specific; quantitative mechanisms could underpin "rules" that operate at the pore-scale leading to more robust, mechanistic models.

Community College Funding: Adopting a Team Approach

ERIC Educational Resources Information Center

Terrell, Thomas E., Jr.

2005-01-01

When it comes to structure, governance, mission, or size, community colleges differ from state to state. One common element in many states, however, is state funding. Whether a state prepares its budget annually or biennially, the human behavior governing the budget process remains the same. Funds are finite. Everyone wants more than can be…

Differential habitat use or intraguild interactions: What structures a carnivore community?

Treesearch

Matthew E. Gompper; Damon B. Lesmeister; Justina C. Ray; Jay R. Malcolm; Roland Kays; Aaron W. Reed

2016-01-01

Differential habitat use and intraguild competition are both thought to be important drivers of animal population sizes and distributions. Habitat associations for individual species are well-established, and interactions between particular pairs of species have been highlighted in many focal studies. However, community-wide assessments of the relative strengths of...

Seasonal variations in the diversity and abundance of diazotrophic communities across soils.

PubMed

Pereira e Silva, Michele C; Semenov, Alexander V; van Elsas, Jan Dirk; Salles, Joana Falcão

2011-07-01

The nitrogen (N)-fixing community is a key functional community in soil, as it replenishes the pool of biologically available N that is lost to the atmosphere via anaerobic ammonium oxidation and denitrification. We characterized the structure and dynamic changes in diazotrophic communities, based on the nifH gene, across eight different representative Dutch soils during one complete growing season, to evaluate the amplitude of the natural variation in abundance and diversity, and identify possible relationships with abiotic factors. Overall, our results indicate that soil type is the main factor influencing the N-fixing communities, which were more abundant and diverse in the clay soils (n=4) than in the sandy soils (n=4). On average, the amplitude of variation in community size as well as the range-weighted richness were also found to be higher in the clay soils. These results indicate that N-fixing communities associated with sandy and clay soil show a distinct amplitude of variation under field conditions, and suggest that the diazotrophic communities associated with clay soil might be more sensitive to fluctuations associated with the season and agricultural practices. Moreover, soil characteristics such as ammonium content, pH and texture most strongly correlated with the variations observed in the diversity, size and structure of N-fixing communities, whose relative importance was determined across a temporal and spatial scale. © 2011 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Local communities obstruct global consensus: Naming game on multi-local-world networks

NASA Astrophysics Data System (ADS)

Lou, Yang; Chen, Guanrong; Fan, Zhengping; Xiang, Luna

2018-02-01

Community structure is essential for social communications, where individuals belonging to the same community are much more actively interacting and communicating with each other than those in different communities within the human society. Naming game, on the other hand, is a social communication model that simulates the process of learning a name of an object within a community of humans, where the individuals can generally reach global consensus asymptotically through iterative pair-wise conversations. The underlying network indicates the relationships among the individuals. In this paper, three typical topologies, namely random-graph, small-world and scale-free networks, are employed, which are embedded with the multi-local-world community structure, to study the naming game. Simulations show that (1) the convergence process to global consensus is getting slower as the community structure becomes more prominent, and eventually might fail; (2) if the inter-community connections are sufficiently dense, neither the number nor the size of the communities affects the convergence process; and (3) for different topologies with the same (or similar) average node-degree, local clustering of individuals obstruct or prohibit global consensus to take place. The results reveal the role of local communities in a global naming game in social network studies.

Inter-subject FDG PET Brain Networks Exhibit Multi-scale Community Structure with Different Normalization Techniques.

PubMed

Sperry, Megan M; Kartha, Sonia; Granquist, Eric J; Winkelstein, Beth A

2018-07-01

Inter-subject networks are used to model correlations between brain regions and are particularly useful for metabolic imaging techniques, like 18F-2-deoxy-2-(18F)fluoro-D-glucose (FDG) positron emission tomography (PET). Since FDG PET typically produces a single image, correlations cannot be calculated over time. Little focus has been placed on the basic properties of inter-subject networks and if they are affected by group size and image normalization. FDG PET images were acquired from rats (n = 18), normalized by whole brain, visual cortex, or cerebellar FDG uptake, and used to construct correlation matrices. Group size effects on network stability were investigated by systematically adding rats and evaluating local network connectivity (node strength and clustering coefficient). Modularity and community structure were also evaluated in the differently normalized networks to assess meso-scale network relationships. Local network properties are stable regardless of normalization region for groups of at least 10. Whole brain-normalized networks are more modular than visual cortex- or cerebellum-normalized network (p < 0.00001); however, community structure is similar at network resolutions where modularity differs most between brain and randomized networks. Hierarchical analysis reveals consistent modules at different scales and clustering of spatially-proximate brain regions. Findings suggest inter-subject FDG PET networks are stable for reasonable group sizes and exhibit multi-scale modularity.

Evolution of cooperation in multilevel public goods games with community structures

NASA Astrophysics Data System (ADS)

Wang, Jing; Wu, Bin; Ho, Daniel W. C.; Wang, Long

2011-03-01

In a community-structured population, public goods games (PGG) occur both within and between communities. Such type of PGG is referred as multilevel public goods games (MPGG). We propose a minimalist evolutionary model of the MPGG and analytically study the evolution of cooperation. We demonstrate that in the case of sufficiently large community size and community number, if the imitation strength within community is weak, i.e., an individual imitates another one in the same community almost randomly, cooperation as well as punishment are more abundant than defection in the long run; if the imitation strength between communities is strong, i.e., the more successful strategy in two individuals from distinct communities is always imitated, cooperation and punishment are also more abundant. However, when both of the two imitation intensities are strong, defection becomes the most abundant strategy in the population. Our model provides insight into the investigation of the large-scale cooperation in public social dilemma among contemporary communities.

Complex interaction of dendritic connectivity and hierarchical patch size on biodiversity in river-like landscapes.

PubMed

Carrara, Francesco; Rinaldo, Andrea; Giometto, Andrea; Altermatt, Florian

2014-01-01

Habitat fragmentation and land use changes are causing major biodiversity losses. Connectivity of the landscape or environmental conditions alone can shape biodiversity patterns. In nature, however, local habitat characteristics are often intrinsically linked to a specific connectivity. Such a link is evident in riverine ecosystems, where hierarchical dendritic structures command related scaling on habitat capacity. We experimentally disentangled the effect of local habitat capacity (i.e., the patch size) and dendritic connectivity on biodiversity in aquatic microcosm metacommunities by suitably arranging patch sizes within river-like networks. Overall, more connected communities that occupy a central position in the network exhibited higher species richness, irrespective of patch size arrangement. High regional evenness in community composition was found only in landscapes preserving geomorphological scaling properties of patch sizes. In these landscapes, some of the rarer species sustained regionally more abundant populations better tracking their own niche requirements compared to landscapes with homogeneous patch size or landscapes with spatially uncorrelated patch size. Our analysis suggests that altering the natural link between dendritic connectivity and patch size strongly affects community composition and population persistence at multiple scales. The experimental results are demonstrating a principle that can be tested in theoretical metacommunity models and eventually be projected to real riverine ecosystems.

Size-Energy Relationships in Ecological Communities

PubMed Central

Sewall, Brent J.; Freestone, Amy L.; Hawes, Joseph E.; Andriamanarina, Ernest

2013-01-01

Hypotheses that relate body size to energy use are of particular interest in community ecology and macroecology because of their potential to facilitate quantitative predictions about species interactions and to clarify complex ecological patterns. One prominent size-energy hypothesis, the energetic equivalence hypothesis, proposes that energy use from shared, limiting resources by populations or size classes of foragers will be independent of body size. Alternative hypotheses propose that energy use will increase with body size, decrease with body size, or peak at an intermediate body size. Despite extensive study, however, size-energy hypotheses remain controversial, due to a lack of directly-measured data on energy use, a tendency to confound distinct scaling relationships, and insufficient attention to the ecological contexts in which predicted relationships are likely to occur. Our goal, therefore, was to directly evaluate size-energy hypotheses while clarifying how results would differ with alternate methods and assumptions. We comprehensively tested size-energy hypotheses in a vertebrate frugivore guild in a tropical forest in Madagascar. Our test of size-energy hypotheses, which is the first to examine energy intake directly, was consistent with the energetic equivalence hypothesis. This finding corresponds with predictions of metabolic theory and models of energy distribution in ecological communities, which imply that body size does not confer an advantage in competition for energy among populations or size classes of foragers. This result was robust to different assumptions about energy regulation. Our results from direct energy measurement, however, contrasted with those obtained with conventional methods of indirect inference from size-density relationships, suggesting that size-density relationships do not provide an appropriate proxy for size-energy relationships as has commonly been assumed. Our research also provides insights into mechanisms underlying local size-energy relationships and has important implications for predicting species interactions and for understanding the structure and dynamics of ecological communities. PMID:23950873

Spatial and body-size dependent response of marine pelagic communities to projected global climate change.

PubMed

Lefort, Stelly; Aumont, Olivier; Bopp, Laurent; Arsouze, Thomas; Gehlen, Marion; Maury, Olivier

2015-01-01

Temperature, oxygen, and food availability directly affect marine life. Climate models project a global warming of the ocean's surface (~+3 °C), a de-oxygenation of the ocean's interior (~-3%) and a decrease in total marine net primary production (~-8%) under the 'business as usual' climate change scenario (RCP8.5). We estimated the effects of these changes on biological communities using a coupled biogeochemical (PISCES)--ecosystems (APECOSM) model forced by the physical outputs of the last generation of the IPSL-CM Earth System Model. The APECOSM model is a size-structured bio-energetic model that simulates the 3D dynamical distributions of three interactive pelagic communities (epipelagic, mesopelagic, and migratory) under the effects of multiple environmental factors. The PISCES-APECOSM model ran from 1850 to 2100 under historical forcing followed by RCP8.5. Our RCP8.5 simulation highlights significant changes in the spatial distribution, biomass, and maximum body-size of the simulated pelagic communities. Biomass and maximum body-size increase at high latitude over the course of the century, reflecting the capacity of marine organisms to respond to new suitable environment. At low- and midlatitude, biomass and maximum body-size strongly decrease. In those regions, large organisms cannot maintain their high metabolic needs because of limited and declining food availability. This resource reduction enhances the competition and modifies the biomass distribution among and within the three communities: the proportion of small organisms increases in the three communities and the migrant community that initially comprised a higher proportion of small organisms is favored. The greater resilience of small body-size organisms resides in their capacity to fulfill their metabolic needs under reduced energy supply and is further favored by the release of predation pressure due to the decline of large organisms. These results suggest that small body-size organisms might be more resilient to climate change than large ones. © 2014 John Wiley & Sons Ltd.

Sample size estimation for alternating logistic regressions analysis of multilevel randomized community trials of under-age drinking.

PubMed

Reboussin, Beth A; Preisser, John S; Song, Eun-Young; Wolfson, Mark

2012-07-01

Under-age drinking is an enormous public health issue in the USA. Evidence that community level structures may impact on under-age drinking has led to a proliferation of efforts to change the environment surrounding the use of alcohol. Although the focus of these efforts is to reduce drinking by individual youths, environmental interventions are typically implemented at the community level with entire communities randomized to the same intervention condition. A distinct feature of these trials is the tendency of the behaviours of individuals residing in the same community to be more alike than that of others residing in different communities, which is herein called 'clustering'. Statistical analyses and sample size calculations must account for this clustering to avoid type I errors and to ensure an appropriately powered trial. Clustering itself may also be of scientific interest. We consider the alternating logistic regressions procedure within the population-averaged modelling framework to estimate the effect of a law enforcement intervention on the prevalence of under-age drinking behaviours while modelling the clustering at multiple levels, e.g. within communities and within neighbourhoods nested within communities, by using pairwise odds ratios. We then derive sample size formulae for estimating intervention effects when planning a post-test-only or repeated cross-sectional community-randomized trial using the alternating logistic regressions procedure.

A generalised significance test for individual communities in networks.

PubMed

Kojaku, Sadamori; Masuda, Naoki

2018-05-09

Many empirical networks have community structure, in which nodes are densely interconnected within each community (i.e., a group of nodes) and sparsely across different communities. Like other local and meso-scale structure of networks, communities are generally heterogeneous in various aspects such as the size, density of edges, connectivity to other communities and significance. In the present study, we propose a method to statistically test the significance of individual communities in a given network. Compared to the previous methods, the present algorithm is unique in that it accepts different community-detection algorithms and the corresponding quality function for single communities. The present method requires that a quality of each community can be quantified and that community detection is performed as optimisation of such a quality function summed over the communities. Various community detection algorithms including modularity maximisation and graph partitioning meet this criterion. Our method estimates a distribution of the quality function for randomised networks to calculate a likelihood of each community in the given network. We illustrate our algorithm by synthetic and empirical networks.

Predation risk suppresses the positive feedback between size structure and cannibalism.

PubMed

Kishida, Osamu; Trussell, Geoffrey C; Ohno, Ayaka; Kuwano, Shinya; Ikawa, Takuya; Nishimura, Kinya

2011-11-01

1. Cannibalism can play a prominent role in the structuring and dynamics of ecological communities. Previous studies have emphasized the importance of size structure and density of cannibalistic species in shaping short- and long-term cannibalism dynamics, but our understanding of how predators influence cannibalism dynamics is limited. This is despite widespread evidence that many prey species exhibit behavioural and morphological adaptations in response to predation risk. 2. This study examined how the presence and absence of predation risk from larval dragonflies Aeshna nigroflava affected cannibalism dynamics in its prey larval salamanders Hynobius retardatus. 3. We found that feedback dynamics between size structure and cannibalism depended on whether dragonfly predation risk was present. In the absence of dragonfly risk cues, a positive feedback between salamander size structure and cannibalism through time occurred because most of the replicates in this treatment contained at least one salamander larvae having an enlarged gape (i.e. cannibal). In contrast, this feedback and the emergence of cannibalism were rarely observed in the presence of the dragonfly risk cues. Once salamander size divergence occurred, experimental reversals of the presence or absence of dragonfly risk cues did not alter existing cannibalism dynamics as the experiment progressed. Thus, the effects of risk on the mechanisms driving cannibalism dynamics likely operated during the early developmental period of the salamander larvae. 4. The effects of dragonfly predation risk on behavioural aspects of cannibalistic interactions among hatchlings may prohibit the initiation of dynamics between size structure and cannibalism. Our predation trials clearly showed that encounter rates among hatchlings and biting and ingestion rates of prospective prey by prospective cannibals were significantly lower in the presence vs. absence of dragonfly predation risk even though the size asymmetry between cannibals and victims was similar in both risk treatments. These results suggest that dragonfly risk cues first suppress cannibalism among hatchlings and then prevent size variation from increasing through time. 5. We suggest that the positive feedback dynamics between size structure and cannibalism and their modification by predation risk may also operate in other systems to shape the population dynamics of cannibalistic prey species as well as overall community dynamics. © 2011 The Authors. Journal of Animal Ecology © 2011 British Ecological Society.

Community Size, Perceptions of Majority Opinion and Opinion Expression.

ERIC Educational Resources Information Center

Salmon, Charles T.; Oshagan, Hayg

A study examined structural determinants of opinion expression by merging two theoretical perspectives: the "spiral of silence" model advanced by Elisabeth Noelle-Neumann, and the structural approach to communication research offered by Phillip Tichenor, George Donohue, and Clarice Olien. The study also distinguished between different…

Size-fractionated diversity of eukaryotic microbial communities in the Eastern Tropical North Pacific oxygen minimum zone.

PubMed

Duret, Manon T; Pachiadaki, Maria G; Stewart, Frank J; Sarode, Neha; Christaki, Urania; Monchy, Sébastien; Srivastava, Ankita; Edgcomb, Virginia P

2015-05-01

Oxygen minimum zones (OMZs) caused by water column stratification appear to expand in parts of the world's ocean, with consequences for marine biogeochemical cycles. OMZ formation is often fueled by high surface primary production, and sinking organic particles can be hotspots of interactions and activity within microbial communities. This study investigated the diversity of OMZ protist communities in two biomass size fractions (>30 and 30-1.6 μm filters) from the world's largest permanent OMZ in the Eastern Tropical North Pacific. Diversity was quantified via Illumina MiSeq sequencing of V4 region of 18S SSU rRNA genes in samples spanning oxygen gradients at two stations. Alveolata and Rhizaria dominated the two size fractions at both sites along the oxygen gradient. Community composition at finer taxonomic levels was partially shaped by oxygen concentration, as communities associated with versus anoxic waters shared only ∼32% of operational taxonomic unit (OTU) (97% sequence identity) composition. Overall, only 9.7% of total OTUs were recovered at both stations and under all oxygen conditions sampled, implying structuring of the eukaryotic community in this area. Size-fractionated communities exhibited different taxonomical features (e.g. Syndiniales Group I in the 1.6-30 μm fraction) that could be explained by the microniches created on the surface-originated sinking particles. © FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Lake warming favours small-sized planktonic diatom species

PubMed Central

Winder, Monika; Reuter, John E.; Schladow, S. Geoffrey

2008-01-01

Diatoms contribute to a substantial portion of primary production in the oceans and many lakes. Owing to their relatively heavy cell walls and high nutrient requirements, planktonic diatoms are expected to decrease with climate warming because of reduced nutrient redistribution and increasing sinking velocities. Using a historical dataset, this study shows that diatoms were able to maintain their biovolume with increasing stratification in Lake Tahoe over the last decades; however, the diatom community structure changed. Increased stratification and reduced nitrogen to phosphorus ratios selected for small-celled diatoms, particularly within the Cyclotella genus. An empirical model showed that a shift in phytoplankton species composition and cell size was consistent within different depth strata, indicating that altered nutrient concentrations were not responsible for the change. The increase in small-celled species was sufficient to decrease the average diatom size and thus sinking velocity, which strongly influences energy transfer through the food web and carbon cycling. Our results show that within the diverse group of diatoms, small-sized species with a high surface area to volume ratio were able to adapt to a decrease in mixing intensity, supporting the hypotheses that abiotic drivers affect the size structure of planktonic communities and that warmer climate favours small-sized diatom cells. PMID:18812287

Natural variability of marine ecosystems inferred from a coupled climate to ecosystem simulation

NASA Astrophysics Data System (ADS)

Le Mézo, Priscilla; Lefort, Stelly; Séférian, Roland; Aumont, Olivier; Maury, Olivier; Murtugudde, Raghu; Bopp, Laurent

2016-01-01

This modeling study analyzes the simulated natural variability of pelagic ecosystems in the North Atlantic and North Pacific. Our model system includes a global Earth System Model (IPSL-CM5A-LR), the biogeochemical model PISCES and the ecosystem model APECOSM that simulates upper trophic level organisms using a size-based approach and three interactive pelagic communities (epipelagic, migratory and mesopelagic). Analyzing an idealized (e.g., no anthropogenic forcing) 300-yr long pre-industrial simulation, we find that low and high frequency variability is dominant for the large and small organisms, respectively. Our model shows that the size-range exhibiting the largest variability at a given frequency, defined as the resonant range, also depends on the community. At a given frequency, the resonant range of the epipelagic community includes larger organisms than that of the migratory community and similarly, the latter includes larger organisms than the resonant range of the mesopelagic community. This study shows that the simulated temporal variability of marine pelagic organisms' abundance is not only influenced by natural climate fluctuations but also by the structure of the pelagic community. As a consequence, the size- and community-dependent response of marine ecosystems to climate variability could impact the sustainability of fisheries in a warming world.

Short-term bioavailability of carbon in soil organic matter fractions of different particle sizes and densities in grassland ecosystems.

PubMed

Breulmann, Marc; Masyutenko, Nina Petrovna; Kogut, Boris Maratovich; Schroll, Reiner; Dörfler, Ulrike; Buscot, François; Schulz, Elke

2014-11-01

The quality, stability and availability of organic carbon (OC) in soil organic matter (SOM) can vary widely between differently managed ecosystems. Several approaches have been developed for isolating SOM fractions to examine their ecological roles, but links between the bioavailability of the OC of size-density fractions and soil microbial communities have not been previously explored. Thus, in the presented laboratory study we investigated the potential bioavailability of OC and the structure of associated microbial communities in different particle-size and density fractions of SOM. For this we used samples from four grassland ecosystems with contrasting management intensity regimes and two soil types: a Haplic Cambisol and a typical Chernozem. A combined size-density fractionation protocol was applied to separate clay-associated SOM fractions (CF1, <1 μm; CF2, 1-2 μm) from light SOM fractions (LF1, <1.8 g cm(-3); LF2, 1.8-2.0 g cm(-3)). These fractions were used as carbon sources in a respiration experiment to determine their potential bioavailability. Measured CO2-release was used as an index of substrate accessibility and linked to the soil microbial community structure, as determined by phospholipid fatty acids (PLFA) analysis. Several key factors controlling decomposition processes, and thus the potential bioavailability of OC, were identified: management intensity and the plant community composition of the grasslands (both of which affect the chemical composition and turnover of OC) and specific properties of individual SOM fractions. The PLFA patterns highlighted differences in the composition of microbial communities associated with the examined grasslands, and SOM fractions, providing the first broad insights into their active microbial communities. From observed interactions between abiotic and biotic factors affecting the decomposition of SOM fractions we demonstrate that increasing management intensity could enhance the potential bioavailability of OC, not only in the active and intermediate SOM pools, but also in the passive pool. Copyright © 2014 Elsevier B.V. All rights reserved.

Habitat Fragmentation can Modulate Drought Effects on the Plant-soil-microbial System in Mediterranean Holm Oak (Quercus ilex) Forests.

PubMed

Flores-Rentería, Dulce; Curiel Yuste, Jorge; Rincón, Ana; Brearley, Francis Q; García-Gil, Juan Carlos; Valladares, Fernando

2015-05-01

Ecological transformations derived from habitat fragmentation have led to increased threats to above-ground biodiversity. However, the impacts of forest fragmentation on soils and their microbial communities are not well understood. We examined the effects of contrasting fragment sizes on the structure and functioning of soil microbial communities from holm oak forest patches in two bioclimatically different regions of Spain. We used a microcosm approach to simulate the annual summer drought cycle and first autumn rainfall (rewetting), evaluating the functional response of a plant-soil-microbial system. Forest fragment size had a significant effect on physicochemical characteristics and microbial functioning of soils, although the diversity and structure of microbial communities were not affected. The response of our plant-soil-microbial systems to drought was strongly modulated by the bioclimatic conditions and the fragment size from where the soils were obtained. Decreasing fragment size modulated the effects of drought by improving local environmental conditions with higher water and nutrient availability. However, this modulation was stronger for plant-soil-microbial systems built with soils from the northern region (colder and wetter) than for those built with soils from the southern region (warmer and drier) suggesting that the responsiveness of the soil-plant-microbial system to habitat fragmentation was strongly dependent on both the physicochemical characteristics of soils and the historical adaptation of soil microbial communities to specific bioclimatic conditions. This interaction challenges our understanding of future global change scenarios in Mediterranean ecosystems involving drier conditions and increased frequency of forest fragmentation.

Soil microbial community successional patterns during forest ecosystem restoration.

PubMed

Banning, Natasha C; Gleeson, Deirdre B; Grigg, Andrew H; Grant, Carl D; Andersen, Gary L; Brodie, Eoin L; Murphy, D V

2011-09-01

Soil microbial community characterization is increasingly being used to determine the responses of soils to stress and disturbances and to assess ecosystem sustainability. However, there is little experimental evidence to indicate that predictable patterns in microbial community structure or composition occur during secondary succession or ecosystem restoration. This study utilized a chronosequence of developing jarrah (Eucalyptus marginata) forest ecosystems, rehabilitated after bauxite mining (up to 18 years old), to examine changes in soil bacterial and fungal community structures (by automated ribosomal intergenic spacer analysis [ARISA]) and changes in specific soil bacterial phyla by 16S rRNA gene microarray analysis. This study demonstrated that mining in these ecosystems significantly altered soil bacterial and fungal community structures. The hypothesis that the soil microbial community structures would become more similar to those of the surrounding nonmined forest with rehabilitation age was broadly supported by shifts in the bacterial but not the fungal community. Microarray analysis enabled the identification of clear successional trends in the bacterial community at the phylum level and supported the finding of an increase in similarity to nonmined forest soil with rehabilitation age. Changes in soil microbial community structure were significantly related to the size of the microbial biomass as well as numerous edaphic variables (including pH and C, N, and P nutrient concentrations). These findings suggest that soil bacterial community dynamics follow a pattern in developing ecosystems that may be predictable and can be conceptualized as providing an integrated assessment of numerous edaphic variables.

Soil Microbial Community Successional Patterns during Forest Ecosystem Restoration ▿†

PubMed Central

Banning, Natasha C.; Gleeson, Deirdre B.; Grigg, Andrew H.; Grant, Carl D.; Andersen, Gary L.; Brodie, Eoin L.; Murphy, D. V.

2011-01-01

Soil microbial community characterization is increasingly being used to determine the responses of soils to stress and disturbances and to assess ecosystem sustainability. However, there is little experimental evidence to indicate that predictable patterns in microbial community structure or composition occur during secondary succession or ecosystem restoration. This study utilized a chronosequence of developing jarrah (Eucalyptus marginata) forest ecosystems, rehabilitated after bauxite mining (up to 18 years old), to examine changes in soil bacterial and fungal community structures (by automated ribosomal intergenic spacer analysis [ARISA]) and changes in specific soil bacterial phyla by 16S rRNA gene microarray analysis. This study demonstrated that mining in these ecosystems significantly altered soil bacterial and fungal community structures. The hypothesis that the soil microbial community structures would become more similar to those of the surrounding nonmined forest with rehabilitation age was broadly supported by shifts in the bacterial but not the fungal community. Microarray analysis enabled the identification of clear successional trends in the bacterial community at the phylum level and supported the finding of an increase in similarity to nonmined forest soil with rehabilitation age. Changes in soil microbial community structure were significantly related to the size of the microbial biomass as well as numerous edaphic variables (including pH and C, N, and P nutrient concentrations). These findings suggest that soil bacterial community dynamics follow a pattern in developing ecosystems that may be predictable and can be conceptualized as providing an integrated assessment of numerous edaphic variables. PMID:21724890

A Stochastic Model for Detecting Overlapping and Hierarchical Community Structure

PubMed Central

Cao, Xiaochun; Wang, Xiao; Jin, Di; Guo, Xiaojie; Tang, Xianchao

2015-01-01

Community detection is a fundamental problem in the analysis of complex networks. Recently, many researchers have concentrated on the detection of overlapping communities, where a vertex may belong to more than one community. However, most current methods require the number (or the size) of the communities as a priori information, which is usually unavailable in real-world networks. Thus, a practical algorithm should not only find the overlapping community structure, but also automatically determine the number of communities. Furthermore, it is preferable if this method is able to reveal the hierarchical structure of networks as well. In this work, we firstly propose a generative model that employs a nonnegative matrix factorization (NMF) formulization with a l2,1 norm regularization term, balanced by a resolution parameter. The NMF has the nature that provides overlapping community structure by assigning soft membership variables to each vertex; the l2,1 regularization term is a technique of group sparsity which can automatically determine the number of communities by penalizing too many nonempty communities; and hence the resolution parameter enables us to explore the hierarchical structure of networks. Thereafter, we derive the multiplicative update rule to learn the model parameters, and offer the proof of its correctness. Finally, we test our approach on a variety of synthetic and real-world networks, and compare it with some state-of-the-art algorithms. The results validate the superior performance of our new method. PMID:25822148

Plant structure predicts leaf litter capture in the tropical montane bromeliad Tillandsia turneri.

PubMed

Ospina-Bautista, F; Estévez Varón, J V

2016-05-03

Leaves intercepted by bromeliads become an important energy and matter resource for invertebrate communities, bacteria, fungi, and the plant itself. The relationship between bromeliad structure, defined as its size and complexity, and accumulated leaf litter was studied in 55 bromeliads of Tillandsia turneri through multiple regression and the Akaike information criterion. Leaf litter accumulation in bromeliads was best explained by size and complexity variables such as plant cover, sheath length, and leaf number. In conclusion, plant structure determines the amount of litter that enters bromeliads, and changes in its structure could affect important processes within ecosystem functioning or species richness.

High frequency mesozooplankton monitoring: Can imaging systems and automated sample analysis help us describe and interpret changes in zooplankton community composition and size structure — An example from a coastal site

NASA Astrophysics Data System (ADS)

Romagnan, Jean Baptiste; Aldamman, Lama; Gasparini, Stéphane; Nival, Paul; Aubert, Anaïs; Jamet, Jean Louis; Stemmann, Lars

2016-10-01

The present work aims to show that high throughput imaging systems can be useful to estimate mesozooplankton community size and taxonomic descriptors that can be the base for consistent large scale monitoring of plankton communities. Such monitoring is required by the European Marine Strategy Framework Directive (MSFD) in order to ensure the Good Environmental Status (GES) of European coastal and offshore marine ecosystems. Time and cost-effective, automatic, techniques are of high interest in this context. An imaging-based protocol has been applied to a high frequency time series (every second day between April 2003 to April 2004 on average) of zooplankton obtained in a coastal site of the NW Mediterranean Sea, Villefranche Bay. One hundred eighty four mesozooplankton net collected samples were analysed with a Zooscan and an associated semi-automatic classification technique. The constitution of a learning set designed to maximize copepod identification with more than 10,000 objects enabled the automatic sorting of copepods with an accuracy of 91% (true positives) and a contamination of 14% (false positives). Twenty seven samples were then chosen from the total copepod time series for detailed visual sorting of copepods after automatic identification. This method enabled the description of the dynamics of two well-known copepod species, Centropages typicus and Temora stylifera, and 7 other taxonomically broader copepod groups, in terms of size, biovolume and abundance-size distributions (size spectra). Also, total copepod size spectra underwent significant changes during the sampling period. These changes could be partially related to changes in the copepod assemblage taxonomic composition and size distributions. This study shows that the use of high throughput imaging systems is of great interest to extract relevant coarse (i.e. total abundance, size structure) and detailed (i.e. selected species dynamics) descriptors of zooplankton dynamics. Innovative zooplankton analyses are therefore proposed and open the way for further development of zooplankton community indicators of changes.

Multi-scale structural community organisation of the human genome.

PubMed

Boulos, Rasha E; Tremblay, Nicolas; Arneodo, Alain; Borgnat, Pierre; Audit, Benjamin

2017-04-11

Structural interaction frequency matrices between all genome loci are now experimentally achievable thanks to high-throughput chromosome conformation capture technologies. This ensues a new methodological challenge for computational biology which consists in objectively extracting from these data the structural motifs characteristic of genome organisation. We deployed the fast multi-scale community mining algorithm based on spectral graph wavelets to characterise the networks of intra-chromosomal interactions in human cell lines. We observed that there exist structural domains of all sizes up to chromosome length and demonstrated that the set of structural communities forms a hierarchy of chromosome segments. Hence, at all scales, chromosome folding predominantly involves interactions between neighbouring sites rather than the formation of links between distant loci. Multi-scale structural decomposition of human chromosomes provides an original framework to question structural organisation and its relationship to functional regulation across the scales. By construction the proposed methodology is independent of the precise assembly of the reference genome and is thus directly applicable to genomes whose assembly is not fully determined.

Examining predator–prey body size, trophic level and body mass across marine and terrestrial mammals

PubMed Central

Tucker, Marlee A.; Rogers, Tracey L.

2014-01-01

Predator–prey relationships and trophic levels are indicators of community structure, and are important for monitoring ecosystem changes. Mammals colonized the marine environment on seven separate occasions, which resulted in differences in species' physiology, morphology and behaviour. It is likely that these changes have had a major effect upon predator–prey relationships and trophic position; however, the effect of environment is yet to be clarified. We compiled a dataset, based on the literature, to explore the relationship between body mass, trophic level and predator–prey ratio across terrestrial (n = 51) and marine (n = 56) mammals. We did not find the expected positive relationship between trophic level and body mass, but we did find that marine carnivores sit 1.3 trophic levels higher than terrestrial carnivores. Also, marine mammals are largely carnivorous and have significantly larger predator–prey ratios compared with their terrestrial counterparts. We propose that primary productivity, and its availability, is important for mammalian trophic structure and body size. Also, energy flow and community structure in the marine environment are influenced by differences in energy efficiency and increased food web stability. Enhancing our knowledge of feeding ecology in mammals has the potential to provide insights into the structure and functioning of marine and terrestrial communities. PMID:25377460

Benthic invertebrate communities and their responses to selected environmental factors in the Kanawha River basin, West Virginia, Virginia, and North Carolina

USGS Publications Warehouse

Chambers, Douglas B.; Messinger, Terence

2001-01-01

The effects of selected environmental factors on the composition and structure of benthic invertebrate communities in the Kanawha River Basin of West Virginia, Virginia and North Carolina were investigated in 1997 and 1998. Environmental factors investigated include physiography, land-use pattern, streamwater chemistry, streambed- sediment chemistry, and habitat characteristics. Land-use patterns investigated include coal mining, agriculture, and low intensity rural-residential patterns, at four main stem and seven tributary sites throughout the basin. Of the 37 sites sampled, basin size and physiography most strongly affected benthic invertebrate-community structure. Land-use practices also affected invertebrate community structure in these basins. The basins that differed most from the minimally affected reference condition were those basins in which coal mining was the dominant nonforest land use, as determined by comparing invertebrate- community metric values among sites. Basins in which agriculture was important were more similar to the reference condition. The effect of coal mining upon benthic invertebrate communities was further studied at 29 sites and the relations among invertebrate communities and the selected environmental factors of land use, streamwater chemistry, streambed- sediment chemistry, and habitat characteristics analyzed. Division of coal-mining synoptic-survey sites based on invertebrate-community composition resulted in two groups?one with more than an average production of 9,000 tons of coal per square mile per year since 1980, and one with lesser or no recent coal production. The group with significant recent coal production showed higher levels of community impairment than the group with little or no recent coal production. Median particle size of streambed sediment, and specific conductance and sulfate concentration of streamwater were most strongly correlated with effects on invertebrate communities. These characteristics were related to mining intensity, as measured by thousands of tons of coal produced per square mile of drainage area.

Temperature-driven regime shifts in the dynamics of size-structured populations.

PubMed

Ohlberger, Jan; Edeline, Eric; Vøllestad, Leif Asbjørn; Stenseth, Nils C; Claessen, David

2011-02-01

Global warming impacts virtually all biota and ecosystems. Many of these impacts are mediated through direct effects of temperature on individual vital rates. Yet how this translates from the individual to the population level is still poorly understood, hampering the assessment of global warming impacts on population structure and dynamics. Here, we study the effects of temperature on intraspecific competition and cannibalism and the population dynamical consequences in a size-structured fish population. We use a physiologically structured consumer-resource model in which we explicitly model the temperature dependencies of the consumer vital rates and the resource population growth rate. Our model predicts that increased temperature decreases resource density despite higher resource growth rates, reflecting stronger intraspecific competition among consumers. At a critical temperature, the consumer population dynamics destabilize and shift from a stable equilibrium to competition-driven generation cycles that are dominated by recruits. As a consequence, maximum age decreases and the proportion of younger and smaller-sized fish increases. These model predictions support the hypothesis of decreasing mean body sizes due to increased temperatures. We conclude that in size-structured fish populations, global warming may increase competition, favor smaller size classes, and induce regime shifts that destabilize population and community dynamics.

River network architecture, genetic effective size and distributional patterns predict differences in genetic structure across species in a dryland stream fish community.

PubMed

Pilger, Tyler J; Gido, Keith B; Propst, David L; Whitney, James E; Turner, Thomas F

2017-05-01

Dendritic ecological network (DEN) architecture can be a strong predictor of spatial genetic patterns in theoretical and simulation studies. Yet, interspecific differences in dispersal capabilities and distribution within the network may equally affect species' genetic structuring. We characterized patterns of genetic variation from up to ten microsatellite loci for nine numerically dominant members of the upper Gila River fish community, New Mexico, USA. Using comparative landscape genetics, we evaluated the role of network architecture for structuring populations within species (pairwise F ST ) while explicitly accounting for intraspecific demographic influences on effective population size (N e ). Five species exhibited patterns of connectivity and/or genetic diversity gradients that were predicted by network structure. These species were generally considered to be small-bodied or habitat specialists. Spatial variation of N e was a strong predictor of pairwise F ST for two species, suggesting patterns of connectivity may also be influenced by genetic drift independent of network properties. Finally, two study species exhibited genetic patterns that were unexplained by network properties and appeared to be related to nonequilibrium processes. Properties of DENs shape community-wide genetic structure but effects are modified by intrinsic traits and nonequilibrium processes. Further theoretical development of the DEN framework should account for such cases. © 2017 John Wiley & Sons Ltd.

Soccer science and the Bayes community: exploring the cognitive implications of modern scientific communication.

PubMed

Shrager, Jeff; Billman, Dorrit; Convertino, Gregorio; Massar, J P; Pirolli, Peter

2010-01-01

Science is a form of distributed analysis involving both individual work that produces new knowledge and collaborative work to exchange information with the larger community. There are many particular ways in which individual and community can interact in science, and it is difficult to assess how efficient these are, and what the best way might be to support them. This paper reports on a series of experiments in this area and a prototype implementation using a research platform called CACHE. CACHE both supports experimentation with different structures of interaction between individual and community cognition and serves as a prototype for computational support for those structures. We particularly focus on CACHE-BC, the Bayes community version of CACHE, within which the community can break up analytical tasks into "mind-sized" units and use provenance tracking to keep track of the relationship between these units. Copyright © 2009 Cognitive Science Society, Inc.

Lake whitefish and lake herring population structure and niche in ten south-central Ontario lakes

USGS Publications Warehouse

Carl, Leon M.; McGuiness, Fiona

2006-01-01

This study compares simple fish communities of ten oligotrophic lakes in south-central Ontario. Species densities and population size structure vary significantly among these lake communities depending on fish species present beyond the littoral zone. Lake whitefish are fewer and larger in the presence of lake herring than in their absence. Diet analysis indicates that lake whitefish shift from feeding on both plankton and benthic prey when lake herring are absent to a primarily benthic feeding niche in the presence of lake herring. When benthic round whitefish are present, lake whitefish size and density decline and they move lower in the lake compared to round whitefish. Burbot are also fewer and larger in lakes with lake herring than in lakes without herring. Burbot, in turn, appear to influence the population structure of benthic coregonine species. Lower densities of benthic lake whitefish and round whitefish are found in lakes containing large benthic burbot than in lakes with either small burbot or where burbot are absent. Predation on the pelagic larvae of burbot and lake whitefish by planktivorous lake herring alters the size and age structure of these populations. As life history theory predicts, those species with poor larval survival appear to adopt a bet-hedging life history strategy of long-lived individuals as a reproductive reserve.

Resources alter the structure and increase stochasticity in bromeliad microfauna communities.

PubMed

Petermann, Jana S; Kratina, Pavel; Marino, Nicholas A C; MacDonald, A Andrew M; Srivastava, Diane S

2015-01-01

Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined.

Resources Alter the Structure and Increase Stochasticity in Bromeliad Microfauna Communities

PubMed Central

Petermann, Jana S.; Kratina, Pavel; Marino, Nicholas A. C.; MacDonald, A. Andrew M.; Srivastava, Diane S.

2015-01-01

Although stochastic and deterministic processes have been found to jointly shape structure of natural communities, the relative importance of both forces may vary across different environmental conditions and across levels of biological organization. We tested the effects of abiotic environmental conditions, altered trophic interactions and dispersal limitation on the structure of aquatic microfauna communities in Costa Rican tank bromeliads. Our approach combined natural gradients in environmental conditions with experimental manipulations of bottom-up interactions (resources), top-down interactions (predators) and dispersal at two spatial scales in the field. We found that resource addition strongly increased the abundance and reduced the richness of microfauna communities. Community composition shifted in a predictable way towards assemblages dominated by flagellates and ciliates but with lower abundance and richness of algae and amoebae. While all functional groups responded strongly and predictably to resource addition, similarity among communities at the species level decreased, suggesting a role of stochasticity in species-level assembly processes. Dispersal limitation did not affect the communities. Since our design excluded potential priority effects we can attribute the differences in community similarity to increased demographic stochasticity of resource-enriched communities related to erratic changes in population sizes of some species. In contrast to resources, predators and environmental conditions had negligible effects on community structure. Our results demonstrate that bromeliad microfauna communities are strongly controlled by bottom-up forces. They further suggest that the relative importance of stochasticity may change with productivity and with the organizational level at which communities are examined. PMID:25775464

Body size and meta-community structure: the allometric scaling of parasitic worm communities in their mammalian hosts.

PubMed

DE Leo, Giulio A; Dobson, Andrew P; Gatto, Marino

2016-06-01

In this paper we derive from first principles the expected body sizes of the parasite communities that can coexist in a mammal of given body size. We use a mixture of mathematical models and known allometric relationships to examine whether host and parasite life histories constrain the diversity of parasite species that can coexist in the population of any host species. The model consists of one differential equation for each parasite species and a single density-dependent nonlinear equation for the affected host under the assumption of exploitation competition. We derive threshold conditions for the coexistence and competitive exclusion of parasite species using invasion criteria and stability analysis of the resulting equilibria. These results are then used to evaluate the range of parasites species that can invade and establish in a target host and identify the 'optimal' size of a parasite species for a host of a given body size; 'optimal' is defined as the body size of a parasite species that cannot be outcompeted by any other parasite species. The expected distributions of parasites body sizes in hosts of different sizes are then compared with those observed in empirical studies. Our analysis predicts the relative abundance of parasites of different size that establish in the host and suggests that increasing the ratio of parasite body size to host body size above a minimum threshold increases the persistence of the parasite population.

Impact of individual interest shift on information dissemination in modular networks

NASA Astrophysics Data System (ADS)

Zhao, Narisa; Cui, Xuelian

2017-01-01

Social networks exhibit strong community structure. Many researches have been done to explore the impacts of community structure on information diffusion but few combined with human behaviors together. In this paper, we focus on how the individual interests' changing behavior impacts the dynamics of information propagation. Firstly, we propose an information dissemination model considering both the community structure and individual interest shift where social reinforcement and time decaying are taken into account. The accuracy of the model is evaluated by comparing the simulation and theoretical results. Further, the numerical results illustrate that both the community structure and the interests changing behavior have effects on the outbreak size of the information dissemination. Specially, lower modularity and higher community connection density will accelerate the speed of information propagation especially when the information maximal lifetime is shorter. In addition, the changes of individual interests in the message have a great impact on the final density of the received through increasing or decreasing the number of satisfied individuals directly. What is more, our findings suggest that when the modularity of the network is higher and the community clustering coefficient is lower individual interest shift behavior will have a heavier effect on the spread scope.

Spatial and temporal repeatability in parasite community structure of tropical fish hosts.

PubMed

Vidal-Martínez, V M; Poulin, R

2003-10-01

An assessment is made of the repeatability of parasite community structure in space for a marine fish, and in space and time for a freshwater fish from south-eastern Mexico. The marine fish species was the red grouper, Epinephelus morio (collected from 9 localities), and the freshwater species was the cichlid, Cichlasoma urophthalmus (collected from 6 localities: including monthly at 2 localities for 1 year, and bimonthly at 1 locality in 1990 and 1999). Pairwise interspecific associations and analyses of nested patterns in the distributions of parasite species among hosts were used in both fish species, with comparisons over time made only with the cichlid. Positive interspecific associations, and nested patterns were noted in some localities for both fish species, and/or at some sampling times for the cichlid fish. However, non-random patterns in the structure of parasite communities in these 2 host species only were observed sporadically. When present, nestedness in both fish species was apparently linked with a positive association between total infection intensities and fish size. Additionally, adjacent localities were more likely to display similar parasite community structure than distant ones. This preliminary result suggests that distance between localities is an important determinant of predictability in parasite community structure.

Efficient discovery of overlapping communities in massive networks

PubMed Central

Gopalan, Prem K.; Blei, David M.

2013-01-01

Detecting overlapping communities is essential to analyzing and exploring natural networks such as social networks, biological networks, and citation networks. However, most existing approaches do not scale to the size of networks that we regularly observe in the real world. In this paper, we develop a scalable approach to community detection that discovers overlapping communities in massive real-world networks. Our approach is based on a Bayesian model of networks that allows nodes to participate in multiple communities, and a corresponding algorithm that naturally interleaves subsampling from the network and updating an estimate of its communities. We demonstrate how we can discover the hidden community structure of several real-world networks, including 3.7 million US patents, 575,000 physics articles from the arXiv preprint server, and 875,000 connected Web pages from the Internet. Furthermore, we demonstrate on large simulated networks that our algorithm accurately discovers the true community structure. This paper opens the door to using sophisticated statistical models to analyze massive networks. PMID:23950224

Analysis of avian communities in Lake Guri, Venezuela, using multiple assembly rule models.

PubMed

Feeley, Kenneth

2003-09-01

This study analyzed the distribution of resident, forest-interior bird species nesting on islands in Lake Guri, Venezuela using several different community assembly rule models. The models that were tested included Diamond's Assembly Rules, Size Structure, Guild Proportionality, Favored States, and Nestedness. It was determined that the species composition of the study communities was only weakly influenced by competition, but that competition did appear to limit the size similarity which is permissible for co-occurring species. There was no tendency for the relative proportion of species within guilds (i.e. insectivore, omnivore, nectivore and frugivore) to remain stable among the islands. When only the insectivorous and omnivorous species were analyzed (using feeding strata as the functional groups) there was some support for the guild proportionality hypothesis. This study found no support for Fox's Favored State hypothesis, possibly due to the overrepresentation of insectivores and omnivores in the species pool. The island communities exhibit a highly nested structure. This high degree of nestedness supports the hypothesis that the assemblages are more strongly determined by differential extinction vulnerability and selective species loss than by interspecific or inter-guild competition. Understanding patterns of community assembly and their underlying forces has important implications for conservation ecology and reserve design.

The problem and promise of scale dependency in community phylogenetics.

PubMed

Swenson, Nathan G; Enquist, Brian J; Pither, Jason; Thompson, Jill; Zimmerman, Jess K

2006-10-01

The problem of scale dependency is widespread in investigations of ecological communities. Null model investigations of community assembly exemplify the challenges involved because they typically include subjectively defined "regional species pools." The burgeoning field of community phylogenetics appears poised to face similar challenges. Our objective is to quantify the scope of the problem of scale dependency by comparing the phylogenetic structure of assemblages across contrasting geographic and taxonomic scales. We conduct phylogenetic analyses on communities within three tropical forests, and perform a sensitivity analysis with respect to two scaleable inputs: taxonomy and species pool size. We show that (1) estimates of phylogenetic overdispersion within local assemblages depend strongly on the taxonomic makeup of the local assemblage and (2) comparing the phylogenetic structure of a local assemblage to a species pool drawn from increasingly larger geographic scales results in an increased signal of phylogenetic clustering. We argue that, rather than posing a problem, "scale sensitivities" are likely to reveal general patterns of diversity that could help identify critical scales at which local or regional influences gain primacy for the structuring of communities. In this way, community phylogenetics promises to fill an important gap in community ecology and biogeography research.

Family physician clinical compensation in an academic environment: moving away from the relative value unit

PubMed Central

Lochner, Jennifer; Trowbridge, Elizabeth; Kamnetz, Sandra; Pandhi, Nancy

2016-01-01

Background and Objectives Primary care physician compensation structures have remained largely volume-based, lagging behind changes in reimbursement that increasingly include population approaches such as capitation, bundled payments, and care management fees. We describe a population health-based physician compensation plan developed for two departmental family medicine faculty groups (residency teaching clinic faculty and community clinic faculty) along with outcomes before and after the plan’s implementation. Methods An observational study was conducted. A pre-post email survey assessed satisfaction with the plan, salary, and salary equity. Physician retention, panel size, and relative value unit (RVU) productivity metrics also were assessed before and after the plan’s implementation. Results Before implementation of the new plan, 18% of residency faculty and 33% of community faculty were satisfied or very satisfied with compensation structure. After implementation, those numbers rose to 47% for residency physicians and 74% for community physicians (p<0.01). Satisfaction with the amount of compensation also rose from 33% to 68% for residency faculty and from 26% to 87% for community faculty (p<0.01). For both groups, panel size per clinical full-time equivalent increased and RVUs moved closer to national benchmarks. RVUs decreased for residency faculty and increased for community faculty. Conclusions Aligning a compensation plan with population health delivery by moving rewards away from RVU productivity and towards panel management resulted in improved physician satisfaction and retention, as well as larger panel sizes. RVU changes were less predictable. Physician compensation is an important component of care model redesign that emphasizes population health. PMID:27272423

The Structure and Distribution of Benthic Communities on a Shallow Seamount (Cobb Seamount, Northeast Pacific Ocean)

PubMed Central

Curtis, Janelle M. R.; Clarke, M. Elizabeth

2016-01-01

Partially owing to their isolation and remote distribution, research on seamounts is still in its infancy, with few comprehensive datasets and empirical evidence supporting or refuting prevailing ecological paradigms. As anthropogenic activity in the high seas increases, so does the need for better understanding of seamount ecosystems and factors that influence the distribution of sensitive benthic communities. This study used quantitative community analyses to detail the structure, diversity, and distribution of benthic mega-epifauna communities on Cobb Seamount, a shallow seamount in the Northeast Pacific Ocean. Underwater vehicles were used to visually survey the benthos and seafloor in ~1600 images (~5 m2 in size) between 34 and 1154 m depth. The analyses of 74 taxa from 11 phyla resulted in the identification of nine communities. Each community was typified by taxa considered to provide biological structure and/or be a primary producer. The majority of the community-defining taxa were either cold-water corals, sponges, or algae. Communities were generally distributed as bands encircling the seamount, and depth was consistently shown to be the strongest environmental proxy of the community-structuring processes. The remaining variability in community structure was partially explained by substrate type, rugosity, and slope. The study used environmental metrics, derived from ship-based multibeam bathymetry, to model the distribution of communities on the seamount. This model was successfully applied to map the distribution of communities on a 220 km2 region of Cobb Seamount. The results of the study support the paradigms that seamounts are diversity 'hotspots', that the majority of seamount communities are at risk to disturbance from bottom fishing, and that seamounts are refugia for biota, while refuting the idea that seamounts have high endemism. PMID:27792782

Prey size diversity hinders biomass trophic transfer and predator size diversity promotes it in planktonic communities

PubMed Central

García-Comas, Carmen; Sastri, Akash R.; Ye, Lin; Chang, Chun-Yi; Lin, Fan-Sian; Su, Min-Sian; Gong, Gwo-Ching; Hsieh, Chih-hao

2016-01-01

Body size exerts multiple effects on plankton food-web interactions. However, the influence of size structure on trophic transfer remains poorly quantified in the field. Here, we examine how the size diversity of prey (nano-microplankton) and predators (mesozooplankton) influence trophic transfer efficiency (using biomass ratio as a proxy) in natural marine ecosystems. Our results support previous studies on single trophic levels: transfer efficiency decreases with increasing prey size diversity and is enhanced with greater predator size diversity. We further show that communities with low nano-microplankton size diversity and high mesozooplankton size diversity tend to occur in warmer environments with low nutrient concentrations, thus promoting trophic transfer to higher trophic levels in those conditions. Moreover, we reveal an interactive effect of predator and prey size diversities: the positive effect of predator size diversity becomes influential when prey size diversity is high. Mechanistically, the negative effect of prey size diversity on trophic transfer may be explained by unicellular size-based metabolic constraints as well as trade-offs between growth and predation avoidance with size, whereas increasing predator size diversity may enhance diet niche partitioning and thus promote trophic transfer. These findings provide insights into size-based theories of ecosystem functioning, with implications for ecosystem predictive models. PMID:26865298

Avian community responses to post-fire forest structure: implications for fire management in mixed conifer forests

Treesearch

Angela White; Patricia Manley; Gina Tarbill; T. W. Richardson; R. E. Russell; H. D. Safford; S. Z. Dobrowski

2016-01-01

Fire is a natural process and the dominant disturbance shaping plant and animal communities in many coniferous forests of the western US. Given that fire size and severity are predicted to increase in the future, it has become increasingly important to understand how wildlife responds to fire and post-fire management. The Angora Fire...

Hydrogeomorphic (HGM) Approach to Assessing Wetland Functions: Guidelines for Developing Guidebooks (Version 2)

DTIC Science & Technology

2013-06-01

setting, landscape position, watershed size), the structural components of the wetland ecosystem (e.g., plants , animals, soil , water, and the...Community Support Characteristic Invertebrate Community Support Landscape/Regional Biodiversity Diversity of native plant species (index, H’) Number of...Flagging GPS and Digital Camera / Spare Batteries Clipboard, Calculator, and Pencils County Soil Survey Plant Identification Keys Munsell

Characterization of Epiphytic Bacterial Communities from Grapes, Leaves, Bark and Soil of Grapevine Plants Grown, and Their Relations

PubMed Central

Martins, Guilherme; Lauga, Béatrice; Miot-Sertier, Cécile; Mercier, Anne; Lonvaud, Aline; Soulas, Marie-Louise; Soulas, Guy; Masneuf-Pomarède, Isabelle

2013-01-01

Despite its importance in plant health and crop quality, the diversity of epiphytic bacteria on grape berries and other plant parts, like leaves and bark, remains poorly described, as does the role of telluric bacteria in plant colonization. In this study, we compare the bacterial community size and structure in vineyard soils, as well as on grapevine bark, leaves and berries. Analyses of culturable bacteria revealed differences in the size and structure of the populations in each ecosystem. The highest bacteria population counts and the greatest diversity of genera were found in soil samples, followed by bark, grapes and leaves. The identification of isolates revealed that some genera – Pseudomonas, Curtobacterium, and Bacillus – were present in all ecosystems, but in different amounts, while others were ecosystem-specific. About 50% of the genera were common to soil and bark, but absent from leaves and grapes. The opposite was also observed: grape and leaf samples presented 50% of genera in common that were absent from trunk and soil. The bacterial community structure analyzed by T-RFLP indicated similarities between the profiles of leaves and grapes, on the one hand, and bark and soil, on the other, reflecting the number of shared T-RFs. The results suggest an interaction between telluric bacterial communities and the epiphytic bacteria present on the different grapevine parts. PMID:24023666

Zooplankton Grazing Effects on Particle Size Spectra under Different Seasonal Conditions

NASA Astrophysics Data System (ADS)

Stamieszkin, K.; Poulton, N.; Pershing, A. J.

2016-02-01

Oceanic particle size spectra can be used to explain and predict variability in carbon export efficiency, since larger particles are more likely to sink to depth than small particles. The distribution of biogenic particle size in the surface ocean is the result of many variables and processes, including nutrient availability, primary productivity, aggregation, remineralization, and grazing. We conducted a series of grazing experiments to test the hypothesis that mesozooplankton shift particle size spectra toward larger particles, via grazing and egestion of relatively large fecal pellets. These experiments were carried out over several months, and used natural communities of mesozooplankton and their microbial prey, collected offshore of the Damariscotta River in the Gulf of Maine. We analyzed the samples using Fluid Imaging Technologies' FlowCam®, a particle imaging system. With this equipment, we processed live samples, decreasing the likelihood of losing or damaging fragile particles, and thereby lessening sources of error in commonly used preservation and enumeration protocols. Our results show how the plankton size spectrum changes as the Gulf of Maine progresses through a seasonal cycle. We explore the relationship of grazing community size structure to its effect on the overall biogenic particle size spectrum. At some times of year, mesozooplankton grazing does not alter the particle size spectrum, while at others it significantly does, affecting the potential for biogenic flux. We also examine prey selectivity, and find that chain diatoms are the only prey group preferentially consumed. Otherwise, we find that complete mesozooplankton communities are "evolved" to fit their prey such that most prey groups are grazed evenly. We discuss a metabolic numerical model which could be used to universalize the relationships between whole gazer and whole microbial communities, with respect to effects on particle size spectra.

Variability in Phytoplankton Morphology and Macromolecular Composition With Nutrient Starvation and The Implications for Oceanic Elemental Stoichiometry

NASA Astrophysics Data System (ADS)

Liefer, J. D.; Benner, I.; Brown, C. M.; Garg, A.; Fiset, C.; Irwin, A. J.; Follows, M. J.; Finkel, Z.

2016-02-01

Trait based modeling efforts are an important tool for predicting the distribution of phytoplankton communities in the ocean and their interaction with elemental stoichiometry. The elemental stoichiometry of phytoplankton is based on their macromolecular composition. Many phytoplankton species accumulate C-rich storage products (carbohydrates and lipids) and reduce N and P-rich functional components (proteins and nucleic acids) upon N- or P-starvation. Reconciling global patterns in C:N:P stoichiometry and phytoplankton community structure and succession requires a better understanding of how phytoplankton macromolecular composition varies across taxa, size class, and growth conditions. We examined changes in cell size and composition from exponential growth to nitrogen starvation in four common phytoplankton species representing two size classes each of chlorophytes and diatoms. Variation in cell size, cell mass, and length of stationary growth phase appeared to be size dependent. The larger species of chlorophyte and diatom had a significant increase in cell mass and cell size with N-starvation and showed no significant change in cell density after starvation for 5-7 days. The smaller size species of both phyla showed no significant change in cell size or mass upon N-starvation and a consistent decline in cell density 1-2 days after peak densities were reached. All species had a similar significant increase in C quota, but changes in N quota and C:N were more variable and species-specific. We also present changes in macromolecular composition and C, N, and P-allocation due to N-starvation and their implications for elemental stoichiometry under natural conditions. These results are compared to field observations of C:N:P stoichiometry and phytoplankton community structure to examine the physiological plasticity that may underlie global oceanic C:N:P variability and demonstrate the importance of this plasticity in trait based models.

Separating the effects of environment and space on tree species distribution: from population to community.

PubMed

Lin, Guojun; Stralberg, Diana; Gong, Guiquan; Huang, Zhongliang; Ye, Wanhui; Wu, Linfang

2013-01-01

Quantifying the relative contributions of environmental conditions and spatial factors to species distribution can help improve our understanding of the processes that drive diversity patterns. In this study, based on tree inventory, topography and soil data from a 20-ha stem-mapped permanent forest plot in Guangdong Province, China, we evaluated the influence of different ecological processes at different spatial scales using canonical redundancy analysis (RDA) at the community level and multiple linear regression at the species level. At the community level, the proportion of explained variation in species distribution increased with grid-cell sizes, primarily due to a monotonic increase in the explanatory power of environmental variables. At the species level, neither environmental nor spatial factors were important determinants of overstory species' distributions at small cell sizes. However, purely spatial variables explained most of the variation in the distributions of understory species at fine and intermediate cell sizes. Midstory species showed patterns that were intermediate between those of overstory and understory species. At the 20-m cell size, the influence of spatial factors was stronger for more dispersal-limited species, suggesting that much of the spatial structuring in this community can be explained by dispersal limitation. Comparing environmental factors, soil variables had higher explanatory power than did topography for species distribution. However, both topographic and edaphic variables were highly spatial structured. Our results suggested that dispersal limitation has an important influence on fine-intermediate scale (from several to tens of meters) species distribution, while environmental variability facilitates species distribution at intermediate (from ten to tens of meters) and broad (from tens to hundreds of meters) scales.

A study to identify winning strategies for the business community during the next pandemic.

PubMed

Spriggs, Martin

2013-01-01

This study examines the relationship between the healthcare system and the corporate sector to answer the following research question: how does the healthcare system best prepare small to medium-sized businesses for the next pandemic influenza? Data were collected and collated through a literature review, electronic survey and semi-structured follow-up telephone interviews. The participants were businesses with membership in the Alberta Chambers of Commerce, a provincial lobby group in Alberta, Canada. The findings indicate strategies that were effective in minimising impact to the business community during the H1N1 pandemic and suggest areas for the business community to improve in preparation for the next pandemic influenza. Recommendations focus on establishing new links for communication between the business community and the healthcare sector and improving strategies to increase the resilience of small to medium-sized businesses for the next pandemic influenza.

Analysis of phytoplankton distribution and community structure in the German Bight with respect to the different size classes

NASA Astrophysics Data System (ADS)

Wollschläger, Jochen; Wiltshire, Karen Helen; Petersen, Wilhelm; Metfies, Katja

2015-05-01

Investigation of phytoplankton biodiversity, ecology, and biogeography is crucial for understanding marine ecosystems. Research is often carried out on the basis of microscopic observations, but due to the limitations of this approach regarding detection and identification of picophytoplankton (0.2-2 μm) and nanophytoplankton (2-20 μm), these investigations are mainly focused on the microphytoplankton (20-200 μm). In the last decades, various methods based on optical and molecular biological approaches have evolved which enable a more rapid and convenient analysis of phytoplankton samples and a more detailed assessment of small phytoplankton. In this study, a selection of these methods (in situ fluorescence, flow cytometry, genetic fingerprinting, and DNA microarray) was placed in complement to light microscopy and HPLC-based pigment analysis to investigate both biomass distribution and community structure of phytoplankton. As far as possible, the size classes were analyzed separately. Investigations were carried out on six cruises in the German Bight in 2010 and 2011 to analyze both spatial and seasonal variability. Microphytoplankton was identified as the major contributor to biomass in all seasons, followed by the nanophytoplankton. Generally, biomass distribution was patchy, but the overall contribution of small phytoplankton was higher in offshore areas and also in areas exhibiting higher turbidity. Regarding temporal development of the community, differences between the small phytoplankton community and the microphytoplankton were found. The latter exhibited a seasonal pattern regarding number of taxa present, alpha- and beta-diversity, and community structure, while for the nano- and especially the picophytoplankton, a general shift in the community between both years was observable without seasonality. Although the reason for this shift remains unclear, the results imply a different response of large and small phytoplankton to environmental influences.

Inferring species roles in metacommunity structure from species co-occurrence networks

PubMed Central

Borthagaray, Ana I.; Arim, Matías; Marquet, Pablo A.

2014-01-01

A long-standing question in community ecology is what determines the identity of species that coexist across local communities or metacommunity assembly. To shed light upon this question, we used a network approach to analyse the drivers of species co-occurrence patterns. In particular, we focus on the potential roles of body size and trophic status as determinants of metacommunity cohesion because of their link to resource use and dispersal ability. Small-sized individuals at low-trophic levels, and with limited dispersal potential, are expected to form highly linked subgroups, whereas large-size individuals at higher trophic positions, and with good dispersal potential, will foster the spatial coupling of subgroups and the cohesion of the whole metacommunity. By using modularity analysis, we identified six modules of species with similar responses to ecological conditions and high co-occurrence across local communities. Most species either co-occur with species from a single module or are connectors of the whole network. Among the latter are carnivorous species of intermediate body size, which by virtue of their high incidence provide connectivity to otherwise isolated communities playing the role of spatial couplers. Our study also demonstrates that the incorporation of network tools to the analysis of metacommunity ecology can help unveil the mechanisms underlying patterns and processes in metacommunity assembly. PMID:25143039

Forest fragmentation and bird community dynamics: inference at regional scales

USGS Publications Warehouse

Boulinier, T.; Nichols, J.D.; Hines, J.E.; Sauer, J.R.; Flather, C.H.; Pollock, K.H.

2001-01-01

With increasing fragmentation of natural areas and a dramatic reduction of forest cover in several parts of the world, quantifying the impact of such changes on species richness and community dynamics has been a subject of much concern. Here, we tested whether in more fragmented landscapes there was a lower number of area-sensitive species and higher local extinction and turnover rates, which could explain higher temporal variability in species richness. To investigate such potential landscape effects at a regional scale, we merged two independent, large-scale monitoring efforts: the North American Breeding Bird Survey (BBS) and the Land Use and Land Cover Classification data from the U.S. Geological Survey. We used methods that accounted for heterogeneity in the probability of detecting species to estimate species richness and temporal changes in the bird communities for BBS routes in three mid-Atlantic U.S. states. Forest breeding bird species were grouped prior to the analyses into area-sensitive and non-area-sensitive species according to previous studies. We tested predictions relating measures of forest structure at one point in time (1974) to species richness at that time and to parameters of forest bird community change over the following 22-yr-period (1975-1996). We used the mean size of forest patches to characterize landscape structure, as high correlations among landscape variables did not allow us to disentangle the relative roles of habitat fragmentation per se and habitat loss. As predicted, together with lower species richness for area-sensitive species on routes surrounded by landscapes with lower mean forest-patch size, we found higher mean year-to-year rates of local extinction. Moreover, the mean year-to-year rates of local turnover (proportion of locally new species) for area-sensitive species were also higher in landscapes with lower mean forest-patch size. These associations were not observed for the non-area-sensitive species group. These results suggest that landscape structure may influence forest bird communities at regional scales through its effects on the total number of species but also on the temporal rates of change in community composition. Evidence for higher rates of local extinction and turnover in more fragmented landscapes suggests that bird communities function as metapopulations at a regional scale, and points out the importance of colonizations and recolonizations from surrounding landscapes to local community dynamics. Further, our results illustrate that the methods used to estimate the community parameters can be a powerful statistical tool in addressing questions relative to the dynamics of communities.

Examining predator-prey body size, trophic level and body mass across marine and terrestrial mammals.

PubMed

Tucker, Marlee A; Rogers, Tracey L

2014-12-22

Predator-prey relationships and trophic levels are indicators of community structure, and are important for monitoring ecosystem changes. Mammals colonized the marine environment on seven separate occasions, which resulted in differences in species' physiology, morphology and behaviour. It is likely that these changes have had a major effect upon predator-prey relationships and trophic position; however, the effect of environment is yet to be clarified. We compiled a dataset, based on the literature, to explore the relationship between body mass, trophic level and predator-prey ratio across terrestrial (n = 51) and marine (n = 56) mammals. We did not find the expected positive relationship between trophic level and body mass, but we did find that marine carnivores sit 1.3 trophic levels higher than terrestrial carnivores. Also, marine mammals are largely carnivorous and have significantly larger predator-prey ratios compared with their terrestrial counterparts. We propose that primary productivity, and its availability, is important for mammalian trophic structure and body size. Also, energy flow and community structure in the marine environment are influenced by differences in energy efficiency and increased food web stability. Enhancing our knowledge of feeding ecology in mammals has the potential to provide insights into the structure and functioning of marine and terrestrial communities. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Habitat fragmentation effects on the orchid bee communities in remnant forests of southeastern Brazil.

