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Last update: November 12, 2013.
1

The Antarctic Food Chain  

NSDL National Science Digital Library

This lesson plan introduces students to the animals of Antarctica and to the Antarctic food chain. Students will draw pictures of a variety of animals and attach the pictures to a wall collage. They will then listen to or read statements about the diet of each animal and draw arrows to show which animals eat which other animals. Students will end up with a food web that illustrates the importance of krill to the Antarctic ecosystem.

2

The Food Web Matching Game  

NSDL National Science Digital Library

In this activity, students construct a food web of Antarctic organisms. Working from a trophic table that provides information about each organisms's role in the food web, they will attempt to place them in their correct positions on a blank food web chart. Links to a glossary are embedded in the text.

3

Polychloronaphthalenes and other dioxin-like compounds in Arctic and Antarctic marine food webs.  

PubMed

Here we report accumulation patterns of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and pesticides (HCB, p,p'DDE) in polar organisms (polar bear from Alaskan Arctic and krill, sharp-spined notothen, crocodile icefish, Antarctic silverfish, Adélie penguin, South polar skua, and Weddell seal from the Ross Sea, Antarctica). PCNs, found in most of the samples, ranged from 1.5 pg/g in krill to 2550 pg/g in South polar skua on a wet weight basis. Lower chlorinated PCNs were the predominant congeners in organisms except skua and polar bear that showed similar PCN homologue patterns. PCDD/F concentrations were <90 pg/g wet wt in polar organisms; PCDD congeners showed peculiar accumulation patterns in different organisms. Correlation existed between PCN and PCB concentrations. PCB, HCF, and p,p'DDE levels were the highest in skua liver (11,150 ng/g wet wt, 345 ng/g wet wt, and 300 ng/g wet wt, respectively). Contribution of PCNs to 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ) was negligible (<0.1%) because of the lack of most toxic congeners. The highest TEQ was found in South polar skua liver (45 pg/g, wet weight). This is the first study to document the occurrence of PCNs in Antarctic organisms. High levels of dioxin-like chemicals in skua suggest the importance of intake via diet and migration habits, thus POP detection can be useful to trace migration behavior. Moreover, POP concentrations in penguin and skua eggs prove their transfer from the mother to eggs. PMID:12214639

Corsolini, Simonetta; Kannan, Kurunthachalam; Imagawa, Takashi; Focardi, Silvano; Giesy, John P

2002-08-15

4

Forest Food Web  

NSDL National Science Digital Library

Food webs are an interconnection of producers, consumers, and decomposers. It is important to understand that a change to any level of the food web directly and indirectly affects other organisms within the food web.

Katie Hale (CSUF;Biological Sciences)

2007-07-14

5

Models for Food Webs  

Microsoft Academic Search

Food webs are complex systems of many interacting biological species. After summarizing some of their properties, this contribution presents different ways of modeling food webs. It briefly mentions static models and discusses dynamical models and their population dynamics equations. The complexity-stability debate is mentioned, and evolutionary food web models are presented as a natural way of obtaining large stable webs.

Barbara Drossel

6

Fun With Food Webs  

NSDL National Science Digital Library

This set of online activities consists of matching games about meadow, arctic and pond food webs. Intended for younger students, each game involves placing images of various plants and animals into their proper places in the food webs.

7

Planktonic microbial assemblages and the potential effects of metazooplankton predation on the food web of lakes from the maritime Antarctica and subAntarctic islands  

Microsoft Academic Search

Antarctica is the continent with the harshest climate on the Earth. Antarctic lakes, however, usually presents liquid water, at least during part of the year or below the ice cover, especially those from the sub-Antarctic islands and the maritime Antarctic region where climatic conditions are less extreme. Planktonic communities in these lakes are mostly dominated by microorganisms, including bacteria and

Antonio Camacho

2006-01-01

8

Forest food web Illustration  

NSDL National Science Digital Library

The lowest level of a food web includes producers, which are plants that make their own energy from the sun. Animals that eat these producers are called primary consumers, and consumers that eat other consumers are called secondary consumers. Decomposers break down dead plants and animals to release nutrients into the soil.

Katie Hale (CSUF;Biological Sciences)

2007-07-14

9

Classroom Activity: Food Webs  

NSDL National Science Digital Library

This lesson plan is designed to help students understand the interrelatedness of food webs and to see how populations of organisms affect each other. Students assume the roles of the various organisms in the ecosystem; the ones that are dependent upon each other are symbolically connected by lengths of yarn. A materials list, instructions, assessment ideas, and educational standards are provided.

10

Forest Food Webs  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms in a temperate forest are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem, three types of consumers, food webs, and food chains. They then create a food web diagram for display in their classrooms. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

2007-03-12

11

Forest Food Webs  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms in a temperate forest are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem, three types of consumers, food webs, and food chains. They then create a food web diagram for display in their classrooms. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

12

Forest Food Webs  

NSDL National Science Digital Library

This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms in a temperate forest are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem, three types of consumers, food webs, and food chains. They then create a food web diagram for display in their classrooms. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.

Cahill, Mary

2007-12-12

13

The Great Lakes Food Web.  

ERIC Educational Resources Information Center

|Presents a play for students in grades four to nine that incorporates the scientific names, physical characteristics, feeding habits, interactions, and interdependence of the plants and animals that make up the Great Lakes food web to facilitate the learning of this complex system. Includes a Great Lakes food web chart. (AIM)|

Baker, Marjane L.

1997-01-01

14

Metal dynamics in an Antarctic food chain.  

PubMed

The concentrations of copper, zinc, cadmium, selenium and mercury were determined in eggs, muscle, liver, kidney and stomach content of nestilings and adults of the Antarctic petrel, Thalassoica antarctica, and its predator, the south polar skua, Chataracta maccormicki, from Svarthamaren, Dronning Maud Land, Antarctica. The dominant food of the petrels is krill, Euphausia superba. The results show relatively high levels of cadmium in krill, which is assumed to be the main reason for the high levels of cadmium in petrels and skuas. Cadmium is almost absent in eggs, but accumulates very rapidly with age in nestlings. The copper concentrations in livers of nestling petrels reach very high levels during growth. This may be seen in connection with physiological development processes. Mercury seems to be accumulated with age and between trophic levels. Among the nestlings, the mercury levels decrease with increasing age, which may be accomplished by the excretion of mercury through the growth of feathers and as a dilution effect during growth. Selenium and mercury are inversely correlated in nestlings. The levels of zinc were similar for different nestling stages and between nestlings and adults in skuas and petrels. PMID:11488240

Nygård, T; Lie, E; Røv, N; Steinnes, E

2001-07-01

15

Research on the Web: Antarctic Weather Stations  

NSDL National Science Digital Library

This Web research activity helps students see the link between wind speeds and geographical features. All directions are included in a printable handout. Students begin by gathering wind-speed measurements for 10 weather stations in Antarctica, converting the data, as needed, to allow comparisons. Next, they record wind data for five consecutive days and calculate the average wind speed for each station. They then examine elevation data for the 10 weather stations. They end by developing a hypothesis for the different patterns they've observed.

16

Universal scaling relations in food webs  

Microsoft Academic Search

The structure of ecological communities is usually represented by food webs. In these webs, we describe species by means of vertices connected by links representing the predations. We can therefore study different webs by considering the shape (topology) of these networks. Comparing food webs by searching for regularities is of fundamental importance, because universal patterns would reveal common principles underlying

Diego Garlaschelli; Guido Caldarelli; Luciano Pietronero

2003-01-01

17

Are diatoms a food source for Antarctic sponges?  

Microsoft Academic Search

Living diatoms are commonly found within Antarctic Porifera, and generally interpreted as additional food source, or as mutualists or parasites of sponge tissues. However, no data are available about temporal variations of the abundance of diatoms inside sponges especially during the winter period. In this paper we analysed the amount of diatom frustules and chlorophaeopigment concentration in six species of

C. Cerrano; B. Calcinai; E. Cucchiari; C. Di Camillo; M. Nigro; F. Regoli; A. Sarà; S. Schiaparelli; C. Totti; G. Bavestrello

2004-01-01

18

Soil Litter: The Food Web  

NSDL National Science Digital Library

Teachers could incorporate this brief radio program into a variety of learning settings. For example, teachers living in the temperate deciduous forest biome can play the program for students when leaves begin to fall in autumn. The program could also be used whenever students anywhere are learning about food webs or soil. Teachers can choose to use either the audio or text version (or both) to give students listening or reading practice.

Planet, Pulse O.

2006-06-27

19

Modeling the microbial food web.  

PubMed

Models of the microbial food web have their origin in the debate over the importance of bacteria as an energetic subsidy for higher trophic levels leading to harvestable fisheries. Conceptualization of the microbial food web preceded numerical models by 10-15 years. Pomeroy's work was central to both efforts. Elements necessary for informative and comprehensive models of microbial loops in plankton communities include coupled carbon and nitrogen flows utilizing a size-based approach to structuring and parameterizing the food web. Realistic formulation of nitrogen flows requires recognition that both nitrogenous and nonnitrogenous organic matter are important substrates for bacteria. Nitrogen regeneration driven by simple mass-specific excretion constants seems to overestimate the role of bacteria in the regeneration process. Quantitative assessment of the link-sink question, in which the original loop models are grounded, requires sophisticated analysis of size-based trophic structures. The effects of recycling complicate calculation of the link between bacteria or dissolved organic matter and mesozooplankton, and indirect effects show that the link might be much stronger than simple analyses have suggested. Examples drawn from a series of oceanic mixed layer plankton models are used to illustrate some of these points. Single-size class models related to traditional P-Z-N approaches are incapable of simulating bacterial biomass cycles in some locations (e.g., Bermuda) but appear to be adequate for more strongly seasonal regimes at higher latitudes. PMID:24186459

Ducklow, H W

1994-09-01

20

Where are the parasites in food webs?  

PubMed Central

This review explores some of the reasons why food webs seem to contain relatively few parasite species when compared to the full diversity of free living species in the system. At present, there are few coherent food web theories to guide scientific studies on parasites, and this review posits that the methods, directions and questions in the field of food web ecology are not always congruent with parasitological inquiry. For example, topological analysis (the primary tool in food web studies) focuses on only one of six important steps in trematode life cycles, each of which requires a stable community dynamic to evolve. In addition, these transmission strategies may also utilize pathways within the food web that are not considered in traditional food web investigations. It is asserted that more effort must be focused on parasite-centric models, and a central theme is that many different approaches will be required. One promising approach is the old energetic perspective, which considers energy as the critical resource for all organisms, and the currency of all food web interactions. From the parasitological point of view, energy can be used to characterize the roles of parasites at all levels in the food web, from individuals to populations to community. The literature on parasite energetics in food webs is very sparse, but the evidence suggests that parasite species richness is low in food webs because parasites are limited by the quantity of energy available to their unique lifestyles.

2012-01-01

21

Food Chains and Food Webs - Balance within Natural Systems  

NSDL National Science Digital Library

This lesson, supported by the provided power point lecture (LESSON 1 and 2 Ecology Lecture Supplement ), introduces students to the concepts of food chains and food webs. Through its use, students learn the difference between producers and consumers and study how these organisms function within their communities to interact in various food chains. Multiple food chains link together to form intricate and balanced food webs. Focus continues to rest on the Sonoran Desert. At the conclusion of this lesson, students are asked to construct a food web using endemic desert species.

Vu Bioengineering Ret Program

22

Universal scaling relations in food webs  

NASA Astrophysics Data System (ADS)

The structure of ecological communities is usually represented by food webs. In these webs, we describe species by means of vertices connected by links representing the predations. We can therefore study different webs by considering the shape (topology) of these networks. Comparing food webs by searching for regularities is of fundamental importance, because universal patterns would reveal common principles underlying the organization of different ecosystems. However, features observed in small food webs are different from those found in large ones. Furthermore, food webs (except in isolated cases) do not share general features with other types of network (including the Internet, the World Wide Web and biological webs). These features are a small-world character and a scale-free (power-law) distribution of the degree (the number of links per vertex). Here we propose to describe food webs as transportation networks by extending to them the concept of allometric scaling (how branching properties change with network size). We then decompose food webs in spanning trees and loop-forming links. We show that, whereas the number of loops varies significantly across real webs, spanning trees are characterized by universal scaling relations.

Garlaschelli, Diego; Caldarelli, Guido; Pietronero, Luciano

2003-05-01

23

Food web structure and biogeochemical processes during oceanic phytoplankton blooms: An inverse model analysis  

NASA Astrophysics Data System (ADS)

The relationship between food web structure and function across two ocean biomes was investigated using an inverse method to recover solutions of food web carbon flows. We estimated the carbon exchanges between major assemblages within plankton food webs in the North Atlantic, using the JGOFS NABE data set (1989) and near the Western Antarctic Peninsula (WAP), using the Palmer Station LTER data set, two areas exhibiting strong seasonal phytoplankton blooms. The recovery of all the potential flows of carbon allowed a system-level analysis, providing insight to processes that are seldom measured in the field and a means of comparing food webs from different regions. In the NABE food web, the dominant carbon flows involved the microorganisms including bacterial carbon demand and grazing by microzooplankton and protozoans. In the WAP food web, krill had the most significant carbon flows including grazing of large phytoplankton and respiration. A comparison between the NABE and the WAP carbon-based food webs showed key differences. Recycling and the activity of the microbial food web were much greater in the NABE food web than in the WAP. However in the WAP inverse solution, the microbial food web was just as important as the classical food web (diatoms to krill to penguins) that is traditionally believed to dominate carbon flows. Carbon flows through the NABE and WAP regions were more highly dependent on recycling than would be anticipated from the size structure of the primary producers, when analyzed using a classification scheme of Legendre, L., Rassoulzadegan, F [1996. Food-web mediated export of biogenic carbon in oceans: hydrodynamic control. Marine Ecology Progress Series 145, 179-193].

Daniels, Robert M.; Richardson, Tammi L.; Ducklow, Hugh W.

2006-03-01

24

The dynamics of spatially coupled food webs  

Microsoft Academic Search

The dynamics of ecological systems include a bewildering number of biotic interactions that unfold over a vast range of spatial scales. Here, employing simple and general empirical arguments concerning the nature of movement, trophic position and behaviour we outline a general theory concerning the role of space and food web structure on food web stability. We argue that consumers link

K. S. McCann; J. B. Rasmussen; J. Umbanhowar

2005-01-01

25

Mountains in the Sea: Food Web Mystery  

NSDL National Science Digital Library

In this activity, students will focus on some unique aspects of food webs in the vicinity of seamounts. They will be able to describe typical marine food webs, and explain why food is generally scarce in the deep-ocean environment. They will then discuss reasons why seamounts may be able to support a higher density of biological organisms than would appear to be possible considering food available from primary production at the ocean's surface. In addition to being tied to the National Science Education Standards, the hands-on, inquiry-based activities includes focus questions, background information for teachers, links to interesting websites, and extensions.

26

Food Chain to Food Web: A Natural Progression?  

ERIC Educational Resources Information Center

|Investigated is the ability of high school pupils and university students to answer questions based on relationships within food webs using sound ecological principles. Research methods used and the results of this study are discussed. (CW)|

Webb, Paul; Boltt, Gill

1990-01-01

27

Parasites in the Wadden Sea food web  

NASA Astrophysics Data System (ADS)

While the free-living fauna of the Wadden Sea has received much interest, little is known on the distribution and effects of parasites in the Wadden Sea food web. However, recent studies on this special type of trophic interaction indicate a high diversity of parasites in the Wadden Sea and suggest a multitude of effects on the hosts. This also includes effects on specific predator–prey relationships and the general structure of the food web. Focussing on molluscs, a major group in the Wadden Sea in terms of biomass and abundance and an important link between primary producers and predators, we review existing studies and exemplify the ecological role of parasites in the Wadden Sea food web. First, we give a brief inventory of parasites occurring in the Wadden Sea, ranging from microparasites (e.g. protozoa, bacteria) to macroparasites (e.g. helminths, parasitic copepods) and discuss the effects of spatial scale on heterogeneities in infection levels. We then demonstrate how parasites can affect host population dynamics by acting as a strong mortality factor, causing mollusc mass mortalities. In addition, we will exemplify how parasites can mediate the interaction strength of predator–prey relationships and affect the topological structure of the Wadden Sea food web as a whole. Finally, we highlight some ongoing changes regarding parasitism in the Wadden Sea in the course of global change (e.g. species introduction, climate change) and identify important future research questions to entangle the role of parasites in the Wadden Sea food web.

Thieltges, David W.; Engelsma, Marc Y.; Wendling, Carolin C.; Wegner, K. Mathias

2013-09-01

28

Food terrorism and food defense on the Web.  

PubMed

Global food supplies are at risk of both accidental and deliberate contamination. As past incidents have demonstrated, food terrorism may cause social, economic, and political disruption. The United States increased its efforts to protect its food after 9/11 by broadening the roles of existing agencies, including the U.S. Department of Agriculture and the Food and Drug Administration, and by making coordination of food defense the responsibility of the Department of Homeland Security. However, weaknesses in the system remain. This article presents background information and Web sites useful for consumers, industry representatives, students, researchers, policy makers, and the librarians that serve them. PMID:18689205

Taylor, Mary Kay

2008-01-01

29

Nutrient dynamics and food-web stability  

SciTech Connect

The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships. What are the effects of limiting nutrients on the stability of ecosystem food webs Most of the literature on food web stability centers around the dynamics of population numbers and/or biomasses. Nevertheless, a growing body of theoretical and empirical research considers the role that both nutrient limitation and recycling can play in stability. In this paper, it is the authors objective to summarize the current understanding of several important types of stability. The theoretical and empirical evidence relating these types of stability and nutrient cycling is described. A central generalization is produced in each case.

DeAngelis, D.L.; Mulholland, P.J.; Palumbo, A.V.; Steinman, A.D.; Huston, M.A.; Elwood, J.W. (Environmental Sciences Div., Oak Ridge National Lab., Oak Ridge, TN (US))

1989-01-01

30

Effects of taxonomic and trophic aggregation on food web properties  

Microsoft Academic Search

Historically, ecologists have been more inter- ested in organisms feeding at the tops of food chains than in organisms feeding at or near the bottom. The problem of taxonomic and trophic inconsistency within and among described food webs is central to criticisms of contemporary food web research. To study the eÄects of taxonomic and trophic aggregation on food web properties,

K. Schoenly; Louis-Felix Bersier

2007-01-01

31

Functional links and robustness in food webs  

Microsoft Academic Search

The robustness of ecosystems to species losses is a central question in ecology, given the current pace of extinctions and the many species threatened by human impacts, including habitat destruction and climate change. Robustness from the perspective of secondary extinctions has been addressed in the context of food webs to consider the complex network of species interactions that underlie responses

Stefano Allesina; Antonio Bodini; Mercedes Pascual

2009-01-01

32

Size, foraging, and food web structure  

PubMed Central

Understanding what structures ecological communities is vital to answering questions about extinctions, environmental change, trophic cascades, and ecosystem functioning. Optimal foraging theory was conceived to increase such understanding by providing a framework with which to predict species interactions and resulting community structure. Here, we use an optimal foraging model and allometries of foraging variables to predict the structure of real food webs. The qualitative structure of the resulting model provides a more mechanistic basis for the phenomenological rules of previous models. Quantitative analyses show that the model predicts up to 65% of the links in real food webs. The deterministic nature of the model allows analysis of the model's successes and failures in predicting particular interactions. Predacious and herbivorous feeding interactions are better predicted than pathogenic, parasitoid, and parasitic interactions. Results also indicate that accurate prediction and modeling of some food webs will require incorporating traits other than body size and diet choice models specific to different types of feeding interaction. The model results support the hypothesis that individual behavior, subject to natural selection, determines individual diets and that food web structure is the sum of these individual decisions.

Petchey, Owen L.; Beckerman, Andrew P.; Riede, Jens O.; Warren, Philip H.

2008-01-01

33

Nutrient dynamics and food-web stability  

Microsoft Academic Search

The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships.

D. L. DeAngelis; P. J. Mulholland; A. V. Palumbo; A. D. Steinman; M. A. Huston; J. W. Elwood

1989-01-01

34

Food web models: a plea for groups  

Microsoft Academic Search

The concept of a group is ubiquitous in biology. It underlies classifications in evolution and ecology, including those used to describe phylogenetic levels, the habitat and functional roles of organisms in ecosystems. Surprisingly, this concept is not explicitly included in simple models for the structure of food webs, the ecological networks formed by consumer-resource interactions. We present here the simplest

Stefano Allesina; Mercedes Pascual

2009-01-01

35

Pollutant Flow Through the Marine Food Web.  

National Technical Information Service (NTIS)

In the first volume of a two-volume report, results are presented of a study undertaken to determine the extent to which chemical contaminants appear to undergo biomagnification in marine food webs. A method for identifying trophic structure was developed...

D. R. Young A. J. Mearns H. A. Schafer G. P. Hershelman R. W. Gossett

1982-01-01

36

MOLECULAR CONTROL POINTS IN RHIZOSPHERE FOOD WEBS  

Microsoft Academic Search

Plant roots play diverse roles in the rhizosphere. They function as organs responsible for structural support, for acquisition of mineral and water resources, and for fostering of symbiotic bacteria and fungi. They also sustain a complex food web of pro- karyotes and eukaryotes in, on, and near the root. In addition to these well-known functions, roots have a recently discovered

Donald A. Phillips; Howard Ferris; Douglas R. Cook; Donald R. Strong

2003-01-01

37

Antarctic  

NSDL National Science Digital Library

Become an expert on the Antarctic habitat!! Begin your search for information by reading below. You can click on the underlined words to take you to the website you want to go to. Have fun! Read carefully. To find out about the habitat you can visit The Arctic: Earth s North Polar Region, Polar Region, and Arctic Tundra. Read the websites carefully to find important facts. Antarctica Animals and Animals in Antarctica will tell you about animals that live in the antarctic. Maya! Emperor Penguin will tell you lots of facts about penguins. To find more facts visit Penguin Facts. At this website ...

Ryan, Ms.

2013-02-12

38

Food Webs in an Estuary.  

ERIC Educational Resources Information Center

|The Maryland Marine Science Education Project has produced a series of mini-units in marine science education for the junior high/middle school classroom. This unit focuses on food chains in an estuary. Although the unit specifically treats the Chesapeake Bay, it may be adapted for use with similar estuarine systems. In addition, the unit may be…

Dunne, Barbara B.

39

COMPARABILITY: THE KEY TO THE APPLICABILITY OF FOOD WEB RESEARCH  

Microsoft Academic Search

However food webs have always been considered as a central issue of ecology, their value and usefulness are frequently questioned. In this paper, I overview some causes of this skepticism and discuss in which cases two or more food webs can be compared. I suggest that the comparability of different food webs is a key to possible applications. I show

F. JORDÁN

2003-01-01

40

Does cadmium pollution change trophic interactions in rockpool food webs?  

Microsoft Academic Search

The authors studied the regulation of phytoplankton and zooplankton biomass in rockpool food webs under chronic cadmium pollution. Experimental food webs with two and three trophic levels were composed of phytoplankton, small-bodied zooplankton (Chydorus sphaericus, Cyclops sp., and rotifers), Daphnia magna, and Notonecta sp., a zooplanktivorous predator. Every food web received a control and cadmium treatment allowing a separate study

Sanna Koivisto; M. Arner; Nils Kautsky

1997-01-01

41

Benthos as the basis for arctic lake food webs  

Microsoft Academic Search

Plankton have traditionally been viewed as the basis for limnetic food webs, with zooplankton acting as a gateway for energy passing between phytoplanktonic primary producers and fish. Often, benthic production has been considered to be important primarily in shallow systems or as a subsidy to planktonic food web pathways. Stable isotope food web analyses of two arctic lakes (NE14 and

Michael E. Sierszen; Michael E. McDonald; Douglas A. Jensen

2003-01-01

42

Quantitative analysis of the local structure of food webs  

Microsoft Academic Search

We analyze the local structure of model and empirical food webs through the statistics of three-node subgraphs. We study analytically and numerically the number of appearances of each subgraph for a simple model of food web topology, the so-called generalized cascade model, and compare them with 17 empirical community food webs from a variety of environments, including aquatic, estuarine, and

J. Camacho; D. B. Stouffer; L. A. N. Amaral

2007-01-01

43

Warmer Oceans Affect Food Web  

NSDL National Science Digital Library

In this video, students learn that the Exxon Valdez oil spill in Alaska in 1989 was not the sole cause of the decline of species in the local ecosystem. Rather, an explanation is posited for why some animal populations were already in decline when the spill occurred. Many of these animals share a common food: the sand lance, a fish whose populations have shrunk with the steady rise in ocean temperature that began in the late 1970s.

Ktoo; Foundation, Wgbh E.; Domain, Teachers'

44

Effects of taxonomic and trophic aggregation on food web properties  

Microsoft Academic Search

Historically, ecologists have been more interested in organisms feeding at the tops of food chains than in organisms feeding\\u000a at or near the bottom. The problem of taxonomic and trophic inconsistency within and among described food webs is central\\u000a to criticisms of contemporary food web research. To study the effects of taxonomic and trophic aggregation on food web properties,\\u000a 38

George Sugihara; L.-F. Bersier; Kenneth Schoenly

1997-01-01

45

Stable isotopes dissect food webs from top to the bottom  

NASA Astrophysics Data System (ADS)

Stable isotopes have been used extensively to study food web functioning, i.e. the flow of energy and matter among organisms. Traditional food-web studies are based on the natural variability of carbon and nitrogen isotopes and are limited to larger organisms that can be physically separated from their environment. Recent developments allow isotope ratio measurements of microbes and this in turn allows then measurement of entire food webs, i.e. from small producers at the bottom to large consumers at the top. Here, I provide a concise review on the use and potential of stable isotope to reconstruct end-to-end food webs. I will first discuss food web reconstruction based on natural abundances isotope data and will then show that the use of stable isotopes as deliberately added tracers provides complementary information. Finally, challenges and opportunities for end-to-end food web reconstructions in a changing world are discussed.

Middelburg, J. J.

2013-09-01

46

Modeling Food-Web Dynamics: Complexity-Stability Implications  

Microsoft Academic Search

We discuss theoretical aspects of the broader food-web research agenda, particularly the background and various approaches used for modeling food-web dynamics in abstract systems with more than two taxa. Much of this type of modeling has oriented itself around the classic and enduring complexity-stability debate in ecology, especially those aspects which relate to the theoretical and associated empirical food-web research

Jennifer A. Dunne; Ulrich Brose; Richard J. Williams; Neo D. Martinez

47

Metacommunity theory explains the emergence of food web complexity.  

PubMed

Food webs are highly complex ecological networks, dynamic in both space and time. Metacommunity models are now at the core of unified theories of biodiversity, but to date they have not addressed food web complexity. Here we show that metacommunity theory can explain the emergence of species-rich food webs with complex network topologies. Our analysis shows that network branching in the food web is maximized at intermediate colonization rates and limited dispersal scales, which also leads to concomitant peaks in species diversity. Increased food web complexity and species diversity are made possible by the structural role played by network branches that are supported by omnivore and generalist feeding links. Thus, in contrast to traditional food web theory, which emphasizes the destabilizing effect of omnivory feeding in closed systems, metacommunity theory predicts that these feeding links, which are commonly observed in empirical food webs, play a critical structural role as food webs assemble in space. As this mechanism functions at the metacommunity level, evidence for its operation in nature will be obtained through multiscale surveys of food web structure. Finally, we apply our theory to reveal the effects of habitat destruction on network complexity and metacommunity diversity. PMID:22084089

Pillai, Pradeep; Gonzalez, Andrew; Loreau, Michel

2011-11-14

48

Plankton, antarctic food chain base, respond to increased ultraviolet radiation  

SciTech Connect

With the growth of the austral spring ozone hole phytoplankton in antarctic waters beneath the depleted ozone layer are now being exposed to twice the amount of ultraviolet radiation as organisms outside the hole. This briefly describes the results of a major study examining this issue. A significant observation was a decrease in phytoplankton production by a minimum of 6-12 percent. Implications for other life forms are discussed briefly along with the effects of increased UV light on the whole ecosystem.

Dybas, C.

1992-12-01

49

The Disruption of Coastal Food Webs  

NSDL National Science Digital Library

This week's In The News addresses recent findings (published in the October 16, 1998 issue of Science) that killer whale predation on sea otters in the North Pacific has "created an ecological chain reaction in nearshore ecosystems." Such ecological chain reactions refer to the disruption of the complex balance between predator and prey species. Killer whales, which traditionally fed on the (now scarce) Steller sea lions and harbor seals, have recently shifted their diet to sea otters. The resulting decline in sea otters has, in turn, led to an increase in sea urchins (sea otter prey), which in turn have deforested many kelp (seaweed) beds in the nearshore marine community. Although killer whales are playing a critical role in the current disruption, this chain of interactions "was probably initiated by anthropogenic changes in the offshore oceanic ecosystem" -- namely, the region's burgeoning fisheries, higher ocean temperatures, and the depletion of baleen whales. Similar "trophic cascades" have been well documented for lakes and in other systems (e.g. Snow Geese in the Arctic), but this research provides a new example of a disrupted food web that may reach a wider audience -- as it involves several highly charismatic vertebrates. The nine resources discussed describe the recent scientific findings, provide background information on food webs, and offer several resources for understanding ecological (trophic) chain reactions.

Payne, Laura X.

1998-01-01

50

Web-Based Training Module, "ALERT: Food Defense ...  

Center for Food Safety and Applied Nutrition (CFSAN)

... News & Events. Constituent Updates. -. Web-Based Training Module, "ALERT: Food Defense Awareness" Now Available in Spanish. August 22, 2008 ... More results from www.fda.gov/food/newsevents/constituentupdates

51

Consequences of symbiosis for food web dynamics.  

PubMed

Basic Lotka-Volterra type models in which mutualism (a type of symbiosis where the two populations benefit both) is taken into account, may give unbounded solutions. We exclude such behaviour using explicit mass balances and study the consequences of symbiosis for the long-term dynamic behaviour of a three species system, two prey and one predator species in the chemostat. We compose a theoretical food web where a predator feeds on two prey species that have a symbiotic relationships. In addition to a species-specific resource, the two prey populations consume the products of the partner population as well. In turn, a common predator forages on these prey populations. The temporal change in the biomass and the nutrient densities in the reactor is described by ordinary differential equations (ODE). Since products are recycled, the dynamics of these abiotic materials must be taken into account as well, and they are described by odes in a similar way as the abiotic nutrients. We use numerical bifurcation analysis to assess the long-term dynamic behaviour for varying degrees of symbiosis. Attractors can be equilibria, limit cycles and chaotic attractors depending on the control parameters of the chemostat reactor. These control parameters that can be experimentally manipulated are the nutrient density of the inflow medium and the dilution rate. Bifurcation diagrams for the three species web with a facultative symbiotic association between the two prey populations, are similar to that of a bi-trophic food chain; nutrient enrichment leads to oscillatory behaviour. Predation combined with obligatory symbiotic prey-interactions has a stabilizing effect, that is, there is stable coexistence in a larger part of the parameter space than for a bi-trophic food chain. However, combined with a large growth rate of the predator, the food web can persist only in a relatively small region of the parameter space. Then, two zero-pair bifurcation points are the organizing centers. In each of these points, in addition to a tangent, transcritical and Hopf bifurcation a global heteroclinic bifurcation is emanating. This heteroclinic cycle connects two saddle equilibria where the predator is absent. Under parameter variation the period of the stable limit cycle goes to infinity and the cycle tends to the heteroclinic cycle. At this global bifurcation point this cycle breaks and the boundary of the basin of attraction disappears abruptly because the separatrix disappears together with the cycle. As a result, it becomes possible that a stable two-nutrient-two-prey population system becomes unstable by invasion of a predator and eventually the predator goes extinct together with the two prey populations, that is, the complete food web is destroyed. This is a form of over-exploitation by the predator population of the two symbiotic prey populations. When obligatory symbiotic prey-interactions are modelled with Liebig's minimum law, where growth is limited by the most limiting resource, more complicated types of bifurcations are found. This results from the fact that the Jacobian matrix changes discontinuously with respect to a varying parameter when another resource becomes most limiting. PMID:15293013

Kooi, B W; Kuijper, L D J; Kooijman, S A L M

2004-01-02

52

The Food Web Matching Game: A Missing Link  

NSDL National Science Digital Library

This extension activity challenges students to answer hypothetical questions about a marine food web they have created. They are asked to hypothesize what might happen if a top predator like the killer whale became extinct, or if fish from the middle levels of the web were overfished, or if a primary producer such as algae were removed from the web.

53

Characteristics of Food Industry Web Sites and "Advergames" Targeting Children  

ERIC Educational Resources Information Center

|Objective: To assess the content of food industry Web sites targeting children by describing strategies used to prolong their visits and foster brand loyalty; and to document health-promoting messages on these Web sites. Design: A content analysis was conducted of Web sites advertised on 2 children's networks, Cartoon Network and Nickelodeon. A…

Culp, Jennifer; Bell, Robert A.; Cassady, Diana

2010-01-01

54

Mercury bioaccumulation in estuarine food webs.  

PubMed

We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone, USA. Barataria Bay and Breton Sound are two neighboring deltaic estuaries that were isolated by levees from the Mississippi River about 100 years ago. These estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected > 2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: (H1) Background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and (H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and -2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (> 10 years) diversion inputs had -1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable-isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion inputs may account for the lessened Hg bioaccumulation in fish. A management consideration from this study is that river restoration projects may unintentionally fertilize SAV and epiphyte-based food webs, leading to higher Hg bioaccumulation in river-impacted floodplains and their food webs. PMID:22611858

Fry, Brian; Chumchal, Matthew M

2012-03-01

55

Investigation a food web: producers, consumers, and decomposers  

NSDL National Science Digital Library

This activity is a field investigation where students list plants and animals they observe. Students will organize their data as producers, consumers, or decomposers and create a food web showing how they affect each other. They will predict what will happen if the food web becomes imbalanced by extinction or over population.

56

Environmental controls on food web regimes: A fluvial perspective  

Microsoft Academic Search

Because food web regimes control the biomass of primary producers (e.g., plants or algae), intermediate consumers (e.g., invertebrates), and large top predators (tuna, killer whales), they are of societal as well as academic interest. Some controls over food web regimes may be internal, but many are mediated by conditions or fluxes over large spatial scales. To understand locally observed changes

Mary E. Power

2006-01-01

57

Dynamics of the Lake Michigan food web, 1970?2000  

Microsoft Academic Search

Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the fac- tors responsible for these changes. Control of sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of lake whitefish (Coregonus clupeaformis) and burbot (Lota lota)

Charles P. Madenjian; Gary L. Fahnenstiel; Thomas H. Johengen; Thomas F. Nalepa; Henry A. Vanderploeg; Guy W. Fleischer; Philip J. Schneeberger; Darren M. Benjamin; Emily B. Smith; James R. Bence; Edward S. Rutherford; Dennis S. Lavis; Dale M. Robertson; David J. Jude; Mark P. Ebener

2002-01-01

58

Bioaccumulation of Phthalate Esters in Aquatic Food-Webs  

Microsoft Academic Search

This chapter explores the bioaccumulation behavior of several phthalate esters in aquatic food-webs. It includes: (i) a compilation of bioconcentration data from reported laboratory studies in the literature, (ii) an overview and discussion of the results from a recently completed food-web bioaccumulation field study, and (iii) an analysis of the results of a bioaccumulation modeling study. The study concludes that

Frank A. P. C. Gobas; Cheryl E. Mackintosh; Glenys Webster; Michael Ikonomou; Thomas F. Parkerton; Kenneth Robillard

59

Food Web Stability: The Influence of Trophic Flows across Habitats  

Microsoft Academic Search

In nature, fluxes across habitats often bring both nu- ory, which plays a central role in consumer-resource in- trient and energetic resources into areas of low productivity from areas of higher productivity. These inputs can alter consumption teractions and food web dynamics. They further rates of consumer and predator species in the recipient food webs, suggested that multichannel omnivory can

Kevin McCann

1998-01-01

60

Compilation and Network Analyses of Cambrian Food Webs  

Microsoft Academic Search

A rich body of empirically grounded theory has developed about food webs—the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages

Jennifer A Dunne; Richard J Williams; Neo D Martinez; Rachel A Wood; Douglas H Erwin

2008-01-01

61

Web Marketing in Food Tourism: A Content Analysis of Web Sites in West Texas  

Microsoft Academic Search

Food is one of the most important elements in tourists' destination choices and travelers' decision-making. Food tourism is thus increasingly becoming an essential subject to researchers in the field of tourism. Consequently, the need for effective food tourism marketing is evident. However, little research has been conducted to examine food tourism marketing on the World Wide Web. This study was

Young H. Kim; Jingxue Yuan; Ben K. Goh; John M. Antun

2009-01-01

62

Food marketing on popular children's web sites: a content analysis.  

PubMed

In 2006 the Institute of Medicine (IOM) concluded that food marketing was a contributor to childhood obesity in the United States. One recommendation of the IOM committee was for research on newer marketing venues, such as Internet Web sites. The purpose of this cross-sectional study was to answer the IOM's call by examining food marketing on popular children's Web sites. Ten Web sites were selected based on market research conducted by KidSay, which identified favorite sites of children aged 8 to 11 years during February 2005. Using a standardized coding form, these sites were examined page by page for the existence, type, and features of food marketing. Web sites were compared using chi2 analyses. Although food marketing was not pervasive on the majority of the sites, seven of the 10 Web sites contained food marketing. The products marketed were primarily candy, cereal, quick serve restaurants, and snacks. Candystand.com, a food product site, contained a significantly greater amount of food marketing than the other popular children's Web sites. Because the foods marketed to children are not consistent with a healthful diet, nutrition professionals should consider joining advocacy groups to pressure industry to reduce online food marketing directed at youth. PMID:18375231

Alvy, Lisa M; Calvert, Sandra L

2008-04-01

63

Compilation and network analyses of cambrian food webs.  

PubMed

A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences. PMID:18447582

Dunne, Jennifer A; Williams, Richard J; Martinez, Neo D; Wood, Rachel A; Erwin, Douglas H

2008-04-29

64

Tracking contaminant flux from aquatic to terrestrial food webs  

EPA Science Inventory

Aquatic insects provide a critical energy subsidy to riparian food webs, yet their role as vectors of contaminants to terrestrial ecosystems is poorly understood. We investigated aquatic resource utilization and contaminant exposure among riparian invertivores (spiders and herpt...

65

Barcoding a Quantified Food Web: Crypsis, Concepts, Ecology and Hypotheses  

PubMed Central

The efficient and effective monitoring of individuals and populations is critically dependent on correct species identification. While this point may seem obvious, identifying the majority of the more than 100 natural enemies involved in the spruce budworm (Choristoneura fumiferana – SBW) food web remains a non-trivial endeavor. Insect parasitoids play a major role in the processes governing the population dynamics of SBW throughout eastern North America. However, these species are at the leading edge of the taxonomic impediment and integrating standardized identification capacity into existing field programs would provide clear benefits. We asked to what extent DNA barcoding the SBW food web would alter our understanding of the diversity and connectence of the food web and the frequency of generalists vs. specialists in different forest habitats. We DNA barcoded over 10% of the insects collected from the SBW food web in three New Brunswick forest plots from 1983 to 1993. For 30% of these specimens, we amplified at least one additional nuclear region. When the nodes of the food web were estimated based on barcode divergences (using molecular operational taxonomic units (MOTU) or phylogenetic diversity (PD) – the food web became much more diverse and connectence was reduced. We tested one measure of food web structure (the “bird feeder effect”) and found no difference compared to the morphologically based predictions. Many, but not all, of the presumably polyphagous parasitoids now appear to be morphologically-cryptic host-specialists. To our knowledge, this project is the first to barcode a food web in which interactions have already been well-documented and described in space, time and abundance. It is poised to be a system in which field-based methods permit the identification capacity required by forestry scientists. Food web barcoding provided an effective tool for the accurate identification of all species involved in the cascading effects of future budworm outbreaks. Integrating standardized barcodes within food webs may ultimately change the face of community ecology. This will be most poignantly felt in food webs that have not yet been quantified. Here, more accurate and precise connections will be within the grasp of any researcher for the first time.

Smith, M. Alex; Eveleigh, Eldon S.; McCann, Kevin S.; Merilo, Mark T.; McCarthy, Peter C.; Van Rooyen, Kathleen I.

2011-01-01

66

Spatial Scales of Carbon Flow in a River Food Web  

Microsoft Academic Search

Spatial extents of food webs that support stream and river consumers are largely unknown, but such information is essential for basic understanding and management of lotic ecosystems. We used predictable variation in algal d13C with water velocity, and measurements of consumer d13C and d15N to examine carbon flow and trophic structure in food webs of the South Fork Eel River

Jacques C. Finlay; Sapna Khandwala; Mary E. Power

2002-01-01

67

Stream food web fueled by methane-derived carbon  

Microsoft Academic Search

Food webs driven by energy from the oxidation of methane are now recognized to be omnipresent in terrestrial and freshwater ecosystems (e.g. lakes, soils and peat bogs), as well as in deep-sea hydrothermal vents and cold seeps. However, the incorporation of methane-derived carbon into stream food webs has never been reported. Here we present the first circumstantial evidence from stable

Ayato Kohzu; Chika Kato; Tomoya Iwata; Daisuke Kishi; Masashi Murakami; Shigeru Nakano; Eitaro Wada

2004-01-01

68

SPIDERS IN DECOMPOSITION FOOD WEBS OF AGROECOSYSTEMS: THEORY AND EVIDENCE  

Microsoft Academic Search

The involvement of spiders in decomposition food webs has the potential to affect agri- cultural productivity through two quite different types of interactions: (1) cascading, top-down effects of spider predation on rates of nutrient mineralization—spider-initiated trophic cascades in the detrital food web that could alter rates of decomposition and release of nutrients to plants; and (2) a bottom-up linkage, through

David H. Wise; William E. Snyder; Juraj Halaj

1999-01-01

69

Soil food web structure during ecosystem development after land abandonment  

Microsoft Academic Search

The re-establishment of natural species rich heathlands on abandoned agricultural land is a common land use change in North-West Europe. However, it can take several decades to re-establish natural species rich heathland vegetation. The development rate has found to depend both on soil food web composition and on soil processes.We measured the soil food web composition in three ex-arable fields

Remko Holtkamp; Paul Kardol; Annemieke van der Wal; Stefan C. Dekker; Wim H. van der Putten; Peter C. de Ruiter

2008-01-01

70

Predicting the effects of temperature on food web connectance.  

PubMed

Few models concern how environmental variables such as temperature affect community structure. Here, we develop a model of how temperature affects food web connectance, a powerful driver of population dynamics and community structure. We use the Arrhenius equation to add temperature dependence of foraging traits to an existing model of food web structure. The model predicts potentially large temperature effects on connectance. Temperature-sensitive food webs exhibit slopes of up to 0.01 units of connectance per 1 degrees C change in temperature. This corresponds to changes in diet breadth of one resource item per 2 degrees C (assuming a food web containing 50 species). Less sensitive food webs exhibit slopes down to 0.0005, which corresponds to about one resource item per 40 degrees C. Relative sizes of the activation energies of attack rate and handling time determine whether warming increases or decreases connectance. Differences in temperature sensitivity are explained by differences between empirical food webs in the body size distributions of organisms. We conclude that models of temperature effects on community structure and dynamics urgently require considerable development, and also more and better empirical data to parameterize and test them. PMID:20513716

Petchey, Owen L; Brose, Ulrich; Rall, Björn C

2010-07-12

71

Phylogeny versus body size as determinants of food web structure.  

PubMed

Food webs are the complex networks of trophic interactions that stoke the metabolic fires of life. To understand what structures these interactions in natural communities, ecologists have developed simple models to capture their main architectural features. However, apparently realistic food webs can be generated by models invoking either predator-prey body-size hierarchies or evolutionary constraints as structuring mechanisms. As a result, this approach has not conclusively revealed which factors are the most important. Here we cut to the heart of this debate by directly comparing the influence of phylogeny and body size on food web architecture. Using data from 13 food webs compiled by direct observation, we confirm the importance of both factors. Nevertheless, phylogeny dominates in most networks. Moreover, path analysis reveals that the size-independent direct effect of phylogeny on trophic structure typically outweighs the indirect effect that could be captured by considering body size alone. Furthermore, the phylogenetic signal is asymmetric: closely related species overlap in their set of consumers far more than in their set of resources. This is at odds with several food web models, which take only the view-point of consumers when assigning interactions. The echo of evolutionary history clearly resonates through current food webs, with implications for our theoretical models and conservation priorities. PMID:22628467

Naisbit, Russell E; Rohr, Rudolf P; Rossberg, Axel G; Kehrli, Patrik; Bersier, Louis-Félix

2012-05-23

72

Phylogeny versus body size as determinants of food web structure  

PubMed Central

Food webs are the complex networks of trophic interactions that stoke the metabolic fires of life. To understand what structures these interactions in natural communities, ecologists have developed simple models to capture their main architectural features. However, apparently realistic food webs can be generated by models invoking either predator–prey body-size hierarchies or evolutionary constraints as structuring mechanisms. As a result, this approach has not conclusively revealed which factors are the most important. Here we cut to the heart of this debate by directly comparing the influence of phylogeny and body size on food web architecture. Using data from 13 food webs compiled by direct observation, we confirm the importance of both factors. Nevertheless, phylogeny dominates in most networks. Moreover, path analysis reveals that the size-independent direct effect of phylogeny on trophic structure typically outweighs the indirect effect that could be captured by considering body size alone. Furthermore, the phylogenetic signal is asymmetric: closely related species overlap in their set of consumers far more than in their set of resources. This is at odds with several food web models, which take only the view-point of consumers when assigning interactions. The echo of evolutionary history clearly resonates through current food webs, with implications for our theoretical models and conservation priorities.

Naisbit, Russell E.; Rohr, Rudolf P.; Rossberg, Axel G.; Kehrli, Patrik; Bersier, Louis-Felix

2012-01-01

73

Biodiversity maintenance in food webs with regulatory environmental feedbacks.  

PubMed

Although the food web is one of the most fundamental and oldest concepts in ecology, elucidating the strategies and structures by which natural communities of species persist remains a challenge to empirical and theoretical ecologists. We show that simple regulatory feedbacks between autotrophs and their environment when embedded within complex and realistic food-web models enhance biodiversity. The food webs are generated through the niche-model algorithm and coupled with predator-prey dynamics, with and without environmental feedbacks at the autotroph level. With high probability and especially at lower, more realistic connectance levels, regulatory environmental feedbacks result in fewer species extinctions, that is, in increased species persistence. These same feedback couplings, however, also sensitize food webs to environmental stresses leading to abrupt collapses in biodiversity with increased forcing. Feedback interactions between species and their material environments anchor food-web persistence, adding another dimension to biodiversity conservation. We suggest that the regulatory features of two natural systems, deep-sea tubeworms with their microbial consortia and a soil ecosystem manifesting adaptive homeostatic changes, can be embedded within niche-model food-web dynamics. PMID:17240397

Bagdassarian, Carey K; Dunham, Amy E; Brown, Christopher G; Rauscher, Daniel

2006-12-15

74

Stable Isotope Tracers of Process in Great Lakes Food Webs  

EPA Science Inventory

Stable isotope analyses of biota are now commonly used to discern trophic pathways between consumers and their foods. However, those same isotope data also hold information about processes that influence the physicochemical setting of food webs as well as biological processes ope...

75

Food web framework for size-structured populations.  

PubMed

We synthesise traditional unstructured food webs, allometric body size scaling, trait-based modelling, and physiologically structured modelling to provide a novel and ecologically relevant tool for size-structured food webs. The framework allows food web models to include ontogenetic growth and life-history omnivory at the individual level by resolving the population structure of each species as a size-spectrum. Each species is characterised by the trait 'size at maturation', and all model parameters are made species independent through scaling with individual body size and size at maturation. Parameter values are determined from cross-species analysis of fish communities as life-history omnivory is widespread in aquatic systems, but may be reparameterised for other systems. An ensemble of food webs is generated and the resulting communities are analysed at four levels of organisation: community level, species level, trait level, and individual level. The model may be solved analytically by assuming that the community spectrum follows a power law. The analytical solution provides a baseline expectation of the results of complex food web simulations, and agrees well with the predictions of the full model on biomass distribution as a function of individual size, biomass distribution as a function of size at maturation, and relation between predator-prey mass ratio of preferred and eaten food. The full model additionally predicts the diversity distribution as a function of size at maturation. PMID:21146543

Hartvig, Martin; Andersen, Ken H; Beyer, Jan E

2010-12-10

76

Environmental controls on food web regimes: A fluvial perspective  

NASA Astrophysics Data System (ADS)

Because food web regimes control the biomass of primary producers (e.g., plants or algae), intermediate consumers (e.g., invertebrates), and large top predators (tuna, killer whales), they are of societal as well as academic interest. Some controls over food web regimes may be internal, but many are mediated by conditions or fluxes over large spatial scales. To understand locally observed changes in food webs, we must learn more about how environmental gradients and boundaries affect the fluxes of energy, materials, or organisms through landscapes or seascapes that influence local species interactions. Marine biologists and oceanographers have overcome formidable challenges of fieldwork on the high seas to make remarkable progress towards this goal. In river drainage networks, we have opportunities to address similar questions at smaller spatial scales, in ecosystems with clear physical structure and organization. Despite these advantages, we still have much to learn about linkages between fluxes from watershed landscapes and local food webs in river networks. Longitudinal (downstream) gradients in productivity, disturbance regimes, and habitat structure exert strong effects on the organisms and energy sources of river food webs, but their effects on species interactions are just beginning to be explored. In fluid ecosystems with less obvious physical structure, like the open ocean, discerning features that control the movement of organisms and affect food web dynamics is even more challenging. In both habitats, new sensing, tracing and mapping technologies have revealed how landscape or seascape features (e.g., watershed divides, ocean fronts or circulation cells) channel, contain or concentrate organisms, energy and materials. Field experiments and direct in situ observations of basic natural history, however, remain as vital as ever in interpreting the responses of biota to these features. We need field data that quantify the many spatial and temporal scales of functional relationships that link environments, fluxes and food web interactions to understand how they will respond to intensifying anthropogenic forcing over the coming decades.

Power, Mary E.

2006-02-01

77

Food Terrorism and Food Defense on the Web  

Microsoft Academic Search

Global food supplies are at risk of both accidental and deliberate contamination. As past incidents have demonstrated, food terrorism may cause social, economic, and political disruption. The United States increased its efforts to protect its food after 9\\/11 by broadening the roles of existing agencies, including the U.S. Department of Agriculture and the Food and Drug Administration, and by making

Mary Kay Taylor

2008-01-01

78

Relevance of evolutionary history for food web structure  

PubMed Central

Explaining the structure of ecosystems is one of the great challenges of ecology. Simple models for food web structure aim at disentangling the complexity of ecological interaction networks and detect the main forces that are responsible for their shape. Trophic interactions are influenced by species traits, which in turn are largely determined by evolutionary history. Closely related species are more likely to share similar traits, such as body size, feeding mode and habitat preference than distant ones. Here, we present a theoretical framework for analysing whether evolutionary history—represented by taxonomic classification—provides valuable information on food web structure. In doing so, we measure which taxonomic ranks better explain species interactions. Our analysis is based on partitioning of the species into taxonomic units. For each partition, we compute the likelihood that a probabilistic model for food web structure reproduces the data using this information. We find that taxonomic partitions produce significantly higher likelihoods than expected at random. Marginal likelihoods (Bayes factors) are used to perform model selection among taxonomic ranks. We show that food webs are best explained by the coarser taxonomic ranks (kingdom to class). Our methods provide a way to explicitly include evolutionary history in models for food web structure.

Eklof, Anna; Helmus, Matthew R.; Moore, M.; Allesina, Stefano

2012-01-01

79

Mercury biomagnification in marine zooplankton food webs in Hudson Bay.  

PubMed

While much research has been carried out on mercury in large marine mammals and associated food webs in northern regions, comparatively less has been conducted on lower trophic levels including zooplankton and the subsequent transfer to predators, which marks the entry of mercury into northern marine food webs. We present here the first database for mercury uptake and transfer exclusively within zooplankton food webs in northern marine waters. We have investigated both total (THg) and monomethylmercury (MMHg) concentrations, and isotopic signatures (?(15)N and ?(13)C) in individual zooplankton taxa collected over a period of eight years (2003-2010) from across Hudson Bay (including Hudson Strait and Foxe Basin) as part of research icebreaker cruises. ?(15)N values ranged from 3.4 to 14.0‰, implying trophic levels ranging from 1 to 4, and THg concentrations ranged from 5 to 242 ng g(-1) dw. Food web linkages were identified within the data set, and mercury biomagnification was evident both with THg and MMHg concentrations increasing from prey to predator, and with trophic magnification factors (TMFs). Total mercury and MMHg transfer in a unique prey-predator linkage (Limacina helicina-Clione limacina) are investigated and discussed with regard to known physiological and biochemical characteristics. The results suggest that exposure to mercury at higher trophic levels including humans can be affected by processes at the bottom of Arctic marine food webs. PMID:23157666

Foster, Karen L; Stern, Gary A; Pazerniuk, Monica A; Hickie, Brendan; Walkusz, Wojciech; Wang, Feiyue; Macdonald, Robie W

2012-11-16

80

THE ROLE OF SPIDERS IN THE DETRITAL FOOD WEB OF AN EASTERN DECIDUOUS FOREST  

Microsoft Academic Search

Historically, terrestrial food web research has focused on describing the structure of aboveground grazing webs, and determining how interactions among plants, herbivores and higher trophic levels influence primary productivity. Detrital food webs however, play a significant role in regulation of ecosystem dynamics through direct impacts on decomposition. Unraveling the complex nature of detrital food web structure is critical to developing

Erin Elizabeth Hladilek

2008-01-01

81

Food web dynamics in a seasonally varying wetland  

USGS Publications Warehouse

A spatially explicit model is developed to simulate the small fish community and its underlying food web, in the freshwater marshes of the Everglades. The community is simplified to a few small fish species feeding on periphyton and invertebrates. Other compartments are detritus, crayfish, and a piscivorous fish species. This unit food web model is applied to each of the 10,000 spatial cells on a 100 x 100 pixel landscape. Seasonal variation in water level is assumed and rules are assigned for fish movement in response to rising and falling water levels, which can cause many spatial cells to alternate between flooded and dry conditions. It is shown that temporal variations of water level on a spatially heterogeneous landscape can maintain at least three competing fish species. In addition, these environmental factors can strongly affect the temporal variation of the food web caused by top-down control from the piscivorous fish.

Deangelis, D. L.; Trexler, J. C.; Donalson, D. D.

2008-01-01

82

Food web dynamics in a seasonally varying wetland.  

PubMed

A spatially explicit model is developed to simulate the small fish community and its underlying food web, in the freshwater marshes of the Everglades. The community is simplified to a few small fish species feeding on periphyton and invertebrates. Other compartments are detritus, crayfish, and a piscivorous fish species. This unit food web model is applied to each of the 10,000 spatial cells on a 100 x 100 pixel landscape. Seasonal variation in water level is assumed and rules are assigned for fish movement in response to rising and falling water levels, which can cause many spatial cells to alternate between flooded and dry conditions. It is shown that temporal variations of water level on a spatially heterogeneous landscape can maintain at least three competing fish species. In addition, these environmental factors can strongly affect the temporal variation of the food web caused by top-down control from the piscivorous fish. PMID:19278288

Deangelis, Donald L; Trexler, Joel C; Donalson, Douglas D

2008-10-01

83

Adaptations in a hierarchical food web of southeastern Lake Michigan  

Microsoft Academic Search

Two issues in ecological network theory are: (1) how to construct an ecological network model and (2) how do entire networks (as opposed to individual species) adapt to changing conditions? We present a novel method for constructing an ecological network model for the food web of southeastern Lake Michigan (USA) and we identify changes in key system properties that are

Ann E. Krause; Ken A. Frank; Michael L. Jones; Thomas F. Nalepa; Richard P. Barbiero; Charles P. Madenjian; Megan Agy; Marlene S. Evans; William W. Taylor; Doran M. Mason; Nancy J. Leonard

2009-01-01

84

MODEL OF CARBON CYCLING IN THE PLANKTONIC FOOD WEB  

EPA Science Inventory

A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. he basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. acteria, p...

85

MODEL OF CARBON CYCLING IN PLANKTONIC FOOD WEBS  

EPA Science Inventory

A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research,The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. acteria, p...

86

Significance of predation by protists in aquatic microbial food webs  

Microsoft Academic Search

Predation in aquatic microbial food webs is dominated by phagotrophic protists, yet these microorganisms are still understudied compared to bacteria and phytoplankton. In pelagic ecosystems, predaceous protists are ubiquitous, range in size from 2 µm flagellates to >100 µm ciliates and dinoflagellates, and exhibit a wide array of feeding strategies. Their trophic states run the gamut from strictly phagotrophic, to

Evelyn B. Sherr; Barry F. Sherr

2002-01-01

87

Toxic marine phytoplankton, zooplankton grazers, and pelagic food webs  

Microsoft Academic Search

Interactions between toxic phytoplankton and their zooplankton grazers are complex. Some zooplanktcrs ingest some toxic phytoplankters with no apparent harm, whereas others are deleteriously affected. Phycotoxins vary in their modes of action, levels of toxicity and solubility, and affect grazers in different ways. Beyond effects on direct grazers, toxins may accumulate in and be transfcrrcd through marine food webs, affecting

JefSerson T. Turner; Patricia A. Tester

1997-01-01

88

Interaction strengths in food webs: issues and opportunities  

Microsoft Academic Search

Summary 1. Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2. Much confusion stems from lack of clarity about whether the

Eric L. Berlow; Anje-Margiet Neutel; Joel E. Cohen; Peter C. de Ruiter; Bo Ebenman; Mark Emmerson; Jeremy W. Fox; Vincent A. A. Jansen; J. Iwan Jones; Giorgos D. Kokkoris; Dmitrii O. Logofet; Alan J. McKane; Jose M. Montoya; Owen Petchey

2004-01-01

89

Critical patch sizes for food-web modules.  

PubMed

Because patch size and connectivity may strongly impact the assemblage of species that occur on a patch, the types of food-web interactions that occur among those species may also depend on spatial structure. Here, we identify whether food-web interactions among salt-marsh-inhabiting arthropods vary with patch size and connectivity, and how such changes in trophic structure might feed back to influence the spatial distribution of prey. In a multiyear survey, patch-restricted predators exhibited steeper occupancy-patch-size relationships than herbivores, and species' critical patch sizes were correlated with overall rarity. As a result, the presence of food-web modules depended strongly on patch size: large and well-connected patches supported complex food-web modules, but only the simplest modules involving the most abundant species were found on small patches. Habitat-generalist spiders dominated on small patches, and predation pressure from such species may contribute to the observed lower densities of mesopredators on small patches. Overall, patch size and connectivity influenced the types of modules present on a patch through differential loss of rare, patch-restricted predators, but predation by generalist predators may be a key mechanism influencing the spatial structure of certain prey species. PMID:22928406

Martinson, Holly M; Fagan, William F; Denno, Robert F

2012-08-01

90

DEVELOPMENT OF A STREAM FOOD WEB MODEL CONSTRAINED BY STABLE ISOTOPE DATA  

EPA Science Inventory

Traditional stream food web studies provide static models of trophic structures. These models provide information about interspecific relationships, but not about material flows through food webs. Traditional ecosystem models developed from budgets or tracers provide quantitative...

91

Designing an Illustrated Food Web to Teach Ecological Concepts: Challenges and Solutions.  

ERIC Educational Resources Information Center

|Argues that food webs are an efficient method through which to communicate the core idea of ecology--that all living things are interconnected. Assesses the challenges and solutions to using illustrated food webs. (Author/CCM)|

Godkin, Celia M.

1999-01-01

92

Drought alters the structure and functioning of complex food webs  

NASA Astrophysics Data System (ADS)

Climate change is expected to make many regions of the world much drier over coming decades. More intense drought would transform rivers with potentially severe but largely unknown consequences at higher (multispecies) levels of organization. Here we show experimentally how the intensification of drought may alter the underlying structure and functioning (biomass flux dynamics) of freshwater food webs--networks of species and their interactions. Drought triggered substantial losses of species and links, especially among predators, leading to the partial collapse of the food webs. Total resource-consumer biomass flux was also strongly suppressed by disturbance, yet several network-level properties (such as connectance and interaction diversity) were conserved, driven by consumer resource fidelity and a substantial reconfiguration of fluxes within the webs as production shifted down the size spectrum from large to small species. Our research demonstrates that drier climates could have far-reaching impacts on the functioning of freshwater ecosystems.

Ledger, Mark E.; Brown, Lee E.; Edwards, François K.; Milner, Alexander M.; Woodward, Guy

2013-03-01

93

Viral dynamics and patterns of lysogeny in saline Antarctic lakes  

Microsoft Academic Search

Antarctic lakes are extreme ecosystems with microbially dominated food webs, in which viruses may be important in controlling\\u000a community dynamics. A year long investigation of two Antarctic saline lakes (Ace and Pendant Lakes) revealed high concentrations\\u000a of virus like particles (VLP) (0.20–1.26 × 108 ml?1), high VLP: bacteria ratios (maximum 70.6) and a seasonal pattern of lysogeny differing from that seen at lower

Johanna Laybourn-Parry; William A. Marshall; Nanette J. Madan

2007-01-01

94

Re-evaluating the omnivory-stability relationship in food webs  

PubMed Central

Under equilibrium conditions, previous theory has shown that the presence of omnivory destabilizes food webs. Correspondingly, omnivory ought to be rare in real food webs. Although, early food web data appeared to verify this, recently many ecologists have found omnivory to be ubiquitous in food web data gathered at a high taxonomic resolution. In this paper, we re-investigate the role of omnivory in food webs using a non-equilibrium perspective. We find that the addition of omnivory to a simple food chain model (thus a simple food web) locally stabilizes the food web in a very complete way. First, non-equilibrium dynamics (e.g. chaos) tend to be eliminated or bounded further away from zero via period-doubling reversals invoked by the omnivorous trophic link. Second, food chains without interior attractors tend to gain a stable interior attractor with moderate amounts of omnivory.

McCann, K.; Hastings, A.

1997-01-01

95

Food habit and prey consumption of Antarctic minke whale Balaenoptera bonaerensis in JARPA research area  

Microsoft Academic Search

We analyzed the stomach contents of Antarctic minke whale (Balaenoptera bonaerensis) in the Southern Ocean. The Antarctic minke whales fed mostly on Antarctic krill (Euphausia superba) in offshore area, and ice krill (E. crystallorophias) in coastal (shallow) area on continental shelf such as Ross Sea and Prydz Bay. The average of fresh stomach contents per capita has decreased year after

TSUTOMU TAMURA; KENJI KONISHI

96

Visualizing the Food-Web Effects of Fishing for Tunas in the Pacific Ocean  

Microsoft Academic Search

We use food-web models to develop visualizations to compare and evaluate the interactions of tuna fisheries with their supporting food webs in the eastern tropical Pacific (ETP) and the central north Pacific (CNP) Oceans. In the ETP and CNP models, individual fisheries use slightly different food webs that are defined by the assemblage of targeted tuna species. Distinct energy pathways

Jefferson T. Hinke; Isaac C. Kaplan; Kerim Aydin; George M. Watters; Robert J. Olson; James F. Kitchell

2004-01-01

97

A Comparison of Soil Food Webs Beneath C3- and C4-Dominated Grasslands  

Technology Transfer Automated Retrieval System (TEKTRAN)

Soil food web structure influences soil organic matter mineralization and plant nutrient availability, but the potential for plants to capitalize on this mechanism by altering soil food web structure has received little attention. We evaluated this potential mechanism by measuring soil food web str...

98

Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure?  