PubMed

Knoll, Fátima do Rosário Naschenveng; Penatti, N C

2012-10-01

The effect of habitat fragmentation on the structure of orchid bee communities was analyzed by the investigation of the existence of a spatial structure in the richness and abundance of Euglossini species and by determining the relationship between these data and environmental factors. The surveys were carried out in four different forest fragments and one university campus. Richness, abundance, and diversity of species were analyzed in relation to abiotic (size of the area, extent of the perimeter, perimeter/area ratio, and shape index) and biotic characteristics (vegetation index of the fragment and of the matrix of each of the locations studied). We observed a highly significant positive correlation between the diversity index and the vegetation index of the fragment, landscape and shape index. Our analysis demonstrated that the observed variation could be explained mainly by the vegetation index and the size of the fragment. Variations in relative abundance showed a tendency toward an aggregated spatial distribution between the fragments studied, as well as between the sampling stations within the same habitat, demonstrating the existence of a spatial structure on a small scale in the populations of Euglossini. This distribution will determine the composition of species that coexist in the area after fragmentation. These data help in understanding the differences and similarities in the structure of communities of Euglossini resulting from forest fragmentation.

Comparison of macroinvertebrate community structure between two riffle-based sampling protocols in Wyoming, Colorado, and Montana, 2000-2001

USGS Publications Warehouse

Peterson, David A.; Zumberge, Jeremy R.

2006-01-01

Samples of benthic macroinvertebrates were collected side-by-side from riffles at 12 stream sites in Wyoming, Colorado, and Montana during 2000-2001, following protocols established by the U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program and the U.S. Environmental Protection Agency Environmental Monitoring and Assessment Program (EMAP). Samples from riffles were collected following NAWQA protocols, using a sampler with 425-micron net mesh-opening size from a total area of 1.25 m2 per sample in multiple riffles. Samples also were collected following EMAP protocols, using a sampler with 500-micron net mesh-opening size from a total area of 0.72 m2 per sample in multiple riffles. The taxonomic identification and enumeration of the samples followed procedures established for each program. Benthic macroinvertebrate community structure was compared between the data sets using individual metrics, a multimetric index, and multivariate analysis. Comparisons between the macroinvertebrate community structures were made after sequentially adjusting both data sets for: (1) ambiguous taxa, (2) taxonomic inconsistencies, and (3) differences in laboratory subsampling. After removal of ambiguous taxa, pair-wise differences in total taxa richness and Ephemeroptera taxa richness were statistically significant (p < 0.05). Differences between the data sets generally were not significant for richness of other taxa, tolerant taxa, semi-voltine taxa, functional feeding groups, diversity, and dominance. Sample scores calculated using the Wyoming Stream Integrity Index were not significantly different between the two data sets. After reconciling both data sets for taxonomic inconsistencies, total taxa richness and Ephemeroptera taxa richness remained significantly different between the data sets. After adjusting the data for differences in laboratory subsampling, the differences in taxa richness were no longer significant. Bray-Curtis similarity coefficients and non-metric multi-dimensional scaling were used to examine macroinvertebrate community structure. Similarity in community structure between sites was affected to a greater extent by taxa reconciliation than by adjustment for subsampling.

Helminth community structure of Tropidurus torquatus (Squamata: Tropiduridae) in a rocky outcrop area of Minas Gerais state, southeastern Brazil.

PubMed

Pereira, Felipe B; Sousa, Bernadete M; Lima, Sueli de Souza

2012-02-01

The helminth community of Tropidurus torquatus (Squamata: Tropiduridae) from a rocky outcrop area located in the state of Minas Gerais, southeastern Brazil, was studied. Ninety-two of the 110 individuals examined (83.6%) harbored helminths. Five species were found, including 3 nematodes ( Physaloptera lutzi , Parapharyngodon bainae , and Oswaldofilaria chabaudi ), 1 unidentified cestode species, and 1 acanthocephalan cystacanth also not identified. Only the nematode species had sufficient data to perform ecological analysis, with P. lutzi exhibiting the highest prevalence (67.3%). Prevalence between male and female hosts differed only for Oswaldofilaria chabaudi , with males exhibiting the highest values. The intensities of infection by P. lutzi and O. chabaudi were different among male and female hosts, with males also exhibiting the highest values. The host body size was positively related to intensity of infection for all nematode species. Local seasonality had some influence on the helminth community structure. Host diet, sexual dimorphism, and behavior (territorialism, forage strategy) represented important factors for the structure of this parasite community. In general, the helminth community was species poor, depauperate, and non-interactive, representing a typical structure observed in lizard hosts.

How does abundance scale with body size in coupled size-structured food webs?

PubMed

Blanchard, Julia L; Jennings, Simon; Law, Richard; Castle, Matthew D; McCloghrie, Paul; Rochet, Marie-Joëlle; Benoît, Eric

2009-01-01

1. Widely observed macro-ecological patterns in log abundance vs. log body mass of organisms can be explained by simple scaling theory based on food (energy) availability across a spectrum of body sizes. The theory predicts that when food availability falls with body size (as in most aquatic food webs where larger predators eat smaller prey), the scaling between log N vs. log m is steeper than when organisms of different sizes compete for a shared unstructured resource (e.g. autotrophs, herbivores and detritivores; hereafter dubbed 'detritivores'). 2. In real communities, the mix of feeding characteristics gives rise to complex food webs. Such complexities make empirical tests of scaling predictions prone to error if: (i) the data are not disaggregated in accordance with the assumptions of the theory being tested, or (ii) the theory does not account for all of the trophic interactions within and across the communities sampled. 3. We disaggregated whole community data collected in the North Sea into predator and detritivore components and report slopes of log abundance vs. log body mass relationships. Observed slopes for fish and epifaunal predator communities (-1.2 to -2.25) were significantly steeper than those for infaunal detritivore communities (-0.56 to -0.87). 4. We present a model describing the dynamics of coupled size spectra, to explain how coupling of predator and detritivore communities affects the scaling of log N vs. log m. The model captures the trophic interactions and recycling of material that occur in many aquatic ecosystems. 5. Our simulations demonstrate that the biological processes underlying growth and mortality in the two distinct size spectra lead to patterns consistent with data. Slopes of log N vs. log m were steeper and growth rates faster for predators compared to detritivores. Size spectra were truncated when primary production was too low for predators and when detritivores experienced predation pressure. 6. The approach also allows us to assess the effects of external sources of mortality (e.g. harvesting). Removal of large predators resulted in steeper predator spectra and increases in their prey (small fish and detritivores). The model predictions are remarkably consistent with observed patterns of exploited ecosystems.

Building community participatory research coalitions from the ground up: the Philadelphia area research community coalition.

PubMed

Johnson, Jerry C; Hayden, U Tara; Thomas, Nicole; Groce-Martin, Jennine; Henry, Thomas; Guerra, Terry; Walker, Alia; West, William; Barnett, Marina; Kumanyika, Shiriki

2009-01-01

A coalition of formal, large organizations and informal, grassroots organizations, recruited through an open process, contrasts with the usual practice of developing a community-based participatory research (CBPR) coalition with a small number of well-developed organizations. This paper describes the process, developmental challenges, and accomplishments of the Philadelphia Area Research Community Coalition (PARCC). The University of Pennsylvania-Cheyney University of Pennsylvania EXPORT Center established the PARCC, an academic-community research partnership of twenty-two diverse organizations of variable size and with variable experience in health research. The EXPORT Center provided the infrastructure and staff support needed to engage in sustained, face-to-face community outreach and to nurture, coordinate, and facilitate the 2.5-year developmental process. The start-up process, governing principles, activities, challenges, and lessons learned are described. Since its inception, PARCC established core work groups, a governance structure, operating principles, research training activities, community health education projects, and several PARCC-affiliated research projects. Organizations across the spectrum of developmental capacity were major contributors to PARCC. The success of PARCC was based on committed and trusted leadership, preexisting relationships, trust among members from the community and academia, research training, extensive time commitment of members to the coalition's work, and rapid development of work group activities. Building a CBPR coalition from the ground up involving organizations of diverse size and at various stages of development presents unique challenges that can be overcome with committed leadership, clear governance principles, and appropriate infrastructure. Engagement in community-based research during the early stages, while still developing trust, structure, and governance procedures can be accomplished as long as training of all partners is conducted and the trust building is not ignored.

Phytoplankton Functional Diversity and New Production during Spring and Summer Blooms in the Subarctic Atlantic Ocean

NASA Astrophysics Data System (ADS)

Van Oostende, N.; Fawcett, S. E.; Ji, Q.; Marconi, D.; Lueders-Dumont, J.; Sigman, D. M.; Ward, B. B.

2016-02-01

In the subarctic Atlantic Ocean, strong seasonal cycles in heat flux drive water column stratification, which governs the supply of nutrients to the euphotic zone that fuels the biological pump. The export efficiency of this pump is largely determined by the degree of phytoplankton nitrate (NO3-) assimilation and phytoplankton community size structure. We investigated nitrogen assimilation and phytoplankton community diversity and size structure on spring and summer cruises to 50-60°N, by using a combination of stable isotope tracer incubations, flow cytometry, microscopy, size-fractionated algal pigments, and nitrogen stable isotope measurements. As expected in springtime, the phytoplankton community was dominated by large (>20 µm) cells while in late summer these constituted only a minor fraction of the assemblage. The weaker density stratification of the water column in the spring compared to the summer allowed for surface nutrient concentrations that were not limiting phytoplankton growth (e.g., [NO3-] >5 µM). Despite stronger water column stratification in the summer, partial consumption of subsurface NO3-, which had recently been supplied to surface waters, allowed for total chlorophyll and particulate nitrogen (PN) to attain similar levels during both seasons. High 15N/14N of NO3- and PN in surface waters is consistent with NO3- utilization. In springtime, however, the phytoplankton community consumed NO3- at PN-normalized rates up to fivefold higher than in summer, despite having comparable uptake rates for ammonium and inorganic carbon. This observation implies that the large phytoplankton species that are abundant in spring, mostly diatoms, contribute disproportionally more to new production than summer phytoplankton communities that are devoid of these large species.

Spatial and temporal structure of a mesocarnivore guild in midwestern north America

Treesearch

Damon B. Lesmeister; Clayton K. Nielsen; Eric M. Schauber; Eric C. Hellgren

2015-01-01

Carnivore guilds play a vital role in ecological communities by cascading trophic effects, energy and nutrient transfer, and stabilizing or destabilizing food webs. Consequently, the structure of carnivore guilds can be critical to ecosystem patterns. Body size is a crucial influence on intraguild interactions, because it affects access to prey resources, effectiveness...

Dynamics of size-fractionated phytoplankton biomass in a monsoonal estuary: Patterns and drivers for seasonal and spatial variability

NASA Astrophysics Data System (ADS)

Rajaneesh, K. M.; Mitbavkar, Smita; Anil, Arga Chandrashekar

2018-07-01

Phytoplankton size-fractionated biomass is an important determinant of the type of food web functioning in aquatic ecosystems. Knowledge about the effect of seasonal salinity gradient on the size-fractionated biomass dynamics is still lacking, especially in tropical estuaries experiencing monsoon. The phytoplankton size-fractionated chlorophyll a biomass (>3 μm and <3 μm) and picophytoplankton community structure were characterized in the monsoonal Zuari estuary, along the west coast of India, from October 2010 to September 2011 across the salinity gradient (0-35). On an annual scale, >3 μm size-fraction was the major contributor to the total phytoplankton chlorophyll a biomass with the ephemeral dominance of <3 μm size-fraction. During monsoon season, freshwater runoff and shorter water residence time resulted in a size-independent response. The lowest annual chlorophyll a biomass concentration of both size-fractions showed signs of recovery with increasing salinity downstream towards the end of the monsoon season. In contrast, the chlorophyll a biomass response was size-dependent during the non-monsoon seasons with the sporadic dominance (>50%) of <3 μm chlorophyll a biomass during high water temperature episodes from downstream to middle estuary during pre-monsoon and at low salinity and high nutrient conditions upstream during post-monsoon. These conditions also influenced the picophytoplankton community structure with picoeukaryotes dominating during the pre-monsoon, phycoerythrin containing Synechococcus during the monsoon and phycocyanin containing Synechococcus during the post-monsoon. This study highlights switching over of dominance in size-fractionated phytoplankton chlorophyll a biomass at intra, inter-seasonal and spatial scales which will likely govern the estuarine trophodynamics.

The structure of microbial community in aggregates of a typical chernozem aggregates under contrasting variants of its agricultural use

NASA Astrophysics Data System (ADS)

Ivanova, E. A.; Kutovaya, O. V.; Tkhakakhova, A. K.; Chernov, T. I.; Pershina, E. V.; Markina, L. G.; Andronov, E. E.; Kogut, B. M.

2015-11-01

The taxonomic structure of microbiomes in aggregates of different sizes from typical chernozems was investigated using sequencing of the 16S rRNA gene. The aggregate fractions of <0.25, 2-5, and >7 mm obtained by sieving of the soil samples at natural moisture were used for analysis. The highest prokaryote biomass (bacteria, archaea) was determined in the fractions <0.25 and aggregates 2-5 mm; the bacterial and archaeal biomass decreased in the following series: fallow > permanent black fallow > permanent winter wheat. The greatest number of fungi was recorded in the fraction <0.25 mm from the soils of the permanent black fallow and in all the studied aggregate fractions in the variant with permanent wheat. The system of agricultural use affected more significantly the structure of the prokaryote community in the chernozem than the size of aggregate fractions did. The most diverse microbial community was recorded in the soil samples of the fallow; the statistically significant maximums of the Shannon diversity indices and indices of phylogenetic diversity (PD) were recorded in the fractions <0.25 and 2-5 mm from the fallow soil. On the whole, the fine soil fractions (<0.25 mm) were characterized by higher diversity indices in comparison with those of the coarser aggregate fractions.

Changes in Soil Microbial Community and Its Effect on Carbon Sequestration Following Afforestation on the Loess Plateau, China.

PubMed

Xiang, Yun; Cheng, Man; Huang, Yimei; An, Shaoshan; Darboux, Frédéric

2017-08-22

Afforestation plays an important role in soil protection and ecological restoration. The objective of this study is to understand the effect of afforestation on soil carbon and soil microbial communities in the Loess Plateau of China. We measured two chemically-separated carbon fractions (i.e., humic acid, HA, and fulvic acid, FA) and soil microbial communities within shrublands (18-year-old Caragana korshinskii Kom (shrubland I) and 28-year-old Caragana korshinskii Kom (shrubland II)) and cropland. The size and structure of the soil microbial community was measured by phospholipid fatty acid (PLFA) analysis. The analysis of C-fractions indicated that at a depth of 0-20 cm, FA-C concentration in shrubland I and shrubland II were 1.7 times that of cropland, while HA-C had similar values across all three sites. Total PLFAs, G⁺ (Gram positive) bacterial, G - (Gram negative) bacterial, and actinobacterial PLFAs were highest in shrubland II, followed by shrubland I and finally cropland. Fungal PLFAs were significantly higher in shrubland II compared to the other sites. Additionally, we found a high degree of synergy between main microbial groups (apart from fungi) with FA-C. We concluded that planting C. korshinskii in abandoned cropland could alter the size and structure of soil microbial community, with these changes being closely related to carbon sequestration and humus formation.

Changes in Soil Microbial Community and Its Effect on Carbon Sequestration Following Afforestation on the Loess Plateau, China

PubMed Central

Xiang, Yun; Huang, Yimei; An, Shaoshan; Darboux, Frédéric

2017-01-01

Afforestation plays an important role in soil protection and ecological restoration. The objective of this study is to understand the effect of afforestation on soil carbon and soil microbial communities in the Loess Plateau of China. We measured two chemically-separated carbon fractions (i.e., humic acid, HA, and fulvic acid, FA) and soil microbial communities within shrublands (18-year-old Caragana korshinskii Kom (shrubland I) and 28-year-old Caragana korshinskii Kom (shrubland II)) and cropland. The size and structure of the soil microbial community was measured by phospholipid fatty acid (PLFA) analysis. The analysis of C-fractions indicated that at a depth of 0–20 cm, FA-C concentration in shrubland I and shrubland II were 1.7 times that of cropland, while HA-C had similar values across all three sites. Total PLFAs, G+ (Gram positive) bacterial, G− (Gram negative) bacterial, and actinobacterial PLFAs were highest in shrubland II, followed by shrubland I and finally cropland. Fungal PLFAs were significantly higher in shrubland II compared to the other sites. Additionally, we found a high degree of synergy between main microbial groups (apart from fungi) with FA-C. We concluded that planting C. korshinskii in abandoned cropland could alter the size and structure of soil microbial community, with these changes being closely related to carbon sequestration and humus formation. PMID:28829374

Assessing differences in macrofaunal assemblages as a factor of sieve mesh size, distance between samples, and time of sampling.

PubMed

Hemery, Lenaïg G; Politano, Kristin K; Henkel, Sarah K

2017-08-01

With increasing cascading effects of climate change on the marine environment, as well as pollution and anthropogenic utilization of the seafloor, there is increasing interest in tracking changes to benthic communities. Macrofaunal surveys are traditionally conducted as part of pre-incident environmental assessment studies and post-incident monitoring studies when there is a potential impact to the seafloor. These surveys usually characterize the structure and/or spatiotemporal distribution of macrofaunal assemblages collected with sediment cores; however, many different sampling protocols have been used. An assessment of the comparability of past and current survey methods was in need to facilitate future surveys and comparisons. This was the aim of the present study, conducted off the Oregon coast in waters 25-35 m deep. Our results show that the use of a sieve with a 1.0-mm mesh size gives results for community structure comparable to results obtained from a 0.5-mm mesh size, which allows reliable comparisons of recent and past spatiotemporal surveys of macroinfauna. In addition to our primary objective of comparing methods, we also found interacting effects of seasons and depths of collection. Seasonal differences (summer and fall) were seen in infaunal assemblages in the wave-induced sediment motion zone but not deeper. Thus, studies where wave-induced sediment motion can structure the benthic communities, especially during the winter months, should consider this effect when making temporal comparisons. In addition, some macrofauna taxa-like polychaetes and amphipods show high interannual variabilities, so spatiotemporal studies should make sure to cover several years before drawing any conclusions.

Evaluation of the Healthy Lifestyles Initiative for Improving Community Capacity for Childhood Obesity Prevention.

PubMed

Berman, Marcie; Bozsik, Frances; Shook, Robin P; Meissen-Sebelius, Emily; Markenson, Deborah; Summar, Shelly; DeWit, Emily; Carlson, Jordan A

2018-02-22

Policy, systems, and environmental approaches are recommended for preventing childhood obesity. The objective of our study was to evaluate the Healthy Lifestyles Initiative, which aimed to strengthen community capacity for policy, systems, and environmental approaches to healthy eating and active living among children and families. The Healthy Lifestyles Initiative was developed through a collaborative process and facilitated by community organizers at a local children's hospital. The initiative supported 218 partners from 170 community organizations through training, action planning, coalition support, one-on-one support, and the dissemination of materials and sharing of resources. Eighty initiative partners completed a brief online survey on implementation strategies engaged in, materials used, and policy, systems, and environmental activities implemented. In accordance with frameworks for implementation science, we assessed associations among the constructs by using linear regression to identify whether and which of the implementation strategies were associated with materials used and implementation of policy, systems, and environmental activities targeted by the initiative. Each implementation strategy was engaged in by 30% to 35% of the 80 survey respondents. The most frequently used materials were educational handouts (76.3%) and posters (66.3%). The most frequently implemented activities were developing or continuing partnerships (57.5%) and reviewing organizational wellness policies (46.3%). Completing an action plan and the number of implementation strategies engaged in were positively associated with implementation of targeted activities (action plan, effect size = 0.82; number of strategies, effect size = 0.51) and materials use (action plan, effect size = 0.59; number of strategies, effect size = 0.52). Materials use was positively associated with implementation of targeted activities (effect size = 0.35). Community-capacity-building efforts can be effective in supporting community organizations to engage in policy, systems, and environmental activities for healthy eating and active living. Multiple implementation strategies are likely needed, particularly strategies that involve a high level of engagement, such as training community organizations and working with them on structured action plans.

Complex, Dynamic Combination of Physical, Chemical and Nutritional Variables Controls Spatio-Temporal Variation of Sandy Beach Community Structure

PubMed Central

Ortega Cisneros, Kelly; Smit, Albertus J.; Laudien, Jürgen; Schoeman, David S.

2011-01-01

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C∶N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right. PMID:21858213

Complex, dynamic combination of physical, chemical and nutritional variables controls spatio-temporal variation of sandy beach community structure.

PubMed

Ortega Cisneros, Kelly; Smit, Albertus J; Laudien, Jürgen; Schoeman, David S

2011-01-01

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C∶N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right.

Modeling household and community transmission of Ebola virus disease: Epidemic growth, spatial dynamics and insights for epidemic control

PubMed Central

Kiskowski, Maria; Chowell, Gerardo

2016-01-01

The mechanisms behind the sub-exponential growth dynamics of the West Africa Ebola virus disease epidemic could be related to improved control of the epidemic and the result of reduced disease transmission in spatially constrained contact structures. An individual-based, stochastic network model is used to model immediate and delayed epidemic control in the context of social contact networks and investigate the extent to which the relative role of these factors may be determined during an outbreak. We find that in general, epidemics quickly establish a dynamic equilibrium of infections in the form of a wave of fixed size and speed traveling through the contact network. Both greater epidemic control and limited community mixing decrease the size of an infectious wave. However, for a fixed wave size, epidemic control (in contrast with limited community mixing) results in lower community saturation and a wave that moves more quickly through the contact network. We also found that the level of epidemic control has a disproportionately greater reductive effect on larger waves, so that a small wave requires nearly as much epidemic control as a larger wave to end an epidemic. PMID:26399855

Modeling household and community transmission of Ebola virus disease: Epidemic growth, spatial dynamics and insights for epidemic control.

PubMed

Kiskowski, Maria; Chowell, Gerardo

2016-01-01

The mechanisms behind the sub-exponential growth dynamics of the West Africa Ebola virus disease epidemic could be related to improved control of the epidemic and the result of reduced disease transmission in spatially constrained contact structures. An individual-based, stochastic network model is used to model immediate and delayed epidemic control in the context of social contact networks and investigate the extent to which the relative role of these factors may be determined during an outbreak. We find that in general, epidemics quickly establish a dynamic equilibrium of infections in the form of a wave of fixed size and speed traveling through the contact network. Both greater epidemic control and limited community mixing decrease the size of an infectious wave. However, for a fixed wave size, epidemic control (in contrast with limited community mixing) results in lower community saturation and a wave that moves more quickly through the contact network. We also found that the level of epidemic control has a disproportionately greater reductive effect on larger waves, so that a small wave requires nearly as much epidemic control as a larger wave to end an epidemic.

Analyzing hidden populations online: topic, emotion, and social network of HIV-related users in the largest Chinese online community.

PubMed

Liu, Chuchu; Lu, Xin

2018-01-05

Traditional survey methods are limited in the study of hidden populations due to the hard to access properties, including lack of a sampling frame, sensitivity issue, reporting error, small sample size, etc. The rapid increase of online communities, of which members interact with others via the Internet, have generated large amounts of data, offering new opportunities for understanding hidden populations with unprecedented sample sizes and richness of information. In this study, we try to understand the multidimensional characteristics of a hidden population by analyzing the massive data generated in the online community. By elaborately designing crawlers, we retrieved a complete dataset from the "HIV bar," the largest bar related to HIV on the Baidu Tieba platform, for all records from January 2005 to August 2016. Through natural language processing and social network analysis, we explored the psychology, behavior and demand of online HIV population and examined the network community structure. In HIV communities, the average topic similarity among members is positively correlated to network efficiency (r = 0.70, p < 0.001), indicating that the closer the social distance between members of the community, the more similar their topics. The proportion of negative users in each community is around 60%, weakly correlated with community size (r = 0.25, p = 0.002). It is found that users suspecting initial HIV infection or first in contact with high-risk behaviors tend to seek help and advice on the social networking platform, rather than immediately going to a hospital for blood tests. Online communities have generated copious amounts of data offering new opportunities for understanding hidden populations with unprecedented sample sizes and richness of information. It is recommended that support through online services for HIV/AIDS consultation and diagnosis be improved to avoid privacy concerns and social discrimination in China.

Shift in a Large River Fish Assemblage: Body-Size and Trophic Structure Dynamics

PubMed Central

Broadway, Kyle J.; Pyron, Mark; Gammon, James R.; Murry, Brent A.

2015-01-01

As the intensity and speed of environmental change increase at both local and global scales it is imperative that we gain a better understanding of the ecological implications of community shifts. While there has been substantial progress toward understanding the drivers and subsequent responses of community change (e.g. lake trophic state), the ecological impacts of food web changes are far less understood. We analyzed Wabash River fish assemblage data collected from 1974-2008, to evaluate temporal variation in body-size structure and functional group composition. Two parameters derived from annual community size-spectra were our major response variables: (1) the regression slope is an index of ecological efficiency and predator-prey biomass ratios, and (2) spectral elevation (regression midpoint height) is a proxy for food web capacity. We detected a large assemblage shift, over at least a seven year period, defined by dramatic changes in abundance (measured as catch-per-unit-effort) of the dominant functional feeding groups among two time periods; from an assemblage dominated by planktivore-omnivores to benthic invertivores. There was a concurrent increase in ecological efficiency (slopes increased over time) following the shift associated with an increase in large-bodied low trophic level fish. Food web capacity remained relatively stable with no clear temporal trends. Thus, increased ecological efficiency occurred simultaneous to a compensatory response that shifted biomass among functional feeding groups. PMID:25902144

Gill monogenean communities (Platyhelminthes, Monogenea, Dactylogyridae) of butterflyfishes from tropical Indo-West Pacific Islands.

PubMed

Reverter, Miriam; Cutmore, Scott C; Bray, Rodney; Cribb, Thomas H; Sasal, Pierre

2016-10-01

We studied the monogenean communities of 34 species of butterflyfish from the tropical Indo-West Pacific, identifying 13 dactylogyrid species (including two species that are presently undescribed). Monogenean assemblages differed significantly between host species in terms of taxonomic structure, intensity and prevalence. Parasite richness ranged from 0 (Chaetodon lunulatus) to 11 (C. auriga, C. citrinellus and C. lunula). Host specificity varied between the dactylogyrids species, being found on 2-29 of the 34 chaetodontid species examined. Sympatric butterflyfish species were typically parasitized by different combinations of dactylogyrid species, suggesting the existence of complex host-parasite interactions. We identified six clusters of butterflyfish species based on the similarities of their dactylogyrid communities. Dactylogyrid richness and diversity were not related to host size, diet specialization, depth range or phylogeny of butterflyfish species. However, there was a weak positive correlation between monogenean richness and diversity and host geographical range. Most communities of dactylogyrids were dominated by Haliotrema aurigae and H. angelopterum, indicating the importance of the genus Haliotrema in shaping monogenean communities of butterflyfishes. This study casts light on the structure of the monogenean communities of butterflyfishes, suggesting that the diversity and complexity of community structures arises from a combination of host species-specific parameters.

Disentangling environmental and spatial effects on phylogenetic structure of angiosperm tree communities in China.

PubMed

Qian, Hong; Chen, Shengbin; Zhang, Jin-Long

2017-07-17

Niche-based and neutrality-based theories are two major classes of theories explaining the assembly mechanisms of local communities. Both theories have been frequently used to explain species diversity and composition in local communities but their relative importance remains unclear. Here, we analyzed 57 assemblages of angiosperm trees in 0.1-ha forest plots across China to examine the effects of environmental heterogeneity (relevant to niche-based processes) and spatial contingency (relevant to neutrality-based processes) on phylogenetic structure of angiosperm tree assemblages distributed across a wide range of environment and space. Phylogenetic structure was quantified with six phylogenetic metrics (i.e., phylogenetic diversity, mean pairwise distance, mean nearest taxon distance, and the standardized effect sizes of these three metrics), which emphasize on different depths of evolutionary histories and account for different degrees of species richness effects. Our results showed that the variation in phylogenetic metrics explained independently by environmental variables was on average much greater than that explained independently by spatial structure, and the vast majority of the variation in phylogenetic metrics was explained by spatially structured environmental variables. We conclude that niche-based processes have played a more important role than neutrality-based processes in driving phylogenetic structure of angiosperm tree species in forest communities in China.

Stochastic Assembly of Bacteria in Microwell Arrays Reveals the Importance of Confinement in Community Development

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, Ryan H.; Timm, Andrea C.; Timm, Collin M.

The structure, function and evolving composition of microbial communities is deeply influenced by the physical and chemical architecture of the local microenvironment. The complexity of this parameter space in naturally occurring systems has made a clear understanding of the key drivers of community development elusive. Here, we examine the role of spatial confinement on community development using a microwell platform that allows for assembly and monitoring of unique microbial communities en masse. This platform was designed to contain microwells with varied size features in order to mimic various levels of spatial confinement found in natural systems. Microbial populations assembled inmore » wells with incrementally smaller size features showed increasingly larger variations in inoculum levels. By exploiting this size dependence, large wells were used to assemble homogenous initial populations of Pseudomonas aeruginosa, allowing for reproducible, directed growth trajectories. In contrast, smaller wells were used to assemble a heterogeneous range of initial populations, resulting in a variety of growth and decay trajectories. This allowed for parallel screening of single member communities across different levels of confinement to identify initial conditions in which P. aeruginosa colonies have dramatically higher probabilities of survival. These results demonstrate a unique approach for manipulating the distribution of initial microbial populations assembled into controlled microenvironments to rapidly identify population and environmental parameters conducive or inhibitive to growth. Additionally, multi-member community assembly was characterized to demonstrate the power of this platform for studying the role of member abundance on microbial competition, mutualism and community succession.« less

Functional strategies drive community assembly of stream fishes along environmental gradients and across spatial scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Troia, Matthew J.; Gido, Keith B.

Trade-offs among functional traits produce multi-trait strategies that shape species interactions with the environment and drive the assembly of local communities from regional species pools. Stream fish communities vary along stream size gradients and among hierarchically structured habitat patches, but little is known about how the dispersion of strategies varies along environmental gradients and across spatial scales. We used null models to quantify the dispersion of reproductive life history, feeding, and locomotion strategies in communities sampled at three spatial scales in a prairie stream network in Kansas, USA. Strategies were generally underdispersed at all spatial scales, corroborating the longstanding notionmore » of abiotic filtering in stream fish communities. We tested for variation in strategy dispersion along a gradient of stream size and between headwater streams draining different ecoregions. Reproductive life history strategies became increasingly underdispersed moving from downstream to upstream, suggesting that abiotic filtering is stronger in headwaters. This pattern was stronger among reaches compared to mesohabitats, supporting the premise that differences in hydrologic regime among reaches filter reproductive life history strategies. Feeding strategies became increasingly underdispersed moving from upstream to downstream, indicating that environmental filters associated with stream size affect the dispersion of feeding and reproductive life history in opposing ways. Weak differences in strategy dispersion were detected between ecoregions, suggesting that different abiotic filters or strategies drive community differences between ecoregions. Lastly, given the pervasiveness of multi-trait strategies in plant and animal communities, we conclude that the assessment of strategy dispersion offers a comprehensive approach for elucidating mechanisms of community assembly.« less

Stochastic Assembly of Bacteria in Microwell Arrays Reveals the Importance of Confinement in Community Development

DOE PAGES

Hansen, Ryan H.; Timm, Andrea C.; Timm, Collin M.; ...

2016-05-06

The structure, function and evolving composition of microbial communities is deeply influenced by the physical and chemical architecture of the local microenvironment. The complexity of this parameter space in naturally occurring systems has made a clear understanding of the key drivers of community development elusive. Here, we examine the role of spatial confinement on community development using a microwell platform that allows for assembly and monitoring of unique microbial communities en masse. This platform was designed to contain microwells with varied size features in order to mimic various levels of spatial confinement found in natural systems. Microbial populations assembled inmore » wells with incrementally smaller size features showed increasingly larger variations in inoculum levels. By exploiting this size dependence, large wells were used to assemble homogenous initial populations of Pseudomonas aeruginosa, allowing for reproducible, directed growth trajectories. In contrast, smaller wells were used to assemble a heterogeneous range of initial populations, resulting in a variety of growth and decay trajectories. This allowed for parallel screening of single member communities across different levels of confinement to identify initial conditions in which P. aeruginosa colonies have dramatically higher probabilities of survival. These results demonstrate a unique approach for manipulating the distribution of initial microbial populations assembled into controlled microenvironments to rapidly identify population and environmental parameters conducive or inhibitive to growth. Additionally, multi-member community assembly was characterized to demonstrate the power of this platform for studying the role of member abundance on microbial competition, mutualism and community succession.« less

Phenology of particle size distributions and primary productivity in the North Pacific subtropical gyre (Station ALOHA)

PubMed Central

Letelier, Ricardo M.; Whitmire, Amanda L.; Barone, Benedetto; Bidigare, Robert R.; Church, Matthew J.; Karl, David M.

2015-01-01

Abstract The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite‐based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction‐based depth profiles of the PSD and pigment‐based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time‐series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction‐based estimations of relative particle size nor pigment‐based PFTs was found to be significantly related to the rate of 14C‐based PP in the light‐saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present‐day bio‐optical PP models for this region. However, at depths of 100–125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2–20 μm particles. PMID:27812434

Phenology of particle size distributions and primary productivity in the North Pacific subtropical gyre (Station ALOHA).

PubMed

White, Angelicque E; Letelier, Ricardo M; Whitmire, Amanda L; Barone, Benedetto; Bidigare, Robert R; Church, Matthew J; Karl, David M

2015-11-01

The particle size distribution (PSD) is a critical aspect of the oceanic ecosystem. Local variability in the PSD can be indicative of shifts in microbial community structure and reveal patterns in cell growth and loss. The PSD also plays a central role in particle export by influencing settling speed. Satellite-based models of primary productivity (PP) often rely on aspects of photophysiology that are directly related to community size structure. In an effort to better understand how variability in particle size relates to PP in an oligotrophic ecosystem, we collected laser diffraction-based depth profiles of the PSD and pigment-based classifications of phytoplankton functional types (PFTs) on an approximately monthly basis at the Hawaii Ocean Time-series Station ALOHA, in the North Pacific subtropical gyre. We found a relatively stable PSD in the upper water column. However, clear seasonality is apparent in the vertical distribution of distinct particle size classes. Neither laser diffraction-based estimations of relative particle size nor pigment-based PFTs was found to be significantly related to the rate of 14 C-based PP in the light-saturated upper euphotic zone. This finding indicates that satellite retrievals of particle size, based on particle scattering or ocean color would not improve parameterizations of present-day bio-optical PP models for this region. However, at depths of 100-125 m where irradiance exerts strong control on PP, we do observe a significant linear relationship between PP and the estimated carbon content of 2-20 μm particles.

HIV prevention interventions to reduce sexual risk for African Americans: the influence of community-level stigma and psychological processes.

PubMed

Reid, Allecia E; Dovidio, John F; Ballester, Estrellita; Johnson, Blair T

2014-02-01

Interventions to improve public health may benefit from consideration of how environmental contexts can facilitate or hinder their success. We examined the extent to which efficacy of interventions to improve African Americans' condom use practices was moderated by two indicators of structural stigma-Whites' attitudes toward African Americans and residential segregation in the communities where interventions occurred. A previously published meta-analytic database was re-analyzed to examine the interplay of community-level stigma with the psychological processes implied by intervention content in influencing intervention efficacy. All studies were conducted in the United States and included samples that were at least 50% African American. Whites' attitudes were drawn from the American National Election Studies, which collects data from nationally representative samples. Residential segregation was drawn from published reports. Results showed independent effects of Whites' attitudes and residential segregation on condom use effect sizes. Interventions were most successful when Whites' attitudes were more positive or when residential segregation was low. These two structural factors interacted: Interventions improved condom use only when communities had both relatively positive attitudes toward African Americans and lower levels of segregation. The effect of Whites' attitudes was more pronounced at longer follow-up intervals and for younger samples and those samples with more African Americans. Tailoring content to participants' values and needs, which may reduce African Americans' mistrust of intervention providers, buffered against the negative influence of Whites' attitudes on condom use. The structural factors uniquely accounted for variance in condom use effect sizes over and above intervention-level features and community-level education and poverty. Results highlight the interplay of social identity and environment in perpetuating intergroup disparities. Potential mechanisms for these effects are discussed along with public health implications. Copyright © 2013 Elsevier Ltd. All rights reserved.

HIV Prevention Interventions to Reduce Sexual Risk for African Americans: The Influence of Community-Level Stigma and Psychological Processes

PubMed Central

Reid, Allecia E.; Dovidio, John F.; Ballester, Estrellita; Johnson, Blair T.

2013-01-01

Interventions to improve public health may benefit from consideration of how environmental contexts can facilitate or hinder their success. We examined the extent to which efficacy of interventions to improve African Americans’ condom use practices was moderated by two indicators of structural stigma—Whites’ attitudes toward African Americans and residential segregation in the communities where interventions occurred. A previously published meta-analytic database was re-analyzed to examine the interplay of community-level stigma with the psychological processes implied by intervention content in influencing intervention efficacy. All studies were conducted in the United States and included samples that were at least 50% African American. Whites’ attitudes were drawn from the American National Election Studies, which collects data from nationally representative samples. Residential segregation was drawn from published reports. Results showed independent effects of Whites’ attitudes and residential segregation on condom use effect sizes. Interventions were most successful when Whites’ attitudes were more positive or when residential segregation was low. These two structural factors interacted: Interventions improved condom use only when communities had both relatively positive attitudes toward African Americans and lower levels of segregation. The effect of Whites’ attitudes was more pronounced at longer follow-up intervals and for younger samples and those samples with more African Americans. Tailoring content to participants’ values and needs, which may reduce African Americans’ mistrust of intervention providers, buffered against the negative influence of Whites’ attitudes on condom use. The structural factors uniquely accounted for variance in condom use effect sizes over and above intervention-level features and community-level education and poverty. Results highlight the interplay of social identity and environment in perpetuating intergroup disparities. Potential mechanisms for these effects are discussed along with public health implications. PMID:24507916

Functional diversity of benthic ciliate communities in response to environmental gradients in a wetland of Yangtze Estuary, China.

PubMed

Xu, Yuan; Fan, Xinpeng; Warren, Alan; Zhang, Liquan; Xu, Henglong

2018-02-01

Researches on the functional diversity of benthic ecosystems have mainly focused on macrofauna, and studies on functional structure of ciliate communities have been based only on trophic- or size-groups. Current research was carried out on the changing patterns of classical and functional diversity of benthic ciliates in response to environmental gradients at three sites in a wetland in Yangtze Estuary. The results showed that changes of environmental factors (e.g. salinity, sediment grain size and hydrodynamic conditions) in the Yangtze Estuary induce variability in species composition and functional trait distribution. Furthermore, increased species richness and diversity did not lead to significant changes in functional diversity due to functional redundancy. However, salt water intrusion of Yangtze Estuary during the dry season could cause reduced functional diversity of ciliate communities. Current study provides the first insight into the functional diversity of ciliate communities in response to environmental gradients. Copyright © 2018 Elsevier Ltd. All rights reserved.

Zooplankton taxonomic and size diversity in Mediterranean coastal lagoons (NE Iberian Peninsula): Influence of hydrology, nutrient composition, food resource availability and predation

NASA Astrophysics Data System (ADS)

Badosa, Anna; Boix, Dani; Brucet, Sandra; López-Flores, Rocío; Gascón, Stéphanie; Quintana, Xavier D.

2007-01-01

The influence of hydrology, nutrient composition, food resource availability and predation on zooplankton taxonomic and size diversity was analyzed in several shallow lagoons of a Mediterranean salt marsh (Baix Ter Wetlands, NE Iberian Peninsula). Taxonomic diversity correlated better with variables related to the trophic state, such as nutrient concentrations, whereas size diversity was more sensitive to fish predation. However, the fish predation influence on the size diversity was only significant when fishes reached high densities. Under low fish densities no predation effects were observed and the food resource availability (FR a) appeared to be more important in structuring the zooplankton community. Nevertheless, the two diversity indexes showed opposite responses to this factor. With increasing FR a the taxonomic diversity increased and the size diversity decreased. Neither taxonomic nor size diversity of the zooplankton community correlated with other physical or biotic factors such as hydrological variability or macroinvertebrate predation. The relationships found suggest that the size diversity is mainly related to biotic interactions, such as fish predation or inter/intraspecific competition, while the taxonomic diversity appears to be more sensitive to abiotic factors such as the nutrient composition.

Predicting community responses to perturbations in the face of imperfect knowledge and network complexity

USGS Publications Warehouse

Novak, Mark; Wootton, J. Timothy; Doak, Daniel F.; Emmerson, Mark; Estes, James A.; Tinker, M. Timothy

2011-01-01

How best to predict the effects of perturbations to ecological communities has been a long-standing goal for both applied and basic ecology. This quest has recently been revived by new empirical data, new analysis methods, and increased computing speed, with the promise that ecologically important insights may be obtainable from a limited knowledge of community interactions. We use empirically based and simulated networks of varying size and connectance to assess two limitations to predicting perturbation responses in multispecies communities: (1) the inaccuracy by which species interaction strengths are empirically quantified and (2) the indeterminacy of species responses due to indirect effects associated with network size and structure. We find that even modest levels of species richness and connectance (∼25 pairwise interactions) impose high requirements for interaction strength estimates because system indeterminacy rapidly overwhelms predictive insights. Nevertheless, even poorly estimated interaction strengths provide greater average predictive certainty than an approach that uses only the sign of each interaction. Our simulations provide guidance in dealing with the trade-offs involved in maximizing the utility of network approaches for predicting dynamics in multispecies communities.

Decline in Topsoil Microbial Quotient, Fungal Abundance and C Utilization Efficiency of Rice Paddies under Heavy Metal Pollution across South China

PubMed Central

Liu, Yongzhuo; Zhou, Tong; Crowley, David; Li, Lianqing; Liu, Dawen; Zheng, Jinwei; Yu, Xinyan; Pan, Genxing; Hussain, Qaiser; Zhang, Xuhui; Zheng, Jufeng

2012-01-01

Agricultural soils have been increasingly subject to heavy metal pollution worldwide. However, the impacts on soil microbial community structure and activity of field soils have been not yet well characterized. Topsoil samples were collected from heavy metal polluted (PS) and their background (BGS) fields of rice paddies in four sites across South China in 2009. Changes with metal pollution relative to the BGS in the size and community structure of soil microorganisms were examined with multiple microbiological assays of biomass carbon (MBC) and nitrogen (MBN) measurement, plate counting of culturable colonies and phospholipids fatty acids (PLFAs) analysis along with denaturing gradient gel electrophoresis (DGGE) profile of 16S rRNA and 18S rRNA gene and real-time PCR assay. In addition, a 7-day lab incubation under constantly 25°C was conducted to further track the changes in metabolic activity. While the decrease under metal pollution in MBC and MBN, as well as in culturable population size, total PLFA contents and DGGE band numbers of bacteria were not significantly and consistently seen, a significant reduction was indeed observed under metal pollution in microbial quotient, in culturable fungal population size and in ratio of fungal to bacterial PLFAs consistently across the sites by an extent ranging from 6% to 74%. Moreover, a consistently significant increase in metabolic quotient was observed by up to 68% under pollution across the sites. These observations supported a shift of microbial community with decline in its abundance, decrease in fungal proportion and thus in C utilization efficiency under pollution in the soils. In addition, ratios of microbial quotient, of fungal to bacterial and qCO2 are proved better indicative of heavy metal impacts on microbial community structure and activity. The potential effects of these changes on C cycling and CO2 production in the polluted rice paddies deserve further field studies. PMID:22701725

Seasonal dynamics in the community structure and trophic structure of testate amoebae inhabiting the Sanjiang peatlands, Northeast China.

PubMed

Song, Lihong; Li, Hongkai; Wang, Kehong; Yan, Xiumin; Wu, Donghui

2018-04-01

Peatlands cover 3% of the earth's land surface but contain 30% of the world's soil carbon pool. Microbial communities constitute a crucial detrital food web for nutrient and carbon cycling in peatlands. Heterotrophic protozoans are considered top predators in the microbial food web; however, they are not yet well understood. In this study, we investigated seasonal dynamics in the community and the trophic structure of testate amoebae in four peatlands. Testate amoebae density and biomass in August were significantly higher than those in May and October. The highest density, 6.7 × 10 4 individual g -1 dry moss, was recorded in August 2014. The highest biomass, 7.7 × 10 2  μg C g -1 dry moss, was recorded in August 2013. Redundancy analyses showed that water-table depth was the most important factor, explaining over one third of the variance in fauna communities in all sampled seasons. High trophic position taxa dominated testate amoebae communities. The Shannon diversity index and community size structure index declined from August to October in 2013 and from May to October in 2014. These seasonal patterns of testate amoebae indicated the seasonal variations of the peatlands' microbial food web and are possibly related to the seasonal carbon dynamics in Northeast Chinese peatlands. Copyright © 2018 Elsevier GmbH. All rights reserved.

Relationships between Algae, Benthic Herbivorous Invertebrates and Fishes in Rocky Sublittoral Communities of a Temperate Sea (Mediterranean)

NASA Astrophysics Data System (ADS)

Ruitton, S.; Francour, P.; Boudouresque, C. F.

2000-02-01

In situ surveys were used to examine the contribution of benthic herbivorous invertebrates and fishes to the organization of Mediterranean rocky sublittoral communities. Shallow (1-3 m) and deep (6-8 m) sampling sites, in natural areas and on man-made structures, were characterized by a structural complexity index (cavity index and mean size of cavity aperture), algal cover (encrusting, turfy, shrubby and arborescent algae) and the density of benthic herbivorous invertebrates and fish. A relationship between structural complexity and biota was only evident for some fish species ( Diplodus spp. and Sarpa salpa) at deep sites, where they not only feed but also shelter. Three benthic herbivorous invertebrates, the sea urchins Paracentrotus lividus and Arbacia lixula, and the limpet Patella caerulea , are associated with communities dominated by encrusting algae. Variations in their abundance and role in structuring algal communities follow a depth gradient: P. caerulea and A. lixula are mainly present at shallow sites and P. lividus at deep sites. These benthic herbivorous invertebrates may account for the structure of shallow algal communities. In contrast, at deep sites, fishes (the omnivorous Diplodus spp. and the herbivorous S. salpa) have a potential importance in controlling sublittoral algae, in addition to invertebrates. It is suggested that the ecological impact of herbivorous and omnivorous fishes in temperate seas could be greater than is generally thought. Experiments should be designed to validate this postulate.

Changes in fish diversity and community structure in the central and southern Yellow Sea from 2003 to 2015

NASA Astrophysics Data System (ADS)

Chen, Yunlong; Shan, Xiujuan; Jin, Xianshi; Johannessen, Arne; Yang, Tao; Dai, Fangqun

2017-07-01

The central and southern Yellow Sea is an important overwintering ground for many fish species in the Bohai Sea and Yellow Sea. For better understanding the status of the fish community after years of heavy exploitation, variations in fish community structure and diversity were analyzed using data from bottom trawls during 2003-2015. Five fish assemblage indices all showed fluctuations without clear trends from 2003 to 2015, yet there were strong positive and significant correlations (P < 0.05) among them. The top-five dominant species accounted for a high weight percentage (49.7%-82.1%) in the annual fish catch. Multivariate analysis showed that two year groups could be pooled for the fish community: Group I consisted of the years 2006, 2007, 2008 and 2015, while Group II consisted of the years 2003, 2004, 2005, 2009, 2010 and 2014; the groups aggregated with 63.71% similarity, indicating a high level of similarity among all years. The multivariate dispersion values were 1.455 and 0.818 for Groups I and II, respectively, indicating greater variances in fish assemblage structure in Group I than that in Group II. Similarity of percentage analysis demonstrated that the average similarities for Group I and Group II were 71.58% and 67.51%, respectively. Size-spectra analysis revealed no consistent trend in the intercept and slope (P > 0.05); there were also no significant differences between the slope of the size-spectra and fishing effort. The catch per unit effort and mean individual weight analyses of the whole fish assemblage both showed a significantly decreasing trend over time. Overall, the results showed that the fish community structure in the central and southern Yellow Sea was relatively stable from 2003 to 2015 and the study could be used as a reference for supporting ecosystem-based fishery management.

Hunting or habitat? Drivers of waterbird abundance and community structure in agricultural wetlands of southern India.

PubMed

Ramachandran, Ramesh; Kumar, Ajith; Gopi Sundar, Kolla S; Bhalla, Ravinder Singh

2017-09-01

The relative impacts of hunting and habitat on waterbird community were studied in agricultural wetlands of southern India. We surveyed wetlands to document waterbird community, and interviewed hunters to document hunting intensity, targeted species, and the motivations for hunting. Our results show that hunting leads to drastic declines in waterbird diversity and numbers, and skew the community towards smaller species. Hunting intensity, water spread, and vegetation cover were the three most important determinants of waterbird abundance and community structure. Species richness, density of piscivorous species, and medium-sized species (31-65 cm) were most affected by hunting. Out of 53 species recorded, 47 were hunted, with a preference for larger birds. Although illegal, hunting has increased in recent years and is driven by market demand. This challenges the widely held belief that waterbird hunting in India is a low intensity, subsistence activity, and undermines the importance of agricultural wetlands in waterbird conservation.

Thermal and Hydrodynamic Environments Mediate Individual and Aggregative Feeding of a Functionally Important Omnivore in Reef Communities

PubMed Central

Frey, Desta L.; Gagnon, Patrick

2015-01-01

In eastern Canada, the destruction of kelp beds by dense aggregations (fronts) of the omnivorous green sea urchin, Strongylocentrotus droebachiensis, is a key determinant of the structure and dynamics of shallow reef communities. Recent studies suggest that hydrodynamic forces, but not sea temperature, determine the strength of urchin-kelp interactions, which deviates from the tenets of the metabolic theory of ecology (MTE). We tested the hypothesis that water temperature can predict short-term kelp bed destruction by S. droebachiensis in calm hydrodynamic environments. Specifically, we experimentally determined relationships among water temperature, body size, and individual feeding in the absence of waves, as well as among wave velocity, season, and aggregative feeding. We quantified variation in kelp-bed boundary dynamics, sea temperature, and wave height over three months at one subtidal site in Newfoundland to test the validity of thermal tipping ranges and regression equations derived from laboratory results. Consistent with the MTE, individual feeding during early summer (June-July) obeyed a non-linear, size- and temperature-dependent relationship: feeding in large urchins was consistently highest and positively correlated with temperature <12°C and dropped within and above the 12–15°C tipping range. This relationship was more apparent in large than small urchins. Observed and expected rates of kelp loss based on sea temperature and urchin density and size structure at the front were highly correlated and differed by one order of magnitude. The present study speaks to the importance of considering body size and natural variation in sea temperature in studies of urchin-kelp interactions. It provides the first compelling evidence that sea temperature, and not only hydrodynamic forces, can predict kelp bed destruction by urchin fronts in shallow reef communities. Studying urchin-seaweed-predator interactions within the conceptual foundations of the MTE holds high potential for improving capacity to predict and manage shifts in marine food web structure and productivity. PMID:25774674

Thermal and hydrodynamic environments mediate individual and aggregative feeding of a functionally important omnivore in reef communities.

PubMed

Frey, Desta L; Gagnon, Patrick

2015-01-01

In eastern Canada, the destruction of kelp beds by dense aggregations (fronts) of the omnivorous green sea urchin, Strongylocentrotus droebachiensis, is a key determinant of the structure and dynamics of shallow reef communities. Recent studies suggest that hydrodynamic forces, but not sea temperature, determine the strength of urchin-kelp interactions, which deviates from the tenets of the metabolic theory of ecology (MTE). We tested the hypothesis that water temperature can predict short-term kelp bed destruction by S. droebachiensis in calm hydrodynamic environments. Specifically, we experimentally determined relationships among water temperature, body size, and individual feeding in the absence of waves, as well as among wave velocity, season, and aggregative feeding. We quantified variation in kelp-bed boundary dynamics, sea temperature, and wave height over three months at one subtidal site in Newfoundland to test the validity of thermal tipping ranges and regression equations derived from laboratory results. Consistent with the MTE, individual feeding during early summer (June-July) obeyed a non-linear, size- and temperature-dependent relationship: feeding in large urchins was consistently highest and positively correlated with temperature <12°C and dropped within and above the 12-15°C tipping range. This relationship was more apparent in large than small urchins. Observed and expected rates of kelp loss based on sea temperature and urchin density and size structure at the front were highly correlated and differed by one order of magnitude. The present study speaks to the importance of considering body size and natural variation in sea temperature in studies of urchin-kelp interactions. It provides the first compelling evidence that sea temperature, and not only hydrodynamic forces, can predict kelp bed destruction by urchin fronts in shallow reef communities. Studying urchin-seaweed-predator interactions within the conceptual foundations of the MTE holds high potential for improving capacity to predict and manage shifts in marine food web structure and productivity.

Methods and measurement variance for field estimations of coral colony planar area using underwater photographs and semi-automated image segmentation.

PubMed

Neal, Benjamin P; Lin, Tsung-Han; Winter, Rivah N; Treibitz, Tali; Beijbom, Oscar; Kriegman, David; Kline, David I; Greg Mitchell, B

2015-08-01

Size and growth rates for individual colonies are some of the most essential descriptive parameters for understanding coral communities, which are currently experiencing worldwide declines in health and extent. Accurately measuring coral colony size and changes over multiple years can reveal demographic, growth, or mortality patterns often not apparent from short-term observations and can expose environmental stress responses that may take years to manifest. Describing community size structure can reveal population dynamics patterns, such as periods of failed recruitment or patterns of colony fission, which have implications for the future sustainability of these ecosystems. However, rapidly and non-invasively measuring coral colony sizes in situ remains a difficult task, as three-dimensional underwater digital reconstruction methods are currently not practical for large numbers of colonies. Two-dimensional (2D) planar area measurements from projection of underwater photographs are a practical size proxy, although this method presents operational difficulties in obtaining well-controlled photographs in the highly rugose environment of the coral reef, and requires extensive time for image processing. Here, we present and test the measurement variance for a method of making rapid planar area estimates of small to medium-sized coral colonies using a lightweight monopod image-framing system and a custom semi-automated image segmentation analysis program. This method demonstrated a coefficient of variation of 2.26% for repeated measurements in realistic ocean conditions, a level of error appropriate for rapid, inexpensive field studies of coral size structure, inferring change in colony size over time, or measuring bleaching or disease extent of large numbers of individual colonies.

Governing Board Manual. Revised June, 1999.

ERIC Educational Resources Information Center

Palomar Community Coll. District, San Marcos, CA.

This document details the governance structure of Palomar Community College. The plan attempts to: (1) provide appropriate representation for each constituent group; (2) delineate committee responsibilities and reporting relationships; (3) establish the appropriate number and size of committees; (4) ensure that operational matters are handled…

Approach to assess consequences of hypoxia disturbance events for benthic ecosystem functioning

NASA Astrophysics Data System (ADS)

Gogina, Mayya; Darr, Alexander; Zettler, Michael L.

2014-01-01

Our study challenges the functional approach for its usefulness in assessing the consequences of hypoxia disturbance events on macrofaunal communities in the south-western Baltic Sea. Time series for two decades of observations from two monitoring stations, one in the Fehmarnbelt (exposed to aperiodic hypoxia), and another in the Darss Rise (normoxic conditions) is used. Our results designate differences of functional structure of benthic fauna communities between sites based on biological traits that characterise species role in modifying the environment, behavioural strategies, morphology and life history, thus suggesting differences in functioning. Hypoxic years reveal sharp increase of the role of sedentary species, suspension filter feeders, epibenthic structures, globulose form, medium/large size of individuals, preponderance of species with long lifespan (caused for instance by remaining ocean quahog). The link of functional and species diversity to the stagnation periods is proposed for the Darss station that exhibit continuous changes and low temporal variability of traits distribution. Before the major inflow in 1993 the increased role of small size organisms, containing calcium carbonate, filter feeders and grazers, higher presence of semi-pelagic species is observed. The hypoxic events and water renewal processes impact the communities not only in respect to species composition but also functionally.

Size-selective toxicity effects of the antimicrobial tylosin on estuarine phytoplankton communities.

PubMed

Kline, Allison; Pinckney, James L

2016-09-01

The purpose of this study was to determine the lethal and sublethal effects of the antimicrobial tylosin on natural estuarine phytoplankton communities. Bioassays were used in experimental treatments with final concentrations of 5 to 1000 μg tylosin l(-1). Maximum percent inhibition ranged from 57 to 85% at concentrations of 200-400 μg tylosin l(-1). Half maximum inhibition concentrations of tylosin were ca. 5x lower for small phytoplankton (<20 μm) relative to larger phytoplankton (>20 μm) and suggests that small phytoplankton are more sensitive to tylosin exposure. Sublethal effects occurred at concentrations as low as 5 μg tylosin l(-1). Environmental concentrations of tylosin (e.g., 0.2-3 μg l(-1)) may have a significant sublethal effect that alters the size structure and composition of phytoplankton communities. The results of this study highlight the potential importance of cell size on toxicity responses of estuarine phytoplankton. Copyright © 2016 Elsevier Ltd. All rights reserved.

Seasonal trophic structure of the Scotia Sea pelagic ecosystem considered through biomass spectra and stable isotope analysis

NASA Astrophysics Data System (ADS)

Tarling, G. A.; Stowasser, G.; Ward, P.; Poulton, A. J.; Zhou, M.; Venables, H. J.; McGill, R. A. R.; Murphy, E. J.

2012-01-01

The biomass size structure of pelagic communities provides a system level perspective that can be instructive when considering trophic interactions. Such perspectives can become even more powerful when combined with taxonomic information and stable isotope analysis. Here we apply these approaches to the pelagic community of the Scotia Sea (Southern Ocean) and consider the structure and development of trophic interactions over different years and seasons. Samples were collected from three open-ocean cruises during the austral spring 2006, summer 2008 and autumn 2009. Three main sampling techniques were employed: sampling bottles for microplankton (0-50 m), vertically hauled fine meshed nets for mesozooplankton (0-400 m) and coarse-meshed trawls for macrozooplankton and nekton (0-1000 m). All samples were identified to the lowest practicable taxonomic level and their abundance, individual body weight and biomass (in terms of carbon) estimated. Slopes of normalised biomass spectrum versus size showed a significant but not substantial difference between cruises and were between -1.09 and -1.06. These slopes were shallower than expected for a community at equilibrium and indicated that there was an accumulation of biomass in the larger size classes (10 1-10 5 mg C ind -1). A secondary structure of biomass domes was also apparent, with the domes being 2.5-3 log 10 intervals apart in spring and summer and 2 log 10 intervals apart in autumn. The recruitment of copepod-consuming macrozooplankton, Euphausia triacantha and Themisto gaudichaudii into an additional biomass dome was responsible for the decrease in the inter-dome interval in autumn. Predator to prey mass ratios estimated from stable isotope analysis reached a minimum in autumn while the estimated trophic level of myctophid fish was highest in that season. This reflected greater amounts of internal recycling and increased numbers of trophic levels in autumn compared to earlier times of the year. The accumulation of biomass in larger size classes throughout the year in the Scotia Sea may reflect the prevalence of species that store energy and have multiyear life-cycles.

Preference for cannibalism and ontogenetic constraints in competitive ability of piscivorous top predators.

PubMed

Byström, Pär; Ask, Per; Andersson, Jens; Persson, Lennart

2013-01-01

Occurrence of cannibalism and inferior competitive ability of predators compared to their prey have been suggested to promote coexistence in size-structured intraguild predation (IGP) systems. The intrinsic size-structure of fish provides the necessary prerequisites to test whether the above mechanisms are general features of species interactions in fish communities where IGP is common. We first experimentally tested whether Arctic char (Salvelinus alpinus) were more efficient as a cannibal than as an interspecific predator on the prey fish ninespine stickleback (Pungitius pungitius) and whether ninespine stickleback were a more efficient competitor on the shared zooplankton prey than its predator, Arctic char. Secondly, we performed a literature survey to evaluate if piscivores in general are more efficient as cannibals than as interspecific predators and whether piscivores are inferior competitors on shared resources compared to their prey fish species. Both controlled pool experiments and outdoor pond experiments showed that char imposed a higher mortality on YOY char than on ninespine sticklebacks, suggesting that piscivorous char is a more efficient cannibal than interspecific predator. Estimates of size dependent attack rates on zooplankton further showed a consistently higher attack rate of ninespine sticklebacks compared to similar sized char on zooplankton, suggesting that ninespine stickleback is a more efficient competitor than char on zooplankton resources. The literature survey showed that piscivorous top consumers generally selected conspecifics over interspecific prey, and that prey species are competitively superior compared to juvenile piscivorous species in the zooplankton niche. We suggest that the observed selectivity for cannibal prey over interspecific prey and the competitive advantage of prey species over juvenile piscivores are common features in fish communities and that the observed selectivity for cannibalism over interspecific prey has the potential to mediate coexistence in size structured intraguild predation systems.

Preference for Cannibalism and Ontogenetic Constraints in Competitive Ability of Piscivorous Top Predators

PubMed Central

Byström, Pär; Ask, Per; Andersson, Jens; Persson, Lennart

2013-01-01

Occurrence of cannibalism and inferior competitive ability of predators compared to their prey have been suggested to promote coexistence in size-structured intraguild predation (IGP) systems. The intrinsic size-structure of fish provides the necessary prerequisites to test whether the above mechanisms are general features of species interactions in fish communities where IGP is common. We first experimentally tested whether Arctic char (Salvelinus alpinus) were more efficient as a cannibal than as an interspecific predator on the prey fish ninespine stickleback (Pungitius pungitius) and whether ninespine stickleback were a more efficient competitor on the shared zooplankton prey than its predator, Arctic char. Secondly, we performed a literature survey to evaluate if piscivores in general are more efficient as cannibals than as interspecific predators and whether piscivores are inferior competitors on shared resources compared to their prey fish species. Both controlled pool experiments and outdoor pond experiments showed that char imposed a higher mortality on YOY char than on ninespine sticklebacks, suggesting that piscivorous char is a more efficient cannibal than interspecific predator. Estimates of size dependent attack rates on zooplankton further showed a consistently higher attack rate of ninespine sticklebacks compared to similar sized char on zooplankton, suggesting that ninespine stickleback is a more efficient competitor than char on zooplankton resources. The literature survey showed that piscivorous top consumers generally selected conspecifics over interspecific prey, and that prey species are competitively superior compared to juvenile piscivorous species in the zooplankton niche. We suggest that the observed selectivity for cannibal prey over interspecific prey and the competitive advantage of prey species over juvenile piscivores are common features in fish communities and that the observed selectivity for cannibalism over interspecific prey has the potential to mediate coexistence in size structured intraguild predation systems. PMID:23894650

Habitat, topographical, and geographical components structuring shrubsteppe bird communities

USGS Publications Warehouse

Knick, S.T.; Rotenberry, J.T.; Leu, M.

2008-01-01

Landscapes available to birds to select for breeding locations are arrayed along multiple dimensions. Identifying the primary gradients structuring shrubsteppe bird communities in the western United States is important because widespread habitat loss and alteration are shifting the environmental template on which these birds depend. We integrated field habitat surveys, GIS coverages, and bird counts from 61 Breeding Bird Survey routes located in shrubsteppe habitats across a >800 000 km2 region to determine the gradients of habitat, topography, and geography underlying bird communities. A small set of habitat features dominated the primary environmental gradients in a canonical ordination; the 13 species in the shrubsteppe bird community were closely packed along the first two axes. Using hierarchical variance partitioning, we identified habitat as the most important pure (31% explained variation) or shared component. Topography (9%) and geography (4%) were minor components but each shared a larger contribution with habitat (habitat-topography 21%; habitat-geography 22%) in explaining the organization of the bird community. In a second tier partition of habitat structure, pure composition (% land cover) was more important (45%) than configuration (patch size and edge) (7%); the two components shared 27% of the explained variation in the bird community axes. Local (9%), community (14%), and landscape (10%) levels contributed equally. Adjacent organizational levels had a larger shared contribution (local-community 26%; community-landscape 27%) than more separated local-landscape levels (21%). Extensive conversion of shrubsteppe habitats to agriculture, exotic annual grasslands, or pinyon (Pinus spp.)-juniper (Juniperus spp.) woodlands is occurring along the primary axes of habitat structure. Because the shrubsteppe bird community was organized along short gradients dominated by habitat features, relatively small shifts in their available environment will exert a strong influence on these bird populations in the absence of buffering by alternative gradients. ?? 2008 The Authors.

The Influential Role of Sociocultural Feedbacks on Community-Managed Irrigation System Behaviors During times of Water Stress

DOE PAGES

Gunda, Thushara; Turner, B. L.; Tidwell, Vincent C.

2018-03-14

Sociohydrological studies use interdisciplinary approaches to explore the complex interactions between physical and social water systems and increase our understanding of emergent and paradoxical system behaviors. The dynamics of community values and social cohesion, however, have received little attention in modeling studies due to quantification challenges. Social structures associated with community-managed irrigation systems around the world, in particular, reflect these communities' experiences with a multitude of natural and social shocks. Using the Valdez acequia (a communally-managed irrigation community in northern New Mexico) as a simulation case study, we evaluate the impact of that community's social structure in governing its responsesmore » to water availability stresses posed by climate change. Specifically, a system dynamics model (developed using insights from community stakeholders and multiple disciplines that captures biophysical, socioeconomic, and sociocultural dynamics of acequia systems) was used to generate counterfactual trajectories to explore how the community would behave with streamflow conditions expected under climate change. We found that earlier peak flows, combined with adaptive measures of shifting crop selection, allowed for greater production of higher value crops and fewer people leaving the acequia. The economic benefits were lost, however, if downstream water pressures increased. Even with significant reductions in agricultural profitability, feedbacks associated with community cohesion buffered the community's population and land parcel sizes from more detrimental impacts, indicating the community's resilience under natural and social stresses. In conclusion, continued exploration of social structures is warranted to better understand these systems' responses to stress and identify possible leverage points for strengthening community resilience.« less

The Influential Role of Sociocultural Feedbacks on Community-Managed Irrigation System Behaviors During times of Water Stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gunda, Thushara; Turner, B. L.; Tidwell, Vincent C.