Microsoft Academic Search

It has been suggested by Cohen and Newman (1985) that many of the patterns in published food webs can be derived from a stochastic model in which the species are arranged in a trophic hierarchy (the ‘cascade model’). We suggest that, if predators are larger than their prey, a trophic hierarchy can be generated on the basis of body size

P. H. Warren; J. H. Lawton

1987-01-01

99

Moving Up the Information Food Chain: Deploying Softbots on the World Wide Web  

Microsoft Academic Search

I view the World Wide Web as an information food chain (figure 1). The maze of pages and hyperlinks that comprise the Web are at the very bottom of the chain. The WebCrawlers and Alta Vistas of the world are information herbivores; they graze on Web pages and regurgitate them as searchable indices. Today, most Web users feed near the

Oren Etzioni

1996-01-01

100

Geo-Spatial Browse and Distribution of NSF-OPP's Antarctic Ice and Climate Data via the Web: Antarctic Cryosphere Access Portal (A-CAP)  

Microsoft Academic Search

A prototype of the Antarctic Cryosphere Access Portal (A-CAP) has been released for public use. Developed at the National Snow and Ice Data Center (NSIDC) Antarctic Glaciological Data Center (AGDC), A-CAP aims to be a geo-visualization and data download tool for AGDC data and other Antarctic-wide parameters, including glaciology, ice core data, snow accumulation, satellite imagery, digital elevation models (DEMs),

R. Bauer; T. Scambos; T. Haran; J. Maurer; J. Bohlander

2008-01-01

101

The more food webs change, the more they stay the same  

PubMed Central

Here, we synthesize a number of recent empirical and theoretical papers to argue that food-web dynamics are characterized by high amounts of spatial and temporal variability and that organisms respond predictably, via behaviour, to these changing conditions. Such behavioural responses on the landscape drive a highly adaptive food-web structure in space and time. Empirical evidence suggests that underlying attributes of food webs are potentially scale-invariant such that food webs are characterized by hump-shaped trophic structures with fast and slow pathways that repeat at different resolutions within the food web. We place these empirical patterns within the context of recent food-web theory to show that adaptable food-web structure confers stability to an assemblage of interacting organisms in a variable world. Finally, we show that recent food-web analyses agree with two of the major predictions of this theory. We argue that the next major frontier in food-web theory and applied food-web ecology must consider the influence of variability on food-web structure.

McCann, Kevin Shear; Rooney, Neil

2009-01-01

102

Fluctuating Silicate:Nitrate Ratios and Coastal Plankton Food Webs  

Microsoft Academic Search

Marine diatoms require dissolved silicate to form an external shell, and their growth becomes Si-limited when the atomic ratio of silicate to dissolved inorganic nitrogen (Si:DIN) approaches 1:1, also known as the ``Redfield ratio.'' Fundamental changes in the diatom-to-zooplankton-to-higher trophic level food web should occur when this ratio falls below 1:1 and the proportion of diatoms in the phytoplankton community

R. Eugene Turner; Naureen Qureshi; Nancy N. Rabalais; Quay Dortch; Dubravko Justic; Richard F. Shaw; Joseph Cope

1998-01-01

103

Trait and density mediated indirect interactions in simple food webs  

Microsoft Academic Search

This article compares indirect trait-mediated interactions in simple resource\\/ consumer\\/predator food webs with those that are density-mediated. It focuses on two well documented responses of consumers to predation risk: decrease in consumer activity and habitat switch. These behavioral effects are transmitted to resources and they cause similar indirect effects as those which are mediated by density changes in consumers. Two

Vlastimil K?ivan; Oswald J. Schmitz

2004-01-01

104

Simulating Food Web Dynamics along a Gradient: Quantifying Human Influence  

PubMed Central

Realistically parameterized and dynamically simulated food-webs are useful tool to explore the importance of the functional diversity of ecosystems, and in particular relations between the dynamics of species and the whole community. We present a stochastic dynamical food web simulation for the Kelian River (Borneo). The food web was constructed for six different locations, arrayed along a gradient of increasing human perturbation (mostly resulting from gold mining activities) along the river. Along the river, the relative importance of grazers, filterers and shredders decreases with increasing disturbance downstream, while predators become more dominant in governing eco-dynamics. Human activity led to increased turbidity and sedimentation which adversely impacts primary productivity. Since the main difference between the study sites was not the composition of the food webs (structure is quite similar) but the strengths of interactions and the abundance of the trophic groups, a dynamical simulation approach seemed to be useful to better explain human influence. In the pristine river (study site 1), when comparing a structural version of our model with the dynamical model we found that structurally central groups such as omnivores and carnivores were not the most important ones dynamically. Instead, primary consumers such as invertebrate grazers and shredders generated a greater dynamical response. Based on the dynamically most important groups, bottom-up control is replaced by the predominant top-down control regime as distance downstream and human disturbance increased. An important finding, potentially explaining the poor structure to dynamics relationship, is that indirect effects are at least as important as direct ones during the simulations. We suggest that our approach and this simulation framework could serve systems-based conservation efforts. Quantitative indicators on the relative importance of trophic groups and the mechanistic modeling of eco-dynamics could greatly contribute to understanding various aspects of functional diversity.

Jordan, Ferenc; Gjata, Nerta; Mei, Shu; Yule, Catherine M.

2012-01-01

105

Does cadmium pollution change trophic interactions in rockpool food webs?  

SciTech Connect

The authors studied the regulation of phytoplankton and zooplankton biomass in rockpool food webs under chronic cadmium pollution. Experimental food webs with two and three trophic levels were composed of phytoplankton, small-bodied zooplankton (Chydorus sphaericus, Cyclops sp., and rotifers), Daphnia magna, and Notonecta sp., a zooplanktivorous predator. Every food web received a control and cadmium treatment allowing a separate study of cadmium and predation effects. After a 3-week stabilization period, cadmium and Notonecta were added and changes in primary productivity, chlorophyll, zooplankton species composition, and biomass were followed during 8 weeks. The results showed that phytoplankton and Daphnia were consumer regulated in both control and cadmium treatments, although resource availability ultimately determined the biomass at each trophic level. Daphnia was the only zooplankton species that reduced phytoplankton and also the only species that was eliminated by Notonecta predation. Notonecta had an indirect positive impact on phytoplankton biomass that increased after the extinction of Daphnia. Cadmium significantly reduced phytoplankton and Daphnia but did not change the trophic interactions between them, i.e., Daphnia and chlorophyll were significantly negatively correlated both in the control and cadmium treatments. Cadmium did not affect the relationship between Daphnia and Notonecta.

Koivisto, S.; Arner, M.; Kautsky, N. [Stockholm Univ. (Sweden)

1997-06-01

106

Food web dynamics in the Scotia Sea in summer: A stable isotope study  

NASA Astrophysics Data System (ADS)

The pelagic food web of the Scotia Sea was studied by analysing natural abundances of nitrogen and carbon stable isotopes of primary producers and pelagic consumers, sampled from the seasonal ice edge in the south to the Antarctic Polar Front in the north. The analysis covered, within a single mid-summer period, particulate organic matter (POM) and 38 taxa, ranging from suspension feeding copepods and salps to omnivorous euphausiids, pelagic fish and higher, land-based predators including fur seals, penguins and flying birds. Spatial variation in ?15N of POM correlated well with nutrient availability and primary productivity. Latitudinal differences in ?13C of POM were closely linked to variations in temperature, nutrients and productivity depending on the frontal region sampled. This translated to equivalent (although smaller) regional ?13C differences among higher trophic levels. The trophic positions of species based on isotope values broadly agreed with previously published dietary data with three important exceptions. First, the carnivorous amphipod Themisto gaudichaudii had anomalously low ?15N values. Second, Euphausia superba had ?15N values that were also surprisingly low, considering the abundant literature suggesting its omnivory. Third, the copepod Rhincalanus gigas, considered a suspension feeder, had unexpectedly high ?15N values rather more in keeping with omnivorous feeding. The consumer ?15N values ranged from 1.2‰ (min.) measured in Salpa thompsoni (designated here as trophic level (TL) 2 across all regions) to 15.2‰ (max.) measured in white-chinned petrels (Procellaria aequinoctialis, calculated as TL5 relative to the TL2 of salps). Excluding seabirds, the resulting food chain length of 3.7 TL (above POM at TL1) was lower than in most other Southern Ocean and temperate marine pelagic ecosystems. The majority (60%) of vertebrate predators occupied only 1-1.5 trophic levels above the herbivorous suspension feeders such as krill. This indicates the existence of the classic short food chain of POM-suspension feeder-vertebrate predator. However the presence of trophic levels 4 and above indicates the existence of alternative trophic pathways, for example involving myctophid fish or carrion, and that some wide-ranging predators which breed at South Georgia also feed outside the region. This conclusion is supported first by the continuum of ?15N values between krill, suspension feeding copepods and myctophid fish, and secondly by higher trophic levels in several of the myctophid species in the low-krill region of the northern Scotia Sea, suggesting latitudinal differences in food web structure and food chain length.

Stowasser, G.; Atkinson, A.; McGill, R. A. R.; Phillips, R. A.; Collins, M. A.; Pond, D. W.

2012-01-01

107

Food web dynamics in the Scotia Sea in summer: A stable isotope study  

NASA Astrophysics Data System (ADS)

The pelagic food web of the Scotia Sea was studied by analysing natural abundances of nitrogen and carbon stable isotopes of primary producers and pelagic consumers, sampled from the seasonal ice edge in the south to the Antarctic Polar Front in the north. The analysis covered, within a single mid-summer period, particulate organic matter (POM) and 38 taxa, ranging from suspension feeding copepods and salps to omnivorous euphausiids, pelagic fish and higher, land-based predators including fur seals, penguins and flying birds. Spatial variation in ? 15N of POM correlated well with nutrient availability and primary productivity. Latitudinal differences in ? 13C of POM were closely linked to variations in temperature, nutrients and productivity depending on the frontal region sampled. This translated to equivalent (although smaller) regional ? 13C differences among higher trophic levels. The trophic positions of species based on isotope values broadly agreed with previously published dietary data with three important exceptions. First, the carnivorous amphipod Themisto gaudichaudii had anomalously low ? 15N values. Second, Euphausia superba had ? 15N values that were also surprisingly low, considering the abundant literature suggesting its omnivory. Third, the copepod Rhincalanus gigas, considered a suspension feeder, had unexpectedly high ? 15N values rather more in keeping with omnivorous feeding. The consumer ? 15N values ranged from 1.2‰ (min.) measured in Salpa thompsoni (designated here as trophic level (TL) 2 across all regions) to 15.2‰ (max.) measured in white-chinned petrels ( Procellaria aequinoctialis, calculated as TL5 relative to the TL2 of salps). Excluding seabirds, the resulting food chain length of 3.7 TL (above POM at TL1) was lower than in most other Southern Ocean and temperate marine pelagic ecosystems. The majority (60%) of vertebrate predators occupied only 1-1.5 trophic levels above the herbivorous suspension feeders such as krill. This indicates the existence of the classic short food chain of POM-suspension feeder-vertebrate predator. However the presence of trophic levels 4 and above indicates the existence of alternative trophic pathways, for example involving myctophid fish or carrion, and that some wide-ranging predators which breed at South Georgia also feed outside the region. This conclusion is supported first by the continuum of ? 15N values between krill, suspension feeding copepods and myctophid fish, and secondly by higher trophic levels in several of the myctophid species in the low-krill region of the northern Scotia Sea, suggesting latitudinal differences in food web structure and food chain length.

Stowasser, G.; Atkinson, A.; McGill, R. A. R.; Phillips, R. A.; Collins, M. A.; Pond, D. W.

2012-01-01

108

Bathymetric food habit changes in the antarctic fish, Notothenia gibberifrons Lönnberg. (Pisces: Nototheniidae)  

Microsoft Academic Search

The dietary composition of the antarctic fish Notothenia gibberifrons Lönnberg in a depth gradient was studied, from sea level until 200 meters in South Bay, Doumer Island, West Antarctic. The diet of this species varied across the depth gradient. Stomachs from specimens captured between the surface and 100 m. depth usually contained mobile benthic organisms, principally Amphipods. Those from below

Carlos A. Moreno; Hector H. Osorio

1977-01-01

109

Ecological Stoichiometry, Biogeochemical Cycling, Invasive Species, and Aquatic Food Webs: San Francisco Estuary and Comparative Systems  

Microsoft Academic Search

Eutrophication has altered food webs across aquatic systems, but effects of nutrient stoichiometry (varying nutrient ratios) on ecosystem structure and function have received less attention. A prevailing assumption has been that nutrients are not ecologically relevant unless concentrations are limiting to phytoplankton. However, changes in nutrient stoichiometry fundamentally affect food quality at all levels of the food web. Here, 30-year

Patricia M. Glibert; David Fullerton; Joann M. Burkholder; Jeffrey C. Cornwell; Todd M. Kana

2011-01-01

110

Land use alters the resistance and resilience of soil food webs to drought  

NASA Astrophysics Data System (ADS)

Soils deliver several ecosystem services including carbon sequestration and nutrient cycling, which are of central importance to climate mitigation and sustainable food production. Soil biota play an important role in carbon and nitrogen cycling, and, although the effects of land use on soil food webs are well documented, the consequences for their resistance and resilience to climate change are not known. We compared the resistance and resilience to drought--which is predicted to increase under climate change--of soil food webs of two common land-use systems: intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web. We found that the fungal-based food web, and the processes of C and N loss it governs, of grassland soil was more resistant, although not resilient, and better able to adapt to drought than the bacterial-based food web of wheat soil. Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss. Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change, and that extensively managed grassland promotes more resistant, and adaptable, fungal-based soil food webs.

de Vries, Franciska T.; Liiri, Mira E.; Bjørnlund, Lisa; Bowker, Matthew A.; Christensen, Søren; Setälä, Heikki M.; Bardgett, Richard D.

2012-04-01

111

Fluctuating silicate:nitrate ratios and coastal plankton food webs  

PubMed Central

Marine diatoms require dissolved silicate to form an external shell, and their growth becomes Si-limited when the atomic ratio of silicate to dissolved inorganic nitrogen (Si:DIN) approaches 1:1, also known as the “Redfield ratio.” Fundamental changes in the diatom-to-zooplankton-to-higher trophic level food web should occur when this ratio falls below 1:1 and the proportion of diatoms in the phytoplankton community is reduced. We quantitatively substantiate these predictions by using a variety of data from the Mississippi River continental shelf, a system in which the Si:DIN loading ratio has declined from around 3:1 to 1:1 during this century because of land-use practices in the watershed. We suggest that, on this shelf, when the Si:DIN ratio in the river decreases to less than 1:1, then (i) copepod abundance changes from >75% to <30% of the total mesozooplankton, (ii) zooplankton fecal pellets become a minor component of the in situ primary production consumed, and (iii) bottom-water oxygen consumption rates become less dependent on relatively fast-sinking (diatom-rich) organic matter packaged mostly as zooplankton fecal pellets. This coastal ecosystem appears to be a pelagic food web dynamically poised to be either a food web composed of diatoms and copepods or one with potentially disruptive harmful algal blooms. The system is directed between these two ecosystem states by Mississippi River water quality, which is determined by land-use practices far inland.

Turner, R. Eugene; Qureshi, Naureen; Rabalais, Nancy N.; Dortch, Quay; Justic, Dubravko; Shaw, Richard F.; Cope, Joseph

1998-01-01

112

Food-web based unified model of macro- and microevolution  

NASA Astrophysics Data System (ADS)

We incorporate the generic hierarchical architecture of foodwebs into a “unified” model that describes both micro- and macroevolutions within a single theoretical framework. This model describes the microevolution in detail by accounting for the birth, ageing, and natural death of individual organisms as well as prey-predator interactions on a hierarchical dynamic food web. It also provides a natural description of random mutations and speciation (origination) of species as well as their extinctions. The distribution of lifetimes of species follows an approximate power law only over a limited regime.

Chowdhury, Debashish; Stauffer, Dietrich

2003-10-01

113

Trophic structure, stability, and parasite persistence threshold in food webs.  

PubMed

Food web structure of free-living species is an important determinant of parasite species richness. Downwardly asymmetric predator-prey interactions (where there are more prey than predator species) have been shown, both theoretically and empirically, to harbour more trophically transmitted parasite species than expected due to chance. Here, we demonstrate that this could be due to the increase in the basic reproductive ratio that the addition of non-host prey species to a system creates. However, we note that the basic reproductive ratio is only increased by those prey that stabilise oscillations in a predator-prey system, and is decreased by those that do not. PMID:23943365

McQuaid, C Finn; Britton, Nicholas F

2013-08-14

114

Biochemical tracers reveal intra-specific differences in the food webs utilized by individual seabirds  

Microsoft Academic Search

Food web structure regulates the pathways and flow rates of energy, nutrients, and contaminants to top predators. Ecologically\\u000a and physiologically meaningful biochemical tracers provide a means to characterize and quantify these transfers within food\\u000a webs. In this study, changes in the ratios of stable N isotopes (e.g., ?15N), fatty acids (FA), and persistent contaminants were used to trace food web

Craig E. Hebert; D. V. Chip Weseloh; Lewis T. Gauthier; Michael T. Arts; Robert J. Letcher

2009-01-01

115

Australian Antarctic Data Centre  

NSDL National Science Digital Library

The Australian Antarctic Division is part of the Australian Government's Department of the Environment and Heritage. Within the department's Web site is the Australian Antarctic Data Centre, which makes all scientific observations and results freely available. Data topics include weather, GIS and mapping, marine science, flora and fauna, and many other topics related to the southern continent.

2002-01-01

116

Biomagnification of polychlorinated biphenyls through a riverine food web  

SciTech Connect

From 1989 to 1993, biota collected from Pottersburg Creek, London, ON, Canada were analyzed for total polychlorinated biphenyls (PCBs) and lipids. Data were analyzed by analysis of covariance (ANCOVA) with lipid as the covariate, to investigate station, time, and trophic effects on PCB accumulation in aquatic organisms. All three variables were highly significant. PCB concentrations in biota decreased along the length of the creek away from the point source. PCB concentrations in biota collected in July 1993 were not significantly different from concentrations in biota collected in July 1990, suggesting that sources into the creek have not been alleviated. The relationship between PCBs and lipid for biota from Pottersburg Creek suggests that organisms accumulate PCBs relative to their position in the food web. Fish and leeches occupying the top of the food web accumulated more PCBs than organisms occupying a lower trophic position (crayfish and oligochaetes/chironomids), indicating that biomagnification through trophic transfer (i.e., the uptake of a chemical through ingestion) is the primary mechanism governing contaminant levels in biota and not bioconcentration (i.e, the uptake of a chemical from water).

Zaranko, D.T.; Kaushik, N.K. [Univ. of Guelph, Ontario (Canada). Dept. of Environmental Biology; Griffiths, R.W. [Ministry of Environment and Energy, London, Ontario (Canada)

1997-07-01

117

The ecological potentials of Phytomyxea ("plasmodiophorids") in aquatic food webs.  

PubMed

The Phytomyxea ("plasmodiophorids") including both Plasmodiophorida and Phagomyxida is a monophyletic group of Eukaryotes composed of obligate biotrophic parasites of green plants, brown algae, diatoms and stramenopiles commonly found in many freshwater, soil and marine environments. However, most research on Phytomyxea has been restricted to plant pathogenic species with agricultural importance, thereby missing the huge ecological potential of this enigmatic group of parasites. Members of the Phytomyxea can induce changes in biomass in their hosts (e.g. hypertrophies of the host tissue) under suitable environmental conditions. Upon infection they alter the metabolism of their hosts, consequently changing the metabolic status of their host. This results in an altered chemical composition of the host tissue, which impacts the diversity of species which feed on the tissues of the infected host and on the zoospores produced by the parasites. Furthermore, significant amounts of nutrients derived from the hosts, both primary producers (plants and algae) and primary consumers (litter decomposers and plant parasites [Oomycetes]), can enter the food web at different trophic levels in form of zoospores and resting spores. Large numbers of zoospores and resting spores are produced which can be eaten by secondary and tertiary consumers, such as grazing zooplankton and metazoan filter-feeders. Therefore, these microbes can act as energy-rich nutrient resources which may significantly alter the trophic relationships in fresh water, soil and marine habitats. Based on the presented data, Phytomyxea can significantly contribute to the complexity and energy transfer within food webs. PMID:21339888

Neuhauser, Sigrid; Kirchmair, Martin; Gleason, Frank H

2011-01-01

118

Model of carbon cycling in planktonic food webs  

SciTech Connect

A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. Bacteria, phytoplankton, three trophic levels of zooplankton, and dissolved organic carbon (DOC) and particulate organic carbon (POC) are modeled. The descriptions of bacterial growth and utilization of the various classes of substrate were treated as universal constants in the application of the model to three distinct ecosystems, ranging from oligotrophic to highly eutrophic. The successful application of the model to these diverse ecosystems supports the basic validity of the description of the microbial food web and the dynamics of carbon flux. The model indicates that the dynamics of bacteria and protozoan zooplankton production govern the rates of oxidation of carbon entering the water column. Explicit consideration of these groups would improve the capability of eutrophication models to predict dissolved oxygen dynamics, particularly when projecting responses to loading changes.

Connolly, J.P. [HydroQual, Inc., Mahwah, NJ (United States); Coffin, R.B. [Environmental Protection Agency, Gulf Breeze, FL (United States). Environmental Research Lab.

1995-10-01

119

Coupled predator-prey oscillations in a chaotic food web.  

PubMed

Coupling of several predator-prey oscillations can generate intriguing patterns of synchronization and chaos. Theory predicts that prey species will fluctuate in phase if predator-prey cycles are coupled through generalist predators, whereas they will fluctuate in anti-phase if predator-prey cycles are coupled through competition between prey species. Here, we investigate predator-prey oscillations in a long-term experiment with a marine plankton community. Wavelet analysis of the species fluctuations reveals two predator-prey cycles that fluctuate largely in anti-phase. The phase angles point at strong competition between the phytoplankton species, but relatively little prey overlap among the zooplankton species. This food web architecture is consistent with the size structure of the plankton community, and generates highly dynamic food webs. Continued alternations in species dominance enable coexistence of the prey species through a non-equilibrium 'killing-the-winner' mechanism, as the system shifts back and forth between the two predator-prey cycles in a chaotic fashion. PMID:19845726

Benincà, Elisa; Jöhnk, Klaus D; Heerkloss, Reinhard; Huisman, Jef

2009-10-20

120

Food web-specific biomagnification of persistent organic pollutants.  

PubMed

Substances that accumulate to hazardous levels in living organisms pose environmental and human-health risks, which governments seek to reduce or eliminate. Regulatory authorities identify bioaccumulative substances as hydrophobic, fat-soluble chemicals having high octanol-water partition coefficients (K(OW))(>/=100,000). Here we show that poorly metabolizable, moderately hydrophobic substances with a K(OW) between 100 and 100,000, which do not biomagnify (that is, increase in chemical concentration in organisms with increasing trophic level) in aquatic food webs, can biomagnify to a high degree in food webs containing air-breathing animals (including humans) because of their high octanol-air partition coefficient (K(OA)) and corresponding low rate of respiratory elimination to air. These low K(OW)-high K(OA) chemicals, representing a third of organic chemicals in commercial use, constitute an unidentified class of potentially bioaccumulative substances that require regulatory assessment to prevent possible ecosystem and human-health consequences. PMID:17626882

Kelly, Barry C; Ikonomou, Michael G; Blair, Joel D; Morin, Anne E; Gobas, Frank A P C

2007-07-13

121

Invasions and Extinctions Reshape Coastal Marine Food Webs  

PubMed Central

The biodiversity of ecosystems worldwide is changing because of species loss due to human-caused extinctions and species gain through intentional and accidental introductions. Here we show that the combined effect of these two processes is altering the trophic structure of food webs in coastal marine systems. This is because most extinctions (?70%) occur at high trophic levels (top predators and other carnivores), while most invasions are by species from lower trophic levels (70% macroplanktivores, deposit feeders, and detritivores). These opposing changes thus alter the shape of marine food webs from a trophic pyramid capped by a diverse array of predators and consumers to a shorter, squatter configuration dominated by filter feeders and scavengers. The consequences of the simultaneous loss of diversity at top trophic levels and gain at lower trophic levels is largely unknown. However, current research suggests that a better understanding of how such simultaneous changes in diversity can impact ecosystem function will be required to manage coastal ecosystems and forecast future changes.

Byrnes, Jarrett E.; Reynolds, Pamela L.; Stachowicz, John J.

2007-01-01

122

Nutritional constraints in terrestrial and freshwater food webs.  

PubMed

Biological and environmental contrasts between aquatic and terrestrial systems have hindered analyses of community and ecosystem structure across Earth's diverse habitats. Ecological stoichiometry provides an integrative approach for such analyses, as all organisms are composed of the same major elements (C, N, P) whose balance affects production, nutrient cycling, and food-web dynamics. Here we show both similarities and differences in the C:N:P ratios of primary producers (autotrophs) and invertebrate primary consumers (herbivores) across habitats. Terrestrial food webs are built on an extremely nutrient-poor autotroph base with C:P and C:N ratios higher than in lake particulate matter, although the N:P ratios are nearly identical. Terrestrial herbivores (insects) and their freshwater counterparts (zooplankton) are nutrient-rich and indistinguishable in C:N:P stoichiometry. In both lakes and terrestrial systems, herbivores should have low growth efficiencies (10-30%) when consuming autotrophs with typical carbon-to-nutrient ratios. These stoichiometric constraints on herbivore growth appear to be qualitatively similar and widespread in both environments. PMID:11117743

Elser, J J; Fagan, W F; Denno, R F; Dobberfuhl, D R; Folarin, A; Huberty, A; Interlandi, S; Kilham, S S; McCauley, E; Schulz, K L; Siemann, E H; Sterner, R W

2000-11-30

123

Food and Beverage Brands that Market to Children and Adolescents on the Internet: A Content Analysis of Branded Web Sites  

ERIC Educational Resources Information Center

|Objective: To identify food and beverage brand Web sites featuring designated children's areas, assess marketing techniques present on those industry Web sites, and determine nutritional quality of branded food items marketed to children. Design: Systematic content analysis of food and beverage brand Web sites and nutrient analysis of food and…

Henry, Anna E.; Story, Mary

2009-01-01

124

Organochlorine pollution in tropical rivers (Guadeloupe): Role of ecological factors in food web bioaccumulation  

Microsoft Academic Search

Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of

Sophie Coat; Dominique Monti; Pierre Legendre; Claude Bouchon; Félix Massat; Gilles Lepoint

2011-01-01

125

Changes in the pelagic microbial food web due to artificial eutrophication  

Microsoft Academic Search

The effect of nutrient enrichment on the structure and carbon flow in the pelagic microbial food web was studied in mesocosm experiments using seawater from the northern Baltic Sea. The experiments included food webs of at least four trophic levels; (1) phytoplankton–bacteria, (2) flagellates, (3) ciliates and (4) mesozooplankton. In the enriched treatments high autotrophic growth rates were observed, followed

Agneta Andersson; Kristina Samuelsson; Pia Haecky; Jan Albertsson

2006-01-01

126

Food web structure of sandy beaches: Temporal and spatial variation using stable isotope analysis  

Microsoft Academic Search

The food web structure of two sandy beach ecosystems with contrasting morphodynamics (dissipative vs. reflective) was examined using stable carbon (?13C) and nitrogen (?15N) isotope analysis. Organic matter sources (POM: particulate organic matter; SOM: sediment organic matter) and consumers (zooplankton, benthic invertebrates and fishes) were sampled seasonally in both sandy beaches. Food webs significantly differed between beaches: even though both

Leandro Bergamino; Diego Lercari; Omar Defeo

2011-01-01

127

Food Webs, Risks of Alien Enemies and Reform of Biological Control  

Microsoft Academic Search

As ilwasions of alien species mount, biological control will become an increasingly important tool of conservation and agriculture. In an effort to understand indirect interactions in biological control, we review food web ecology in terms of resource competition, trophic cascades, intraguild predation, apparent competition, omnivory and a diverse set of tritrophic interactions. The most inclusive study suggests that food webs

D. R. Strong; R. W. Pemberton

2001-01-01

128

Comparison of the structure of lower and upper estuary food webs for Yaquina Bay (OR)  

EPA Science Inventory

Food web models can be used to estimate effects of water quality, habitat distribution or species loss on productivity, carbon flow and ecosystem service production in Pacific NW estuaries. Here we present a comparison of floral and faunal data used to parameterize food web mode...

129

Can You Build It? Using Manipulatives to Assess Student Understanding of Food-Web Concepts  

ERIC Educational Resources Information Center

|This article outlines an exercise that assesses student knowledge of food-web and energy-flow concepts. Students work in teams and use manipulatives to build food-web models based on criteria assigned by the instructor. The models are then peer reviewed according to guidelines supplied by the instructor.|

Grumbine, Richard

2012-01-01

130

Defining and Measuring Trophic Role Similarity in Food Webs Using Regular Equivalence  

Microsoft Academic Search

We present a graph theoretic model of analysing food web structure called regular equivalence. Regular equivalence is a method for partitioning the species in a food web into “isotrophic classes” that play the same structural roles, even if they are not directly consuming the same prey or if they do not share the same predators. We contrast regular equivalence models,

JOSEPH J. LUCZKOVICH; STEPHEN P. BORGATTI; JEFFREY C. JOHNSON; MARTIN G. EVERETT

2003-01-01

131

Exploring Fish Diversity as a Determinant of Ecosystem Properties in Aquatic Food Webs  

ERIC Educational Resources Information Center

|Dramatic biodiversity changes occurring globally from species loss and invasion have altered native food webs and ecosystem processes. My research objectives are to understand the consequences of fish diversity to freshwater systems by (1) examining the food web consequences of multiple top predators, (2) determining how biodiversity influences…

Carey, Michael P.

2009-01-01

132

Food chain length and omnivory determine the stability of a marine subtidal food web.  

PubMed

1. Using a subtidal marine food web as a model system, we examined how food chain length (predators present or absent) and the prevalence of omnivory influenced temporal stability (and its components) of herbivores and plants. We held the density of top predators constant but manipulated their identity to generate a gradient in omnivory prevalence. 2. We measured temporal stability as the inverse of the coefficient of variation of abundance over time. Predators and omnivory could influence temporal stability through effects on abundance (the 'abundance' effect), summed variance across taxa (the 'portfolio effect') or summed covariances among taxa (the 'covariance effect'). 3. We found that increasing food chain length by predator addition destabilized aggregate herbivore abundance through their cascading effects on abundances. Thus, predators destabilized herbivores through the overyielding effect. We also found that the stability of herbivore abundance and microalgae declined with increasing prevalence of omnivory among top predators. Aggregate macroalgae was not affected, but the stability of one algal taxon increased with the prevalence of omnivory. 4. Our results suggest that herbivores are more sensitive than plants to changes in food web structure because of predator additions by invasion or deletions such as might occur via harvesting and habitat loss. PMID:21250990

Long, Zachary T; Bruno, John F; Duffy, J Emmett

2011-01-20

133

Food webs: a ladder for picking strawberries or a practical tool for practical problems?  

PubMed Central

While food webs have provided a rich vein of research material over the last 50 years, they have largely been the subject matter of the pure ecologist working in natural habitats. While there are some notable exceptions to this trend, there are, as I explain in this paper, many applied questions that could be answered using a food web approach. The paper is divided into two halves. The first half provides a brief review of six areas where food webs have begun to be used as an applied tool: restoration ecology, alien species, biological control, conservation ecology, habitat management and global warming. The second half outlines five areas in which a food web approach could prove very rewarding: urban ecology, agroecology, habitat fragmentation, cross-habitat food webs and ecosystem services.

Memmott, Jane

2009-01-01

134

The Bering Sea—A dynamic food web perspective  

NASA Astrophysics Data System (ADS)

The Bering Sea is a high-latitude, semi-enclosed sea that supports extensive fish, seabird, marine mammal, and invertebrate populations and some of the world's most productive fisheries. The region consists of several distinct biomes that have undergone wide-scale population variation, in part due to fisheries, but also in part due to the effects of interannual and decadal-scale climatic variation. While recent decades of ocean observation have highlighted possible links between climate and species fluctuations, mechanisms linking climate and population fluctuations are only beginning to be understood. Here, we examine the food webs of Bering Sea ecosystems with particular reference to some key shifts in widely distributed, abundant fish populations and their links with climate variation. Both climate variability and fisheries have substantially altered the Bering Sea ecosystem in the past, but their relative importance in shaping the current ecosystem state remains uncertain.

Aydin, Kerim; Mueter, Franz

2007-11-01

135

Food-web constraints on biodiversity-ecosystem functioning relationships  

PubMed Central

The consequences of biodiversity loss for ecosystem functioning and ecosystem services have aroused considerable interest during the past decade. Recent work has focused mainly on the impact of species diversity within single trophic levels, both experimentally and theoretically. Experiments have usually showed increased plant biomass and productivity with increasing plant diversity. Changes in biodiversity, however, may affect ecosystem processes through trophic interactions among species as well. An important current challenge is to understand how these trophic interactions affect the relationship between biodiversity and ecosystem functioning. Here we present a mechanistic model of an ecosystem with multiple trophic levels in which plants compete for a limiting soil nutrient. In contrast to previous studies that focused on single trophic levels, we show that plant biomass does not always increase with plant diversity and that changes in biodiversity can lead to complex if predictable changes in ecosystem processes. Our analysis demonstrates that food-web structure can profoundly influence ecosystem properties.

Thebault, Elisa; Loreau, Michel

2003-01-01

136

Biological vs. Physical Mixing Effects on Benthic Food Web Dynamics  

PubMed Central

Biological particle mixing (bioturbation) and solute transfer (bio-irrigation) contribute extensively to ecosystem functioning in sediments where physical mixing is low. Macrobenthos transports oxygen and organic matter deeper into the sediment, thereby likely providing favourable niches to lower trophic levels (i.e., smaller benthic animals such as meiofauna and bacteria) and thus stimulating mineralisation. Whether this biological transport facilitates fresh organic matter assimilation by the metazoan lower part of the food web through niche establishment (i.e., ecosystem engineering) or rather deprives them from food sources, is so far unclear. We investigated the effects of the ecosystem engineers Lanice conchilega (bio-irrigator) and Abra alba (bioturbator) compared to abiotic physical mixing events on survival and food uptake of nematodes after a simulated phytoplankton bloom. The 13C labelled diatom Skeletonema costatum was added to 4 treatments: (1) microcosms containing the bioturbator, (2) microcosms containing the bio-irrigator, (3) control microcosms and (4) microcosms with abiotic manual surface mixing. Nematode survival and subsurface peaks in nematode density profiles were most pronounced in the bio-irrigator treatment. However, nematode specific uptake (??13C) of the added diatoms was highest in the physical mixing treatment, where macrobenthos was absent and the diatom 13C was homogenised. Overall, nematodes fed preferentially on bulk sedimentary organic material rather than the added diatoms. The total C budget (µg C m?2), which included TO13C remaining in the sediment, respiration, nematode and macrobenthic uptake, highlighted the limited assimilation by the metazoan benthos and the major role of bacterial respiration. In summary, bioturbation and especially bio-irrigation facilitated the lower trophic levels mainly over the long-term through niche establishment. Since the freshly added diatoms represented only a limited food source for nematodes, the macrobenthic effect was more pronounced in niche establishment than the negative structuring effects such as competition.

Braeckman, Ulrike; Provoost, Pieter; Moens, Tom; Soetaert, Karline; Middelburg, Jack J.; Vincx, Magda; Vanaverbeke, Jan

2011-01-01

137

Terrestrial subsidies to lake food webs: an experimental approach.  

PubMed

Cross-ecosystem movements of material and energy are ubiquitous. Aquatic ecosystems typically receive material that also includes organic matter from the surrounding catchment. Terrestrial-derived (allochthonous) organic matter can enter aquatic ecosystems in dissolved or particulate form. Several studies have highlighted the importance of dissolved organic carbon to aquatic consumers, but less is known about allochthonous particulate organic carbon (POC). Similarly, most studies showing the effects of allochthonous organic carbon (OC) on aquatic consumers have investigated pelagic habitats; the effects of allochthonous OC on benthic communities are less well studied. Allochthonous inputs might further decrease primary production through light reduction, thereby potentially affecting autotrophic resource availability to consumers. Here, an enclosure experiment was carried out to test the importance of POC input and light availability on the resource use in a benthic food web of a clear-water lake. Corn starch (a C(4) plant) was used as a POC source due to its insoluble nature and its distinct carbon stable isotope value (?(13)C). The starch carbon was closely dispersed over the bottom of the enclosures to study the fate of a POC source exclusively available to sediment biota. The addition of starch carbon resulted in a clear shift in the isotopic signature of surface-dwelling herbivorous and predatory invertebrates. Although the starch carbon was added solely to the sediment surface, the carbon originating from the starch reached zooplankton. We suggest that allochthonous POC can subsidize benthic food webs directly and can be further transferred to pelagic systems, thereby highlighting the importance of benthic pathways for pelagic habitats. PMID:21971586

Bartels, Pia; Cucherousset, Julien; Gudasz, Cristian; Jansson, Mats; Karlsson, Jan; Persson, Lennart; Premke, Katrin; Rubach, Anja; Steger, Kristin; Tranvik, Lars J; Eklöv, Peter

2011-10-05

138

Watershed and Lake Influences on the Energetic Base of Coastal Wetland Food Webs across the Great Lakes Basin  

EPA Science Inventory

This manuscript examines the responses of Great Lakes coastal wetland food webs to nutrient enrichment and identifies three classes of systems whose food webs respond differently. Or is that differentially? Anyway, coastal wetlands with relatively long hydraulic residence times ...

139

Lipids of Antarctic Ocean amphipods: food chain interactions and the occurrence of novel biomarkers  

Microsoft Academic Search

Antarctic hyperiid (Themisto gaudichaudi, Hyperia macrocephalus, and Primno macropa) and gammarid amphipods (Eusirus perdentatus and Orchomene rossi) were collected near Elephant Island, located in the South Shetland Islands, during January and February 1997 and 1998. Polar lipid (PL) was the major lipid class in all amphipods (58–88% of total lipid), except for T. gaudichaudi in which triacylglycerol (TAG) was dominant

Matthew M Nelson; Ben D Mooney; Peter D Nichols; Charles F Phleger

2001-01-01

140

Food web architecture and basal resources interact to determine biomass and stoichiometric cascades along a benthic food web.  

PubMed

Understanding the effects of predators and resources on primary producers has been a major focus of interest in ecology. Within this context, the trophic cascade concept especially concerning the pelagic zone of lakes has been the focus of the majority of these studies. However, littoral food webs could be especially interesting because base trophic levels may be strongly regulated by consumers and prone to be light limited. In this study, the availability of nutrients and light and the presence of an omnivorous fish (Hyphessobrycon bifasciatus) were manipulated in enclosures placed in a humic coastal lagoon (Cabiúnas Lagoon, Macaé - RJ) to evaluate the individual and interactive effects of resource availability (nutrients and light) and food web configuration on the biomass and stoichiometry of periphyton and benthic grazers. Our findings suggest that light and nutrients interact to determine periphyton biomass and stoichiometry, which propagates to the consumer level. We observed a positive effect of the availability of nutrients on periphytic biomass and grazers' biomass, as well as a reduction of periphytic C?N?P ratios and an increase of grazers' N and P content. Low light availability constrained the propagation of nutrient effects on periphyton biomass and induced higher periphytic C?N?P ratios. The effects of fish presence strongly interacted with resource availability. In general, a positive effect of fish presence was observed for the total biomass of periphyton and grazer's biomass, especially with high resource availability, but the opposite was found for periphytic autotrophic biomass. Fish also had a significant effect on periphyton stoichiometry, but no effect was observed on grazers' stoichiometric ratios. In summary, we observed that the indirect effect of fish predation on periphyton biomass might be dependent on multiple resources and periphyton nutrient stoichiometric variation can affect consumers' stoichiometry. PMID:21789234

Guariento, Rafael D; Carneiro, Luciana S; Caliman, Adriano; Leal, João J F; Bozelli, Reinaldo L; Esteves, Francisco A

2011-07-18

141

Polar Chains and Webs  

NSDL National Science Digital Library

In this activity students will put into practice the evaluation component of the scientific method while comparing and contrasting the similarities and differences of the food chains and webs of polar animal life. Students will learn about classification and ecology through the real life experiences and connections of professionals who have been in the field. Through developing skills in teamwork and planning, this activity will allow students to understand the similarities and differences of the Arctic and Antarctic regions, their animal life and the food chains and webs supporting them. Students will: locate the Arctic region and Antarctica on globes and maps; identify similarities and differences in their animal life; and show and explain the food chain of a specific species and the food web of that species while discussing their interrelationships.

Kolb, Sandra; Griffith, Rick

142

Trophic transfer of contaminants in a changing arctic marine food web: Cumberland Sound, Nunavut, Canada.  

PubMed

Contaminant dynamics in arctic marine food webs may be impacted by current climate-induced food web changes including increases in transient/subarctic species. We quantified food web organochlorine transfer in the Cumberland Sound (Nunavut, Canada) arctic marine food web in the presence of transient species using species-specific biomagnification factors (BMFs), trophic magnification factors (TMFs), and a multifactor model that included ?(15)N-derived trophic position and species habitat range (transient versus resident), and also considered ?(13)C-derived carbon source, thermoregulatory group, and season. Transient/subarctic species relative to residents had higher prey-to-predator BMFs of biomagnifying contaminants (1.4 to 62 for harp seal, Greenland shark, and narwhal versus 1.1 to 20 for ringed seal, arctic skate, and beluga whale, respectively). For contaminants that biomagnified in a transient-and-resident food web and a resident-only food web scenario, TMFs were higher in the former (2.3 to 10.1) versus the latter (1.7 to 4.0). Transient/subarctic species have higher tissue contaminant levels and greater BMFs likely due to higher energetic requirements associated with long-distance movements or consumption of more contaminated prey in regions outside of Cumberland Sound. These results demonstrate that, in addition to climate change-related long-range transport/deposition/revolatilization changes, increasing numbers of transient/subarctic animals may alter food web contaminant dynamics. PMID:22957980

McKinney, Melissa A; McMeans, Bailey C; Tomy, Gregg T; Rosenberg, Bruno; Ferguson, Steven H; Morris, Adam; Muir, Derek C G; Fisk, Aaron T

2012-09-07

143

Perfluorinated compounds in the Antarctic region: ocean circulation provides prolonged protection from distant sources.  

PubMed

In order to investigate the extent to which Perfluorinated Contaminants (PFCs) have permeated the Southern Ocean food web to date, a range of Antarctic, sub-Antarctic and Antarctic-migratory biota were analysed for key ionic PFCs. Based upon the geographical distribution pattern and ecology of biota with detectable vs. non-detectable PFC burdens, an evaluation of the potential contributory roles of alternative system input pathways is made. Our analytical findings, together with previous reports, reveal only the occasional occurrence of PFCs in migratory biota and vertebrate predators with foraging ranges extending into or north of the Antarctic Circumpolar Current (ACC). Geographical contamination patterns observed correspond most strongly with those expected from delivery via hydrospheric transport as governed by the unique oceanographic features of the Southern Ocean. We suggest that hydrospheric transport will form a slow, but primary, input pathway of PFCs to the Antarctic region. PMID:20584566

Bengtson Nash, Susan; Rintoul, Stephen R; Kawaguchi, So; Staniland, Iain; van den Hoff, John; Tierney, Megan; Bossi, Rossana

2010-07-02

144

Designing an illustrated food web to teach ecological concepts: challenges and solutions.  

PubMed

The core idea in ecology is that all living things are interconnected. Food webs are an efficient way to communicate this message, and though they can be depicted non-pictorially, illustrated food webs are far more appealing to the general audience. Because of their inherent complexity, however, they present a considerable organizational and design challenge for the illustrator. Based on seven years of teaching illustrated food webs to students in Biomedical Communications at the University of Toronto, this paper outlines those challenges and presents solutions. PMID:10216827

Godkin, C M

1999-01-01

145

A unifying approach for food webs, phylogeny, social networks, and statistics  

PubMed Central

A food web consists of nodes, each consisting of one or more species. The role of each node as predator or prey determines the trophic relations that weave the web. Much effort in trophic food web research is given to understand the connectivity structure, or the nature and degree of dependence among nodes. Social network analysis (SNA) techniques—quantitative methods commonly used in the social sciences to understand network relational structure—have been used for this purpose, although postanalysis effort or biological theory is still required to determine what natural factors contribute to the feeding behavior. Thus, a conventional SNA alone provides limited insight into trophic structure. Here we show that by using novel statistical modeling methodologies to express network links as the random response of within- and internode characteristics (predictors), we gain a much deeper understanding of food web structure and its contributing factors through a unified statistical SNA. We do so for eight empirical food webs: Phylogeny is shown to have nontrivial influence on trophic relations in many webs, and for each web trophic clustering based on feeding activity and on feeding preference can differ substantially. These and other conclusions about network features are purely empirical, based entirely on observed network attributes while accounting for biological information built directly into the model. Thus, statistical SNA techniques, through statistical inference for feeding activity and preference, provide an alternative perspective of trophic clustering to yield comprehensive insight into food web structure.

Chiu, Grace S.; Westveld, Anton H.

2011-01-01

146

Potential for Biomagnification of Contaminants within Marine and Freshwater Food Webs.  

National Technical Information Service (NTIS)

This report reviews the literature on the biomagnification of toxic heavy metals and organic contaminants within marine and freshwater food webs and is limited to gill-breathing species. The toxic metals included arsenic, cadmium, copper, lead mercury (bo...

S. H. Kay

1984-01-01

147

Predator hunting mode influences patterns of prey use from grazing and epigeic food webs.  

PubMed

Multichannel omnivory by generalist predators, especially the use of both grazing and epigeic prey, has the potential to increase predator abundance and decrease herbivore populations. However, predator use of the epigeic web (soil surface detritus/microbe/algae consumers) varies considerably for reasons that are poorly understood. We therefore used a stable isotope approach to determine whether prey availability and predator hunting style (active hunting vs. passive web-building) impacted the degree of multichannel omnivory by the two most abundant predators on an intertidal salt marsh, both spiders. We found that carbon isotopic values of herbivores remained constant during the growing season, while values for epigeic feeders became dramatically more enriched such that values for the two webs converged in August. Carbon isotopic values for both spider species remained midway between the two webs as values for epigeic feeders shifted, indicating substantial use of prey from both food webs by both spider species. As the season progressed, prey abundance in the grazing food web increased while prey abundance in the epigeic web remained constant or declined. In response, prey consumption by the web-building spider shifted toward the grazing web to a much greater extent than did consumption by the hunting spider, possibly because passive web-capture is more responsive to changes in prey availability. Although both generalist predator species engaged in multichannel omnivory, hunting mode influenced the extent to which these predators used prey from the grazing and epigeic food webs, and could thereby influence the strength of trophic cascades in both food webs. PMID:22926724

Wimp, Gina M; Murphy, Shannon M; Lewis, Danny; Douglas, Margaret R; Ambikapathi, Ramya; Van-Tull, Lie'Ann; Gratton, Claudio; Denno, Robert F

2012-08-25

148

Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat  

Microsoft Academic Search

BackgroundFood web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood.Methodology\\/Principal FindingsUsing

Amanda C. Spivak; Elizabeth A. Canuel; J. Emmett Duffy; J. Paul Richardson; John F. Bruno

2009-01-01

149

Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes  

Microsoft Academic Search

The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable\\u000a isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. ?13C and ?15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the\\u000a literature. ?13C of

John K. Pinnegar; N. V. C. Polunin

2000-01-01

150

Food Marketing on Popular Children’s Web Sites: A Content Analysis  

Microsoft Academic Search

In 2006 the Institute of Medicine (IOM) concluded that food marketing was a contributor to childhood obesity in the United States. One recommendation of the IOM committee was for research on newer marketing venues, such as Internet Web sites. The purpose of this cross-sectional study was to answer the IOM’s call by examining food marketing on popular children’s Web sites.

Lisa M. Alvy; Sandra L. Calvert

2008-01-01

151

13 C label identifies eelgrass ( Zostera marina ) Carbon in an Alaskan estuarine food web  

Microsoft Academic Search

The food web of Izembek Lagoon, Alaska draws most of its carbon from eelgrass (Zostera marina) and phytoplankton. The13C:12C ratios of these primary producers are sufficiently different to enable their contributions to consumers to be estimated from consumer13C:12C ratios. Although the technique is conceptually simple, carbon inputs from other sources and isotope fractionations occurring in the food web limit its

T. McConnaughey; C. P. McRoy

1979-01-01

152

Food web topology and parasites in the pelagic zone of a subarctic lake  

USGS Publications Warehouse

Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3. More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4. For trophically transmitted parasites, the number of parasite-host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5. The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. ?? 2009 British Ecological Society.

Amundsen, P. -A.; Lafferty, K. D.; Knudsen, R.; Primicerio, R.; Klemetsen, A.; Kuris, A. M.

2009-01-01

153

Spatial differences in East scotia ridge hydrothermal vent food webs: influences of chemistry, microbiology and predation on trophodynamics.  

PubMed

The hydrothermal vents on the East Scotia Ridge are the first to be explored in the Antarctic and are dominated by large peltospiroid gastropods, stalked barnacles (Vulcanolepas sp.) and anomuran crabs (Kiwa sp.) but their food webs are unknown. Vent fluid and macroconsumer samples were collected at three vent sites (E2, E9N and E9S) at distances of tens of metres to hundreds of kilometres apart with contrasting vent fluid chemistries to describe trophic interactions and identify potential carbon fixation pathways using stable isotopes. ?(13)C of dissolved inorganic carbon from vent fluids ranged from -4.6‰ to 0.8‰ at E2 and from -4.4‰ to 1.5‰ at E9. The lowest macroconsumer ?(13)C was observed in peltospiroid gastropods (-30.0‰ to -31.1‰) and indicated carbon fixation via the Calvin-Benson-Bassham (CBB) cycle by endosymbiotic gamma-Proteobacteria. Highest ?(13)C occurred in Kiwa sp. (-19.0‰ to -10.5‰), similar to that of the epibionts sampled from their ventral setae. Kiwa sp. ?(13)C differed among sites, which were attributed to spatial differences in the epibiont community and the relative contribution of carbon fixed via the reductive tricarboxylic acid (rTCA) and CBB cycles assimilated by Kiwa sp. Site differences in carbon fixation pathways were traced into higher trophic levels e.g. a stichasterid asteroid that predates on Kiwa sp. Sponges and anemones at the periphery of E2 assimilated a proportion of epipelagic photosynthetic primary production but this was not observed at E9N. Differences in the ?(13)C and ?(34)S values of vent macroconsumers between E2 and E9 sites suggest the relative contributions of photosynthetic and chemoautotrophic carbon fixation (rTCA v CBB) entering the hydrothermal vent food webs vary between the sites. PMID:23762393

Reid, William D K; Sweeting, Christopher J; Wigham, Ben D; Zwirglmaier, Katrin; Hawkes, Jeffrey A; McGill, Rona A R; Linse, Katrin; Polunin, Nicholas V C

2013-06-07

154

Methane Carbon Supports Aquatic Food Webs to the Fish Level  

PubMed Central

Large amounts of the greenhouse gas methane (CH4) are produced by anaerobic mineralization of organic matter in lakes. In spite of extensive freshwater CH4 emissions, most of the CH4 is typically oxidized by methane oxidizing bacteria (MOB) before it can reach the lake surface and be emitted to the atmosphere. In turn, it has been shown that the CH4-derived biomass of MOB can provide the energy and carbon for zooplankton and macroinvertebrates. In this study, we demonstrate the presence of specific fatty acids synthesized by MOB in fish tissues having low carbon stable isotope ratios. Fish species, zooplankton, macroinvertebrates and the water hyacinth Eichhornia crassipes were collected from a shallow lake in Brazil and analyzed for fatty acids (FA) and carbon stable isotope ratios (?13C). The fatty acids 16?1?8c, 16?1?8t, 16?1?6c, 16?1?5t, 18?1?8c and 18?1?8t were used as signature for MOB. The ?13C ratios varied from ?27.7‰ to ?42.0‰ and the contribution of MOB FA ranged from 0.05% to 0.84% of total FA. Organisms with higher total content of MOB FAs presented lower ?13C values (i.e. they were more depleted in 13C), while organisms with lower content of MOB signature FAs showed higher ?13C values. An UPGMA cluster analysis was carried out to distinguish grouping of organisms in relation to their MOB FA contents. This combination of stable isotope and fatty acid tracers provides new evidence that assimilation of methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level.

Sanseverino, Angela M.; Bastviken, David; Sundh, Ingvar; Pickova, Jana; Enrich-Prast, Alex

2012-01-01

155

Methane carbon supports aquatic food webs to the fish level.  

PubMed

Large amounts of the greenhouse gas methane (CH(4)) are produced by anaerobic mineralization of organic matter in lakes. In spite of extensive freshwater CH(4) emissions, most of the CH(4) is typically oxidized by methane oxidizing bacteria (MOB) before it can reach the lake surface and be emitted to the atmosphere. In turn, it has been shown that the CH(4)-derived biomass of MOB can provide the energy and carbon for zooplankton and macroinvertebrates. In this study, we demonstrate the presence of specific fatty acids synthesized by MOB in fish tissues having low carbon stable isotope ratios. Fish species, zooplankton, macroinvertebrates and the water hyacinth Eichhornia crassipes were collected from a shallow lake in Brazil and analyzed for fatty acids (FA) and carbon stable isotope ratios (?(13)C). The fatty acids 16:1?8c, 16:1?8t, 16:1?6c, 16:1?5t, 18:1?8c and 18:1?8t were used as signature for MOB. The ?(13)C ratios varied from -27.7‰ to -42.0‰ and the contribution of MOB FA ranged from 0.05% to 0.84% of total FA. Organisms with higher total content of MOB FAs presented lower ?(13)C values (i.e. they were more depleted in (13)C), while organisms with lower content of MOB signature FAs showed higher ?(13)C values. An UPGMA cluster analysis was carried out to distinguish grouping of organisms in relation to their MOB FA contents. This combination of stable isotope and fatty acid tracers provides new evidence that assimilation of methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level. PMID:22880091

Sanseverino, Angela M; Bastviken, David; Sundh, Ingvar; Pickova, Jana; Enrich-Prast, Alex

2012-08-07

156

Food Chains & Webs. A Multimedia CD-ROM. [CD-ROM].  

ERIC Educational Resources Information Center

This CD-ROM is designed for classroom and individual use to teach and learn about food chains and food webs. Integrated animations, custom graphics, three-dimensional representations, photographs, and sound are featured for use in user-controlled activities. Interactive lessons are available to reinforce the subject material. Pre- and post-testing…

2001

157

Community food web, decomposition and nitrogen mineralisation in a stratified Scots pine forest soil  

Microsoft Academic Search

A soil community food web model was used to improve the understanding of what factors govern the mineralisation of nutrients and carbon and the decay of dead organic matter. The model derives the rates of C and N mineralisation by organisms by splitting their uptake rate of food resources into a rate at which faeces or prey remains are added

Matty Berg; Ruiter de P. C; Wim Didden; Martien Janssen; Ton Schouten; Herman Verhoef

2001-01-01

158

Interaction strength combinations and the overfishing of a marine food web  

Microsoft Academic Search

The stability of ecological communities largely depends on the strength of interactions between predators and their prey. Here we show that these interaction strengths are structured nonrandomly in a large Caribbean marine food web. Specifically, the cooccurrence of strong interactions on two consecutive levels of food chains occurs less frequently than expected by chance. Even when they occur, these strongly

Jordi Bascompte; Carlos J. Melián; Enric Sala

2005-01-01

159

Defining ecospace of Arctic marine food webs using a novel quantitative approach  

NASA Astrophysics Data System (ADS)

The Arctic is currently facing unprecedented change with developmental, physical and climatological changes. Food webs within the marine Arctic environment are highly susceptible to anthropogenic stressors and have thus far been understudied. Stable isotopes, in conjunction with a novel set of metrics, may provide a framework that allows us to understand which areas of the Arctic are most vulnerable to change. The objective of this study was to use linear distance metrics applied to stable isotopes to a) define and quantify four Arctic marine food webs in ecospace; b) enable quantifiable comparisons among the four food webs and with other ecosystems; and, c) evaluate vulnerability of the four food webs to anthropogenic stressors such as climate change. The areas studied were Hudson Bay, Beaufort Sea, Lancaster Sound and North Water Polynya. Each region was selected based on the abundance of previous research and published and available stable isotope data in peer-review literature. We selected species to cover trophic levels ranging from particulate matter to polar bears with consideration of pelagic, benthic and ice-associated energy pathways. We interpret higher diversity in baseline carbon energy as signifying higher stability in food web structure. Based on this, the Beaufort Sea food web had the highest stability; the Beaufort Sea food web occupied the largest isotopic niche space and was supported by multiple carbon sources. Areas with top-down control system, such as Lancaster Sound and North Water Polynya, would be the first to experience an increase in trophic redundancy and possible hardships from external stressors, as they have fewer basal carbon sources and greater numbers of mid-high level consumers. We conclude that a diverse carbon energy based ecosystem such as the Beaufort Sea and Hudson Bay regions are more resilient to change than a top down control system.

Gale, M.; Loseto, L. L.

2011-12-01

160

Vertical flux of biogenic carbon in the ocean: Is there food web control?  

SciTech Connect

Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions. 29 refs., 3 figs., 1 tab.

Rivkin, R.B.; Legendre, L.; Deibel, D. [and others

1996-05-24

161

Cycling Through the Food Web: Let's Go on a Research Cruise  

NSDL National Science Digital Library

This site presents an account of a research cruise to investigate how the food webs in different oceanic habitats vary. The scientists wanted to see ocean life in its natural environment and conduct experiments that would not be possible in the laboratory. They looked specifically at three types of ocean habitat: the open ocean, the continental shelf, and an upwelling area. The researchers were hoping to learn the answers to two questions: 'How well do the actual marine food webs match our food chain models for the three habitats?' and 'How does the microbial community in each food web change with depth?'. Students can follow their research and fill out an activity and question checklist as they go along. There is also a page of information for teachers.

162

Nutrition content of food and beverage products on Web sites popular with children.  

PubMed

We assessed the nutritional quality of branded food and beverage products advertised on 28 Web sites popular with children. Of the 77 advertised products for which nutritional information was available, 49 met Institute of Medicine criteria for foods to avoid, 23 met criteria for foods to neither avoid nor encourage, and 5 met criteria for foods to encourage. There is a need for further research on the nature and extent of food and beverage advertising online to aid policymakers as they assess the impact of this marketing on children. PMID:19443816

Lingas, Elena O; Dorfman, Lori; Bukofzer, Eliana

2009-05-14

163

Food web structure in the high Arctic Canada Basin: evidence from d 13 C and d 15 N analysis  

Microsoft Academic Search

The food-web structure of the Arctic deep Canada Basin was investigated in summer 2002 using carbon and nitrogen stable isotope tracers. Overall food-web length of the range of organisms sampled occupied four trophic levels, based on 3.8‰ trophic level enrichment (? 15N range: 5.3–17.7‰). It was, thus, 0.5–1 trophic levels longer than food webs in both Arctic shelf and temperate

K. Iken; BA Bluhm; R. Gradinger

2005-01-01

164

Species Richness and Trophic Diversity Increase Decomposition in a Co-Evolved Food Web  

PubMed Central

Ecological communities show great variation in species richness, composition and food web structure across similar and diverse ecosystems. Knowledge of how this biodiversity relates to ecosystem functioning is important for understanding the maintenance of diversity and the potential effects of species losses and gains on ecosystems. While research often focuses on how variation in species richness influences ecosystem processes, assessing species richness in a food web context can provide further insight into the relationship between diversity and ecosystem functioning and elucidate potential mechanisms underpinning this relationship. Here, we assessed how species richness and trophic diversity affect decomposition rates in a complete aquatic food web: the five trophic level web that occurs within water-filled leaves of the northern pitcher plant, Sarracenia purpurea. We identified a trophic cascade in which top-predators — larvae of the pitcher-plant mosquito — indirectly increased bacterial decomposition by preying on bactivorous protozoa. Our data also revealed a facultative relationship in which larvae of the pitcher-plant midge increased bacterial decomposition by shredding detritus. These important interactions occur only in food webs with high trophic diversity, which in turn only occur in food webs with high species richness. We show that species richness and trophic diversity underlie strong linkages between food web structure and dynamics that influence ecosystem functioning. The importance of trophic diversity and species interactions in determining how biodiversity relates to ecosystem functioning suggests that simply focusing on species richness does not give a complete picture as to how ecosystems may change with the loss or gain of species.

Baiser, Benjamin; Ardeshiri, Roxanne S.; Ellison, Aaron M.

2011-01-01

165

Is benthic food web structure related to diversity of marine macrobenthic communities?  

NASA Astrophysics Data System (ADS)

Numerical structure and the organisation of food webs within macrozoobenthic communities has been assessed in the European waters (Svalbard, Barents Sea, Baltic Sea, North Sea, Atlantic Ocean and the Mediterranean Sea) to address the interactions between biodiversity and ecosystem functioning. Abundance and classical species diversity indices (S, H?, J) of macrofaunal communities were related to principal attributes of food webs (relative trophic level and food chain length, FCL) that were determined from carbon and nitrogen stable isotope values. Structure of marine macrobenthos varies substantially at a geographical scale; total abundance ranges from 63 ind. m-2 to 34,517 ind. m-2, species richness varies from 3 to 166 and the Shannon-Weaver diversity index from 0.26 to 3.26 while Pielou’s evenness index is below 0.73. The major source of energy for macrobenthic communities is suspended particulate organic matter, consisting of phytoplankton and detrital particles, sediment particulate organic matter, and microphytobenthos in varying proportions. These food sources support the presence of suspension- and deposit-feeding communities, which dominate numerically on the sea floor. Benthic food webs include usually four to five trophic levels (FCL varies from 3.08 to 4.86). Most species are assigned to the second trophic level (primary consumers), fewer species are grouped in the third trophic level (secondary consumers), and benthic top predators are the least numerous. Most species cluster primarily at the lowest trophic level that is consistent with the typical organization of pyramidal food webs. Food chain length increases with biodiversity, highlighting a positive effect of more complex community structure on food web organisation. In more diverse benthic communities, energy is transferred through more trophic levels while species-poor communities sustain a shorter food chain.

Soko?owski, A.; Wo?owicz, M.; Asmus, H.; Asmus, R.; Carlier, A.; Gasiunaité, Z.; Grémare, A.; Hummel, H.; Lesutiené, J.; Razinkovas, A.; Renaud, P. E.; Richard, P.; K?dra, M.

2012-08-01

166

Niche evolution, trophic structure, and species turnover in model food webs.  

PubMed

The features that govern the stability and persistence of species interaction networks, such as food webs, remain elusive, but recent work suggests that the distribution and strength of trophic links play an important role. Potential omnivory-stability relationships have been investigated and debated extensively, but we still have a relatively poor understanding of how levels of omnivory relate to the stability of diverse food webs. Here, we use an evolutionary assembly model to investigate how different trade-offs in resource use influence both food web structure and dynamic stability during the assembly process. We build on a previous model by allowing speciation along with the evolution of two traits: body size and feeding-niche width. Across a wide range of conditions, the level of omnivory in a food web is positively related to its dynamic instability (variability and species turnover). Parameter values favoring omnivory also allow a wider range of phenotypes to invade, often displacing existing species. This high species turnover leaves signatures in reconstructed phylogenies, with shorter branches connecting extant species in more omnivorous food webs. Our findings suggest that features of the environment may influence both trophic structure and dynamic stability, leading to emergent omnivory-stability relationships. PMID:19459779

Ingram, Travis; Harmon, Luke J; Shurin, Jonathan B

2009-07-01

167

Legacy effects of drought on plant growth and the soil food web.  