Sociohydrological studies use interdisciplinary approaches to explore the complex interactions between physical and social water systems and increase our understanding of emergent and paradoxical system behaviors. The dynamics of community values and social cohesion, however, have received little attention in modeling studies due to quantification challenges. Social structures associated with community-managed irrigation systems around the world, in particular, reflect these communities' experiences with a multitude of natural and social shocks. Using the Valdez acequia (a communally-managed irrigation community in northern New Mexico) as a simulation case study, we evaluate the impact of that community's social structure in governing its responsesmore » to water availability stresses posed by climate change. Specifically, a system dynamics model (developed using insights from community stakeholders and multiple disciplines that captures biophysical, socioeconomic, and sociocultural dynamics of acequia systems) was used to generate counterfactual trajectories to explore how the community would behave with streamflow conditions expected under climate change. We found that earlier peak flows, combined with adaptive measures of shifting crop selection, allowed for greater production of higher value crops and fewer people leaving the acequia. The economic benefits were lost, however, if downstream water pressures increased. Even with significant reductions in agricultural profitability, feedbacks associated with community cohesion buffered the community's population and land parcel sizes from more detrimental impacts, indicating the community's resilience under natural and social stresses. In conclusion, continued exploration of social structures is warranted to better understand these systems' responses to stress and identify possible leverage points for strengthening community resilience.« less

The Influential Role of Sociocultural Feedbacks on Community-Managed Irrigation System Behaviors During Times of Water Stress

NASA Astrophysics Data System (ADS)

Gunda, T.; Turner, B. L.; Tidwell, V. C.

2018-04-01

Sociohydrological studies use interdisciplinary approaches to explore the complex interactions between physical and social water systems and increase our understanding of emergent and paradoxical system behaviors. The dynamics of community values and social cohesion, however, have received little attention in modeling studies due to quantification challenges. Social structures associated with community-managed irrigation systems around the world, in particular, reflect these communities' experiences with a multitude of natural and social shocks. Using the Valdez acequia (a communally-managed irrigation community in northern New Mexico) as a simulation case study, we evaluate the impact of that community's social structure in governing its responses to water availability stresses posed by climate change. Specifically, a system dynamics model (developed using insights from community stakeholders and multiple disciplines that captures biophysical, socioeconomic, and sociocultural dynamics of acequia systems) was used to generate counterfactual trajectories to explore how the community would behave with streamflow conditions expected under climate change. We found that earlier peak flows, combined with adaptive measures of shifting crop selection, allowed for greater production of higher value crops and fewer people leaving the acequia. The economic benefits were lost, however, if downstream water pressures increased. Even with significant reductions in agricultural profitability, feedbacks associated with community cohesion buffered the community's population and land parcel sizes from more detrimental impacts, indicating the community's resilience under natural and social stresses. Continued exploration of social structures is warranted to better understand these systems' responses to stress and identify possible leverage points for strengthening community resilience.

The impact of 850,000 years of climate changes on the structure and dynamics of mammal food webs.

PubMed

Nenzén, Hedvig K; Montoya, Daniel; Varela, Sara

2014-01-01

Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans) on Iberian Holocene mammal communities.

The Impact of 850,000 Years of Climate Changes on the Structure and Dynamics of Mammal Food Webs

PubMed Central

Nenzén, Hedvig K.; Montoya, Daniel; Varela, Sara

2014-01-01

Most evidence of climate change impacts on food webs comes from modern studies and little is known about how ancient food webs have responded to climate changes in the past. Here, we integrate fossil evidence from 71 fossil sites, body-size relationships and actualism to reconstruct food webs for six large mammal communities that inhabited the Iberian Peninsula at different times during the Quaternary. We quantify the long-term dynamics of these food webs and study how their structure changed across the Quaternary, a period for which fossil data and climate changes are well known. Extinction, immigration and turnover rates were correlated with climate changes in the last 850 kyr. Yet, we find differences in the dynamics and structural properties of Pleistocene versus Holocene mammal communities that are not associated with glacial-interglacial cycles. Although all Quaternary mammal food webs were highly nested and robust to secondary extinctions, general food web properties changed in the Holocene. These results highlight the ability of communities to re-organize with the arrival of phylogenetically similar species without major structural changes, and the impact of climate change and super-generalist species (humans) on Iberian Holocene mammal communities. PMID:25207754

Physical disturbance to ecological niches created by soil structure alters community composition of methanotrophs.

PubMed

Kumaresan, Deepak; Stralis-Pavese, Nancy; Abell, Guy C J; Bodrossy, Levente; Murrell, J Colin

2011-10-01

Aggregates of different sizes and stability in soil create a composite of ecological niches differing in terms of physico-chemical and structural characteristics. The aim of this study was to identify, using DNA-SIP and mRNA-based microarray analysis, whether shifts in activity and community composition of methanotrophs occur when ecological niches created by soil structure are physically perturbed. Landfill cover soil was subject to three treatments termed: 'control' (minimal structural disruption), 'sieved' (sieved soil using 2 mm mesh) and 'ground' (grinding using mortar and pestle). 'Sieved' and 'ground' soil treatments exhibited higher methane oxidation potentials compared with the 'control' soil treatment. Analysis of the active community composition revealed an effect of physical disruption on active methanotrophs. Type I methanotrophs were the most active methanotrophs in 'sieved' and 'ground' soil treatments, whereas both Type I and Type II methanotrophs were active in the 'control' soil treatment. The result emphasize that changes to a particular ecological niche may not result in an immediate change to the active bacterial composition and change in composition will depend on the ability of the bacterial communities to respond to the perturbation. © 2011 Society for Applied Microbiology and Blackwell Publishing Ltd.

Intraspecific variation in body size does not alter the effects of mesopredators on prey.

PubMed

Gallagher, Austin J; Brandl, Simon J; Stier, Adrian C

2016-12-01

As humans continue to alter the species composition and size structure of marine food webs, it is critical to understand size-dependent effects of predators on prey. Yet, how shifts in predator body size mediate the effect of predators is understudied in tropical marine ecosystems, where anthropogenic harvest has indirectly increased the density and size of small-bodied predators. Here, we combine field surveys and a laboratory feeding experiment in coral reef fish communities to show that small and large predators of the same species can have similar effects. Specifically, surveys show that the presence of a small predator ( Paracirrhites arcatus ) was correlated with lower chances of prey fish presence, but these correlations were independent of predator size. Experimental trials corroborated the size-independent effect of the predator; attack rates were indistinguishable between small and large predators, suggesting relatively even effects of hawkfish in various size classes on the same type of prey. Our results indicate that the effects of small predators on coral reefs can be size-independent, suggesting that variation in predator size-structure alone may not always affect the functional role of these predators.

A universal driver of macroevolutionary change in the size of marine phytoplankton over the Cenozoic

PubMed Central

Finkel, Z. V.; Sebbo, J.; Feist-Burkhardt, S.; Irwin, A. J.; Katz, M. E.; Schofield, O. M. E.; Young, J. R.; Falkowski, P. G.

2007-01-01

The size structure of phytoplankton assemblages strongly influences energy transfer through the food web and carbon cycling in the ocean. We determined the macroevolutionary trajectory in the median size of dinoflagellate cysts to compare with the macroevolutionary size change in other plankton groups. We found the median size of the dinoflagellate cysts generally decreases through the Cenozoic. Diatoms exhibit an extremely similar pattern in their median size over time, even though species diversity of the two groups has opposing trends, indicating that the macroevolutionary size change is an active response to selection pressure rather than a passive response to changes in diversity. The changes in the median size of dinoflagellate cysts are highly correlated with both deep ocean temperatures and the thermal gradient between the surface and deep waters, indicating the magnitude and frequency of nutrient availability may have acted as a selective factor in the macroevolution of cell size in the plankton. Our results suggest that climate, because it affects stratification in the ocean, is a universal abiotic driver that has been responsible for macroevolutionary changes in the size structure of marine planktonic communities over the past 65 million years of Earth's history. PMID:18077334

Empirical correspondence between trophic transfer efficiency in freshwater food webs and the slope of their size spectra.

PubMed

Mehner, Thomas; Lischke, Betty; Scharnweber, Kristin; Attermeyer, Katrin; Brothers, Soren; Gaedke, Ursula; Hilt, Sabine; Brucet, Sandra

2018-06-01

The density of organisms declines with size, because larger organisms need more energy than smaller ones and energetic losses occur when larger organisms feed on smaller ones. A potential expression of density-size distributions are Normalized Biomass Size Spectra (NBSS), which plot the logarithm of biomass independent of taxonomy within bins of logarithmic organismal size, divided by the bin width. Theoretically, the NBSS slope of multi-trophic communities is exactly -1.0 if the trophic transfer efficiency (TTE, ratio of production rates between adjacent trophic levels) is 10% and the predator-prey mass ratio (PPMR) is fixed at 10 4 . Here we provide evidence from four multi-trophic lake food webs that empirically estimated TTEs correspond to empirically estimated slopes of the respective community NBSS. Each of the NBSS considered pelagic and benthic organisms spanning size ranges from bacteria to fish, all sampled over three seasons in 1 yr. The four NBSS slopes were significantly steeper than -1.0 (range -1.14 to -1.19, with 95% CIs excluding -1). The corresponding average TTEs were substantially lower than 10% in each of the four food webs (range 1.0% to 3.6%, mean 1.85%). The overall slope merging all biomass-size data pairs from the four systems (-1.17) was almost identical to the slope predicted from the arithmetic mean TTE of the four food webs (-1.18) assuming a constant PPMR of 10 4 . Accordingly, our empirical data confirm the theoretically predicted quantitative relationship between TTE and the slope of the biomass-size distribution. Furthermore, we show that benthic and pelagic organisms can be merged into a community NBSS, but future studies have yet to explore potential differences in habitat-specific TTEs and PPMRs. We suggest that community NBSS may provide valuable information on the structure of food webs and their energetic pathways, and can result in improved accuracy of TTE-estimates. © 2018 by the Ecological Society of America.

Are submarine groundwater discharges affecting the structure and physiological status of rocky intertidal communities?

PubMed

Piló, D; Barbosa, A B; Teodósio, M A; Encarnação, J; Leitão, F; Range, P; Krug, L A; Cruz, J; Chícharo, L

2018-05-01

This study evaluated the impacts of submarine groundwater discharges (SGD) on a rocky intertidal community of South Portugal, during April-November 2011. Chlorophyll-a concentration was higher at the SGD site in respect to the Reference site. Epibenthic community structure differed between sites, with an increase in Chthamalus spp. and a decrease in macroalgae coverage at the SGD site. The abundance and body size of Mytilus galloprovincialis were consistently higher at the SGD site. During mid-spring, under potentially higher SGD and less favorable conditions for coastal phytoplankton, the ecophysiological condition of M. galloprovincialis and G. umbilicalis was also higher at the SGD site. These beneficial effects on filter-feeders and herbivores probably resulted from local increases in prey availability, supported by SGD-driven nutrient inputs. Conversely, P. depressa was not favoured by SGD, probably due to a lower dependency on algae as food. The analysis of epibenthic community structure and ecophysiological condition represents a promising approach to disentangle the ecological impacts of SGD on intertidal ecosystems. Copyright © 2018 Elsevier Ltd. All rights reserved.

Functional traits determine tree growth and ecosystem productivity of a tropical montane forest: Insights from a long-term nutrient manipulation experiment.

PubMed

Báez, Selene; Homeier, Jürgen

2018-01-01

Trait-response effects are critical to forecast community structure and biomass production in highly diverse tropical forests. Ecological theory and few observation studies indicate that trees with acquisitive functional traits would respond more strongly to higher resource availability than those with conservative traits. We assessed how long-term tree growth in experimental nutrient addition plots (N, P, and N + P) varied as a function of morphological traits, tree size, and species identity. We also evaluated how trait-based responses affected stand scale biomass production considering the community structure. We found that tree growth depended on interactions between functional traits and the type or combination of nutrients added. Common species with acquisitive functional traits responded more strongly to nutrient addition, mainly to N + P. Phosphorous enhanced the growth rates of species with acquisitive and conservative traits, had mostly positive effects on common species and neutral or negative effects in rare species. Moreover, trees receiving N + P grew faster irrespective of their initial size relative to trees in control or to trees in other treatment plots. Finally, species responses were highly idiosyncratic suggesting that community processes including competition and niche dimensionality may be altered under increased resource availability. We found no statistically significant effects of nutrient additions on aboveground biomass productivity because acquisitive species had a limited potential to increase their biomass, possibly due to their generally lower wood density. In contrast, P addition increased the growth rates of species characterized by more conservative resource strategies (with higher wood density) that were poorly represented in the plant community. We provide the first long-term experimental evidence that trait-based responses, community structure, and community processes modulate the effects of increased nutrient availability on biomass productivity in a tropical forest. © 2017 John Wiley & Sons Ltd.

Reef Fishes at All Trophic Levels Respond Positively to Effective Marine Protected Areas

PubMed Central

Soler, German A.; Edgar, Graham J.; Thomson, Russell J.; Kininmonth, Stuart; Campbell, Stuart J.; Dawson, Terence P.; Barrett, Neville S.; Bernard, Anthony T. F.; Galván, David E.; Willis, Trevor J.; Alexander, Timothy J.; Stuart-Smith, Rick D.

2015-01-01

Marine Protected Areas (MPAs) offer a unique opportunity to test the assumption that fishing pressure affects some trophic groups more than others. Removal of larger predators through fishing is often suggested to have positive flow-on effects for some lower trophic groups, in which case protection from fishing should result in suppression of lower trophic groups as predator populations recover. We tested this by assessing differences in the trophic structure of reef fish communities associated with 79 MPAs and open-access sites worldwide, using a standardised quantitative dataset on reef fish community structure. The biomass of all major trophic groups (higher carnivores, benthic carnivores, planktivores and herbivores) was significantly greater (by 40% - 200%) in effective no-take MPAs relative to fished open-access areas. This effect was most pronounced for individuals in large size classes, but with no size class of any trophic group showing signs of depressed biomass in MPAs, as predicted from higher predator abundance. Thus, greater biomass in effective MPAs implies that exploitation on shallow rocky and coral reefs negatively affects biomass of all fish trophic groups and size classes. These direct effects of fishing on trophic structure appear stronger than any top down effects on lower trophic levels that would be imposed by intact predator populations. We propose that exploitation affects fish assemblages at all trophic levels, and that local ecosystem function is generally modified by fishing. PMID:26461104

Fish community structure in freshwater karstic water bodies of the Sian Ka'an Reserve in the Yucatan peninsula, Mexico

USGS Publications Warehouse

Zambrano, L.; Vazquez-Dominguez, E.; Garcia-Bedoya, D.; Loftus, W.F.; Trexler, J.C.

2006-01-01

We evaluated the relationship between limnetic characteristics and fish community structure (based on species richness, abundance and individual size) in contrasting but interconnected inland aquatic habitats of freshwater karstic wetlands in the Yucatan peninsula, Mexico. In the western hemisphere, freshwater karstic wetlands are found in south-eastern Mexico, northern Belize, western Cuba, Andros Island, Bahamas and the Everglades of southern Florida. Only in the Everglades have fish communities been well described. Karstic wetlands are typically oligotrophic because calcium carbonate binds phosphorus, making it relatively unavailable for plants. Fourteen permanent and seasonally flooded water bodies were sampled in both wet and dry seasons in Sian Ka'an Biosphere Reserve, in the Mexican state of Quintana Roo. Water systems were divided by morphology in four groups: cenotes with vegetation (CWV), cenotes without vegetation (CNV), wetlands (WTL), and temporal cenotes (TPC). Discriminant analysis based on physical characteristics such as turbidity, temperature, depth and oxygen confirmed that these habitats differed in characteristics known to influence fish communities. A sample-based rarefaction test showed that species richness was significantly different between water systems groups, showing that WTL and CWV had higher richness values than CNV and TPC. The most abundant fish families, Poeciliidae, Cichlidae and Characidae, differed significantly in average size among habitats and seasons. Seasonal and inter-annual variation, reflecting temporal variation in rainfall, strongly influenced the environmental differences between shallow and deep habitats, which could be linked to fish size and life cycles. Five new records of species were found for the reserve, and one new record for Quintana Roo state. ?? 2006 by Verlag Dr. Friedrich Pfeil.

Development of Structural Geology and Tectonics Data System with Field and Lab Interface

NASA Astrophysics Data System (ADS)

Newman, J.; Tikoff, B.; Walker, J. D.; Good, J.; Michels, Z. D.; Ash, J.; Andrew, J.; Williams, R. T.; Richard, S. M.

2015-12-01

We have developed a prototype Data System for Structural Geology and Tectonics (SG&T). The goal of this effort is to enable recording and sharing data within the geoscience community, to encourage interdisciplinary research, and to facilitate the investigation of scientific questions that cannot currently be addressed. The development of the Data System emphasizes community input in order to build a system that encompasses the needs of researchers, in terms of data and usability. SG&T data is complex for a variety of reasons, including the wide range of temporal and spatial scales (many orders of magnitude each), the complex three-dimensional geometry of some geological structures, inherent spatial nature of the data, and the difficulty of making temporal inferences from spatial observations. To successful implement the step of developing a SG&T data system, we must simultaneously solve three problems: 1) How to digitize SG&T data; 2) How to design a software system that is applicable; and 3) How to construct a very flexible user interface. To address the first problem, we introduce the "Spot" concept, which allows tracking of hierarchical and spatial relations between structures at all scales, and will link map scale, mesoscale, and laboratory scale data. A Spot, in this sense, is analogous to the beam size of analytical equipment used for in situ analysis of rocks; it is the size over which a measurement or quantity is applicable. A Spot can be a single measurement, an aggregation of individual measurements, or even establish relationships between numerous other Spots. We address the second problem through the use of a Graph database to better preserve the myriad of potentially complex relationships. In order to construct a flexible user interface that follows a natural workflow, and that serves the needs of the community, we have begun the process of engaging the SG&T community in order to utilize the expertise of a large group of scientists to ensure the quality and usability of this data system. These activities have included Town Halls, subdiscipline-specific workshops to develop community standards, and pilot projects to test the data system in the field during the study of a variety of geologic structures.

Stochastic Assembly of Bacteria in Microwell Arrays Reveals the Importance of Confinement in Community Development

PubMed Central

Hansen, Ryan H.; Timm, Andrea C.; Timm, Collin M.; Bible, Amber N.; Morrell-Falvey, Jennifer L.; Pelletier, Dale A.; Simpson, Michael L.; Doktycz, Mitchel J.; Retterer, Scott T.

2016-01-01

The structure and function of microbial communities is deeply influenced by the physical and chemical architecture of the local microenvironment and the abundance of its community members. The complexity of this natural parameter space has made characterization of the key drivers of community development difficult. In order to facilitate these characterizations, we have developed a microwell platform designed to screen microbial growth and interactions across a wide variety of physical and initial conditions. Assembly of microbial communities into microwells was achieved using a novel biofabrication method that exploits well feature sizes for control of innoculum levels. Wells with incrementally smaller size features created populations with increasingly larger variations in inoculum levels. This allowed for reproducible growth measurement in large (20 μm diameter) wells, and screening for favorable growth conditions in small (5, 10 μm diameter) wells. We demonstrate the utility of this approach for screening and discovery using 5 μm wells to assemble P. aeruginosa colonies across a broad distribution of innoculum levels, and identify those conditions that promote the highest probability of survivial and growth under spatial confinement. Multi-member community assembly was also characterized to demonstrate the broad potential of this platform for studying the role of member abundance on microbial competition, mutualism and community succession. PMID:27152511

Extension of research data repository system to support direct compute access to biomedical datasets: enhancing Dataverse to support large datasets

PubMed Central

McKinney, Bill; Meyer, Peter A.; Crosas, Mercè; Sliz, Piotr

2016-01-01

Access to experimental X-ray diffraction image data is important for validation and reproduction of macromolecular models and indispensable for the development of structural biology processing methods. In response to the evolving needs of the structural biology community, we recently established a diffraction data publication system, the Structural Biology Data Grid (SBDG, data.sbgrid.org), to preserve primary experimental datasets supporting scientific publications. All datasets published through the SBDG are freely available to the research community under a public domain dedication license, with metadata compliant with the DataCite Schema (schema.datacite.org). A proof-of-concept study demonstrated community interest and utility. Publication of large datasets is a challenge shared by several fields, and the SBDG has begun collaborating with the Institute for Quantitative Social Science at Harvard University to extend the Dataverse (dataverse.org) open-source data repository system to structural biology datasets. Several extensions are necessary to support the size and metadata requirements for structural biology datasets. In this paper, we describe one such extension—functionality supporting preservation of filesystem structure within Dataverse—which is essential for both in-place computation and supporting non-http data transfers. PMID:27862010

Population structure of an invasive parthenogenetic gastropod in coastal lakes and estuaries of northern KwaZulu-Natal, South Africa.

PubMed

Miranda, Nelson A F; Perissinotto, Renzo; Appleton, Christopher C

2011-01-01

Estuaries and coastal lakes receive little attention despite being heavily invaded by non-indigenous invasive species (NIS). In these situations, studies of population dynamics in invaded habitats can provide valuable insights into how NIS interact with new environments. Tarebia granifera is a prosobranch gastropod from south-east Asia which has invaded other sub-tropical parts of the world. This study addresses whether a small number of key environmental factors influences gastropod communities, and specifically how the population density and size structure of T. granifera were influenced by environmental change in estuaries and coastal lakes in southern Africa. T. granifera's density, number of brooded juveniles and size structure were measured at the St. Lucia Estuary, Mgobozeleni Estuary, Lake Sibaya and Lake Nhlange. Size structure was classified according to shell height (SH). All dissected individuals were found to be female and free from trematode infection. Salinity, water depth, temperature, and pH were the main factors correlated with population density of gastropod communities. T. granifera often reached densities well over 1000 ind. m(-2), displacing indigenous gastropods and becoming a dominant component of the benthic community. T. granifera successfully invaded estuaries despite frequent exposure to high salinity and desiccation, which could together eliminate >97% of the population. The persistence of T. granifera was ensured due to its high fecundity and the environmental tolerance of large adults (20-30 mm SH) which carried an average of 158±12.8 SD brooded juveniles. Repeat introductions were not essential for the success of this parthenogenetic NIS. There is a need for a broader study on the reproductive biology of T. granifera (including the previously overlooked "brood pouch ecology"), which affects population dynamics and may be relevant to other parthenogenetic NIS, such as Melanoides tuberculata and Potamopyrgus antipodarum.

Soil Viral Communities Vary Temporally and along a Land Use Transect as Revealed by Virus-Like Particle Counting and a Modified Community Fingerprinting Approach (fRAPD)

PubMed Central

Narr, Anja; Nawaz, Ali; Wick, Lukas Y.; Harms, Hauke; Chatzinotas, Antonis

2017-01-01

Environmental surveys on soil viruses are still rare and mostly anecdotal, i. e., they mostly report on viruses at one location or for only a few sampling dates. Detailed time-series analysis with multiple samples can reveal the spatio-temporal dynamics of viral communities and provide important input as to how viruses interact with their potential hosts and the environment. Such surveys, however, require fast, easy-to-apply and reliable methods. In the present study we surveyed monthly across 13 months the abundance of virus-like particles (VLP) and the structure of the viral communities in soils along a land use transect (i.e., forest, pasture, and cropland). We evaluated 32 procedures to extract VLP from soil using different buffers and mechanical methods. The most efficient extraction was achieved with 1× saline magnesium buffer in combination with 20 min vortexing. For community structure analysis we developed an optimized fingerprinting approach (fluorescent RAPD-PCR; fRAPD) by combining RAPD-PCR with fluorescently labeled primers in order to size the obtained fragments on a capillary sequencing machine. With the concomitantly collected data of soil specific factors and weather data, we were able to find correlations of viral abundance and community structure with environmental variables and sampling site. More specifically, we found that soil specific factors such as pH and total nitrogen content played a significant role in shaping both soil viral abundance and community structure. The fRAPD analysis revealed high temporal changes and clustered the viral communities according to sampling sites. In particular we observed that temperature and rainfall shaped soil viral communities in non-forest sites. In summary our findings suggest that sampling site was a key factor for shaping the abundance and community structure of soil viruses, and when site vegetation was reduced, temperature and rainfall were also important factors. PMID:29067022

Succession and diversity of microorganisms and their association with physicochemical properties during green waste thermophilic composting.

PubMed

Liu, Ling; Wang, Shuqi; Guo, Xiaoping; Zhao, Tingning; Zhang, Bolin

2018-03-01

A comprehensive characterization of the bacterial diversity associated to thermophilic stages of green waste composting was achieved. In this study, eight different treatments (T1-T8) and three replicated lab-scale green waste composting were carried out to compare the effect of the cellulase (i.e. 0, 2%), microbial inoculum (i.e. 0, 2 and 4%) and particle size (i.e. 2 and 5 mm) on bacterial community structure. Physicochemical properties and bacterial communities of T1-T8 composts were observed, and the bacterial structure and diversity were examined by high-throughput sequencing via a MiSeq platform. The results showed that the most abundant phyla among the treatments were the Firmicutes, Chloroflexi and Proteobacteria. The shannon index and non-metric multidimensional scaling (NMDS) showed higher bacterial abundance and diversity at the metaphase of composting. Comparing with 5-mm treatments, particle size of 2-mm had a richer diversity of bacterial communities. The addition of cellulase and a microbial inoculum could promote the fermentation temperature, reduce the compost pH and C/N ratio and result in higher GI index. The humic substance (HS) and humic acid (HA) contents for 2-mm particle size treatments were higher than those of 5-mm treatments. Canonical correspondence analysis suggested that differences in bacterial abundance and diversity significantly correlated with HA, E 4 /E 6 and temperature, and the relationship between bacterial diversity and environmental parameters was affected by composting stages. Based on these results, the application of cellulase to promote green waste composting was feasible, and particle size was identified as a potential control of composting physicochemical properties and bacterial diversity. Copyright © 2017 Elsevier Ltd. All rights reserved.

Improving resolution of dynamic communities in human brain networks through targeted node removal

PubMed Central

Turner, Benjamin O.; Miller, Michael B.; Carlson, Jean M.

2017-01-01

Current approaches to dynamic community detection in complex networks can fail to identify multi-scale community structure, or to resolve key features of community dynamics. We propose a targeted node removal technique to improve the resolution of community detection. Using synthetic oscillator networks with well-defined “ground truth” communities, we quantify the community detection performance of a common modularity maximization algorithm. We show that the performance of the algorithm on communities of a given size deteriorates when these communities are embedded in multi-scale networks with communities of different sizes, compared to the performance in a single-scale network. We demonstrate that targeted node removal during community detection improves performance on multi-scale networks, particularly when removing the most functionally cohesive nodes. Applying this approach to network neuroscience, we compare dynamic functional brain networks derived from fMRI data taken during both repetitive single-task and varied multi-task experiments. After the removal of regions in visual cortex, the most coherent functional brain area during the tasks, community detection is better able to resolve known functional brain systems into communities. In addition, node removal enables the algorithm to distinguish clear differences in brain network dynamics between these experiments, revealing task-switching behavior that was not identified with the visual regions present in the network. These results indicate that targeted node removal can improve spatial and temporal resolution in community detection, and they demonstrate a promising approach for comparison of network dynamics between neuroscientific data sets with different resolution parameters. PMID:29261662

Evaluation of a model of violence risk assessment among forensic psychiatric patients.

PubMed

Douglas, Kevin S; Ogloff, James R P; Hart, Stephen D

2003-10-01

This study tested the interrater reliability and criterion-related validity of structured violence risk judgments made by using one application of the structured professional judgment model of violence risk assessment, the HCR-20 violence risk assessment scheme, which assesses 20 key risk factors in three domains: historical, clinical, and risk management. The HCR-20 was completed for a sample of 100 forensic psychiatric patients who had been found not guilty by reason of a mental disorder and were subsequently released to the community. Violence in the community was determined from multiple file-based sources. Interrater reliability of structured final risk judgments of low, moderate, or high violence risk made on the basis of the structured professional judgment model was acceptable (weighted kappa=.61). Structured final risk judgments were significantly predictive of postrelease community violence, yielding moderate to large effect sizes. Event history analyses showed that final risk judgments made with the structured professional judgment model added incremental validity to the HCR-20 used in an actuarial (numerical) sense. The findings support the structured professional judgment model of risk assessment as well as the HCR-20 specifically and suggest that clinical judgment, if made within a structured context, can contribute in meaningful ways to the assessment of violence risk.

Evaluation of the Healthy Lifestyles Initiative for Improving Community Capacity for Childhood Obesity Prevention

PubMed Central

Berman, Marcie; Bozsik, Frances; Shook, Robin P.; Meissen-Sebelius, Emily; Markenson, Deborah; Summar, Shelly; DeWit, Emily

2018-01-01

Purpose and Objectives Policy, systems, and environmental approaches are recommended for preventing childhood obesity. The objective of our study was to evaluate the Healthy Lifestyles Initiative, which aimed to strengthen community capacity for policy, systems, and environmental approaches to healthy eating and active living among children and families. Intervention Approach The Healthy Lifestyles Initiative was developed through a collaborative process and facilitated by community organizers at a local children’s hospital. The initiative supported 218 partners from 170 community organizations through training, action planning, coalition support, one-on-one support, and the dissemination of materials and sharing of resources. Evaluation Methods Eighty initiative partners completed a brief online survey on implementation strategies engaged in, materials used, and policy, systems, and environmental activities implemented. In accordance with frameworks for implementation science, we assessed associations among the constructs by using linear regression to identify whether and which of the implementation strategies were associated with materials used and implementation of policy, systems, and environmental activities targeted by the initiative. Results Each implementation strategy was engaged in by 30% to 35% of the 80 survey respondents. The most frequently used materials were educational handouts (76.3%) and posters (66.3%). The most frequently implemented activities were developing or continuing partnerships (57.5%) and reviewing organizational wellness policies (46.3%). Completing an action plan and the number of implementation strategies engaged in were positively associated with implementation of targeted activities (action plan, effect size = 0.82; number of strategies, effect size = 0.51) and materials use (action plan, effect size = 0.59; number of strategies, effect size = 0.52). Materials use was positively associated with implementation of targeted activities (effect size = 0.35). Implications for Public Health Community-capacity–building efforts can be effective in supporting community organizations to engage in policy, systems, and environmental activities for healthy eating and active living. Multiple implementation strategies are likely needed, particularly strategies that involve a high level of engagement, such as training community organizations and working with them on structured action plans. PMID:29470168

Linking Microbial Community Structure to β-Glucosidic Function in Soil Aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bailey, Vanessa L.; Fansler, Sarah J.; Stegen, James C.

2013-10-01

To link microbial community 16S structure to a measured function in a natural soil we have scaled both DNA and β-glucosidase assays down to a volume of soil that may approach a unique microbial community. β-glucosidase activity was assayed in 450 individual aggregates which were then sorted into classes of high or low activities, from which groups of 10 or 11 aggregates were identified and grouped for DNA extraction and pyrosequencing. Tandem assays of ATP were conducted for each aggregate in order to normalize these small groups of aggregates for biomass size. In spite of there being no significant differencesmore » in the richness or diversity of the microbial communities associated with high β-glucosidase activities compared with the communities associated with low β-glucosidase communities, several analyses of variance clearly show that the communities of these two groups differ. The separation of these groups is partially driven by the differential abundances of members of the Chitinophagaceae family. It may be that observed functional differences in otherwise similar soil aggregates can be largely attributed to differences in resource availability, rather than to presence or absence of particular taxonomic groups.« less

Nurse practitioner caseload in primary health care: Scoping review.

PubMed

Martin-Misener, Ruth; Kilpatrick, Kelley; Donald, Faith; Bryant-Lukosius, Denise; Rayner, Jennifer; Valaitis, Ruta; Carter, Nancy; Miller, Patricia A; Landry, Véronique; Harbman, Patricia; Charbonneau-Smith, Renee; McKinlay, R James; Ziegler, Erin; Boesveld, Sarah; Lamb, Alyson

2016-10-01

To identify recommendations for determining patient panel/caseload size for nurse practitioners in community-based primary health care settings. Scoping review of the international published and grey literature. The search included electronic databases, international professional and governmental websites, contact with experts, and hand searches of reference lists. Eligible papers had to (a) address caseload or patient panels for nurse practitioners in community-based primary health care settings serving an all-ages population; and (b) be published in English or French between January 2000 and July 2014. Level one testing included title and abstract screening by two team members. Relevant papers were retained for full text review in level two testing, and reviewed by two team members. A third reviewer acted as a tiebreaker. Data were extracted using a structured extraction form by one team member and verified by a second member. Descriptive statistics were estimated. Content analysis was used for qualitative data. We identified 111 peer-reviewed articles and grey literature documents. Most of the papers were published in Canada and the United States after 2010. Current methods to determine panel/caseload size use large administrative databases, provider work hours and the average number of patient visits. Most of the papers addressing the topic of patient panel/caseload size in community-based primary health care were descriptive. The average number of patients seen by nurse practitioners per day varied considerably within and between countries; an average of 9-15 patients per day was common. Patient characteristics (e.g., age, gender) and health conditions (e.g., multiple chronic conditions) appear to influence patient panel/caseload size. Very few studies used validated tools to classify patient acuity levels or disease burden scores. The measurement of productivity and the determination of panel/caseload size is complex. Current metrics may not capture activities relevant to community-based primary health care nurse practitioners. Tools to measure all the components of these role are needed when determining panel/caseload size. Outcomes research is absent in the determination of panel/caseload size. There are few systems in place to track and measure community-based primary health care nurse practitioner activities. The development of such mechanisms is an important next step to assess community-based primary health care nurse practitioner productivity and determine patient panel/caseload size. Decisions about panel/caseload size must take into account the effects of nurse practitioner activities on outcomes of care. Copyright © 2016 Elsevier Ltd. All rights reserved.

Neighborhood Research from a Spatially Oriented Strengths Perspective

ERIC Educational Resources Information Center

Mowbray, Carol T.; Woolley, Michael E.; Grogan-Kaylor, Andrew; Gant, Larry M.; Gilster, Megan E.; Williams Shanks, Trina R.

2007-01-01

Research investigating neighborhood effects on children and families has been largely deficit and individual-focused, investigated structural variables, and has typically produced equivocal findings and small effect sizes. We suggest an approach focused on community strengths and resources that stresses the role of measures of social interaction…

Effects of timber harvesting on birds in the Black Hills of South Dakota and Wyoming, USA

Treesearch

Brian L. Dykstra; Mark A. Rumble; Lester D. Flake

1997-01-01

Timber harvest alters structural characteristics in ponderosa pine forests. In the Black Hills, harvested stands with 40-70% overstory canopy cover are managed as sapling/pole (3.0 - 22.9 cm dbh) or mature (> 22.9 cm dbh) stands. Changing the forest structure to two size classes has unknown effects on bird communities in this region. We counted birds in 20 harvested...

Ecological Structure of Recent and Last Glacial Mammalian Faunas in Northern Eurasia: The Case of Altai-Sayan Refugium

PubMed Central

Pavelková Řičánková, Věra; Robovský, Jan; Riegert, Jan

2014-01-01

Pleistocene mammalian communities display unique features which differ from present-day faunas. The paleocommunities were characterized by the extraordinarily large body size of herbivores and predators and by their unique structure consisting of species now inhabiting geographically and ecologically distinct natural zones. These features were probably the result of the unique environmental conditions of ice age ecosystems. To analyze the ecological structure of Last Glacial and Recent mammal communities we classified the species into biome and trophic-size categories, using Principal Component analysis. We found a marked similarity in ecological structure between Recent eastern Altai-Sayan mammalian assemblages and comparable Pleistocene faunas. The composition of Last Glacial and Recent eastern Altai-Sayan assemblages were characterized by the occurrence of large herbivore and predator species associated with steppe, desert and alpine biomes. These three modern biomes harbor most of the surviving Pleistocene mammals. None of the analyzed Palearctic Last Glacial faunas showed affinity to the temperate forest, taiga, or tundra biome. The Eastern part of the Altai-Sayan region could be considered a refugium of the Last Glacial-like mammalian assemblages. Glacial fauna seems to persist up to present in those areas where the forest belt does not separate alpine vegetation from the steppes and deserts. PMID:24454791

Regional processes in mangrove ecosystems: Spatial scaling relationships, biomass, and turnover rates following catastrophic disturbance

USGS Publications Warehouse

Ward, G.A.; Smith, T. J.; Whelan, K.R.T.; Doyle, T.W.

2006-01-01

Physiological processes and local-scale structural dynamics of mangroves are relatively well studied. Regional-scale processes, however, are not as well understood. Here we provide long-term data on trends in structure and forest turnover at a large scale, following hurricane damage in mangrove ecosystems of South Florida, U.S.A. Twelve mangrove vegetation plots were monitored at periodic intervals, between October 1992 and March 2005. Mangrove forests of this region are defined by a -1.5 scaling relationship between mean stem diameter and stem density, mirroring self-thinning theory for mono-specific stands. This relationship is reflected in tree size frequency scaling exponents which, through time, have exhibited trends toward a community average that is indicative of full spatial resource utilization. These trends, together with an asymptotic standing biomass accumulation, indicate that coastal mangrove ecosystems do adhere to size-structured organizing principles as described for upland tree communities. Regenerative dynamics are different between areas inside and outside of the primary wind-path of Hurricane Andrew which occurred in 1992. Forest dynamic turnover rates, however, are steady through time. This suggests that ecological, more-so than structural factors, control forest productivity. In agreement, the relative mean rate of biomass growth exhibits an inverse relationship with the seasonal range of porewater salinities. The ecosystem average in forest scaling relationships may provide a useful investigative tool of mangrove community biomass relationships, as well as offer a robust indicator of general ecosystem health for use in mangrove forest ecosystem management and restoration. ?? Springer 2006.

Effects of sedimentary sulfide on community structure, population dynamics, and colonization depth of macrozoobenthos in organic-rich estuarine sediments.

PubMed

Kanaya, Gen; Uehara, Tadayasu; Kikuchi, Eisuke

2016-08-15

An annual field survey and in situ recolonization experiment revealed the effects of sedimentary sulfide (H2S) on macrozoobenthos in a eutrophic brackish lagoon. Species diversity was much lower throughout the year in muddy opportunist-dominant sulfidic areas. Mass mortality occurred during warmer months under elevated H2S levels. An enclosure experiment demonstrated that sedimentary H2S modified community composition, size structure, and colonization depth of macrozoobenthos. Species-specific responses to each sediment type (sand, sulfidic mud, and mud with H2S removed) resulted in changes in the established community structure. Dominant polychaetes (Hediste spp., Pseudopolydora spp., and Capitella teleta) occurred predominantly in a thin surface layer in the presence of H2S. On the other hand, organic-rich mud facilitated settlement of polychaete larvae if it does not contain H2S. These results demonstrate that sediment characteristics, including H2S level and organic content, were key structuring factors for the macrozoobenthic assemblage in organically polluted estuarine sediments. Copyright © 2016 Elsevier Ltd. All rights reserved.

Characterization and analysis of temporal and spatial variations in habitat and macroinvertebrate community structure, Fountain Creek basin, Colorado Springs and vicinity, Colorado, 1998-2001

USGS Publications Warehouse

Bruce, James F.

2002-01-01

The Fountain Creek Basin in and around Colorado Springs, Colorado, is affected by various land- and water-use activities. Biological, hydrological, water-quality, and land-use data were collected at 10 sites in the Fountain Creek Basin from April 1998 through April 2001 to provide a baseline characterization of macroinvertebrate communities and habitat conditions for comparison in subsequent studies; and to assess variation in macroinvertebrate community structure relative to habitat quality. Analysis of variance results indicated that instream and riparian variables were not affected by season, but significant differences were found among sites. Nine metrics were used to describe and evaluate macroinvertebrate community structure. Statistical analysis indicated that for six of the nine metrics, significant variability occurred between spring and fall seasons for 60 percent of the sites. Cluster analysis (unweighted pair group method average) using macroinvertebrate presence-absence data showed a well-defined separation between spring and fall samples. Six of the nine metrics had significant spatial variation. Cluster analysis using Sorenson?s Coefficient of Community values computed from macroinvertebrate density (number of organisms per square meter) data showed that macroinvertebrate community structure was more similar among tributary sites than main-stem sites. Canonical correspondence analysis identified a substrate particle-size gradient from site-specific species-abundance data and environmental correlates that decreased the 10 sites to 5 site clusters and their associated taxa.

Atoll-scale patterns in coral reef community structure: Human signatures on Ulithi Atoll, Micronesia.

PubMed

Crane, Nicole L; Nelson, Peter; Abelson, Avigdor; Precoda, Kristin; Rulmal, John; Bernardi, Giacomo; Paddack, Michelle

2017-01-01

The dynamic relationship between reefs and the people who utilize them at a subsistence level is poorly understood. This paper characterizes atoll-scale patterns in shallow coral reef habitat and fish community structure, and correlates these with environmental characteristics and anthropogenic factors, critical to conservation efforts for the reefs and the people who depend on them. Hierarchical clustering analyses by site for benthic composition and fish community resulted in the same 3 major clusters: cluster 1-oceanic (close proximity to deep water) and uninhabited (low human impact); cluster 2-oceanic and inhabited (high human impact); and cluster 3-lagoonal (facing the inside of the lagoon) and inhabited (highest human impact). Distance from village, reef exposure to deep water and human population size had the greatest effect in predicting the fish and benthic community structure. Our study demonstrates a strong association between benthic and fish community structure and human use across the Ulithi Atoll (Yap State, Federated States of Micronesia) and confirms a pattern observed by local people that an 'opportunistic' scleractinian coral (Montipora sp.) is associated with more highly impacted reefs. Our findings suggest that small human populations (subsistence fishing) can nevertheless have considerable ecological impacts on reefs due, in part, to changes in fishing practices rather than overfishing per se, as well as larger global trends. Findings from this work can assist in building local capacity to manage reef resources across an atoll-wide scale, and illustrates the importance of anthropogenic impact even in small communities.

Functional and phylogenetic structure of island bird communities.

PubMed

Si, Xingfeng; Cadotte, Marc W; Zeng, Di; Baselga, Andrés; Zhao, Yuhao; Li, Jiaqi; Wu, Yiru; Wang, Siyu; Ding, Ping

2017-05-01

Biodiversity change in anthropogenically transformed habitats is often nonrandom, yet the nature and importance of the different mechanisms shaping community structure are unclear. Here, we extend the classic Theory of Island Biogeography (TIB) to account for nonrandom processes by incorporating species traits and phylogenetic relationships into a study of faunal relaxation following habitat loss and fragmentation. Two possible mechanisms can create nonrandom community patterns on fragment islands. First, small and isolated islands might consist of similar or closely related species because they are environmentally homogeneous or select for certain shared traits, such as dispersal ability. Alternatively, communities on small islands might contain more dissimilar or distantly related species than on large islands because limited space and resource availability result in greater competitive exclusion among species with high niche overlap. Breeding birds were surveyed on 36 islands and two mainland sites annually from 2010 to 2014 in the Thousand Island Lake region, China. We assessed community structure of breeding birds on these subtropical land-bridge islands by integrating species' trait and evolutionary distances. We additionally analysed habitat heterogeneity and variance in size ratios to distinguish biotic and abiotic processes of community assembly. Results showed that functional-phylogenetic diversity increased with island area, and decreased with isolation. Bird communities on the mainland were more diverse and generally less clustered than island bird communities and not different than randomly assembled communities. Bird communities on islands tend to be functionally similar and phylogenetically clustered, especially on small and isolated islands. The nonrandom decline in species diversity and change in bird community structure with island area and isolation, along with the relatively homogeneous habitats on small islands, support the environmental filtering hypothesis. Our study demonstrates the importance of integrating multiple forms of diversity for understanding the effects of habitat loss and fragmentation, and further reveals that TIB could be extended to community measures by moving beyond assumptions of species equivalency in colonisation rates and extinction susceptibilities. © 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.

Meiofaunal community structure in Thermaikos Gulf: Response to intense trawling pressure

NASA Astrophysics Data System (ADS)

Lampadariou, N.; Hatziyanni, E.; Tselepides, A.

2005-12-01

Among the most important impacts of trawling is the disturbance of the benthic environment as well as the mortality of the larger benthic organisms, which is caused by the passage of the fishing gear. Meiofauna, which are among the smallest benthic organisms, may be more resistant to disturbance by trawling since they are likely to be re-suspended rather than killed by trawls. Their short generation times allow populations to withstand elevated mortality. In this study, we determined the effect of trawling disturbance, season and sediment type on the structure of meiofaunal communities in a commercial fishing ground in Thermaikos Gulf, north Aegean Sea, Greece. The trawling season is limited to 8 months between October and May. A grid of five nearshore stations was chosen along a north-south productivity gradient and an additional offshore station was included as a reference point. Sediment chemistry and meiofaunal community structure were studied before the trawling season started, as well as 1 and 4 months after the initiation of the fishing period. Results showed that there were no short term (30 days) trawling impacts on meiofauna in terms of abundance and community structure but that there were recognizable effects on the community structure of nematodes and the abundance of polychaetes. In contrast, most meiofaunal taxa displayed significant seasonal variability, 4 months after the initiation of the fishing period; however, other closely related factors such as temperature, sediment particle size and primary productivity are more likely to be responsible for the observed patterns.

Body-size spectra of biofilm-dwelling protozoa and their seasonal shift in coastal ecosystems.

PubMed

Zhao, Lu; Xu, Guangjian; Wang, Zheng; Xu, Henglong

2016-10-01

Community-based assessment of protozoa is usually performed at a taxon-dependent resolution. As an inherent 'taxon-free' trait, however, body-size spectrum has proved to be a highly informative indicator to summarize the functional structure of a community in both community research and monitoring programs in aquatic ecosystems. To demonstrate the relationships between the taxon-free resolution of protozoan communities and water conditions, the body-size spectra of biofilm-dwelling protozoa and their seasonal shift and environmental drivers were explored based on an annual dataset collected monthly from coastal waters of the Yellow Sea, northern China. Body sizes were calculated in equivalent spherical diameter (ESD). Among a total of 8 body-size ranks, S2 (19-27μm), S3 (28-36μm), S4 (37-50μm) and S5 (53-71μm) were the top four levels in frequency of occurrence, while rank S1 (13-17μm), S2 and S4 were the dominant levels in abundance. These dominants showed a clear seasonal succession: S2/S4 (spring)→S2/S4 (summer)→S4 (autumn)→S2 (winter) in frequency of occurrence; S1 (spring)→S4 (summer)→S2 (autumn)→S1 (winter) in abundance. Bootstrapped average analysis showed a clear seasonal shift in body-size spectra of the protozoa during a 1-year cycle, and the best-matching analysis demonstrated that the temporal variations in frequency of occurrence and abundance were significantly correlated with water temperature, pH, dissolved oxygen (DO), alone or in combination with chemical oxygen demand (COD) and nutrients. Thus, the body-size spectra of biofilm-dwelling protozoa were seasonally shaped and might be used as a time and cost efficient bioindicator of water quality in marine ecosystems. Copyright © 2016 Elsevier GmbH. All rights reserved.

Conserving Tropical Tree Diversity and Forest Structure: The Value of Small Rainforest Patches in Moderately-Managed Landscapes

PubMed Central

Hernández-Ruedas, Manuel A.; Arroyo-Rodríguez, Víctor; Meave, Jorge A.; Martínez-Ramos, Miguel; Ibarra-Manríquez, Guillermo; Martínez, Esteban; Jamangapé, Gilberto; Melo, Felipe P. L.; Santos, Bráulio A.

2014-01-01

Rainforests are undergoing severe deforestation and fragmentation worldwide. A huge amount of small forest patches are being created, but their value in conserving biodiversity and forest structure is still controversial. Here, we demonstrate that in a species-rich and moderately-managed Mexican tropical landscape small rainforest patches (<100 ha) can be highly valuable for the conservation of tree diversity and forest structure. These patches showed diverse communities of native plants, including endangered species, and a new record for the country. Although the number of logged trees increased in smaller patches, patch size was a poor indicator of basal area, stem density, number of species, genera and families, and community evenness. Cumulative species-area curves indicated that all patches had a similar contribution to the regional species diversity. This idea also was supported by the fact that patches strongly differed in floristic composition (high β-diversity), independently of patch size. Thus, in agreement with the land-sharing approach, our findings support that small forest patches in moderately-managed landscapes should be included in conservation initiatives to maintain landscape heterogeneity, species diversity, and ecosystem services. PMID:24901954

Conserving tropical tree diversity and forest structure: the value of small rainforest patches in moderately-managed landscapes.

PubMed

Hernández-Ruedas, Manuel A; Arroyo-Rodríguez, Víctor; Meave, Jorge A; Martínez-Ramos, Miguel; Ibarra-Manríquez, Guillermo; Martínez, Esteban; Jamangapé, Gilberto; Melo, Felipe P L; Santos, Bráulio A

2014-01-01

Rainforests are undergoing severe deforestation and fragmentation worldwide. A huge amount of small forest patches are being created, but their value in conserving biodiversity and forest structure is still controversial. Here, we demonstrate that in a species-rich and moderately-managed Mexican tropical landscape small rainforest patches (<100 ha) can be highly valuable for the conservation of tree diversity and forest structure. These patches showed diverse communities of native plants, including endangered species, and a new record for the country. Although the number of logged trees increased in smaller patches, patch size was a poor indicator of basal area, stem density, number of species, genera and families, and community evenness. Cumulative species-area curves indicated that all patches had a similar contribution to the regional species diversity. This idea also was supported by the fact that patches strongly differed in floristic composition (high β-diversity), independently of patch size. Thus, in agreement with the land-sharing approach, our findings support that small forest patches in moderately-managed landscapes should be included in conservation initiatives to maintain landscape heterogeneity, species diversity, and ecosystem services.

Predicting community responses to perturbations in the face of imperfect knowledge and network complexity

USGS Publications Warehouse

Novak, M.; Wootton, J.T.; Doak, D.F.; Emmerson, M.; Estes, J.A.; Tinker, M.T.

2011-01-01

How best to predict the effects of perturbations to ecological communities has been a long-standing goal for both applied and basic ecology. This quest has recently been revived by new empirical data, new analysis methods, and increased computing speed, with the promise that ecologically important insights may be obtainable from a limited knowledge of community interactions. We use empirically based and simulated networks of varying size and connectance to assess two limitations to predicting perturbation responses in multispecies communities: (1) the inaccuracy by which species interaction strengths are empirically quantified and (2) the indeterminacy of species responses due to indirect effects associated with network size and structure. We find that even modest levels of species richness and connectance (??25 pairwise interactions) impose high requirements for interaction strength estimates because system indeterminacy rapidly overwhelms predictive insights. Nevertheless, even poorly estimated interaction strengths provide greater average predictive certainty than an approach that uses only the sign of each interaction. Our simulations provide guidance in dealing with the trade-offs involved in maximizing the utility of network approaches for predicting dynamics in multispecies communities. ?? 2011 by the Ecological Society of America.

Limiting similarity and functional diversity along environmental gradients

USGS Publications Warehouse

Schwilk, D.W.; Ackerly, D.D.

2005-01-01

Recent developments in community models emphasize the importance of incorporating stochastic processes (e.g. ecological drift) in models of niche-structured community assembly. We constructed a finite, spatially explicit, lottery model to simulate the distribution of species in a one-dimensional landscape with an underlying gradient in environmental conditions. Our framework combines the potential for ecological drift with environmentally-mediated competition for space in a heterogeneous environment. We examined the influence of niche breadth, dispersal distances, community size (total number of individuals) and the breadth of the environmental gradient on levels of species and functional trait diversity (i.e. differences in niche optima). Three novel results emerge from this model: (1) niche differences between adjacent species (e.g. limiting similarity) increase in smaller communities, because of the interaction of competitive effects and finite population sizes; (2) immigration from a regional species pool, stochasticity and niche-assembly generate a bimodal distribution of species residence times ('transient' and 'resident') under a heterogeneous environment; and (3) the magnitude of environmental heterogeneity has a U-shaped effect on diversity, because of shifts in species richness of resident vs. transient species. These predictions illustrate the potential importance of stochastic (although not necessarily neutral) processes in community assembly. ??2005 Blackwell Publishing Ltd/CNRS.

Centrarchid assemblages in Mississippi state-operated fishing lakes

USGS Publications Warehouse

Olive, J.A.; Miranda, L.E.; Hubbard, W.D.

2005-01-01

We evaluated electrofishing catch per effort in 27 state-operated fishing lakes in Mississippi to identify patterns of centrarchid community composition and to determine whether those patterns were related to selected environmental characteristics and to artificial nutrient enrichment. Ordination with detrended correspondence analysis recognized two major axes accounting for 77% of the variability in species ordination. Axis 1 showed a distinct separation between the body sizes of various species. A notable exception was the density of small (<30 cm) largemouth bass Micropterus salmoides, which aligned with the large individuals of other centrarchid species. This pattern suggested that through predation, high densities of small largemouth bass exerted significant control over the size structure of fish communities. Axis 2 separated species of crappies Pomoxis spp., suggesting that conditions other than strong species interactions also moderated the composition of crappies in the assemblages. However, neither lake morphometry nor watershed composition exhibited a major influence over axes 1 or 2. In small, intensively managed lakes with low habitat complexity, the regulatory importance of biotic interactions may overwhelm that of abiotic factors. Nutrient enrichment influenced community structure by changing the densities of bluegill Lepomis macrochirus and largemouth bass substantially but had a minor or no effect on other species. The management techniques used in these state-operated lakes are usually targeted toward a particular species without adequately considering the other species within the community. Our results show that attention to community-level interactions could provide valuable insight into factors that affect the quality of the fishery, insight that is not available through traditional population-level assessments. ?? Copyright by the American Fisheries Society 2005.

Environmental and Spatial Influences on Biogeography and Community Structure of Benthic Diatoms

NASA Astrophysics Data System (ADS)

Plante, C.; Hill-Spanik, K.; Lowry, J.

2016-02-01

Several theoretical and practical reasons suggest that benthic microalgae could be useful bioindicators. For instance, an ideal indicator species or community would be associated with a given habitat due to local physical conditions or biotic interactions (i.e., `environmental filtering'), not due to dispersal limitation. Due to their small size, immense abundances, and reliance on passive dispersal, the popular notion about micro-organisms is that `Everything is everywhere, but, the environment selects' (Baas-Becking 1934). Although much recent research concerning planktonic bacteria and dispersal limitation has been conducted, very little in this regard is known about microeukaryotes, especially benthic microbes. The purpose of our study was to identify and compare spatial and environmental influences on benthic diatom community structure and biogeography. In summer 2015, sediment was sampled at various spatial scales from four barrier island beaches in South Carolina, USA, and high-throughput (Ion Torrent) DNA sequencing was used to characterize diatom assemblages. ANOSIM and principal coordinates analysis revealed that communities were statistically distinct on the four islands. Community dissimilarity was compared to both spatial distance and environmental differences to determine potential influences of these variables on community structure. We found that geographic distance had the strongest correlation with community similarity, with and without one anomalous location, while differences in temperature (air, water, and sediment), nutrients, organic matter, and turbidity also had significant but weaker relationships with community structure. Surprisingly, air temperature, which changes on very short time scales, appeared to be the environmental factor most strongly related to diatom species composition, potentially implicating some unmeasured variable (e.g., cloud cover). However, we also found that temperature and geographic distance were strongly correlated. Future research will expand the spatial scope of this preliminary study and employ techniques (partial Mantel tests) to control for co-variation among variables.

SIZE, STRUCTURE AND FUNCTIONALITY IN SHALLOW COVE COMMUNITIES IN RI

EPA Science Inventory

We are using an ecosystem approach to examine the ecological integrity and important habitats in small estuarine coves. We sampled the small undeveloped Coggeshall Cove during the sununer of 1999. The cove was sampled at high tide at every 15 cm of substrate elevation along trans...

Size Matters: The Contribution of Mega-Infauna to the Food Webs and Ecosystem Services of an Oregon Estuary

EPA Science Inventory

Large-bodied, invertebrates are common to infaunal communities of NE Pacific estuaries (e.g., bivalves, polychaetes, burrowing shrimps), but their contribution to the ecological structure, function and ecosystem services of most estuaries has been poorly characterized because the...

Are trade-offs among species' ecological interactions scale dependent? A test using pitcher-plant inquiline species.

PubMed

Kneitel, Jamie M

2012-01-01

Trade-offs among species' ecological interactions is a pervasive explanation for species coexistence. The traits associated with trade-offs are typically measured to mechanistically explain species coexistence at a single spatial scale. However, species potentially interact at multiple scales and this may be reflected in the traits among coexisting species. I quantified species' ecological traits associated with the trade-offs expected at both local (competitive ability and predator tolerance) and regional (competitive ability and colonization rate) community scales. The most common species (four protozoa and a rotifer) from the middle trophic level of a pitcher plant (Sarracenia purpurea) inquiline community were used to link species traits to previously observed patterns of species diversity and abundance. Traits associated with trade-offs (competitive ability, predator tolerance, and colonization rate) and other ecological traits (size, growth rate, and carrying capacity) were measured for each of the focal species. Traits were correlated with one another with a negative relationship indicative of a trade-off. Protozoan and rotifer species exhibited a negative relationship between competitive ability and predator tolerance, indicative of coexistence at the local community scale. There was no relationship between competitive ability and colonization rate. Size, growth rate, and carrying capacity were correlated with each other and the trade-off traits: Size was related to both competitive ability and predator tolerance, but growth rate and carrying capacity were correlated with predator tolerance. When partial correlations were conducted controlling for size, growth rate and carrying capacity, the trade-offs largely disappeared. These results imply that body size is the trait that provides the basis for ecological interactions and trade-offs. Altogether, this study showed that the examination of species' traits in the context of coexistence at different scales can contribute to our understanding of the mechanisms underlying community structure.

New body mass estimates of British Pleistocene wolves: Palaeoenvironmental implications and competitive interactions

NASA Astrophysics Data System (ADS)

Flower, L. O. H.

2016-10-01

Body mass was reconstructed for early Middle Pleistocene Canis mosbachensis and late Middle to Late Pleistocene Canis lupus from key assemblages in Britain, to explore the presence of temporal size variability and whether size fluctuations were related to changes in climate and environment or to differences in Pleistocene carnivore community structure. Using the well-known body mass predictor of lower carnassial (m1) tooth length, combined with an extant canid dataset incorporating 25 species, least squares regression was used to assess allometric scaling prior to modelling the relationship between body mass and m1 length, producing a new predictive equation of Pleistocene canid body mass. The medium-sized C. mosbachensis had relatively stable body mass, with remarkable consistency in size compared to populations in the late Early Pleistocene of Europe. Periodical fluctuations in climatic conditions had a minimal effect on C. mosbachensis size over time, with the terrestrial connection between Britain and mainland Europe at this time key in promoting body mass stability by enabling movement away from less favourable conditions and to follow prey into refugia. Overall changes in carnivore guild structure were of minimal influence to C. mosbachensis in Britain, as the continued predominance of larger carnivores, in particular a larger canid, effectively constrained C. mosbachensis. In contrast, the body mass of larger-sized C. lupus was highly temporally varied, with an increasing size trend evident into the Devensian. Similar body size in the penultimate interglacial (MIS 7) and Middle Devensian (MIS 3) populations likely reflects palaeoenvironmental similarity and comparable carnivore community and prey spectrums, with larger predators effectively constraining C. lupus. However, the severely cold conditions of the Early Devensian (MIS 5a) may have caused a Bergmannian response in wolves, leading to their comparatively much larger size, with C. lupus further ecologically "liberated" by an absence of larger multiple larger predators at this time.

Soil properties drive a negative correlation between species diversity and genetic diversity in a tropical seasonal rainforest

PubMed Central

Xu, Wumei; Liu, Lu; He, Tianhua; Cao, Min; Sha, Liqing; Hu, Yuehua; Li, Qiaoming; Li, Jie

2016-01-01

A negative species-genetic diversity correlation (SGDC) could be predicted by the niche variation hypothesis, whereby an increase in species diversity within community reduces the genetic diversity of the co-occurring species because of the reduction in average niche breadth; alternatively, competition could reduce effective population size and therefore genetic diversity of the species within community. We tested these predictions within a 20 ha tropical forest dynamics plot (FDP) in the Xishuangbanna tropical seasonal rainforest. We established 15 plots within the FDP and investigated the soil properties, tree diversity, and genetic diversity of a common tree species Beilschmiedia roxburghiana within each plot. We observed a significant negative correlation between tree diversity and the genetic diversity of B. roxburghiana within the communities. Using structural equation modeling, we further determined that the inter-plot environmental characteristics (soil pH and phosphorus availability) directly affected tree diversity and that the tree diversity within the community determined the genetic diversity of B. roxburghiana. Increased soil pH and phosphorus availability might promote the coexistence of more tree species within community and reduce genetic diversity of B. roxburghiana for the reduced average niche breadth; alternatively, competition could reduce effective population size and therefore genetic diversity of B. roxburghiana within community. PMID:26860815

Soil properties drive a negative correlation between species diversity and genetic diversity in a tropical seasonal rainforest.

PubMed

Xu, Wumei; Liu, Lu; He, Tianhua; Cao, Min; Sha, Liqing; Hu, Yuehua; Li, Qiaoming; Li, Jie

2016-02-10

A negative species-genetic diversity correlation (SGDC) could be predicted by the niche variation hypothesis, whereby an increase in species diversity within community reduces the genetic diversity of the co-occurring species because of the reduction in average niche breadth; alternatively, competition could reduce effective population size and therefore genetic diversity of the species within community. We tested these predictions within a 20 ha tropical forest dynamics plot (FDP) in the Xishuangbanna tropical seasonal rainforest. We established 15 plots within the FDP and investigated the soil properties, tree diversity, and genetic diversity of a common tree species Beilschmiedia roxburghiana within each plot. We observed a significant negative correlation between tree diversity and the genetic diversity of B. roxburghiana within the communities. Using structural equation modeling, we further determined that the inter-plot environmental characteristics (soil pH and phosphorus availability) directly affected tree diversity and that the tree diversity within the community determined the genetic diversity of B. roxburghiana. Increased soil pH and phosphorus availability might promote the coexistence of more tree species within community and reduce genetic diversity of B. roxburghiana for the reduced average niche breadth; alternatively, competition could reduce effective population size and therefore genetic diversity of B. roxburghiana within community.

mizer: an R package for multispecies, trait-based and community size spectrum ecological modelling.

PubMed

Scott, Finlay; Blanchard, Julia L; Andersen, Ken H

2014-10-01

Size spectrum ecological models are representations of a community of individuals which grow and change trophic level. A key emergent feature of these models is the size spectrum; the total abundance of all individuals that scales negatively with size. The models we focus on are designed to capture fish community dynamics useful for assessing the community impacts of fishing.We present mizer , an R package for implementing dynamic size spectrum ecological models of an entire aquatic community subject to fishing. Multiple fishing gears can be defined and fishing mortality can change through time making it possible to simulate a range of exploitation strategies and management options. mizer implements three versions of the size spectrum modelling framework: the community model, where individuals are only characterized by their size; the trait-based model, where individuals are further characterized by their asymptotic size; and the multispecies model where additional trait differences are resolved.A range of plot, community indicator and summary methods are available to inspect the results of the simulations.

Community Structure of a Bank-Firm Credit Network in Japan

NASA Astrophysics Data System (ADS)

Iyetomi, Hiroshi; Matsuura, Yuki

2014-03-01

We study temporal change of community structure in a Japanese credit network formed by banks and listed firms through their financial relations over the last 30 years. The credit connectedness is regarded as a potenital source of systemic risk. Our network is a bipartite graph consisting of two species of nodes connected with bidirectional links. The direction of links is identified with that of risk flows and their weights are relative credit/loan with respect to the targets. In a partial credit network obtained only with the links pointing from firms toward banks, the city banks forms one major community in most of the time period to share risk when firms go wrong. On the other hand, a partial network only with the links from banks toward firms is decomposed into communities of similar size each of which has its own city bank, reflecting the main-bank system in Japan. Finally we take overlapping parts of the two community sets to find cores of the risk concentration in the credit network. This work was supported by JSPS KAKENHI Grant Number 22300080.

Comparison of Coral Reef Ecosystems along a Fishing Pressure Gradient

PubMed Central

Weijerman, Mariska; Fulton, Elizabeth A.; Parrish, Frank A.

2013-01-01

Three trophic mass-balance models representing coral reef ecosystems along a fishery gradient were compared to evaluate ecosystem effects of fishing. The majority of the biomass estimates came directly from a large-scale visual survey program; therefore, data were collected in the same way for all three models, enhancing comparability. Model outputs–such as net system production, size structure of the community, total throughput, production, consumption, production-to-respiration ratio, and Finn’s cycling index and mean path length–indicate that the systems around the unpopulated French Frigate Shoals and along the relatively lightly populated Kona Coast of Hawai’i Island are mature, stable systems with a high efficiency in recycling of biomass. In contrast, model results show that the reef system around the most populated island in the State of Hawai’i, O’ahu, is in a transitional state with reduced ecosystem resilience and appears to be shifting to an algal-dominated system. Evaluation of the candidate indicators for fishing pressure showed that indicators at the community level (e.g., total biomass, community size structure, trophic level of the community) were most robust (i.e., showed the clearest trend) and that multiple indicators are necessary to identify fishing perturbations. These indicators could be used as performance indicators when compared to a baseline for management purposes. This study shows that ecosystem models can be valuable tools in identification of the system state in terms of complexity, stability, and resilience and, therefore, can complement biological metrics currently used by monitoring programs as indicators for coral reef status. Moreover, ecosystem models can improve our understanding of a system’s internal structure that can be used to support management in identification of approaches to reverse unfavorable states. PMID:23737951

Altitude acts as an environmental filter on phylogenetic composition, traits and diversity in bee communities.

PubMed

Hoiss, Bernhard; Krauss, Jochen; Potts, Simon G; Roberts, Stuart; Steffan-Dewenter, Ingolf

2012-11-07

Knowledge about the phylogeny and ecology of communities along environmental gradients helps to disentangle the role of competition-driven processes and environmental filtering for community assembly. In this study, we evaluated patterns in species richness, phylogenetic structure and life-history traits of bee communities along altitudinal gradients in the Alps, Germany. We found a linear decline in species richness and abundance but increasing phylogenetic clustering in communities with increasing altitude. The proportion of social- and ground-nesting species, as well as mean body size and altitudinal range of bee communities, increased with increasing altitude, whereas the mean geographical distribution decreased. Our results suggest that community assembly at high altitudes is dominated by environmental filtering effects, whereas the relative importance of competition increases at low altitudes. We conclude that inherent phylogenetic and ecological species attributes at high altitudes pose a threat for less competitive alpine specialists with ongoing climate change.

Altitude acts as an environmental filter on phylogenetic composition, traits and diversity in bee communities

PubMed Central

Hoiss, Bernhard; Krauss, Jochen; Potts, Simon G.; Roberts, Stuart; Steffan-Dewenter, Ingolf

2012-01-01

Knowledge about the phylogeny and ecology of communities along environmental gradients helps to disentangle the role of competition-driven processes and environmental filtering for community assembly. In this study, we evaluated patterns in species richness, phylogenetic structure and life-history traits of bee communities along altitudinal gradients in the Alps, Germany. We found a linear decline in species richness and abundance but increasing phylogenetic clustering in communities with increasing altitude. The proportion of social- and ground-nesting species, as well as mean body size and altitudinal range of bee communities, increased with increasing altitude, whereas the mean geographical distribution decreased. Our results suggest that community assembly at high altitudes is dominated by environmental filtering effects, whereas the relative importance of competition increases at low altitudes. We conclude that inherent phylogenetic and ecological species attributes at high altitudes pose a threat for less competitive alpine specialists with ongoing climate change. PMID:22933374

Abiotic Factors Affecting Benthic Invertebrate Biomass and Community Structure in a Fourth-Order Rocky Mountain Watershed

NASA Astrophysics Data System (ADS)

Chanat, J. G.; Clements, W. H.; MacDonald, L. H.

2005-05-01

The potential ecological impact of excess streambed sediment resulting from forest management activities is a persistent concern for land managers. This study examined the relationship between streambed sediment, along with other site- and reach-scale abiotic factors, and benthic macroinvertebrate community structure in a 272 km2 basin in the Colorado Front Range. Physical habitat parameters and invertebrates were sampled in late summer at 68 sites located in sixteen stream reaches. Invertebrate data were used to formulate twenty indices of community structure. Multiple regression identified site-level substrate particle size as the most important predictor of six indices, including total density (R2 = 0.22), biomass (R2 = 0.17), and taxa richness (R2 = 0.32). All of the remaining fourteen indices were most strongly predicted by reach-level variables, including discharge (percent shredders, R2 = 0.24; Plecoptera density, R2 = 0.29), and elevation (percent collector-filterers, R2 = 0.28; Trichoptera density, R2 = 0.37). Although the sites represented a wide range of substrate composition and embeddedness, no physical variable associated with fine sediment appeared as a strong predictor of any of the twenty indices. Thus, sediment is not among the most important factors associated with site-to-site variability of benthic community structure in this relatively pristine watershed.

The Impact of Fish Predation and Cyanobacteria on Zooplankton Size Structure in 96 Subtropical Lakes

PubMed Central

Zhang, Jing; Xie, Ping; Tao, Min; Guo, Longgen; Chen, Jun; Li, Li; XueZhen Zhang; Zhang, Lu

2013-01-01

Zooplankton are relatively small in size in the subtropical regions. This characteristic has been attributed to intense predation pressure, high nutrient loading and cyanobacterial biomass. To provide further information on the effect of predation and cyanobacteria on zooplankton size structure, we analyzed data from 96 shallow aquaculture lakes along the Yangtze River. Contrary to former studies, both principal components analysis and multiple regression analysis showed that the mean zooplankton size was positively related to fish yield. The studied lakes were grouped into three types, namely, natural fishing lakes with low nutrient loading (Type1), planktivorous fish-dominated lakes (Type 2), and eutrophic lakes with high cyanobacterial biomass (Type 3). A marked difference in zooplankton size structure was found among these groups. The greatest mean zooplankton size was observed in Type 2 lakes, but zooplankton density was the lowest. Zooplankton abundance was highest in Type 3 lakes and increased with increasing cyanobacterial biomass. Zooplankton mean size was negatively correlated with cyanobacterial biomass. No obvious trends were found in Type 1 lakes. These results were reflected by the normalized biomass size spectrum, which showed a unimodal shape with a peak at medium sizes in Type 2 lakes and a peak at small sizes in Type 3 lakes. These results indicated a relative increase in medium-sized and small-sized species in Types 2 and 3 lakes, respectively. Our results suggested that fish predation might have a negative effect on zooplankton abundance but a positive effect on zooplankton size structure. High cyanobacterial biomass most likely caused a decline in the zooplankton size and encouraged the proliferation of small zooplankton. We suggest that both planktivorous fish and cyanobacteria have substantial effects on the shaping of zooplankton community, particularly in the lakes in the eastern plain along the Yangtze River where aquaculture is widespread and nutrient loading is high. PMID:24124552

The impact of fish predation and cyanobacteria on zooplankton size structure in 96 subtropical lakes.

PubMed

Zhang, Jing; Xie, Ping; Tao, Min; Guo, Longgen; Chen, Jun; Li, Li; Xuezhen Zhang; Zhang, Lu

2013-01-01

Zooplankton are relatively small in size in the subtropical regions. This characteristic has been attributed to intense predation pressure, high nutrient loading and cyanobacterial biomass. To provide further information on the effect of predation and cyanobacteria on zooplankton size structure, we analyzed data from 96 shallow aquaculture lakes along the Yangtze River. Contrary to former studies, both principal components analysis and multiple regression analysis showed that the mean zooplankton size was positively related to fish yield. The studied lakes were grouped into three types, namely, natural fishing lakes with low nutrient loading (Type1), planktivorous fish-dominated lakes (Type 2), and eutrophic lakes with high cyanobacterial biomass (Type 3). A marked difference in zooplankton size structure was found among these groups. The greatest mean zooplankton size was observed in Type 2 lakes, but zooplankton density was the lowest. Zooplankton abundance was highest in Type 3 lakes and increased with increasing cyanobacterial biomass. Zooplankton mean size was negatively correlated with cyanobacterial biomass. No obvious trends were found in Type 1 lakes. These results were reflected by the normalized biomass size spectrum, which showed a unimodal shape with a peak at medium sizes in Type 2 lakes and a peak at small sizes in Type 3 lakes. These results indicated a relative increase in medium-sized and small-sized species in Types 2 and 3 lakes, respectively. Our results suggested that fish predation might have a negative effect on zooplankton abundance but a positive effect on zooplankton size structure. High cyanobacterial biomass most likely caused a decline in the zooplankton size and encouraged the proliferation of small zooplankton. We suggest that both planktivorous fish and cyanobacteria have substantial effects on the shaping of zooplankton community, particularly in the lakes in the eastern plain along the Yangtze River where aquaculture is widespread and nutrient loading is high.

Chronic Polyaromatic Hydrocarbon (PAH) Contamination Is a Marginal Driver for Community Diversity and Prokaryotic Predicted Functioning in Coastal Sediments

PubMed Central

Jeanbille, Mathilde; Gury, Jérôme; Duran, Robert; Tronczynski, Jacek; Ghiglione, Jean-François; Agogué, Hélène; Saïd, Olfa Ben; Taïb, Najwa; Debroas, Didier; Garnier, Cédric; Auguet, Jean-Christophe

2016-01-01

Benthic microorganisms are key players in the recycling of organic matter and recalcitrant compounds such as polyaromatic hydrocarbons (PAHs) in coastal sediments. Despite their ecological importance, the response of microbial communities to chronic PAH pollution, one of the major threats to coastal ecosystems, has received very little attention. In one of the largest surveys performed so far on coastal sediments, the diversity and composition of microbial communities inhabiting both chronically contaminated and non-contaminated coastal sediments were investigated using high-throughput sequencing on the 18S and 16S rRNA genes. Prokaryotic alpha-diversity showed significant association with salinity, temperature, and organic carbon content. The effect of particle size distribution was strong on eukaryotic diversity. Similarly to alpha-diversity, beta-diversity patterns were strongly influenced by the environmental filter, while PAHs had no influence on the prokaryotic community structure and a weak impact on the eukaryotic community structure at the continental scale. However, at the regional scale, PAHs became the main driver shaping the structure of bacterial and eukaryotic communities. These patterns were not found for PICRUSt predicted prokaryotic functions, thus indicating some degree of functional redundancy. Eukaryotes presented a greater potential for their use as PAH contamination biomarkers, owing to their stronger response at both regional and continental scales. PMID:27594854

[Civil status and suicide].

PubMed

Gaxiola-Robles, Ramón; Bitzer-Quintero, Oscar Kurt; García-González, Adolfo; Celis-de la Rosa, Alfredo

2009-01-01

To determine if civil status acts as a risk factor in suicide and how it modifies according to gender, age and population size. A retrospective study which analyzes information from the mortality data from the National Institute of Statistics, Geography and Information, from 1998 to 2002. Variables like suicides age, sex, cause of death, federal entity, population size and civil status were registered. Single men showed twofold risk for committing suicide. Women did not show any associated risk for suicide according to civil status. The risk of married men for committing suicide increased gradually with age. Medium-sized communities with less than 19,999 habitants presented the highest risk for habitants to commit suicide. Suicide is associated to gender especially to men who are not married and living in small and medium-sized communities. One explanation could be the lack of integrated behavior as defined by Emile Durkheim, where the physical density of society will determine behavior and ideas. This social structure phenomenon is called the "moral cocoon." This works around the individual being less individualistic and granting him/her the feeling of belonging to a group.

Effects of seed predators of different body size on seed mortality in Bornean logged forest.

PubMed

Hautier, Yann; Saner, Philippe; Philipson, Christopher; Bagchi, Robert; Ong, Robert C; Hector, Andy

2010-07-19

The Janzen-Connell hypothesis proposes that seed and seedling enemies play a major role in maintaining high levels of tree diversity in tropical forests. However, human disturbance may alter guilds of seed predators including their body size distribution. These changes have the potential to affect seedling survival in logged forest and may alter forest composition and diversity. We manipulated seed density in plots beneath con- and heterospecific adult trees within a logged forest and excluded vertebrate predators of different body sizes using cages. We show that small and large-bodied predators differed in their effect on con- and heterospecific seedling mortality. In combination small and large-bodied predators dramatically decreased both con- and heterospecific seedling survival. In contrast, when larger-bodied predators were excluded small-bodied predators reduced conspecific seed survival leaving seeds coming from the distant tree of a different species. Our results suggest that seed survival is affected differently by vertebrate predators according to their body size. Therefore, changes in the body size structure of the seed predator community in logged forests may change patterns of seed mortality and potentially affect recruitment and community composition.

Effects of Seed Predators of Different Body Size on Seed Mortality in Bornean Logged Forest

PubMed Central

Hautier, Yann; Saner, Philippe; Philipson, Christopher; Bagchi, Robert; Ong, Robert C.; Hector, Andy

2010-01-01

Background The Janzen-Connell hypothesis proposes that seed and seedling enemies play a major role in maintaining high levels of tree diversity in tropical forests. However, human disturbance may alter guilds of seed predators including their body size distribution. These changes have the potential to affect seedling survival in logged forest and may alter forest composition and diversity. Methodology/Principal Findings We manipulated seed density in plots beneath con- and heterospecific adult trees within a logged forest and excluded vertebrate predators of different body sizes using cages. We show that small and large-bodied predators differed in their effect on con- and heterospecific seedling mortality. In combination small and large-bodied predators dramatically decreased both con- and heterospecific seedling survival. In contrast, when larger-bodied predators were excluded small-bodied predators reduced conspecific seed survival leaving seeds coming from the distant tree of a different species. Conclusions/Significance Our results suggest that seed survival is affected differently by vertebrate predators according to their body size. Therefore, changes in the body size structure of the seed predator community in logged forests may change patterns of seed mortality and potentially affect recruitment and community composition. PMID:20657841

Initialization, Prediction and Diagnosis of the Rapid Intensification of Tropical Cyclones using the Australian Community Climate and Earth System Simulator, ACCESS

DTIC Science & Technology

2012-10-12

structure on the evolving storm behaviour. 13 7. Large scale influences on Rapid Intensification and Extratropical Transition: RI and ET...assimilation techniques to better initialize and validate TC structures (including the intense inner core and storm asymmetries) consistent with the large...Without vortex specification, initial conditions usually contain a weak and misplaced circulation. Based on estimates of central pressure and storm size

Stability-to-instability transition in the structure of large-scale networks

NASA Astrophysics Data System (ADS)

Hu, Dandan; Ronhovde, Peter; Nussinov, Zohar

2012-12-01

We examine phase transitions between the “easy,” “hard,” and “unsolvable” phases when attempting to identify structure in large complex networks (“community detection”) in the presence of disorder induced by network “noise” (spurious links that obscure structure), heat bath temperature T, and system size N. The partition of a graph into q optimally disjoint subgraphs or “communities” inherently requires Potts-type variables. In earlier work [Philos. Mag.1478-643510.1080/14786435.2011.616547 92, 406 (2012)], when examining power law and other networks (and general associated Potts models), we illustrated that transitions in the computational complexity of the community detection problem typically correspond to spin-glass-type transitions (and transitions to chaotic dynamics in mechanical analogs) at both high and low temperatures and/or noise. The computationally “hard” phase exhibits spin-glass type behavior including memory effects. The region over which the hard phase extends in the noise and temperature phase diagram decreases as N increases while holding the average number of nodes per community fixed. This suggests that in the thermodynamic limit a direct sharp transition may occur between the easy and unsolvable phases. When present, transitions at low temperature or low noise correspond to entropy driven (or “order by disorder”) annealing effects, wherein stability may initially increase as temperature or noise is increased before becoming unsolvable at sufficiently high temperature or noise. Additional transitions between contending viable solutions (such as those at different natural scales) are also possible. Identifying community structure via a dynamical approach where “chaotic-type” transitions were found earlier. The correspondence between the spin-glass-type complexity transitions and transitions into chaos in dynamical analogs might extend to other hard computational problems. In this work, we examine large networks (with a power law distribution in cluster size) that have a large number of communities (q≫1). We infer that large systems at a constant ratio of q to the number of nodes N asymptotically tend towards insolvability in the limit of large N for any positive T. The asymptotic behavior of temperatures below which structure identification might be possible, T×=O[1/lnq], decreases slowly, so for practical system sizes, there remains an accessible, and generally easy, global solvable phase at low temperature. We further employ multivariate Tutte polynomials to show that increasing q emulates increasing T for a general Potts model, leading to a similar stability region at low T. Given the relation between Tutte and Jones polynomials, our results further suggest a link between the above complexity transitions and transitions associated with random knots.

Food web structure shaped by habitat size and climate across a latitudinal gradient.

PubMed

Romero, Gustavo Q; Piccoli, Gustavo C O; de Omena, Paula M; Gonçalves-Souza, Thiago

2016-10-01

Habitat size and climate are known to affect the trophic structure and dynamics of communities, but their interactive effects are poorly understood. Organisms from different trophic levels vary in terms of metabolic requirements and heat dissipation. Indeed, larger species such as keystone predators require more stable climatic conditions than their prey. Likewise, habitat size disproportionally affects large-sized predators, which require larger home ranges and are thus restricted to larger habitats. Therefore, food web structure in patchy ecosystems is expected to be shaped by habitat size and climate variations. Here we investigate this prediction using natural aquatic microcosm (bromeliad phytotelmata) food webs composed of litter resources (mainly detritus), detritivores, mesopredators, and top predators (damselflies). We surveyed 240 bromeliads of varying sizes (water retention capacity) across 12 open restingas in SE Brazil spread across a wide range of tropical latitudes (-12.6° to -27.6°, ca. 2,000 km) and climates (Δ mean annual temperature = 5.3°C). We found a strong increase in predator-to-detritivore mass ratio with habitat size, which was representative of a typical inverted trophic pyramid in larger ecosystems. However, this relationship was contingent among the restingas; slopes of linear models were steeper in more stable and favorable climates, leading to inverted trophic pyramids (and top-down control) being more pronounced in environments with more favorable climatic conditions. By contrast, detritivore-resource and mesopredator-detritivore mass ratios were not affected by habitat size or climate variations across latitudes. Our results highlight that the combined effects of habitat size, climate and predator composition are pivotal to understanding the impacts of multiple environmental factors on food web structure and dynamics. © 2016 by the Ecological Society of America.

Relationships between adaptive and neutral genetic diversity and ecological structure and functioning: a meta-analysis

PubMed Central

Whitlock, Raj

2014-01-01

Understanding the effects of intraspecific genetic diversity on the structure and functioning of ecological communities is a fundamentally important part of evolutionary ecology and may also have conservation relevance in identifying the situations in which genetic diversity coincides with species-level diversity.Early studies within this field documented positive relationships between genetic diversity and ecological structure, but recent studies have challenged these findings. Conceptual synthesis has been hampered because studies have used different measures of intraspecific variation (phenotypically adaptive vs. neutral) and have considered different measures of ecological structure in different ecological and spatial contexts. The aim of this study is to strengthen conceptual understanding by providing an empirical synthesis quantifying the relationship between genetic diversity and ecological structure.Here, I present a meta-analysis of the relationship between genetic diversity within plant populations and the structure and functioning of associated ecological communities (including 423 effect sizes from 70 studies). I used Bayesian meta-analyses to examine (i) the strength and direction of this relationship, (ii) the extent to which phenotypically adaptive and neutral (molecular) measures of diversity differ in their association with ecological structure and (iii) variation in outcomes among different measures of ecological structure and in different ecological contexts.Effect sizes measuring the relationship between adaptive diversity (genotypic richness) and both community- and ecosystem-level ecological responses were small, but significantly positive. These associations were supported by genetic effects on species richness and productivity, respectively.There was no overall association between neutral genetic diversity and measures of ecological structure, but a positive correlation was observed under a limited set of demographic conditions. These results suggest that adaptive and neutral genetic diversity should not be treated as ecologically equivalent measures of intraspecific variation.Synthesis. This study advances the debate over whether relationships between genetic diversity and ecological structure are either simply positive or negative, by showing how the strength and direction of these relationships changes with different measures of diversity and in different ecological contexts. The results provide a solid foundation for assessing when and where an expanded synthesis between ecology and genetics will be most fruitful. PMID:25210204

Baselines and null hypotheses for climate change: Phytoplankton biomass structure in the California Current

NASA Astrophysics Data System (ADS)

Landry, M. R.; Taylor, A. G.

2016-02-01

Phytoplankton community structure is shaped both by the bottom-up influences of the physical-chemical environment and by the top-down impacts of food webs. Emergent patterns in the contemporary ocean can thus be "null hypotheses" of future changes assuming that the underlying structuring relationships remain intact but only shift spatially. To provide such a context for the California Current Ecosystem (CCE) and adjacent open-ocean ecosystems, we used a combination of digital epifluorescence microscopy and flow cytometry to investigate variability of phytoplankton biomass, composition and size structure across gradients of ecosystem richness, as represented by total autotrophic carbon (AC). Biomass of large micro-sized (>20 µm) phytoplankton increases as a power function with system richness. Nano-sized cells (2-20 µm) increase at a lower rate at low AC, and level off at high AC. Pico-sized cells (<2-µm) do not clearly dominate at low AC and decline significantly at high AC, neither predicted by competition theory. This study provides several new insights into structural relationships and mechanisms in the CCE: 1) diatoms and dinoflagellates co-dominate the micro-phytoplankton size class throughout the range of system richness; 2) nano-phytoplankton co-dominate biomass in oligotrophic (low AC) waters, suggesting widespread mixotrophy rather than direct competition with pico-phytoplankton for nutrients; and 3) the pico-phytoplankton decline at high AC impacts small eukaryotes as well as photosynthetic bacteria, consistent with a broad stimulation of grazing pressure on all bacterial-sized cells in richer systems. Observed variability in heterotrophic bacteria and nano-flagellate grazers with system richness is consistent with this mechanism.

A local immunization strategy for networks with overlapping community structure

NASA Astrophysics Data System (ADS)

Taghavian, Fatemeh; Salehi, Mostafa; Teimouri, Mehdi

2017-02-01

Since full coverage treatment is not feasible due to limited resources, we need to utilize an immunization strategy to effectively distribute the available vaccines. On the other hand, the structure of contact network among people has a significant impact on epidemics of infectious diseases (such as SARS and influenza) in a population. Therefore, network-based immunization strategies aim to reduce the spreading rate by removing the vaccinated nodes from contact network. Such strategies try to identify more important nodes in epidemics spreading over a network. In this paper, we address the effect of overlapping nodes among communities on epidemics spreading. The proposed strategy is an optimized random-walk based selection of these nodes. The whole process is local, i.e. it requires contact network information in the level of nodes. Thus, it is applicable to large-scale and unknown networks in which the global methods usually are unrealizable. Our simulation results on different synthetic and real networks show that the proposed method outperforms the existing local methods in most cases. In particular, for networks with strong community structures, high overlapping membership of nodes or small size communities, the proposed method shows better performance.

Response of rhizosphere microbial community structure and diversity to heavy metal co-pollution in arable soil.

PubMed

Deng, Linjing; Zeng, Guangming; Fan, Changzheng; Lu, Lunhui; Chen, Xunfeng; Chen, Ming; Wu, Haipeng; He, Xiaoxiao; He, Yan

2015-10-01

Due to the emerging environmental issues related to heavy metals, concern about the soil quality of farming lands near manufacturing district is increasing. Investigating the function of soil microorganisms exposed to long-term heavy metal contamination is meaningful and important for agricultural soil utilization. This article studied the potential influence of several heavy metals on microbial biomass, activity, abundance, and community composition in arable soil near industrial estate in Zhuzhou, Hunan province, China. The results showed that soil organic contents (SOC) were significantly positive correlated with heavy metals, whereas dehydrogenase activity (DHA) was greatly depressed by the heavy metal stress. Negative correlation was found between heavy metals and basal soil respiration (BSR), and no correlation was found between heavy metals and microbial biomass content (MBC). The quantitative PCR (QPCR) and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis could suggest that heavy metal pollution has significantly decreased abundance of bacteria and fungi and also changed their community structure. The results could contribute to evaluate heavy metal pollution level in soil. By combining different environmental parameters, it would promote the better understanding of heavy metal effect on the size, structure, and activity of microbial community in arable soil.

Implications of dredging induced changes in sediment particle size composition for the structure and function of marine benthic macrofaunal communities.

PubMed

Cooper, K M; Curtis, M; Wan Hussin, W M R; Barrio Froján, C R S; Defew, E C; Nye, V; Paterson, D M

2011-10-01

A meta-analysis approach was used to assess the effect of dredging induced changes in sediment composition, under different conditions of natural physical disturbance, for the structure and function of marine benthic macrofaunal communities. Results showed the sensitivity of macrofaunal communities increased as both the proportion of gravel increased and the level of natural physical disturbance decreased. These findings may be explained by the close association of certain taxa with the gravel fraction, and the influence of natural physical disturbance which, as it increases, tends to restrict the colonisation by these species. We conclude that maintaining the gravel content of surface sediments after dredging and, where practicable, locating extraction sites in areas of higher natural disturbance will minimise the potential for long-term negative impacts on the macrofauna. Crown Copyright © 2011. Published by Elsevier Ltd. All rights reserved.

Lag effects in the impacts of mass coral bleaching on coral reef fish, fisheries, and ecosystems.

PubMed

Graham, Nicholas A J; Wilson, Shaun K; Jennings, Simon; Polunin, Nicholas V C; Robinson, Jan; Bijoux, Jude P; Daw, Tim M

2007-10-01

Recent episodes of coral bleaching have led to wide-scale loss of reef corals and raised concerns over the effectiveness of existing conservation and management efforts. The 1998 bleaching event was most severe in the western Indian Ocean, where coral declined by up to 90% in some locations. Using fisheries-independent data, we assessed the long-term impacts of this event on fishery target species in the Seychelles, the overall size structure of the fish assemblage, and the effectiveness of two marine protected areas (MPAs) in protecting fish communities. The biomass of fished species above the size retained in fish traps changed little between 1994 and 2005, indicating no current effect on fishery yields. Biomass remained higher in MPAs, indicating they were effective in protecting fish stocks. Nevertheless, the size structure of the fish communities, as described with size-spectra analysis, changed in both fished areas and MPAs, with a decline in smaller fish (<30 cm) and an increase in larger fish (>45 cm). We believe this represents a time-lag response to a reduction in reef structural complexity brought about because fishes are being lost through natural mortality and fishing, and are not being replaced by juveniles. This effect is expected to be greater in terms of fisheries productivity and, because congruent patterns are observed for herbivores, suggests that MPAs do not offer coral reefs long-term resilience to bleaching events. Corallivores and planktivores declined strikingly in abundance, particularly in MPAs, and this decline was associated with a similar pattern of decline in their preferred corals. We suggest that climate-mediated disturbances, such as coral bleaching, be at the fore of conservation planning for coral reefs.

Functional Process Zones Characterizing Aquatic Insect Communities in Streams of the Brazilian Cerrado.

PubMed

Godoy, B S; Simião-Ferreira, J; Lodi, S; Oliveira, L G

2016-04-01

Stream ecology studies see to understand ecological dynamics in lotic systems. The characterization of streams into Functional Process Zones (FPZ) has been currently debated in stream ecology because aquatic communities respond to functional processes of river segments. Therefore, we tested if different functional process zones have different number of genera and trophic structure using the aquatic insect community of Neotropical streams. We also assessed whether using physical and chemical variables may complement the approach of using FPZ to model communities of aquatic insects in Cerrado streams. This study was conducted in 101 streams or rivers from the central region of the state of Goiás, Brazil. We grouped the streams into six FPZ associated to size of the river system, presence of riparian forest, and riverbed heterogeneity. We used Bayesian models to compare number of genera and relative frequency of the feeding groups between FPZs. Streams classified in different FPZs had a different number of genera, and the largest and best preserved rivers had an average of four additional genera. Trophic structure exhibited low variability among FPZs, with little difference both in the number of genera and in abundance. Using functional process zones in Cerrado streams yielded good results for Ephemeroptera, Plecoptera, and Trichoptera communities. Thus, species distribution and community structure in the river basin account for functional processes and not necessarily for the position of the community along a longitudinal dimension of the lotic system.

Neighborhood diversity of large trees shows independent species patterns in a mixed dipterocarp forest in Sri Lanka.

PubMed

Punchi-Manage, Ruwan; Wiegand, Thorsten; Wiegand, Kerstin; Getzin, Stephan; Huth, Andreas; Gunatilleke, C V Savitri; Gunatilleke, I A U Nimal

2015-07-01

Interactions among neighboring individuals influence plant performance and should create spatial patterns in local community structure. In order to assess the role of large trees in generating spatial patterns in local species richness, we used the individual species-area relationship (ISAR) to evaluate the species richness of trees of different size classes (and dead trees) in circular neighborhoods with varying radius around large trees of different focal species. To reveal signals of species interactions, we compared the ISAR function of the individuals of focal species with that of randomly selected nearby locations. We expected that large trees should strongly affect the community structure of smaller trees in their neighborhood, but that these effects should fade away with increasing size class. Unexpectedly, we found that only few focal species showed signals of species interactions with trees of the different size classes and that this was less likely for less abundant focal species. However, the few and relatively weak departures from independence were consistent with expectations of the effect of competition for space and the dispersal syndrome on spatial patterns. A noisy signal of competition for space found for large trees built up gradually with increasing life stage; it was not yet present for large saplings but detectable for intermediates. Additionally, focal species with animal-dispersed seeds showed higher species richness in their neighborhood than those with gravity- and gyration-dispersed seeds. Our analysis across the entire ontogeny from recruits to large trees supports the hypothesis that stochastic effects dilute deterministic species interactions in highly diverse communities. Stochastic dilution is a consequence of the stochastic geometry of biodiversity in species-rich communities where the identities of the nearest neighbors of a given plant are largely unpredictable. While the outcome of local species interactions is governed for each plant by deterministic fitness and niche differences, the large variability of competitors causes also a large variability in the outcomes of interactions and does not allow for strong directed responses at the species level. Collectively, our results highlight the critical effect of the stochastic geometry of biodiversity in structuring local spatial patterns of tropical forest diversity.

Extension of research data repository system to support direct compute access to biomedical datasets: enhancing Dataverse to support large datasets.

PubMed

McKinney, Bill; Meyer, Peter A; Crosas, Mercè; Sliz, Piotr

2017-01-01

Access to experimental X-ray diffraction image data is important for validation and reproduction of macromolecular models and indispensable for the development of structural biology processing methods. In response to the evolving needs of the structural biology community, we recently established a diffraction data publication system, the Structural Biology Data Grid (SBDG, data.sbgrid.org), to preserve primary experimental datasets supporting scientific publications. All datasets published through the SBDG are freely available to the research community under a public domain dedication license, with metadata compliant with the DataCite Schema (schema.datacite.org). A proof-of-concept study demonstrated community interest and utility. Publication of large datasets is a challenge shared by several fields, and the SBDG has begun collaborating with the Institute for Quantitative Social Science at Harvard University to extend the Dataverse (dataverse.org) open-source data repository system to structural biology datasets. Several extensions are necessary to support the size and metadata requirements for structural biology datasets. In this paper, we describe one such extension-functionality supporting preservation of file system structure within Dataverse-which is essential for both in-place computation and supporting non-HTTP data transfers. © 2016 New York Academy of Sciences.

Recolonization of macrozoobenthos on defaunated sediments in a hypertrophic brackish lagoon: effects of sulfide removal and sediment grain size.

PubMed

Kanaya, Gen

2014-04-01

Influences of sediment types on recolonization of estuarine macrozoobenthos were tested using enclosures in a hypertrophic lagoon. Three types of azoic sediment, sand (S), sulfide-rich mud (M), and mud removed of sulfide through iron addition (MFe), were set in field for 35 days during a hypoxic period. A total of 14 taxa including opportunistic polychaetes and amphipods occurred. Infaunal community in S treatment was characterized by highest diversity, total density and biomass, and population density of five dominant taxa, while those parameters were lowest in M treatment. Sulfide removal in MFe treatment achieved much higher density, biomass, and population densities of several taxa in the sediment. Multivariate analyses demonstrated that the established community structure was unique to each treatment. These imply that dissolved sulfide level as well as sediment grain size is a key determinant for the community composition and recolonization speed of early colonists in estuarine soft-bottom habitats. Copyright © 2014 Elsevier Ltd. All rights reserved.

Emergent neutrality drives phytoplankton species coexistence

PubMed Central

Segura, Angel M.; Calliari, Danilo; Kruk, Carla; Conde, Daniel; Bonilla, Sylvia; Fort, Hugo

2011-01-01

The mechanisms that drive species coexistence and community dynamics have long puzzled ecologists. Here, we explain species coexistence, size structure and diversity patterns in a phytoplankton community using a combination of four fundamental factors: organism traits, size-based constraints, hydrology and species competition. Using a ‘microscopic’ Lotka–Volterra competition (MLVC) model (i.e. with explicit recipes to compute its parameters), we provide a mechanistic explanation of species coexistence along a niche axis (i.e. organismic volume). We based our model on empirically measured quantities, minimal ecological assumptions and stochastic processes. In nature, we found aggregated patterns of species biovolume (i.e. clumps) along the volume axis and a peak in species richness. Both patterns were reproduced by the MLVC model. Observed clumps corresponded to niche zones (volumes) where species fitness was highest, or where fitness was equal among competing species. The latter implies the action of equalizing processes, which would suggest emergent neutrality as a plausible mechanism to explain community patterns. PMID:21177680

Ecosystem size structure response to 21st century climate projection: large fish abundance decreases in the central North Pacific and increases in the California Current.

PubMed

Woodworth-Jefcoats, Phoebe A; Polovina, Jeffrey J; Dunne, John P; Blanchard, Julia L

2013-03-01

Output from an earth system model is paired with a size-based food web model to investigate the effects of climate change on the abundance of large fish over the 21st century. The earth system model, forced by the Intergovernmental Panel on Climate Change (IPCC) Special report on emission scenario A2, combines a coupled climate model with a biogeochemical model including major nutrients, three phytoplankton functional groups, and zooplankton grazing. The size-based food web model includes linkages between two size-structured pelagic communities: primary producers and consumers. Our investigation focuses on seven sites in the North Pacific, each highlighting a specific aspect of projected climate change, and includes top-down ecosystem depletion through fishing. We project declines in large fish abundance ranging from 0 to 75.8% in the central North Pacific and increases of up to 43.0% in the California Current (CC) region over the 21st century in response to change in phytoplankton size structure and direct physiological effects. We find that fish abundance is especially sensitive to projected changes in large phytoplankton density and our model projects changes in the abundance of large fish being of the same order of magnitude as changes in the abundance of large phytoplankton. Thus, studies that address only climate-induced impacts to primary production without including changes to phytoplankton size structure may not adequately project ecosystem responses. © 2012 Blackwell Publishing Ltd.

Atoll-scale patterns in coral reef community structure: Human signatures on Ulithi Atoll, Micronesia

PubMed Central

Nelson, Peter; Abelson, Avigdor; Precoda, Kristin; Rulmal, John; Bernardi, Giacomo; Paddack, Michelle

2017-01-01

The dynamic relationship between reefs and the people who utilize them at a subsistence level is poorly understood. This paper characterizes atoll-scale patterns in shallow coral reef habitat and fish community structure, and correlates these with environmental characteristics and anthropogenic factors, critical to conservation efforts for the reefs and the people who depend on them. Hierarchical clustering analyses by site for benthic composition and fish community resulted in the same 3 major clusters: cluster 1–oceanic (close proximity to deep water) and uninhabited (low human impact); cluster 2–oceanic and inhabited (high human impact); and cluster 3–lagoonal (facing the inside of the lagoon) and inhabited (highest human impact). Distance from village, reef exposure to deep water and human population size had the greatest effect in predicting the fish and benthic community structure. Our study demonstrates a strong association between benthic and fish community structure and human use across the Ulithi Atoll (Yap State, Federated States of Micronesia) and confirms a pattern observed by local people that an ‘opportunistic’ scleractinian coral (Montipora sp.) is associated with more highly impacted reefs. Our findings suggest that small human populations (subsistence fishing) can nevertheless have considerable ecological impacts on reefs due, in part, to changes in fishing practices rather than overfishing per se, as well as larger global trends. Findings from this work can assist in building local capacity to manage reef resources across an atoll-wide scale, and illustrates the importance of anthropogenic impact even in small communities. PMID:28489903

Simulation modeling to understand how selective foraging by beaver can drive the structure and function of a willow community

USGS Publications Warehouse

Peinetti, H.R.; Baker, B.W.; Coughenour, M.B.

2009-01-01

Beaver-willow (Castor-Salix) communities are a unique and vital component of healthy wetlands throughout the Holarctic region. Beaver selectively forage willow to provide fresh food, stored winter food, and construction material. The effects of this complex foraging behavior on the structure and function of willow communities is poorly understood. Simulation modeling may help ecologists understand these complex interactions. In this study, a modified version of the SAVANNA ecosystem model was developed to better understand how beaver foraging affects the structure and function of a willow community in a simulated riparian ecosystem in Rocky Mountain National Park, Colorado (RMNP). The model represents willow in terms of plant and stem dynamics and beaver foraging in terms of the quantity and quality of stems cut to meet the energetic and life history requirements of beaver. Given a site where all stems were equally available, the model suggested a simulated beaver family of 2 adults, 2 yearlings, and 2 kits required a minimum of 4 ha of willow (containing about10 stems m-2) to persist in a steady-state condition. Beaver created a willow community where the annual net primary productivity (ANPP) was 2 times higher and plant architecture was more diverse than the willow community without beaver. Beaver foraging created a plant architecture dominated by medium size willow plants, which likely explains how beaver can increase ANPP. Long-term simulations suggested that woody biomass stabilized at similar values even though availability differed greatly at initial condition. Simulations also suggested that willow ANPP increased across a range of beaver densities until beaver became food limited. Thus, selective foraging by beaver increased productivity, decreased biomass, and increased structural heterogeneity in a simulated willow community.

Land-use and land-management change: relationships with earthworm and fungi communities and soil structural properties.

PubMed

Spurgeon, David J; Keith, Aidan M; Schmidt, Olaf; Lammertsma, Dennis R; Faber, Jack H

2013-12-01

Change in land use and management can impact massively on soil ecosystems. Ecosystem engineers and other functional biodiversity in soils can be influenced directly by such change and this in turn can affect key soil functions. Here, we employ meta-analysis to provide a quantitative assessment of the effects of changes in land use and land management across a range of successional/extensification transitions (conventional arable → no or reduced tillage → grassland → wooded land) on community metrics for two functionally important soil taxa, earthworms and fungi. An analysis of the relationships between community change and soil structural properties was also included. Meta-analysis highlighted a consistent trend of increased earthworm and fungal community abundances and complexity following transitions to lower intensity and later successional land uses. The greatest changes were seen for early stage transitions, such as introduction of reduced tillage regimes and conversion to grassland from arable land. Not all changes, however, result in positive effects on the assessed community metrics. For example, whether woodland conversion positively or negatively affects community size and complexity depends on woodland type and, potentially, the changes in soil properties, such as pH, that may occur during conversion. Alterations in soil communities tended to facilitate subsequent changes in soil structure and hydrology. For example, increasing earthworm abundances and functional group composition were shown to be positively correlated with water infiltration rate (dependent on tillage regime and habitat characteristics); while positive changes in fungal biomass measures were positively associated with soil microaggregate stability. These findings raise the potential to manage landscapes to increase ecosystem service provision from soil biota in relation to regulation of soil structure and water flow.

Physical Factors Correlate to Microbial Community Structure and Nitrogen Cycling Gene Abundance in a Nitrate Fed Eutrophic Lagoon.

PubMed

Highton, Matthew P; Roosa, Stéphanie; Crawshaw, Josie; Schallenberg, Marc; Morales, Sergio E

2016-01-01

Nitrogenous run-off from farmed pastures contributes to the eutrophication of Lake Ellesmere, a large shallow lagoon/lake on the east coast of New Zealand. Tributaries periodically deliver high loads of nitrate to the lake which likely affect microbial communities therein. We hypothesized that a nutrient gradient would form from the potential sources (tributaries) creating a disturbance resulting in changes in microbial community structure. To test this we first determined the existence of such a gradient but found only a weak nitrogen (TN) and phosphorous gradient (DRP). Changes in microbial communities were determined by measuring functional potential (quantification of nitrogen cycling genes via nifH , nirS , nosZI , and nosZII using qPCR), potential activity (via denitrification enzyme activity), as well as using changes in total community (via 16S rRNA gene amplicon sequencing). Our results demonstrated that changes in microbial communities at a phylogenetic (relative abundance) and functional level (proportion of the microbial community carrying nifH and nosZI genes) were most strongly associated with physical gradients (e.g., lake depth, sediment grain size, sediment porosity) and not nutrient concentrations. Low nitrate influx at the time of sampling is proposed as a factor contributing to the observed patterns.

A Functional Approach to Zooplankton Communities in Mountain Lakes Stocked With Non-Native Sportfish Under a Changing Climate

NASA Astrophysics Data System (ADS)

Redmond, Laura E.; Loewen, Charlie J. G.; Vinebrooke, Rolf D.

2018-03-01

Cumulative impacts of multiple stressors on freshwater biodiversity and ecosystem function likely increase with elevation, thereby possibly placing alpine communities at greatest risk. Here, consideration of species traits enables stressor effects on taxonomic composition to be translated into potential functional impacts. We analyzed data for 47 taxa across 137 mountain lakes and ponds spanning large latitudinal (491 km) and elevational (1,399 m) gradients in western Canada, to assess regional and local factors of the taxonomic composition and functional structure of zooplankton communities. Multivariate community analyses revealed that small body size, clonal reproduction via parthenogenesis, and lack of pigmentation were species traits associated with both introduced non-native sportfish and also environmental conditions reflecting a warmer and drier climate—namely higher water temperatures, shallower water depths, and more chemically concentrated water. Thus, historical introductions of sportfish appear to have potentially induced greater tolerance in zooplankton communities of future climatic warming, especially in previously fishless alpine lakes. Although alpine lake communities occupied a relatively small functional space (i.e., low functional diversity), they were contained within the broader regional functional structure. Therefore, our findings point to the importance of dispersal by lower montane species to the future functional stability of alpine communities.

Too risky to settle: avian community structure changes in response to perceived predation risk on adults and offspring

USGS Publications Warehouse

Hua, Fangyuan; Fletcher, Robert J.; Sieving, Kathryn E.; Dorazio, Robert M.

2013-01-01

Predation risk is widely hypothesized as an important force structuring communities, but this potential force is rarely tested experimentally, particularly in terrestrial vertebrate communities. How animals respond to predation risk is generally considered predictable from species life-history and natural-history traits, but rigorous tests of these predictions remain scarce. We report on a large-scale playback experiment with a forest bird community that addresses two questions: (i) does perceived predation risk shape the richness and composition of a breeding bird community? And (ii) can species life-history and natural-history traits predict prey community responses to different types of predation risk? On 9 ha plots, we manipulated cues of three avian predators that preferentially prey on either adult birds or offspring, or both, throughout the breeding season. We found that increased perception of predation risk led to generally negative responses in the abundance, occurrence and/or detection probability of most prey species, which in turn reduced the species richness and shifted the composition of the breeding bird community. Species-level responses were largely predicted from the key natural-history trait of body size, but we did not find support for the life-history theory prediction of the relationship between species' slow/fast life-history strategy and their response to predation risk.

High frequency responses of nanoplankton and microplankton to wind-driven upwelling off northern Chile

NASA Astrophysics Data System (ADS)

Aguilera, Victor; Escribano, Ruben; Herrera, Liliana

2009-08-01

Autotrophic and heterotrophic nanoplankton and microplankton vary widely in quantity and composition in coastal upwelling zones, causing a highly heterogeneous distribution of food resources for higher trophic levels. Here, we assessed daily changes in size-fractioned biomass and community structure of nanoplankton and microplankton at two upwelling sites off northern Chile, Mejillones (23°S) and Chipana (21°S), during summer 2006, winter 2006 and summer 2007 as related to changes in oceanographic conditions upon upwelling variation. We found highly-significant changes in quantity and community structure (species diversity and richness) of both nanoplankton and microplankton fractions after 3-5 days of observations. These changes were coupled to an intermittent upwelling regime reflected in the alongshore component of the wind. After a few days the whole community was modified in terms of species and size structure. Over-imposing this variability, during winter 2006 there was a strong perturbation of remote origin that substantially impacted temperature, oxygenation and stratification of the water column. This "abnormal" warming event altered the upwelling regime, but its impact on abundance and composition of the nanoplankton and microplankton fractions was uncertain. Over the short-time scale however, we found a strong coupling between daily changes in the alongshore component of wind and nanoplankton and microplankton abundances and their structure. All these findings indicate that despite the high biological productivity of this upwelling region, high frequency variation induced by wind forcing may be a major regulator of food resources (quantity and quality) for primary consumers, such as zooplankton, fish larvae and benthic organisms in the near-shore area. This high frequency variation may also impose a key constrain for prey-predator encounter rates and survival of short-lived zooplankton and invertebrate and fish larvae in the upwelling zone.

Community structure of Aspergillus flavus and A. parasiticus in major almond producing areas of California, United States

USDA-ARS?s Scientific Manuscript database

Several nut crops including almonds, pistachios, and walnuts can become contaminated with mycotoxins. Of greatest economic significance are aflatoxins, which are mainly produced by members of Aspergillus section Flavi. The distribution of the two sclerotial-size morphotypes of A. flavus (i.e. S and ...

Ecology in Urban Education.

ERIC Educational Resources Information Center

Johnson, Letitia K.; Ryan, Michael

In this course guide to the teaching of urban ecology, six learning activities on the following topics are outlined: (1) city location and growth; (2) an in-depth study of New Orleans; (3) city shape and structure; (4) size and spacing of cities; (5) cities with special functions; (6) local community study. Educational objectives for each activity…

Uncovering collective listening habits and music genres in bipartite networks.

PubMed

Lambiotte, R; Ausloos, M

2005-12-01

In this paper, we analyze web-downloaded data on people sharing their music library, that we use as their individual musical signatures. The system is represented by a bipartite network, nodes being the music groups and the listeners. Music groups' audience size behaves like a power law, but the individual music library size is an exponential with deviations at small values. In order to extract structures from the network, we focus on correlation matrices, that we filter by removing the least correlated links. This percolation idea-based method reveals the emergence of social communities and music genres, that are visualized by a branching representation. Evidence of collective listening habits that do not fit the neat usual genres defined by the music industry indicates an alternative way of classifying listeners and music groups. The structure of the network is also studied by a more refined method, based upon a random walk exploration of its properties. Finally, a personal identification-community imitation model for growing bipartite networks is outlined, following Potts ingredients. Simulation results do reproduce quite well the empirical data.

Uncovering collective listening habits and music genres in bipartite networks

NASA Astrophysics Data System (ADS)

Lambiotte, R.; Ausloos, M.

2005-12-01

In this paper, we analyze web-downloaded data on people sharing their music library, that we use as their individual musical signatures. The system is represented by a bipartite network, nodes being the music groups and the listeners. Music groups’ audience size behaves like a power law, but the individual music library size is an exponential with deviations at small values. In order to extract structures from the network, we focus on correlation matrices, that we filter by removing the least correlated links. This percolation idea-based method reveals the emergence of social communities and music genres, that are visualized by a branching representation. Evidence of collective listening habits that do not fit the neat usual genres defined by the music industry indicates an alternative way of classifying listeners and music groups. The structure of the network is also studied by a more refined method, based upon a random walk exploration of its properties. Finally, a personal identification-community imitation model for growing bipartite networks is outlined, following Potts ingredients. Simulation results do reproduce quite well the empirical data.

Sandy beaches in a coastline vulnerable to erosion in Atlantic Canada: Macrobenthic community structure in relation to backshore and physical features

NASA Astrophysics Data System (ADS)

MacMillan, Mitchell R.; Duarte, Cristian; Quijón, Pedro A.

2017-07-01

Most literature suggests that sandy beach macrobenthic communities are structured by physical factors. However, an aspect that has not been studied in detail is whether those physical factors change with erosion or the association of beaches to backshore features like sand dunes, till bluffs, and sandstone cliffs. We addressed this question by sampling 14 sandy beaches on the north shore of Prince Edward Island, Atlantic Canada. Two null hypotheses were tested: first, there is no relationship between physical factors and community descriptors across sandy beaches, and second, there is no difference among beaches associated with distinct backshore features both in terms of physical factors and community descriptors. In order to test these hypotheses, samples of macrobenthic organisms and measurements of grain size, slope, beach deposit index and erosion rates were obtained. Our surveys collected a total of 14 taxa numerically dominated by the spionid polychaete Scolelepis squamata. With regards to the first hypothesis, regression analyses showed that community descriptors were all positively related to erosion rates while unrelated to the variation in grain size, slope and beach deposit index. As for the second hypothesis, erosion rates were significantly different among beaches associated to till bluffs (highest), dunes and sandstone cliffs (lowest). Meanwhile, the other physical factors did not significantly differ among backshore features. Species richness was highest in beaches associated to till bluffs and lowest in those associated to sandstone cliffs. Abundance values were also lowest in beaches associated to sandstone cliffs, and their community composition was significantly different to those associated to dunes and till bluffs. We suggest that the relationship between erosion rates and community descriptors is complex and may be mediated by the availability of nutrients: higher erosion levels might account for higher concentrations of nutrients for suspension feeders, the numerically dominant organisms in this system. We call for further attention to the relationship between erosion and suspended nutrients.

Animal diversity and ecosystem functioning in dynamic food webs

NASA Astrophysics Data System (ADS)

Schneider, Florian D.; Brose, Ulrich; Rall, Björn C.; Guill, Christian

2016-10-01

Species diversity is changing globally and locally, but the complexity of ecological communities hampers a general understanding of the consequences of animal species loss on ecosystem functioning. High animal diversity increases complementarity of herbivores but also increases feeding rates within the consumer guild. Depending on the balance of these counteracting mechanisms, species-rich animal communities may put plants under top-down control or may release them from grazing pressure. Using a dynamic food-web model with body-mass constraints, we simulate ecosystem functions of 20,000 communities of varying animal diversity. We show that diverse animal communities accumulate more biomass and are more exploitative on plants, despite their higher rates of intra-guild predation. However, they do not reduce plant biomass because the communities are composed of larger, and thus energetically more efficient, plant and animal species. This plasticity of community body-size structure reconciles the debate on the consequences of animal species loss for primary productivity.

Habitat fragmentation effects depend on complex interactions between population size and dispersal ability: Modeling influences of roads, agriculture and residential development across a range of life-history characteristics [chapter 20

Treesearch

Samuel A. Cushman; Bradley W. Compton; Kevin McGarigal

2010-01-01

Habitat loss and fragmentation are widely believed to be the most important drivers of extinction (Leakey and Lewin 1995). The habitats in which organisms live are spatially structured at a number of scales, and these patterns interact with organism perception and behavior to drive population dynamics and community structure (Johnson et al. 1992). Anthropogenic habitat...

A qualitative approach using the integrative model of behaviour change to identify intervention strategies to increase optimal child restraint practices among culturally and linguistically diverse families in New South Wales.

PubMed

Brown, Julie; Burton, Danielle; Nikolin, Stevan; Crooks, Philippa Jane; Hatfield, Julie; Bilston, Lynne E

2013-02-01

To qualitatively explore barriers to optimal child restraint use using the integrative behaviour change model in culturally and linguistically diverse (CALD) communities in New South Wales (NSW), Australia. A semi-structured discussion was used to conduct 11 language specific focus groups in Arabic, Assyrian, Cantonese, Mandarin, Vietnamese and Turkish. Translated transcriptions were analysed using the major concepts of the integrative behaviour change model. Restraint use intent among CALD community carers is related to perceived safety of their children and complying with the law. While most participants appreciated the safety benefits of correct and appropriate use, a minority did not. Child restraint legislation may positively influence social norms, and enforcement appears to increase parental self-efficacy. However, concerns over child comfort may negatively influence both norms and self-efficacy. There are clear deficits in knowledge that may act as barriers as well as confusion over best practice in safely transporting children. Large family size, vehicle size and cost appear to be real environmental constraints in CALD communities. Determinants of intent and deficits in knowledge in this diverse range of CALD communities in NSW Australia are similar to those reported in other qualitative studies regardless of the population studied. This indicates that key messages should be the same regardless of the target population. However, for CALD communities there is a specific need to ensure access to detailed information through appropriate delivery strategies and languages. Furthermore, practical constraints such as cost of restraints and family size may be particularly important in CALD communities.

Correlations between community size and student perceptions of value.

PubMed

Anderson, Susan M; Simanton, Edward

2017-01-01

The purpose of this study was to determine if medical students' feeling of being valued was correlated to community size. The study, conducted in several communities in South Dakota, examined students' feeling of value relating to attending physicians, healthcare teams and patients. Student value items were added to student satisfaction surveys sent out to students at the end of their primary clinical year and data collected from two graduating classes of students (n=114). Student responses were grouped by clinical campus and mean responses by community size were calculated. Additionally, student encounter logs were reviewed for study participants to gauge participation levels during clinical encounters. The degree to which students felt valued by their physician attending, the healthcare team and the patients decreased consistently as community size increased. Differences were statistically significant between students in the smallest and largest communities. Additionally, students in the community of 15 000 felt significantly more valued than students in the community of 170 000. Furthermore, there also appears to be a relationship between the percentage of participation in patient care by students and community size. Students in the smaller, rural communities participated at a higher percentage rather than observing. There appears to be a relationship between community size and the extent to which students feel value. The degree to which students felt valued decreased consistently as community size increased. Differences were statistically significant between students in the smallest communities and the two largest communities. Students in the smaller, rural communities participated at a higher percentage. Additional studies are needed to address whether students participate more as a result of feeling valued, or whether participation leads to an enhanced perception of value by students.

Characteristics of bacterial community in cloud water at Mt Tai: similarity and disparity under polluted and non-polluted cloud episodes

NASA Astrophysics Data System (ADS)

Wei, Min; Xu, Caihong; Chen, Jianmin; Zhu, Chao; Li, Jiarong; Lv, Ganglin

2017-04-01

Bacteria are widely distributed in atmospheric aerosols and are indispensable components of clouds, playing an important role in the atmospheric hydrological cycle. However, limited information is available about the bacterial community structure and function, especially for the increasing air pollution in the North China Plain. Here, we present a comprehensive characterization of bacterial community composition, function, variation, and environmental influence for cloud water collected at Mt Tai from 24 July to 23 August 2014. Using Miseq 16S rRNA gene sequencing, the highly diverse bacterial community in cloud water and the predominant phyla of Proteobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes were investigated. Bacteria that survive at low temperature, radiation, and poor nutrient conditions were found in cloud water, suggesting adaption to an extreme environment. The bacterial gene functions predicted from the 16S rRNA gene using the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) suggested that the pathways related to metabolism and disease infections were significantly correlated with the predominant genera. The abundant genera Acinetobacter, Stenotrophomonas, Pseudomonas, and Empedobacter originated from a wide range of habitats including cloud condensation nuclei and ice nuclei active species, opportunistic pathogens, and functional species, demonstrating the importance of ecology and health in cloud water. Cluster analysis including hierarchical cluster (Hcluster) and principal coordinate analysis (PCoA) indicated a significant disparity between polluted and non-polluted samples. Linear discriminant analysis effect size (LEfSe) demonstrated that potential pathogens were enriched in the polluted cloud samples, whereas the diverse ecological function groups were significant in the non-polluted samples. Discrepant community structure determined by redundancy analysis (RDA) indicated that the major ions in cloud water and PM2. 5 in the atmosphere have a negative impact on bacteria, playing a vital role in shaping microbial community structure. The major ions might provide nutrition to bacteria and directly influence the bacterial community, whereas PM2. 5 in air has an indirect impact on bacterial community structure. During wet deposition, soluble particulate matter was dissolved in water droplets resulting in elevated concentration in cloud water. PM2. 5 was possibly associated with different origins and pathways of air mass as determined using source tracking by the backward trajectory, mainly related to long-range transport. This work enhanced our understanding of the characteristics of bacterial ecology in the atmospheric aqueous phase, highlighting the potential influence of environmental variables on the bacterial community in cloud processes. It may provide fundamental information of the bacterial community response in cloud water under increasing pollution. However, due to the limited sample size (13 samples) collected at the summit of Mt Tai, these issues need in-depth discussion. Further studies based on an annual series of field observation experiments and laboratory simulations will continue to track these issues.

Efficient local behavioral-change strategies to reduce the spread of epidemics in networks

NASA Astrophysics Data System (ADS)

Bu, Yilei; Gregory, Steve; Mills, Harriet L.

2013-10-01

It has recently become established that the spread of infectious diseases between humans is affected not only by the pathogen itself but also by changes in behavior as the population becomes aware of the epidemic, for example, social distancing. It is also well known that community structure (the existence of relatively densely connected groups of vertices) in contact networks influences the spread of disease. We propose a set of local strategies for social distancing, based on community structure, that can be employed in the event of an epidemic to reduce the epidemic size. Unlike most social distancing methods, ours do not require individuals to know the disease state (infected or susceptible, etc.) of others, and we do not make the unrealistic assumption that the structure of the entire contact network is known. Instead, the recommended behavior change is based only on an individual's local view of the network. Each individual avoids contact with a fraction of his/her contacts, using knowledge of his/her local network to decide which contacts should be avoided. If the behavior change occurs only when an individual becomes ill or aware of the disease, these strategies can substantially reduce epidemic size with a relatively small cost, measured by the number of contacts avoided.

Weak and Habitat-Dependent Effects of Nutrient Pollution on Macrofaunal Communities of Southeast Australian Estuaries

PubMed Central

Nicastro, Andrea; Bishop, Melanie J.

2013-01-01

Among the impacts of coastal settlements to estuaries, nutrient pollution is often singled out as a leading cause of modification to the ecological communities of soft sediments. Through sampling of 48 sites, distributed among 16 estuaries of New South Wales, Australia, we tested the hypotheses that (1) anthropogenic nutrient loads would be a better predictor of macrofaunal communities than estuarine geomorphology or local sediment characteristics; and (2) local environmental context, as determined largely by sediment characteristics, would modify the relationship between nutrient loading and community composition. Contrary to the hypothesis, multivariate multiple regression analyses revealed that sediment grain size was the best predictor of macrofaunal assemblage composition. When samples were stratified according to median grain size, relationships between faunal communities and nitrogen loading and latitude emerged, but only among estuaries with sandier sediments. In these estuaries, capitellid and nereid polychaetes and chironomid larvae were the taxa that showed the strongest correlations with nutrient loading. Overall, this study failed to provide evidence of a differential relationship between diffuse nutrient enrichment and benthic macrofauna across a gradient of 7° of latitude and 4°C temperature. Nevertheless, as human population growth continues to place increasing pressure on southeast Australian estuaries, manipulative field studies examining when and where nutrient loading will lead to significant changes in estuarine community structure are needed. PMID:23799037

Effects of trifluralin on the soil microbial community and functional groups involved in nitrogen cycling.

PubMed

Du, Pengqiang; Wu, Xiaohu; Xu, Jun; Dong, Fengshou; Liu, Xingang; Zheng, Yongquan

2018-04-10

Large amounts of trifluralin are applied each year for weed control; however, its effects on soil microbial communities and functions are unknown. Two agricultural soils, one silty loam and one silty clay were spiked with TFL (0, 0.84, 8.4, and 84 mg kg -1 ) and studied the effects using a laboratory microcosm approach. The half-lives were 44.19-61.83 d in all cases. Bacterial abundance increased 1.12-5.56 times by TFL, but the diversity decreased. From the next-generation sequencing results, TFL altered the bacterial community structure, which initially diverged from the control community structure, then recovered, and then diverged again. Linear discriminant analysis effect size indicated that Sphingomonas and Xanthomonadaceae were the predominant species on day 7 and 15 in TFL treatments. N 2 -fixing bacteria were initially increased, then decreased, and then recovered, and it was positively correlated with NH 4 + -N content. Compared with the control, ammonia-oxidizing bacteria were decreased by 25.51-92.63%, ammonia-oxidizing archaea were decreased by 17.12-85.21% (except day 7), and the NO 3 - -N concentration was also inhibited. In contrast to bacteria, fungal abundance was inhibited without any observable effects on fungal diversity or community structure. These results suggest that TFL impacts soil bacterial community and alters functional microorganisms involved in soil N processing. Copyright © 2018 Elsevier B.V. All rights reserved.

Antagonistic interactions are sufficient to explain self-assemblage of bacterial communities in a homogeneous environment: a computational modeling approach

PubMed Central

Zapién-Campos, Román; Olmedo-Álvarez, Gabriela; Santillán, Moisés

2015-01-01

Most of the studies in Ecology have been devoted to analyzing the effects the environment has on individuals, populations, and communities, thus neglecting the effects of biotic interactions on the system dynamics. In the present work we study the structure of bacterial communities in the oligotrophic shallow water system of Churince, Cuatro Cienegas, Mexico. Since the physicochemical conditions of this water system are homogeneous and quite stable in time, it is an excellent candidate to study how biotic factors influence the structure of bacterial communities. In a previous study, the binary antagonistic interactions of 78 bacterial strains, isolated from Churince, were experimentally determined. We employ these data to develop a computer algorithm to simulate growth experiments in a cellular grid representing the pond. Remarkably, in our model, the dynamics of all the simulated bacterial populations is determined solely by antagonistic interactions. Our results indicate that all bacterial strains (even those that are antagonized by many other bacteria) survive in the long term, and that the underlying mechanism is the formation of bacterial community patches. Patches corresponding to less antagonistic and highly susceptible strains are consistently isolated from the highly-antagonistic bacterial colonies by patches of neutral strains. These results concur with the observed features of the bacterial community structure previously reported. Finally, we study how our findings depend on factors like initial population size, differential population growth rates, homogeneous population death rates, and enhanced bacterial diffusion. PMID:26052318

Common Infrastructure for Neo Scientific and Planetary Defense Missions

NASA Technical Reports Server (NTRS)

Adams, Robert; Wilks, Rodney

2009-01-01

While defending the Earth against collisions with asteroids and comets has garnered increasing attention over the past few decades, our knowledge of the threats and methods of mitigation remain inadequate. There exists a considerable gap in knowledge regarding the size, composition, location, internal structure and formation of near earth asteroids and comets. Although estimates have been made, critical experiments have not yet been conducted on the effectiveness of various proposed mitigation techniques. Closing this knowledge gap is of interest to both the planetary defense and planetary science communities. Increased scientific knowledge of asteroid and comet composition and structure can confirm or advance current theories about the formation of the solar system. This proposal suggests a joint effort between these two communities to provide an economical architecture that supports multiple launches of characterization and mitigation payloads with minimal response time. The science community can use this architecture for characterization missions of opportunity when multiple scientific targets or targets of uncommon scientific value present themselves, while the planetary defense community would be able to fire characterization or mitigation payloads at targets that present a threat to the Earth. Both communities would benefit from testing potential mitigation techniques, which would reveal information on the internal structure of asteroids and comets. In return, the Earth would have the beginnings of a viable response system should an impact threat prove real in the near future.

Identifying the Community Structure of the Food-Trade International Multi-Network

NASA Technical Reports Server (NTRS)

Torreggiani, S.; Mangioni, G.

2018-01-01

Achieving international food security requires improved understanding of how international trade networks connect countries around the world through the import-export flows of food commodities. The properties of international food trade networks are still poorly documented, especially from a multi-network perspective. In particular, nothing is known about the multi-network's community structure. Here we find that the individual crop-specific layers of the multi-network have densely connected trading groups, a consistent characteristic over the period 2001-2011. Further, the multi-network is characterized by low variability over this period but with substantial heterogeneity across layers in each year. In particular, the layers are mostly assortative: more-intensively connected countries tend to import from and export to countries that are themselves more connected. We also fit econometric models to identify social, economic and geographic factors explaining the probability that any two countries are co-present in the same community. Our estimates indicate that the probability of country pairs belonging to the same food trade community depends more on geopolitical and economic factors-such as geographical proximity and trade-agreement co-membership-than on country economic size and/or income. These community-structure findings of the multi-network are especially valuable for efforts to understand past and emerging dynamics in the global food system, especially those that examine potential 'shocks' to global food trade.

Identifying the community structure of the food-trade international multi-network

NASA Astrophysics Data System (ADS)

Torreggiani, S.; Mangioni, G.; Puma, M. J.; Fagiolo, G.

2018-05-01

Achieving international food security requires improved understanding of how international trade networks connect countries around the world through the import-export flows of food commodities. The properties of international food trade networks are still poorly documented, especially from a multi-network perspective. In particular, nothing is known about the multi-network’s community structure. Here we find that the individual crop-specific layers of the multi-network have densely connected trading groups, a consistent characteristic over the period 2001–2011. Further, the multi-network is characterized by low variability over this period but with substantial heterogeneity across layers in each year. In particular, the layers are mostly assortative: more-intensively connected countries tend to import from and export to countries that are themselves more connected. We also fit econometric models to identify social, economic and geographic factors explaining the probability that any two countries are co-present in the same community. Our estimates indicate that the probability of country pairs belonging to the same food trade community depends more on geopolitical and economic factors—such as geographical proximity and trade-agreement co-membership—than on country economic size and/or income. These community-structure findings of the multi-network are especially valuable for efforts to understand past and emerging dynamics in the global food system, especially those that examine potential ‘shocks’ to global food trade.

Compartments in a marine food web associated with phylogeny, body mass, and habitat structure.

PubMed

Rezende, Enrico L; Albert, Eva M; Fortuna, Miguel A; Bascompte, Jordi

2009-08-01

A long-standing question in community ecology is whether food webs are organized in compartments, where species within the same compartment interact frequently among themselves, but show fewer interactions with species from other compartments. Finding evidence for this community organization is important since compartmentalization may strongly affect food web robustness to perturbation. However, few studies have found unequivocal evidence of compartments, and none has quantified the suite of mechanisms generating such a structure. Here, we combine computational tools from the physics of complex networks with phylogenetic statistical methods to show that a large marine food web is organized in compartments, and that body size, phylogeny, and spatial structure are jointly associated with such a compartmentalized structure. Sharks account for the majority of predatory interactions within their compartments. Phylogenetically closely related shark species tend to occupy different compartments and have divergent trophic levels, suggesting that competition may play an important role structuring some of these compartments. Current overfishing of sharks has the potential to change the structural properties, which might eventually affect the stability of the food web.