PubMed

Soils deliver important ecosystem services, such as nutrient provision for plants and the storage of carbon (C) and nitrogen (N), which are greatly impacted by drought. Both plants and soil biota affect soil C and N availability, which might in turn affect their response to drought, offering the potential to feed back on each other's performance. In a greenhouse experiment, we compared legacy effects of repeated drought on plant growth and the soil food web in two contrasting land-use systems: extensively managed grassland, rich in C and with a fungal-based food web, and intensively managed wheat lower in C and with a bacterial-based food web. Moreover, we assessed the effect of plant presence on the recovery of the soil food web after drought. Drought legacy effects increased plant growth in both systems, and a plant strongly reduced N leaching. Fungi, bacteria, and their predators were more resilient after drought in the grassland soil than in the wheat soil. The presence of a plant strongly affected the composition of the soil food web, and alleviated the effects of drought for most trophic groups, regardless of the system. This effect was stronger for the bottom trophic levels, whose resilience was positively correlated to soil available C. Our results show that plant belowground inputs have the potential to affect the recovery of belowground communities after drought, with implications for the functions they perform, such as C and N cycling. PMID:22555357

de Vries, Franciska Trijntje; Liiri, Mira E; Bjørnlund, Lisa; Setälä, Heikki M; Christensen, Søren; Bardgett, Richard D

2012-05-04

168

Evaluating the effects of trophic complexity on a keystone predator by disassembling a partial intraguild predation food web.  

PubMed

1. Many taxa can be found in food webs that differ in trophic complexity, but it is unclear how trophic complexity affects the performance of particular taxa. In pond food webs, larvae of the salamander Ambystoma opacum occupy the intermediate predator trophic position in a partial intraguild predation (IGP) food web and can function as keystone predators. Larval A. opacum are also found in simpler food webs lacking either top predators or shared prey. 2. We conducted an experiment where a partial IGP food web was simplified, and we measured the growth and survival of larval A. opacum in each set of food webs. Partial IGP food webs that had either a low abundance or high abundance of total prey were also simplified by independently removing top predators and/or shared prey. 3. Removing top predators always increased A. opacum survival, but removal of shared prey had no effect on A. opacum survival, regardless of total prey abundance. 4. Surprisingly, food web simplification had no effect on the growth of A. opacum when present in food webs with a low abundance of prey but had important effects on A. opacum growth in food webs with a high abundance of prey. Simplifying a partial IGP food web with a high abundance of prey reduced A. opacum growth when either top predators or shared prey were removed from the food web and the loss of top predators and shared prey influenced A. opacum growth in a non-additive fashion. 5. The non-additive response in A. opacum growth appears to be the result of supplemental prey availability augmenting the beneficial effects of top predators. Top predators had a beneficial effect on A. opacum populations by reducing the abundance of A. opacum present and thereby reducing the intensity of intraspecific competition. 6. Our study indicates that the effects of food web simplification on the performance of A. opacum are complex and depend on both how a partial IGP food web is simplified and how abundant prey are in the food web. These findings are important because they demonstrate how trophic complexity can create variation in the performance of intermediate predators that play important roles in temporary pond food webs. PMID:21950407

Davenport, Jon M; Chalcraft, David R

2011-09-23

169

Distributions of key exposure factors controlling the uptake of xenobiotic chemicals in an estuarine food web  

SciTech Connect

A critical evaluation of literature on the behavior, physiology, and ecology of common estuarine organisms was conducted in an attempt to develop probabilistic distributions for those variables that influence the uptake of xenobiotic chemicals from sediments, water, and food sources. The ranges, central tendencies, and distributions of several key parameter values were identified for dominant organisms from various trophic levels, including the polychaete Nereis virens, mummichog (Fundulus heteroclitus), blue crab (Callinectes sapidus), and striped bass (Morone saxatilis). The exposure factors of interest included ingestion rate for various food sources, growth rate, respiration rate, excretion rate, body weight, wet/dry weight ratio, lipid content, chemical assimilation efficiency, and food assimilation efficiency. These exposure factors are critical to the execution of mechanistic food web models, which, when properly calibrated, can be used to estimate tissue concentrations of nonionic chemicals in aquatic organisms based on knowledge of the bioenergetics and feeding interactions within a food web and the sediment and water concentrations of chemicals. In this article the authors describe the use of distributions for various exposure factors in the context of a mechanistic bioaccumulation model that is amenable to probabilistic analyses for multiple organisms within a food web. A case study is provided which compares the estimated versus measured concentrations of five polychlorinated biphenyl (PCB) congeners in a representative food web from the tidal portion of the Passaic River, New Jersey, USA. The results suggest that the model is accurate within an order of magnitude or less in estimating the bioaccumulation of PCBs in this food web without calibration. The results of a model sensitivity analysis suggest that the input parameters which most influence the output of the model are both chemical and organism specific.

Iannuzzi, T.J.; Harrington, N.W.; Shear, N.M.; Curry, C.L.; Carlson-Lynch, H.; Henning, M.H. [ChemRisk, Portland, ME (United States); Su, S.H. [Bailey Research Associates, Inc., New York, NY (United States); Rabbe, D.E. [Chemical Land Holdings, Inc., Kearny, NJ (United States)

1996-11-01

170

Hydrological and Biogeochemical Controls on Seasonal and Spatial Differences in Food Webs in the Everglades  

NASA Astrophysics Data System (ADS)

Stable isotopes can be used to determine the relative trophic positions of biota within a food web, and to improve our understanding of the biomagnification of contaminants. Plants at the base of the food web uptake dissolved organic carbon (DIC) and nitrogen (DIN) for growth, and their tissue reflects the isotopic composition of these sources. Animals then mirror the isotopic composition of the primary producers, as modified by consumer-diet fractionations at successive trophic steps. During 1995-99, we collected algae, macrophyte, invertebrate, and fish samples from 15 USGS sites in the Everglades and analyzed them for d13C and d15N with the goal of characterizing seasonal and spatial differences in food web relations. Carbon isotopes effectively distinguish between two main types of food webs: ones where algae is the dominant base of the food web, which are characteristic of relatively pristine marsh sites with long hydroperiods, and ones where macrophyte debris appears to be a significant source of nutrients, which are apparently characteristic of shorter hydroperiod sites, and nutrient-impacted marshes and canals. There usually is an inverse relation between d13C and d15N of organisms over time, especially in more pristine environments, reflecting seasonal changes in the d13C of DIC and the d15N of DIN. The d13C and d15N of algae also show strong positive correlations with seasonal changes in water levels. This variability is substantially damped up the food chain, probably because of the longer integration times of animals vs. plants. We speculate that these seasonal shifts in water level result in changes in biogeochemical reactions and nutrient levels, with corresponding variations in the d15N and d13C of biota. For example, small changes in water level may change the balance of photosynthesis, bacterial respiration, and atmospheric exchange reactions that control the d13C of DIC. Such changes will probably also affect the d15N of dissolved inorganic N (DIN) because of corresponding changes in N uptake and redox conditions. During the dry season, the marshes probably become more anoxic because of shallower water levels, less photosynthesis, and increased quantities of decaying vegetation. During this season, macrophyte debris appears to be a significant source of nutrients to local food webs. Our isotope data are consistent with seasonal differences in food webs, related to seasonal differences in water levels. Hence, biota isotopes provide a powerful tool for monitoring how future ecosystem changes, in particular changes in hydroperiod, will affect food webs across the Everglades.

Kendall, C.; Wankel, S. D.; Bemis, B. E.; Rawlik, P. S.; Krabbenhoft, D. P.; Lange, T.

2002-05-01

171

Do edge responses cascade up or down a multi-trophic food web?  

PubMed

Despite nearly 100?years of edge studies, there has been little effort to document how edge responses 'cascade' to impact multi-trophic food webs. We examined changes within two, four-tiered food webs located on opposite sides of a habitat edge. Based on a 'bottom-up' resource-based model, we predicted plant resources would decline near edges, causing similar declines in specialist herbivores and their associated predators, while a generalist predator was predicted to increase due to complementary resource use. As predicted, we found declines in both specialist herbivores and predators near edges, but, contrary to expectations, this was not driven by gradients in plant resources. Instead, the increase in generalist predators near edges offers one alternative explanation for the observed declines. Furthermore, our results suggest how recent advances in food web theory could improve resource-based edge models, and vice versa. PMID:21790930

Wimp, Gina M; Murphy, Shannon M; Lewis, Danny; Ries, Leslie

2011-07-26

172

Mechanistic theory and modelling of complex food-web dynamics in Lake Constance.  

PubMed

Mechanistic understanding of consumer-resource dynamics is critical to predicting the effects of global change on ecosystem structure, function and services. Such understanding is severely limited by mechanistic models' inability to reproduce the dynamics of multiple populations interacting in the field. We surpass this limitation here by extending general consumer-resource network theory to the complex dynamics of a specific ecosystem comprised by the seasonal biomass and production patterns in a pelagic food web of a large, well-studied lake. We parameterised our allometric trophic network model of 24 guilds and 107 feeding relationships using the lake's food web structure, initial spring biomasses and body-masses. Adding activity respiration, the detrital loop, minimal abiotic forcing, prey resistance and several empirically observed rates substantially increased the model's fit to the observed seasonal dynamics and the size-abundance distribution. This process illuminates a promising approach towards improving food-web theory and dynamic models of specific habitats. PMID:22513046

Boit, Alice; Martinez, Neo D; Williams, Richard J; Gaedke, Ursula

2012-04-18

173

Topographically driven predictions for river food webs: responses to land cover and climate change  

NASA Astrophysics Data System (ADS)

Fluxes of materials and energy, as well as the performances and interactions of organisms in food webs are strongly influenced by topography and vegetation. We have been using a "predictive mapping" approach to investigate how resource fluxes and food web interactions change down the Eel River drainage network in Northwestern California. In this talk, I will focus on hydrologic and food web controls on the production and fate of dominant primary producers in the river (macroalgae, diatoms and cyanobacteria). Algal mediated processes (e.g. nitrogen-fixation) and processes that limit algal abundance (e.g. grazer control) change abruptly through the season and down drainage networks. Field surveys and mensurative experiments that map the drainage network positions of these changes, and manipulative field experiments that uncover their causes, set the stage for predictive mapping, which is necessary if not sufficient for forecasts of river ecosystem response to changes in climate, land use, or biota.

Power, M. E.; Dietrich, W. E.; Finlay, J. C.; Bode, C. A.; Hondzo, M.; Limm, M.; National Center for Earth Surface Dynamics

2011-12-01

174

More than a meal… integrating non-feeding interactions into food webs.  

PubMed

Ecology Letters (2012) ABSTRACT: Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature. PMID:22313549

Kéfi, Sonia; Berlow, Eric L; Wieters, Evie A; Navarrete, Sergio A; Petchey, Owen L; Wood, Spencer A; Boit, Alice; Joppa, Lucas N; Lafferty, Kevin D; Williams, Richard J; Martinez, Neo D; Menge, Bruce A; Blanchette, Carol A; Iles, Alison C; Brose, Ulrich

2012-02-01

175

A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change  

Microsoft Academic Search

The Antarctic continental shelf is large, deep (500 1000 m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the

Craig R. Smith; Sarah Mincks; David J. Demaster

2006-01-01

176

Food for thought: Risks of non-native species transfer to the Antarctic region with fresh produce  

Microsoft Academic Search

To understand fully the risk of biological invasions, it is necessary to quantify propagule pressure along all introduction pathways. In the Antarctic region, importation of fresh produce is a potentially high risk, but as yet unquantified pathway. To address this knowledge gap, >11,250 fruit and vegetables sent to nine research stations in Antarctica and the sub-Antarctic islands, were examined for

Kevin A. Hughes; Jennifer E. Lee; Megumu Tsujimoto; Satoshi Imura; Dana M. Bergstrom; Chris Ware; Marc Lebouvier; Ad H. L. Huiskes; Niek J. M. Gremmen; Yves Frenot; Paul D. Bridge; Steven L. Chown

2011-01-01

177

Parasites affect food web structure primarily through increased diversity and complexity.  

PubMed

Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites "dominate" food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization, identifies limitations of current food web models, and provides direction for future structural and dynamical models. PMID:23776404

Dunne, Jennifer A; Lafferty, Kevin D; Dobson, Andrew P; Hechinger, Ryan F; Kuris, Armand M; Martinez, Neo D; McLaughlin, John P; Mouritsen, Kim N; Poulin, Robert; Reise, Karsten; Stouffer, Daniel B; Thieltges, David W; Williams, Richard J; Zander, Claus Dieter

2013-06-11

178

Effects of lake acidification and recovery on the stability of zooplankton food webs  

SciTech Connect

The effect of food web structure on community stability and resilience has rarely been examined using empirical data. Yet there is a practical application for such studies insofar as resistance stability determines the ability of a system to adsorb' anthropogenic stress and adjustment stability determines the reversibility of resulting damage. The stability of zooplankton food webs in 46 Precambrian Shield lakes was examined using data collected in the 1970s, when pH ranged from 3.8 to 7.0, and in 1990, when pH had increased by up to two units in some lakes. Acidification overcame resistance stability at pH <5.0, as evidenced by decreases in species richness, numbers of predatory and competitive links, directed connectance, predator generalization, and linkage density, identified by analysis of variance. Adjustment stability was demonstrated by changes in food web attributes in lakes with higher pH in 1990 than in the 1970s. Species richness, numbers of predatory and competitive links, linkage density, and predator generalization all increased relative to the 1970s values. Food web attributes of recovering' lakes were statistically indistinguishable from those of lakes of similar pH that had not been more acidic in the 1970s. Similar trajectors of food web change were followed during environmental degradation and recovery. Planktonic food webs of anthropogenically acidified lakes may eventually recover to resemble their pre-acidification condition, given sufficient time without acidic inputs. Whether adjustment stability is a general feature of anthropogenically stressed systems remains to be determined. 42 refs., 2 figs., 4 tabs.

Locke, A. (Gulf Fisheries Centre, Moncton, News Brunswick (Canada)); Sprules, W.G. (Univ. of Toronto, Ontario (Canada))

1994-03-01

179

Parasites Affect Food Web Structure Primarily through Increased Diversity and Complexity  

PubMed Central

Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites “dominate” food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasites' roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasites' feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization, identifies limitations of current food web models, and provides direction for future structural and dynamical models.

Dunne, Jennifer A.; Lafferty, Kevin D.; Dobson, Andrew P.; Hechinger, Ryan F.; Kuris, Armand M.; Martinez, Neo D.; McLaughlin, John P.; Mouritsen, Kim N.; Poulin, Robert; Reise, Karsten; Stouffer, Daniel B.; Thieltges, David W.; Williams, Richard J.; Zander, Claus Dieter

2013-01-01

180

The Serengeti food web: empirical quantification and analysis of topological changes under increasing human impact.  

PubMed

1.?To address effects of land use and human overexploitation on wildlife populations, it is essential to better understand how human activities have changed species composition, diversity and functioning. Theoretical studies modelled how network properties change under human-induced, non-random species loss. However, we lack data on realistic species-loss sequences in threatened, real-world food webs to parameterize these models. 2.?Here, we present a first size-structured topological food web of one of the most pristine terrestrial ecosystems in the world, the Serengeti ecosystem (Tanzania). The food web consists of 95 grouped nodes and includes both invertebrates and vertebrates ranging from body masses between 10(-7) and 10(4) kg. 3.?We study the topological changes in this food web that result from the simulated IUCN-based species-loss sequence representing current species vulnerability to human disturbances in and around this savanna ecosystem. We then compare this realistic extinction scenario with other extinction sequences based on body size and connectance and perform an analysis of robustness of this savanna food web. 4.?We demonstrate that real-world species loss in this case starts with the biggest (mega) herbivores and top predators, causing higher predator-prey mass ratios. However, unlike theoretically modelled linear species deletion sequences, this causes poor-connected species to be lost first, while more highly connected species become lost as human impact progresses. This food web shows high robustness to decreasing body size and increasing connectance deletion sequences compared with a high sensitivity to the decreasing connectance deletion scenario. 5.?Furthermore, based on the current knowledge of the Serengeti ecosystem, we discuss how the focus on food web topology alone, disregarding nontrophic interactions, may lead to an underestimation of human impacts on wildlife communities, with the number of trophic links affected by a factor of two. 6.?This study underlines the importance of integrative efforts between the development of food web theory and basic field work approaches in the quantification of the structure of interaction networks to sustain natural ecosystems in a changing world. PMID:21155772

de Visser, Sara N; Freymann, Bernd P; Olff, Han

2010-12-14

181

Bioaccumulation and biomagnification of polybrominated diphenyl ethers in a food web of Lake Michigan.  

PubMed

Polybrominated diphenyl ethers are hydrophobic chemicals and can biomagnify in food chains. Little is known about the biomagnification of PBDEs in the Lake Michigan food web. Plankton, Diporeia, lake whitefish, lake trout, and Chinook salmon were collected from Lake Michigan in 2006 between April and August. Fish liver and muscle and whole invertebrates were analyzed for six PBDEs (BDE-47, 99, 100, 153, 154, and 209). Carbon and nitrogen stable isotope ratios (delta(13)C and delta(15)N) were also quantified in order to establish the trophic structure of the food web. Geometric means of Sigma PBDE concentrations in fish ranged from 0.562 to 1.61 microg/g-lipid. BDE-209 concentrations ranged from 0.184 to 1.23 microg/g-lipid in all three fish species. Sigma BDE-47, 99, and 209 comprised 80-94% of Sigma PBDE molar concentration. Within each fish species, there were no significant differences in PBDE concentrations between liver and muscle. The highest concentration of BDE-209 (144 microg/g-lipid) was detected in Diporeia. Based on analysis of delta(15)N and PBDE concentrations, BDE-47 and 100 were found to biomagnify, whereas BDE-209 did not. A significant negative correlation between BDE-209 and trophic level was found in this food web. Biomagnification factors were also calculated and again BDE-47 and 100 biomagnified between food web members whereas BDE-209 did not. Diporeia could be one of the main dietary sources of BDE-209 for fish in Lake Michigan; BDE-47 and 100 biomagnified within this food chain; the concentration of BDE-209 decreased at higher trophic levels, suggesting partial uptake and/or biotransformation of BDE-209 in the Lake Michigan food web. PMID:19882349

Kuo, Yin-Ming; Sepúlveda, Maria S; Hua, Inez; Ochoa-Acuña, Hugo G; Sutton, Trent M

2009-11-01

182

Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study  

USGS Publications Warehouse

Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean Zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, ke = 0.025, 0.155, and 0.25 d-1, respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se > 15 ??g g-1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of Zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.

Stewart, A. R.; Luoma, S. N.; Schlekat, C. E.; Doblin, M. A.; Hieb, K. A.

2004-01-01

183

All wet or dried up? Real differences between aquatic and terrestrial food webs  

PubMed Central

Ecologists have greatly advanced our understanding of the processes that regulate trophic structure and dynamics in ecosystems. However, the causes of systematic variation among ecosystems remain controversial and poorly elucidated. Contrasts between aquatic and terrestrial ecosystems in particular have inspired much speculation, but only recent empirical quantification. Here, we review evidence for systematic differences in energy flow and biomass partitioning between producers and herbivores, detritus and decomposers, and higher trophic levels. The magnitudes of different trophic pathways vary considerably, with less herbivory, more decomposers and more detrital accumulation on land. Aquatic–terrestrial differences are consistent across the global range of primary productivity, indicating that structural contrasts between the two systems are preserved despite large variation in energy input. We argue that variable selective forces drive differences in plant allocation patterns in aquatic and terrestrial environments that propagate upward to shape food webs. The small size and lack of structural tissues in phytoplankton mean that aquatic primary producers achieve faster growth rates and are more nutritious to heterotrophs than their terrestrial counterparts. Plankton food webs are also strongly size-structured, while size and trophic position are less strongly correlated in most terrestrial (and many benthic) habitats. The available data indicate that contrasts between aquatic and terrestrial food webs are driven primarily by the growth rate, size and nutritional quality of autotrophs. Differences in food-web architecture (food chain length, the prevalence of omnivory, specialization or anti-predator defences) may arise as a consequence of systematic variation in the character of the producer community.

Shurin, Jonathan B; Gruner, Daniel S; Hillebrand, Helmut

2005-01-01

184

Food web pathway determines how selenium affects aquatic ecosystems: a San Francisco Bay case study.  

PubMed

Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, ke = 0.025, 0.155, and 0.25 d(-1), respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se >15 microg g(-1) dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts. PMID:15461158

Stewart, A Robin; Luoma, Samuel N; Schlekat, Christian E; Doblin, Martina A; Hieb, Kathryn A

2004-09-01

185

Variable and complex food web structures revealed by exploring missing trophic links between birds and biofilm.  

PubMed

Ecology Letters (2012) ABSTRACT: Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics. PMID:22304245

Kuwae, Tomohiro; Miyoshi, Eiichi; Hosokawa, Shinya; Ichimi, Kazuhiko; Hosoya, Jun; Amano, Tatsuya; Moriya, Toshifumi; Kondoh, Michio; Ydenberg, Ronald C; Elner, Robert W

2012-02-01

186

Food web structure in a Salix subfragilis dominated wetland in Hangang estuary using stable isotopes and fatty acid biomarkers  

Microsoft Academic Search

We investigated food webs of a Salix subfragilis-dominated wetland in the Janghang wetland in the Hangang estuary, which is very close to the Demilitarized Zone, along the west coast of Korea. Our study focused on understanding sesarmine crab (Sesarma dehaani)-related food webs in a S. subfragilis forest. For our study, we used carbon and nitrogen stable isotopes and fatty acid

Donguk Han; Dongwoo Yang; Eun Joo Lee; Sangkyu Park

2012-01-01

187

Food web structure in a Salix subfragilis dominated wetland in Hangang estuary using stable isotopes and fatty acid biomarkers  

Microsoft Academic Search

We investigated food webs of a Salix subfragilis-dominated wetland in the Janghang wetland in the Hangang estuary, which is very close to the Demilitarized Zone, along the west coast of Korea. Our study focused on understanding sesarmine crab (Sesarma dehaani)-related food webs in a S. subfragilis forest. For our study, we used carbon and nitrogen stable isotopes and fatty acid

Donguk Han; Dongwoo Yang; Eun Joo Lee; Sangkyu Park

2011-01-01

188

Analogous aquatic and terrestrial food webs in the high Arctic: The structuring force of a harsh climate  

Microsoft Academic Search

Understanding food web structure and dynamics remains a central theme in ecology. Whilst differences between aquatic and terrestrial food webs have been the focus of several studies, we aim to reveal similarities where abiotic conditions are particularly extreme such as in the high Arctic. We propose that here, the combination of a short growing season, low temperature and low light,

René van der Wal; Dag O. Hessen

2009-01-01

189

Food web complexity enhances community stability and climate regulation in a geophysiological model  

Microsoft Academic Search

A central debate in community ecology concerns the relationship between the complexity of communities and their stability. How does the richness of food web structures affect their resistance and resilience to perturbation? Most mathematical models of communities have shown that stability declines as complexity increases but so far, modellers have not included the material environment in their calculations. Here an

Stephan P. Harding

1999-01-01

190

Possible Effects of Genetically Modified Plants on Insects in the Plant Food Web  

Microsoft Academic Search

Abstract: During the last years, there has been increasing focus on the environmental effects of genetically modified plants, not only hybridization and gene flow, but also effects on insects. A general overview of possible effects of genetically modified plants on insects ,is presented. Insects from different levels of the plant food web ,are included: herbivores (pests and non-pests), pollinators, predators\\/parasitoids

Eline B. Hågvar; Solveig Aasen

191

Evidence for biomagnification of rubidium in freshwater and marine food webs  

Microsoft Academic Search

Rubidium (Rb), a rarely studied alkali metal, may be an essential ultra-trace element for humans and other organisms. However, very little information exists in regard to the concentrations and distribution of Rb in freshwater and marine food webs. We measured Rb concentrations in freshwater fish from Lake Erie and two Arctic lakes (Lake Hazen and Resolute Lake) and in seabirds,

Linda M. Campbell; Aaron T. Fisk; Xiaowa Wang; Günter Köck; Derek C. G. Muir

2005-01-01

192

Seeking Emotional Involvement in Science Education: Food-Chains and Webs.  

ERIC Educational Resources Information Center

Documents a study of emotion in two grade 8 science classrooms. Describes a lesson on food-chains and webs designed with a conceptual and an emotional agenda. Discusses issues of emotion, sensation and relevance in science teaching. (Author/MM)

Alsop, Steve

2001-01-01

193

Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta  

USGS Publications Warehouse

Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that detritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production. ?? 2005 Estuarine Research Federation.

Sobczak, W. V.; Cloern, J. E.; Jassby, A. D.; Cole, B. E.; Schraga, T. S.; Arnsberg, A.

2005-01-01

194

FOOD WEB STRUCTURE AS A POTENTIAL INDICATOR OF NUTRIENT ENRICHMENT IN GREAT LAKES COASTAL WETLANDS  

EPA Science Inventory

Analyses of the food webs of Great Lakes coastal wetlands verify the role of algae as an energetic foundation, and also suggest that fundamental changes occur in response to both natural and anthropogenic influences. We analyzed coastal wetlands with a range of nutrient concentra...

195

Macroalgal palatability and the flux of ciguatera toxins through marine food webs  

Microsoft Academic Search

The benthic dinoflagellate Gambierdiscus toxicus produces polyether toxins that cause ciguatera fish poisoning in humans. The toxins initially enter food webs when fish forage on macroalgae, or other substrates, hosting this epiphytic dinoflagellate. Population studies of G. toxicus and risk assessments in ciguatera-prone regions often rely on quantifying dinoflagellates on macroalgae. Underlying these studies is the assumption that the algae

Edwin Cruz-Rivera; Tracy A. Villareal

2006-01-01

196

Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts  

Microsoft Academic Search

Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we

Marta Coll; Allison Schmidt; Tamara Romanuk; Heike K. Lotze

2011-01-01

197

HYDROLOGY AND NUTRIENT EFFECTS ON FOOD-WEB STRUCTURE IN TEN LAKE SUPERIOR COASTAL WETLANDS  

EPA Science Inventory

The manuscript examines the effects of hydrology and nutrient enrichment on food-web structure. We find that the hydraulic residence time is a paramount constraint upon the relative contributions of planktonic versus benthic production to the fish community. Nutrient enrichment...

198

Persistence of net heterotrophy in lakes during nutrient addition and food web manipulations  

Microsoft Academic Search

Net ecosystem production (NEP) is the difference between gross primary production (GPP) and community respiration (R). We estimated in situ NEP using three independent approaches (net CO2 gas flux, net O 2 gas flux, and continuous diel O2 measurements) over a 4-7 yr period in a series of small lakes in which food webs were manipulated and nutrient loadings were

Jonathan J. Cole; Michael L. Pace; Stephen R. Carpenter; James F. Kitchell

2000-01-01

199

Structural and functional succession in the nematode fauna of a soil food web  

Microsoft Academic Search

Soil microplots were amended with organic materials of varying nature and complexity but providing similar amounts of carbon. Materials were either placed on the soil surface or incorporated. Unamended and mineral fertilizer control plots were established. Plots were maintained vegetation-free so that the food web activity was fueled by resident soil organic matter and the input material. Enrichment-opportunist bacterivore nematodes

H. Ferris; M. M. Matute

2003-01-01

200

Detection of inconspicuous epiphytic algae supporting food webs in seagrass meadows  

Microsoft Academic Search

Detritus from common seagrasses and other marine angiosperms may often be a less important basis for estuarine food webs than previously believed. In NW Gulf of Mexico seagrass meadows, epiphytic algae have high productivities, palatability, and a more important trophic role than common large plants have. Interdisciplinary field experiments show (1) intensive night-time ingestion of epiphytes by various invertebrate “detritivores”,

Christopher L. Kitting; Brian Fry; Mark D. Morgan

1984-01-01

201

Soil fauna and soil function in the fabric of the food web  

Microsoft Academic Search

Over the last four decades, spanning David Coleman's career, and in no small measure thanks to him, soil ecologists have made tremendous progress in describing and understanding the overwhelming complexity of biological, biophysical and biochemical interactions in soil. These interactions shape the soil as a habitat for the soil food web and the vegetation and, thereby, regulate the two main

L. Brussaard; M. M. Pulleman; E. Ouédraogo; A. Mando

2006-01-01

202

Linking Food Webs and Biogeochemical Processes in Wetlands: Insights From Sulfur Isotopes  

Microsoft Academic Search

To better understand the transfer of nutrients into prairie wetland food webs we have investigated the cycling of S (via S isotope systematics and geochemistry) in a prairie wetland landscape by characterizing sources (ground water, interstitial water, surface water) and processes in a small catchment comprised of four wetlands in eastern South Dakota. We focused on S to derive process

C. A. Stricker; G. R. Guntenspergen; R. O. Rye

2005-01-01

203

Temporal Variation in Regulation of Production in a Pelagic Food Web Model.  

National Technical Information Service (NTIS)

The authors examined the implications of differential resource use and predator-prey relations in a seasonal environment, formalized as a pelagic food web model, on temporal changes in the relative importance of bottom-up and top-down structuring of the p...

S. M. Bartell A. L. Brenkert R. V. O'Neill R. H. Gardner

1987-01-01

204

Effects of light reduction on food webs and associated ecosystem services of Yaquina Bay  

EPA Science Inventory

Reduced water clarity can affect estuarine primary production but little is known of its subsequent effects to consumer guilds or ecosystem services. We investigated those effects using inverse analysis of modeled food webs of the lower (polyhaline) and upper (mesohaline) reache...

205

Aquatic food web dynamics on a floodplain in the Okavango delta, Botswana  

Microsoft Academic Search

The study presents the succession of food web compartments during the annual flood of a floodplain of the great inland delta, Okavango, Botswana, and emphasizes how the floodplains serve as key recruitment areas for fish. By onset of the flood, the rather nutrient poor water from the main river becomes strongly enriched by inorganic nutrients and organic debris as it

P. Høberg; M. Lindholm; L. Ramberg; D. O. Hessen

2002-01-01

206

Grazing food web view from compound-specific stable isotope analysis of amino acids  

Technology Transfer Automated Retrieval System (TEKTRAN)

Knowledge of the trophic position (TP) of organisms in food webs allows ecologists to track energy flow and trophic linkages among organisms in complex networks of ecosystems. Compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a relatively new method with the high p...

207

Anadromous alewives ( Alosa pseudoharengus ) contribute marine-derived nutrients to coastal stream food webs  

Microsoft Academic Search

Diadromous fish are an important link between marine and freshwater food webs. Pacific salmon (Oncorhyn- chus spp.) strongly impact nutrient dynamics in inland waters and anadromous alewife (Alosa pseudoharengus) may play a similar ecological role along the Atlantic coast. The annual spawning migration of anadromous alewife contributes, on average, 1050 g of nitrogen and 120 g of phosphorus to Bride

Annika W. Walters; Rebecca T. Barnes; David M. Post

2009-01-01

208

Tracing Fluxes Of Aquatic Production And Contaminants Into Terrestrial Food Webs With Nitrogen Stable Isotopes  

Microsoft Academic Search

Biomagnifying contaminants such as mercury can be transported and redistributed across the watershed by streams and rivers. Their fate and effects on consumers depend on food web transfer both within and between aquatic and terrestrial ecosystems. The Truckee River (Ca\\/Ne) is heavily contaminated by Hg originating from century-old upstream mining operations. We used nitrogen stable isotope analysis to trace the

A. Rivard; G. Cabana; W. Rainey; M. Power

2005-01-01

209

Estuarine Microbial Food Web Patterns in a Lake Erie Coastal Wetland  

Microsoft Academic Search

Composition and distribution of planktonic protists were examined relative to microbial food web dynamics (growth, grazing, and nitrogen cycling rates) at the Old Woman Creek (OWC) National Estuarine Research Reserve during an episodic storm event in July 2003. More than 150 protistan taxa were identified based on morphology. Species richness and microbial biomass measured via microscopy and flow cytometry increased

P. J. Lavrentyev; M. J. McCarthy; D. M. Klarer; F. Jochem; W. S. Gardner

2004-01-01

210

Monitoring Food Web Changes in Tide-Restored Salt Marshes: A Carbon Stable Isotope Approach  

Microsoft Academic Search

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, and Fundulus heteroclitus isotope values (d 13 C, d 15 N, d 34 S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged from Spartina alterniflora-dominated reference marshes, marshes

ANDREW S. WOZNIAK; CHARLES T. ROMAN; S AM C. WAINRIGHT; R ICHARD A. MCKINNEY

2006-01-01

211

Contribution of Allochthonous Carbon Subsidies to the Minho Estuary Lower Food Web  

EPA Science Inventory

To study the contribution of autochthonous and allochthonous organic matter (OM) sources fuelling the lower food web in Minho River estuary (N-Portugal, Europe), we characterized the carbon (?13C) and nitrogen (?15N) stable isotope ratios of zooplankton and their potential OM sou...