Bacterial diversity of soil aggregates of different sizes in various land use conditions

NASA Astrophysics Data System (ADS)

Ivanova, Ekaterina; Azida, Thakahova; Olga, Kutovaya

2014-05-01

The patterns of soil microbiome structure may be a universal and very sensitive indicator of soil quality (soil "health") used for optimization and biologization of agricultural systems. The understanding of how microbial diversity influenses, and is influenced by, the environment can only be attained by analyses at scales relevant to those at which processes influencing microbial diversity actually operate. The basic structural and functional unit of the soil is a soil aggregate, which is actually a microcosm of the associative co-existing groups of microorganisms that form characteristic ecological food chains. It is known that many important microbial processes occur in spatially segregated microenvironments in soil leading to a microscale biogeography. The Metagenomic library of typical chernozem in conditions of different land use systems was created. Total genomic DNA was extracted from 0.5 g of the frozen soil after mechanical destruction. Sample preparation and sequencing was performed on a GS Junior ("Roche»", Switzerland) according to manufacturer's recommendations, using the universal primers to the variable regions V4 gene 16S - rRNA - F515 (GTGCCAGCMGCCGCGGTAA) and R806 (GGACT-ACVSGGGTATCTAAT). It is shown that the system of land use is a stronger determinant of the taxonomic composition of the soil microbial community, rather than the size of the structural units. In soil samples from different land use systems the presence of accessory components was revealed. They may be used as indicators of processes of soil recovery, soil degradation or soil exhaustion processes occuring in the agroecosystems. The comparative analysis of microbial communities of chernozem aggregates investigated demonstrates the statistically valuable differences in the amount of bacterial phyla and Archean domain content as well as the species richness in aggregates of various size fractions. The occurrence of specific components in the taxonomic structure of micro-and macro-aggregates may indicate the presence of a certain size fraction in the structure of the investigated soil. The study of soils' metagenome is promising for the development of both soil microbiology, and for the soil processes trends in soils of anthropogenic origin.

Reading Quizzes Improve Exam Scores for Community College Students.

PubMed

Pape-Lindstrom, Pamela; Eddy, Sarah; Freeman, Scott

2018-06-01

To test the hypothesis that adding course structure may encourage self-regulated learning skills resulting in an increase in student exam performance in the community college setting, we added daily preclass online, open-book reading quizzes to an introductory biology course. We compared three control terms without reading quizzes and three experimental terms with online, open-book reading quizzes; the instructor of record, class size, and instructional time did not vary. Analyzing the Bloom's taxonomy level of a random sample of exam questions indicated a similar cognitive level of high-stakes assessments across all six terms in the study. To control for possible changes in student preparation or ability over time, we calculated each student's grade point average in courses other than biology during the term under study and included it as a predictor variable in our regression models. Our final model showed that students in the experimental terms had significantly higher exam scores than students in the control terms. This result shows that online reading quizzes can boost achievement in community college students. We also comment on the importance of discipline-based education research in community college settings and the structure of our community college/4-year institution collaboration.

Influence of habitat heterogeneity on the community structure of deep-sea harpacticoid communities from a canyon and an escarpment site on the continental rise off California

NASA Astrophysics Data System (ADS)

Thistle, David; Sedlacek, Linda; Carman, Kevin R.; Barry, James P.

2017-05-01

The sediment-covered deep-sea floor was initially thought to be environmentally homogeneous. Recent work has shown otherwise, and deep-sea ecologists have been searching for ecologically important environmental heterogeneities on different spatial and temporal scales, with particular interest in canyons. Here we report results for harpacticoid copepods from a site at 3262 m depth in the axis of Monterey Canyon and one on an escarpment 46 km away at 3090 m depth. Multivariate community analyses revealed significant differences between sites in community structure. Absolute abundance, the ratio of subadult copepodites to adults, species density, the proportion of the harpacticoid individuals that emerged, and the proportion that lived in tubes were significantly lower at the canyon site than at the escarpment site. The proportion of the harpacticoid individuals that belonged to the surface-dweller life-style group was significantly higher than at the escarpment site. These marked differences imply that ecologically important environmental heterogeneities exist. We speculate that differences between the sites in food conditions and sediment grain-size distributions are among them.

Limited effects of a keystone species: Trends of sea otters and kelp forests at the Semichi Islands, Alaska

USGS Publications Warehouse

Konar, Brenda

2000-01-01

Sea otters are well known as a keystone species because of their ability to transform sea urchin-dominated communities into kelp-dominated communities by preying on sea urchins and thus reducing the intensity of herbivory. After being locally extinct for more than a century, sea otters re-colonized the Semichi Islands in the Aleutian Archipelago, Alaska in the early 1990s. Here, otter populations increased to about 400 individuals by 1994, but rapidly declined to about 100 by 1997. Roughly 7 yr after initial otter re-colonization, there were only marginal changes in sea urchin biomass, mean maximum test size, and kelp density. These small changes may be the first steps in the cascading effects on community structure typically found with the invasion of a keystone species. However, no wholesale change in community structure occurred following re-colonization and growth of the sea otter population. Instead, this study describes a transition state and identifies factors such as keystone species density and residence time that can be important in dictating the degree to which otter effects are manifested.

A meta-analysis of lesser prairie-chicken nesting and brood-rearing habitats: implications for habitat management

USGS Publications Warehouse

Hagen, Christian A.; Grisham, Blake A.; Boal, Clint W.; Haukos, David A.

2013-01-01

The distribution and range of lesser prairie-chicken (Tympanuchus pallidicinctus) has been reduced by >90% since European settlement of the Great Plains of North America. Currently, lesser prairie-chickens occupy 3 general vegetation communities: sand sagebrush (Artemisia filifolia), sand shinnery oak (Quercus havardii), and mixed-grass prairies juxtaposed with Conservation Reserve Program grasslands. As a candidate for protection under the Endangered Species Act, there is a need for a synthesis that characterizes habitat structure rangewide. Thus, we conducted a meta-analysis of vegetation characteristics at nest sites and brood habitats to determine whether there was an overall effect (Hedges' d) of habitat selection and to estimate average (95% CI) habitat characteristics at use sites. We estimated effect sizes (di) from the difference between use (nests and brood sites) and random sampling sites for each study (n = 14), and derived an overall effect size (d++). There was a general effect for habitat selection as evidenced by low levels of variation in effect sizes across studies and regions. There was a small to medium effect (d++) = 0.20-0.82) of selection for greater vertical structure (visual obstruction) by nesting females in both vegetation communities, and selection against bare ground (d++ = 0.20-0.58). Females with broods exhibited less selectivity for habitat components except for vertical structure. The variation of d++ was greater during nesting than brooding periods, signifying a seasonal shift in habitat use, and perhaps a greater range of tolerance for brood-rearing habitat. The overall estimates of vegetation cover were consistent with those provided in management guidelines for the species.

Community Structure and Survival of Tertiary Relict Thuja sutchuenensis (Cupressaceae) in the Subtropical Daba Mountains, Southwestern China

PubMed Central

Tang, Cindy Q.; Yang, Yongchuan; Ohsawa, Masahiko; Momohara, Arata; Yi, Si-Rong; Robertson, Kevin; Song, Kun; Zhang, Shi-Qiang; He, Long-Yuan

2015-01-01

A rare coniferous Tertiary relict tree species, Thuja sutchuenensis Franch, has survived in the Daba Mountains of southwestern China. It was almost eliminated by logging during the past century. We measured size and age structures and interpreted regeneration dynamics of stands of the species in a variety of topographic contexts and community associations. Forest communities containing T. sutchuenensis were of three types: (1) the Thuja community dominated by T. sutchuenensis, growing on cliffs; (2) the Thuja-Quercus-Cyclobalanopsis community dominated by T. sutchuenensis, Quercus engleriana and Cyclobalanopsis oxyodon, along with Fagus engleriana and Carpinus fargesiana, on steep slopes; (3) the Thuja-Tsuga-Quercus community dominated by T. sutchuenensis, Tsuga chinensis, and Quercus spinosa, on crest ridges. The established seedlings/saplings were found in limestone crevices, on scarred cliff-faces, cliff-edges, fallen logs, canopy gaps and forest margins. The radial growth rate was 0.5-1.1 mm per year. Its growth forms were distorted. It had strong sprouting ability after disturbances. The T. sutchuenensis population thrives on cliffs where there is little competition from other species because of harsh conditions and rockslide disturbances. It is shade-intolerant but stress-tolerant. Its regeneration has depended on natural disturbances. PMID:25928845

Coding Early Naturalists' Accounts into Long-Term Fish Community Changes in the Adriatic Sea (1800–2000)

PubMed Central

Fortibuoni, Tomaso; Libralato, Simone; Raicevich, Saša; Giovanardi, Otello; Solidoro, Cosimo

2010-01-01

The understanding of fish communities' changes over the past centuries has important implications for conservation policy and marine resource management. However, reconstructing these changes is difficult because information on marine communities before the second half of the 20th century is, in most cases, anecdotal and merely qualitative. Therefore, historical qualitative records and modern quantitative data are not directly comparable, and their integration for long-term analyses is not straightforward. We developed a methodology that allows the coding of qualitative information provided by early naturalists into semi-quantitative information through an intercalibration with landing proportions. This approach allowed us to reconstruct and quantitatively analyze a 200-year-long time series of fish community structure indicators in the Northern Adriatic Sea (Mediterranean Sea). Our analysis provides evidence of long-term changes in fish community structure, including the decline of Chondrichthyes, large-sized and late-maturing species. This work highlights the importance of broadening the time-frame through which we look at marine ecosystem changes and provides a methodology to exploit, in a quantitative framework, historical qualitative sources. To the purpose, naturalists' eyewitness accounts proved to be useful for extending the analysis on fish community back in the past, well before the onset of field-based monitoring programs. PMID:21103349

Planktonic food web structure at a coastal time-series site: I. Partitioning of microbial abundances and carbon biomass

NASA Astrophysics Data System (ADS)

Caron, David A.; Connell, Paige E.; Schaffner, Rebecca A.; Schnetzer, Astrid; Fuhrman, Jed A.; Countway, Peter D.; Kim, Diane Y.

2017-03-01

Biogeochemistry in marine plankton communities is strongly influenced by the activities of microbial species. Understanding the composition and dynamics of these assemblages is essential for modeling emergent community-level processes, yet few studies have examined all of the biological assemblages present in the plankton, and benchmark data of this sort from time-series studies are rare. Abundance and biomass of the entire microbial assemblage and mesozooplankton (>200 μm) were determined vertically, monthly and seasonally over a 3-year period at a coastal time-series station in the San Pedro Basin off the southwestern coast of the USA. All compartments of the planktonic community were enumerated (viruses in the femtoplankton size range [0.02-0.2 μm], bacteria + archaea and cyanobacteria in the picoplankton size range [0.2-2.0 μm], phototrophic and heterotrophic protists in the nanoplanktonic [2-20 μm] and microplanktonic [20-200 μm] size ranges, and mesozooplankton [>200 μm]. Carbon biomass of each category was estimated using standard conversion factors. Plankton abundances varied over seven orders of magnitude across all categories, and total carbon biomass averaged approximately 60 μg C l-1 in surface waters of the 890 m water column over the study period. Bacteria + archaea comprised the single largest component of biomass (>1/3 of the total), with the sum of phototrophic protistan biomass making up a similar proportion. Temporal variability at this subtropical station was not dramatic. Monthly depth-specific and depth-integrated biomass varied 2-fold at the station, while seasonal variances were generally <50%. This study provides benchmark information for investigating long-term environmental forcing on the composition and dynamics of the microbes that dominate food web structure and function at this coastal observatory.

The Future of Small- and Medium-Sized Communities in the Prairie Region.

ERIC Educational Resources Information Center

Wellar, Barry S., Ed.

Four papers are featured. The first is a statistical overview and analysis of past, present and future happenings to small communities in the Region; it focuses on two indicators: (1) population growth or declining community class size and, (2) the changing distribution of commercial outlets by community class size. The other three papers report…

Variation of phytoplankton assemblages along the Mozambique coast as revealed by HPLC and microscopy

NASA Astrophysics Data System (ADS)

Sá, C.; Leal, M. C.; Silva, A.; Nordez, S.; André, E.; Paula, J.; Brotas, V.

2013-05-01

This study is an integrated overview of pigment and microscopic analysis of phytoplankton communities throughout the Mozambican coast. Collected samples revealed notable patterns of phytoplankton occurrence and distribution, with community structure changing between regions and sample depth. Pigment data showed Delagoa Bight, Sofala Bank and Angoche as the most productive regions throughout the sampled area. In general, micro-sized phytoplankton, particularly diatoms, were important contributors to biomass both at surface and sub-surface maximum (SSM) samples, although were almost absent in the northern stations. In contrast, nano- and pico-sized phytoplankton revealed opposing patterns. Picophytoplankton were most abundant at surface, as opposed to nanophytoplankton, which were more abundant at the SSM. Microphytoplankton were associated with cooler southern water masses, while picophytoplankton were related to warmer northern water masses. Nanophytoplankton were found to increase their contribution to biomass with increasing SSM. Microscopy information on the genera and species level revealed the diatoms Chaetoceros spp., Proboscia alata, Pseudo-nitzschia spp., Cylindrotheca closterium and Hemiaulus haukii as the most abundant taxa of the micro-sized phytoplankton. Discosphaera tubifera and Emiliania huxleyi were the most abundant coccolithophores, nano-sized phytoplankton.

Microbial eukaryote plankton communities of high-mountain lakes from three continents exhibit strong biogeographic patterns.

PubMed

Filker, Sabine; Sommaruga, Ruben; Vila, Irma; Stoeck, Thorsten

2016-05-01

Microbial eukaryotes hold a key role in aquatic ecosystem functioning. Yet, their diversity in freshwater lakes, particularly in high-mountain lakes, is relatively unknown compared with the marine environment. Low nutrient availability, low water temperature and high ultraviolet radiation make most high-mountain lakes extremely challenging habitats for life and require specific molecular and physiological adaptations. We therefore expected that these ecosystems support a plankton diversity that differs notably from other freshwater lakes. In addition, we hypothesized that the communities under study exhibit geographic structuring. Our rationale was that geographic dispersal of small-sized eukaryotes in high-mountain lakes over continental distances seems difficult. We analysed hypervariable V4 fragments of the SSU rRNA gene to compare the genetic microbial eukaryote diversity in high-mountain lakes located in the European Alps, the Chilean Altiplano and the Ethiopian Bale Mountains. Microbial eukaryotes were not globally distributed corroborating patterns found for bacteria, multicellular animals and plants. Instead, the plankton community composition emerged as a highly specific fingerprint of a geographic region even on higher taxonomic levels. The intraregional heterogeneity of the investigated lakes was mirrored in shifts in microbial eukaryote community structure, which, however, was much less pronounced compared with interregional beta-diversity. Statistical analyses revealed that on a regional scale, environmental factors are strong predictors for plankton community structures in high-mountain lakes. While on long-distance scales (>10 000 km), isolation by distance is the most plausible scenario, on intermediate scales (up to 6000 km), both contemporary environmental factors and historical contingencies interact to shift plankton community structures. © 2016 John Wiley & Sons Ltd.

Estimating the resolution limit of the map equation in community detection

NASA Astrophysics Data System (ADS)

Kawamoto, Tatsuro; Rosvall, Martin

2015-01-01

A community detection algorithm is considered to have a resolution limit if the scale of the smallest modules that can be resolved depends on the size of the analyzed subnetwork. The resolution limit is known to prevent some community detection algorithms from accurately identifying the modular structure of a network. In fact, any global objective function for measuring the quality of a two-level assignment of nodes into modules must have some sort of resolution limit or an external resolution parameter. However, it is yet unknown how the resolution limit affects the so-called map equation, which is known to be an efficient objective function for community detection. We derive an analytical estimate and conclude that the resolution limit of the map equation is set by the total number of links between modules instead of the total number of links in the full network as for modularity. This mechanism makes the resolution limit much less restrictive for the map equation than for modularity; in practice, it is orders of magnitudes smaller. Furthermore, we argue that the effect of the resolution limit often results from shoehorning multilevel modular structures into two-level descriptions. As we show, the hierarchical map equation effectively eliminates the resolution limit for networks with nested multilevel modular structures.

Variability in the phytoplankton community of Kavaratti reef ecosystem (northern Indian Ocean) during peak and waning periods of El Niño 2016.

PubMed

Karati, Kusum Komal; Vineetha, G; Madhu, N V; Anil, P; Dayana, M; Shihab, B K; Muhsin, A I; Riyas, C; Raveendran, T V

2017-11-29

El Niño, an interannual climate event characterized by elevated oceanic temperature, is a prime threat for coral reef ecosystems worldwide, owing to their thermal threshold sensitivity. Phytoplankton plays a crucial role in the sustenance of reef trophodynamics. The cell size of the phytoplankton forms the "master morphological trait" with implications for growth, resource acquisition, and adaptability to nutrients. In the context of a strong El Niño prediction for 2015-2016, the present study was undertaken to evaluate the variations in the size-structured phytoplankton of Kavaratti reef waters, a major coral atoll along the southeast coast of India. The present study witnessed a remarkable change in the physicochemical environment of the reef water and massive coral bleaching with the progression of El Niño 2015-2016 from its peak to waning phase. The fluctuations observed in sea surface temperature, pH, and nutrient concentration of the reef water with the El Niño progression resulted in a remarkable shift in phytoplankton size structure, abundance, and community composition of the reef waters. Though low nutrient concentration of the waning phase resulted in lower phytoplankton biomass and abundance, the diazotroph Trichodesmium erythraeum predominated the reef waters, owing to its capability of the atmospheric nitrogen fixation and dissolved organic phosphate utilization.

Detecting Habitats and Ecosystem Functions Considering the Mesozooplankton Size and Diversity Structures and Environmental Conditions in the Gulf of Lion, NW Mediterranean Sea

NASA Astrophysics Data System (ADS)

Carlotti, F.; Espinasse, B.; Zhou, M.; Jean-Luc, D.

2016-02-01

Environmental conditions and zooplankton size structure and taxonomic diversity were investigated in the Gulf of Lion in May 2010 and January 2011. The integrated physical and biological measurements provided a 3D view with high spatial resolution of the physical and biological variables and their correlations over the whole gulf. The effects of physical processes such as freshwater input, coastal upwelling, and water column mixing by winds on phytoplankton and zooplankton distributions were analyzed using these data. Several analytic tests were performed in order to define several ecoregions representing different habitats of plankton communities. Three habitats were distinguished based on statistical analysis performed on biological and physical variables: (1) the coastal area characterized by shallow waters, high chl a concentrations, and a steep slope of the normalized biomass size spectrum (NBSS); (2) the area affected by the Rhône with high stratification and flat NBSS slope; and (3) the continental shelf with a deep mixed layer, relatively low particle concentrations, and moderate NBSS slope. The zooplankton diversity was characterized by spatial differences in community composition among the Rhône plume area, the coastal shelf, and shelf break waters. Defining habitat is a relevant approach to designing new zooplankton sampling strategies, validating distribution models and including the zooplankton compartment in trophodynamic studies.

Community size and composition of ammonia oxidizers and denitrifiers in an alluvial intertidal wetland ecosystem

PubMed Central

Hu, Ziye; Meng, Han; Shi, Jin-Huan; Bu, Nai-Shun; Fang, Chang-Ming; Quan, Zhe-Xue

2014-01-01

Global nitrogen cycling is mainly mediated by the activity of microorganisms. Nitrogen cycle processes are mediated by functional groups of microorganisms that are affected by constantly changing environmental conditions and substrate availability. In this study, we investigated the temporal and spatial patterns of nitrifier and denitrifier communities in an intertidal wetland. Soil samples were collected over four distinct seasons from three locations with different vegetative cover. Multiple environmental factors and process rates were measured and analyzed together with the community size and composition profiles. We observed that the community size and composition of the nitrifiers and denitrifiers are affected significantly by seasonal factors, while vegetative cover affected the community composition. The seasonal impacts on the community size of ammonia oxidizing archaea (AOA) are much higher than that of ammonia oxidizing bacteria (AOB). The seasonal change was a more important indicator for AOA community composition patterns, while vegetation was more important for the AOB community patterns. The microbial process rates were correlated with both the community size and composition. PMID:25101072

Fast detection of the fuzzy communities based on leader-driven algorithm

NASA Astrophysics Data System (ADS)

Fang, Changjian; Mu, Dejun; Deng, Zhenghong; Hu, Jun; Yi, Chen-He

2018-03-01

In this paper, we present the leader-driven algorithm (LDA) for learning community structure in networks. The algorithm allows one to find overlapping clusters in a network, an important aspect of real networks, especially social networks. The algorithm requires no input parameters and learns the number of clusters naturally from the network. It accomplishes this using leadership centrality in a clever manner. It identifies local minima of leadership centrality as followers which belong only to one cluster, and the remaining nodes are leaders which connect clusters. In this way, the number of clusters can be learned using only the network structure. The LDA is also an extremely fast algorithm, having runtime linear in the network size. Thus, this algorithm can be used to efficiently cluster extremely large networks.

Archaeobotanical evidence for climate as a driver of ecological community change across the anthropocene boundary.

PubMed

Ellis, Christopher J; Yahr, Rebecca; Belinchón, Rocío; Coppins, Brian J

2014-07-01

The biodiversity response to climate change is a major focus in conservation research and policy. Predictive models that are used to project the impact of climate change scenarios - such as bioclimatic envelope models - are widely applied and have come under severe scrutiny. Criticisms of such models have focussed on at least two problems. First, there is an assumption that climate is the primary driver of observed species distributions ('climatic equilibrium'), when other biogeographical controls are often reliably established. Second, a species' sensitivity to macroclimate may become less relevant when impacts are down-scaled to a local level, incorporating a modifying effect of species interactions structuring communities. This article examines the role of different drivers (climate, pollution and landscape habitat structure) in explaining spatial community variation for a widely applied bioindicator group: lichen epiphytes. To provide an analysis free of 'legacy effects' (e.g. formerly higher pollution loads), the study focused on hazel stems as a relatively short-lived and recently colonized substratum. For communities during the present day, climate is shown to interact with stem size/age as the most likely explanation of community composition, thus coupling a macroclimatic and community-scale effect. The position of present-day communities was projected into ordination space for eight sites in England and compared to the position of historical epiphyte communities from the same sites, reconstructed using preserved hazel wattles dating mainly to the 16th Century. This comparison of community structure for the late- to post-Mediaeval period, with the post-Industrial period, demonstrated a consistent shift among independent sites towards warmer and drier conditions, concurrent with the end of the Little Ice Age. Long-term temporal sensitivity of epiphyte communities to climate variation thus complements spatial community patterns. If more widely applied, preserved lichen epiphytes have potential to generate new baseline conditions of environment and biodiversity for preindustrial lowland Europe. © 2014 John Wiley & Sons Ltd.

The relationship between observational scale and explained variance in benthic communities

PubMed Central

Flood, Roger D.; Frisk, Michael G.; Garza, Corey D.; Lopez, Glenn R.; Maher, Nicole P.

2018-01-01

This study addresses the impact of spatial scale on explaining variance in benthic communities. In particular, the analysis estimated the fraction of community variation that occurred at a spatial scale smaller than the sampling interval (i.e., the geographic distance between samples). This estimate is important because it sets a limit on the amount of community variation that can be explained based on the spatial configuration of a study area and sampling design. Six benthic data sets were examined that consisted of faunal abundances, common environmental variables (water depth, grain size, and surficial percent cover), and sonar backscatter treated as a habitat proxy (categorical acoustic provinces). Redundancy analysis was coupled with spatial variograms generated by multiscale ordination to quantify the explained and residual variance at different spatial scales and within and between acoustic provinces. The amount of community variation below the sampling interval of the surveys (< 100 m) was estimated to be 36–59% of the total. Once adjusted for this small-scale variation, > 71% of the remaining variance was explained by the environmental and province variables. Furthermore, these variables effectively explained the spatial structure present in the infaunal community. Overall, no scale problems remained to compromise inferences, and unexplained infaunal community variation had no apparent spatial structure within the observational scale of the surveys (> 100 m), although small-scale gradients (< 100 m) below the observational scale may be present. PMID:29324746

Are Trade-Offs Among Species’ Ecological Interactions Scale Dependent? A Test Using Pitcher-Plant Inquiline Species

PubMed Central

Kneitel, Jamie M.

2012-01-01

Trade-offs among species’ ecological interactions is a pervasive explanation for species coexistence. The traits associated with trade-offs are typically measured to mechanistically explain species coexistence at a single spatial scale. However, species potentially interact at multiple scales and this may be reflected in the traits among coexisting species. I quantified species’ ecological traits associated with the trade-offs expected at both local (competitive ability and predator tolerance) and regional (competitive ability and colonization rate) community scales. The most common species (four protozoa and a rotifer) from the middle trophic level of a pitcher plant (Sarracenia purpurea) inquiline community were used to link species traits to previously observed patterns of species diversity and abundance. Traits associated with trade-offs (competitive ability, predator tolerance, and colonization rate) and other ecological traits (size, growth rate, and carrying capacity) were measured for each of the focal species. Traits were correlated with one another with a negative relationship indicative of a trade-off. Protozoan and rotifer species exhibited a negative relationship between competitive ability and predator tolerance, indicative of coexistence at the local community scale. There was no relationship between competitive ability and colonization rate. Size, growth rate, and carrying capacity were correlated with each other and the trade-off traits: Size was related to both competitive ability and predator tolerance, but growth rate and carrying capacity were correlated with predator tolerance. When partial correlations were conducted controlling for size, growth rate and carrying capacity, the trade-offs largely disappeared. These results imply that body size is the trait that provides the basis for ecological interactions and trade-offs. Altogether, this study showed that the examination of species’ traits in the context of coexistence at different scales can contribute to our understanding of the mechanisms underlying community structure. PMID:22844526

Spatial and temporal variation of an ice-adapted predator's feeding ecology in a changing Arctic marine ecosystem.

PubMed

Yurkowski, David J; Ferguson, Steven H; Semeniuk, Christina A D; Brown, Tanya M; Muir, Derek C G; Fisk, Aaron T

2016-03-01

Spatial and temporal variation can confound interpretations of relationships within and between species in terms of diet composition, niche size, and trophic position (TP). The cause of dietary variation within species is commonly an ontogenetic niche shift, which is a key dynamic influencing community structure. We quantified spatial and temporal variations in ringed seal (Pusa hispida) diet, niche size, and TP during ontogeny across the Arctic-a rapidly changing ecosystem. Stable carbon and nitrogen isotope analysis was performed on 558 liver and 630 muscle samples from ringed seals and on likely prey species from five locations ranging from the High to the Low Arctic. A modest ontogenetic diet shift occurred, with adult ringed seals consuming more forage fish (approximately 80 versus 60 %) and having a higher TP than subadults, which generally decreased with latitude. However, the degree of shift varied spatially, with adults in the High Arctic presenting a more restricted niche size and consuming more Arctic cod (Boreogadus saida) than subadults (87 versus 44 %) and adults at the lowest latitude (29 %). The TPs of adult and subadult ringed seals generally decreased with latitude (4.7-3.3), which was mainly driven by greater complexity in trophic structure within the zooplankton communities. Adult isotopic niche size increased over time, likely due to the recent circumpolar increases in subarctic forage fish distribution and abundance. Given the spatial and temporal variability in ringed seal foraging ecology, ringed seals exhibit dietary plasticity as a species, suggesting adaptability in terms of their diet to climate change.

Size Matters — Determinants of Modern, Community-Oriented Mental Health Services

PubMed Central

Ala-Nikkola, Taina; Pirkola, Sami; Kontio, Raija; Joffe, Grigori; Pankakoski, Maiju; Malin, Maili; Sadeniemi, Minna; Kaila, Minna; Wahlbeck, Kristian

2014-01-01

Governances, structures and contents of mental health services are being reformed across countries. There is a need for data to support those changes. The aim of this study was to explore the quality, i.e., diversity and community orientation, and quantity, i.e., personnel resources, of mental health and substance abuse services (MHS) and evaluate correlation between population needs and quality and quantity of MHS. The European Service Mapping Schedule—Revised (ESMS-R) was used to classify mental health and substance abuse services in southern Finland. Municipal-level aggregate data, local data on unemployment rate, length of education, age of retirement, proportion of single households, alcohol sales and a composite mental health index were used as indicators of population mental health needs. Population size correlated strongly with service diversity, explaining 84% of the variance. Personnel resources did not associate with diversity or community orientation. The indicators of mental health services need did not have the expected association with quality and quantity of services. In terms of service organization, the results may support larger population bases, at least 150,000 adult inhabitants, when aiming for higher diversity. PMID:25153471

Modeling Global Spatial-Temporal Evolution of Society: Hyperbolic Growth and Historical Cycles

NASA Astrophysics Data System (ADS)

Kurkina, E. S.

2011-09-01

The global historical processes are under consideration; and laws of global evolution of the world community are studied. The world community is considered as a united complex self-developing and self-organizing system. It supposed that the main driving force of social-economical evolution was the positive feedback between the population size and the level of technological development, which was a cause of growth in blow-up regime both of population and of global economic indexes. The study is supported by the results of mathematical modeling founded on a nonlinear heat equation with a source. Every social-economical epoch characterizes by own specific spatial distributed structures. So the global dynamics of world community during the whole history is investigated throughout the prism of the developing of spatial-temporal structures. The model parameters have been chosen so that 1) total population follows stable hyperbolic growth, consistently with the demographic data; 2) the evolution of the World-System goes through 11 stages corresponding to the main historical epochs.

Effects of haze pollution on microbial community changes and correlation with chemical components in atmospheric particulate matter.

PubMed

Sun, Yujiao; Xu, Shangwei; Zheng, Danyang; Li, Jie; Tian, Hezhong; Wang, Yong

2018-05-10

In this study, particulate matter (PM) with aerodynamic diameters of ≤2.5 and ≤10 μm (PM 2.5 and PM 10 , respectively), which was found at different concentrations in spring, was collected in Beijing. The chemical composition and bacterial community diversity of PM were determined, and the relationship between them was studied by 16S rRNA sequencing and mathematical statistics. Chemical composition analysis revealed greater relative percentages of total organic compounds (TOC) and secondary ions (NO 3 - , SO 4 2- , and NH 4 + ). The concentrations of Ca 2+ , Na + , Mg 2+ , K + and SO 4 2- increased in high-concentration PM, which was associated with the contribution of soil, dust and soot. Microbiological analysis revealed 1191 operational taxonomic units. Microbial community structure was stable at the phylum level. The most abundant phyla were Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes and Cyanobacteria. Community clustering analysis at the genus level showed that the difference in bacterial community structure between different PM concentrations (clean air vs. smog) was greater than that between different particle sizes. The dominant genera varied in different concentrations of PM. An unclassified genus of Cyanobacteria and Comamonadaceae were most abundant in low- and high-concentration PM, respectively. The microbial community structure was dynamic at the genus level due to different environmental factors. The dominant bacteria in high-concentration PM were widely distributed in soils, indicating that the soil contributed more to the increase in the PM. The individual microbes that were detected did not increase significantly as the PM concentration increased. The bacterial community structure was strongly correlated with K + , Ca 2+ , Na + , Mg 2+ , SO 4 2- and TOC in high-concentration PM and had a good correlation with NO 3 - , Cl - , NH 4 + and TIC in low-concentration PM. Soil and dust contributed to the increase in the concentration of the particles, and the relevant chemical components also produced differences in the bacterial community structure in different concentrations of PM. Copyright © 2018. Published by Elsevier B.V.

Fine-scale spatial patterns in the demersal fish and invertebrate community in a northwest Atlantic ecosystem

NASA Astrophysics Data System (ADS)

Malek, Anna J.; Collie, Jeremy S.; Gartland, James

2014-06-01

The abundance, biomass, diversity, and species composition of the demersal fish and invertebrate community in Rhode Island Sound and Block Island Sound, an area identified for offshore renewable energy development, were evaluated for spatial and seasonal structure. We conducted 58 otter trawls and 51 beam trawls in the spring, summer and fall of 2009-2012, and incorporated additional data from 88 otter trawls conducted by the Northeast Area Monitoring and Assessment Program. We used regionally-grouped abundance, biomass, diversity, and size spectra to assess spatial patterns in the aggregate fish community, and hierarchical cluster analysis to evaluate trends in species assemblages. Our analyses revealed coherent gradients in fish community biomass, diversity and species composition extending from inshore to offshore waters, as well as patterns related to the differing bathymetry of Rhode Island and Block Island Sounds. The fish communities around Block Island and Cox's Ledge are particularly diverse, suggesting that the proximity of hard bottom habitat may be important in structuring fish communities in this area. Species assemblages in Rhode Island and Block Island Sounds are characterized by a combination of piscivores (silver hake, summer flounder, spiny dogfish), benthivores (American lobster, black sea bass, Leucoraja spp. skates, scup) and planktivores (sea scallop), and exhibit geographic patterns that are persistent from year to year, yet variable by season. Such distributions reflect the cross-shelf migration of fish and invertebrate species in the spring and fall, highlighting the importance of considering seasonal fish behavior when planning construction schedules for offshore development projects. The fine spatial scale (10 s of kms) of this research makes it especially valuable for local marine spatial planning efforts by identifying local-scale patterns in fish community structure that will enable future assessment of the ecological impacts of offshore development. As such, this knowledge of the spatial and temporal structure of the demersal fish community in Rhode Island and Block Island Sounds will help to guide the placement of offshore structures so as to preserve the ecological and economic value of the area.

Macroinvertebrates as indicators of fish absence in naturally fishless lakes

USGS Publications Warehouse

Schilling, Emily Gaenzle; Loftin, C.S.; Huryn, Alexander D.

2009-01-01

1. Little is known about native communities in naturally fishless lakes in eastern North America, a region where fish stocking has led to a decline in these habitats. 2. Our study objectives were to: (i) characterise and compare macroinvertebrate communities in fishless lakes found in two biophysical regions of Maine (U.S.A.): kettle lakes in the eastern lowlands and foothills and headwater lakes in the central and western mountains; (ii) identify unique attributes of fishless lake macroinvertebrate communities compared to lakes with fish and (iii) develop a method to efficiently identify fishless lakes when thorough fish surveys are not possible. 3. We quantified macroinvertebrate community structure in the two physiographic fishless lake types (n = 8 kettle lakes; n = 8 headwater lakes) with submerged light traps and sweep nets. We also compared fishless lake macroinvertebrate communities to those in fish-containing lakes (n = 18) of similar size, location and maximum depth. We used non-metric multidimensional scaling to assess differences in community structure and t-tests for taxon-specific comparisons between lakes. 4. Few differences in macroinvertebrate communities between the two physiographic fishless lake types were apparent. Fishless and fish-containing lakes had numerous differences in macroinvertebrate community structure, abundance, taxonomic composition and species richness. Fish presence or absence was a stronger determinant of community structure in our study than differences in physical conditions relating to lake origin and physiography. 5. Communities in fishless lakes were more speciose and abundant than in fish-containing lakes, especially taxa that are large, active and free-swimming. Families differing in abundance and taxonomic composition included Notonectidae, Corixidae, Gyrinidae, Dytiscidae, Aeshnidae, Libellulidae and Chaoboridae. 6. We identified six taxa unique to fishless lakes that are robust indicators of fish absence: Graphoderus liberus, Hesperocorixa spp., Dineutus spp., Chaoborus americanus, Notonecta insulata and Callicorixa spp. These taxa are collected most effectively with submerged light traps. 7. Naturally fishless lakes warrant conservation, because they provide habitat for a unique suite of organisms that thrive in the absence of fish predation. ?? 2008 Blackwell Publishing Ltd.

"Whatever average is:" understanding African-American mothers' perceptions of infant weight, growth, and health.

PubMed

Thompson, Amanda L; Adair, Linda; Bentley, Margaret E

2014-06-01

Biomedical researchers have raised concerns that mothers' inability to recognize infant and toddler overweight poses a barrier to stemming increasing rates of overweight and obesity, particularly among low-income or minority mothers. Little anthropological research has examined the sociocultural, economic or structural factors shaping maternal perceptions of infant and toddler size or addressed biomedical depictions of maternal misperception as a "socio-cultural problem." We use qualitative and quantitative data from 237 low-income, African-American mothers to explore how they define 'normal' infant growth and infant overweight. Our quantitative results document that mothers' perceptions of infant size change with infant age, are sensitive to the size of other infants in the community, and are associated with concerns over health and appetite. Qualitative analysis documents that mothers are concerned with their children's weight status and assess size in relation to their infants' cues, local and societal norms of appropriate size, interactions with biomedicine, and concerns about infant health and sufficiency. These findings suggest that mothers use multiple models to interpret and respond to child weight. An anthropological focus on the complex social and structural factors shaping what is considered 'normal' and 'abnormal' infant weight is critical for shaping appropriate and successful interventions.

Community meetings on a military inpatient psychiatric unit: a question of balance.

PubMed

Lange, C L; Bradley, J C

2001-01-01

Community meetings are a mainstay of any inpatient psychiatric unit. Although they differ in frequency, attendance, leadership, and size, they all maintain a similar purpose of acculturating the members to the values of the ward and encouraging responsible behavior and effective communication. The military inpatient psychiatric unit is no different, although it does have several unique factors that affect the management of the community meeting. Specifically, these factors are the inherent military rank structure, which often conflicts with the rank of staff and other patients, the incorporation of a civilian population into a military culture, and a greater focus on patient transitions from military to civilian society. We describe and discuss the common variables of community meetings, elucidate how the military aspects affect the meeting, and offer potential suggestions for the management of this unique large dynamic group.

Size Matters: Community Size, HIV Stigma, & Gender Differences

PubMed Central

Gonzalez, Adam; Miller, Carol T.; Solomon, Sondra E.; Bunn, Janice Yanushka; Cassidy, Daniel G.

2012-01-01

Conclusions regarding HIV stigma in rural areas are hampered by lack of agreement about rural classification. This investigation examined perceptions of HIV stigma among males and females with HIV/AIDS in metropolitan, micropolitan, and rural areas. Two-hundred people with HIV/AIDS completed a measure of perceived HIV stigma. Their county or town of residence was used to classify community size. Results indicated that community size was related to one aspect of perceived stigma, disclosure concerns, differently for men and women. Rural women reported more disclosure concerns than did metropolitan and micropolitan women. They also reported more disclosure concerns than rural men. Men in micropolitan communities reported more disclosure concerns than men in rural areas and tended to report more disclosure concerns than men in metropolitan areas. Understanding the relationship of community size to HIV stigmatization requires acknowledging that many communities are neither urban nor rural, and it requires considering gender differences. PMID:18815878

Metagenomic insights into particles and their associated microbiota in a coastal margin ecosystem

PubMed Central

Simon, Holly M.; Smith, Maria W.; Herfort, Lydie

2014-01-01

Our previously published research was one of the pioneering studies on the use of metagenomics to directly compare taxonomic and metabolic properties of aquatic microorganisms from different filter size-fractions. We compared size-fractionated water samples representing free-living and particle-attached communities from four diverse habitats in the Columbia River coastal margin, analyzing 12 metagenomes consisting of >5 million sequence reads (>1.6 Gbp). With predicted peptide and rRNA data we evaluated eukaryotic, bacterial and archaeal populations across size fractions and related their properties to attached and free-living lifestyles, and their potential roles in carbon and nutrient cycling. In this focused review, we expand our discussion on the use of high-throughput sequence data to relate microbial community structure and function to the origin, fate and transport of particulate organic matter (POM) in coastal margins. We additionally discuss the potential impact of the priming effect on organic matter cycling at the land-ocean interface, and build a case for the importance, in particle-rich estuaries and coastal margin waters, of microbial activities in low-oxygen microzones within particle interiors. PMID:25250019

Eco-evolutionary dynamics in urbanized landscapes: evolution, species sorting and the change in zooplankton body size along urbanization gradients.

PubMed

Brans, Kristien I; Govaert, Lynn; Engelen, Jessie M T; Gianuca, Andros T; Souffreau, Caroline; De Meester, Luc

2017-01-19

Urbanization causes both changes in community composition and evolutionary responses, but most studies focus on these responses in isolation. We performed an integrated analysis assessing the relative contribution of intra- and interspecific trait turnover to the observed change in zooplankton community body size in 83 cladoceran communities along urbanization gradients quantified at seven spatial scales (50-3200 m radii). We also performed a quantitative genetic analysis on 12 Daphnia magna populations along the same urbanization gradient. Body size in zooplankton communities generally declined with increasing urbanization, but the opposite was observed for communities dominated by large species. The contribution of intraspecific trait variation to community body size turnover with urbanization strongly varied with the spatial scale considered, and was highest for communities dominated by large cladoceran species and at intermediate spatial scales. Genotypic size at maturity was smaller for urban than for rural D. magna populations and for animals cultured at 24°C compared with 20°C. While local genetic adaptation likely contributed to the persistence of D. magna in the urban heat islands, buffering for the phenotypic shift to larger body sizes with increasing urbanization, community body size turnover was mainly driven by non-genetic intraspecific trait change.This article is part of the themed issue 'Human influences on evolution, and the ecological and societal consequences'. © 2016 The Author(s).

Eco-evolutionary dynamics in urbanized landscapes: evolution, species sorting and the change in zooplankton body size along urbanization gradients

PubMed Central

Souffreau, Caroline

2017-01-01

Urbanization causes both changes in community composition and evolutionary responses, but most studies focus on these responses in isolation. We performed an integrated analysis assessing the relative contribution of intra- and interspecific trait turnover to the observed change in zooplankton community body size in 83 cladoceran communities along urbanization gradients quantified at seven spatial scales (50–3200 m radii). We also performed a quantitative genetic analysis on 12 Daphnia magna populations along the same urbanization gradient. Body size in zooplankton communities generally declined with increasing urbanization, but the opposite was observed for communities dominated by large species. The contribution of intraspecific trait variation to community body size turnover with urbanization strongly varied with the spatial scale considered, and was highest for communities dominated by large cladoceran species and at intermediate spatial scales. Genotypic size at maturity was smaller for urban than for rural D. magna populations and for animals cultured at 24°C compared with 20°C. While local genetic adaptation likely contributed to the persistence of D. magna in the urban heat islands, buffering for the phenotypic shift to larger body sizes with increasing urbanization, community body size turnover was mainly driven by non-genetic intraspecific trait change. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’. PMID:27920375

Abundance, distribution, trends, and ownership patterns of early successional forests in the northeastern United States

Treesearch

Robert T. Brooks

2003-01-01

Early-successional forests are ephemeral and distinct forest communities, maintained by disturbance and dominated by small-sized trees and shrubs. These structural and compositional conditions form a unique habitat that is preferred by many wildlife species. Various sources have indicated that there have been declines in early-successional forest area and in the...

Reproduction and community structure of fish from winter catch sites from industrial shrimp bycatch from the northeast and southeast Mexican Pacific.

PubMed

Tirado-Ibarra, Jorge de Jesus; Loya-Rodriguez, Mariany; Morales-Arevalo, Jose Carlos; Muñoz-Garcia, Isabel Rosario; Martinez-Perez, Francisco; Ramirez-Perez, Jorge Saul; Jimenez-Gutierrez, Laura Rebeca

2018-01-01

The shrimp fishery is one of the most important fisheries in the world, although the low selectivity from trawling nets has led to the capture of a large number of non-target species. Shrimp-bycatch species include a large number of fish and invertebrate species, of which fish species are the most abundant. The present study aims to determine the community structure as well as the average sizes at first maturity of the fish species from shrimp-bycatch caught from industrial fisheries in the Mexican Pacific from Sinaloa to Guerrero, from January to March 2015. The shrimp-bycatch fish diversity value was found to be 2.22. A total of 37 species of finfish were found, of which five were considered rare. The fish species with the highest Importance Value Index (IVI) levels were Pseudupeneus grandisquamis , Paralichthys woolmani , Lutjanus peru and Diapterus peruvianus . The average size at first maturity was calculated for all species. Of the analysed organisms, 90% were in the juvenile stage, including species with riverine and artisanal fisheries. The present study demonstrates the risk within marine populations to different non-target species due to the poor selectivity of shrimp trawls.

Stylized facts in social networks: Community-based static modeling

NASA Astrophysics Data System (ADS)

Jo, Hang-Hyun; Murase, Yohsuke; Török, János; Kertész, János; Kaski, Kimmo

2018-06-01

The past analyses of datasets of social networks have enabled us to make empirical findings of a number of aspects of human society, which are commonly featured as stylized facts of social networks, such as broad distributions of network quantities, existence of communities, assortative mixing, and intensity-topology correlations. Since the understanding of the structure of these complex social networks is far from complete, for deeper insight into human society more comprehensive datasets and modeling of the stylized facts are needed. Although the existing dynamical and static models can generate some stylized facts, here we take an alternative approach by devising a community-based static model with heterogeneous community sizes and larger communities having smaller link density and weight. With these few assumptions we are able to generate realistic social networks that show most stylized facts for a wide range of parameters, as demonstrated numerically and analytically. Since our community-based static model is simple to implement and easily scalable, it can be used as a reference system, benchmark, or testbed for further applications.

High refuge availability on coral reefs increases the vulnerability of reef-associated predators to overexploitation.

PubMed

Rogers, Alice; Blanchard, Julia L; Newman, Steven P; Dryden, Charlie S; Mumby, Peter J

2018-02-01

Refuge availability and fishing alter predator-prey interactions on coral reefs, but our understanding of how they interact to drive food web dynamics, community structure and vulnerability of different trophic groups is unclear. Here, we apply a size-based ecosystem model of coral reefs, parameterized with empirical measures of structural complexity, to predict fish biomass, productivity and community structure in reef ecosystems under a broad range of refuge availability and fishing regimes. In unfished ecosystems, the expected positive correlation between reef structural complexity and biomass emerges, but a non-linear effect of predation refuges is observed for the productivity of predatory fish. Reefs with intermediate complexity have the highest predator productivity, but when refuge availability is high and prey are less available, predator growth rates decrease, with significant implications for fisheries. Specifically, as fishing intensity increases, predators in habitats with high refuge availability exhibit vulnerability to over-exploitation, resulting in communities dominated by herbivores. Our study reveals mechanisms for threshold dynamics in predators living in complex habitats and elucidates how predators can be food-limited when most of their prey are able to hide. We also highlight the importance of nutrient recycling via the detrital pathway, to support high predator biomasses on coral reefs. © 2018 by the Ecological Society of America.

Grazers structure the bacterial and algal diversity of aquatic metacommunities.

PubMed

Birtel, Julia; Matthews, Blake

2016-12-01

Consumers can have strong effects on the biotic and abiotic dynamics of spatially-structured ecosystems. In metacommunities, dispersing consumers can alter local assembly dynamics either directly through trophic interactions or indirectly by modifying local environmental conditions. In aquatic systems, very little is known about how key grazers, such as Daphnia, structure the microbial diversity of metacommunities and influence bacterial-mediated ecosystem functions. In an outdoor mesocosm experiment with replicate metacommunities (two 300 L mesocosms), we tested how the presence and absence of Daphnia and the initial density of the microbial community (manipulated via dilution) influenced the diversity and community structure of algae and bacteria, and several ecosystem properties (e.g., pH, dissolved substances) and functions (e.g., enzyme activity, respiration). We found that Daphnia strongly affected the local and regional diversity of both phytoplankton and bacteria, the taxonomic composition of bacterial communities, the biomass of algae, and ecosystem metabolism (i.e., respiration). Diluting the microbial inoculum (0.2-5 μm size fraction) to the metacommunities increased local phytoplankton diversity, decreased bacteria beta-diversity, and changed the relative abundance of bacterial classes. Changes in the rank abundance of different bacterial groups exhibited phylogenetic signal, implying that closely related bacteria species might share similar responses to the presence of Daphnia. © 2016 by the Ecological Society of America.

Association of marine viral and bacterial communities with reference black carbon particles under experimental conditions: an analysis with scanning electron, epifluorescence and confocal laser scanning microscopy.

PubMed

Cattaneo, Raffaela; Rouviere, Christian; Rassoulzadegan, Fereidoun; Weinbauer, Markus G

2010-11-01

Black carbon (BC), the product of incomplete combustion of fossil fuels and biomass, constitutes a significant fraction of the marine organic carbon pool. However, little is known about the possible interactions of BC and marine microorganisms. Here, we report the results of experiments using a standard reference BC material in high concentrations to investigate basic principles of the dynamics of natural bacterial and viral communities with BC particles. We assessed the attachment of viral and bacterial communities using scanning electron, epifluorescence and confocal laser scanning microscopy and shifts in bacterial community composition using 16S rRNA gene denaturing gradient gel electrophoresis (DGGE). In 24-h time-course experiments, BC particles showed a strong potential for absorbing viruses and bacteria. Total viral abundance was reduced, whereas total bacterial abundance was stimulated in the BC treatments. Viral and bacterial abundance on BC particles increased with particle size, whereas the abundances of BC-associated viruses and bacteria per square micrometer surface area decreased significantly with BC particle size. DGGE results suggested that BC has the potential to change bacterial community structure and favour phylotypes related to Glaciecola sp. Our study indicates that BC could influence processes mediated by bacteria and viruses in marine ecosystems. © 2010 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Influence of plankton community structure on the sinking velocity of marine aggregates

NASA Astrophysics Data System (ADS)

Bach, L. T.; Boxhammer, T.; Larsen, A.; Hildebrandt, N.; Schulz, K. G.; Riebesell, U.

2016-08-01

About 50 Gt of carbon is fixed photosynthetically by surface ocean phytoplankton communities every year. Part of this organic matter is reprocessed within the plankton community to form aggregates which eventually sink and export carbon into the deep ocean. The fraction of organic matter leaving the surface ocean is partly dependent on aggregate sinking velocity which accelerates with increasing aggregate size and density, where the latter is controlled by ballast load and aggregate porosity. In May 2011, we moored nine 25 m deep mesocosms in a Norwegian fjord to assess on a daily basis how plankton community structure affects material properties and sinking velocities of aggregates (Ø 80-400 µm) collected in the mesocosms' sediment traps. We noted that sinking velocity was not necessarily accelerated by opal ballast during diatom blooms, which could be due to relatively high porosity of these rather fresh aggregates. Furthermore, estimated aggregate porosity (Pestimated) decreased as the picoautotroph (0.2-2 µm) fraction of the phytoplankton biomass increased. Thus, picoautotroph-dominated communities may be indicative for food webs promoting a high degree of aggregate repackaging with potential for accelerated sinking. Blooms of the coccolithophore Emiliania huxleyi revealed that cell concentrations of 1500 cells/mL accelerate sinking by about 35-40%, which we estimate (by one-dimensional modeling) to elevate organic matter transfer efficiency through the mesopelagic from 14 to 24%. Our results indicate that sinking velocities are influenced by the complex interplay between the availability of ballast minerals and aggregate packaging; both of which are controlled by plankton community structure.

Environmental Effects on Mesozooplankton Size Structure and Export Flux at Station ALOHA, North Pacific Subtropical Gyre

NASA Astrophysics Data System (ADS)

Valencia, Bellineth; Décima, Moira; Landry, Michael R.

2018-02-01

Using size-fractionated mesozooplankton biomass data collected over 23 years (1994-2016) of increasing primary production (PP) at station ALOHA (A Long-Term Oligotrophic Habitat Assessment), we evaluate how changing environmental conditions affect mesozooplankton size structure, trophic cycling, and export fluxes in the subtropical North Pacific. From generalized additive model analysis, size structure is significantly influenced by a nonlinear relationship with sea surface temperature that is mainly driven by the strong 1997-1998 El Niño and a positive and linear relationship with PP. Increasing PP has more strongly enhanced the biomass of smaller (0.2-0.5 mm) and larger (>5 mm) mesozooplankton, increasing evenness of the biomass spectra, while animals of 2-5 mm, the major size class for vertically migrating mesozooplankton, show no long-term trend. Measured PP is sufficient to meet feeding requirements that satisfy mesozooplankton respiration and growth rates, as determined by commonly used empirical relationships based on animal size and temperature, consistent with a tightly coupled food web with one intermediate level for protistan consumers. Estimated fecal pellet production suggests an enhanced contribution of mesozooplankton to passive particle export relative to the material collected in 150 m sediment traps. In contrast, the biomass of vertically migrants does not vary systematically with PP due to the varying responses of the different size classes. These results illustrate some complexities in understanding how varying environmental conditions can affect carbon cycling and export processes at the community level in open-ocean oligotrophic systems, which need to be confirmed and better understood by process-oriented mechanistic study.

Bacterial Community Dynamics in Full-Scale Activated Sludge Bioreactors: Operational and Ecological Factors Driving Community Assembly and Performance

PubMed Central

Valentín-Vargas, Alexis; Toro-Labrador, Gladys; Massol-Deyá, Arturo A.

2012-01-01

The assembling of bacterial communities in conventional activated sludge (CAS) bioreactors was thought, until recently, to be chaotic and mostly unpredictable. Studies done over the last decade have shown that specific, and often, predictable random and non-random factors could be responsible for that process. These studies have also motivated a “structure–function” paradigm that is yet to be resolved. Thus, elucidating the factors that affect community assembly in the bioreactors is necessary for predicting fluctuations in community structure and function. For this study activated sludge samples were collected during a one-year period from two geographically distant CAS bioreactors of different size. Combining community fingerprinting analysis and operational parameters data with a robust statistical analysis, we aimed to identify relevant links between system performance and bacterial community diversity and dynamics. In addition to revealing a significant β-diversity between the bioreactors’ communities, results showed that the largest bioreactor had a less dynamic but more efficient and diverse bacterial community throughout the study. The statistical analysis also suggests that deterministic factors, as opposed to stochastic factors, may have a bigger impact on the community structure in the largest bioreactor. Furthermore, the community seems to rely mainly on mechanisms of resistance and functional redundancy to maintain functional stability. We suggest that the ecological theories behind the Island Biogeography model and the species-area relationship were appropriate to predict the assembly of bacterial communities in these CAS bioreactors. These results are of great importance for engineers and ecologists as they reveal critical aspects of CAS systems that could be applied towards improving bioreactor design and operation. PMID:22880016

Strategies of zooplanktivory shape the dynamics and diversity of littoral plankton communities: a mesocosm approach

PubMed Central

Helenius, Laura K; Aymà Padrós, Anna; Leskinen, Elina; Lehtonen, Hannu; Nurminen, Leena

2015-01-01

Planktivorous fish can exert strong top-down control on zooplankton communities. By incorporating different feeding strategies, from selective particulate feeding to cruising filter feeding, fish species target distinct prey. In this study, we investigated the effects of two species with different feeding strategies, the three-spined stickleback (Gasterosteus aculeatus (L.)) and roach (Rutilus rutilus (L.)), on a low-diversity brackish water zooplankton community using a 16-day mesocosm experiment. The experiment was conducted on a small-bodied spring zooplankton community in high-nutrient conditions, as well as a large-bodied summer community in low-nutrient conditions. Effects were highly dependent on the initial zooplankton community structure and hence seasonal variation. In a small-bodied community with high predation pressure and no dispersal or migration, the selective particulate-feeding stickleback depleted the zooplankton community and decreased its diversity more radically than the cruising filter-feeding roach. Cladocerans rather than copepods were efficiently removed by predation, and their removal caused altered patterns in rotifer abundance. In a large-bodied summer community with initial high taxonomic and functional diversity, predation pressure was lower and resource availability was high for omnivorous crustaceans preying on other zooplankton. In this community, predation maintained diversity, regardless of predator species. During both experimental periods, predation influenced the competitive relationship between the dominant calanoid copepods, and altered species composition and size structure of the zooplankton community. Changes also occurred to an extent at the level of nontarget prey, such as microzooplankton and rotifers, emphasizing the importance of subtle predation effects. We discuss our results in the context of the adaptive foraging mechanism and relate them to the natural littoral community. PMID:26045953

Similarity in parasite community structure may be used to trace latitudinal migrations of Odontesthes smitti along Argentinean coasts.

PubMed

Carballo, M C; Cremonte, F; Navone, G T; Timi, J T

2012-01-01

The aims of this study were to determine the existence of migratory movements and to identify ecological stocks of the silverside Odontesthes smitti along its distribution in the Southern Atlantic Ocean, using metazoan parasites as biological tags. Samples were obtained from San José Gulf (SJ) (42° 25' S; 64° 07' W) and Nuevo Gulf (NG) (42° 47' S; 65° 02' W) in north Patagonia during winter and summer and in waters off Mar del Plata (MDP) (38° 03' S; 57° 32' W), Bonaerense region, during winter. Fifteen parasite species were collected. Multivariate statistical procedures on parasite community data showed strong effect of host size on the structure of parasite assemblages. Taking into account the variations among samples due to host size, the differential structure of parasite communities between SJ and NG suggests that fish inhabiting these localities could belong to different ecological stocks. Fish from MDP and SJ caught in summer showed similar composition in their parasite assemblages, which is congruent with a migratory cycle that implies that fish caught in MDP during winter inhabit SJ during summer. Further evidence of the Patagonian origin of MDP O. smitti is the presence of the digenean Proctotrema bartolii in fish from both regions. Proctotrema bartolii is acquired by O. smitti only in the Magellanic province, where its intermediate host, Darina solenoides, is distributed. The analyses suggest that O. smitti inhabiting north Patagonian gulfs could belong to different ecological stocks and that O. smitti caught in MDP could have come from SJ. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

Structure of the Epiphyte Community in a Tropical Montane Forest in SW China

PubMed Central

Zhao, Mingxu; Geekiyanage, Nalaka; Xu, Jianchu; Khin, Myo Myo; Nurdiana, Dian Ridwan; Paudel, Ekananda; Harrison, Rhett Daniel

2015-01-01

Vascular epiphytes are an understudied and particularly important component of tropical forest ecosystems. However, owing to the difficulties of access, little is known about the properties of epiphyte-host tree communities and the factors structuring them, especially in Asia. We investigated factors structuring the vascular epiphyte-host community and its network properties in a tropical montane forest in Xishuangbanna, SW China. Vascular epiphytes were surveyed in six plots located in mature forests. Six host and four micro-site environmental factors were investigated. Epiphyte diversity was strongly correlated with host size (DBH, diameter at breast height), while within hosts the highest epiphyte diversity was in the middle canopy and epiphyte diversity was significantly higher in sites with canopy soil or a moss mat than on bare bark. DBH, elevation and stem height explained 22% of the total variation in the epiphyte species assemblage among hosts, and DBH was the most important factor which alone explained 6% of the variation. Within hosts, 51% of the variation in epiphyte assemblage composition was explained by canopy position and substrate, and the most important single factor was substrate which accounted for 16% of the variation. Analysis of network properties indicated that the epiphyte host community was highly nested, with a low level of epiphyte specialization, and an almost even interaction strength between epiphytes and host trees. Together, these results indicate that large trees harbor a substantial proportion of the epiphyte community in this forest. PMID:25856457

Generalized epidemic process on modular networks.

PubMed

Chung, Kihong; Baek, Yongjoo; Kim, Daniel; Ha, Meesoon; Jeong, Hawoong

2014-05-01

Social reinforcement and modular structure are two salient features observed in the spreading of behavior through social contacts. In order to investigate the interplay between these two features, we study the generalized epidemic process on modular networks with equal-sized finite communities and adjustable modularity. Using the analytical approach originally applied to clique-based random networks, we show that the system exhibits a bond-percolation type continuous phase transition for weak social reinforcement, whereas a discontinuous phase transition occurs for sufficiently strong social reinforcement. Our findings are numerically verified using the finite-size scaling analysis and the crossings of the bimodality coefficient.

Genetic variants associated with cardiac structure and function: a meta-analysis and replication of genome-wide association data.

PubMed

Vasan, Ramachandran S; Glazer, Nicole L; Felix, Janine F; Lieb, Wolfgang; Wild, Philipp S; Felix, Stephan B; Watzinger, Norbert; Larson, Martin G; Smith, Nicholas L; Dehghan, Abbas; Grosshennig, Anika; Schillert, Arne; Teumer, Alexander; Schmidt, Reinhold; Kathiresan, Sekar; Lumley, Thomas; Aulchenko, Yurii S; König, Inke R; Zeller, Tanja; Homuth, Georg; Struchalin, Maksim; Aragam, Jayashri; Bis, Joshua C; Rivadeneira, Fernando; Erdmann, Jeanette; Schnabel, Renate B; Dörr, Marcus; Zweiker, Robert; Lind, Lars; Rodeheffer, Richard J; Greiser, Karin Halina; Levy, Daniel; Haritunians, Talin; Deckers, Jaap W; Stritzke, Jan; Lackner, Karl J; Völker, Uwe; Ingelsson, Erik; Kullo, Iftikhar; Haerting, Johannes; O'Donnell, Christopher J; Heckbert, Susan R; Stricker, Bruno H; Ziegler, Andreas; Reffelmann, Thorsten; Redfield, Margaret M; Werdan, Karl; Mitchell, Gary F; Rice, Kenneth; Arnett, Donna K; Hofman, Albert; Gottdiener, John S; Uitterlinden, Andre G; Meitinger, Thomas; Blettner, Maria; Friedrich, Nele; Wang, Thomas J; Psaty, Bruce M; van Duijn, Cornelia M; Wichmann, H-Erich; Munzel, Thomas F; Kroemer, Heyo K; Benjamin, Emelia J; Rotter, Jerome I; Witteman, Jacqueline C; Schunkert, Heribert; Schmidt, Helena; Völzke, Henry; Blankenberg, Stefan

2009-07-08

Echocardiographic measures of left ventricular (LV) structure and function are heritable phenotypes of cardiovascular disease. To identify common genetic variants associated with cardiac structure and function by conducting a meta-analysis of genome-wide association data in 5 population-based cohort studies (stage 1) with replication (stage 2) in 2 other community-based samples. Within each of 5 community-based cohorts comprising the EchoGen consortium (stage 1; n = 12 612 individuals of European ancestry; 55% women, aged 26-95 years; examinations between 1978-2008), we estimated the association between approximately 2.5 million single-nucleotide polymorphisms (SNPs; imputed to the HapMap CEU panel) and echocardiographic traits. In stage 2, SNPs significantly associated with traits in stage 1 were tested for association in 2 other cohorts (n = 4094 people of European ancestry). Using a prespecified P value threshold of 5 x 10(-7) to indicate genome-wide significance, we performed an inverse variance-weighted fixed-effects meta-analysis of genome-wide association data from each cohort. Echocardiographic traits: LV mass, internal dimensions, wall thickness, systolic dysfunction, aortic root, and left atrial size. In stage 1, 16 genetic loci were associated with 5 echocardiographic traits: 1 each with LV internal dimensions and systolic dysfunction, 3 each with LV mass and wall thickness, and 8 with aortic root size. In stage 2, 5 loci replicated (6q22 locus associated with LV diastolic dimensions, explaining <1% of trait variance; 5q23, 12p12, 12q14, and 17p13 associated with aortic root size, explaining 1%-3% of trait variance). We identified 5 genetic loci harboring common variants that were associated with variation in LV diastolic dimensions and aortic root size, but such findings explained a very small proportion of variance. Further studies are required to replicate these findings, identify the causal variants at or near these loci, characterize their functional significance, and determine whether they are related to overt cardiovascular disease.

Indirect Short- and Long-Term Effects of Aboveground Invertebrate and Vertebrate Herbivores on Soil Microarthropod Communities

PubMed Central

Vandegehuchte, Martijn L.; Raschein, Ursina; Schütz, Martin; Gwiazdowicz, Dariusz J.; Risch, Anita C.

2015-01-01

Recognition is growing that besides ungulates, small vertebrate and invertebrate herbivores are important drivers of grassland functioning. Even though soil microarthropods play key roles in several soil processes, effects of herbivores—especially those of smaller body size—on their communities are not well understood. Therefore, we progressively excluded large, medium and small vertebrate and invertebrate herbivores for three growing seasons using size-selective fences in two vegetation types in subalpine grasslands; short-grass and tall-grass vegetation generated by high and low historical levels of ungulate grazing. Herbivore exclusions generally had few effects on microarthropod communities, but exclusion of all herbivore groups resulted in decreased total springtail and Poduromorpha richness compared with exclusion of only ungulates and medium-sized mammals, regardless of vegetation type. The tall-grass vegetation had a higher total springtail richness and mesostigmatid mite abundance than the short-grass vegetation and a different oribatid mite community composition. Although several biotic and abiotic variables differed between the exclusion treatments and vegetation types, effects on soil microarthropods were best explained by differences in nutrient and fibre content of the previous year’s vegetation, a proxy for litter quality, and to a lesser extent soil temperature. After three growing seasons, smaller herbivores had a stronger impact on these functionally important soil microarthropod communities than large herbivores. Over longer time-scales, however, large grazers created two different vegetation types and thereby influenced microarthropod communities bottom-up, e.g. by altering resource quality. Hence, both short- and long-term consequences of herbivory affected the structure of the soil microarthropod community. PMID:25738942

Shifts in community size structure drive temperature invariance of secondary production in a stream-warming experiment.

PubMed

Nelson, Daniel; Benstead, Jonathan P; Huryn, Alexander D; Cross, Wyatt F; Hood, James M; Johnson, Philip W; Junker, James R; Gíslason, Gísli M; Ólafsson, Jón S

2017-07-01

A central question at the interface of food-web and climate change research is how secondary production, or the formation of heterotroph biomass over time, will respond to rising temperatures. The metabolic theory of ecology (MTE) hypothesizes the temperature-invariance of secondary production, driven by matched and opposed forces that reduce biomass of heterotrophs while increasing their biomass turnover rate (production : biomass, or P:B) with warming. To test this prediction at the whole community level, we used a geothermal heat exchanger to experimentally warm a stream in southwest Iceland by 3.8°C for two years. We quantified invertebrate community biomass, production, and P : B in the experimental stream and a reference stream for one year prior to warming and two years during warming. As predicted, warming had a neutral effect on community production, but this result was not driven by opposing effects on community biomass and P:B. Instead, warming had a positive effect on both the biomass and production of larger-bodied, slower-growing taxa (e.g., larval black flies, dipteran predators, snails) and a negative effect on small-bodied taxa with relatively high growth rates (e.g., ostracods, larval chironomids). We attribute these divergent responses to differences in thermal preference between small- vs. large-bodied taxa. Although metabolic demand vs. resource supply must ultimately constrain community production, our results highlight the potential for idiosyncratic community responses to warming, driven by variation in thermal preference and body size within regional species pools. © 2017 by the Ecological Society of America.

Benthic Community Structure and Sediment Geochemical Properties at Hydrocarbon Seeps Along the Continental Slope of the Western North Atlantic

NASA Astrophysics Data System (ADS)

Demopoulos, A. W.; Bourque, J. R.; Brooke, S.