212

Food web and fluid in pitchers of Nepenthes mirabilis in Zhuhai, China  

Microsoft Academic Search

Here we report a complex food web and special fluid properties in pitchers of Nepenthes mirabilis in Zhuhai, Guangdong Province, China. It attracts ants and flying insects with floral and exrafloral nectaries, color of pitcher and flower, and possibly flower odor. Its slippery rim and collar trap preys, but some wasps can hold legs on the outside of the rim.

Yuejin Huae; Hongqi Lie

2005-01-01

213

Cascading predation effects of Daphnia and copepods on microbial food web components  

Microsoft Academic Search

SUMMARY 1. We performed a mesocosm experiment to investigate the structuring and cascading effects of two predominant crustacean mesozooplankton groups on microbial food web components. The natural summer plankton community of a mesotrophic lake was exposed to density gradients of Daphnia and copepods. Regression analysis was used to reveal top- down impacts of mesozooplankton on protists and bacteria after days

ECKART Z OLLNER; B ARBARA S ANTER; M AARTEN B OERSMA

2003-01-01

214

Contribution of nematodes to the structure and function of the soil food web.  

PubMed

As carbon and energy flow through the soil food web they are depleted by the metabolic and production functions of organisms. To be sustained, a "long" food web, with a large biomass at higher trophic levels, must receive a high rate of rhizodeposition or detrital subsidy, or be top-populated by organisms of slow growth and long life cycle. Disturbed soil food webs tend to be bottom heavy and recalcitrant to restoration due to the slow growth of upper predator populations, physical and chemical constraints of the soil matrix, biological imbalances, and the relatively low mobility and invasion potential of soil organisms. The functional roles of nematodes, determined by their metabolic and behavioral activities, may be categorized as ecosystem services, disservices or effect-neutral. Among the disservices attributable to nematodes are overgrazing, which diminishes services of prey organisms, and plant-damaging herbivory, which reduces carbon fixation and availability to other organisms in the food web. Unfortunately, management to ameliorate potential disservices of certain nematodes results in unintended but long-lasting diminution of the services of others. Beneficial roles of nematodes may be enhanced by environmental stewardship that fosters greater biodiversity and, consequently, complementarity and continuity of their services. PMID:22736838

Ferris, Howard

2010-03-01

215

The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient  

EPA Science Inventory

Estuarine food webs function within a heterogeneous mosaic and are supported by a mix of primary producers from both local and distant sources. Processes governing the exchange and consumption of organic matter (OM), however, are poorly understood. To study the contribution of ...

216

UV Effects on Marine Planktonic Food Webs: A Synthesis of Results from Mesocosm Studies  

Microsoft Academic Search

UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical,

Claude Belzile; Serge Demers; Gustavo A. Ferreyra; Irene Schloss; Christian Nozais; Karine Lacoste; Behzad Mostajir; Suzanne Roy; Michel Gosselin; Emilien Pelletier; Sônia M. F. Gianesella; Maria Vernet

2006-01-01

217

Dams and downstream aquatic biodiversity: Potential food web consequences of hydrologic and geomorphic change  

SciTech Connect

Responses of rivers and river ecosystems to dams are complex and varied, as they depend on local sediment supplies, geomorphic constraints, climate, dam structure and operation, and key attributes of the biota. Therefore, {open_quotes}one-size-fits-all{close_quotes} prescriptions cannot substitute for local knowledge in developing prescriptions for dam structure and operation to protect local biodiversity. One general principle is self-evident: that biodiversity is best protected in rivers where physical regimes are the most natural. A sufficiently natural regime of flow variation is particularly crucial for river biota and food webs. We review our research and that of others to illustrate the ecological importance of alternating periods of low an high flow, of periodic bed scour, and of floodplain inundation and dewatering. These fluctuations regulate both the life cycles of river biota and species interactions in the food webs that sustain them. Even if the focus of biodiversity conservation efforts is on a target species rather than whole ecosystems, a food web perspective is necessary, because populations of any species depend critically on how their resources, prey, and potential predators also respond to environmental change. In regulated rivers, managers must determine how the frequency, magnitude, and timing of hydrologic events interact to constrain or support species and food webs. Simple ecological modeling, tailored to local systems, may provide a framework and some insight into explaining ecosystem response to dams and should give direction to mitigation efforts. 78 refs.

Power, M.E.; Dietrich, W.E.; Finlay, J.C. [Univ. of California, Berkeley, CA (United States)

1996-11-01

218

MONITORING FOOD WEB CHANGES IN TIDE-RESTORED SALT MARSHES: A CARBON STABLE ISOTOPE APPROACH  

EPA Science Inventory

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, and Fundulus heteroclitus isotope values (d13C , d15N, d34S) were examined to assess their use as an indicator for changes in food web support functions in tidally-restored sal...

219

The direct and indirect impact of Daphnia and Cyclops on a freshwater microbial food web  

Microsoft Academic Search

Experiments were conducted in a mesotrophic North German lake to examine the influence of metazoan zooplankton on the microbial food web. The presence and absence of Daphnia and Cyclops were manipulated in two cross-classified in situ experiments conducted in May and June 1994, during and after the clear-water phase. Ciliates had high population growth rates in the absence of predation

Stephen A. Wickham

1998-01-01

220

Food web properties in aquatic microcosms with litter mixtures are predictable from component species  

Microsoft Academic Search

Many aquatic systems depend on allochthonous organic matter. Quality of litter differs between plant species. Therefore, the composition of the surrounding veg- etation may influence litter decomposition and other processes in aquatic food webs. We recorded the abundance of insect larvae, as well as the diversity of cultivable fungi and bacteria, the metabolic diversity of the microflora, and leaf litter

Martin Schädler; Tanja Rottstock; Roland Brandl

2005-01-01

221

Mangrove detrital system: decomposition processes and their role in estuarine food webs  

Microsoft Academic Search

The report describes a research program directed to the role of the decomposition of leaf material from the red mangrove (Rhizophora mangle) in the food web of estuaries, how these processes work and what alterations can be expected with environmental perturbations. The program was designed to examine the following components of the decomposition process involving carbon and nitrogen inputs\\/outputs: (1)

Fell

1978-01-01

222

Trophic efficiency of the planktonic food web in a coastal ecosystem dominated by Phaeocystis colonies  

Microsoft Academic Search

The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major

V. Rousseaua; S. Becquevort; J.-Y. Parent; S. Gasparini; M.-H. Darob; M. Tackxb; C. Lancelot

2000-01-01

223

Grazing experiments and model simulations of the role of zooplankton in Phaeocystis food webs  

Microsoft Academic Search

A combined empirical and modelling study was conducted to further examine the potential importance of grazing by zooplankton in pelagic food webs in which Phaeocystis is a significant or dominant component. Laboratory experiments were designed to measure ingestion of Phaeocystis and other potential prey items which co-occur with Phaeocystis. Grazers included copepods and ciliates, and prey included Phaeocystis colonies and

P. G. Verity

2000-01-01

224

BSAFs and Food Web Modeling for Establishing Contaminant Relationships between Biota and Sediment  

EPA Science Inventory

The presentation will cover how to measure and evaluate BSAFs (biota-sediment accumulation factors), and how to construct, calibrate, validate, and evaluate food web models. The presentation will also discuss the advantages of the two approaches for establishing contaminant rel...

225

Farming practices change food web structures in cereal aphid-parasitoid-hyperparasitoid communities.  

PubMed

Agricultural intensification has been shown to result in a decline in biodiversity across many taxa, but the changes in community structure and species interactions remain little understood. We have analysed and compared the structure of feeding interactions for cereal aphids and their primary and secondary parasitoids in organically and conventionally managed winter wheat fields using quantitative food web metrics (interaction evenness, generality, vulnerability, link density). Despite little variation in the richness of each trophic group, food web structures between the two farming systems differed remarkably. In contrast to common expectations, aphids and primary parasitoids were characterized by (1) a higher evenness of interaction frequencies (interaction evenness) in conventional fields, which cascaded to interactions at the next trophic level, with (2) a higher interaction evenness, (3) a higher ratio of primary parasitoid taxa per secondary parasitoid (generality) and (4) a higher link density. Aphid communities in the organically managed fields almost exclusively consisted of a single ear-colonizing species, Sitobion avenae, while highly fertilized conventional fields were mainly infested by leaf-colonizing aphids that benefit from the nutritional status of winter wheat. In conclusion, agricultural intensification appears to foster the complexity of aphid-parasitoid food webs, thereby not supporting the general expectation on the importance of organic farming practices for species richness and food web complexity. PMID:22736196

Lohaus, Katharina; Vidal, Stefan; Thies, Carsten

2012-06-27

226

Mangrove Detrital System: Decomposition Processes and Their Role in Estuarine Food Webs.  

National Technical Information Service (NTIS)

The report describes a research program directed to the role of the decomposition of leaf material from the red mangrove (Rhizophora mangle) in the food web of estuaries, how these processes work and what alterations can be expected with environmental per...

J. W. Fell

1978-01-01

227

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

PubMed

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. PMID:19490028

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

2009-05-21

228

Spatial price equilibrium and food webs: The economics of predator-prey networks  

Microsoft Academic Search

In this paper, we prove that the equilibrium of predator-prey networks is, in fact, a spatial price equilibrium. This result demonstrates the underlying economics of predator- prey relationships and interactions and provides a foundation for the formulation and analysis of complex food webs, which are nature's supply chains, through the formalism of network equilibrium. Moreover, it rigorously links the equilibrium

Anna Nagurney; Ladimer S. Nagurney

2011-01-01

229

Food web structure and mercury transfer in two contrasting Ugandan highland crater lakes (East Africa)  

Microsoft Academic Search

Volcanic crater lakes scattered throughout western Uganda are important local sources of water and fish. Two representative but contrasting crater lakes near the Kibale National Park were sampled in 2000; the hyper-eutrophic Lake Saka, which is highly affected by agricultural prac- tices, and the mesotrophic Lake Nkuruba that is still sur- rounded by intact forest. The food web structures in

L. Campbell; R. E. Hecky; D. G. Dixon; L. J. Chapman

2006-01-01

230

A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change  

Microsoft Academic Search

The Antarctic continental shelf is large, deep (500–1000m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the nature and

Craig R. Smith; Sarah Mincks; David J. DeMaster

2006-01-01

231

Accumulation of selenium in a model freshwater microbial food web.  

PubMed Central

The transfer of selenium between bacteria and the ciliated protozoan, Paramecium putrinum, was examined in laboratory cultures. The population growth of the ciliate was not inhibited in the presence of the highest concentrations of dissolved selenite or selenate tested (10(3) micrograms liter-1). Experiments with radioactive 75selenite or 75selenate indicated that accumulation of selenium by ciliates through time was low when feeding and metabolism were reduced by incubating at 0 degrees C. However, selenium accumulated in ciliate biomass during incubation with dissolved 75Se and bacteria at 24 degrees C and also when bacteria prelabeled with 75Se were offered as food in the absence of dissolved selenium. When 75Se-labeled bacterial food was diluted by the addition of nonradioactive bacteria, the amount of selenite and selenate in ciliates decreased over time, indicating depuration by the ciliates. In longer-term (> 5-day) fed-batch incubations with 75selenite-labeled bacteria, the selenium concentration in ciliates equilibrated at approximately 1.4 micrograms of Se g (dry weight)-1. The selenium content of ciliates was similar to that of their bacterial food on a dry-weight basis. These data indicate that selenium uptake by this ciliate occurred primarily during feeding and that biomagnification of selenium did not occur in this simple food chain.

Sanders, R W; Gilmour, C C

1994-01-01

232

Food web interactions and nutrients dynamics in polyculture ponds  

Microsoft Academic Search

Artificial feed and fertilizers are the main sources of nutrients supporting fish growth in aquaculture ponds. The majority of the added nutrients are lost to the sediment, where they are no longer available for natural food production. By increasing resuspension of the sediment through the introduction of benthivorous fish, nutrient loss may be reduced, because of the re-mobilisation of nutrients

M. M. Rahman

2006-01-01

233

Carbon flows in the benthic food web at the deep-sea observatory HAUSGARTEN (Fram Strait)  

NASA Astrophysics Data System (ADS)

The HAUSGARTEN observatory is located in the eastern Fram Strait (Arctic Ocean) and used as long-term monitoring site to follow changes in the Arctic benthic ecosystem. Linear inverse modelling was applied to decipher carbon flows among the compartments of the benthic food web at the central HAUSGARTEN station (2500 m) based on an empirical data set consisting of data on biomass, prokaryote production, total carbon deposition and community respiration. The model resolved 99 carbon flows among 4 abiotic and 10 biotic compartments, ranging from prokaryotes up to megafauna. Total carbon input was 3.78±0.31 mmol C m -2 d -1, which is a comparatively small fraction of total primary production in the area. The community respiration of 3.26±0.20 mmol C m -2 d -1 is dominated by prokaryotes (93%) and has lower contributions from surface-deposit feeding macro- (1.7%) and suspension feeding megafauna (1.9%), whereas contributions from nematode and other macro- and megabenthic compartments were limited to <1%. The high prokaryotic contribution to carbon processing suggests that functioning of the benthic food web at the central HAUSGARTEN station is comparable to abyssal plain sediments that are characterised by strong energy limitation. Faunal diet compositions suggest that labile detritus is important for deposit-feeding nematodes (24% of their diet) and surface-deposit feeding macrofauna (˜44%), but that semi-labile detritus is more important in the diets of deposit-feeding macro- and megafauna. Dependency indices on these food sources were also calculated as these integrate direct (i.e. direct grazing and predator-prey interactions) and indirect (i.e. longer loops in the food web) pathways in the food web. Projected sea-ice retreats for the Arctic Ocean typically anticipate a decrease in the labile detritus flux to the already food-limited benthic food web. The dependency indices indicate that faunal compartments depend similarly on labile and semi-labile detritus, which suggests that the benthic biota may be more sensitive to changes in labile detritus inputs than when assessed from diet composition alone. Species-specific responses to different types of labile detritus inputs, e.g. pelagic algae versus sympagic algae, however, are presently unknown and are needed to assess the vulnerability of individual components of the benthic food web.

van Oevelen, Dick; Bergmann, Melanie; Soetaert, Karline; Bauerfeind, Eduard; Hasemann, Christiane; Klages, Michael; Schewe, Ingo; Soltwedel, Thomas; Budaeva, Nataliya E.

2011-11-01

234

Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning  

PubMed Central

Networks of trophic links (food webs) are used to describe and understand mechanistic routes for translocation of energy (biomass) between species. However, a relatively low proportion of ecosystems have been studied using food web approaches due to difficulties in making observations on large numbers of species. In this paper we demonstrate that Machine Learning of food webs, using a logic-based approach called A/ILP, can generate plausible and testable food webs from field sample data. Our example data come from a national-scale Vortis suction sampling of invertebrates from arable fields in Great Britain. We found that 45 invertebrate species or taxa, representing approximately 25% of the sample and about 74% of the invertebrate individuals included in the learning, were hypothesized to be linked. As might be expected, detritivore Collembola were consistently the most important prey. Generalist and omnivorous carabid beetles were hypothesized to be the dominant predators of the system. We were, however, surprised by the importance of carabid larvae suggested by the machine learning as predators of a wide variety of prey. High probability links were hypothesized for widespread, potentially destabilizing, intra-guild predation; predictions that could be experimentally tested. Many of the high probability links in the model have already been observed or suggested for this system, supporting our contention that A/ILP learning can produce plausible food webs from sample data, independent of our preconceptions about “who eats whom.” Well-characterised links in the literature correspond with links ascribed with high probability through A/ILP. We believe that this very general Machine Learning approach has great power and could be used to extend and test our current theories of agricultural ecosystem dynamics and function. In particular, we believe it could be used to support the development of a wider theory of ecosystem responses to environmental change.

Bohan, David A.; Caron-Lormier, Geoffrey; Muggleton, Stephen; Raybould, Alan; Tamaddoni-Nezhad, Alireza

2011-01-01

235

Organochlorine pollution in tropical rivers (Guadeloupe): role of ecological factors in food web bioaccumulation.  

PubMed

Concentrations of organochlorine pesticides and stable isotope ratios of nitrogen and carbon were measured in a tropical freshwater ecosystem to evaluate the contamination level of biota and examine the bioaccumulation patterns of pollutants through the food web. Chemical analyses showed a general and heavy contamination of the entire food web. They revealed the strong accumulation of pollutants by juveniles of diadromous fishes and shrimps, as they re-enter the river. The role of ecological factors in the bioaccumulation of pesticides was evaluated. Whereas the most persistent pollutants (chlordecone and monohydro-chlordecone) were related to the organisms diet and habitat, bioaccumulation of ?-HCH was only influenced by animal lipid content. The biomagnification potential of chlordecone through the food chain has been demonstrated. It highlighted the importance of trophic transfer in this compound bioaccumulation process. In contrast, bioconcentration by passive diffusion from water seemed to be the main exposure route of biota to ?-HCH. PMID:21440344

Coat, Sophie; Monti, Dominique; Legendre, Pierre; Bouchon, Claude; Massat, Félix; Lepoint, Gilles

2011-03-25

236

The role of ammonites in the Mesozoic marine food web revealed by jaw preservation.  

PubMed

Ammonites are prominent in macroevolutionary studies because of their abundance and diversity in the fossil record, but their paleobiology and position in the marine food web are not well understood due to the lack of preserved soft tissue. We present three-dimensional reconstructions of the buccal apparatus in the Mesozoic ammonite Baculites with the use of synchrotron x-ray microtomography. Buccal mass morphology, combined with the coexistence of food remains found in the buccal mass, suggests that these ammonites fed on plankton. This diet may have extended to all aptychophoran ammonites, which share the same buccal mass morphology. Understanding the role of these ammonites in the Mesozoic food web provides insights into their radiation in the Early Jurassic, as well as their extinction at the end of the Cretaceous/early Paleogene. PMID:21212354

Kruta, Isabelle; Landman, Neil; Rouget, Isabelle; Cecca, Fabrizio; Tafforeau, Paul

2011-01-01

237

River Food Web Response to Large-Scale Riparian Zone Manipulations  

PubMed Central

Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks.

Wootton, J. Timothy

2012-01-01

238

River food web response to large-scale riparian zone manipulations.  

PubMed

Conservation programs often focus on select species, leading to management plans based on the autecology of the focal species, but multiple ecosystem components can be affected both by the environmental factors impacting, and the management targeting, focal species. These broader effects can have indirect impacts on target species through the web of interactions within ecosystems. For example, human activity can strongly alter riparian vegetation, potentially impacting both economically-important salmonids and their associated river food web. In an Olympic Peninsula river, Washington state, USA, replicated large-scale riparian vegetation manipulations implemented with the long-term (>40 yr) goal of improving salmon habitat did not affect water temperature, nutrient limitation or habitat characteristics, but reduced canopy cover, causing reduced energy input via leaf litter, increased incident solar radiation (UV and PAR) and increased algal production compared to controls. In response, benthic algae, most insect taxa, and juvenile salmonids increased in manipulated areas. Stable isotope analysis revealed a predominant contribution of algal-derived energy to salmonid diets in manipulated reaches. The experiment demonstrates that riparian management targeting salmonids strongly affects river food webs via changes in the energy base, illustrates how species-based management strategies can have unanticipated indirect effects on the target species via the associated food web, and supports ecosystem-based management approaches for restoring depleted salmonid stocks. PMID:23284786

Wootton, J Timothy

2012-12-20

239

Reducing methylmercury accumulation in the food webs of San Francisco Bay and its local watersheds.  

PubMed

San Francisco Bay (California, USA) and its local watersheds present an interesting case study in estuarine mercury (Hg) contamination. This review focuses on the most promising avenues for attempting to reduce methylmercury (MeHg) contamination in Bay Area aquatic food webs and identifying the scientific information that is most urgently needed to support these efforts. Concern for human exposure to MeHg in the region has led to advisories for consumption of sport fish. Striped bass from the Bay have the highest average Hg concentration measured for this species in USA estuaries, and this degree of contamination has been constant for the past 40 years. Similarly, largemouth bass in some Bay Area reservoirs have some of the highest Hg concentrations observed in the entire US. Bay Area wildlife, particularly birds, face potential impacts to reproduction based on Hg concentrations in the tissues of several Bay species. Source control of Hg is one of the primary possible approaches for reducing MeHg accumulation in Bay Area aquatic food webs. Recent findings (particularly Hg isotope measurements) indicate that the decades-long residence time of particle-associated Hg in the Bay is sufficient to allow significant conversion of even the insoluble forms of Hg into MeHg. Past inputs have been thoroughly mixed throughout this shallow and dynamic estuary. The large pool of Hg already present in the ecosystem dominates the fraction converted to MeHg and accumulating in the food web. Consequently, decreasing external Hg inputs can be expected to reduce MeHg in the food web, but it will likely take many decades to centuries before those reductions are achieved. Extensive efforts to reduce loads from the largest Hg mining source (the historic New Almaden mining district) are underway. Hg is spread widely across the urban landscape, but there are a number of key sources, source areas, and pathways that provide opportunities to capture larger quantities of Hg and reduce loads from urban runoff. Atmospheric deposition is a lower priority for source control in the Bay Area due to a combination of a lack of major local sources. Internal net production of MeHg is the dominant source of MeHg that enters the food web. Controlling internal net production is the second primary management approach, and has the potential to reduce food web MeHg in some habitats more effectively and within a much shorter time-frame. Controlling net MeHg production and accumulation in the food web of upstream reservoirs and ponds is very promising due to the many features of these ecosystems that can be manipulated. The most feasible control options in tidal marshes relate to the design of flow patterns and subhabitats in restoration projects. Options for controlling MeHg production in open Bay habitat are limited due primarily to the highly dispersed distribution of Hg throughout the ecosystem. Other changes in these habitats may also have a large influence on food web MeHg, including temperature changes due to global warming, sea level rise, food web alterations due to introduced species and other causes, and changes in sediment supply. Other options for reducing or mitigating exposure and risk include controlling bioaccumulation, cleanup of contaminated sites, and reducing other factors (e.g., habitat availability) that limit at-risk wildlife populations. PMID:23122771

Davis, J A; Looker, R E; Yee, D; Marvin-Di Pasquale, M; Grenier, J L; Austin, C M; McKee, L J; Greenfield, B K; Brodberg, R; Blum, J D

2012-11-02

240

Chain or Web?  

NSDL National Science Digital Library

This reference provides a brief description of marine food webs. It presents food web terminology, explains the relationship between food chains and food webs, and introduces the concept of microbial loops.

241

Trophic coupling between two adjacent benthic food webs within a man-made intertidal area: A stable isotopes evidence  

Microsoft Academic Search

This study aimed at establishing the effects of human-made physical modifications on the trophic structure and functioning of an intertidal benthic food web in Arcachon Bay (France). The main food sources and the most representative consumers were sampled on an artificial rocky dyke and its adjacent seagrass meadow. The food sources of consumers were inferred through the use of carbon

Gauthier Schaal; Pascal Riera; Cédric Leroux

2008-01-01

242

Methylmercury enters an aquatic food web through acidophilic microbial mats in Yellowstone National Park, Wyoming  

USGS Publications Warehouse

Summary Microbial mats are a visible and abundant life form inhabiting the extreme environments in Yellowstone National Park (YNP), WY, USA. Little is known of their role in food webs that exist in the Park's geothermal habitats. Eukaryotic green algae associated with a phototrophic green/purple Zygogonium microbial mat community that inhabits low-temperature regions of acidic (pH ??? 3.0) thermal springs were found to serve as a food source for stratiomyid (Diptera: Stratiomyidae) larvae. Mercury in spring source water was taken up and concentrated by the mat biomass. Monomethylmercury compounds (MeHg +), while undetectable or near the detection limit (0.025 ng l -1) in the source water of the springs, was present at concentrations of 4-7 ng g-1 dry weight of mat biomass. Detection of MeHg + in tracheal tissue of larvae grazing the mat suggests that MeHg+ enters this geothermal food web through the phototrophic microbial mat community. The concentration of MeHg+ was two to five times higher in larval tissue than mat biomass indicating MeHg+ biomagnification occurred between primary producer and primary consumer trophic levels. The Zygogonium mat community and stratiomyid larvae may also play a role in the transfer of MeHg+ to species in the food web whose range extends beyond a particular geothermal feature of YNP. ?? 2008 The Authors. Journal compilation ?? 2008 Society for Applied Microbiology and Blackwell Publishing Ltd.

Boyd, E. S.; King, S.; Tomberlin, J. K.; Nordstrom, D. K.; Krabbenhoft, D. P.; Barkay, T.; Geesey, G. G.

2009-01-01

243

Density outbursts in a food web model with a closed nutrient cycle  

NASA Astrophysics Data System (ADS)

A spatial three level food web model with a closed nutrient cycle is presented and analyzed via Monte Carlo simulations. The food web consists of three trophic levels. The basal level species (called resources, R) corresponds to primary producers in real ecosystems. The species at an intermediate level (consumers, C) relates to herbivores. It feeds on the resources. The consumers themselves constitute food for the top level species (predators, P), which corresponds to carnivores. The remains of the consumers and predators (detritus, D) provide nutrient for the resources. The time evolution of the model reveals two asymptotic states: an absorbing one with all species being extinct, and a coexisting one, in which concentrations of all species are non-zero. There are two possible ways for the system to reach the absorbing state. In some cases the densities increase very quickly at the beginning of a simulation and then decline slowly and almost monotonically. In others, well pronounced peaks in the R, C and D densities appear regularly before the extinction. Those peaks correspond to density outbursts (waves) traveling through the system. We investigate the mechanisms leading to the waves. In particular, we show that the percolation of the detritus (i.e. the accumulation of nutrients) is necessary for the emergence of the waves. Moreover, our results corroborate the hypothesis that top-level predators play an essential role in maintaining the stability of a food web (top-down control).

Szwabi?ski, Janusz

2013-09-01

244

All wet or dried up? Real differences between aquatic and terrestrial food webs.  

PubMed

Ecologists have greatly advanced our understanding of the processes that regulate trophic structure and dynamics in ecosystems. However, the causes of systematic variation among ecosystems remain controversial and poorly elucidated. Contrasts between aquatic and terrestrial ecosystems in particular have inspired much speculation, but only recent empirical quantification. Here, we review evidence for systematic differences in energy flow and biomass partitioning between producers and herbivores, detritus and decomposers, and higher trophic levels. The magnitudes of different trophic pathways vary considerably, with less herbivory, more decomposers and more detrital accumulation on land. Aquatic-terrestrial differences are consistent across the global range of primary productivity, indicating that structural contrasts between the two systems are preserved despite large variation in energy input. We argue that variable selective forces drive differences in plant allocation patterns in aquatic and terrestrial environments that propagate upward to shape food webs. The small size and lack of structural tissues in phytoplankton mean that aquatic primary producers achieve faster growth rates and are more nutritious to heterotrophs than their terrestrial counterparts. Plankton food webs are also strongly size-structured, while size and trophic position are less strongly correlated in most terrestrial (and many benthic) habitats. The available data indicate that contrasts between aquatic and terrestrial food webs are driven primarily by the growth rate, size and nutritional quality of autotrophs. Differences in food-web architecture (food chain length, the prevalence of omnivory, specialization or anti-predator defences) may arise as a consequence of systematic variation in the character of the producer community. PMID:16519227

Shurin, Jonathan B; Gruner, Daniel S; Hillebrand, Helmut

2006-01-01

245

Canyon conditions impact carbon flows in food webs of three sections of the Nazaré canyon  

NASA Astrophysics Data System (ADS)

Submarine canyons transport large amounts of sediment and organic matter (OM) from the continental shelf to the abyssal plain. Three carbon-based food web models were constructed for the upper (300-750 m water depth), middle (2700-3500 m) and lower section (4000-5000 m) of the Nazaré canyon (eastern Atlantic Ocean) using linear inverse modeling to examine how the food web is influenced by the characteristics of the respective canyon section. The models were based on an empirical dataset consisting of biomass and carbon processing data, and general physiological data constraints from the literature. Environmental conditions, most notably organic matter (OM) input and hydrodynamic activity, differed between the canyon sections and strongly affected the benthic food web structure. Despite the large difference in depth, the OM inputs into the food webs of the upper and middle sections were of similar magnitude (7.98±0.84 and 9.30±0.71 mmol C m -2 d -1, respectively). OM input to the lower section was however almost 6-7 times lower (1.26±0.03 mmol C m -2 d -1). Carbon processing in the upper section was dominated by prokaryotes (70% of total respiration), though there was a significant meiofaunal (21%) and smaller macrofaunal (9%) contribution. The high total faunal contribution to carbon processing resembles that found in shallower continental shelves and upper slopes, although the meiofaunal contribution is surprisingly high and suggest that high current speeds and sediment resuspension in the upper canyon favor the role of the meiofauna. The high OM input and conditions in the accreting sediments of the middle canyon section were more beneficial for megafauna (holothurians), than for the other food web compartments. The high megafaunal biomass (516 mmol C m -2), their large contribution to respiration (56% of total respiration) and secondary production (0.08 mmol C m -2 d -1) shows that these accreting sediments in canyons are megafaunal hotspots in the deep-sea. Conversely, carbon cycling in the lower canyon section was strongly dominated by prokaryotes (86% of respiration) and the food web structure therefore resembled that of lower slope and abyssal plain sediments. This study shows that elevated OM input in canyons may favor the faunal contribution to carbon processing and create hotspots of faunal biomass and carbon processing along the continental shelf.

van Oevelen, Dick; Soetaert, Karline; Garcia, R.; de Stigter, Henko C.; Cunha, Marina R.; Pusceddu, Antonio; Danovaro, Roberto

2011-12-01

246

Food webs and physical biological coupling on pan-Arctic shelves: Unifying concepts and comprehensive perspectives  

NASA Astrophysics Data System (ADS)

Perhaps more than in any other ocean, our understanding of the continental shelves of the Arctic Mediterranean is decidedly disciplinary, regional and fractured, and this shortcoming must be addressed if we are to face and prepare for climate change. A fundamental flaw is that while excellent process studies exist, and while recent ship-based expeditions have added greatly to our collective body of knowledge, an integrated and fully pan-Arctic perspective on the structure and function of food webs on Arctic shelves is lacking. Based on the collective overviews given in Progress in Oceanography xx, xx xx, we attempt to address this issue. To build a perspective that inter-connects the various shelf regions we suggest three unifying typologies affecting food webs that will hopefully allow inter-comparison of regional investigations. The first is for shelf geography, wherein shelves are classified according to their role in the Arctic throughflow. The second is for ice climate, wherein the various ice regimes are examined for their specific impacts on food web dynamics. The third is for stratification where it is argued that the source of buoyancy, thermal or haline, impacts production and the vertical carbon flux. We then address the connection between physical habitat and biota on pan-Arctic (and global climate) scales. This discussion begins with the recognition that the Arctic Ocean is integral to the World Ocean via its thermohaline (“estuarine”) exchanges with the Atlantic and Pacific. As such the Arctic and its shelves act as a double estuary, wherein incoming waters become both lighter (positive estuary), by mixing with freshwater sources, and heavier (negative estuary) by cooling and brine release. Shelves are central to such transformations. This complex interconnectivity coupling of the Arctic Ocean to its sub-Arctic (and more productive) neighbors demands that food webs be considered through a macroecological view that includes an ecology of advection. We argue that the macroecological view is required if we are to understand and model food webs under forcing along climate gradients. To aid this effort we introduce the concept of contiguous domains, wherein physical habitats are joined by common features that will allow inter-comparisons of existing and future food webs over large scales and climatic gradients. Finally, we speculate on the range of possible futures for Arctic shelves based on the palaeo-record.

Carmack, Eddy; Wassmann, Paul

2006-10-01

247

Some lower food web organisms in the nutrition of marine harpacticoid copepods: an experimental study  

NASA Astrophysics Data System (ADS)

Some lower food web organisms from the marine littoral environment were studied as food for harpacticoid copepods. In laboratory experiments, it could be shown that, among the ciliates, the slow-moving Uronema sp. was taken up while the fast-moving Euplotes sp. was not. Asterionella glacialis, a pennate diatom with spiny projections, was unsuitable as food. The centric diatom Skeletonema costatum was ingested by all harpacticoid species tested, including Tisbe holothuriae, Paramphiascella vararensis, Amphiascoides debilis and Dactylopodia vulgaris. All are epibenthic and phytal species occurring in the shallow waters of Helgoland (North Sea). The amount of ciliate and algal carbon taken up was less than that provided by bacteria under laboratory conditions. However, some diatom food may be essential for the development of D. vulgaris.

Rieper, Marianna

1985-12-01

248

Experimental warming transforms multiple predator effects in a grassland food web.  

PubMed

This experimental study tests new theory for multiple predator effects on communities by using warming to alter predator habitat use and hence direct and indirect interactions in a grassland food web containing two dominant spider predator species, a dominant grasshopper herbivore and grass and herb plants. Experimental warming further offers insight into how climate change might alter direct and indirect effects. Under ambient environmental conditions, spiders used habitat in spatially complementary locations. Consistent with predictions, the multiple predator effect on grasshoppers and on plants was the average of the individual predator effects. Warming strengthened the single predator effects. It also caused the spider species to overlap lower in the vegetation canopy. Consistent with predictions, the system was transformed into an intraguild predation system with the consequent extinction of one spider species. The results portend climate caused loss of predator diversity with important consequences for food web structure and function. PMID:19780788

Barton, Brandon T; Schmitz, Oswald J

2009-09-23

249

Food-web structure in low- and high-dimensional trophic niche spaces  

PubMed Central

A question central to modelling and, ultimately, managing food webs concerns the dimensionality of trophic niche space, that is, the number of independent traits relevant for determining consumer–resource links. Food-web topologies can often be interpreted by assuming resource traits to be specified by points along a line and each consumer's diet to be given by resources contained in an interval on this line. This phenomenon, called intervality, has been known for 30 years and is widely acknowledged to indicate that trophic niche space is close to one-dimensional. We show that the degrees of intervality observed in nature can be reproduced in arbitrary-dimensional trophic niche spaces, provided that the processes of evolutionary diversification and adaptation are taken into account. Contrary to expectations, intervality is least pronounced at intermediate dimensions and steadily improves towards lower- and higher-dimensional trophic niche spaces.

Rossberg, Axel G.; Brannstrom, Ake; Dieckmann, Ulf

2010-01-01

250

The relationships between mercury and selenium in plankton and fish from a tropical food web  

Microsoft Academic Search

Background, aim, and scope  Selenium (Se) has been shown to reduce mercury (Hg) bioavailability and trophic transfer in aquatic ecosystems. The study\\u000a of methylmercury (MeHg) and Se bioaccumulation by plankton is therefore of great significance in order to obtain a better\\u000a understanding of the estuarine processes concerning Hg and Se accumulation and biomagnification throughout the food web. In\\u000a the western South

Helena do A. Kehrig; Tércia G. Seixas; Elisabete A. Palermo; Aida P. Baêta; Christina W. Castelo-Branco; Olaf Malm; Isabel Moreira

2009-01-01

251

Synergism between research and simulation models of estuarine microbial food webs  

Microsoft Academic Search

Construction of mathematical simulation models helps to organize current information and extend inferences from available\\u000a data. During the past two decades, microbial ecology has undergone rapid developments in both quantity and quality of available\\u000a data. In particular, considerable advances have been made in our knowledge of microbial food web dynamics in the Duplin River\\u000a watershed at Sapelo Island, Georgia. Here

Robert R. Christian; Richard L. Wetzel

1991-01-01

252

Food web analysis of southern California coastal wetlands using multiple stable isotopes  

Microsoft Academic Search

Carbon, nitrogen, and sulfur stable isotopes were used to characterize the food webs (i.e., sources of carbon and trophic\\u000a status of consumers) in Tijuana Estuary and San Dieguito Lagoon. Producer groups were most clearly differentiated by carbon,\\u000a then by sulfur, and least clearly by nitrogen isotope measurements. Consumer 15N isotopic enrichment suggested that there are four trophic levels in the

Thomas J. Kwak; Joy B. Zedler

1997-01-01

253

Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structure  

Microsoft Academic Search

The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state

Katleen Van der Gucht; Tom Vandekerckhove; Nele Vloemans; Sylvie Cousin; Koenraad Muylaert; Koen Sabbe; Moniek Gillis; Steven Declerk; Luc De Meester; Wim Vyverman

2005-01-01

254

Tracing Mississippi River influences in estuarine food webs of coastal Louisiana.  

PubMed

The Breton Sound estuary in southern Louisiana receives large amounts of Mississippi River water via a controlled diversion structure at the upstream end of the estuary. We used stable isotopes to trace spatial and seasonal responses of the downstream food web to winter and spring introductions of river water. Analysis of delta13C, delta15N, and delta34S in the common local consumers such as grass shrimp (Palaemonetes sp.), barnacles (Balanus sp.), and small plankton-feeding fish (bay anchovies, Anchoa mitchilli) showed that the diversion was associated with two of the five major source regimes that were supporting food webs: a river regime near the diversion and a river-influenced productive marsh regime farther away from the diversion. Mixing models identified a third river-influenced source regime at the marine end of the estuary where major natural discharge from the Bird's Foot Delta wraps around into estuarine waters. The remaining two source regimes represented typical estuarine conditions: local freshwater sources especially from precipitation and a brackish source regime representing higher salinity marine influences. Overall, the Mississippi River diversion accounted for 75% of food web support in the upper estuary and 25% in the middle estuary, with influence strongest along known flow pathways and closest to the diversion. Isotopes also traced seasonal changes in river contributions, and indicated increased plant community productivity along the major flow path of diversion water. In the Breton Sound estuary, bottom-up forcing of food webs is strongly linked to river introductions and discharge, occurring in spatial and temporal patterns predictable from known river input regimes and known hydrologic circulation patterns. PMID:16041544

Wissel, Björn; Fry, Brian

2005-07-22

255

Role of chemical and ecological factors in trophic transfer of organic chemicals in aquatic food webs  

Microsoft Academic Search

Trophic transfer of chlorinated organic contaminants was investigated in an aquatic community composed of zooplankton, benthic invertebrates, and fish. Biomagnification, measured as the increase in lipid-based chemical concentrations in predator over that in prey, was observed for high-K[sub OW] chemicals (log K[sub OW] > 6.3). Low-K[sub OW] chemicals (log K[sub OW] < 5.5) did not biomagnify in the food web,

Ronald W. Russell; Frank A. P. C. Gobas; G. Douglas Haffner

1999-01-01

256

Field evidence of trait-mediated indirect interactions in a rocky intertidal food web  

Microsoft Academic Search

Studies on the implications of food web interactions to community structure have often focused on density-mediated interactions between predators and their prey. This approach emphasizes the importance of predator regulation of prey density via consumption (i.e. lethal effects), which, in turn, leads to cascading effects on the prey's resources. A more recent and contrasting view emphasizes the importance of non-lethal

Geoffrey C. Trussell; Patrick J. Ewanchuk; Mark D. Bertness

2002-01-01

257

Agriculture and Food Related Theses and Dissertations Available on the Web  

Microsoft Academic Search

Electronic theses and dissertations (ET\\/Ds) produced by graduate students in agricultural and food science programs at land-grant universities provide current research results as Web-based information that can be accessed from one's own computer. Those land-grant universities that are members of the Networked Digital Library of Theses and Dissertations (NDLTD) participate in the addition of their electronically submitted or digitally scanned

Lona L. Hoover

2006-01-01

258

Food Web Changes over Fourteen Years Following Introduction of Rainbow Smelt into a Colorado Reservoir  

Microsoft Academic Search

Rainbow smelt Osmerus mordaxwere introduced into Horsetooth Reservoir, Colorado, in 1983 to increase prey availability for walleyes Stizostedion vitreum.The introduction was highly successful. Rainbow smelt abundance reached at least 0.4 fish\\/m 3 within 6 years, and walleye growth improved by 50%. Zooplankton sampling provided the first clues that the Horsetooth Reservoir food web was undergoing dramatic changes in response to

Brett M. Johnson; John P. Goettl

1999-01-01

259

Monitoring food web changes in tide-restored salt marshes: A carbon stable isotope approach  

Microsoft Academic Search

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended particulate matter, andFundulus heteroclitus isotope values (?13C, ?15N, ?34S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes.\\u000a Study sites, located throughout the southern New England region (USA), ranged fromSpartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration,

Andrew S. Wozniak; Charles T. Roman; Sam C. Wainright; Richard A. McKinney; Mary-Jane James-Pirri

2006-01-01

260

Mercury bioaccumulation and trophic transfer in the terrestrial food web of a montane forest  

Microsoft Academic Search

We investigated mercury (Hg) concentrations in a terrestrial food web in high elevation forests in Vermont. Hg concentrations\\u000a increased from autotrophic organisms to herbivores < detritivores < omnivores < carnivores. Within the carnivores studied,\\u000a raptors had higher blood Hg concentrations than their songbird prey. The Hg concentration in the blood of the focal study\\u000a species, Bicknell’s thrush (Catharus bicknelli), varied over the course of the summer

Christopher C. RimmerEric; Eric K. Miller; Kent P. McFarland; Robert J. Taylor; Steven D. Faccio

2010-01-01

261

Linking aboveground and belowground food webs through carbon and nitrogen stable isotope analyses  

Microsoft Academic Search

Carbon and nitrogen stable isotope ratios (?13C and ?15N) have been used for more than two decades in analyses of food web structure. The utility of isotope ratio measurements is\\u000a based on the observation that consumer ?13C values are similar (15N values are about 3‰ higher than those of their diet. The technique has been applied most often to aquatic

Fujio Hyodo; Ayato Kohzu; Ichiro Tayasu

2010-01-01

262

Influence of lake characteristics on the biomagnification of persistent organic pollutants in lake trout food webs.  

PubMed

The biomagnification of polychlorinated biphenyls (PCBs) and major organochlorine pesticides (OCPs) was studied using lake trout (Salvelinus namaycush) and other food web organisms collected from 17 lakes in Canada and the northeastern United States between 1998 and 2001. Whole lake trout (n = 357) concentrations of the sum (Sigma) of 57 PCB congeners ranged between 1.67 and 2,890 ng/g wet weight (median 61.5 ng/g wet wt). Slimy sculpin had the highest mean concentrations of SigmaPCB of all forage fish (32-73 ng/g wet wt). Positive relationships between log (lipid wt) concentrations of PCB congener 153, PCB congener 52, p,p'-dichlorodiphenyldichloroethylene, hexachlorobenzene, cis-chlordane, trans-nonachlor, or dieldrin and trophic level (determined using stable nitrogen isotope ratios) were found for most of the 17 food webs, indicating biomagnification of these PCBs and OCPs. The p,p'-dichlorodiphenyldichloroethylene had the highest trophic magnification factors (TMFs) of the 14 individual compounds studied, averaging 4.0 +/- 1.8 across the 17 lakes, followed by trans-nonachlor (3.6 +/- 1.5) and PCB congener 153 (3.4 +/- 1.2). Average TMFs for 14 individual PCBs or OCPs were significantly correlated with log octanol-water partition coefficient, implying that the rate of accumulation along the food web is dependent on hydrophobicity and recalcitrance. Significant correlations (p < 0.05) were found between TMFs of SigmaPCBs, hexachlorobenzene, alpha-hexachlorocyclohexane, and lindane and lake area, latitude, and longitude, but not for 11 other PCBs or OCPs. Overall, the results of the present study show that biomagnification of PCBs and most OCPs, as measured by TMFs, is only weakly influenced by such factors as latitude and longitude. Exceptions are hexachlorocyclohexane isomers and hexachlorobenzene, which had generally greater TMFs in northern lakes, possibly due to lower rates of elimination and biotransformation in the food web. PMID:18444699

Houde, Magali; Muir, Derek C G; Kidd, Karen A; Guildford, Stephanie; Drouillard, Ken; Evans, Marlene S; Wang, Xiaowa; Whittle, D Michael; Haffner, Doug; Kling, Hedy

2008-10-01

263

Trait-Mediated Indirect Interactions in a Simple Aquatic Food Web  

Microsoft Academic Search

This investigation examines the role of trait-mediated indirect interactions in a simple aquatic food web. We conducted the experiments in cattle watering tanks in order to establish whether competitive and predator-prey interactions between two species are affected by other species in the system; i.e., are pairwise interaction strengths affected by the background species assemblage? We examined the survival and growth

Scott D. Peacor; Earl E. Werner

1997-01-01

264

High Complexity Food Webs in Low-diversity Eastern Pacific Reef–Coral Communities  

Microsoft Academic Search

Community-wide feeding interrelationships in a low-diversity coral reef off the Pacific coast of Panamá (Uva Island reef) demonstrate complex pathways involving herbivore, strong corallivore, and carnivore interactions. Four trophic levels with 31 interguild links are identified in a generalized food web, and documented feeding interrelationships with 287+ species links are portrayed in a coral–corallivore subweb. The importance of trophic groups

Peter W. Glynn

2004-01-01

265

Effects of network and dynamical model structure on species persistence in large model food webs  

Microsoft Academic Search

Four models of network structure are combined with models of bioenergetic dynamics to study the role of food web topology\\u000a and nonlinear dynamics on species coexistence in complex ecological networks. Network models range from the highly structured\\u000a niche model to loosely constrained energetically feasible random networks. Bioenergetic models differ in how they represent\\u000a primary production, functional responses, and consumption by

Richard J. Williams

2008-01-01

266

Facing the necessity of describing estuarine ecosystems: a review of food web ecology study techniques  

Microsoft Academic Search

Estuarine areas are sites of human pressures and degradation. In order to maintain and\\/or restore the quality of estuarine\\u000a ecosystems, it is necessary to describe their structure and functioning. For that reason, many recent scientific works focus\\u000a on food webs, which are depicted as being good indicators of the functioning of aquatic ecosystems. Hence it is necessary\\u000a to question how

Stéphanie Pasquaud; Jérémy Lobry; Pierre Elie

2007-01-01

267

A theoretical approach to structuring mechanisms in the pelagic food web  

Microsoft Academic Search

In the literature there is a commonly used idealized concept of the foodweb structure in the pelagic photic zone food web,\\u000a based to a large extenton size dependent relationships. An outline is here given of how theelementary size-related physical\\u000a laws of diffusion and sinking, combinedwith the assumption of predators being size selective in their choice ofprey, give\\u000a a theoretical foundation

T. Frede Thingstad

1997-01-01

268

Ant-Hemipteran Mutualisms: Keystone Interactions that Alter Food Web Dynamics and Influence Plant Fitness  

Microsoft Academic Search

Predicting the direct and indirect effects of natural enemies on herbivorous insects in species-rich, highly connected arthropod\\u000a food webs can be extremely difficult. Community ecologists developed the keystone species concept to help simplify this task.\\u000a Keystone species are species that have disproportionately large effects on the abundance of many interacting species in a\\u000a community. Keystone species, however, can be difficult

Micky D. Eubanks; John D. Styrsky

269

Effect of microbes on contaminant transfer in the Lake Superior food web.  

PubMed

The partitioning of PCBs to natural populations of aquatic heterotrophic bacteria from Lake Superior was measured in both field and laboratory studies to better understand the role of bacteria and the microbial food web in persistent, bioaccumulative, toxic organic contaminant (PBT) transfer. A filtration method that separated material >1 microm from that <1 microm was used to collect and measure PCB concentrations in the bacterial fraction. We used bacterial biovolume and a conversion factor to calculate bacterial carbon, which was used to normalize PCB concentrations. The range of total PCB concentrations in the bacterial fraction (61-337 ng/g organic carbon; OC) was similar, but generally higher than that of the total particulate fraction (36-324 ng/g OC). Measured log bioaccumulation factors (BAFoc, bacterial fraction; Koc, total particulate) were significantly greater in the bacterial fraction than in the total particulate fraction (bacterial range 6.7-7.3, total particulate range 5.8-7.0). Laboratory experiments demonstrated that a hexachlorobiphenyl reached steady state with a natural community of Lake Superior bacteria within 48 h and had a mean log BAFoc of 7.5 +/- 1.9. The octanol/ water partition coefficient (Kow) consistently under-predicted BAFoc, however, the magnitude of the under-prediction was still within the range of uncertainty in food web modeling (factors of 3-9). Food web modeling and risk assessment of PBT bioaccumulation in aquatic systems could be improved by considering the microbial food web (bacteria and its protozoan grazers) as a previously unaccounted for pathway of contaminant transfer. PMID:16475328

Hudson, Matthew J; Swackhamer, Deborah L; Cotner, James B

2005-12-15

270

Succession processes in a food web of a two autotroph--one herbivore system.  

PubMed

This paper deals with the succession process of a food web model consisting of one herbivore, two autotrophs and available nutrient in the environment in a closed nutrient flux. The model provides a way of describing successional changes in the form of species replacement with increasing nutrient levels. It is shown that distinct threshold (with upper and lower) values of nutrient are required for progression of succession process. PMID:11084235

Kesh, D; Sarkar, A K; Roy, A B

271

Nitrogen addition and warming independently influence the belowground micro-food web in a temperate steppe.  

PubMed

Climate warming and atmospheric nitrogen (N) deposition are known to influence ecosystem structure and functioning. However, our understanding of the interactive effect of these global changes on ecosystem functioning is relatively limited, especially when it concerns the responses of soils and soil organisms. We conducted a field experiment to study the interactive effects of warming and N addition on soil food web. The experiment was established in 2006 in a temperate steppe in northern China. After three to four years (2009-2010), we found that N addition positively affected microbial biomass and negatively influenced trophic group and ecological indices of soil nematodes. However, the warming effects were less obvious, only fungal PLFA showed a decreasing trend under warming. Interestingly, the influence of N addition did not depend on warming. Structural equation modeling analysis suggested that the direct pathway between N addition and soil food web components were more important than the indirect connections through alterations in soil abiotic characters or plant growth. Nitrogen enrichment also affected the soil nematode community indirectly through changes in soil pH and PLFA. We conclude that experimental warming influenced soil food web components of the temperate steppe less than N addition, and there was little influence of warming on N addition effects under these experimental conditions. PMID:23544140

Li, Qi; Bai, Huahua; Liang, Wenju; Xia, Jianyang; Wan, Shiqiang; van der Putten, Wim H

2013-03-27

272

Tracing Fluxes Of Aquatic Production And Contaminants Into Terrestrial Food Webs With Nitrogen Stable Isotopes  

NASA Astrophysics Data System (ADS)

Biomagnifying contaminants such as mercury can be transported and redistributed across the watershed by streams and rivers. Their fate and effects on consumers depend on food web transfer both within and between aquatic and terrestrial ecosystems. The Truckee River (Ca/Ne) is heavily contaminated by Hg originating from century-old upstream mining operations. We used nitrogen stable isotope analysis to trace the incorporation of Hg transported by the Truckee and transferred by emerging aquatic insects into the riparian food web. N-isotope ratios and Hg of aquatic primary consumers were significantly elevated compared to that of terrestrial arthropods (13.3 vs 5.6 % and 110 vs 17 ngg-1). Estimates of dependence on aquatics in 16 riparian passerine bird species based on blood delta 15N ranged between 0.0 and 0.95 and were significantly related to Hg in blood. Similar correlations between Hg and delta 15N measured in tail tips of western fence lizard (Sceloporus occidentalis) collected at increasing distances from the river were observed. High inter-individual variation in bird Hg was highly correlated with delta 15N. These results show how stable isotopes and contaminant fluxes can reveal important food web linkages across aquatic/terrestrial ecotones.

Rivard, A.; Cabana, G.; Rainey, W.; Power, M.

2005-05-01

273

Growth, feeding and ecological roles of the mixotrophic and heterotrophic dinoflagellates in marine planktonic food webs  

NASA Astrophysics Data System (ADS)

Planktonic mixotrophic and heterotrophic dinoflagellates are ubiquitous protists and often abundant in marine environments. Recently many phototrophic dinoflagellate species have been revealed to be mixotrophic organisms and also it is suggested that most dinoflagellates may be mixotrophic or heterotrophic protists. The mixotrophic and heterotrophic dinoflagellates are able to feed on diverse prey items including bacteria, picoeukaryotes, nanoflagellates, diatoms, other dinoflagellates, heterotrophic protists, and metazoans due to their diverse feeding mechanisms. In turn they are ingested by many kinds of predators. Thus, the roles of the dinoflagellates in marine planktonic food webs are very diverse. The present paper reviewed the kind of prey which mixotrophic and heterotrophic dinoflagellates are able to feed on, feeding mechanisms, growth and ingestion rates of dinoflagellates, grazing impact by dinoflagellate predators on natural prey populations, predators on dinoflagellates, and red tides dominated by dinoflagellates. Based on this information, we suggested a new marine planktonic food web focusing on mixotrophic and heterotrophic dinoflagellates and provided an insight on the roles of dinoflagellates in the food web.

Jeong, Hae Jin; Yoo, Yeong Du; Kim, Jae Seong; Seong, Kyeong Ah; Kang, Nam Seon; Kim, Tae Hoon

2010-06-01

274

Trophic magnification of poly- and perfluorinated compounds in a subtropical food web.  

PubMed

Perfluorinated compounds (PFCs) are known to biomagnify in temperate and Arctic food webs, but little is known about their behavior in subtropical systems. The environmental distribution and biomagnification of PFCs, extractable organic fluorine (EOF), and total fluorine were investigated in a subtropical food web. Surface water, sediment, phytoplankton, zooplankton, gastropods, worms, shrimps, fishes, and waterbirds collected in the Mai Po Marshes Nature Reserve in Hong Kong were analyzed. Trophic magnification was observed for perfluorooctanesulfonate (PFOS), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnDA), and perfluorododecanoate (PFDoDA) in this food web. Risk assessment results for PFOS, PFDA, and perfluorooctanoate (PFOA) suggest that current PFC concentrations in waterbird livers are unlikely to pose adverse biological effects to waterbirds. All hazard ratio (HR) values reported for PFOS and PFOA are less than one, which suggests that the detected levels will not cause any immediate health effects to the Hong Kong population through the consumption of shrimps and fishes. However, only 10-12% of the EOF in the shrimp samples was comprised of known PFCs, indicating the need for further investigation to identify unknown fluorinated compounds in wildlife. PMID:21644538

Loi, Eva I H; Yeung, Leo W Y; Taniyasu, Sachi; Lam, Paul K S; Kannan, Kurunthachalam; Yamashita, Nobuyoshi

2011-06-06

275

Lipids of Prokaryotic Origin at the Base of Marine Food Webs  

PubMed Central

In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered “extremophiles” and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, high/low salinity and pH. Bacterial cells are even able to produce polyunsaturated fatty acids, contrarily to what was considered until the 1990s, helping the regulation of the membrane fluidity triggered by temperature and pressure and providing protection from oxidative stress. In marine ecosystems, bacteria may either act as a sink of carbon, contribute to nutrient recycling to photo-autotrophs or bacterial organic matter may be transferred to other trophic links in aquatic food webs. The present work aims to provide a comprehensive review on lipid production in bacteria and archaea and to discuss how their lipids, of both heterotrophic and chemoautotrophic origin, contribute to marine food webs.

de Carvalho, Carla C. C. R.; Caramujo, Maria Jose

2012-01-01

276

Evolution mediates the effects of apex predation on aquatic food webs.  

PubMed

Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance. PMID:23720548

Urban, Mark C

2013-05-29

277

Biomagnification of mercury in selected species from an Arctic marine food web in Svalbard.  

PubMed

Concentrations and biomagnification of total mercury (TotHg) and methyl mercury (MeHg) were studied in selected species from the pelagic food web in Kongsfjorden, Svalbard. Twelve species of zooplankton, fish and seabirds, were sampled representing a gradient of trophic positions in the Svalbard marine food web. TotHg and MeHg were analysed in liver, muscle and/or whole specimens. The present study is the first to provide MeHg levels in seabirds from the Svalbard area. The relative MeHg levels decreased with increasing levels of TotHg in seabird tissues. Stable isotopes of nitrogen (delta(15)N) were used to determine the trophic levels and the rate of biomagnification of mercury in the food web. A linear relationship between mercury levels and trophic position was found for all seabird species combined and their trophic level, but there was no relationship within species. Biomagnification factors were all >1 for both TotHg and MeHg, indicating biomagnification from prey to predator. TotHg levels in the different seabirds were similar to levels detected in the Kongsfjorden area in the 1990s. PMID:19454364

Jaeger, Iris; Hop, Haakon; Gabrielsen, Geir W

2009-05-19

278

Biomagnification of mercury through the benthic food webs of a temperate estuary: Masan Bay, Korea.  

PubMed

The authors examined food web magnification factors of total mercury (THg) and methylmercury (MeHg) for the benthic organisms in Masan Bay, a semiclosed, temperate estuary located on the southeastern coast of Korea. For benthic invertebrates, concentrations of THg and MeHg (%MeHg) ranged from 9.57 to 195 and 2.56 to 111 ng/g dry weight (12.2-85.6%), respectively. Benthic fish THg and MeHg (%MeHg) concentrations ranged widely from 10.8 to 618 and 2.90 to 529 ng/g dry weight (22.9-93.9%), respectively. The linear regression slopes of log [Hg] relative to ?(15)N (i.e., food web magnification factors) found for the Masan Bay benthic organisms were 0.119 for THg and 0.168 for MeHg. These values are similar to the food web magnification factors of benthic organisms and lower than those of pelagic organisms of various coastal marine environments. It suggests that pelagic organisms might be at greater risk of THg and MeHg accumulation than benthic biota. PMID:22447737

Kim, Eunhee; Kim, Hyunji; Shin, Kyung-hoon; Kim, Min-seob; Kundu, Sampa Rani; Lee, Byeong-gweon; Han, Seunghee

2012-04-18

279

Nitrogen Addition and Warming Independently Influence the Belowground Micro-Food Web in a Temperate Steppe  

PubMed Central

Climate warming and atmospheric nitrogen (N) deposition are known to influence ecosystem structure and functioning. However, our understanding of the interactive effect of these global changes on ecosystem functioning is relatively limited, especially when it concerns the responses of soils and soil organisms. We conducted a field experiment to study the interactive effects of warming and N addition on soil food web. The experiment was established in 2006 in a temperate steppe in northern China. After three to four years (2009–2010), we found that N addition positively affected microbial biomass and negatively influenced trophic group and ecological indices of soil nematodes. However, the warming effects were less obvious, only fungal PLFA showed a decreasing trend under warming. Interestingly, the influence of N addition did not depend on warming. Structural equation modeling analysis suggested that the direct pathway between N addition and soil food web components were more important than the indirect connections through alterations in soil abiotic characters or plant growth. Nitrogen enrichment also affected the soil nematode community indirectly through changes in soil pH and PLFA. We conclude that experimental warming influenced soil food web components of the temperate steppe less than N addition, and there was little influence of warming on N addition effects under these experimental conditions.

Li, Qi; Bai, Huahua; Liang, Wenju; Xia, Jianyang; Wan, Shiqiang; van der Putten, Wim H.

2013-01-01

280

Mercury Bioavailability and Bioaccumulation in Estuarine Food Webs in the Gulf of Maine  

PubMed Central

Marine food webs are important links between Hg in the environment and human exposure via consumption of fish. Estuaries contain sediment repositories of Hg and are also critical habitat for marine fish and shellfish species consumed by humans. MeHg biotransfers from sites of production in estuarine sediments to higher trophic levels via both benthic and pelagic pathways. In this study, we investigated the potential for Hg biotransfer to estuarine food webs across a Hg contamination gradient in the Gulf of Maine. Despite the variation in sediment Hg concentrations across sites (>100 fold), Hg concentrations in biota ranged by only 2–4 fold for each species across sites. Sediment contamination alone explained some variation in Hg and MeHg concentrations in biota across sites. However, biogeochemical and ecological factors also explained significant variation in Hg bioaccumulation across species. Contaminated sites had higher total organic carbon concentrations in sediments, which related to a decrease in Hg bioaccumulation (measured as biota-sediment concentration factors, BSCF). Moreover, concentrations of MeHg were higher in pelagic-feeding than benthic-feeding fauna (determined from delta 13C) indicating the importance of pelagic pathways in transferring MeHg. Lastly, the proportion of total Hg as MeHg increased with trophic level (measured as delta 15N). These results reveal the importance of both biogeochemical and ecological factors in determining the bioavailability and trophic transfer of MeHg in estuarine food webs.

Chen, Celia Y.; Dionne, Michele; Mayes, Brandon M.; Ward, Darren M.; Sturup, Stefan; Jackson, Brian P.

2009-01-01

281

Lipids of prokaryotic origin at the base of marine food webs.  

PubMed

In particular niches of the marine environment, such as abyssal trenches, icy waters and hot vents, the base of the food web is composed of bacteria and archaea that have developed strategies to survive and thrive under the most extreme conditions. Some of these organisms are considered "extremophiles" and modulate the fatty acid composition of their phospholipids to maintain the adequate fluidity of the cellular membrane under cold/hot temperatures, elevated pressure, high/low salinity and pH. Bacterial cells are even able to produce polyunsaturated fatty acids, contrarily to what was considered until the 1990s, helping the regulation of the membrane fluidity triggered by temperature and pressure and providing protection from oxidative stress. In marine ecosystems, bacteria may either act as a sink of carbon, contribute to nutrient recycling to photo-autotrophs or bacterial organic matter may be transferred to other trophic links in aquatic food webs. The present work aims to provide a comprehensive review on lipid production in bacteria and archaea and to discuss how their lipids, of both heterotrophic and chemoautotrophic origin, contribute to marine food webs. PMID:23342392

de Carvalho, Carla C C R; Caramujo, Maria José

2012-12-01

282

Salmon Life Histories, Habitat, and Food Webs in the Columbia River Estuary: An Overview of Research Results, 2002-2006.  

National Technical Information Service (NTIS)

From 2002 through 2006 we investigated historical and contemporary variations in juvenile Chinook salmon Oncorhynchus tshawytscha life histories, habitat associations, and food webs in the lower Columbia River estuary (mouth to rkm 101). At near-shore bea...

A. Baptista D. L. Bottom G. Anderson J. Burke M. Bural

2008-01-01

283

Fuel Reduction Effects on a Key Sierra Food Web. (Final Report, Project 01B-3-3-05).  

National Technical Information Service (NTIS)

Using a full-factorial experimental design, this project examined the effects of prescribed burning and mechanical thinning on the food web interactions among small mammals, truffle-producing ectomycorrhizae, and dominant forest trees in Sierra Nevada mix...

D. A. Kelt M. North M. D. Meyer

2005-01-01

284

Cesium: Potassium Index of Food Web Structure and Biomagnification of Trace Elements in a Polluted Harbor of Southern California.  

National Technical Information Service (NTIS)

A biological technique of quantifying trophic position in marine food webs, and a chemical technique of quantifying 'structure' in feeding relationships and resultant biomagnification potential, were applied to a polluted harbor ecosystem. The chemical in...

D. R. Young A. J. Mearns T. K. Jan

1987-01-01

285

Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web  

PubMed Central

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño–Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.