2015-12-01

Hydrocarbon seeps support distinct benthic communities capable of utilizing reduced chemical compounds for nutrition. In recent years, methane seepage has been increasingly documented along the continental slope of the U.S. Atlantic margin. In 2012 and 2013, two seeps were investigated in this region: a shallow site near Baltimore Canyon (410-450 m) and a deep site near Norfolk Canyon (1600 m). Both sites contain extensive mussel beds and microbial mats. Sediment cores and grab samples were collected to quantify the abundance, diversity, and community structure of benthic macrofauna (>300 mm) in relationship to the associated sediment environment (organic carbon and nitrogen, stable isotopes 13C and 15N, grain size, and depth) of mussel beds, mats, and slope habitats. Macrofaunal densities in microbial mats were four times greater than those present in mussel beds and slope sediments. Macrofaunal communities were distinctly different both between depths and among habitat types. Specifically, microbial mat sediments were dominated by the annelid families Dorvilleidae, Capitellidae, and Tubificidae, while mussel habitats had higher proportions of crustaceans. Diversity was lower in Baltimore microbial mat habitats, but higher in mussel and slope sediments compared to Norfolk seep habitats found at deeper depths. Multivariate statistical analysis identified sediment carbon:nitrogen (C:N) ratios and 13C values as important variables for structuring the macrofaunal communities. Higher C:N ratios were present within microbial mat habitats and depleted 13C values occurred in sediments adjacent to mussel beds found in Norfolk Canyon seeps. Differences in the quality and source of organic matter present in the seep habitats are known to be important drivers in macrofaunal community structure and associated food webs. The multivariate analysis provides new insight into the relative importance of the seep sediment quality in supporting dense macrofaunal communities compared to other seeps found throughout the region.

Temporal variation in bat-fruit interactions: Foraging strategies influence network structure over time

NASA Astrophysics Data System (ADS)

Zapata-Mesa, Natalya; Montoya-Bustamante, Sebastián; Murillo-García, Oscar E.

2017-11-01

Mutualistic interactions, such as seed dispersal, are important for the maintenance of structure and stability of tropical communities. However, there is a lack of information about spatial and temporal variation in plant-animal interaction networks. Thus, our goal was to assess the effect of bat's foraging strategies on temporal variation in the structure and robustness of bat-fruit networks in both a dry and a rain tropical forest. We evaluated monthly variation in bat-fruit networks by using seven structure metrics: network size, average path length, nestedness, modularity, complementary specialization, normalized degree and betweenness centrality. Seed dispersal networks showed variations in size, species composition and modularity; did not present nested structures and their complementary specialization was high compared to other studies. Both networks presented short path lengths, and a constantly high robustness, despite their monthly variations. Sedentary bat species were recorded during all the study periods and occupied more central positions than nomadic species. We conclude that foraging strategies are important structuring factors that affect the dynamic of networks by determining the functional roles of frugivorous bats over time; thus sedentary bats are more important than nomadic species for the maintenance of the network structure, and their conservation is a must.

Inducible defenses in prey intensify predator cannibalism.

PubMed

Kishida, Osamu; Trussell, Geoffrey C; Nishimura, Kinya; Ohgushi, Takayuki

2009-11-01

Trophic cascades are often a potent force in ecological communities, but abiotic and biotic heterogeneity can diffuse their influence. For example, inducible defenses in many species create variation in prey edibility, and size-structured interactions, such as cannibalism, can shift predator diets away from heterospecific prey. Although both factors diffuse cascade strength by adding heterogeneity to trophic interactions, the consequences of their interactioh remain poorly understood. We show that inducible defenses in tadpole prey greatly intensify cannibalism in predatory larval salamanders. The likelihood of cannibalism was also strongly influenced by asymmetries in salamander size that appear to be most important in the presence of defended prey. Hence, variation in prey edibility and the size structure of the predator may synergistically affect predator-prey population dynamics by reducing prey mortality and increasing predator mortality via cannibalism. We also suggest that the indirect effects of prey defenses may shape the evolution of predator traits that determine diet breadth and how trophic dynamics unfold in natural systems.

Structural vulnerability of the French swine industry trade network to the spread of infectious diseases.

PubMed

Rautureau, S; Dufour, B; Durand, B

2012-07-01

The networks generated by live animal movements are the principal vector for the propagation of infectious agents between farms, and their topology strongly affects how fast a disease may spread. The structural characteristics of networks may thus provide indicators of network vulnerability to the spread of infectious disease. This study applied social network analysis methods to describe the French swine trade network. Initial analysis involved calculating several parameters to characterize networks and then identifying high-risk subgroups of holdings for different time scales. Holding-specific centrality measurements ('degree', 'betweenness' and 'ingoing infection chain'), which summarize the place and the role of holdings in the network, were compared according to the production type. In addition, network components and communities, areas where connectedness is particularly high and could influence the speed and the extent of a disease, were identified and analysed. Dealer holdings stood out because of their high centrality values suggesting that these holdings may control the flow of animals in part of the network. Herds with growing units had higher values for degree and betweenness centrality, representing central positions for both spreading and receiving disease, whereas herds with finishing units had higher values for in-degree and ingoing infection chain centrality values and appeared more vulnerable with many contacts through live animal movements and thus at potentially higher risk for introduction of contagious diseases. This reflects the dynamics of the swine trade with downward movements along the production chain. But, the significant heterogeneity of farms with several production units did not reveal any particular type of production for targeting disease surveillance or control. Besides, no giant strong connected component was observed, the network being rather organized according to communities of small or medium size (<20% of network size). Because of this fragmentation, the swine trade network appeared less structurally vulnerable than ruminant trade networks. This fragmentation is explained by the hierarchical structure, which thus limits the structural vulnerability of the global trade network. However, inside communities, the hierarchical structure of the swine production system would favour the spread of an infectious agent (especially if introduced in breeding herds).

Microbial community variation in cryoconite granules on Qaanaaq Glacier, NW Greenland.

PubMed

Uetake, Jun; Tanaka, Sota; Segawa, Takahiro; Takeuchi, Nozomu; Nagatsuka, Naoko; Motoyama, Hideaki; Aoki, Teruo

2016-09-01

Cryoconite granules are aggregations of microorganisms with mineral particles that form on glacier surfaces. To understand the processes by which the granules develop, this study focused on the altitudinal distribution of the granules and photosynthetic microorganisms on the glacier, bacterial community variation with granules size and environmental factors affecting the growth of the granules. Size-sorted cryoconite granules collected from five different sites on Qaanaaq Glacier were analyzed. C and N contents were significantly higher in large (diameter greater than 250 μm) granules than in smaller (diameter 30-249 μm) granules. Bacterial community structures, based on 16S rRNA gene amplicon sequencing, were different between the smaller and larger granules. The filamentous cyanobacterium Phormidesmis priestleyi was the dominant bacterial species in larger granules. Multivariate analysis suggests that the abundance of mineral particles on the glacier surface is the main factor controlling growth of these cyanobacteria. These results show that the supply of mineral particles on the glacier enhances granule development, that P. priestleyi is likely the key species for primary production and the formation of the granules and that the bacterial community in the granules changes over the course of the granule development. © FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Community size as a factor in health partnerships in community parks and recreation, 2007.

PubMed

Payne, Laura L; Zimmermann, Jo An M; Mowen, Andrew J; Orsega-Smith, Elizabeth; Godbey, Geoffrey C

2013-07-25

Although partnerships between park and recreation agencies and health agencies are prevalent, little research has examined partnership characteristics and effectiveness among communities of different sizes. The objective of this study was to determine whether park and recreation leaders' perceptions of partnership characteristics, effectiveness, and outcomes vary by community size. A web-based survey was completed in 2007 by 1,217 National Recreation and Park Association members. Community size was divided into 4 categories: very small, small, medium, and large. Questions measured agencies' recognition of the need for partnerships, their level of experience, and the effectiveness and outcomes of partnerships. Larger communities were significantly more likely to recognize the need for and have more experience with partnerships than smaller communities. Very small and large communities partnered significantly more often with senior services, nonprofit health promotion agencies, and public health agencies than did small and medium ones. Large and small communities were significantly more likely than very small and medium communities to agree that their decision making in partnerships is inclusive and that they have clearly defined goals and objectives. Large communities were significantly more likely than very small communities to report that their partnership helped leverage resources, make policy changes, meet their mission statement, and link to funding opportunities. Community size shapes partnership practices, effectiveness, and outcomes. Very small communities are disadvantaged in developing and managing health partnerships. Increasing education, training, and funding opportunities for small and rural park and recreation agencies may enable them to more effectively partner with organizations to address community health concerns.

Community Size as a Factor in Health Partnerships in Community Parks and Recreation, 2007

PubMed Central

Zimmermann, Jo An M.; Mowen, Andrew J.; Orsega-Smith, Elizabeth; Godbey, Geoffrey C.

2013-01-01

Introduction Although partnerships between park and recreation agencies and health agencies are prevalent, little research has examined partnership characteristics and effectiveness among communities of different sizes. The objective of this study was to determine whether park and recreation leaders’ perceptions of partnership characteristics, effectiveness, and outcomes vary by community size. Methods A web-based survey was completed in 2007 by 1,217 National Recreation and Park Association members. Community size was divided into 4 categories: very small, small, medium, and large. Questions measured agencies’ recognition of the need for partnerships, their level of experience, and the effectiveness and outcomes of partnerships. Results Larger communities were significantly more likely to recognize the need for and have more experience with partnerships than smaller communities. Very small and large communities partnered significantly more often with senior services, nonprofit health promotion agencies, and public health agencies than did small and medium ones. Large and small communities were significantly more likely than very small and medium communities to agree that their decision making in partnerships is inclusive and that they have clearly defined goals and objectives. Large communities were significantly more likely than very small communities to report that their partnership helped leverage resources, make policy changes, meet their mission statement, and link to funding opportunities. Conclusion Community size shapes partnership practices, effectiveness, and outcomes. Very small communities are disadvantaged in developing and managing health partnerships. Increasing education, training, and funding opportunities for small and rural park and recreation agencies may enable them to more effectively partner with organizations to address community health concerns. PMID:23886043

Predator-induced demographic shifts in coral reef fish assemblages

USGS Publications Warehouse

Ruttenberg, B.I.; Hamilton, S.L.; Walsh, S.M.; Donovan, M.K.; Friedlander, A.; DeMartini, E.; Sala, E.; Sandin, S.A.

2011-01-01

In recent years, it has become apparent that human impacts have altered community structure in coastal and marine ecosystems worldwide. Of these, fishing is one of the most pervasive, and a growing body of work suggests that fishing can have strong effects on the ecology of target species, especially top predators. However, the effects of removing top predators on lower trophic groups of prey fishes are less clear, particularly in highly diverse and trophically complex coral reef ecosystems. We examined patterns of abundance, size structure, and age-based demography through surveys and collection-based studies of five fish species from a variety of trophic levels at Kiritimati and Palmyra, two nearby atolls in the Northern Line Islands. These islands have similar biogeography and oceanography, and yet Kiritimati has ~10,000 people with extensive local fishing while Palmyra is a US National Wildlife Refuge with no permanent human population, no fishing, and an intact predator fauna. Surveys indicated that top predators were relatively larger and more abundant at unfished Palmyra, while prey functional groups were relatively smaller but showed no clear trends in abundance as would be expected from classic trophic cascades. Through detailed analyses of focal species, we found that size and longevity of a top predator were lower at fished Kiritimati than at unfished Palmyra. Demographic patterns also shifted dramatically for 4 of 5 fish species in lower trophic groups, opposite in direction to the top predator, including decreases in average size and longevity at Palmyra relative to Kiritimati. Overall, these results suggest that fishing may alter community structure in complex and non-intuitive ways, and that indirect demographic effects should be considered more broadly in ecosystem-based management. ?? 2011 Ruttenberg et al.

Predator-Induced Demographic Shifts in Coral Reef Fish Assemblages

PubMed Central

Ruttenberg, Benjamin I.; Hamilton, Scott L.; Walsh, Sheila M.; Donovan, Mary K.; Friedlander, Alan; DeMartini, Edward; Sala, Enric; Sandin, Stuart A.

2011-01-01

In recent years, it has become apparent that human impacts have altered community structure in coastal and marine ecosystems worldwide. Of these, fishing is one of the most pervasive, and a growing body of work suggests that fishing can have strong effects on the ecology of target species, especially top predators. However, the effects of removing top predators on lower trophic groups of prey fishes are less clear, particularly in highly diverse and trophically complex coral reef ecosystems. We examined patterns of abundance, size structure, and age-based demography through surveys and collection-based studies of five fish species from a variety of trophic levels at Kiritimati and Palmyra, two nearby atolls in the Northern Line Islands. These islands have similar biogeography and oceanography, and yet Kiritimati has ∼10,000 people with extensive local fishing while Palmyra is a US National Wildlife Refuge with no permanent human population, no fishing, and an intact predator fauna. Surveys indicated that top predators were relatively larger and more abundant at unfished Palmyra, while prey functional groups were relatively smaller but showed no clear trends in abundance as would be expected from classic trophic cascades. Through detailed analyses of focal species, we found that size and longevity of a top predator were lower at fished Kiritimati than at unfished Palmyra. Demographic patterns also shifted dramatically for 4 of 5 fish species in lower trophic groups, opposite in direction to the top predator, including decreases in average size and longevity at Palmyra relative to Kiritimati. Overall, these results suggest that fishing may alter community structure in complex and non-intuitive ways, and that indirect demographic effects should be considered more broadly in ecosystem-based management. PMID:21698165

The consequences of balanced harvesting of fish communities

PubMed Central

Jacobsen, Nis S.; Gislason, Henrik; Andersen, Ken H.

2014-01-01

Balanced harvesting, where species or individuals are exploited in accordance with their productivity, has been proposed as a way to minimize the effects of fishing on marine fish communities and ecosystems. This calls for a thorough examination of the consequences balanced harvesting has on fish community structure and yield. We use a size- and trait-based model that resolves individual interactions through competition and predation to compare balanced harvesting with traditional selective harvesting, which protects juvenile fish from fishing. Four different exploitation patterns, generated by combining selective or unselective harvesting with balanced or unbalanced fishing, are compared. We find that unselective balanced fishing, where individuals are exploited in proportion to their productivity, produces a slightly larger total maximum sustainable yield than the other exploitation patterns and, for a given yield, the least change in the relative biomass composition of the fish community. Because fishing reduces competition, predation and cannibalism within the community, the total maximum sustainable yield is achieved at high exploitation rates. The yield from unselective balanced fishing is dominated by small individuals, whereas selective fishing produces a much higher proportion of large individuals in the yield. Although unselective balanced fishing is predicted to produce the highest total maximum sustainable yield and the lowest impact on trophic structure, it is effectively a fishery predominantly targeting small forage fish. PMID:24307676

The size of an ethno-cultural community as a social determinant of health for Chinese seniors.

PubMed

Chau, Shirley; Lai, Daniel W L

2011-12-01

The present study investigated the link between the sizes of the Chinese community to the health of Chinese seniors in Canada. A secondary data analysis of survey data from a representative sample of 2,272 Chinese older adults aged 55 and over was conducted. Hierarchical regression analyses were performed to assess the effects of the size of Chinese communities in Chinese seniors' health. Chinese seniors residing in the community with a small Chinese population reported better physical and mental health than the Chinese seniors residing in communities with a larger Chinese population. The findings were contrary to expectations that health of Chinese seniors should be higher in cities with large Chinese communities. These findings raise new questions for future investigations into the dynamics and impact of ethnic community size, and the importance of studying intragroup differences within ethno-cultural groups to better understand health disparities in ethnic groups.

The co-evolution of cultures, social network communities, and agent locations in an extension of Axelrod’s model of cultural dissemination

NASA Astrophysics Data System (ADS)

Pfau, Jens; Kirley, Michael; Kashima, Yoshihisa

2013-01-01

We introduce a variant of the Axelrod model of cultural dissemination in which agents change their physical locations, social links, and cultures. Numerical simulations are used to investigate the evolution of social network communities and the cultural diversity within and between these communities. An analysis of the simulation results shows that an initial peak in the cultural diversity within network communities is evident before agents segregate into a final configuration of culturally homogeneous communities. Larger long-range interaction probabilities facilitate the initial emergence of culturally diverse network communities, which leads to a more pronounced initial peak in cultural diversity within communities. At equilibrium, the number of communities, and hence cultures, increases when the initial cultural diversity increases. However, the number of communities decreases when the lattice size or population density increases. A phase transition between two regimes of initial cultural diversity is evident. For initial diversities below a critical value, a single network community and culture emerges that dominates the population. For initial diversities above the critical value, multiple culturally homogeneous communities emerge. The critical value of initial diversity at which this transition occurs increases with increasing lattice size and population density and generally with increasing absolute population size. We conclude that larger initial diversities promote cultural heterogenization, while larger lattice sizes, population densities, and in fact absolute population sizes promote homogenization.

The impact of wave exposure on the meiofauna of Gelidium pristoides (Turner) Kuetzing (Gelidiales: Rhodophyta)

NASA Astrophysics Data System (ADS)

Gibbons, M. J.

1988-12-01

The impact of wave exposure on the meiofaunal communities colonising Gelidium pristoides, was examined on five shores around False Bay, South Africa. Under conditions of constant algal structure and mass, and in tufts with similar epiphyte and sediment loads, exposure had a profound impact on meiofaunal communities. Algae on sheltered shores supported significantly greater numbers of animals in the size range 63-280 μm (predominantly copepods, copepod nauplii and ostracods), while those on exposed shores supported a greater number of amphipods and bivalves. Total meiofaunal biomass per tuft remained constant irrespective of shore type. Differences between shores are discussed in terms of algal structure and animal size and morphology. Gelidium tufts are open-plan and offer little resistance to water movement; as the frond diameter is wider than the meiofauna are long, small animals are likely to be flushed more easily from exposed than sheltered shores. Differences in the abundance of permanent meiofauna between shores may, however, reflect ifferences in the organic content of sediments, although this was not examined. It is also suggested that meiofaunal communities on plants from different shores are influenced by the total algal and macrofaunal standing stocks, which act as banks of meiofauna and influence the regularity and magnitude of immigration. Extrapolating these data to the whole shore indicates that while the biomass of meiofauna may be greater on exposed than sheltered shores, the proportional contribution of meiofauna to total secondary production is greater under more sheltered conditions.

Study of methanogen communities associated with different rumen protozoal populations

PubMed Central

Belanche, Alejandro; de la Fuente, Gabriel; Newbold, Charles J

2014-01-01

Protozoa-associated methanogens (PAM) are considered one of the most active communities in the rumen methanogenesis. This experiment investigated whether methanogens are sequestrated within rumen protozoa, and structural differences between rumen free-living methanogens and PAM. Rumen protozoa were harvested from totally faunated sheep, and six protozoal fractions (plus free-living microorganisms) were generated by sequential filtration. Holotrich-monofaunated sheep were also used to investigate the holotrich-associated methanogens. Protozoal size determined the number of PAM as big protozoa had 1.7–3.3 times more methanogen DNA than smaller protozoa, but also more endosymbiotic bacteria (2.2- to 3.5-fold times). Thus, similar abundance of methanogens with respect to total bacteria were observed across all protozoal fractions and free-living microorganisms, suggesting that methanogens are not accumulated within rumen protozoa in a greater proportion to that observed in the rumen as a whole. All rumen methanogen communities had similar diversity (22.2 ± 3.4 TRFs). Free-living methanogens composed a conserved community (67% similarity within treatment) in the rumen with similar diversity but different structures than PAM (P < 0.05). On the contrary, PAM constituted a more variable community (48% similarity), which differed between holotrich and total protozoa (P < 0.001). Thus, PAM constitutes a community, which requires further investigation as part of methane mitigation strategies. PMID:25195951

Ice cover extent drives phytoplankton and bacterial community structure in a large north-temperate lake: implications for a warming climate.

PubMed

Beall, B F N; Twiss, M R; Smith, D E; Oyserman, B O; Rozmarynowycz, M J; Binding, C E; Bourbonniere, R A; Bullerjahn, G S; Palmer, M E; Reavie, E D; Waters, Lcdr M K; Woityra, Lcdr W C; McKay, R M L

2016-06-01

Mid-winter limnological surveys of Lake Erie captured extremes in ice extent ranging from expansive ice cover in 2010 and 2011 to nearly ice-free waters in 2012. Consistent with a warming climate, ice cover on the Great Lakes is in decline, thus the ice-free condition encountered may foreshadow the lakes future winter state. Here, we show that pronounced changes in annual ice cover are accompanied by equally important shifts in phytoplankton and bacterial community structure. Expansive ice cover supported phytoplankton blooms of filamentous diatoms. By comparison, ice free conditions promoted the growth of smaller sized cells that attained lower total biomass. We propose that isothermal mixing and elevated turbidity in the absence of ice cover resulted in light limitation of the phytoplankton during winter. Additional insights into microbial community dynamics were gleaned from short 16S rRNA tag (Itag) Illumina sequencing. UniFrac analysis of Itag sequences showed clear separation of microbial communities related to presence or absence of ice cover. Whereas the ecological implications of the changing bacterial community are unclear at this time, it is likely that the observed shift from a phytoplankton community dominated by filamentous diatoms to smaller cells will have far reaching ecosystem effects including food web disruptions. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.

Shifts of microbial community structure in soils of a photovoltaic plant observed using tag-encoded pyrosequencing of 16S rRNA.

PubMed

Wu, Shijin; Li, Yuan; Wang, Penghua; Zhong, Li; Qiu, Lequan; Chen, Jianmeng

2016-04-01

The environmental risk of fluoride and chloride pollution is pronounced in soils adjacent to solar photovoltaic sites. The elevated levels of fluoride and chloride in these soils have had significant impacts on the population size and overall biological activity of the soil microbial communities. The microbial community also plays an essential role in remediation of these soils. Questions remain as to how the fluoride and chloride contamination and subsequent remediation at these sites have impacted the population structure of the soil microbial communities. We analyzed the microbial communities in soils collected from close to a solar photovoltaic enterprise by pyrosequencing of the 16S rRNA tag. In addition, we used multivariate statistics to identity the relationships shared between sequence diversity and heterogeneity in the soil environment. The overall microbial communities were surprisingly diverse, harboring a wide variety of taxa and sharing significant correlations with different degrees of fluoride and chloride contamination. The contaminated soils harbored abundant bacteria that were probably resistant to the high acidity, high fluoride and chloride concentration, and high osmotic pressure environment. The dominant genera were Sphingomonas, Subgroup_6_norank, Clostridium sensu stricto, Nitrospira, Rhizomicrobium, and Acidithiobacillus. The results of this study provide new information regarding a previously uncharacterized ecosystem and show the value of high-throughput sequencing in the study of complex ecosystems.

Local richness along gradients in the Siskiyou herb flora: R.H. Whittaker revisited

USGS Publications Warehouse

Grace, James B.; Harrison, Susan; Damschen, Ellen Ingman

2011-01-01

In his classic study in the Siskiyou Mountains (Oregon, USA), one of the most botanically rich forested regions in North America, R. H. Whittaker (1960) foreshadowed many modern ideas on the multivariate control of local species richness along environmental gradients related to productivity. Using a structural equation model to analyze his data, which were never previously statistically analyzed, we demonstrate that Whittaker was remarkably accurate in concluding that local herb richness in these late-seral forests is explained to a large extent by three major abiotic gradients (soils, topography, and elevation), and in turn, by the effects of these gradients on tree densities and the numbers of individual herbs. However, while Whittaker also clearly appreciated the significance of large-scale evolutionary and biogeographic influences on community composition, he did not fully articulate the more recent concept that variation in the species richness of local communities could be explained in part by variation in the sizes of regional species pools. Our model of his data is among the first to use estimates of regional species pool size to explain variation in local community richness along productivity-related gradients. We find that regional pool size, combined with a modest number of other interacting abiotic and biotic factors, explains most of the variation in local herb richness in the Siskiyou biodiversity hotspot.

Baseline assessment of fish communities, benthic macroinvertebrate communities, and stream habitat and land use, Big Thicket National Preserve, Texas, 1999-2001

USGS Publications Warehouse

Moring, J. Bruce

2003-01-01

The Big Thicket National Preserve comprises 39,300 hectares in the form of nine preserve units connected by four stream corridor units (with two more corridor units proposed) distributed over the lower Neches and Trinity River Basins of southeastern Texas. Fish and benthic macroinvertebrate data were collected at 15 stream sites (reaches) in the preserve during 1999–2001 for a baseline assessment and a comparison of communities among stream reaches. The fish communities in the preserve were dominated by minnows (family Cyprinidae) and sunfishes (family Centrarchidae). Reaches with smaller channel sizes generally had higher fish species richness than the larger reaches in the Neches River and Pine Island Bayou units of the preserve. Fish communities in geographically adjacent reaches were most similar in overall community structure. The blue sucker, listed by the State as a threatened species, was collected in only one reach—a Neches River reach a few miles downstream from the Steinhagen Lake Dam. Riffle beetles (family Elmidae) and midges (family Chironomidae) dominated the aquatic insect communities at the 14 reaches sampled for aquatic insects in the preserve. The Ephemeroptera, Plecoptera and Trichoptera (EPT) Index, an index sensitive to water-quality degradation, was smallest at the Little Pine Island Bayou near Beaumont reach that is in a State 303(d)-listed stream segment on Little Pine Island Bayou. Trophic structure of the aquatic insect communities is consistent with the river continuum concept with shredder and scraper insect taxa more abundant in reaches with smaller stream channels and filter feeders more abundant in reaches with larger channels. Aquatic insect community metrics were not significantly correlated to any of the stream-habitat or land-use explanatory variables. The percentage of 1990s urban land use in the drainage areas upstream from 12 bioassessment reaches were negatively correlated to the reach structure index, which indicates less stable habitat for aquatic biota.

Microbial community production, respiration, and structure of the microbial food web of an ecosystem in the northeastern Atlantic Ocean

NASA Astrophysics Data System (ADS)

Maixandeau, Anne; LefèVre, Dominique; Karayanni, Hera; Christaki, Urania; van Wambeke, France; Thyssen, Melilotus; Denis, Michel; FernáNdez, Camila I.; Uitz, Julia; Leblanc, Karine; QuéGuiner, Bernard

2005-07-01

Gross community production (GCP), dark community respiration (DCR), and the biomass of the different size classes of organisms in the microbial community were measured in the northeastern Atlantic basin as part of the Programme Océan Multidisciplinaire Méso Echelle (POMME) project. The field experiment was conducted during three seasons (winter, spring, and late summer-fall) in 2001. Samples were collected from four different mesoscale structures within the upper 100 m. GCP rates increased from winter (101 ± 24 mmol O2 m-2 d-1) to spring (153 ± 27 mmol O2 m-2 d-1) and then decreased from spring to late summer (44 ± 18 mmol O2 m-2 d-1). DCR rates increased from winter (-47 ± 18 mmol O2 m-2 d-1) to spring (-97 ± 7 mmol O2 m-2 d-1) and then decreased from spring to late summer (50 ± 7 mmol O2 m-2 d-1). The onset of stratification depended on latitude as well as on the presence of mesoscale structures (eddies), and this largely contributed to the variability of GCP. The trophic status of the POMME area was defined as net autotrophic, with a mean annual net community production rate of +38 ± 18 mmol O2 m-2 d-1, exhibiting a seasonal variation from +2 ± 20 mmol O2 m-2 d-1 to +57 ± 20 mmol O2 m-2 d-1. This study highlights that small organisms (picoautotrophs, nanoautotrophs, and bacteria) are the main organisms contributing to biological fluxes throughout the year and that episodic blooms of microphytoplankton are related to mesoscale structures.

The community diversity of two Caribbean MPAs invaded by lionfish does not support the biotic resistance hypothesis

NASA Astrophysics Data System (ADS)

Cobián-Rojas, Dorka; Schmitter-Soto, Juan J.; Aguilar Betancourt, Consuelo M.; Aguilar-Perera, Alfonso; Ruiz-Zárate, Miguel Á.; González-Sansón, Gaspar; Chevalier Monteagudo, Pedro P.; Herrera Pavón, Roberto; García Rodríguez, Alain; Corrada Wong, Raúl I.; Cabrera Guerra, Delmis; Salvat Torres, Héctor; Perera Valderrama, Susana

2018-04-01

Marine protected areas (MPAs) conserve diversity and abundance of fish communities. According to the biotic resistance hypothesis, communities with higher diversity and abundance should resist invasions better. To test this idea, the presence of lionfish in two Caribbean MPAs was studied: Parque Nacional Guanahacabibes (PNG) in Cuba and Parque Nacional Arrecifes de Xcalak (PNAX) in Mexico. Selection of these MPAs was based on both their different levels of success with enforcement and different abundances of native fish, with a more abundant native fish fauna at PNG. Underwater visual censuses were used to evaluate both the native fish structure and composition and at the same time distribution and abundance of lionfish. The abundance of potential predators on lionfish was also measured to determine possible effects of lionfish on both the abundance and the size of its prey and competitors. Lionfish showed higher abundance and larger size in PNG compared to PNAX, even though its probable competitors and predators were also more abundant and larger in PNG. Prey abundance and size decreased after the invasion. No correlation was detected between potential predators and lionfish, which might indicate natural predation is not substantial. In PNAX, lower abundance of prey, potential competitors and predators can also be attributed to historical overfishing, but this did not provide an advantage to lionfish. Lionfish were less abundant and reached smaller sizes in PNAX compared to PNG. This work confirms the effectiveness of lionfish culling at PNAX, but does not support the biotic resistence hypothesis that native fish might have controlled this invasive species.

Experimentally testing and assessing the predictive power of species assembly rules for tropical canopy ants

PubMed Central

Fayle, Tom M; Eggleton, Paul; Manica, Andrea; Yusah, Kalsum M; Foster, William A

2015-01-01

Understanding how species assemble into communities is a key goal in ecology. However, assembly rules are rarely tested experimentally, and their ability to shape real communities is poorly known. We surveyed a diverse community of epiphyte-dwelling ants and found that similar-sized species co-occurred less often than expected. Laboratory experiments demonstrated that invasion was discouraged by the presence of similarly sized resident species. The size difference for which invasion was less likely was the same as that for which wild species exhibited reduced co-occurrence. Finally we explored whether our experimentally derived assembly rules could simulate realistic communities. Communities simulated using size-based species assembly exhibited diversities closer to wild communities than those simulated using size-independent assembly, with results being sensitive to the combination of rules employed. Hence, species segregation in the wild can be driven by competitive species assembly, and this process is sufficient to generate observed species abundance distributions for tropical epiphyte-dwelling ants. PMID:25622647

Tree Size Inequality Reduces Forest Productivity: An Analysis Combining Inventory Data for Ten European Species and a Light Competition Model.

PubMed

Bourdier, Thomas; Cordonnier, Thomas; Kunstler, Georges; Piedallu, Christian; Lagarrigues, Guillaume; Courbaud, Benoit

2016-01-01

Plant structural diversity is usually considered as beneficial for ecosystem functioning. For instance, numerous studies have reported positive species diversity-productivity relationships in plant communities. However, other aspects of structural diversity such as individual size inequality have been far less investigated. In forests, tree size inequality impacts directly tree growth and asymmetric competition, but consequences on forest productivity are still indeterminate. In addition, the effect of tree size inequality on productivity is likely to vary with species shade-tolerance, a key ecological characteristic controlling asymmetric competition and light resource acquisition. Using plot data from the French National Geographic Agency, we studied the response of stand productivity to size inequality for ten forest species differing in shade tolerance. We fitted a basal area stand production model that included abiotic factors, stand density, stand development stage and a tree size inequality index. Then, using a forest dynamics model we explored whether mechanisms of light interception and light use efficiency could explain the tree size inequality effect observed for three of the ten species studied. Size inequality negatively affected basal area increment for seven out of the ten species investigated. However, this effect was not related to the shade tolerance of these species. According to the model simulations, the negative tree size inequality effect could result both from reduced total stand light interception and reduced light use efficiency. Our results demonstrate that negative relationships between size inequality and productivity may be the rule in tree populations. The lack of effect of shade tolerance indicates compensatory mechanisms between effect on light availability and response to light availability. Such a pattern deserves further investigations for mixed forests where complementarity effects between species are involved. When studying the effect of structural diversity on ecosystem productivity, tree size inequality is a major facet that should be taken into account.

The Determinants of Staff and Resident Activity in Residential Services for People with Severe Intellectual Disability: Moving beyond Size, Building Design, Location and Number of Staff.

ERIC Educational Resources Information Center

Felce, David

1998-01-01

Draws together the results of seven studies that investigated factors influencing the effects of service quality in community-based residential services for people with severe mental retardation. Results found that quality of staff and resident activity is dependent on an interaction between the structure, orientation, and procedures followed…

Downstream effects of stream flow diversion on channel characteristics and riparian vegetation in the Colorado Rocky Mountains, USA

Treesearch

Simeon T. Caskey; Tyanna S. Blaschak; Ellen Wohl; Elizabeth Schnackenberg; David M. Merritt; Kathleen A. Dwire

2015-01-01

Flow diversions are widespread and numerous throughout the semi-arid mountains of the western United States. Diversions vary greatly in their structure and ability to divert water, but can alter the magnitude and duration of base and peak flows, depending upon their size and management. Channel geometry and riparian plant communities have adapted to unique hydrologic...

New methods for estimating non-timber forest product output: an Appalachian case study

Treesearch

Steve Kruger; James Chamberlain

2015-01-01

Assessing the size and structure of non-timber forest product (NTFP) markets is difficult due to a lack of knowledge about NTFP supply chains. Harvesting ginseng and other wild medicinal plants has long provided a source of income and cultural identity in Appalachian communities in the eastern United States. With the exception of ginseng, the extent of the harvest of...

p-Coumaric Acid Influenced Cucumber Rhizosphere Soil Microbial Communities and the Growth of Fusarium oxysporum f.sp. cucumerinum Owen

PubMed Central

Zhou, Xingang; Wu, Fengzhi

2012-01-01

Background Autotoxicity of cucumber root exudates or decaying residues may be the cause of the soil sickness of cucumber. However, how autotoxins affect soil microbial communities is not yet fully understood. Methodology/Principal Findings The aims of this study were to study the effects of an artificially applied autotoxin of cucumber, p-coumaric acid, on cucumber seedling growth, rhizosphere soil microbial communities, and Fusarium oxysporum f.sp. cucumerinum Owen (a soil-borne pathogen of cucumber) growth. Abundance, structure and composition of rhizosphere bacterial and fungal communities were analyzed with real-time PCR, PCR-denaturing gradient gel electrophoresis (DGGE) and clone library methods. Soil dehydrogenase activity and microbial biomass C (MBC) were determined to indicate the activity and size of the soil microflora. Results showed that p-coumaric acid (0.1–1.0 µmol/g soil) decreased cucumber leaf area, and increased soil dehydrogenase activity, MBC and rhizosphere bacterial and fungal community abundances. p-Coumaric acid also changed the structure and composition of rhizosphere bacterial and fungal communities, with increases in the relative abundances of bacterial taxa Firmicutes, Betaproteobacteria, Gammaproteobacteria and fungal taxa Sordariomycete, Zygomycota, and decreases in the relative abundances of bacterial taxa Bacteroidetes, Deltaproteobacteria, Planctomycetes, Verrucomicrobia and fungal taxon Pezizomycete. In addition, p-coumaric acid increased Fusarium oxysporum population densities in soil. Conclusions/Significance These results indicate that p-coumaric acid may play a role in the autotoxicity of cucumber via influencing soil microbial communities. PMID:23118972

p-Coumaric acid influenced cucumber rhizosphere soil microbial communities and the growth of Fusarium oxysporum f.sp. cucumerinum Owen.

PubMed

Zhou, Xingang; Wu, Fengzhi

2012-01-01

Autotoxicity of cucumber root exudates or decaying residues may be the cause of the soil sickness of cucumber. However, how autotoxins affect soil microbial communities is not yet fully understood. The aims of this study were to study the effects of an artificially applied autotoxin of cucumber, p-coumaric acid, on cucumber seedling growth, rhizosphere soil microbial communities, and Fusarium oxysporum f.sp. cucumerinum Owen (a soil-borne pathogen of cucumber) growth. Abundance, structure and composition of rhizosphere bacterial and fungal communities were analyzed with real-time PCR, PCR-denaturing gradient gel electrophoresis (DGGE) and clone library methods. Soil dehydrogenase activity and microbial biomass C (MBC) were determined to indicate the activity and size of the soil microflora. Results showed that p-coumaric acid (0.1-1.0 µmol/g soil) decreased cucumber leaf area, and increased soil dehydrogenase activity, MBC and rhizosphere bacterial and fungal community abundances. p-Coumaric acid also changed the structure and composition of rhizosphere bacterial and fungal communities, with increases in the relative abundances of bacterial taxa Firmicutes, Betaproteobacteria, Gammaproteobacteria and fungal taxa Sordariomycete, Zygomycota, and decreases in the relative abundances of bacterial taxa Bacteroidetes, Deltaproteobacteria, Planctomycetes, Verrucomicrobia and fungal taxon Pezizomycete. In addition, p-coumaric acid increased Fusarium oxysporum population densities in soil. These results indicate that p-coumaric acid may play a role in the autotoxicity of cucumber via influencing soil microbial communities.

The structural role of weak and strong links in a financial market network

NASA Astrophysics Data System (ADS)

Garas, A.; Argyrakis, P.; Havlin, S.

2008-05-01

We investigate the properties of correlation based networks originating from economic complex systems, such as the network of stocks traded at the New York Stock Exchange (NYSE). The weaker links (low correlation) of the system are found to contribute to the overall connectivity of the network significantly more than the strong links (high correlation). We find that nodes connected through strong links form well defined communities. These communities are clustered together in more complex ways compared to the widely used classification according to the economic activity. We find that some companies, such as General Electric (GE), Coca Cola (KO), and others, can be involved in different communities. The communities are found to be quite stable over time. Similar results were obtained by investigating markets completely different in size and properties, such as the Athens Stock Exchange (ASE). The present method may be also useful for other networks generated through correlations.

Uncovering the community structure in signed social networks based on greedy optimization

NASA Astrophysics Data System (ADS)

Chen, Yan; Yan, Jiaqi; Yang, Yu; Chen, Junhua

2017-05-01

The formality of signed relationships has been recently adopted in a lot of complicated systems. The relations among these entities are complicated and multifarious. We cannot indicate these relationships only by positive links, and signed networks have been becoming more and more universal in the study of social networks when community is being significant. In this paper, to identify communities in signed networks, we exploit a new greedy algorithm, taking signs and the density of these links into account. The main idea of the algorithm is the initial procedure of signed modularity and the corresponding update rules. Specially, we employ the “Asymmetric and Constrained Belief Evolution” procedure to evaluate the optimal number of communities. According to the experimental results, the algorithm is proved to be able to run well. More specifically, the proposed algorithm is very efficient for these networks with medium size, both dense and sparse.

One Size Does Not Fit All: Effective Community-Engaged Outreach Practices with Immigrant Communities

ERIC Educational Resources Information Center

Smalkoski, Kari; Axtell, Sara; Zimmer, Jeanne; Noor, Ibrahim

2016-01-01

Generic outreach approaches are commonly used to target as many individuals as possible in a cultural community to achieve a greater response rate. However, this one-size-fits-all tactic is rarely effective. Community-engaged outreach practices have been successful with immigrant communities in Minnesota's Twin Cities. When practitioners,…

Increasing the Size of the Microbial Biomass Altered Bacterial Community Structure which Enhances Plant Phosphorus Uptake

PubMed Central

Shen, Pu; Murphy, Daniel Vaughan; George, Suman J.; Lapis-Gaza, Hazel; Xu, Minggang

2016-01-01

Agricultural production can be limited by low phosphorus (P) availability, with soil P being constrained by sorption and precipitation reactions making it less available for plant uptake. There are strong links between carbon (C) and nitrogen (N) availability and P cycling within soil P pools, with microorganisms being an integral component of soil P cycling mediating the availability of P to plants. Here we tested a conceptual model that proposes (i) the addition of readily-available organic substrates would increase the size of the microbial biomass thus exhausting the pool of easily-available P and (ii) this would cause the microbial biomass to access P from more recalcitrant pools. In this model it is hypothesised that the size of the microbial population is regulating access to less available P rather than the diversity of organisms contained within this biomass. To test this hypothesis we added mixtures of simple organic compounds that reflect typical root exudates at different C:N ratios to a soil microcosm experiment and assessed changes in soil P pools, microbial biomass and bacterial diversity measures. We report that low C:N ratio (C:N = 12.5:1) artificial root exudates increased the size of the microbial biomass while high C:N ratio (C:N = 50:1) artificial root exudates did not result in a similar increase in microbial biomass. Interestingly, addition of the root exudates did not alter bacterial diversity (measured via univariate diversity indices) but did alter bacterial community structure. Where C, N and P supply was sufficient to support plant growth the increase observed in microbial biomass occurred with a concurrent increase in plant yield. PMID:27893833

To cut or not to cut? Assessing the modular structure of brain networks.

PubMed

Chang, Yu-Teng; Pantazis, Dimitrios; Leahy, Richard M

2014-05-01

A wealth of methods has been developed to identify natural divisions of brain networks into groups or modules, with one of the most prominent being modularity. Compared with the popularity of methods to detect community structure, only a few methods exist to statistically control for spurious modules, relying almost exclusively on resampling techniques. It is well known that even random networks can exhibit high modularity because of incidental concentration of edges, even though they have no underlying organizational structure. Consequently, interpretation of community structure is confounded by the lack of principled and computationally tractable approaches to statistically control for spurious modules. In this paper we show that the modularity of random networks follows a transformed version of the Tracy-Widom distribution, providing for the first time a link between module detection and random matrix theory. We compute parametric formulas for the distribution of modularity for random networks as a function of network size and edge variance, and show that we can efficiently control for false positives in brain and other real-world networks. Copyright © 2014 Elsevier Inc. All rights reserved.

Opinion dynamics in a group-based society

NASA Astrophysics Data System (ADS)

Gargiulo, F.; Huet, S.

2010-09-01

Many models have been proposed to analyze the evolution of opinion structure due to the interaction of individuals in their social environment. Such models analyze the spreading of ideas both in completely interacting backgrounds and on social networks, where each person has a finite set of interlocutors. In this paper we analyze the reciprocal feedback between the opinions of the individuals and the structure of the interpersonal relationships at the level of community structures. For this purpose we define a group-based random network and we study how this structure co-evolves with opinion dynamics processes. We observe that the adaptive network structure affects the opinion dynamics process helping the consensus formation. The results also show interesting behaviors in regards to the size distribution of the groups and their correlation with opinion structure.

Phase transition of Surprise optimization in community detection

NASA Astrophysics Data System (ADS)

Xiang, Ju; Tang, Yan-Ni; Gao, Yuan-Yuan; Liu, Lang; Hao, Yi; Li, Jian-Ming; Zhang, Yan; Chen, Shi

2018-02-01

Community detection is one of important issues in the research of complex networks. In literatures, many methods have been proposed to detect community structures in the networks, while they also have the scope of application themselves. In this paper, we investigate an important measure for community detection, Surprise (Aldecoa and Marín, Sci. Rep. 3 (2013) 1060), by focusing on the critical points in the merging and splitting of communities. We firstly analyze the critical behavior of Surprise and give the phase diagrams in community-partition transition. The results show that the critical number of communities for Surprise has a super-exponential increase with the increase of the link-density difference, while it is close to that of Modularity for small difference between inter- and intra-community link densities. By directly optimizing Surprise, we experimentally test the results on various networks, following a series of comparisons with other classical methods, and further find that the heterogeneity of networks could quicken the splitting of communities. On the whole, the results show that Surprise tends to split communities due to various reasons such as the heterogeneity in link density, degree and community size, and it thus exhibits higher resolution than other methods, e.g., Modularity, in community detection. Finally, we provide several approaches for enhancing Surprise.

How disturbances and management practices affect bird communities in a Carpathian river ecosystem?

NASA Astrophysics Data System (ADS)

Lacko, Jozef; Topercer, Ján; Súľovský, Marek

2018-04-01

We studied how interactions between disturbances, succession, human alterations and other habitat and landscape attributes affect bird community patterns in a lower reach of a large West Carpathian river Váh with complex disturbance and alteration histories. Breeding-bird communities, their habitats (54 variables) and surrounding landscapes (11 metrics) were sampled using standardized point counts with limited distances at 40 riparian sites divided among two transects along a 12.9 km river stretch. The most frequent and abundant birds were generalists typically associated with forest edge habitats, such as Parus major, Sylvia atricapilla, Fringilla coelebs, Oriolus oriolus, Phylloscopus collybita, Sturnus vulgaris, Turdus merula and Luscinia megarhynchos. Abundances show significant increase at the lower transect responding apparently to greater size and heterogeneity of riparian habitats and more abundant food supply linked to more diverse and intense human influences in a suburban zone. Both indirect (NMDS) and direct ordination (CCA) revealed remarkably large number of evenly important factors underlying riparian bird-habitat interactions. It suggests considerable environmental heterogeneity and complexity of these interactions as a likely outcome of long and complex disturbance and alteration histories of the area. Yet structure and relative importance of first two gradients (longitudinal and lateral linkages) remains simple and stable, complying well with predictions of river continuum concept and stream ecosystem theory. Of the nine statistically significant variables most strongly correlated with first two CCA axes, percentages of Helianthus tuberosus, footpaths, fields, Calystegia sepium and steep banks uphold our hypotheses predicting significant effects of invasive species, visitor disturbances, agricultural land use and unaltered river banks/bed on bird community composition and structure. A small but significant contribution of patch size standard deviation within a 150 m radius to the CCA model provides the sole evidence for a hypothesized effect of adjacent terrestrial landscapes on riparian bird communities over different scales of patch size variability. Percentages of fields, invasive species and vertical banks along with average tree diameter were also the most productive predictors across our generalized linear models of riparian bird species diversity, evenness and abundance. Adopting an integrated river basin management, maintaining or restoring both longitudinal and lateral connectivity, taking advantage of natural processes and traditional management practices to maintain or restore riverine biodiversity can be recommended by our data in support of more systematic and evidence-based decision-making.

National Biological Service Research Supports Watershed Planning

USGS Publications Warehouse

Snyder, Craig D.

1996-01-01

The National Biological Service's Leetown Science Center is investigating how human impacts on watershed, riparian, and in-stream habitats affect fish communities. The research will provide the basis for a Ridge and Valley model that will allow resource managers to accurately predict and effectively mitigate human impacts on water quality. The study takes place in the Opequon Creek drainage basin of West Virginia. A fourth-order tributary of the Potomac, the basin falls within the Ridge and Valley. The study will identify biological components sensitive to land use patterns and the condition of the riparian zone; the effect of stream size, location, and other characteristics on fish communities; the extent to which remote sensing can reliable measure the riparian zone; and the relationship between the rate of landscape change and the structure of fish communities.

Seasonal cycles, phylogenetic assembly, and functional diversity of orchid bee communities.

PubMed

Ramírez, Santiago R; Hernández, Carlos; Link, Andres; López-Uribe, Margarita M

2015-05-01

Neotropical rainforests sustain some of the most diverse terrestrial communities on Earth. Euglossine (or orchid) bees are a diverse lineage of insect pollinators distributed throughout the American tropics, where they provide pollination services to a staggering diversity of flowering plant taxa. Elucidating the seasonal patterns of phylogenetic assembly and functional trait diversity of bee communities can shed new light into the mechanisms that govern the assembly of bee pollinator communities and the potential effects of declining bee populations. Male euglossine bees collect, store, and accumulate odoriferous compounds (perfumes) to subsequently use during courtship display. Thus, synthetic chemical baits can be used to attract and monitor euglossine bee populations. We conducted monthly censuses of orchid bees in three sites in the Magdalena valley of Colombia - a region where Central and South American biotas converge - to investigate the structure, diversity, and assembly of euglossine bee communities through time in relation to seasonal climatic cycles. In particular, we tested the hypothesis that phylogenetic community structure and functional trait diversity changed in response to seasonal rainfall fluctuations. All communities exhibited strong to moderate phylogenetic clustering throughout the year, with few pronounced bursts of phylogenetic overdispersion that coincided with the transition from wet-to-dry seasons. Despite the heterogeneous distribution of functional traits (e.g., body size, body mass, and proboscis length) and the observed seasonal fluctuations in phylogenetic diversity, we found that functional trait diversity, evenness, and divergence remained constant during all seasons in all communities. However, similar to the pattern observed with phylogenetic diversity, functional trait richness fluctuated markedly with rainfall in all sites. These results emphasize the importance of considering seasonal fluctuations in community assembly and provide a glimpse to the potential effects that climatic alterations may have on both pollinator communities and the ecosystem services they provide.

Social capital and health: civic engagement, community size, and recall of health messages.

PubMed

Viswanath, Kasisomayajula; Randolph Steele, Whitney; Finnegan, John R

2006-08-01

We explored the effects of community integration and pluralism on recall of cardiovascular disease health information messages. With 1980-1983 data from the Minnesota Heart Health Program, we examined whether ties to community groups were associated with recall of health messages, and whether this relation was modified by size and degree of differentiation of the community. A higher level of civic engagement through ties to community groups was associated with better recall of health messages. Ties to community groups independently contributed to better message recall even after control for gender, education, and other variables. The moderating role of community size was non-significant but intriguing. Community group membership could increase exposure to health messages, providing a critical pathway for social capital to influence health promotion and, thus, public health outcomes.

Community Size, Community Attachment and Newspaper Readership.

ERIC Educational Resources Information Center

Stephens, Lowndes F.

Residents in several states and communities ranging in size from farms to inner cities of more than 500,000 people were surveyed to further explore the strong relationship between community ties and newspaper readership indicated by results of a previous study sponsored by the American Newspaper Publishers Association. The findings revealed that…

Marine fish community structure and habitat associations on the Canadian Beaufort shelf and slope

NASA Astrophysics Data System (ADS)

Majewski, Andrew R.; Atchison, Sheila; MacPhee, Shannon; Eert, Jane; Niemi, Andrea; Michel, Christine; Reist, James D.

2017-03-01

Marine fishes in the Canadian Beaufort Sea have complex interactions with habitats and prey, and occupy a pivotal position in the food web by transferring energy between lower- and upper-trophic levels, and also within and among habitats (e.g., benthic-pelagic coupling). The distributions, habitat associations, and community structure of most Beaufort Sea marine fishes, however, are unknown thus precluding effective regulatory management of emerging offshore industries in the region (e.g., hydrocarbon development, shipping, and fisheries). Between 2012 and 2014, Fisheries and Oceans Canada conducted the first baseline survey of offshore marine fishes, their habitats, and ecological relationships in the Canadian Beaufort Sea. Benthic trawling was conducted at 45 stations spanning 18-1001 m depths across shelf and slope habitats. Physical oceanographic variables (depth, salinity, temperature, oxygen), biological variables (benthic chlorophyll and integrated water-column chlorophyll) and sediment composition (grain size) were assessed as potential explanatory variables for fish community structure using a non-parametric statistical approach. Selected stations were re-sampled in 2013 and 2014 for a preliminary assessment of inter-annual variability in the fish community. Four distinct fish assemblages were delineated on the Canadian Beaufort Shelf and slope: 1) Nearshore-shelf: <50 m depth, 2) Offshore-shelf: >50 and ≤200 m depths, 3) Upper-slope: ≥200 and ≤500 m depths, and 4) Lower-slope: ≥500 m depths. Depth was the environmental variable that best explained fish community structure, and each species assemblage was spatially associated with distinct aspects of the vertical water mass profile. Significant differences in the fish community from east to west were not detected, and the species composition of the assemblages on the Canadian Beaufort Shelf have not changed substantially over the past decade. This community analysis provides a framework for testing hypotheses regarding the trophic dynamics and ecosystem roles of Beaufort Sea marine fishes, including biological linkages (i.e., fish movements and trophic interactions) among offshore habitats. Understanding regional-scale habitat associations will also provide context to identify potentially unique and/or sensitive habitats and fish community characteristics, thus aiding identification of ecologically and biologically significant areas, and to inform conservation efforts.

Predator Persistence through Variability of Resource Productivity in Tritrophic Systems.

PubMed

Soudijn, Floor H; de Roos, André M

2017-12-01

The trophic structure of species communities depends on the energy transfer between trophic levels. Primary productivity varies strongly through time, challenging the persistence of species at higher trophic levels. Yet resource variability has mostly been studied in systems with only one or two trophic levels. We test the effect of variability in resource productivity in a tritrophic model system including a resource, a size-structured consumer, and a size-specific predator. The model complies with fundamental principles of mass conservation and the body-size dependence of individual-level energetics and predator-prey interactions. Surprisingly, we find that resource variability may promote predator persistence. The positive effect of variability on the predator arises through periods with starvation mortality of juvenile prey, which reduces the intraspecific competition in the prey population. With increasing variability in productivity and starvation mortality in the juvenile prey, the prey availability increases in the size range preferred by the predator. The positive effect of prey mortality on the trophic transfer efficiency depends on the biologically realistic consideration of body size-dependent and food-dependent functions for growth and reproduction in our model. Our findings show that variability may promote the trophic transfer efficiency, indicating that environmental variability may sustain species at higher trophic levels in natural ecosystems.

Concept development of a Mach 4 high-speed civil transport

NASA Technical Reports Server (NTRS)

Domack, Christopher S.; Dollyhigh, Samuel M.; Beissner, Fred L., Jr.; Geiselhart, Karl A.; Mcgraw, Marvin E., Jr.; Shields, Elwood W.; Swanson, Edward E.

1990-01-01

A study was conducted to configure and analyze a 250 passenger, Mach 4 High Speed Civil Transport with a design range of 6500 n.mi. The design mission assumed an all-supersonic cruise segment and no community noise or sonic boom constraints. The study airplane was developed in order to examine the technology requirements for such a vehicle and to provide an unconstrained baseline from which to assess changes in technology levels, sonic boom limits, or community noise constraints in future studies. The propulsion, structure, and materials technologies utilized in the sizing of the study aircraft were assumed to represent a technology availability date of 2015. The study airplane was a derivative of a previously developed Mach 3 concept and utilized advanced afterburning turbojet engines and passive airframe thermal protection. Details of the configuration development, aerodynamic design, propulsion system, mass properties, and mission performance are presented. The study airplane was estimated to weigh approx. 866,000 lbs. Although an aircraft of this size is a marginally acceptable candidate to fit into the world airport infrastructure, it was concluded that the inclusion of community noise or sonic boom constraints would quickly cause the aircraft to grow beyond acceptable limits using the assumed technology levels.

Energetic and ecological constraints on population density of reef fishes.

PubMed

Barneche, D R; Kulbicki, M; Floeter, S R; Friedlander, A M; Allen, A P

2016-01-27

Population ecology has classically focused on pairwise species interactions, hindering the description of general patterns and processes of population abundance at large spatial scales. Here we use the metabolic theory of ecology as a framework to formulate and test a model that yields predictions linking population density to the physiological constraints of body size and temperature on individual metabolism, and the ecological constraints of trophic structure and species richness on energy partitioning among species. Our model was tested by applying Bayesian quantile regression to a comprehensive reef-fish community database, from which we extracted density data for 5609 populations spread across 49 sites around the world. Our results indicate that population density declines markedly with increases in community species richness and that, after accounting for richness, energetic constraints are manifested most strongly for the most abundant species, which generally are of small body size and occupy lower trophic groups. Overall, our findings suggest that, at the global scale, factors associated with community species richness are the major drivers of variation in population density. Given that populations of species-rich tropical systems exhibit markedly lower maximum densities, they may be particularly susceptible to stochastic extinction. © 2016 The Author(s).

Energetic and ecological constraints on population density of reef fishes

PubMed Central

Barneche, D. R.; Kulbicki, M.; Floeter, S. R.; Friedlander, A. M.; Allen, A. P.

2016-01-01

Population ecology has classically focused on pairwise species interactions, hindering the description of general patterns and processes of population abundance at large spatial scales. Here we use the metabolic theory of ecology as a framework to formulate and test a model that yields predictions linking population density to the physiological constraints of body size and temperature on individual metabolism, and the ecological constraints of trophic structure and species richness on energy partitioning among species. Our model was tested by applying Bayesian quantile regression to a comprehensive reef-fish community database, from which we extracted density data for 5609 populations spread across 49 sites around the world. Our results indicate that population density declines markedly with increases in community species richness and that, after accounting for richness, energetic constraints are manifested most strongly for the most abundant species, which generally are of small body size and occupy lower trophic groups. Overall, our findings suggest that, at the global scale, factors associated with community species richness are the major drivers of variation in population density. Given that populations of species-rich tropical systems exhibit markedly lower maximum densities, they may be particularly susceptible to stochastic extinction. PMID:26791611

Changes in microbial community characteristics and soil organic matter with nitrogen additions in two tropical forests.

PubMed

Cusack, Daniela F; Silver, Whendee L; Torn, Margaret S; Burton, Sarah D; Firestone, Mary K

2011-03-01

Microbial communities and their associated enzyme activities affect the amount and chemical quality of carbon (C) in soils. Increasing nitrogen (N) deposition, particularly in N-rich tropical forests, is likely to change the composition and behavior of microbial communities and feed back on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to N deposition and shifts in soil organic matter (SOM) quality and quantity. We used phospholipid fatty acid (PLFA) analysis and microbial enzyme assays in soils to assess microbial community responses to long-term N additions in two distinct tropical rain forests. We used soil density fractionation and 13C nuclear magnetic resonance (NMR) spectroscopy to measure related changes in SOM pool sizes and chemical quality. Microbial biomass increased in response to N fertilization in both tropical forests and corresponded to declines in pools of low-density SOM. The chemical quality of this soil C pool reflected ecosystem-specific changes in microbial community composition. In the lower-elevation forest, there was an increase in gram-negative bacteria PLFA biomass, and there were significant losses of labile C chemical groups (O-alkyls). In contrast, the upper-elevation tropical forest had an increase in fungal PLFAs with N additions and declines in C groups associated with increased soil C storage (alkyls). The dynamics of microbial enzymatic activities with N addition provided a functional link between changes in microbial community structure and SOM chemistry. Ecosystem-specific changes in microbial community composition are likely to have far-reaching effects on soil carbon storage and cycling. This study indicates that microbial communities in N-rich tropical forests can be sensitive to added N, but we can expect significant variability in how ecosystem structure and function respond to N deposition among tropical forest types.

Linking internal and external bacterial community control gives mechanistic framework for pelagic virus-to-bacteria ratios.

PubMed

Våge, Selina; Pree, Bernadette; Thingstad, T Frede

2016-11-01

For more than 25 years, virus-to-bacteria ratios (VBR) have been measured and interpreted as indicators of the importance of viruses in aquatic ecosystems, yet a generally accepted theory for understanding mechanisms controlling VBR is still lacking. Assuming that the denominator (total bacterial abundance) is primarily predator controlled, while viral lysis compensates for host growth rates exceeding this grazing loss, the numerator (viral abundance) reflects activity differences between prokaryotic hosts. VBR is then a ratio between mechanisms generating structure within the bacterial community and interactions between different plankton functional types controlling bacterial community size. We here show how these arguments can be formalized by combining a recently published model for co-evolutionary host-virus interactions, with a previously published "minimum" model for the microbial food web. The result is a framework where viral lysis links bacterial diversity to microbial food web structure and function, creating relationships between different levels of organization that are strongly modified by organism-level properties such as cost of resistance. © 2016 The Authors. Environmental Microbiology Reports published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Linking internal and external bacterial community control gives mechanistic framework for pelagic virus‐to‐bacteria ratios

PubMed Central

Pree, Bernadette; Thingstad, T. Frede

2016-01-01

Summary For more than 25 years, virus‐to‐bacteria ratios (VBR) have been measured and interpreted as indicators of the importance of viruses in aquatic ecosystems, yet a generally accepted theory for understanding mechanisms controlling VBR is still lacking. Assuming that the denominator (total bacterial abundance) is primarily predator controlled, while viral lysis compensates for host growth rates exceeding this grazing loss, the numerator (viral abundance) reflects activity differences between prokaryotic hosts. VBR is then a ratio between mechanisms generating structure within the bacterial community and interactions between different plankton functional types controlling bacterial community size. We here show how these arguments can be formalized by combining a recently published model for co‐evolutionary host‐virus interactions, with a previously published “minimum” model for the microbial food web. The result is a framework where viral lysis links bacterial diversity to microbial food web structure and function, creating relationships between different levels of organization that are strongly modified by organism‐level properties such as cost of resistance. PMID:27231817

Echo Chambers: Emotional Contagion and Group Polarization on Facebook.

PubMed

Del Vicario, Michela; Vivaldo, Gianna; Bessi, Alessandro; Zollo, Fabiana; Scala, Antonio; Caldarelli, Guido; Quattrociocchi, Walter

2016-12-01

Recent findings showed that users on Facebook tend to select information that adhere to their system of beliefs and to form polarized groups - i.e., echo chambers. Such a tendency dominates information cascades and might affect public debates on social relevant issues. In this work we explore the structural evolution of communities of interest by accounting for users emotions and engagement. Focusing on the Facebook pages reporting on scientific and conspiracy content, we characterize the evolution of the size of the two communities by fitting daily resolution data with three growth models - i.e. the Gompertz model, the Logistic model, and the Log-logistic model. Although all the models appropriately describe the data structure, the Logistic one shows the best fit. Then, we explore the interplay between emotional state and engagement of users in the group dynamics. Our findings show that communities' emotional behavior is affected by the users' involvement inside the echo chamber. Indeed, to an higher involvement corresponds a more negative approach. Moreover, we observe that, on average, more active users show a faster shift towards the negativity than less active ones.

Diversity and Activity of Communities Inhabiting Plastic Debris in the North Pacific Gyre.

PubMed

Bryant, Jessica A; Clemente, Tara M; Viviani, Donn A; Fong, Allison A; Thomas, Kimberley A; Kemp, Paul; Karl, David M; White, Angelicque E; DeLong, Edward F

2016-01-01

Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known, however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the "great Pacific garbage patch." The concentration of plastic particles in surface seawater within different size classes (2 to 5 mm and >5 mm) ranged from 0.35 to 3.7 particles m -3 across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production - community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa , Cyanobacteria , Alphaproteobacteria , and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from the surrounding picoplankton and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes, and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions, and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways, and biogeochemical activities that are distinct from those of free-living planktonic microbial communities. IMPORTANCE Marine plastic debris is a growing concern that has captured the general public's attention. While the negative impacts of plastic debris on oceanic macrobiota, including mammals and birds, are well documented, little is known about its influence on smaller marine residents, including microbes that have key roles in ocean biogeochemistry. Our work provides a new perspective on microbial communities inhabiting microplastics that includes its effect on microbial biogeochemical activities and a description of the cross-domain communities inhabiting plastic particles. This study is among the first molecular ecology, plastic debris biota surveys in the North Pacific Subtropical Gyre. It has identified fundamental differences in the functional potential and taxonomic composition of plastic-associated microbes versus planktonic microbes found in the surrounding open-ocean habitat. Author Video : An author video summary of this article is available.

Social Capital and Health: Civic Engagement, Community Size, and Recall of Health Messages

PubMed Central

Viswanath, Kasisomayajula; Randolph Steele, Whitney; Finnegan, John R.

2006-01-01

Objectives. We explored the effects of community integration and pluralism on recall of cardiovascular disease health information messages. Methods. With 1980–1983 data from the Minnesota Heart Health Program, we examined whether ties to community groups were associated with recall of health messages, and whether this relation was modified by size and degree of differentiation of the community. Results. A higher level of civic engagement through ties to community groups was associated with better recall of health messages. Ties to community groups independently contributed to better message recall even after control for gender, education, and other variables. The moderating role of community size was non-significant but intriguing. Conclusions. Community group membership could increase exposure to health messages, providing a critical pathway for social capital to influence health promotion and, thus, public health outcomes. PMID:16809608

A framework for detecting communities of unbalanced sizes in networks

NASA Astrophysics Data System (ADS)

Žalik, Krista Rizman; Žalik, Borut

2018-01-01

Community detection in large networks has been a focus of recent research in many of fields, including biology, physics, social sciences, and computer science. Most community detection methods partition the entire network into communities, groups of nodes that have many connections within communities and few connections between them and do not identify different roles that nodes can have in communities. We propose a community detection model that integrates more different measures that can fast identify communities of different sizes and densities. We use node degree centrality, strong similarity with one node from community, maximal similarity of node to community, compactness of communities and separation between communities. Each measure has its own strength and weakness. Thus, combining different measures can benefit from the strengths of each one and eliminate encountered problems of using an individual measure. We present a fast local expansion algorithm for uncovering communities of different sizes and densities and reveals rich information on input networks. Experimental results show that the proposed algorithm is better or as effective as the other community detection algorithms for both real-world and synthetic networks while it requires less time.

A methodology for selecting optimum organizations for space communities

NASA Technical Reports Server (NTRS)

Ragusa, J. M.

1978-01-01

This paper suggests that a methodology exists for selecting optimum organizations for future space communities of various sizes and purposes. Results of an exploratory study to identify an optimum hypothetical organizational structure for a large earth-orbiting multidisciplinary research and applications (R&A) Space Base manned by a mixed crew of technologists are presented. Since such a facility does not presently exist, in situ empirical testing was not possible. Study activity was, therefore, concerned with the identification of a desired organizational structural model rather than the empirical testing of it. The principal finding of this research was that a four-level project type 'total matrix' model will optimize the effectiveness of Space Base technologists. An overall conclusion which can be reached from the research is that application of this methodology, or portions of it, may provide planning insights for the formal organizations which will be needed during the Space Industrialization Age.

STRUCTURAL ECONOMIC CHANGE AND INTERNATIONAL MIGRATION FROM MEXICO AND POLAND

PubMed Central

Massey, Douglas S.; Kalter, Frank; Pren, Karen A.

2010-01-01

In this article we use uniquely comparable data sets from two very different settings to examine how exogenous economic transformations affect the likelihood and selectivity of international out-migration. Specifically, we use data from the Mexican Migration Project to construct event history files predicting first U.S. trips from seven communities in the state of Veracruz, which until recently sent very few migrants abroad. Similarly, using data from the Polish Migration Project, we derive comparable event history files predicting first trips to Germany from four Polish communities, which also sent few migrants abroad before the 1980s. Our analyses suggest that the onset of structural adjustment in both places had a significant effect in raising the probability of international migration, even when controlling for a set of standard variables specified by other theories to influence migration propensity, such as the size of the binational income gap and various indicators of human and social capital. PMID:21765550

Research for the Community: Bates Students Learn as They Work Magic for Lewiston and Auburn

ERIC Educational Resources Information Center

Harward, Donald W.

2001-01-01

When a fire breaks out in the twin cities of Lewiston and Auburn, Maine, the firefighter response time is just a bit quicker these days, thanks to student research at Bates College. When the alarm sounds, firefighters click on a computer map that tells them the size of the burning structure, the quickest route to the fire, the closest hydrant and…

Reproduction and community structure of fish from winter catch sites from industrial shrimp bycatch from the northeast and southeast Mexican Pacific

PubMed Central

Muñoz-Garcia, Isabel Rosario; Martinez-Perez, Francisco; Ramirez-Perez, Jorge Saul

2018-01-01

The shrimp fishery is one of the most important fisheries in the world, although the low selectivity from trawling nets has led to the capture of a large number of non-target species. Shrimp-bycatch species include a large number of fish and invertebrate species, of which fish species are the most abundant. The present study aims to determine the community structure as well as the average sizes at first maturity of the fish species from shrimp-bycatch caught from industrial fisheries in the Mexican Pacific from Sinaloa to Guerrero, from January to March 2015. The shrimp-bycatch fish diversity value was found to be 2.22. A total of 37 species of finfish were found, of which five were considered rare. The fish species with the highest Importance Value Index (IVI) levels were Pseudupeneus grandisquamis, Paralichthys woolmani, Lutjanus peru and Diapterus peruvianus. The average size at first maturity was calculated for all species. Of the analysed organisms, 90% were in the juvenile stage, including species with riverine and artisanal fisheries. The present study demonstrates the risk within marine populations to different non-target species due to the poor selectivity of shrimp trawls. PMID:29507841

[Effects of large bio-manipulation fish pen on community structure of crustacean zooplankton in Meiliang Bay of Taihu Lake].

PubMed

Ke, Zhi-Xin; Xie, Ping; Guo, Long-Gen; Xu, Jun; Zhou, Qiong

2012-08-01

In 2005, a large bio-manipulation pen with the stock of silver carp and bighead carp was built to control the cyanobacterial bloom in Meiliang Bay of Taihu Lake. This paper investigated the seasonal variation of the community structure of crustacean zooplankton and the water quality within and outside the pen. There were no significant differences in the environmental parameters and phytoplankton biomass within and outside the pen. The species composition and seasonal dynamics of crustacean zooplankton within and outside the pen were similar, but the biomass of crustacean zooplankton was greatly suppressed by silver carp and bighead carp. The total crustacean zooplankton biomass and cladocerans biomass were significantly lower in the pen (P < 0.05). In general, silver carp and bighead carp exerted more pressure on cladoceran species than on copepod species. A distinct seasonal succession of crustacean zooplankton was observed in the Bay. Many crustacean species were only dominated in given seasons. Large-sized crustacean (mainly Daphnia sp. and Cyclops vicnus) dominated in winter and spring, while small-sized species (mainly Bosmina sp., Ceriodaphnia cornuta, and Limnoithona sinensis) dominated in summer and autumn. Canonical correspondence analysis showed that water transparency, temperature, and phytoplankton biomass were the most important factors affecting the seasonal succession of the crustacean.

Recently Deglaciated High-Altitude Soils of the Himalaya: Diverse Environments, Heterogenous Bacterial Communities and Long-Range Dust Inputs from the Upper Troposphere

PubMed Central

Stres, Blaz; Sul, Woo Jun; Murovec, Bostjan; Tiedje, James M.

2013-01-01

Background The Himalaya with its altitude and geographical position forms a barrier to atmospheric transport, which produces much aqueous-particle monsoon precipitation and makes it the largest continuous ice-covered area outside polar regions. There is a paucity of data on high-altitude microbial communities, their native environments and responses to environmental-spatial variables relative to seasonal and deglaciation events. Methodology/Principal Findings Soils were sampled along altitude transects from 5000 m to 6000 m to determine environmental, spatial and seasonal factors structuring bacterial communities characterized by 16 S rRNA gene deep sequencing. Dust traps and fresh-snow samples were used to assess dust abundance and viability, community structure and abundance of dust associated microbial communities. Significantly different habitats among the altitude-transect samples corresponded to both phylogenetically distant and closely-related communities at distances as short as 50 m showing high community spatial divergence. High within-group variability that was related to an order of magnitude higher dust deposition obscured seasonal and temporal rearrangements in microbial communities. Although dust particle and associated cell deposition rates were highly correlated, seasonal dust communities of bacteria were distinct and differed significantly from recipient soil communities. Analysis of closest relatives to dust OTUs, HYSPLIT back-calculation of airmass trajectories and small dust particle size (4–12 µm) suggested that the deposited dust and microbes came from distant continental, lacustrine and marine sources, e.g. Sahara, India, Caspian Sea and Tibetan plateau. Cyanobacteria represented less than 0.5% of microbial communities suggesting that the microbial communities benefitted from (co)deposited carbon which was reflected in the psychrotolerant nature of dust-particle associated bacteria. Conclusions/Significance The spatial, environmental and temporal complexity of the high-altitude soils of the Himalaya generates ongoing disturbance and colonization events that subject heterogeneous microniches to stochastic colonization by far away dust associated microbes and result in the observed spatially divergent bacterial communities. PMID:24086740

Environmental change and predator diversity drive alpha and beta diversity in freshwater macro and microorganisms.

PubMed

Antiqueira, Pablo Augusto P; Petchey, Owen L; Dos Santos, Viviane Piccin; de Oliveira, Valéria Maia; Romero, Gustavo Quevedo

2018-05-17

Global biodiversity is eroding due to anthropogenic causes such as climate change, habitat loss, and trophic simplification of biological communities. Most studies address only isolated causes within a single group of organisms; however, biological groups of different trophic levels may respond in particular ways to different environmental impacts. Our study used natural microcosms to investigate the predicted individual and interactive effects of warming, changes in top predator diversity, and habitat size on the alpha and beta diversity of macrofauna, microfauna and bacteria. Alpha diversity (i.e., richness within each bromeliad) generally explained a larger proportion of the gamma diversity (partitioned in alpha and beta diversity). Overall, dissimilarity between communities occurred due to species turnover and not species loss (nestedness). Nevertheless, the three biological groups responded differently to each environmental stressor. Microfauna were the most sensitive group, with alpha and beta diversity being affected by environmental changes (warming and habitat size) and trophic structure (diversity of top predators). Macrofauna alpha and beta diversity was sensitive to changes in predator diversity and habitat size, but not warming. In contrast, the bacterial community was not influenced by the treatments. The community of each biological group was not mutually concordant with the environmental and trophic changes. Our results demonstrate that distinct anthropogenic impacts differentially affect the components of macro and microorganism diversity through direct and indirect effects (i.e., bottom-up and top-down effects). Therefore, a multitrophic and multispecies approach is necessary to assess the effects of different anthropogenic impacts on biodiversity. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

A Demographic Deficit? Local Population Aging and Access to Services in Rural America, 1990–2010

PubMed Central

Thiede, Brian; Brown, David L.; Sanders, Scott R.; Glasgow, Nina; Kulcsar, Laszlo J.

2017-01-01

Population aging is being experienced by many rural communities in the U.S., as evidenced by increases in the median age and the high incidence of natural population decrease. The implications of these changes in population structure for the daily lives of the residents in such communities have received little attention. We address this issue in the current study by examining the relationship between population aging and the availability of service-providing establishments in the rural U.S. between 1990 and 2010. Using data mainly from the U.S. Census Bureau and the Bureau of Labor Statistics, we estimate a series of fixed-effects regression models to identify the relationship between median age and establishment counts net of changes in overall population and other factors. We find a significant, but non-linear relationship between county median age and the total number of service-providing establishments, and counts of most specific types of services. We find a positive effect of total population size across all of our models. This total population effect is consistent with other research, but the independent effects of age structure that we observe represent a novel finding and suggest that age structure is a salient factor in local rural development and community wellbeing. PMID:28757660

Biodiversity and community composition of sediment macrofauna associated with deep-sea Lophelia pertusa habitats in the Gulf of Mexico

USGS Publications Warehouse

Demopoulos, Amanda W.J.; Bourque, Jill R.; Frometa, Janessy

2014-01-01

Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats (Lophelia pertusa) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm−2 and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa. Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L. pertusa may influence the macrofaunal community structure beyond the edges of the reef. This study represents the first assessment of L. pertusa-associated sediment communities in the GOM and provides baseline data that can help define the role of transition zones, from deep reefs to soft sediments, in shaping macrofaunal community structure and maintaining biodiversity; this information can help guide future conservation and management activities.

Size and species diversity of zooplankton communities in fluctuating Mediterranean salt marshes

NASA Astrophysics Data System (ADS)

Brucet, Sandra; Boix, Dani; López-Flores, Rocío; Badosa, Anna; Quintana, Xavier D.

2006-04-01

Differences in size and species diversity were analysed in a zooplankton community of a Mediterranean salt marsh (Empordà wetlands, NE Iberian Peninsula), where the dominance of a single species was frequent. In the permanent salt marsh, species diversity and size diversity had similar patterns along zooplankton succession. In the temporary salt marsh species diversity was high after flooding and diminished once water inputs ceased. As species diversity declined size diversity increased. Eventually, one species of calanoid dominated the zooplankton community. The high size diversity in situations of calanoid dominance was possibly due to the co-occurrence of different developmental stages, each of which have different diets. Size diversity would thus indicate trophic niche segregation among different sizes. The combined use of species and size diversity values allows the identification of the successional phases.

Geographical variation in body size and sexual size dimorphism in an Australian lizard, Boulenger's Skink (Morethia boulengeri).

PubMed

Michael, Damian R; Banks, Sam C; Piggott, Maxine P; Cunningham, Ross B; Crane, Mason; MacGregor, Christopher; McBurney, Lachlan; Lindenmayer, David B

2014-01-01

Ecogeographical rules help explain spatial and temporal patterns in intraspecific body size. However, many of these rules, when applied to ectothermic organisms such as reptiles, are controversial and require further investigation. To explore factors that influence body size in reptiles, we performed a heuristic study to examine body size variation in an Australian lizard, Boulenger's Skink Morethia boulengeri from agricultural landscapes in southern New South Wales, south-eastern Australia. We collected tissue and morphological data on 337 adult lizards across a broad elevation and climate gradient. We used a model-selection procedure to determine if environmental or ecological variables best explained body size variation. We explored the relationship between morphology and phylogenetic structure before modeling candidate variables from four broad domains: (1) geography (latitude, longitude and elevation), (2) climate (temperature and rainfall), (3) habitat (vegetation type, number of logs and ground cover attributes), and (4) management (land use and grazing history). Broad phylogenetic structure was evident, but on a scale larger than our study area. Lizards were sexually dimorphic, whereby females had longer snout-vent length than males, providing support for the fecundity selection hypothesis. Body size variation in M. boulengeri was correlated with temperature and rainfall, a pattern consistent with larger individuals occupying cooler and more productive parts of the landscape. Climate change forecasts, which predict warmer temperature and increased aridity, may result in reduced lizard biomass and decoupling of trophic interactions with potential implications for community organization and ecosystem function.

Planning Community-Based Assessments of HIV Educational Intervention Programs in Sub-Saharan Africa

ERIC Educational Resources Information Center

Kelcey, Ben; Shen, Zuchao

2017-01-01

A key consideration in planning studies of community-based HIV education programs is identifying a sample size large enough to ensure a reasonable probability of detecting program effects if they exist. Sufficient sample sizes for community- or group-based designs are proportional to the correlation or similarity of individuals within communities.…

Drug and Alcohol Use among Youth in Rural Communities.

ERIC Educational Resources Information Center

Edwards, Ruth W.

This paper compares data on the prevalence of alcohol and other drug use by students in grades 8 and 12 across four sizes of communities. Data from the American Drug and Alcohol Survey (ADAS), administered in approximately 250 communities during the 1992-93 and 1993-94 school years, were analyzed for four community sizes: very small (population…

Empty Niches after Extinctions Increase Population Sizes of Modern Corals.

PubMed

Prada, Carlos; Hanna, Bishoy; Budd, Ann F; Woodley, Cheryl M; Schmutz, Jeremy; Grimwood, Jane; Iglesias-Prieto, Roberto; Pandolfi, John M; Levitan, Don; Johnson, Kenneth G; Knowlton, Nancy; Kitano, Hiroaki; DeGiorgio, Michael; Medina, Mónica

2016-12-05

Large environmental fluctuations often cause mass extinctions, extirpating species and transforming communities [1, 2]. While the effects on community structure are evident in the fossil record, demographic consequences for populations of individual species are harder to evaluate because fossils reveal relative, but not absolute, abundances. However, genomic analyses of living species that have survived a mass extinction event offer the potential for understanding the demographic effects of such environmental fluctuations on extant species. Here, we show how environmental variation since the Pliocene has shaped demographic changes in extant corals of the genus Orbicella, major extant reef builders in the Caribbean that today are endangered. We use genomic approaches to estimate previously unknown current and past population sizes over the last 3 million years. Populations of all three Orbicella declined around 2-1 million years ago, coincident with the extinction of at least 50% of Caribbean coral species. The estimated changes in population size are consistent across the three species despite their ecological differences. Subsequently, two shallow-water specialists expanded their population sizes at least 2-fold, over a time that overlaps with the disappearance of their sister competitor species O. nancyi (the organ-pipe Orbicella). Our study suggests that populations of Orbicella species are capable of rebounding from reductions in population size under suitable conditions and that the effective population size of modern corals provides rich standing genetic variation for corals to adapt to climate change. For conservation genetics, our study suggests the need to evaluate genetic variation under appropriate demographic models. Copyright © 2016 Elsevier Ltd. All rights reserved.

Distribution, diversity and abundance of bacterial laccase-like genes in different particle size fractions of sediments in a subtropical mangrove ecosystem.

PubMed

Luo, Ling; Zhou, Zhi-Chao; Gu, Ji-Dong

2015-10-01

This study investigated the diversity and abundance of bacterial lacasse-like genes in different particle size fractions, namely sand, silt, and clay of sediments in a subtropical mangrove ecosystem. Moreover, the effects of nutrient conditions on bacterial laccase-like communities as well as the correlation between nutrients and, both the abundance and diversity indices of laccase-like bacteria in particle size fractions were also studied. Compared to bulk sediments, Bacteroidetes, Caldithrix, Cyanobacteria and Chloroflexi were dominated in all 3 particle-size fractions of intertidal sediment (IZ), but Actinobacteria and Firmicutes were lost after the fractionation procedures used. The diversity index of IZ fractions decreased in the order of bulk > clay > silt > sand. In fractions of mangrove forest sediment (MG), Verrucomicrobia was found in silt, and both Actinobacteria and Bacteroidetes appeared in clay, but no new species were found in sand. The declining order of diversity index in MG fractions was clay > silt > sand > bulk. Furthermore, the abundance of lacasse-like bacteria varied with different particle-size fractions significantly (p < 0.05), and decreased in the order of sand > clay > silt in both IZ and MG fractions. Additionally, nutrient availability was found to significantly affect the diversity and community structure of laccase-like bacteria (p < 0.05), while the total organic carbon contents were positively related to the abundance of bacterial laccase-like genes in particle size fractions (p < 0.05). Therefore, this study further provides evidence that bacterial laccase plays a vital role in turnover of sediment organic matter and cycling of nutrients.

Size matters at deep-sea hydrothermal vents: different diversity and habitat fidelity patterns of meio- and macrofauna

PubMed Central

Gollner, Sabine; Govenar, Breea; Fisher, Charles R.; Bright, Monika

2015-01-01

Species with markedly different sizes interact when sharing the same habitat. Unravelling mechanisms that control diversity thus requires consideration of a range of size classes. We compared patterns of diversity and community structure for meio- and macrofaunal communities sampled along a gradient of environmental stress at deep-sea hydrothermal vents on the East Pacific Rise (9° 50′ N) and neighboring basalt habitats. Both meio- and macrofaunal species richnesses were lowest in the high-stress vent habitat, but macrofaunal richness was highest among intermediate-stress vent habitats. Meiofaunal species richness was negatively correlated with stress, and highest on the basalt. In these deep-sea basalt habitats surrounding hydrothermal vents, meiofaunal species richness was consistently higher than that of macrofauna. Consideration of the physiological capabilities and life history traits of different-sized animals suggests that different patterns of diversity may be caused by different capabilities to deal with environmental stress in the 2 size classes. In contrast to meiofauna, adaptations of macrofauna may have evolved to allow them to maintain their physiological homeostasis in a variety of hydrothermal vent habitats and exploit this food-rich deep-sea environment in high abundances. The habitat fidelity patterns also differed: macrofaunal species occurred primarily at vents and were generally restricted to this habitat, but meiofaunal species were distributed more evenly across proximate and distant basalt habitats and were thus not restricted to vent habitats. Over evolutionary time scales these contrasting patterns are likely driven by distinct reproduction strategies and food demands inherent to fauna of different sizes. PMID:26166922

Mapping Plant Diversity and Composition Across North Carolina Piedmont Forest Landscapes Using Lidar-Hyperspectral Remote Sensing

NASA Astrophysics Data System (ADS)

Hakkenberg, Christopher R.

Forest modification, from local stress to global change, has given rise to efforts to model, map, and monitor critical properties of forest communities like structure, composition, and diversity. Predictive models based on data from spatially-nested field plots and LiDAR-hyperspectral remote sensing systems are one particularly effective means towards the otherwise prohibitively resource-intensive task of consistently characterizing forest community dynamics at landscape scales. However, to date, most predictive models fail to account for actual (rather than idealized) species and community distributions, are unsuccessful in predicting understory components in structurally and taxonomically heterogeneous forests, and may suffer from diminished predictive accuracy due to incongruity in scale and precision between field plot samples, remotely-sensed data, and target biota of varying size and density. This three-part study addresses these and other concerns in the modeling and mapping of emergent properties of forest communities by shifting the scope of prediction from the individual or taxon to the whole stand or community. It is, after all, at the stand scale where emergent properties like functional processes, biodiversity, and habitat aggregate and manifest. In the first study, I explore the relationship between forest structure (a proxy for successional demographics and resource competition) and tree species diversity in the North Carolina Piedmont, highlighting the empirical basis and potential for utilizing forest structure from LiDAR in predictive models of tree species diversity. I then extend these conclusions to map landscape pattern in multi-scale vascular plant diversity as well as turnover in community-continua at varying compositional resolutions in a North Carolina Piedmont landscape using remotely-sensed LiDAR-hyperspectral estimates of topography, canopy structure, and foliar biochemistry. Recognizing that the distinction between correlation and causation mirrors that between knowledge and understanding, all three studies distinguish between prediction of pattern and inference of process. Thus, in addition to advancing mapping methodologies relevant to a range of forest ecosystem management and monitoring applications, all three studies are noteworthy for assessing the ecological relationship between environmental predictors and emergent landscape patterns in plant composition and diversity in North Carolina Piedmont forests.

The power of the kashrut: older but shorter. The impact of religious nutritional and hygienic rules on stature and life expectancy of Jewish conscripts in the early 19th century.

PubMed

Tassenaar, V; Karel, E H

2016-06-01

We test the impact of several demographic, economic and social factors on stature in an early nineteenth century environment. We use a database of conscripts from the period 1818-1860 of a rural province in The Netherlands (Drenthe). This area had a rather high biological standard of living. This database of 413 conscripts contains information about family structure, family rank order, height, tax income, occupation and age of death. Conscripts came from two communities: one from a particular village (Oosterhesselen) and the other was Jewish conscripts that came from the countryside of the province. Our statistical analysis shows a positive significant relationship between family size and height, which confirms the resource dilution theory. Remarkably, the sign of the relation between family size and life expectancy is inverse. Other factors such as the potato crisis and income had the expected effect on conscript heights. The community effect was strong. Jewish conscripts were much shorter than their counterparts. Access to nutrition, the specific food laws and other factors can explain this difference. An increasing sibship size had a negative impact on body height but positive effects on life expectancy when adulthood was reached. Specifically for the Jewish community was the positive effect of the death of the father on conscript height. The mechanisms behind this phenomenon are unclear and open for further research.

Team assembly mechanisms determine collaboration network structure and team performance.

PubMed

Guimerà, Roger; Uzzi, Brian; Spiro, Jarrett; Amaral, Luís A Nunes

2005-04-29

Agents in creative enterprises are embedded in networks that inspire, support, and evaluate their work. Here, we investigate how the mechanisms by which creative teams self-assemble determine the structure of these collaboration networks. We propose a model for the self-assembly of creative teams that has its basis in three parameters: team size, the fraction of newcomers in new productions, and the tendency of incumbents to repeat previous collaborations. The model suggests that the emergence of a large connected community of practitioners can be described as a phase transition. We find that team assembly mechanisms determine both the structure of the collaboration network and team performance for teams derived from both artistic and scientific fields.

Effects of long-term changes in the benthic community on yellow perch in Saginaw Bay, Lake Huron

USGS Publications Warehouse

Schaeffer, Jeffrey S.; Diana, James S.; Haas, Robert C.

2000-01-01

Abundance, mortality, age and growth, food habits, and energetics of a yellow perch Perca flavescens population were investigated in eutrophic Saginaw Bay, Lake Huron during May to October, 1986 to 1988, and compared population characteristics with historical data from times when eutrophic conditions were less severe. During 1986 to 1988, yellow perch were abundant, but grew slowly and experienced high natural mortality. A size threshold was present at 150 to 180 mm beyond which few individuals survived, and sex ratios became biased toward males. An energetic model suggested that yellow perch were food limited; as they increased in size they spent a greater proportion of the growing season near maintenance ration. Low feeding rates were a consequence of subsistence on small chironomid larvae. Piscivory provided little energetic relief. Historical data suggested that availability of large benthic prey such as nymphs of the burrowing mayfly Hexagenia was important to yellow perch. Yellow perch formerly consumed Hexagenia, but mayflies were extirpated from Saginaw Bay during 1953 to 1965, and never recovered. When Hexagenia was present, yellow perch growth was moderate to fast depending on population size, size thresholds were not present, and yellow perch reached large size and older age despite moderate to high fishing mortality. Decreases in yellow perch growth rates during 1952 to 1955 coincided with extirpation of Hexagenia. Fast growth of yellow perch did occur after Hexagenia became extirpated, but only when fishing mortality was high, population size was small, and some large benthic invertebrates remained. Eutrophication of Saginaw Bay appeared to affect yellow perch by changing species composition and reducing size structure of the benthic community.

Comparisons of fish species traits from small streams to large rivers

USGS Publications Warehouse

Goldstein, R.M.; Meador, M.R.

2004-01-01

To examine the relations between fish community function and stream size, we classified 429 lotic freshwater fish species based on multiple categories within six species traits: (1) substrate preference, (2) geomorphic preference, (3) trophic ecology, (4) locomotion morphology, (5) reproductive strategy, and (6) stream size preference. Stream size categories included small streams, small, medium, and large rivers, and no size preference. The frequencies of each species trait category were determined for each stream size category based on life history information from the literature. Cluster analysis revealed the presence of covarying groups of species trait categories. One cluster (RUN) included the traits of planktivore and herbivore feeding ecology, migratory reproductive behavior and broadcast spawning, preferences for main-channel habitats, and a lack of preferences for substrate type. The frequencies of classifications for the RUN cluster varied significantly across stream size categories (P = 0.009), being greater for large rivers than for small streams and rivers. Another cluster (RIFFLE) included the traits of invertivore feeding ecology, simple nester reproductive behavior, a preference for riffles, and a preference for bedrock, boulder, and cobble-rubble substrate. No significant differences in the frequency of classifications among stream size categories were detected for the RIFFLE cluster (P = 0.328). Our results suggest that fish community function is structured by large-scale differences in habitat and is different for large rivers than for small streams and rivers. Our findings support theoretical predictions of variation in species traits among stream reaches based on ecological frameworks such as landscape filters, habitat templates, and the river continuum concept. We believe that the species trait classifications presented here provide an opportunity for further examination of fish species' relations to physical, chemical, and biological factors in lotic habitats ranging from small streams to large rivers.

Bacterial Biogeography across the Amazon River-Ocean Continuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doherty, Mary; Yager, Patricia L.; Moran, Mary Ann

Spatial and temporal patterns in microbial biodiversity across the Amazon river-ocean continuum were investigated along ~675 km of the lower Amazon River mainstem, in the Tapajos River tributary, and in the plume and coastal ocean during low and high river discharge using amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples (0.2-2.0 μm and >2.0 μm). River communities varied among tributaries, but mainstem communities were spatially homogeneous and tracked seasonal changes in river discharge and co-varying factors. Co-occurrence network analysis identified strongly interconnected river assemblages during high (May) and low (December) discharge periods, and weakly interconnected transitionalmore » assemblages in September, suggesting that this system supports two seasonal microbial communities linked to river discharge. In contrast, plume communities showed little seasonal differences and instead varied spatially tracking salinity. However, salinity explained only a small fraction of community variability, and plume communities in blooms of diatom-diazotroph assemblages were strikingly different than those in other high salinity plume samples. This suggests that while salinity physically structures plumes through buoyancy and mixing, the composition of plume-specific communities is controlled by other factors including nutrients, phytoplankton community composition, and dissolved organic matter chemistry. Co-occurrence networks identified interconnected assemblages associated with the highly productive low salinity nearshore region, diatom-diazotroph blooms, and the plume edge region, and weakly interconnected assemblages in high salinity regions. This suggests that the plume supports a transitional community influenced by immigration of ocean bacteria from the plume edge, and by species sorting as these communities adapt to local environmental conditions. Few studies have explored patterns of microbial diversity in tropical rivers and coastal oceans. Comparison of Amazon continuum microbial communities to those from temperate and arctic systems suggest that river discharge and salinity are master variables structuring a range of environmental conditions that control bacterial communities across the river-ocean continuum.« less

Bacterial Biogeography across the Amazon River-Ocean Continuum.

PubMed

Doherty, Mary; Yager, Patricia L; Moran, Mary Ann; Coles, Victoria J; Fortunato, Caroline S; Krusche, Alex V; Medeiros, Patricia M; Payet, Jérôme P; Richey, Jeffrey E; Satinsky, Brandon M; Sawakuchi, Henrique O; Ward, Nicholas D; Crump, Byron C

2017-01-01

Spatial and temporal patterns in microbial biodiversity across the Amazon river-ocean continuum were investigated along ∼675 km of the lower Amazon River mainstem, in the Tapajós River tributary, and in the plume and coastal ocean during low and high river discharge using amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples (0.2-2.0 μm and >2.0 μm). River communities varied among tributaries, but mainstem communities were spatially homogeneous and tracked seasonal changes in river discharge and co-varying factors. Co-occurrence network analysis identified strongly interconnected river assemblages during high (May) and low (December) discharge periods, and weakly interconnected transitional assemblages in September, suggesting that this system supports two seasonal microbial communities linked to river discharge. In contrast, plume communities showed little seasonal differences and instead varied spatially tracking salinity. However, salinity explained only a small fraction of community variability, and plume communities in blooms of diatom-diazotroph assemblages were strikingly different than those in other high salinity plume samples. This suggests that while salinity physically structures plumes through buoyancy and mixing, the composition of plume-specific communities is controlled by other factors including nutrients, phytoplankton community composition, and dissolved organic matter chemistry. Co-occurrence networks identified interconnected assemblages associated with the highly productive low salinity near-shore region, diatom-diazotroph blooms, and the plume edge region, and weakly interconnected assemblages in high salinity regions. This suggests that the plume supports a transitional community influenced by immigration of ocean bacteria from the plume edge, and by species sorting as these communities adapt to local environmental conditions. Few studies have explored patterns of microbial diversity in tropical rivers and coastal oceans. Comparison of Amazon continuum microbial communities to those from temperate and arctic systems suggest that river discharge and salinity are master variables structuring a range of environmental conditions that control bacterial communities across the river-ocean continuum.

Bacterial Biogeography across the Amazon River-Ocean Continuum

DOE PAGES

Doherty, Mary; Yager, Patricia L.; Moran, Mary Ann; ...

2017-05-23

Spatial and temporal patterns in microbial biodiversity across the Amazon river-ocean continuum were investigated along ~675 km of the lower Amazon River mainstem, in the Tapajos River tributary, and in the plume and coastal ocean during low and high river discharge using amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples (0.2-2.0 μm and >2.0 μm). River communities varied among tributaries, but mainstem communities were spatially homogeneous and tracked seasonal changes in river discharge and co-varying factors. Co-occurrence network analysis identified strongly interconnected river assemblages during high (May) and low (December) discharge periods, and weakly interconnected transitionalmore » assemblages in September, suggesting that this system supports two seasonal microbial communities linked to river discharge. In contrast, plume communities showed little seasonal differences and instead varied spatially tracking salinity. However, salinity explained only a small fraction of community variability, and plume communities in blooms of diatom-diazotroph assemblages were strikingly different than those in other high salinity plume samples. This suggests that while salinity physically structures plumes through buoyancy and mixing, the composition of plume-specific communities is controlled by other factors including nutrients, phytoplankton community composition, and dissolved organic matter chemistry. Co-occurrence networks identified interconnected assemblages associated with the highly productive low salinity nearshore region, diatom-diazotroph blooms, and the plume edge region, and weakly interconnected assemblages in high salinity regions. This suggests that the plume supports a transitional community influenced by immigration of ocean bacteria from the plume edge, and by species sorting as these communities adapt to local environmental conditions. Few studies have explored patterns of microbial diversity in tropical rivers and coastal oceans. Comparison of Amazon continuum microbial communities to those from temperate and arctic systems suggest that river discharge and salinity are master variables structuring a range of environmental conditions that control bacterial communities across the river-ocean continuum.« less

Bacterial Biogeography across the Amazon River-Ocean Continuum

PubMed Central

Doherty, Mary; Yager, Patricia L.; Moran, Mary Ann; Coles, Victoria J.; Fortunato, Caroline S.; Krusche, Alex V.; Medeiros, Patricia M.; Payet, Jérôme P.; Richey, Jeffrey E.; Satinsky, Brandon M.; Sawakuchi, Henrique O.; Ward, Nicholas D.; Crump, Byron C.

2017-01-01

Spatial and temporal patterns in microbial biodiversity across the Amazon river-ocean continuum were investigated along ∼675 km of the lower Amazon River mainstem, in the Tapajós River tributary, and in the plume and coastal ocean during low and high river discharge using amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples (0.2–2.0 μm and >2.0 μm). River communities varied among tributaries, but mainstem communities were spatially homogeneous and tracked seasonal changes in river discharge and co-varying factors. Co-occurrence network analysis identified strongly interconnected river assemblages during high (May) and low (December) discharge periods, and weakly interconnected transitional assemblages in September, suggesting that this system supports two seasonal microbial communities linked to river discharge. In contrast, plume communities showed little seasonal differences and instead varied spatially tracking salinity. However, salinity explained only a small fraction of community variability, and plume communities in blooms of diatom-diazotroph assemblages were strikingly different than those in other high salinity plume samples. This suggests that while salinity physically structures plumes through buoyancy and mixing, the composition of plume-specific communities is controlled by other factors including nutrients, phytoplankton community composition, and dissolved organic matter chemistry. Co-occurrence networks identified interconnected assemblages associated with the highly productive low salinity near-shore region, diatom-diazotroph blooms, and the plume edge region, and weakly interconnected assemblages in high salinity regions. This suggests that the plume supports a transitional community influenced by immigration of ocean bacteria from the plume edge, and by species sorting as these communities adapt to local environmental conditions. Few studies have explored patterns of microbial diversity in tropical rivers and coastal oceans. Comparison of Amazon continuum microbial communities to those from temperate and arctic systems suggest that river discharge and salinity are master variables structuring a range of environmental conditions that control bacterial communities across the river-ocean continuum. PMID:28588561

Comparisons between POC and zooplankton swimmer flux from sediment traps in the subarctic and subtropical North Pacific

NASA Astrophysics Data System (ADS)

Yokoi, Naoya; Abe, Yoshiyuki; Kitamura, Minoru; Honda, Makio C.; Yamaguchi, Atsushi

2018-03-01

Seasonal changes in zooplankton swimmer (ZS) abundance, biomass and community structure were evaluated based on samples collected by moored sediment traps at a depth of 200 m in the subarctic (SA) and subtropical (ST) western North Pacific. Based on these samples, we made comparisons on two topics: 1) latitudinal (subarctic vs. subtropical) changes in ZS abundance, biomass and community and 2) quantitative differences between the ZS and particle organic carbon (POC) fluxes based on data from moored or drifting sediment traps. The results showed that the ZS flux was greater in the SA (annual mean: 311 ind. m-2 day-1 or 258 mg C m-2 day-1) than in the ST (135 ind. m-2 day-1 or 38 mg C m-2 day-1). The peak ZS flux was observed from July-August in the SA and from April-May in the ST. The dominant taxa were Copepoda and Chaetognatha in the SA and Ostracoda and Mollusca in the ST. These latitudinal differences are likely related to the dominance of large-sized Copepoda in the SA, regional differences in the timing of the spring phytoplankton bloom, and the magnitude and size structure of primary producers. The percent composition of ZS to the total C flux (= ZS+POC flux) varied by region: 85-95% in the SA and 47-75% in the ST. These differences between the ZS composition and the total C flux are most likely caused by the dominance of large-sized Copepoda (Neocalanus spp. and Eucalanus bungii) in the SA.

Parasites of a marine benthic fish in the Southwestern Atlantic: searching for geographical recurrent patterns of community structure.

PubMed

Vales, Damián Gustavo; García, Néstor Aníbal; Crespo, Enrique Alberto; Timi, Juan Tomás

2011-02-01

Parasite communities of Raneya brasiliensis are described and its parasites used as biological tags to discriminate its populations. Fish were caught in two zones of the Argentine Sea: one sample from San Jorge Gulf (Patagonian Region) and three samples from off the coast of Buenos Aires (Bonaerense Region). A total of 183 fish were examined for parasites and 11 species were found. Host body size and its ecology are pointed out as drivers of the paucity of taxa found. Multivariate similarity analyses allowed the identification of three stocks: one in the San Jorge Gulf, and two other in the Bonaerense Region. The parasite species that contributed most to the separation of the samples were generally those identified as biological markers in previous studies in the area. Patterns of distance decay in similarity among communities in R. brasiliensis were found; with dissimilarity values between distant localities being higher than between close ones. Whereas the composition and structure of parasite assemblages in Bonaerense waters reflect those of other fish species in this region, being mainly determined by the composition of the compound community, no repeatable patterns were found in the composition of parasites assemblages when R. brasiliensis was compared with other hosts species in Patagonia.

The robustness of ecosystems to the species loss of community

NASA Astrophysics Data System (ADS)

Cai, Qing; Liu, Jiming

2016-10-01

To study the robustness of ecosystems is crucial to promote the sustainable development of human society. This paper aims to analyze the robustness of ecosystems from an interesting viewpoint of the species loss of community. Unlike the existing definitions, we first introduce the notion of a community as a population of species belonging to the same trophic level. We then put forward a novel multiobjective optimization model which can be utilized to discover community structures from arbitrary unipartite networks. Because an ecosystem is commonly represented as a multipartite network, we further introduce a mechanism of competition among species whereby a multipartite network is transformed into a unipartite signed network without loss of species interaction information. Finally, we examine three strategies to test the robustness of an ecosystem. Our experiments indicate that ecosystems are robust to random species loss of community but fragile to target ones. We also investigate the relationships between the robustness of an ecosystem and that of its community composed network both to species loss. Our experiments indicate that the robustness analysis of a large-scale ecosystem to species loss may be akin to that of its community composed network which is usually small in size.

Beech cupules as keystone structures for soil fauna.

PubMed

Melguizo-Ruiz, Nereida; Jiménez-Navarro, Gerardo; Moya-Laraño, Jordi

2016-01-01

Facilitative or positive interactions are ubiquitous in nature and play a fundamental role in the configuration of ecological communities. In particular, habitat modification and niche construction, in which one organism locally modifies abiotic conditions and favours other organisms by buffering the effects of adverse environmental factors, are among the most relevant facilitative interactions. In line with this, 'keystone structures', which provide resources, refuge, or advantageous services decisive for other species, may allow the coexistence of various species and thus considerably contribute to diversity maintenance. Beech cupules are woody husks harbouring beech fruits that remain in the forest soil for relatively long periods of time. In this study, we explored the potential role of these cupules in the distribution and maintenance of the soil fauna inhabiting the leaf litter layer. We experimentally manipulated cupule availability and soil moisture in the field to determine if such structures are limiting and can provide moist shelter to soil animals during drought periods, contributing to minimize desiccation risks. We measured invertebrate abundances inside relative to outside the cupules, total abundances in the leaf litter and animal body sizes, in both dry and wet experimental plots. We found that these structures are preferentially used by the most abundant groups of smaller soil animals-springtails, mites and enchytraeids-during droughts. Moreover, beech cupules can be limiting, as an increase in use was found with higher cupule densities, and are important resources for many small soil invertebrates, driving the spatial structure of the soil community and promoting higher densities in the leaf litter, probably through an increase in habitat heterogeneity. We propose that fruit woody structures should be considered 'keystone structures' that contribute to soil community maintenance. Therefore, beech trees may indirectly facilitate soil fauna activities through their decaying fruit husks, hence acting as ecosystem engineers.

Effects of management on aquatic tree-hole communities in temperate forests are mediated by detritus amount and water chemistry.

PubMed

Gossner, Martin M; Lade, Peggy; Rohland, Anja; Sichardt, Nora; Kahl, Tiemo; Bauhus, Jürgen; Weisser, Wolfgang W; Petermann, Jana S

2016-01-01

Arthropod communities in water-filled tree holes may be sensitive to impacts of forest management, for example via changes in environmental conditions such as resource input. We hypothesized that increasing forest management intensity (ForMI) negatively affects arthropod abundance and richness and shifts community composition and trophic structure of tree hole communities. We predicted that this shift is caused by reduced habitat and resource availability at the forest stand scale as well as reduced tree hole size, detritus amount and changed water chemistry at the tree holes scale. We mapped 910 water-filled tree holes in two regions in Germany and studied 199 tree hole inhabiting arthropod communities. We found that increasing ForMI indeed significantly reduced arthropod abundance and richness in water-filled tree holes. The most important indirect effects of management intensity on tree hole community structure were the reduced amounts of detritus for the tree hole inhabiting organisms and changed water chemistry at the tree hole scale, both of which seem to act as a habitat filter. Although habitat availability at the forest stand scale decreased with increasing management intensity, this unexpectedly increased local arthropod abundance in individual tree holes. However, regional species richness in tree holes significantly decreased with increasing management intensity, most likely due to decreased habitat diversity. We did not find that the management-driven increase in plant diversity at the forest stand scale affected communities of individual tree holes, for example via resource availability for adults. Our results suggest that management of temperate forests has to target a number of factors at different scales to conserve diverse arthropod communities in water-filled tree holes. © 2015 The Authors. Journal of Animal Ecology © 2015 British Ecological Society.

Ecological Interactions in Dinosaur Communities: Influences of Small Offspring and Complex Ontogenetic Life Histories

PubMed Central

Codron, Daryl; Carbone, Chris; Clauss, Marcus

2013-01-01

Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs’ successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well. PMID:24204749

Ecological interactions in dinosaur communities: influences of small offspring and complex ontogenetic life histories.

PubMed

Codron, Daryl; Carbone, Chris; Clauss, Marcus

2013-01-01

Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs' successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.

Economic Impacts of Highway Relief Routes on Small- and Medium-Size Communities: Case Studies

DOT National Transportation Integrated Search

2001-09-01

Original Report Date: March 2000. Highway relief routes may have a variety of impacts on small- and medium-size communities, both positive and negative. On the positive side, communities benefit from a reduction in traffic through the heart of the co...

Engineering a new class of thermal spray nano-based microstructures from agglomerated nanostructured particles, suspensions and solutions: an invited review

NASA Astrophysics Data System (ADS)

Fauchais, P.; Montavon, G.; Lima, R. S.; Marple, B. R.

2011-03-01

From the pioneering works of McPherson in 1973 who identified nanometre-sized features in thermal spray conventional alumina coatings (using sprayed particles in the tens of micrometres size range) to the most recent and most advanced work aimed at manufacturing nanostructured coatings from nanometre-sized feedstock particles, the thermal spray community has been involved with nanometre-sized features and feedstock for more than 30 years. Both the development of feedstock (especially through cryo-milling, and processes able to manufacture coatings structured at the sub-micrometre or nanometre sizes, such as micrometre-sized agglomerates made of nanometre-sized particles for feedstock) and the emergence of thermal spray processes such as suspension and liquid precursor thermal spray techniques have been driven by the need to manufacture coatings with enhanced properties. These techniques result in two different types of coatings: on the one hand, those with a so-called bimodal structure having nanometre-sized zones embedded within micrometre ones, for which the spray process is similar to that of conventional coatings and on the other hand, sub-micrometre or nanostructured coatings achieved by suspension or solution spraying. Compared with suspension spraying, solution precursor spraying uses molecularly mixed precursors as liquids, avoiding a separate processing route for the preparation of powders and enabling the synthesis of a wide range of oxide powders and coatings. Such coatings are intended for use in various applications ranging from improved thermal barrier layers and wear-resistant surfaces to thin solid electrolytes for solid oxide fuel cell systems, among other numerous applications. Meanwhile these processes are more complex to operate since they are more sensitive to parameter variations compared with conventional thermal spray processes. Progress in this area has resulted from the unique combination of modelling activities, the evolution of diagnostic tools and strategies, and experimental advances that have enabled the development of a wide range of coating structures exhibiting in numerous cases unique properties. Several examples are detailed. In this paper the following aspects are presented successively (i) the two spray techniques used for manufacturing such coatings: thermal plasma and HVOF, (ii) sensors developed for in-flight diagnostics of micrometre-sized particles and the interaction of a liquid and hot gas flow, (iii) three spray processes: conventional spraying using micrometre-sized agglomerates of nanometre-sized particles, suspension spraying and solution spraying and (iv) the emerging issues resulting from the specific structures of these materials, particularly the characterization of these coatings and (v) the potential industrial applications. Further advances require the scientific and industrial communities to undertake new research and development activities to address, understand and control the complex mechanisms occurring, in particular, thermal flow—liquid drops or stream interactions when considering suspension and liquid precursor thermal spray techniques. Work is still needed to develop new measurement devices to diagnose in-flight droplets or particles below 2 µm average diameter and to validate that the assumptions made for liquid-hot gas interactions. Efforts are also required to further develop some of the characterization protocols suitable to address the specificities of such nanostructured coatings, as some existing 'conventional' protocols usually implemented on thermal spray coatings are not suitable anymore, in particular to address the void network architectures from which numerous coatings properties are derived.

Community phylogenetics at the biogeographical scale: cold tolerance, niche conservatism and the structure of North American forests.

PubMed

Hawkins, Bradford A; Rueda, Marta; Rangel, Thiago F; Field, Richard; Diniz-Filho, José Alexandre F; Linder, Peter

2014-01-01

Aim The fossil record has led to a historical explanation for forest diversity gradients within the cool parts of the Northern Hemisphere, founded on a limited ability of woody angiosperm clades to adapt to mid-Tertiary cooling. We tested four predictions of how this should be manifested in the phylogenetic structure of 91,340 communities: (1) forests to the north should comprise species from younger clades (families) than forests to the south; (2) average cold tolerance at a local site should be associated with the mean family age (MFA) of species; (3) minimum temperature should account for MFA better than alternative environmental variables; and (4) traits associated with survival in cold climates should evolve under a niche conservatism constraint. Location The contiguous United States. Methods We extracted angiosperms from the US Forest Service's Forest Inventory and Analysis database. MFA was calculated by assigning age of the family to which each species belongs and averaging across the species in each community. We developed a phylogeny to identify phylogenetic signal in five traits: realized cold tolerance, seed size, seed dispersal mode, leaf phenology and height. Phylogenetic signal representation curves and phylogenetic generalized least squares were used to compare patterns of trait evolution against Brownian motion. Eleven predictors structured at broad or local scales were generated to explore relationships between environment and MFA using random forest and general linear models. Results Consistent with predictions, (1) southern communities comprise angiosperm species from older families than northern communities, (2) cold tolerance is the trait most strongly associated with local MFA, (3) minimum temperature in the coldest month is the environmental variable that best describes MFA, broad-scale variables being much stronger correlates than local-scale variables, and (4) the phylogenetic structures of cold tolerance and at least one other trait associated with survivorship in cold climates indicate niche conservatism. Main conclusions Tropical niche conservatism in the face of long-term climate change, probably initiated in the Late Cretaceous associated with the rise of the Rocky Mountains, is a strong driver of the phylogenetic structure of the angiosperm component of forest communities across the USA. However, local deterministic and/or stochastic processes account for perhaps a quarter of the variation in the MFA of local communities.

Abundance fluctuations among benthic invertebrates in two pacific estuaries

USGS Publications Warehouse

Nichols, Frederic H.

1985-01-01

Long-term studies were used to examine (1) contrasting time scales and mechanisms of structural variations within two benthic communities and (2) the usefulness of long data sets for evaluating human impact. A 10-year study of a San Francisco Bay mudflat, the details of which are reported elsewhere, has revealed large short-term (on the order of months) variations in species abundances within a community composed predominantly of opportunistic species. The study site, located in a highly urbanized estuary, is subject to the influence of a nearby sewage-treatment facility. However, rapid changes in population size of the common species, in part due to periodic natural habitat disturbance, impedes the detection of anthropogenic influences on community composition. Only a very long-term data set may provide evidence of progressive change. Data collected for a 20-year period on the benthic community at 200 m depth in the main basin of Puget Sound, an environment subject to little apparent habitat disturbance show that numerical abundance of the common species can also change markedly. Here, however, numerical dominance shifts from one species to another at irregular, multiyear intervals. Recent increases in two heretofore rare species, and a significant increase in total numbers of individuals suggest that long-term changes may be occurring in this community. These two long-term data sets demonstrate the importance of measuring both the amplitude and the periodicity of fluctuations in population size of aquatic species as well as long-term fluctuations and patterns in environmental factors before attempting to demonstrate the effect of anthropogenic influences on aquatic communities. The results of these studies also demonstrate the usefulness of long-term data sets for revealing the potential importance of interactions among species in determining abundance patterns in the soft-bottom benthos.

Temporal variation in the mating structure of Sanday, Orkney Islands.

PubMed

Brennan, E R; Relethford, J H

1983-01-01

Pedigree and vital statistics data from the population of Sanday, Orkney Islands, Scotland, were used to assess temporal changes in population structure. Secular trends in patterns of mate choice were analysed for three separate birth cohorts of spouses: 1855-1884, 1885-1924 and 1925-1964. The degree to which mating was random or assortative with respect to both genealogical and geographic distance was determined by comparing average characteristics of all potential mates of married males with those of actual wives. We integrated this procedure, originally developed by Dyke (1971), into a three-fold investigation of population structure: (1) comparison of random and non-random components of relatedness as measured from pedigree data; (2) an analysis of marital distance distributions for actual and potential mates of married males; and (3) the relationship between genealogical relatedness and geographic distance. As population size decreased from 1881 to the present, total kinship and spatial distances between spouses increased. Whereas the random component of relatedness increased over time, consanguinity avoidance was sufficient to decrease the total coefficient of kinship over time. Part of the increase in consanguinity avoidance was associated with isolate breakdown, as distances between island-born spouses, as well as the total amount of off-island migration, increased from the mid-nineteenth century to the present. Mate choice was influenced by geographic distance for all time periods, although this effect diminished over time. Since decreases in population size, concomitant with increases in consanguinity avoidance and community exogamy, have probably occurred quite frequently in small human populations, as well as in rural Western communities in the past century, observed secular trends illustrate the potential for change in population structure characteristic of isolate breakdown.

Trait overdispersion and the role of sociality in the assembly of social spider communities across the Americas.

PubMed

Fernandez-Fournier, Philippe; Guevara, Jennifer; Hoffman, Catherine; Avilés, Leticia

2018-05-21

Among the factors that may lead to differences in resource use among closely related species, body size and morphology have been traditionally considered to play a role in community assembly. Here we argue that for animals that live and forage in groups, level of sociality, reflecting differences in group size and cooperative tendencies, can be an additional and powerful dimension separating species in niche space. We compare 50+ communities of the social spider genus Anelosimus across the Americas against a null model that accounts for known effects of biotic and abiotic factors on the distribution of social systems in the genus. We show that these communities are more overdispersed than expected by chance in either or both body size and level of sociality, traits we have previously shown to be associated with differences in resource utilization (prey size, microhabitat, and phenology). We further show that the contribution of sociality to differences in the size of the prey captured is two to three times greater than that of body size, suggesting that changes in group size and cooperative tendencies may be more effective than changes in body size at separating species in niche space.

Spatial variations in annual cycles of body-size spectra of planktonic ciliates and their environmental drivers in marine ecosystems.

PubMed

Xu, Henglong; Jiang, Yong; Xu, Guangjian

2016-11-15

Body-size spectra has proved to be a useful taxon-free resolution to summarize a community structure for bioassessment. The spatial variations in annual cycles of body-size spectra of planktonic ciliates and their environmental drivers were studied based on an annual dataset. Samples were biweekly collected at five stations in a bay of the Yellow Sea, northern China during a 1-year cycle. Based on a multivariate approach, the second-stage analysis, it was shown that the annual cycles of the body-size spectra were significantly different among five sampling stations. Correlation analysis demonstrated that the spatial variations in the body-size spectra were significantly related to changes of environmental conditions, especially dissolved nitrogen, alone or in combination with salinity and dissolve oxygen. Based on results, it is suggested that the nutrients may be the environmental drivers to shape the spatial variations in annual cycles of planktonic ciliates in terms of body-size spectra in marine ecosystems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nest survival relative to patch size in a highly fragmented shortgrass prairie landscape

USGS Publications Warehouse

Skagen, S.K.; Yackel Adams, A.A.; Adams, R.D.

2005-01-01

Understanding the influences of habitat fragmentation on vertebrate populations is essential for the protection and ecological restoration of strategic sites for native species. We examined the effects of prairie fragmentation on avian reproductive success using artificial and natural nests on 26 randomly selected, privately owned patches of shortgrass prairie ranging in size from 7 to 454 ha within a cropland matrix in Washington County, Colorado, summer 2000. Survival trends of artificial and natural nests differed. Daily survival of artificial nests increased with patch size up to about 65 ha and differed little at larger patch sizes, whereas daily survival of Lark Bunting (Calamospiza melanocorys) and Horned Lark (Eremophila alpestris) nests decreased with increasing size of the grassland patch. We hypothesize that our unexpected findings of lower survival of natural nests with increasing patch sizes and different trends between artificial and natural nests are due to the particular structure of predator communities in our study area and the ways in which individual predators respond to artificial and natural nests. We recommend that the value of small habitat patches in highly fragmented landscapes not be overlooked.

The roles of ecological first principles and evolutionary contingency in unraveling ecosystem response and reconstruction during the Permian-Triassic transition.

NASA Astrophysics Data System (ADS)

Roopnarine, P. D.; Weik, A.; Dineen, A.; Angielczyk, K.

2016-12-01

The Permian-Triassic mass extinction (PTME) is the most severe mass extinction recorded in Earth's history. Effects on the biosphere were complicated and often contradictory, e.g. selective species extinctions and exceptional species survival; prolonged miniaturization of some Early Triassic clades but rapid increases of size in others; and both simplified and complex trophic structures in various E. Triassic ecosystems. Here we present the results of a new generalized model of paleocommunity global stability (number of species capable of persistent coexistence in the absence of external perturbation), suggesting that community dynamics in response to species extinction, and the addition of new species in the aftermath of the PTME, is best understood as a complex outcome of predictable community dynamics and contingent, unpredictable evolutionary pathways. We applied the model to the best known PTME transitional terrestrial ecosystem, the Karoo Basin of South Africa. The model verifies previous claims that global stability scales negatively with increasing species richness and the strength of interspecific interactions. We also show that global stability scales negatively with intrinsic population growth rates. Taxon-rich Permian communities could therefore have persisted only under a restricted range of those parameters. Communities during three phases of the PTME, however, exhibited greater global stability than would be predicted from the pre-PTME communities. Those communities could therefore have maintained relative stabilities under a broader range of parameters, implying that species could have adapted by modifying life history and ecological traits with lesser negative consequences to community stability. The earliest post-PTME community with increased species richness, however, was less stable than would be predicted from pre-PTME communities. In both the extinction and aftermath communities, nonlinear deviations from the general scaling of stability result from structural features unique to those communities, perhaps limiting our ability to forecast biospheric responses to extreme perturbations.

Community Context of Sober Living Houses

PubMed Central

Henderson, Diane; Trocki, Karen; Evans, Kristy; Wittman, Fried

2012-01-01

The success or failure of programs designed to address alcohol and drug problems can be profoundly influenced by the communities where they are located. Support from the community is vital for long term stability and conflict with the community can harm a program’s reputation or even result in closure. This study examined the community context of sober living houses (SLHs) in one Northern California community by interviewing key stakeholder groups. SLHs are alcohol and drug free living environments for individuals attempting to abstain from substance use. Previous research on residents of SLHs showed they make long-term improvements on measures of substance use, psychiatric symptoms, arrests, and employment. Interviews were completed with house managers, neighbors, and key informants from local government and community organizations. Overall, stakeholders felt SLHs were necessary and had a positive impact on the community. It was emphasized that SLHs needed to practice a “good neighbor” policy that prohibited substance use and encouraged community service. Size and density of SLHs appeared to influence neighbor perceptions. For small (six residents or less), sparsely populated houses, a strategy of blending in with the neighborhood seemed to work. However, it was clear that larger, densely populated houses need to actively manage relationships with community stakeholders. Strategies for improving relationships with immediate neighbors, decreasing stigma, and broadening the leadership structure are discussed. Implications for a broad array of community based programs are discussed. PMID:24478615

Effects of fungicides and biofungicides on population density and community structure of soil oribatid mites.

PubMed

Al-Assiuty, Abdel-Naieem I M; Khalil, Mohamed A; Ismail, Abdel-Wahab A; van Straalen, Nico M; Ageba, Mohamed F

2014-01-01

To compare the side-effects of chemical versus biofungicides on non-target organisms in agricultural soil, a study of population structure, spatial distribution and fecundity of oribatid mites, a diverse and species-rich group of microarthropods indicative of decomposer activity in soil was done. Plots laid out in agricultural fields of a research station in Egypt, were cultivated with cucumber and treated with two chemical fungicides: Ridomil Plus 50% wp (active ingredients=metalaxyl and copper oxychloride) and Dithane M-45 (active ingredient=mancozeb), and two biofungicides: Plant Guard (containing the antagonistic fungus Trichoderma harzianum) and Polyversum (containing the fungi-parasitic oomycete Pythium oligandrum). All treatments were done using both low-volume and high-volume spraying techniques to check whether any effects were dependent on the method of application. Oribatid mite communities were assessed from soil core samples collected during the growing season. Total abundance of oribatids was not different across the plots, but some species decreased in number, while one species increased. Species diversity and community equitability decreased with the application of chemical and biofungicides especially when using high-volume spraying. In control plots most oribatid species showed a significant degree of aggregation, which tended to decrease under fungicide treatment. Ridomil Plus, Plant Guard and Polyversum had a negative effect on the gravid/ungravid ratio of some species. Egg number averaged over the whole adult population was not directly related to the application of chemical and biofungicides but it showed a species-specific relationship with population density. In general biofungicides had a smaller effect on population size and community structure of oribatid mite species than chemical fungicides. The results indicate that biofungicides may be the preferred option when aiming to prevent side-effects on sensitive groups among the species-rich soil detritivore community. © 2013.

State of microbial communities in paleosols buried under kurgans of the desert-steppe zone in the Middle Bronze Age (27th-26th centuries BC) in relation to the dynamics of climate humidity

NASA Astrophysics Data System (ADS)

Khomutova, T. E.; Demkina, T. S.; Borisov, A. V.; Shishlina, I. I.

2017-02-01

The size and structure of microbial pool in light chestnut paleosols and paleosolonetz buried under kurgans of the Middle Bronze Age 4600-4500 years ago (the burial mound heights are 45-173 cm), as well as in recent analogues in the desert-steppe zone (Western Ergeni, Salo-Manych Ridge), have been studied. In paleosol profiles, the living microbial biomass estimated from the content of phospholipids varies from 35 to 258% of the present-day value; the active biomass (responsive to glucose addition) in paleosols is 1‒3 orders of magnitude lower than in recent analogues. The content of soil phospholipids is recalculated to that of microbial carbon, and its share in the total soil organic carbon is determined: it is 4.5-7.0% in recent soils and up to three times higher in the remained organic carbon of paleosols. The stability of microbial communities in the B1 horizon of paleosols is 1.3-2.2 times higher than in the upper horizon; in recent soils, it has a tendency to a decrease. The share of microorganisms feeding on plant residues in the ecological-trophic structure of paleosol microbial communities is higher by 23-35% and their index of oligotrophy is 3-5 times lower than in recent analogues. The size of microbial pool and its structure indicate a significantly higher input of plant residues into soils 4600-4500 years ago than in the recent time, which is related to the increase in atmospheric humidity in the studied zone. However, the occurrence depths of salt accumulations in profiles of the studied soils contradict this supposition. A short-term trend of increase in climate humidity is supposed, as indicated by microbial parameters (the most sensitive soil characteristics) or changes in the annual variation of precipitation (its increase in the warm season) during the construction of the mounds under study.

Genetic variability in the Guahibo population from Venezuela.

PubMed

Moral, Pedro; Marini, Elisabetta; Esteban, Esther; Mameli, Giuseppa Elisa; Succa, Valeria; Vona, Giuseppe

2002-01-01

Four communities from Guahibo of Venezuela were analyzed for the genetic variants of nine erythrocyte enzymes and five serum proteins. Of the 14 loci determined, four were monomorphic. Significant frequency differentiation among communities, was present for ESD and TF markers. In general, Guahibo allele frequencies are in the variation ranges described for South American groups. The analysis indicates a relatively higher affinity of Guahibos with other Venezuelan groups within an irregular pattern of genetic distances that are likely related to the complex demographic history of the South American groups. Genetic diversity estimates reveal a moderate degree of genetic structure between the four Guahibo communities. This intra-tribal variability in Guahibo appears to be lower than in Venezuelan Piaroa but higher than in other Amerindians and could be attributed to a combined effect of low population size and relative isolation of communities. At a continental level, the distribution of genetic diversity is consistent with preferential population movements along the eastern and western coastal areas.

Microbial community structure in the gut of the New Zealand insect Auckland tree weta (Hemideina thoracica).

PubMed

Waite, David W; Dsouza, Melissa; Biswas, Kristi; Ward, Darren F; Deines, Peter; Taylor, Michael W

2015-05-01

The endemic New Zealand weta is an enigmatic insect. Although the insect is well known by its distinctive name, considerable size, and morphology, many basic aspects of weta biology remain unknown. Here, we employed cultivation-independent enumeration techniques and rRNA gene sequencing to investigate the gut microbiota of the Auckland tree weta (Hemideina thoracica). Fluorescence in situ hybridisation performed on different sections of the gut revealed a bacterial community of fluctuating density, while rRNA gene-targeted amplicon pyrosequencing revealed the presence of a microbial community containing high bacterial diversity, but an apparent absence of archaea. Bacteria were further studied using full-length 16S rRNA gene sequences, with statistical testing of bacterial community membership against publicly available termite- and cockroach-derived sequences, revealing that the weta gut microbiota is similar to that of cockroaches. These data represent the first analysis of the weta microbiota and provide initial insights into the potential function of these microorganisms.

Fishing down nutrients on coral reefs.

PubMed

Allgeier, Jacob E; Valdivia, Abel; Cox, Courtney; Layman, Craig A

2016-08-16

Fishing is widely considered a leading cause of biodiversity loss in marine environments, but the potential effect on ecosystem processes, such as nutrient fluxes, is less explored. Here, we test how fishing on Caribbean coral reefs influences biodiversity and ecosystem functions provided by the fish community, that is, fish-mediated nutrient capacity. Specifically, we modelled five processes of nutrient storage (in biomass) and supply (via excretion) of nutrients, as well as a measure of their multifunctionality, onto 143 species of coral reef fishes across 110 coral reef fish communities. These communities span a gradient from extreme fishing pressure to protected areas with little to no fishing. We find that in fished sites fish-mediated nutrient capacity is reduced almost 50%, despite no substantial changes in the number of species. Instead, changes in community size and trophic structure were the primary cause of shifts in ecosystem function. These findings suggest that a broader perspective that incorporates predictable impacts of fishing pressure on ecosystem function is imperative for effective coral reef conservation and management.

Effect of Metal Oxide Nanoparticles on Microbial Community Structure and Function in Two Different Soil Types

PubMed Central

Frenk, Sammy; Ben-Moshe, Tal; Dror, Ishai; Berkowitz, Brian; Minz, Dror

2013-01-01

Increased availability of nanoparticle-based products will, inevitably, expose the environment to these materials. Engineered nanoparticles (ENPs) may thus find their way into the soil environment via wastewater, dumpsters and other anthropogenic sources; metallic oxide nanoparticles comprise one group of ENPs that could potentially be hazardous for the environment. Because the soil bacterial community is a major service provider for the ecosystem and humankind, it is critical to study the effects of ENP exposure on soil bacteria. These effects were evaluated by measuring bacterial community activity, composition and size following exposure to copper oxide (CuO) and magnetite (Fe3O4) nanosized (<50 nm) particles. Two different soil types were examined: a sandy loam (Bet-Dagan) and a sandy clay loam (Yatir), under two ENP concentrations (1%, 0.1%). Results indicate that the bacterial community in Bet-Dagan soil was more susceptible to change due to exposure to these ENPs, relative to Yatir soil. More specifically, CuO had a strong effect on bacterial hydrolytic activity, oxidative potential, community composition and size in Bet-Dagan soil. Few effects were noted in the Yatir soil, although 1% CuO exposure did cause a significant decreased oxidative potential and changes to community composition. Fe3O4 changed the hydrolytic activity and bacterial community composition in Bet-Dagan soil but did not affect the Yatir soil bacterial community. Furthermore, in Bet-Dagan soil, abundance of bacteria annotated to OTUs from the Bacilli class decreased after addition of 0.1% CuO but increased with 1% CuO, while in Yatir soil their abundance was reduced with 1% CuO. Other important soil bacterial groups, including Rhizobiales and Sphingobacteriaceae, were negatively affected by CuO addition to soil. These results indicate that both ENPs are potentially harmful to soil environments. Furthermore, it is suggested that the clay fraction and organic matter in different soils interact with the ENPs and reduce their toxicity. PMID:24349575

The roles of ecology, behaviour and effective population size in the evolution of a community.

PubMed

Hung, Chih-Ming; Drovetski, Sergei V; Zink, Robert M

2017-07-01

Organismal traits such as ecological specialization and migratory behaviour may affect colonization potential, population persistence and degree of isolation, factors that determine the composition and genetic structure of communities. However, studies focusing on community assembly rarely consider these factors jointly. We sequenced 16 nuclear genes and one mitochondrial gene from Caucasian and European populations of 30 forest-dwelling avian species that represent diverse ecological (specialist-generalist) and behavioural (migratory-resident) backgrounds. We tested the effects of organismal traits on population divergence and community assembly in the Caucasus forest, a continental mountain island setting. We found that (i) there is no concordance in divergence times between the Caucasus forest bird populations and their European counterparts, (ii) habitat specialists tend to be more divergent than generalists and (iii) residents tend to be more divergent than migrants. Thus, specialists and residents contribute to the high level of endemism of Caucasus forest avifauna more than do generalists and migrants. Patterns of genetic differentiation are better explained by differences in effective population sizes, an often overlooked factor in comparative studies of phylogeography and speciation, than by divergence times or levels of gene flow. Our results suggest that the Caucasus forest avifauna was assembled through time via dispersal and/or multiple vicariant events, rather than originating simultaneously via a single isolation event. Our study is one of the first multilocus, multispecies analyses revealing how ecological and migratory traits impact the evolutionary history of community formation on a continental island. © 2017 John Wiley & Sons Ltd.

Universal phase transition in community detectability under a stochastic block model.

PubMed

Chen, Pin-Yu; Hero, Alfred O

2015-03-01

We prove the existence of an asymptotic phase-transition threshold on community detectability for the spectral modularity method [M. E. J. Newman, Phys. Rev. E 74, 036104 (2006) and Proc. Natl. Acad. Sci. (USA) 103, 8577 (2006)] under a stochastic block model. The phase transition on community detectability occurs as the intercommunity edge connection probability p grows. This phase transition separates a subcritical regime of small p, where modularity-based community detection successfully identifies the communities, from a supercritical regime of large p where successful community detection is impossible. We show that, as the community sizes become large, the asymptotic phase-transition threshold p* is equal to √[p1p2], where pi(i=1,2) is the within-community edge connection probability. Thus the phase-transition threshold is universal in the sense that it does not depend on the ratio of community sizes. The universal phase-transition phenomenon is validated by simulations for moderately sized communities. Using the derived expression for the phase-transition threshold, we propose an empirical method for estimating this threshold from real-world data.

Brood size modifications affect plumage bacterial assemblages of European starlings.

PubMed

Lucas, Françoise S; Moureau, Benoit; Jourdie, Violaine; Heeb, Philipp

2005-02-01

During reproduction, birds face trade-offs between time and energy devoted to parental effort and traits associated with self-maintenance. We manipulated brood sizes to investigate the effects of such trade-offs on feather bacterial densities and the structure of bacterial assemblages on feathers in adult European starlings, Sturnus vulgaris, and in vitro feather degradation. As predicted by a trade-off between parental effort and self-maintenance, we found that birds with enlarged broods had more free-living bacteria on their feathers than birds with reduced broods. Furthermore, we found a significant interaction between brood manipulation and original brood size on free-living bacterial densities suggesting that the trade-off is mediated by the adults' initial reproductive investment. In contrast, brood size manipulations had no significant effect on densities of attached bacteria. Using ribosomal intergenic spacer analysis (RISA), we demonstrated that brood manipulations significantly modified the structure (band pattern) of feather-degrading bacterial assemblages, but had no significant effect on their richness (number of bands) or the in vitro feather degradation. In vitro feather degradation varied in relation to the premanipulation brood size and positively with the richness of the feather degrading bacterial community. Besides brood manipulation effect, we found that ecological factors and individual traits, such as the age, the nest location or the capture date, shaped bacterial assemblages and feather degradation capacities.

Size effects on insect hovering aerodynamics: an integrated computational study.

PubMed

Liu, H; Aono, H

2009-03-01

Hovering is a miracle of insects that is observed for all sizes of flying insects. Sizing effect in insect hovering on flapping-wing aerodynamics is of interest to both the micro-air-vehicle (MAV) community and also of importance to comparative morphologists. In this study, we present an integrated computational study of such size effects on insect hovering aerodynamics, which is performed using a biology-inspired dynamic flight simulator that integrates the modelling of realistic wing-body morphology, the modelling of flapping-wing and body kinematics and an in-house Navier-Stokes solver. Results of four typical insect hovering flights including a hawkmoth, a honeybee, a fruit fly and a thrips, over a wide range of Reynolds numbers from O(10(4)) to O(10(1)) are presented, which demonstrate the feasibility of the present integrated computational methods in quantitatively modelling and evaluating the unsteady aerodynamics in insect flapping flight. Our results based on realistically modelling of insect hovering therefore offer an integrated understanding of the near-field vortex dynamics, the far-field wake and downwash structures, and their correlation with the force production in terms of sizing and Reynolds number as well as wing kinematics. Our results not only give an integrated interpretation on the similarity and discrepancy of the near- and far-field vortex structures in insect hovering but also demonstrate that our methods can be an effective tool in the MAVs design.

Land-Use Change Alters Host and Vector Communities and May Elevate Disease Risk.

PubMed

Guo, Fengyi; Bonebrake, Timothy C; Gibson, Luke

2018-04-24

Land-use change has transformed most of the planet. Concurrently, recent outbreaks of various emerging infectious diseases have raised great attention to the health consequences of anthropogenic environmental degradation. Here, we assessed the global impacts of habitat conversion and other land-use changes on community structures of infectious disease hosts and vectors, using a meta-analysis of 37 studies. From 331 pairwise comparisons of disease hosts/vectors in pristine (undisturbed) and disturbed areas, we found a decrease in species diversity but an increase in body size associated with land-use changes, potentially suggesting higher risk of infectious disease transmission in disturbed habitats. Neither host nor vector abundance, however, changed significantly following disturbance. When grouped by subcategories like disturbance type, taxonomic group, pathogen type and region, changes in host/vector community composition varied considerably. Fragmentation and agriculture in particular benefit host and vector communities and therefore might elevate disease risk. Our results indicate that while habitat disturbance could alter disease host/vector communities in ways that exacerbate pathogen prevalence, the relationship is highly context-dependent and influenced by multiple factors.

Go big or … don't? A field-based diet evaluation of freshwater piscivore and prey fish size relationships

PubMed Central

Ahrenstorff, Tyler D.; Diana, James S.; Fetzer, William W.; Jones, Thomas S.; Lawson, Zach J.; McInerny, Michael C.; Santucci, Victor J.; Vander Zanden, M. Jake

2018-01-01

Body size governs predator-prey interactions, which in turn structure populations, communities, and food webs. Understanding predator-prey size relationships is valuable from a theoretical perspective, in basic research, and for management applications. However, predator-prey size data are limited and costly to acquire. We quantified predator-prey total length and mass relationships for several freshwater piscivorous taxa: crappie (Pomoxis spp.), largemouth bass (Micropterus salmoides), muskellunge (Esox masquinongy), northern pike (Esox lucius), rock bass (Ambloplites rupestris), smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus). The range of prey total lengths increased with predator total length. The median and maximum ingested prey total length varied with predator taxon and length, but generally ranged from 10–20% and 32–46% of predator total length, respectively. Predators tended to consume larger fusiform prey than laterally compressed prey. With the exception of large muskellunge, predators most commonly consumed prey between 16 and 73 mm. A sensitivity analysis indicated estimates can be very accurate at sample sizes greater than 1,000 diet items and fairly accurate at sample sizes greater than 100. However, sample sizes less than 50 should be evaluated with caution. Furthermore, median log10 predator-prey body mass ratios ranged from 1.9–2.5, nearly 50% lower than values previously reported for freshwater fishes. Managers, researchers, and modelers could use our findings as a tool for numerous predator-prey evaluations from stocking size optimization to individual-based bioenergetics analyses identifying prey size structure. To this end, we have developed a web-based user interface to maximize the utility of our models that can be found at www.LakeEcologyLab.org/pred_prey. PMID:29543856

Go big or … don't? A field-based diet evaluation of freshwater piscivore and prey fish size relationships.

PubMed

Gaeta, Jereme W; Ahrenstorff, Tyler D; Diana, James S; Fetzer, William W; Jones, Thomas S; Lawson, Zach J; McInerny, Michael C; Santucci, Victor J; Vander Zanden, M Jake

2018-01-01

Body size governs predator-prey interactions, which in turn structure populations, communities, and food webs. Understanding predator-prey size relationships is valuable from a theoretical perspective, in basic research, and for management applications. However, predator-prey size data are limited and costly to acquire. We quantified predator-prey total length and mass relationships for several freshwater piscivorous taxa: crappie (Pomoxis spp.), largemouth bass (Micropterus salmoides), muskellunge (Esox masquinongy), northern pike (Esox lucius), rock bass (Ambloplites rupestris), smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus). The range of prey total lengths increased with predator total length. The median and maximum ingested prey total length varied with predator taxon and length, but generally ranged from 10-20% and 32-46% of predator total length, respectively. Predators tended to consume larger fusiform prey than laterally compressed prey. With the exception of large muskellunge, predators most commonly consumed prey between 16 and 73 mm. A sensitivity analysis indicated estimates can be very accurate at sample sizes greater than 1,000 diet items and fairly accurate at sample sizes greater than 100. However, sample sizes less than 50 should be evaluated with caution. Furthermore, median log10 predator-prey body mass ratios ranged from 1.9-2.5, nearly 50% lower than values previously reported for freshwater fishes. Managers, researchers, and modelers could use our findings as a tool for numerous predator-prey evaluations from stocking size optimization to individual-based bioenergetics analyses identifying prey size structure. To this end, we have developed a web-based user interface to maximize the utility of our models that can be found at www.LakeEcologyLab.org/pred_prey.

Modeling Temporal Variation in Social Network: An Evolutionary Web Graph Approach

NASA Astrophysics Data System (ADS)

Mitra, Susanta; Bagchi, Aditya

A social network is a social structure between actors (individuals, organization or other social entities) and indicates the ways in which they are connected through various social relationships like friendships, kinships, professional, academic etc. Usually, a social network represents a social community, like a club and its members or a city and its citizens etc. or a research group communicating over Internet. In seventies Leinhardt [1] first proposed the idea of representing a social community by a digraph. Later, this idea became popular among other research workers like, network designers, web-service application developers and e-learning modelers. It gave rise to a rapid proliferation of research work in the area of social network analysis. Some of the notable structural properties of a social network are connectedness between actors, reachability between a source and a target actor, reciprocity or pair-wise connection between actors with bi-directional links, centrality of actors or the important actors having high degree or more connections and finally the division of actors into sub-structures or cliques or strongly-connected components. The cycles present in a social network may even be nested [2, 3]. The formal definition of these structural properties will be provided in Sect. 8.2.1. The division of actors into cliques or sub-groups can be a very important factor for understanding a social structure, particularly the degree of cohesiveness in a community. The number, size, and connections among the sub-groups in a network are useful in understanding how the network, as a whole, is likely to behave.

The importance of scaling for detecting community patterns: success and failure in assemblages of introduced species

USGS Publications Warehouse

Allen, Craig R.; Angeler, David G.; Moulton, Michael P.; Holling, Crawford S.

2015-01-01

Community saturation can help to explain why biological invasions fail. However, previous research has documented inconsistent relationships between failed invasions (i.e., an invasive species colonizes but goes extinct) and the number of species present in the invaded community. We use data from bird communities of the Hawaiian island of Oahu, which supports a community of 38 successfully established introduced birds and where 37 species were introduced but went extinct (failed invasions). We develop a modified approach to evaluate the effects of community saturation on invasion failure. Our method accounts (1) for the number of species present (NSP) when the species goes extinct rather than during its introduction; and (2) scaling patterns in bird body mass distributions that accounts for the hierarchical organization of ecosystems and the fact that interaction strength amongst species varies with scale. We found that when using NSP at the time of extinction, NSP was higher for failed introductions as compared to successful introductions, supporting the idea that increasing species richness and putative community saturation mediate invasion resistance. Accounting for scale-specific patterns in body size distributions further improved the relationship between NSP and introduction failure. Results show that a better understanding of invasion outcomes can be obtained when scale-specific community structure is accounted for in the analysis.

Natural and human-induced variability in the composition of fish assemblages in the Northwestern Cuban shelf.

PubMed

González-Sansón, Gaspar; Aguilar, Consuelo; Hernández, Ivet; Cabrera, Yureidy; Suarez-Montes, Noelis; Bretos, Fernando; Guggenheim, David

2009-09-01

The main goal of the study was to obtain field data to build a baseline of fish assemblage composition that can be used comparatively for future analyses of the impact of human actions in the region. A basic network of 68 sampling stations was defined for the entire region (4,050 km2). Fish assemblage species and size composition was estimated using visual census methods at three different spatial scales: a) entire region, b) inside the main reef area and c) along a human impact coastal gradient. Multivariate numerical analyses revealed habitat type as the main factor inducing spatial variability of fish community composition, while the level of human impact appears to play the main role in fish assemblage composition changes along the coast. A trend of decreasing fish size toward the east supports the theory of more severe human impact due to overfishing and higher urban pollution in that direction. This is the first detailed study along the northwest coast of Cuba that focuses on fish community structure and the natural and human-induced variations at different spatial scales for the entire NW shelf. This research also provides input for a more comprehensive understanding of coastal marine fish communities' status in the Gulf of Mexico basin.

Development of population structure and spatial distribution patterns of a restored forest during 17-year succession (1993-2010) in Pingshuo opencast mine spoil, China.

PubMed

Zhao, Zhongqiu; Wang, Lianhua; Bai, Zhongke; Pan, Ziguan; Wang, Yun

2015-07-01

Afforestation of native tree species is often recommended for ecological restoration in mining areas, but the understanding of the ecological processes of restored vegetation is quite limited. In order to provide insight of the ecological processes of restored vegetation, in this study, we investigate the development of the population structure and spatial distribution patterns of restored Robinia pseudoacacia (ROPS) and Pinus tabuliformis (PITA) mixed forests during the 17 years of the mine spoil period of the Pingshuo opencast mine, Shanxi Province, China. After a 17-year succession, apart from the two planted species, Ulmus pumila (ULPU), as an invasive species, settled in the plot along with a large number of small diameter at breast height (DBH) size. In total, there are 10,062 living individual plants, much more than that at the plantation (5105), and ROPS had become the dominant species with a section area with a breast height of 9.40 m(2) hm(-2) and a mean DBH of 6.72 cm, much higher than both PITA and ULPU. The DBH size classes of all the total species showed inverted J-shaped distributions, which may have been a result of the large number of small regenerated ULPU trees. The DBH size classes of both ROPS and PITA showed peak-type structures with individuals mainly gathering in the moderate DBH size class, indicating a relatively healthy DBH size class structure. Meanwhile, invasive ULPU were distributed in a clear L shape, concentrating on the small DBH size class, indicating a relatively low survival rate for adult trees. Both ROPS and PITA species survival in the plantation showed uniform and aggregated distribution at small scales and random with scales increasing. ULPU showed a strong aggregation at small scales as well as random with scales increasing. Both the population structure and spatial distribution indicated that ROPS dominates and will continue to dominate the community in the future succession, which should be continuously monitored.

Distribution and spatial variation of hydrothermal faunal assemblages at Lucky Strike (Mid-Atlantic Ridge) revealed by high-resolution video image analysis

NASA Astrophysics Data System (ADS)

Cuvelier, Daphne; Sarrazin, Jozée; Colaço, Ana; Copley, Jon; Desbruyères, Daniel; Glover, Adrian G.; Tyler, Paul; Serrão Santos, Ricardo

2009-11-01

Whilst the fauna inhabiting hydrothermal vent structures in the Atlantic Ocean is reasonably well known, less is understood about the spatial distributions of the fauna in relation to abiotic and biotic factors. In this study, a major active hydrothermal edifice (Eiffel Tower, at 1690 m depth) on the Lucky Strike vent field (Mid-Atlantic Ridge (MAR)) was investigated. Video transects were carried out by ROV Victor 6000 and complete image coverage was acquired. Four distinct assemblages, ranging from dense larger-sized Bathymodiolus mussel beds to smaller-sized mussel clumps and alvinocaridid shrimps, and two types of substrata were defined based on high definition photographs and video imagery. To evaluate spatial variation, faunal distribution was mapped in three dimensions. A high degree of patchiness characterizes this 11 m high sulfide structure. The differences observed in assemblage and substratum distribution were related to habitat characteristics (fluid exits, depth and structure orientation). Gradients in community structure were observed, which coincided with an increasing distance from the fluid exits. A biological zonation model for the Eiffel Tower edifice was created in which faunal composition and distribution can be visually explained by the presence/absence of fluid exits.

Simpler grammar, larger vocabulary: How population size affects language

PubMed Central

2018-01-01

Languages with many speakers tend to be structurally simple while small communities sometimes develop languages with great structural complexity. Paradoxically, the opposite pattern appears to be observed for non-structural properties of language such as vocabulary size. These apparently opposite patterns pose a challenge for theories of language change and evolution. We use computational simulations to show that this inverse pattern can depend on a single factor: ease of diffusion through the population. A population of interacting agents was arranged on a network, passing linguistic conventions to one another along network links. Agents can invent new conventions, or replicate conventions that they have previously generated themselves or learned from other agents. Linguistic conventions are either Easy or Hard to diffuse, depending on how many times an agent needs to encounter a convention to learn it. In large groups, only linguistic conventions that are easy to learn, such as words, tend to proliferate, whereas small groups where everyone talks to everyone else allow for more complex conventions, like grammatical regularities, to be maintained. Our simulations thus suggest that language, and possibly other aspects of culture, may become simpler at the structural level as our world becomes increasingly interconnected. PMID:29367397

Evaluating factors that predict the structure of a commensalistic epiphyte–phorophyte network

PubMed Central

Sáyago, Roberto; Lopezaraiza-Mikel, Martha; Quesada, Mauricio; Álvarez-Añorve, Mariana Yolotl; Cascante-Marín, Alfredo; Bastida, Jesus Ma.

2013-01-01

A central issue in ecology is the understanding of the establishment of biotic interactions. We studied the factors that affect the assembly of the commensalistic interactions between vascular epiphytes and their host plants. We used an analytical approach that considers all individuals and species of epiphytic bromeliads and woody hosts and non-hosts at study plots. We built models of interaction probabilities among species to assess if host traits and abundance and spatial overlap of species predict the quantitative epiphyte–host network. Species abundance, species spatial overlap and host size largely predicted pairwise interactions and several network metrics. Wood density and bark texture of hosts also contributed to explain network structure. Epiphytes were more common on large hosts, on abundant woody species, with denser wood and/or rougher bark. The network had a low level of specialization, although several interactions were more frequent than expected by the models. We did not detect a phylogenetic signal on the network structure. The effect of host size on the establishment of epiphytes indicates that mature forests are necessary to preserve diverse bromeliad communities. PMID:23407832

A Study of Coordinated Service Provision and Administrative Procedures in Selected University Communities.

ERIC Educational Resources Information Center

Clemson Univ., SC. Strom Thurmond Inst. of Government and Public Affairs.

This study investigated the existence of coordinated/consolidated services between colleges and universities and their communities by surveying 27 university communities of similar size and/or characteristics to Clemson University (South Carolina). The report begins with the profiles of the universities selected: their size in acreage, enrollment,…

The influence of floral symmetry, dependence on pollinators and pollination generalization on flower size variation

PubMed Central

Lázaro, A.; Totland, Ø.

2014-01-01

Background and Aims The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared with actinomorphic flowers. However, the degree of ecological generalization and of dependence on pollinators varies greatly among species of both flower symmetry types and this may also affect flower size variation. Methods Data on 43 species from two contrasting communities (one alpine and one lowland community) were used to test the relationships and interactions between flower size phenotypic variation, floral symmetry, ecological pollination generalization and species' dependence on pollinators. Key Results Contrary to what was expected, higher flower size variation was found in zygomorphic than in actinomorphic species in the lowland community, and no difference in flower size variation was found between symmetry types in the alpine community. The relationship between floral symmetry and flower size variation depended on ecological generalization and species' dependence on pollinators, although the influence of ecological generalization was only detected in the alpine community. Zygomorphic species that were highly dependent on pollinators and that were ecologically specialized were less variable in flower size than ecologically generalist and selfing zygomorphic species, supporting the pollinator-mediated stabilizing selection hypothesis. However, these relationships were not found in actinomorphic species, probably because they are not dependent on any particular pollinator for efficient pollination and therefore their flower size always shows moderate levels of variation. Conclusions The study suggests that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species' dependence on pollinators. PMID:24838838

The influence of floral symmetry, dependence on pollinators and pollination generalization on flower size variation.

PubMed

Lázaro, A; Totland, O

2014-07-01

The pollinator-mediated stabilizing selection hypothesis suggests that the specialized pollination system of zygomorphic flowers might cause stabilizing selection, reducing their flower size variation compared with actinomorphic flowers. However, the degree of ecological generalization and of dependence on pollinators varies greatly among species of both flower symmetry types and this may also affect flower size variation. Data on 43 species from two contrasting communities (one alpine and one lowland community) were used to test the relationships and interactions between flower size phenotypic variation, floral symmetry, ecological pollination generalization and species' dependence on pollinators. Contrary to what was expected, higher flower size variation was found in zygomorphic than in actinomorphic species in the lowland community, and no difference in flower size variation was found between symmetry types in the alpine community. The relationship between floral symmetry and flower size variation depended on ecological generalization and species' dependence on pollinators, although the influence of ecological generalization was only detected in the alpine community. Zygomorphic species that were highly dependent on pollinators and that were ecologically specialized were less variable in flower size than ecologically generalist and selfing zygomorphic species, supporting the pollinator-mediated stabilizing selection hypothesis. However, these relationships were not found in actinomorphic species, probably because they are not dependent on any particular pollinator for efficient pollination and therefore their flower size always shows moderate levels of variation. The study suggests that the relationship between flower size variation and floral symmetry may be influenced by population-dependent factors, such as ecological generalization and species' dependence on pollinators. © The Author 2014. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Rhizosphere effect of colonizer plant species on the development of soil microbial community during primary succession on postmining sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elhottova, D.; Kristufek, V.; Maly, S.

2009-07-01

The impact of pioneer plant species Tussilago farfara on structural, functional, and growth characterization of microbial community colonizing the spoil colliery substrate was studied in a laboratory microcosm experiment. Microcosms consisting of spoil substrate (0.7 dm{sup 3} of tertiary alkaline clay sediment from Sokolov brown-coal mine area) from a pioneer site (without vegetation, 5 years after heaping) were cultivated in a greenhouse with one plant of this species. Plant roots substantially increased microbial diversity and biomass after one season (7 months) of cultivation. Roots influenced the microbial community and had nearly twice the size, higher growth, and metabolic potential inmore » comparison to the control. The development of microbial specialists improves the plant nutrient status. Bacterial nitrogen (N{sub 2}) fixators (Bradyrhizobium japonicum, Rhizobium radiobacter) and arbuscular mycorrhizal fungi were confirmed in the rhizosphere of Tussilago farfara.« less

The landscape ecology and microbiota of the human nose, mouth and throat

PubMed Central

Proctor, Diana M.; Relman, David A.

2017-01-01

Landscape ecology examines the relationships between the spatial arrangement of different landforms and the processes that give rise to spatial and temporal patterns in local community structure. These relationships that underlie the patterns of the microbial communities that inhabit the human body, and in particular, those of the nose, mouth and throat, deserve greater attention. Important questions include what defines the size of a population (i.e., ‘patch’) in a given body site; what defines the boundaries of distinct patches within a single body site, and where and over what spatial scales within a body site are gradients detected. This review looks at the landscape ecology in the upper respiratory tract and mouth, and seeks greater clarity about the physiological factors, whether immunological, chemical or physical, that govern microbial community composition and function, and the ecological traits that underlie health and disease. PMID:28407480

The importance of sponges and mangroves in supporting fish communities on degraded coral reefs in Caribbean Panama.

PubMed

Seemann, Janina; Yingst, Alexandra; Stuart-Smith, Rick D; Edgar, Graham J; Altieri, Andrew H

2018-01-01

Fish communities associated with coral reefs worldwide are threatened by habitat degradation and overexploitation. We assessed coral reefs, mangrove fringes, and seagrass meadows on the Caribbean coast of Panama to explore the influences of their proximity to one another, habitat cover, and environmental characteristics in sustaining biomass, species richness and trophic structure of fish communities in a degraded tropical ecosystem. We found 94% of all fish across all habitat types were of small body size (≤10 cm), with communities dominated by fishes that usually live in habitats of low complexity, such as Pomacentridae (damselfishes) and Gobiidae (gobies). Total fish biomass was very low, with the trend of small fishes from low trophic levels over-represented, and top predators under-represented, relative to coral reefs elsewhere in the Caribbean. For example, herbivorous fishes comprised 27% of total fish biomass in Panama relative to 10% in the wider Caribbean, and the small parrotfish Scarus iseri comprised 72% of the parrotfish biomass. We found evidence that non-coral biogenic habitats support reef-associated fish communities. In particular, the abundance of sponges on a given reef and proximity of mangroves were found to be important positive correlates of reef fish species richness, biomass, abundance and trophic structure. Our study indicates that a diverse fish community can persist on degraded coral reefs, and that the availability and arrangement within the seascape of other habitat-forming organisms, including sponges and mangroves, is critical to the maintenance of functional processes in such ecosystems.

The importance of sponges and mangroves in supporting fish communities on degraded coral reefs in Caribbean Panama

PubMed Central

Yingst, Alexandra; Stuart-Smith, Rick D.; Edgar, Graham J.; Altieri, Andrew H.

2018-01-01

Fish communities associated with coral reefs worldwide are threatened by habitat degradation and overexploitation. We assessed coral reefs, mangrove fringes, and seagrass meadows on the Caribbean coast of Panama to explore the influences of their proximity to one another, habitat cover, and environmental characteristics in sustaining biomass, species richness and trophic structure of fish communities in a degraded tropical ecosystem. We found 94% of all fish across all habitat types were of small body size (≤10 cm), with communities dominated by fishes that usually live in habitats of low complexity, such as Pomacentridae (damselfishes) and Gobiidae (gobies). Total fish biomass was very low, with the trend of small fishes from low trophic levels over-represented, and top predators under-represented, relative to coral reefs elsewhere in the Caribbean. For example, herbivorous fishes comprised 27% of total fish biomass in Panama relative to 10% in the wider Caribbean, and the small parrotfish Scarus iseri comprised 72% of the parrotfish biomass. We found evidence that non-coral biogenic habitats support reef-associated fish communities. In particular, the abundance of sponges on a given reef and proximity of mangroves were found to be important positive correlates of reef fish species richness, biomass, abundance and trophic structure. Our study indicates that a diverse fish community can persist on degraded coral reefs, and that the availability and arrangement within the seascape of other habitat-forming organisms, including sponges and mangroves, is critical to the maintenance of functional processes in such ecosystems. PMID:29610704

Why are there more arboreal ant species in primary than in secondary tropical forests?

PubMed

Klimes, Petr; Idigel, Cliffson; Rimandai, Maling; Fayle, Tom M; Janda, Milan; Weiblen, George D; Novotny, Vojtech

2012-09-01

1. Species diversity of arboreal arthropods tends to increase during rainforest succession so that primary forest communities comprise more species than those from secondary vegetation, but it is not well understood why. Primary forests differ from secondary forests in a wide array of factors whose relative impacts on arthropod diversity have not yet been quantified. 2. We assessed the effects of succession-related determinants on a keystone ecological group, arboreal ants, by conducting a complete census of 1332 ant nests from all trees with diameter at breast height ≥ 5 cm occurring within two (unreplicated) 0·32-ha plots, one in primary and one in secondary lowland forest in New Guinea. Specifically, we used a novel rarefaction-based approach to match number, size distribution and taxonomic structure of trees in primary forest communities to those in secondary forest and compared the resulting numbers of ant species. 3. In total, we recorded 80 nesting ant species from 389 trees in primary forest but only 42 species from 295 trees in secondary forest. The two habitats did not differ in the mean number of ant species per tree or in the relationship between ant diversity and tree size. However, the between-tree similarity of ant communities was higher in secondary forest than in primary forest, as was the between-tree nest site similarity, suggesting that secondary trees were more uniform in providing nesting microhabitats. 4. Using our rarefaction method, the difference in ant species richness between two forest types was partitioned according to the effects of higher tree density (22·6%), larger tree size (15·5%) and higher taxonomic diversity of trees (14·3%) in primary than in secondary forest. The remaining difference (47·6%) was because of higher beta diversity of ant communities between primary forest trees. In contrast, difference in nest density was explained solely by difference in tree density. 5. Our study shows that reduction in plant taxonomic diversity in secondary forests is not the main driver of the reduction in canopy ant species richness. We suggest that the majority of arboreal species losses in secondary tropical forests are attributable to simpler vegetation structure, combined with lower turnover of nesting microhabitats between trees. © 2012 The Authors. Journal of Animal Ecology © 2012 British Ecological Society.

New Age of Fishes initiated by the Cretaceous-Paleogene mass extinction

NASA Astrophysics Data System (ADS)

Sibert, Elizabeth C.; Norris, Richard D.

2015-07-01

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous-Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern "age of fishes."

Trophic cascade facilitates coral recruitment in a marine reserve

PubMed Central

Mumby, Peter J.; Harborne, Alastair R.; Williams, Jodene; Kappel, Carrie V.; Brumbaugh, Daniel R.; Micheli, Fiorenza; Holmes, Katherine E.; Dahlgren, Craig P.; Paris, Claire B.; Blackwell, Paul G.

2007-01-01

Reduced fishing pressure and weak predator–prey interactions within marine reserves can create trophic cascades that increase the number of grazing fishes and reduce the coverage of macroalgae on coral reefs. Here, we show that the impacts of reserves extend beyond trophic cascades and enhance the process of coral recruitment. Increased fish grazing, primarily driven by reduced fishing, was strongly negatively correlated with macroalgal cover and resulted in a 2-fold increase in the density of coral recruits within a Bahamian reef system. Our conclusions are robust because four alternative hypotheses that may generate a spurious correlation between grazing and coral recruitment were tested and rejected. Grazing appears to influence the density and community structure of coral recruits, but no detectable influence was found on the overall size-frequency distribution, community structure, or cover of corals. We interpret this absence of pattern in the adult coral community as symptomatic of the impact of a recent disturbance event that masks the recovery trajectories of individual reefs. Marine reserves are not a panacea for conservation but can facilitate the recovery of corals from disturbance and may help sustain the biodiversity of organisms that depend on a complex three-dimensional coral habitat. PMID:17488824

New Age of Fishes initiated by the Cretaceous-Paleogene mass extinction.

PubMed

Sibert, Elizabeth C; Norris, Richard D

2015-07-14

Ray-finned fishes (Actinopterygii) comprise nearly half of all modern vertebrate diversity, and are an ecologically and numerically dominant megafauna in most aquatic environments. Crown teleost fishes diversified relatively recently, during the Late Cretaceous and early Paleogene, although the exact timing and cause of their radiation and rise to ecological dominance is poorly constrained. Here we use microfossil teeth and shark dermal scales (ichthyoliths) preserved in deep-sea sediments to study the changes in the pelagic fish community in the latest Cretaceous and early Paleogene. We find that the Cretaceous-Paleogene (K/Pg) extinction event marked a profound change in the structure of ichthyolith communities around the globe: Whereas shark denticles outnumber ray-finned fish teeth in Cretaceous deep-sea sediments around the world, there is a dramatic increase in the proportion of ray-finned fish teeth to shark denticles in the Paleocene. There is also an increase in size and numerical abundance of ray-finned fish teeth at the boundary. These changes are sustained through at least the first 24 million years of the Cenozoic. This new fish community structure began at the K/Pg mass extinction, suggesting the extinction event played an important role in initiating the modern "age of fishes."

Designing long-term fish community assessments in connecting channels: Lessons from the Saint Marys River

USGS Publications Warehouse

Schaeffer, Jeff; Rogers, Mark W.; Fielder, David G.; Godby, Neal; Bowen, Anjanette K.; O'Connor, Lisa; Parrish, Josh; Greenwood, Susan; Chong, Stephen; Wright, Greg

2014-01-01

Long-term surveys are useful in understanding trends in connecting channel fish communities; a gill net assessment in the Saint Marys River performed periodically since 1975 is the most comprehensive connecting channels sampling program within the Laurentian Great Lakes. We assessed efficiency of that survey, with intent to inform development of assessments at other connecting channels. We evaluated trends in community composition, effort versus estimates of species richness, ability to detect abundance changes for four species, and effects of subsampling yellow perch catches on size and age-structure metrics. Efficiency analysis revealed low power to detect changes in species abundance, whereas reduced effort could be considered to index species richness. Subsampling simulations indicated that subsampling would have allowed reliable estimates of yellow perch (Perca flavescens) population structure, while greatly reducing the number of fish that were assigned ages. Analyses of statistical power and efficiency of current sampling protocols are useful for managers collecting and using these types of data as well as for the development of new monitoring programs. Our approach provides insight into whether survey goals and objectives were being attained and can help evaluate ability of surveys to answer novel questions that arise as management strategies are refined.

Phytoplankton variability and community structure in relation to hydrographic features in the NE Aegean frontal area (NE Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Lagaria, A.; Mandalakis, M.; Mara, P.; Frangoulis, C.; Karatsolis, B.-Th.; Pitta, P.; Triantaphyllou, M.; Tsiola, A.; Psarra, S.

2017-10-01

The structure of phytoplankton community in the salinity-stratified Northeastern Aegean frontal area adjacent to the Dardanelles Straits was investigated on a seasonal basis (autumn, spring and summer) and in relation to circulating water masses: the modified Black Sea Water (BSW) and the Levantine Water (LW). By employing High Performance Liquid Chromatography (HPLC) for the analysis of phytoplankton pigments in conjunction with conventional cell counting methodologies (i.e. inverted light microscopy, flow cytometry) and primary production measurements, a comprehensive qualitative and quantitative characterization of phytoplankton community composition and its activity was conducted. Chlorophyll-a normalized production and estimated growth rates presented the highest values within the 'fresh' BSW mass during summer, though generally growth rates were low (<0.4 d-1) at all seasons. The spatiotemporal variation of BSW outflow was found to greatly affect the relative contribution of pico-, nano- and micro-phytoplankton to total phytoplankton biomass and production. Large cell organisms, and in particular diatoms, were closely associated with the surface BSW masses outflowing from the Straits. Our results showed that all phytoplankton size components were significant over time and space suggesting a rather multivorous food web functioning of the system.

Pleistocene megafaunal interaction networks became more vulnerable after human arrival.

PubMed

Pires, Mathias M; Koch, Paul L; Fariña, Richard A; de Aguiar, Marcus A M; dos Reis, Sérgio F; Guimarães, Paulo R

2015-09-07

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions. © 2015 The Author(s).

Pleistocene megafaunal interaction networks became more vulnerable after human arrival

PubMed Central

Pires, Mathias M.; Koch, Paul L.; Fariña, Richard A.; de Aguiar, Marcus A. M.; dos Reis, Sérgio F.; Guimarães, Paulo R.

2015-01-01

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions. PMID:26336175

Nestedness of desert bat assemblages: species composition patterns in insular and terrestrial landscapes.

PubMed

Frick, Winifred F; Hayes, John P; Heady, Paul A

2009-01-01

Nested patterns of community composition exist when species at depauperate sites are subsets of those occurring at sites with more species. Nested subset analysis provides a framework for analyzing species occurrences to determine non-random patterns in community composition and potentially identify mechanisms that may shape faunal assemblages. We examined nested subset structure of desert bat assemblages on 20 islands in the southern Gulf of California and at 27 sites along the Baja California peninsula coast, the presumable source pool for the insular faunas. Nested structure was analyzed using a conservative null model that accounts for expected variation in species richness and species incidence across sites (fixed row and column totals). Associations of nestedness and island traits, such as size and isolation, as well as species traits related to mobility, were assessed to determine the potential role of differential extinction and immigration abilities as mechanisms of nestedness. Bat faunas were significantly nested in both the insular and terrestrial landscape and island size was significantly correlated with nested structure, such that species on smaller islands tended to be subsets of species on larger islands, suggesting that differential extinction vulnerabilities may be important in shaping insular bat faunas. The role of species mobility and immigration abilities is less clearly associated with nestedness in this system. Nestedness in the terrestrial landscape is likely due to stochastic processes related to random placement of individuals and this may also influence nested patterns on islands, but additional data on abundances will be necessary to distinguish among these potential mechanisms.

Phytoecological evaluation with detail floristic appraisal of the vegetation arround Malam Jabba, Swat, Pakistan

PubMed Central

Rashid, Abdur; Swati, Mohammad Farooq; Sher, Hassan; Al-Yemeni, Mohammad N

2011-01-01

Objective To determine the present status of plant communities and their possible association with the habitat in Malam Jabba, Swat, Pakistan. Methods A study on the phytoecology was conducted in various ecologically important sites of Malam Jabba, Swat, Pakistan from 2002 to 2004. The altitude of these sites ranged from 1 200 m to 3 200 m. Quadrat method was used for evaluation of plants communities and the data on these attributes was converted to relative values. The plant communities were named after 3 leading species with highest importance values. Biological spectrum of the flora based on the life form was prepared by following Raunkiar's life form classes. Results The floristic composition and structure of the study area were found to be 200 species belonging to 75 families. Asteraceae, Lamiaceae and Poaceae were important families in the study area. The biological spectrum showed that therophytic and hemicrytophytic life form and micro-nonophyllous leaf sizes were dominant in the area. The air and soil temperatures were decreasing with increasing elevation. Both the air and soil temperatures were relatively higher in south slopes than on the northeast slopes. The vegetation analysis of the area indicated eleven plant communities around the area. The present vegetation is the relics of moist temperate coniferous forest in the area. The communities reflect highly deteriorated conditions. Both the structure and composition of the surrounding vegetation were associated with the types of habitats. Conclusions The conservation of the remaining populations of the reported communities will be best achieved by proper time of sustainable harvesting. It is only possible with the participation of local communities. PMID:23569814

The Importance of Maize Management on Dung Beetle Communities in Atlantic Forest Fragments

PubMed Central

Campos, Renata Calixto; Hernández, Malva Isabel Medina

2015-01-01

Dung beetle community structures changes due to the effects of destruction, fragmentation, isolation and decrease in tropical forest area, and therefore are considered ecological indicators. In order to assess the influence of type of maize cultivated and associated maize management on dung beetle communities in Atlantic Forest fragments surrounded by conventional and transgenic maize were evaluated 40 Atlantic Forest fragments of different sizes, 20 surrounded by GM maize and 20 surrounded by conventional maize, in February 2013 and 2014 in Southern Brazil. After applying a sampling protocol in each fragment (10 pitfall traps baited with human feces or carrion exposed for 48 h), a total of 3454 individuals from 44 species were captured: 1142 individuals from 38 species in GM maize surrounded fragments, and 2312 from 42 species in conventional maize surrounded fragments. Differences in dung beetle communities were found between GM and conventional maize communities. As expected for fragmented areas, the covariance analysis showed a greater species richness in larger fragments under both conditions; however species richness was greater in fragments surrounded by conventional maize. Dung beetle structure in the forest fragments was explained by environmental variables, fragment area, spatial distance and also type of maize (transgenic or conventional) associated with maize management techniques. In Southern Brazil’s scenario, the use of GM maize combined with associated agricultural management may be accelerating the loss of diversity in Atlantic Forest areas, and consequently, important ecosystem services provided by dung beetles may be lost. PMID:26694874

The Importance of Maize Management on Dung Beetle Communities in Atlantic Forest Fragments.

PubMed

Campos, Renata Calixto; Hernández, Malva Isabel Medina

2015-01-01

Dung beetle community structures changes due to the effects of destruction, fragmentation, isolation and decrease in tropical forest area, and therefore are considered ecological indicators. In order to assess the influence of type of maize cultivated and associated maize management on dung beetle communities in Atlantic Forest fragments surrounded by conventional and transgenic maize were evaluated 40 Atlantic Forest fragments of different sizes, 20 surrounded by GM maize and 20 surrounded by conventional maize, in February 2013 and 2014 in Southern Brazil. After applying a sampling protocol in each fragment (10 pitfall traps baited with human feces or carrion exposed for 48 h), a total of 3454 individuals from 44 species were captured: 1142 individuals from 38 species in GM maize surrounded fragments, and 2312 from 42 species in conventional maize surrounded fragments. Differences in dung beetle communities were found between GM and conventional maize communities. As expected for fragmented areas, the covariance analysis showed a greater species richness in larger fragments under both conditions; however species richness was greater in fragments surrounded by conventional maize. Dung beetle structure in the forest fragments was explained by environmental variables, fragment area, spatial distance and also type of maize (transgenic or conventional) associated with maize management techniques. In Southern Brazil's scenario, the use of GM maize combined with associated agricultural management may be accelerating the loss of diversity in Atlantic Forest areas, and consequently, important ecosystem services provided by dung beetles may be lost.

Diversity and Activity of Communities Inhabiting Plastic Debris in the North Pacific Gyre

PubMed Central

Bryant, Jessica A.; Clemente, Tara M.; Viviani, Donn A.; Fong, Allison A.; Thomas, Kimberley A.; Kemp, Paul; Karl, David M.; White, Angelicque E.

2016-01-01

ABSTRACT Marine plastic debris has become a significant concern in ocean ecosystems worldwide. Little is known, however, about its influence on microbial community structure and function. In 2008, we surveyed microbial communities and metabolic activities in seawater and on plastic on an oceanographic expedition through the “great Pacific garbage patch.” The concentration of plastic particles in surface seawater within different size classes (2 to 5 mm and >5 mm) ranged from 0.35 to 3.7 particles m−3 across sampling stations. These densities and the particle size distribution were consistent with previous values reported in the North Pacific Ocean. Net community oxygen production (NCP = gross primary production − community respiration) on plastic debris was positive and so net autotrophic, whereas NCP in bulk seawater was close to zero. Scanning electron microscopy and metagenomic sequencing of plastic-attached communities revealed the dominance of a few metazoan taxa and a diverse assemblage of photoautotrophic and heterotrophic protists and bacteria. Bryozoa, Cyanobacteria, Alphaproteobacteria, and Bacteroidetes dominated all plastic particles, regardless of particle size. Bacteria inhabiting plastic were taxonomically distinct from the surrounding picoplankton and appeared well adapted to a surface-associated lifestyle. Genes with significantly higher abundances among plastic-attached bacteria included che genes, secretion system genes, and nifH genes, suggesting enrichment for chemotaxis, frequent cell-to-cell interactions, and nitrogen fixation. In aggregate, our findings suggest that plastic debris forms a habitat for complex microbial assemblages that have lifestyles, metabolic pathways, and biogeochemical activities that are distinct from those of free-living planktonic microbial communities. IMPORTANCE Marine plastic debris is a growing concern that has captured the general public’s attention. While the negative impacts of plastic debris on oceanic macrobiota, including mammals and birds, are well documented, little is known about its influence on smaller marine residents, including microbes that have key roles in ocean biogeochemistry. Our work provides a new perspective on microbial communities inhabiting microplastics that includes its effect on microbial biogeochemical activities and a description of the cross-domain communities inhabiting plastic particles. This study is among the first molecular ecology, plastic debris biota surveys in the North Pacific Subtropical Gyre. It has identified fundamental differences in the functional potential and taxonomic composition of plastic-associated microbes versus planktonic microbes found in the surrounding open-ocean habitat. Author Video: An author video summary of this article is available. PMID:27822538

Improving the Small-Business Role in Turkish Defense Acquisitions: Recommendations from U.S. Best Practices

DTIC Science & Technology

2010-06-01

not take into account the effects of the Global Crisis as it impacts the small business assistance programs. Data related to Small and Medium Sized...unanticipated by many scholars and members of the policy community , but what was even more surprising than the resurgence itself was the primary...innovative because of their responsiveness to “changing market demands,” flexible structures, and “efficient internal communication ” (Mogee, 2003, p. 3

Comparison of burbot populations across adjacent native and introduced ranges

USGS Publications Warehouse

Walters, Annika W.; Mandeville, Elizabeth G.; Saunders, W. Carl; Gerrity, Paul C.; Skorupski, Joseph A.; Underwood, Zachary E.; Gardunio, Eric I.

2017-01-01

Introduced species are a threat to biodiversity. Burbot, Lota lota, a fish native to the Wind River Drainage, Wyoming and a species of conservation concern, have been introduced into the nearby Green River Drainage, Wyoming, where they are having negative effects on native fish species. We compared these native and introduced burbot populations to evaluate potential mechanisms that could be leading to introduction success. We examined genetic ancestry, physical habitat characteristics, community composition, and burbot abundance, relative weight, and size structure between the native and introduced range to elucidate potential differences. The origin of introduced burbot in Flaming Gorge Reservoir is most likely Boysen Reservoir and several nearby river populations in the native Wind River Drainage. Burbot populations did not show consistent differences in abundance, size structure, and relative weight between drainages, though Fontenelle Reservoir, in the introduced drainage, had the largest burbot. There were also limited environmental and community composition differences, though reservoirs in the introduced drainage had lower species richness and a higher percentage of non-native fish species than the reservoir in the native drainage. Burbot introduction in the Green River Drainage is likely an example of reservoir construction creating habitat with suitable environmental conditions to allow a southwards range expansion of this cold-water species. An understanding of the factors driving introduction success can allow better management of species, both in their introduced and native range.

Light Absorption by Suspended Particles in the Red Sea: Effect of Phytoplankton Community Size Structure and Pigment Composition

NASA Astrophysics Data System (ADS)

Kheireddine, Malika; Ouhssain, Mustapha; Organelli, Emanuele; Bricaud, Annick; Jones, Burton H.

2018-02-01

The light absorption properties of phytoplankton (aph(λ)) and nonalgal particles (anap(λ)) associated with phytoplankton pigments were analyzed across the Red Sea, in the upper 200 m depth, between October 2014 and August 2016. The contribution by nonalgal particles to the total particulate light absorption (aph(λ) + anap(λ)) was highly variable (23 ± 17% at 440 nm) and no relationship between anap(440) and chlorophyll a concentration, [TChl a], was observed. Phytoplankton-specific phytoplankton absorption coefficients at 440 and 676 nm for a given [TChl a], aph*(440), and aph∗(676) were slightly higher than those derived from average relationships for open ocean waters within the surface layer as well as along the water column. Variations in the concentration of photosynthetic and photoprotective pigments were noticeable by changes in phytoplankton community size structure as well as in aph∗(λ). This study revealed that a higher proportion of picophytoplankton and an increase in photoprotective pigments (mainly driven by zeaxanthin) tended to be responsible for the higher aph∗(λ) values found in the Red Sea as compared to other oligotrophic regions with similar [TChl a]. Understanding this variability across the Red Sea may help improve the accuracy of biogeochemical parameters, such as [TChl a], derived from in situ measurements and ocean color remote sensing at a regional scale.

76 FR 56141 - Notice of Intent To Request New Information Collection

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-12

... level surveys of similar scope and size. The sample for each selected community will be strategically... of 2 hours per sample community. Full Study: The maximum sample size for the full study is 2,812... questionnaires. The initial sample size for this phase of the research is 100 respondents (10 respondents per...

Evaluation of the Community Multiscale Air Quality (CMAQ) modeling system against size-resolved measurements of inorganic particle composition across sites in North America

EPA Science Inventory

This work evaluates particle size-composition distributions simulated by the Community Multiscale Air Quality (CMAQ) model using Micro-Orifice Uniform Deposit Impactor (MOUDI) measurements at 18 sites across North America. Size-resolved measurements of particulate SO₄<...

Spatial scale of similarity as an indicator of metacommunity stability in exploited marine systems.

PubMed

Shackell, Nancy L; Fisher, Jonathan A D; Frank, Kenneth T; Lawton, Peter

2012-01-01

The spatial scale of similarity among fish communities is characteristically large in temperate marine systems: connectivity is enhanced by high rates of dispersal during the larval/juvenile stages and the increased mobility of large-bodied fish. A larger spatial scale of similarity (low beta diversity) is advantageous in heavily exploited systems because locally depleted populations are more likely to be "rescued" by neighboring areas. We explored whether the spatial scale of similarity changed from 1970 to 2006 due to overfishing of dominant, large-bodied groundfish across a 300 000-km2 region of the Northwest Atlantic. Annually, similarities among communities decayed slowly with increasing geographic distance in this open system, but through time the decorrelation distance declined by 33%, concomitant with widespread reductions in biomass, body size, and community evenness. The decline in connectivity stemmed from an erosion of community similarity among local subregions separated by distances as small as 100 km. Larger fish, of the same species, contribute proportionally more viable offspring, so observed body size reductions will have affected maternal output. The cumulative effect of nonlinear maternal influences on egg/larval quality may have compromised the spatial scale of effective larval dispersal, which may account for the delayed recovery of certain member species. Our study adds strong support for using the spatial scale of similarity as an indicator of metacommunity stability both to understand the spatial impacts of exploitation and to refine how spatial structure is used in management plans.

Antibiotic exposure perturbs the gut microbiota and elevates mortality in honeybees

PubMed Central

Shaffer, Zack; Moran, Nancy A.

2017-01-01

Gut microbiomes play crucial roles in animal health, and shifts in the gut microbial community structure can have detrimental impacts on hosts. Studies with vertebrate models and human subjects suggest that antibiotic treatments greatly perturb the native gut community, thereby facilitating proliferation of pathogens. In fact, persistent infections following antibiotic treatment are a major medical issue. In apiculture, antibiotics are frequently used to prevent bacterial infections of larval bees, but the impact of antibiotic-induced dysbiosis (microbial imbalance) on bee health and susceptibility to disease has not been fully elucidated. Here, we evaluated the effects of antibiotic exposure on the size and composition of honeybee gut communities. We monitored the survivorship of bees following antibiotic treatment in order to determine if dysbiosis of the gut microbiome impacts honeybee health, and we performed experiments to determine whether antibiotic exposure increases susceptibility to infection by opportunistic pathogens. Our results show that antibiotic treatment can have persistent effects on both the size and composition of the honeybee gut microbiome. Antibiotic exposure resulted in decreased survivorship, both in the hive and in laboratory experiments in which bees were exposed to opportunistic bacterial pathogens. Together, these results suggest that dysbiosis resulting from antibiotic exposure affects bee health, in part due to increased susceptibility to ubiquitous opportunistic pathogens. Not only do our results highlight the importance of the gut microbiome in honeybee health, but they also provide insights into how antibiotic treatment affects microbial communities and host health. PMID:28291793

Soil incubation studies with Cry1Ac protein indicate no adverse effect of Bt crops on soil microbial communities.

PubMed

Zhaolei, Li; Naishun, Bu; Xueping, Chen; Jun, Cui; Manqiu, Xiao; Zhiping, Song; Ming, Nie; Changming, Fang

2018-05-15

Bt crops that are transgenic crops engineered to produce Bt toxins which occur naturally with Bacillus thuringiensis (Bt) have been widely planted and its environmental risk assessment has been heavily debated. The effects of Bt crops on soil microbial communities are possible through changing the quantity and quality of C inputs and potential toxic activity of Bt protein on soil organisms. To date, the direct effects of Bt protein on soil microorganisms is unclear. Here we added Cry1Ac, one of the most commonly used Bt protein in Bt crops, to the soil and monitored changes in soil bacterial, fungal and archaeal diversities and community structures using ribosomal DNA-fingerprinting method, as well as their population sizes by real-time PCR over a 100-day period. Despite the fact that variations were observed in the indices of evenness, diversity and population sizes of bacteria, fungi and archaea with different Cry1Ac addition rates up to 100ngg -1 soil, the indices of soil microbial diversities and evennesses did not significantly shift with Cry1Ac protein addition, nor did population sizes change over time. The diversities of the dominant bacteria, fungi and archaea were not significantly changed, given Cry1Ac protein addition rates over a period of 100 days. These results suggested that Bt protein derived by cultivations of transgenic Bt crops is unlikely to cause transient or even persisting significant changes in soil microorganisms in field. Copyright © 2017 Elsevier Inc. All rights reserved.

Pollutants degradation performance and microbial community structure of aerobic granular sludge systems using inoculums adapted at mild and low temperature.

PubMed

Muñoz-Palazon, Barbara; Pesciaroli, Chiara; Rodriguez-Sanchez, Alejandro; Gonzalez-Lopez, Jesús; Gonzalez-Martinez, Alejandro

2018-08-01

Three aerobic granular sequencing batch reactors were inoculated using different inocula from Finland, Spain and a mix of both in order to investigate the effect over the degradation performance and the microbial community structure. The Finnish inoculum achieved a faster granulation and a higher depollution performance within the first two month of operation. However, after 90 days of operation, similar physico-chemical values were observed. On the other hand, the Real-time PCR showed that Archaea diminished from inoculum to granular biomass, while Bacteria and Fungi numbers remained stable. All granular biomass massive parallel sequencing studies were similar regardless of the inocula from which they formed, as confirmed by singular value decomposition principal coordinates analysis, expected effect size of OTUs, and β-diversity analyses. Thermoproteaceae, Meganema and a Trischosporonaceae members were the dominant phylotypes for the three domains studied. The analysis of oligotype distribution demonstrated that a fungal oligotype was ubiquitous. The dominant OTUs of Bacteria were correlated with bioreactors performance. The results obtained determined that the microbial community structure of aerobic granular sludge was similar regardless of their inocula, showing that the granulation of biomass is related to several phylotypes. This will be of future importance for the implementation of aerobic granular sludge to full-scale systems. Copyright © 2018 Elsevier Ltd. All rights reserved.

NA{sup +}, K{sup +}-ATPase, histopathological, and genetic responses of Corbicula fluminea to sediment-associated copper

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, S.

1995-12-31

Time-dependent responses to sediment-associated copper were studies at hierarchical levels of biological organization along an extreme concentration gradient (40 to 40,000 mg/kg total Cu). Laboratory and in situ estimates of molecular to tissue-level responses (Na/K-ATPase activity, DNA content, histopathology) were monitored in Corbicula fluminea (Asiatic clam), and compared with laboratory and field based survival of Corbicula and Elimia teres (an indigenous Gastropoda). Mollusc survival was, in turn, compared with effects on macrobenthic community composition along the stream/[Cu] gradient. Relationships between selected sediment characteristics and the bioavailability and toxicity of sediment associated copper were also investigated. Sediment-associated copper depressed Na/K-ATPase activitymore » and led to histopathological damage of renal and gill epithelia (vacuolization, degeneration), indicating that impaired ion regulation was an important mechanism of toxicity. Concurrent reductions in DNA content were believed to be secondary effects due to cell death, not an indication of genotoxicity. Sublethal responses were significantly correlated with survival in both species; however, while survival in situ was indicative of differences in community structure, laboratory-based survival was not. Copper levels in tissues were indicative of exposure, but were not significantly correlated with adverse effects. Copper levels in sediments, interstitial water, and overlying water varied independently of sediment characteristics except pH. Cu/AVS ratios were predictive of Corbicula and Elimia survival, but were not significantly related to differences in community structure. Instead, macrobenthic community structure was influenced by other sediment factors (grain size, Eh, pH).« less

Species-abundance--seed-size patterns within a plant community affected by grazing disturbance.

PubMed

Wu, Gao-lin; Shang, Zhan-huan; Zhu, Yuan-jun; Ding, Lu-ming; Wang, Dong

2015-04-01

Seed size has been advanced as a key factor that influences the dynamics of plant communities, but there are few empirical or theoretical predictions of how community dynamics progress based on seed size patterns. Information on the abundance of adults, seedlings, soil seed banks, seed rains, and the seed mass of 96 species was collected in alpine meadows of the Qinghai-Tibetan Plateau (China), which had different levels of grazing disturbance. The relationships between seed-mass-abundance patterns for adults, seedlings, the soil seed bank, and seed rain in the plant community were evaluated using regression models. Results showed that grazing levels affected the relationship between seed size and abundance properties of adult species, seedlings, and the soil seed bank, suggesting that there is a shift in seed-size--species-abundance relationships as a response to the grazing gradient. Grazing had no effect on the pattern of seed-size-seed-rain-abundance at four grazing levels. Grazing also had little effect on the pattern of seed-size--species-abundance and pattern of seed-size--soil-seed-bank-abundance in meadows with no grazing, light grazing, and moderate grazing), but there was a significant negative effect in meadows with heavy grazing. Grazing had little effect on the pattern of seed-size--seedling-abundance with no grazing, but had significant negative effects with light, moderate, and heavy grazing, and the |r| values increased with grazing levels. This indicated that increasing grazing pressure enhanced the advantage of smaller-seeded species in terms of the abundances of adult species, seedlings, and soil seed banks, whereas only the light grazing level promoted the seed rain abundance of larger-seeded species in the plant communities. This study suggests that grazing disturbances are favorable for increasing the species abundance for smaller-seeded species but not for the larger-seeded species in an alpine meadow community. Hence, there is a clear advantage of the smaller-seeded species over the larger-seeded species with increases in the grazing level.

Macroscale patterns in body size of intertidal crustaceans provide insights on climate change effects.

PubMed

Jaramillo, Eduardo; Dugan, Jenifer E; Hubbard, David M; Contreras, Heraldo; Duarte, Cristian; Acuña, Emilio; Schoeman, David S

2017-01-01

Predicting responses of coastal ecosystems to altered sea surface temperatures (SST) associated with global climate change, requires knowledge of demographic responses of individual species. Body size is an excellent metric because it scales strongly with growth and fecundity for many ectotherms. These attributes can underpin demographic as well as community and ecosystem level processes, providing valuable insights for responses of vulnerable coastal ecosystems to changing climate. We investigated contemporary macroscale patterns in body size among widely distributed crustaceans that comprise the majority of intertidal abundance and biomass of sandy beach ecosystems of the eastern Pacific coasts of Chile and California, USA. We focused on ecologically important species representing different tidal zones, trophic guilds and developmental modes, including a high-shore macroalga-consuming talitrid amphipod (Orchestoidea tuberculata), two mid-shore scavenging cirolanid isopods (Excirolana braziliensis and E. hirsuticauda), and a low-shore suspension-feeding hippid crab (Emerita analoga) with an amphitropical distribution. Significant latitudinal patterns in body sizes were observed for all species in Chile (21° - 42°S), with similar but steeper patterns in Emerita analoga, in California (32°- 41°N). Sea surface temperature was a strong predictor of body size (-4% to -35% °C-1) in all species. Beach characteristics were subsidiary predictors of body size. Alterations in ocean temperatures of even a few degrees associated with global climate change are likely to affect body sizes of important intertidal ectotherms, with consequences for population demography, life history, community structure, trophic interactions, food-webs, and indirect effects such as ecosystem function. The consistency of results for body size and temperature across species with different life histories, feeding modes, ecological roles, and microhabitats inhabiting a single widespread coastal ecosystem, and for one species, across hemispheres in this space-for-time substitution, suggests predictions of ecosystem responses to thermal effects of climate change may potentially be generalised, with important implications for coastal conservation.

Macroscale patterns in body size of intertidal crustaceans provide insights on climate change effects

PubMed Central

Dugan, Jenifer E.; Hubbard, David M.; Contreras, Heraldo; Duarte, Cristian; Acuña, Emilio; Schoeman, David S.

2017-01-01

Predicting responses of coastal ecosystems to altered sea surface temperatures (SST) associated with global climate change, requires knowledge of demographic responses of individual species. Body size is an excellent metric because it scales strongly with growth and fecundity for many ectotherms. These attributes can underpin demographic as well as community and ecosystem level processes, providing valuable insights for responses of vulnerable coastal ecosystems to changing climate. We investigated contemporary macroscale patterns in body size among widely distributed crustaceans that comprise the majority of intertidal abundance and biomass of sandy beach ecosystems of the eastern Pacific coasts of Chile and California, USA. We focused on ecologically important species representing different tidal zones, trophic guilds and developmental modes, including a high-shore macroalga-consuming talitrid amphipod (Orchestoidea tuberculata), two mid-shore scavenging cirolanid isopods (Excirolana braziliensis and E. hirsuticauda), and a low-shore suspension-feeding hippid crab (Emerita analoga) with an amphitropical distribution. Significant latitudinal patterns in body sizes were observed for all species in Chile (21° - 42°S), with similar but steeper patterns in Emerita analoga, in California (32°- 41°N). Sea surface temperature was a strong predictor of body size (-4% to -35% °C-1) in all species. Beach characteristics were subsidiary predictors of body size. Alterations in ocean temperatures of even a few degrees associated with global climate change are likely to affect body sizes of important intertidal ectotherms, with consequences for population demography, life history, community structure, trophic interactions, food-webs, and indirect effects such as ecosystem function. The consistency of results for body size and temperature across species with different life histories, feeding modes, ecological roles, and microhabitats inhabiting a single widespread coastal ecosystem, and for one species, across hemispheres in this space-for-time substitution, suggests predictions of ecosystem responses to thermal effects of climate change may potentially be generalised, with important implications for coastal conservation. PMID:28481897

The specific role of fungal community structure on soil aggregation and carbon sequestration: results from long-term field study in a paddy soil

NASA Astrophysics Data System (ADS)

Murugan, Rajasekaran; Kumar, Sanjay

2015-04-01

Soil aggregate stability is a crucial soil property that affects soil biota, biogeochemical processes and C sequestration. The relationship between soil aggregate stability and soil C cycling is well known but the influence of specific fungal community structure on this relationship is largely unknown in paddy soils. The aim of the present study was to evaluate the long-term fertilisation (mineral fertiliser-MIN; farmyard manure-FYM; groundnut oil cake-GOC) effects on soil fungal community shifts associated with soil aggregates under rice-monoculture (RRR) and rice-legume-rice (RLR) systems. Fungal and bacterial communities were characterized using phospholipid fatty acids, and glucosamine and muramic acid were used as biomarkers for fungal and bacterial residues, respectively. Microbial biomass C and N, fungal biomass and residues were significantly higher in the organic fertiliser treatments than in the MIN treatment, for all aggregate sizes under both crop rotation systems. In general, fungal/bacterial biomass ratio and fungal residue C/bacterial residue C ratio were significantly higher in macroaggregate fractions (> 2000 and 250-2000 μm) than in microaggregate fractions (53-250 and <53 μm). In both crop rotation systems, the long-term application of FYM and GOC led to increased accumulation of saprotrophic fungi (SF) in aggregate fractions > 2000 μm. In contrast, we found that arbuscular mycorrhizal fungi (AMF) was surprisingly higher in aggregate fractions > 2000 μm than in aggregate fraction 250-2000 μm under MIN treatment. The RLR system showed significantly higher AMF biomass and fungal residue C/ bacterial residue C ratio in both macroaggregate fractions compared to the RRR system. The strong relationships between SF, AMF and water stable aggregates shows the specific contribution of fungi community on soil aggregate stability. Our results highlight the fact that changes within fungal community structure play an important role in shaping the soil aggregate stability and C sequestration in tropical agricultural ecosystems.

Body size phenology in a regional bee fauna: a temporal extension of Bergmann's rule.

PubMed

Osorio-Canadas, Sergio; Arnan, Xavier; Rodrigo, Anselm; Torné-Noguera, Anna; Molowny, Roberto; Bosch, Jordi

2016-12-01

Bergmann's rule originally described a positive relationship between body size and latitude in warm-blooded animals. Larger animals, with a smaller surface/volume ratio, are better enabled to conserve heat in cooler climates (thermoregulatory hypothesis). Studies on endothermic vertebrates have provided support for Bergmann's rule, whereas studies on ectotherms have yielded conflicting results. If the thermoregulatory hypothesis is correct, negative relationships between body size and temperature should occur in temporal in addition to geographical gradients. To explore this possibility, we analysed seasonal activity patterns in a bee fauna comprising 245 species. In agreement with our hypothesis of a different relationship for large (endothermic) and small (ectothermic) species, we found that species larger than 27.81 mg (dry weight) followed Bergmann's rule, whereas species below this threshold did not. Our results represent a temporal extension of Bergmann's rule and indicate that body size and thermal physiology play an important role in structuring community phenology. © 2016 John Wiley & Sons Ltd/CNRS.

Growth and production of the copepod community in the southern area of the Humboldt Current System

NASA Astrophysics Data System (ADS)

Escribano, R.; Bustos-Ríos, E.; Hidalgo, P.; Morales, C. E.

2015-02-01

Zooplankton production is a critical issue for understanding marine ecosystem structure and dynamics, however, its time-space variations are mostly unknown in most systems. In this study, estimates of copepod growth and production (CP) in the coastal upwelling and coastal transition zones off central-southern Chile (∼35-37° S) were obtained from annual cycles during a 3 year time series (2004, 2005, and 2006) at a fixed shelf station and from spring-summer surveys during the same years. C-specific growth rates (g) varied extensively among species and under variable environmental conditions; however, g values were not correlated to either near surface temperature or copepod size. Copepod biomass (CB) and CP were higher within the coastal upwelling zone (<50 km) and both decreased substantially from 2004 to 2006. Annual CP ranged between 24 and 52 g C m-2 year-1 with a~mean annual P/B ratio of 2.7. We estimated that CP could consume up to 60% of the annual primary production (PP) in the upwelling zone but most of the time is around 8%. Interannual changes in CB and CP values were associated with changes in the copepod community structure, the dominance of large-sized forms replaced by small-sized species from 2004 to 2006. This change was accompanied by more persistent and time extended upwelling during the same seasonal period. Extended upwelling may have caused large losses of CB from the upwelling zone due to an increase in offshore advection of coastal plankton. On a larger scale, these results suggest that climate-related impacts of increasing wind-driven upwelling in coastal upwelling systems may generate a negative trend in zooplankton biomass.

Spatial Variation in Anaerobic Microbial Communities in Wetland Margin Soils

NASA Astrophysics Data System (ADS)

Rich, H.; Kannenberg, S.; Ludwig, S.; Nelson, L. C.; Spawn, S.; Porterfield, J.; Schade, J. D.

2012-12-01

Climate change is predicted to increase the severity and frequency of precipitation and drought events, which may result in substantial temporal variation in the size of wetlands. Wetlands are the world's largest natural emitter of methane, a greenhouse gas that is 20 times more effective at trapping heat than carbon dioxide. Changes in the dynamics of wetland size may lead to changes in the extent and timing of inundation of soils in ephemeral margins, which is likely to influence microbes that rely on anoxic conditions. The impact on process rates may depend on the structure of the community of microbes present in the soil, however, the link between microbial structure and patterns in process rates in soils is not well understood. Our goal was to use molecular techniques to compare microorganism communities in two wetlands that differ in the extent and duration of inundation of marginal soils to assess how these communities may change with changes in climate, and the potential consequences for methane production. This will allow us to examine how community composition changes with soil conditions such as moisture content, frequency of drought and abundance of available carbon. The main focus of this project was to determine the presence or absence of acetoclastic (AC) and hydrogenotrophic (HT) methanogens. AC methanogens use acetate as their main substrate, while HT methanogens use Hydrogen and Carbon dioxide. The relative proportion of these pathways depends on soil conditions, such as competition with other anaerobic microbes and the amount of labile carbon, and spatial patterns in the presence of each can give insight into the soil conditions of a wetland site. We sampled soil from three different wetland ponds of varying permanence in the St Olaf Natural Lands in Northfield, Minnesota, and extracted DNA from these soil samples with a MoBio PowerSoil DNA Isolation Kit. With PCR and seven different primer sets, we tested the extracted DNA for the presence of four different methanogen taxa as well as denitrifying, iron reducing and sulfate reducing bacteria. We used the percentage of soil replicates that tested positive for a primer as an indicator of the population size of each microorganism at each site. The results of the presence/absence test suggested a relationship between soil moisture and abundance of methanogens. The sites with over 25% moisture content showed a higher percent presence than the soil sites with under 25% moisture content for all taxa except for sulfate reducing bacteria. The impact of soil moisture is likely due to negative effects of oxygen on methanogens. However, the presence of methanogens in drier soils shows that methanogens can still exist in a dormant state in aerobic environments. Methanogens may be ubiquitous but vary in population size and activity depending on soil conditions. With changes in wetland soil moisture in response to changes in precipitation patterns, the populations of methanogens may change, affecting the amount of methane production and ultimately the amount of heat trapped by the atmosphere.

How selection structures species abundance distributions

PubMed Central

Magurran, Anne E.; Henderson, Peter A.

2012-01-01

How do species divide resources to produce the characteristic species abundance distributions seen in nature? One way to resolve this problem is to examine how the biomass (or capacity) of the spatial guilds that combine to produce an abundance distribution is allocated among species. Here we argue that selection on body size varies across guilds occupying spatially distinct habitats. Using an exceptionally well-characterized estuarine fish community, we show that biomass is concentrated in large bodied species in guilds where habitat structure provides protection from predators, but not in those guilds associated with open habitats and where safety in numbers is a mechanism for reducing predation risk. We further demonstrate that while there is temporal turnover in the abundances and identities of species that comprise these guilds, guild rank order is conserved across our 30-year time series. These results demonstrate that ecological communities are not randomly assembled but can be decomposed into guilds where capacity is predictably allocated among species. PMID:22787020