Murphy, E.J; Watkins, J.L; Trathan, P.N; Reid, K; Meredith, M.P; Thorpe, S.E; Johnston, N.M; Clarke, A; Tarling, G.A; Collins, M.A; Forcada, J; Shreeve, R.S; Atkinson, A; Korb, R; Whitehouse, M.J; Ward, P; Rodhouse, P.G; Enderlein, P; Hirst, A.G; Martin, A.R; Hill, S.L; Staniland, I.J; Pond, D.W; Briggs, D.R; Cunningham, N.J; Fleming, A.H

2006-01-01

286

Spatial and temporal operation of the Scotia Sea ecosystem: a review of large-scale links in a krill centred food web.  

PubMed

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell-Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño-Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts. PMID:17405210

Murphy, E J; Watkins, J L; Trathan, P N; Reid, K; Meredith, M P; Thorpe, S E; Johnston, N M; Clarke, A; Tarling, G A; Collins, M A; Forcada, J; Shreeve, R S; Atkinson, A; Korb, R; Whitehouse, M J; Ward, P; Rodhouse, P G; Enderlein, P; Hirst, A G; Martin, A R; Hill, S L; Staniland, I J; Pond, D W; Briggs, D R; Cunningham, N J; Fleming, A H

2007-01-29

287

Effects of Seasonal and Spatial Differences in Food Webs on Mercury Concentrations in Fish in the Everglades  

Microsoft Academic Search

A clear understanding of the aquatic food web is essential for determining the entry points and subsequent biomagnification pathways of contaminants such as methyl-mercury (MeHg) in the Everglades. Anthropogenic changes in nutrients can significantly affect the entry points of MeHg by changing food web structure from one dominated by algal productivity to one dominated by macrophytes and associated microbial activity.

C. Kendall; B. E. Bemis; S. D. Wankel; P. S. Rawlik; T. Lange; D. P. Krabbenhoft

2002-01-01

288

Feeding by larvae of intertidal invertebrates: assessing their position in pelagic food webs.  

PubMed

One of the leading determinants of the structure and dynamics of marine populations is the rate of arrival of new individuals to local sites. While physical transport processes play major roles in delivering larvae to the shore, these processes become most important after larvae have survived the perils of life in the plankton, where they usually suffer great mortality. The lack of information regarding larval feeding makes it difficult to assess the effects of food supply on larval survival, or the role larvae may play in nearshore food webs. Here, we examine the spectrum of food sizes and food types consumed by the larvae of two intertidal barnacle species and of the predatory gastropod Concholepas concholepas. We conducted replicated experiments in which larvae were exposed to the food size spectrum (phytoplankton, microprotozoan and autotrophic picoplankton) found in nearshore waters in central Chile. Results show that barnacle nauplii and gastropod veligers are omnivorous grazers, incorporating significant fractions of heterotrophs in their diets. In accordance with their feeding mechanisms and body size, barnacle nauplii were able to feed on autotrophic picoplankton (<5 microm) and did not consume the largest phytoplankton cells, which made the bulk of phytoplankton biomass in spring-summer blooms. Balanoid nauplii exhibited higher ingestion rates than the smaller-bodied chthamaloid larvae. Newly hatched C. concholepas larvae also consumed picoplankton cells, while competent larvae of this species ingested mostly the largest phytoplankton cells and heterotrophic protozoans. Results suggest that persistent changes in the structure of pelagic food webs can have important effects on the species-specific food availability for invertebrate larvae, which can result in large-scale differences in recruitment rates of a given species, and in the relative recruitment success of the different species that make up benthic communities. PMID:16637369

Vargas, Cristian A; Manríquez, Patricio H; Navarrete, Sergio A

2006-02-01

289

Food web structure of the coastal area adjacent to the Tagus estuary revealed by stable isotope analysis  

NASA Astrophysics Data System (ADS)

The identification of energy sources, pathways and trophic linkages among organisms is crucial for the understanding of food web dynamics. Stable isotopes were used to identify the trophic level of food web components and track the incorporation of organic matter of different origins in the coastal ecosystem adjacent to the Tagus estuary. It was shown that the river Tagus is a major source of organic carbon to this system. Also, the wide difference in ?13C among the primary consumers allowed the identification of the pelagic and the benthic energy pathways. The maximum trophic level observed was 2.4 for Sepia officinalis. This value is indicative of a short food web. It was concluded that the diet of the upper trophic level species relies directly on the lower food web levels to a considerable extent, instead of relying mostly on intermediate trophic level species. Moreover, the ?15N values of primary consumers were very close to that of particulate organic matter, probably due to poorly known processes occurring at the basis of the food web. This lowers the trophic length of the whole food web. Reliance on benthic affinity prey was high for all upper trophic level secondary consumers.

Vinagre, C.; Máguas, C.; Cabral, H. N.; Costa, M. J.

2012-01-01

290

Evidence of butyltin biomagnification along the Northern Adriatic food-web (Mediterranean Sea) elucidated by stable isotope ratios.  

PubMed

The biomagnification of tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), and total butyltins (?BT) was analyzed in the Northern Adriatic food-web (Mediterranean) considering trophodynamic interactions among species and carbon sources in the food-web. Although it is acknowledged that these contaminants bioaccumulate in marine organisms, it is still controversial whether they biomagnify along food-webs. A wide range of species was considered, from plankton feeders to top predators, whose trophic level (TL) was assessed measuring the biological enrichment of nitrogen stable isotopes (?(15)N). Carbon isotopic signature (?(13)C) was used to trace carbon sources in the food-web (terrestrial vs marine). At least one butyltin species was detected in the majority of samples, and TBT was the predominant contaminant. A significant positive relationship was found between TL and butyltin concentrations, implying food-web biomagnification. Coherently, the Trophic Magnification Factor resulted higher than 1, ranging between 3.88 for ?BT and 4.62 for DBT. A negative but not significant correlation was instead found between ?(13)C and butyltin concentrations, indicating a slight decreasing gradient of contaminants concentrations in species according to the coastal influence as carbon source in their diet. However, trophodynamic mechanisms are likely more important factors in determining butyltin distribution in the Northern Adriatic food-web. PMID:23465397

Fortibuoni, Tomaso; Noventa, Seta; Rampazzo, Federico; Gion, Claudia; Formalewicz, Malgorzata; Berto, Daniela; Raicevich, Saša

2013-03-21

291

Quantity and quality: unifying food web and ecosystem perspectives on the role of resource subsidies in freshwaters.  

PubMed

Although the study of resource subsidies has emerged as a key topic in both ecosystem and food web ecology, the dialogue over their role has been limited by separate approaches that emphasize either subsidy quantity or quality. Considering quantity and quality together may provide a simple, but previously unexplored, framework for identifying the mechanisms that govern the importance of subsidies for recipient food webs and ecosystems. Using a literature review of > 90 studies of open-water metabolism in lakes and streams, we show that high-flux, low-quality subsidies can drive freshwater ecosystem dynamics. Because most of these ecosystems are net heterotrophic, allochthonous inputs must subsidize respiration. Second, using a literature review of subsidy quality and use, we demonstrate that animals select for high-quality food resources in proportions greater than would be predicted based on food quantity, and regardless of allochthonous or autochthonous origin. This finding suggests that low-flux, high-quality subsidies may be selected for by animals, and in turn may disproportionately affect food web and ecosystem processes (e.g., animal production, trophic energy or organic matter flow, trophic cascades). We then synthesize and review approaches that evaluate the role of subsidies and explicitly merge ecosystem and food web perspectives by placing food web measurements in the context of ecosystem budgets, by comparing trophic and ecosystem production and fluxes, and by constructing flow food webs. These tools can and should be used to address future questions about subsidies, such as the relative importance of subsidies to different trophic levels and how subsidies may maintain or disrupt ecosystem stability and food web interactions. PMID:21797150

Marcarelli, Amy M; Baxter, Colden V; Mineau, Madeleine M; Hall, Robert O

2011-06-01

292

Convergence of trophic interaction strengths in grassland food webs through metabolic scaling of herbivore biomass.  

PubMed

1. Food web theory hypothesizes that trophic interaction strengths of consumers should vary with consumer metabolic body mass (mass(0·75) ) rather than simply with consumer body mass (mass(1·0) ) owing to constraints on consumption imposed by metabolic demand for and metabolic capacity to process nutrients and energy. Accordingly, species with similar metabolic body masses should have similar trophic interaction strengths. 2. We experimentally tested this hypothesis by assembling food webs comprised of species of arthropod predators, small sap-feeding and large leaf-chewing insect herbivores and herbaceous plants in a New England, USA meadow grassland. The experiment comprised of a density-matching treatment where herbivore species were stocked into field mesocosms at equal densities to quantify baseline species identity and metabolic body mass effects. The experiment also comprised of a metabolic biomass-matching treatment where smaller sap-feeding herbivore (SH) species were stocked into mesocosms such that the product of their density and metabolic body mass (metabolic biomass) was equal to the large herbivore (LH) species. We compared the magnitude of the direct effects of herbivore species on plants in the different treatments. We also compared the magnitude of indirect effects between predators and plants mediated by herbivores in the different treatments. 3. Consistent with the hypothesis, we found that increasing metabolic biomass translated into a 9-14-fold increase in magnitude of herbivore direct effects and up to a fivefold increase in indirect effects on plants. Moreover, metabolic biomass matching caused interaction strengths among herbivore species to converge. This result came about through increases in the herbivore mean effects as well as decreases in variation in effects among treatment replicates as herbivore metabolic biomass increased. 4. We found, however, that herbivore feeding mode rather than herbivore metabolic biomass explained differences in the sign of indirect effects in the different food webs. 5. We conclude that increasing herbivore metabolic biomass not only strengthened the direct and indirect effects on plants but also made those effects more consistent across space. Nevertheless, metabolic biomass alone could not completely explain variation in the nature of indirect effects in the food web, suggesting that additional consideration of consumer traits like feeding mode will provide a more nuanced understanding of trophic interaction strengths in food webs. PMID:21722105

Schmitz, Oswald J; Price, Jessica R

2011-07-01

293

Humans strengthen bottom-up effects and weaken trophic cascades in a terrestrial food web.  

PubMed

Ongoing debate about whether food webs are primarily regulated by predators or by primary plant productivity, cast as top-down and bottom-up effects, respectively, may becoming superfluous. Given that most of the world's ecosystems are human dominated we broadened this dichotomy by considering human effects in a terrestrial food-web. We studied a multiple human-use landscape in southwest Alberta, Canada, as opposed to protected areas where previous terrestrial food-web studies have been conducted. We used structural equation models (SEMs) to assess the strength and direction of relationships between the density and distribution of: (1) humans, measured using a density index; (2) wolves (Canis lupus), elk (Cervus elpahus) and domestic cattle (Bos taurus), measured using resource selection functions, and; (3) forage quality, quantity and utilization (measured at vegetation sampling plots). Relationships were evaluated by taking advantage of temporal and spatial variation in human density, including day versus night, and two landscapes with the highest and lowest human density in the study area. Here we show that forage-mediated effects of humans had primacy over predator-mediated effects in the food web. In our parsimonious SEM, occurrence of humans was most correlated with occurrence of forage (??=?0.637, p<0.0001). Elk and cattle distribution were correlated with forage (elk day: ??=?0.400, p<0.0001; elk night: ??=?0.369, p<0.0001; cattle day: ??=?0.403, p<0.0001; cattle, night: ??=?0.436, p<0.0001), and the distribution of elk or cattle and wolves were positively correlated during daytime (elk: ??=?0.293, p <0.0001, cattle: ??=?0.303, p<0.0001) and nighttime (elk: ??=?0.460, p<0.0001, cattle: ??=?0.482, p<0.0001). Our results contrast with research conducted in protected areas that suggested human effects in the food web are primarily predator-mediated. Instead, human influence on vegetation may strengthen bottom-up predominance and weaken top-down trophic cascades in ecosystems. We suggest that human influences on ecosystems may usurp top-down and bottom-up effects. PMID:23667705

Muhly, Tyler B; Hebblewhite, Mark; Paton, Dale; Pitt, Justin A; Boyce, Mark S; Musiani, Marco

2013-05-08

294

Food quantity and quality regulation of trophic transfer between primary producers and a keystone grazer (Daphnia) in pelagic freshwater food webs  

Microsoft Academic Search

The transfer of energy and nutrients from plants to animals is a key process in all ecosystems. In lakes, inefficient transfer of primary producer derived energy can result in low animal growth rates, accumulation of nuisance phytoplankton blooms and dissipation of energy from the ecosystem. Most research on carbon transfer efficiency in pelagic food webs has focused on either food

Jonas Persson; Michael T. Brett; Tobias Vrede; Joseph L. Ravet

2007-01-01

295

Reorganization of Southern Ocean plankton ecosystem at the onset of Antarctic glaciation.  

PubMed

The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (~33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean. PMID:23599491

Houben, Alexander J P; Bijl, Peter K; Pross, Jörg; Bohaty, Steven M; Passchier, Sandra; Stickley, Catherine E; Röhl, Ursula; Sugisaki, Saiko; Tauxe, Lisa; van de Flierdt, Tina; Olney, Matthew; Sangiorgi, Francesca; Sluijs, Appy; Escutia, Carlota; Brinkhuis, Henk; Dotti, Carlota Escutia; Klaus, Adam; Fehr, Annick; Williams, Trevor; Bendle, James A P; Carr, Stephanie A; Dunbar, Robert B; Flores, José-Abel; Gonzàlez, Jhon J; Hayden, Travis G; Iwai, Masao; Jimenez-Espejo, Francisco J; Katsuki, Kota; Kong, Gee Soo; McKay, Robert M; Nakai, Mutsumi; Pekar, Stephen F; Riesselman, Christina; Sakai, Toyosaburo; Salzmann, Ulrich; Shrivastava, Prakash K; Tuo, Shouting; Welsh, Kevin; Yamane, Masako

2013-04-19

296

Impact of proliferation strategies on food web viability in a model with closed nutrient cycle  

NASA Astrophysics Data System (ADS)

A food web model with a closed nutrient cycle is presented and analyzed via Monte Carlo simulations. The model consists of three trophic levels, each of which is populated by animals of one distinct species. While the species at the intermediate level feeds on the basal species, and is eaten by the predators living at the highest level, the basal species itself uses the detritus of animals from higher levels as the food resource. The individual organisms remain localized, but the species can invade new lattice areas via proliferation. The impact of different proliferation strategies on the viability of the system is investigated. From the phase diagrams generated in the simulations it follows that in general a strategy with the intermediate level species searching for food is the best for the survival of the system. The results indicate that both the intermediate and top level species play a critical role in maintaining the structure of the system.

Szwabi?ski, Janusz

2012-11-01

297

Melting glaciers: a probable source of DDT to the Antarctic marine ecosystem.  

PubMed

Persistent organic pollutants reach polar regions by long-range atmospheric transport and biomagnify through the food web accumulating in higher trophic level predators. We analyzed Adélie penguin (Pygoscelis adeliae) samples collected from 2004 to 2006 to evaluate current levels of sigmaDDT (p,p'-DDT + p,p'-DDE) in these birds, which are confined to Antarctica. Ratios of p,p'-DDT to p,p'-DDE in Adélie penguins have declined significantly since 1964 indicating current exposure to old rather than new sources of sigmaDDT. However, sigmaDDT has not declined in Adélie penguins from the Western Antarctic Peninsula for more than 30 years and the presence of p,p'-DDT in these birds indicates that there is a current source of DDT to the Antarctic marine food web. DDT has been banned or severely restricted since peak use in the 1970s, implicating glacier meltwater as a likely source for DDT contamination in coastal Antarctic seas. Our estimates indicate that 1-4 kg x y(-1) sigmaDDT are currently being released into coastal waters along the Western Antarctic Ice Sheet due to glacier ablation. PMID:18589951

Geisz, Heidi N; Dickhut, Rebecca M; Cochran, Michele A; Fraser, William R; Ducklow, Hugh W

2008-06-01

298

Linking ecosystems, food webs, and fish production: Subsidies in salmonid watersheds  

USGS Publications Warehouse

Physical characteristics of riverine habitats, such as large wood abundance, pool geometry and abundance, riparian vegetation cover, and surface flow conditions, have traditionally been thought to constrain fish production in these ecosystems. Conversely, the role of food resources (quantity and quality) in controlling fish production has received far less attention and consideration, though they can also be key productivity drivers. Traditional freshwater food web illustrations have typically conveyed the notion that most fish food is produced within the local aquatic habitat itself, but the concepts and model we synthesize in this article show that most fish food comes from external or very distant sources-including subsidies from marine systems borne from adult returns of anadromous fishes, from fishless headwater tributaries that transport prey to downstream fish, and from adjacent streamside vegetation and associated habitats. The model we propose further illustrates how key trophic pathways and food sources vary through time and space throughout watersheds. Insights into how food supplies affect fishes can help guide how we view riverine ecosystems, their structure and function, their interactions with marine and terrestrial systems, and how we manage natural resources, including fish, riparian habitats, and forests.

Wipfli, M. S.; Baxter, C. V.

2010-01-01

299

Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat  

PubMed Central

Background Food web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood. Methodology/Principal Findings Using an experimental seagrass mesocosm system, we factorially manipulated water column nutrient concentrations, food chain length, and diversity of crustacean grazers to address two questions: (1) Does food web composition modulate the effects of nutrient enrichment on plant and grazer biomasses and stoichiometry? (2) Do ecosystem fluxes of dissolved oxygen and nutrients more closely reflect above-ground biomass and community structure or sediment processes? Nutrient enrichment and grazer presence generally had strong effects on biomass accumulation, stoichiometry, and ecosystem fluxes, whereas predator effects were weaker or absent. Nutrient enrichment had little effect on producer biomass or net ecosystem production but strongly increased seagrass nutrient content, ecosystem flux rates, and grazer secondary production, suggesting that enhanced production was efficiently transferred from producers to herbivores. Gross ecosystem production (oxygen evolution) correlated positively with above-ground plant biomass, whereas inorganic nutrient fluxes were unrelated to plant or grazer biomasses, suggesting dominance by sediment microbial processes. Finally, grazer richness significantly stabilized ecosystem processes, as predators decreased ecosystem production and respiration only in the zero- and one- species grazer treatments. Conclusions/Significance Overall, our results indicate that consumer presence and species composition strongly influence ecosystem responses to nutrient enrichment, and that increasing herbivore diversity can stabilize ecosystem flux rates in the face of perturbations.

Spivak, Amanda C.; Canuel, Elizabeth A.; Duffy, J. Emmett; Richardson, J. Paul

2009-01-01

300

Antarctic Meteorology Online from the British Antarctic Survey  

NSDL National Science Digital Library

The Antarctic Meteorology Online Web site is provided by the British Antarctic Survey and the Natural Environment Research Council. Visitors will find weather reports provided by the dozens of stations located in the Antarctic. The Web master has made these data accessible by each specific station; by a clickable map; by a list of all land, ship, or buoy stations; or by an oracle database interface. The reports are at least 10 minutes old and are normally not more than six hours old. The information provided includes a graph of pressure and temperature, as well as links to previous reports, which make the site a good and easily accessible resource. This site is also reviewed in the November 27, 2002 Scout Report.

2001-01-01

301

Modelling food web complexity: The consequences of individual-based, spatially explicit behavioural ecology on trophic interactions  

Microsoft Academic Search

We present a prototype simulator that enables one to explore the influence of individual behaviour on the dynamics and structural complexity of food webs. In the simulations, individuals act according to simple, biologically plausible rules in a spatially explicit setting. We present the results of a series of simulation experiments on artificial, tri-trophic level food chains used to calibrate the

Oswald J. Schmitz; Ginger Booth

1997-01-01

302

THE CONTRIBUTION OF MICROARTHROPODS TO ABOVE GROUND FOOD WEBS: A REVIEW AND MODEL OF BELOW GROUND TRANSFER IN A CONIFEROUS FOREST  

EPA Science Inventory

Although belowground food webs have received much attention, studies concerning microarthropods in nondetrital food webs are scarce. Because adult oribatid mites often number between 250,000-500,000/m(2) in coniferous forests, microarthropods are a potential food resource for mic...

303

Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web  

USGS Publications Warehouse

We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa present in Halodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity ??? 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers, and piscivores. These trophic groups, cross-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups.

Luczkovich, J. J.; Ward, G. P.; Johnson, J. C.; Christian, R. R.; Baird, D.; Neckles, H.; Rizzo, W. M.

2002-01-01

304

Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web  

USGS Publications Warehouse

We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa. present in Hatodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity greater than or equal to 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers, and piscivores. These trophic groups, cross-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups.

Luczkovich, J.J.; Ward, G.P.; Johnson, J.C.; Christian, R.R.; Baird, D.; Neckles, H.; Rizzo, W.M.

2002-01-01

305

Effects of zebra mussels on food webs: Interactions with juvenile bluegill and water residence time  

USGS Publications Warehouse

We evaluated how water residence time mediated the impact of zebra mussels Dreissena polymorpha and bluegill sunfish Lepomis macrochirus on experimental food webs established in 1100-1 outdoor mesocosms. Water residence time was manipulated as a surrogate for seston resupply - a critical variable affecting growth and survival of suspension-feeding invertebrates. We used a 2 x 2 x 2 factorial experimental design with eight treatment combinations (3 replicates/treatment) including the presence or absence of Dreissena (2000 per m2), juvenile bluegill (40 per mesocosm), and short (1100 1 per d) or long (220 1 per d) water residence time. Measures of seston concentration (chlorophyll a, turbidity and suspended solids) were greater in the short- compared to long water-residence mesocosms, but intermediate in short water-residence mesocosms containing Dreissena. Abundance of rotifers (Keratella and Polyarthra) was reduced in Dreissena mesocosms and elevated in short residence time mesocosms. Cladocera abundance, in general, was unaffected by the presence of Dreissena; densities were higher in short-residence time mesocosms, and reduced in the presence of Lepomis. The growth of juvenile Lepomis were unaffected by Dreissena because of abundant benthic food. The final total mass of Dreissena was significantly greater in short- than long-residence mesocosms. Impacts of Dreissena on planktonic food webs may not only depend on the density of zebra mussels but also on the residence time of the surrounding water and the resupply of seston. ?? 1997 Kluwer Academic Publishers.

Richardson, W. B.; Bartsch, L. A.

1997-01-01

306

Influence of Flow Regime on the Food web of a Dryland River System  

NASA Astrophysics Data System (ADS)

Australian dryland rivers are among the most variable and unpredictable in the world in terms of their flow regimes. Although renowned for their spectacular floods over vast floodplains, rivers exist for much of the time as discrete waterholes, which are important refugia for aquatic biota. During these dry spells, aquatic food webs in waterholes are clearly supported by algal production, despite the high natural turbidity and significant terrestrial carbon inputs. However, the relative importance of pelagic and benthic sources is less clear. Although fish rarely have stable isotope signatures consistent with a phytoplankton diet, gut contents analysis suggests that zooplankton can be a significant component of diets. Planktonic sources of carbon appear to be important during and immediately after flood events, where aquatic production on inundated floodplains provides an immense food resource. As waterholes become isolated post-flood, we predict that benthic sources of production become increasingly important as algae develop along the relatively stable shoreline. More frequent flow pulses connect waterholes and enhance their physical persistence, but may disrupt the formation of these productive algal mats. We propose that the relative importance of benthic and pelagic algal production to dryland river food webs varies in response to recent flow history.

Bunn, S. E.; Balcombe, S. R.; Fellows, C. S.; McKenzie-Smith, F. J.

2005-05-01

307

Impacts of elevated terrestrial nutrient loads and temperature on pelagic food-web efficiency and fish production.  

PubMed

Both temperature and terrestrial organic matter have strong impacts on aquatic food-web dynamics and production. Temperature affects vital rates of all organisms, and terrestrial organic matter can act both as an energy source for lower trophic levels, while simultaneously reducing light availability for autotrophic production. As climate change predictions for the Baltic Sea and elsewhere suggest increases in both terrestrial matter runoff and increases in temperature, we studied the effects on pelagic food-web dynamics and food-web efficiency in a plausible future scenario with respect to these abiotic variables in a large-scale mesocosm experiment. Total basal (phytoplankton plus bacterial) production was slightly reduced when only increasing temperatures, but was otherwise similar across all other treatments. Separate increases in nutrient loads and temperature decreased the ratio of autotrophic:heterotrophic production, but the combined treatment of elevated temperature and terrestrial nutrient loads increased both fish production and food-web efficiency. CDOM: Chl a ratios strongly indicated that terrestrial and not autotrophic carbon was the main energy source in these food webs and our results also showed that zooplankton biomass was positively correlated with increased bacterial production. Concomitantly, biomass of the dominant calanoid copepod Acartia sp. increased as an effect of increased temperature. As the combined effects of increased temperature and terrestrial organic nutrient loads were required to increase zooplankton abundance and fish production, conclusions about effects of climate change on food-web dynamics and fish production must be based on realistic combinations of several abiotic factors. Moreover, our results question established notions on the net inefficiency of heterotrophic carbon transfer to the top of the food web. PMID:23505052

Lefébure, R; Degerman, R; Andersson, A; Larsson, S; Eriksson, L-O; Båmstedt, U; Byström, P

2013-02-11

308

Modeling selenium bioaccumulation through arthropod food webs in San Francisco Bay, California, USA  

USGS Publications Warehouse

Trophic transfer is the main process by which upper trophic level wildlife are exposed to selenium. Transfers through lower levels of a predator's food web thus can be instrumental in determining the threat of selenium in an ecosystem. Little is known about Se transfer through pelagic, zooplankton-based food webs in San Francisco Bay ([SFB], CA, USA), which serve as an energy source for important predators such as striped bass. A dynamic multipathway bioaccumulation model was used to model Se transfer from phytoplankton to pelagic copepods to carnivorous mysids (Neomysis mercedis). Uptake rates of dissolved Se, depuration rates, and assimilation efficiencies (AE) for the model were determined for copepods and mysids in the laboratory. Small (73-250 ??m) and large (250-500 ??m) herbivorous zooplankton collected from SFB (Oithona/Limnoithona and Acartia sp.) assimilated Se with similar efficiencies (41-52%) from phytoplankton. Mysids assimilated 73% of Se from small herbivorous zooplankton; Se AE was significantly lower (61%) than larger herbivorous zooplankton. Selenium depuration rates were high for both zooplankton and mysids (12-25% d-1), especially compared to bivalves (2-3% d-1). The model predicted steady state Se concentrations in mysids similar to those observed in the field. The predicted concentration range (1.5-5.4 ??g g -1) was lower than concentrations of 4.5 to 24 ??g g-1 observed in bivalves from the bay. Differences in efflux between mysids and bivalves were the best explanation for the differences in uptake. The results suggest that the risk of selenium toxicity to predators feeding on N. mercedis would be less than the risk to predators feeding on bivalves. Management of selenium contamination should include food webs analyses to focus on the most important exposure pathways identified for a given watershed.

Schlekat, C. E.; Purkerson, D. G.; Luoma, S. N.

2004-01-01

309

Revealing species-specific trophic links in soil food webs: molecular identification of scarab predators.  

PubMed

Soil food webs are particularly important in terrestrial systems, but studying them is difficult. Here we report on the first study to apply a molecular approach to identify species-specific trophic interactions in below-ground food webs. To identify the invertebrate predator guild of the garden chafer Phyllopertha horticola (Coleoptera, Scarabaeidae) whose root-feeding larvae can be highly abundant in grasslands, a specific DNA marker was developed. It allowed detection of P. horticola egg and white grub meals within the gut content of Poecilus versicolor (Coleoptera, Carabidae) larvae for up to 24 h post-feeding. Soil samples from an alpine grassland revealed a diverse below-ground macro-invertebrate community with earthworms, P. horticola larvae, and centipedes as well as beetle larvae as the most abundant detritivores, herbivores, and predators, respectively. Garden chafer DNA was detected in 18.6%, 4.1%, and 4.4% of field-collected Geophilidae (n = 124), beetle larvae (n = 159), and Lithobiidae (n = 49), respectively. We conclude that most of the investigated predators actively preyed on P. horticola, as secondary predation is unlikely to be detected in below-ground systems. Moreover, scavenging most likely contributes only to a small percentage of the revealed trophic links due to the low availability of carrion. Sampling date did not influence prey detection rates, indicating that both P. horticola eggs and larvae were preyed on. Only 2.7% of the below-ground predators tested positive for earthworms, an alternative, highly abundant prey, suggesting that P. horticola represents an important prey source for centipedes and predatory beetle larvae during summer within the soil food web. PMID:17391275

Juen, A; Traugott, M

2007-04-01

310

Bioaccumulation syndrome: identifying factors that make some stream food webs prone to elevated mercury bioaccumulation  

PubMed Central

Mercury is a ubiquitous contaminant in aquatic ecosystems, posing a significant health risk to humans and wildlife that eat fish. Mercury accumulates in aquatic food webs as methylmercury (MeHg), a particularly toxic and persistent organic mercury compound. While mercury in the environment originates largely from anthropogenic activities, MeHg accumulation in freshwater aquatic food webs is not a simple function of local or regional mercury pollution inputs. Studies show that even sites with similar mercury inputs can produce fish with mercury concentrations ranging over an order of magnitude. While much of the foundational work to identify the drivers of variation in mercury accumulation has focused on freshwater lakes, mercury contamination in stream ecosystems is emerging as an important research area. Here, we review recent research on mercury accumulation in stream-dwelling organisms. Taking a hierarchical approach, we identify a suite of characteristics of individual consumers, food webs, streams, watersheds, and regions that are consistently associated with elevated MeHg concentrations in stream fish. We delineate a conceptual, mechanistic basis for explaining the ecological processes that underlie this vulnerability to MeHg. Key factors, including suppressed individual growth of consumers, low rates of primary and secondary production, hydrologic connection to methylation sites (e.g. wetlands), heavily forested catchments, and acidification are frequently associated with increased MeHg concentrations in fish across both streams and lakes. Hence, we propose that these interacting factors define a syndrome of characteristics that drive high MeHg production and bioaccumulation rates across these freshwater aquatic ecosystems. Finally, based on an understanding of the ecological drivers of MeHg accumulation, we identify situations when anthropogenic effects and management practices could significantly exacerbate or ameliorate MeHg accumulation in stream fish.

Ward, Darren M.; Nislow, Keith H.; Folt, Carol L.

2010-01-01

311

Are Algae Relevant to the Detritus-Based Food Web in Tank-Bromeliads?  

PubMed Central

We assessed the occurrence of algae in five species of tank-bromeliads found in contrasting environmental sites in a Neotropical, primary rainforest around the Nouragues Research Station, French Guiana. The distributions of both algal abundance and biomass were examined based on physical parameters, the morphological characteristics of bromeliad species and with regard to the structure of other aquatic microbial communities held in the tanks. Algae were retrieved in all of the bromeliad species with mean densities ranging from ?102 to 104 cells/mL. Their biomass was positively correlated to light exposure and bacterial biomass. Algae represented a tiny component of the detrital food web in shaded bromeliads but accounted for up to 30 percent of the living microbial carbon in the tanks of Catopsis berteroniana, located in a highly exposed area. Thus, while nutrient supplies are believed to originate from wind-borne particles and trapped insects (i.e., allochtonous organic matter), our results indicate that primary producers (i.e., autochtonous organic matter) are present in this insectivorous bromeliad. Using a 24-h incubation of size-fractionated and manipulated samples from this plant, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated that the dominant algal taxon, Bumilleriopsis sp., like protozoa and rotifers, is a significant part of the diet of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C. berteroniana and might form the basis of a complementary non-detrital food web.

Brouard, Olivier; Le Jeune, Anne-Helene; Leroy, Celine; Cereghino, Regis; Roux, Olivier; Pelozuelo, Laurent; Dejean, Alain; Corbara, Bruno; Carrias, Jean-Francois

2011-01-01

312

Trophodynamics of some PFCs and BFRs in a western Canadian Arctic marine food web.  

PubMed

The trophodynamics of per- and polyfluorinated compounds and bromine-based flame retardants were examined in components of a marine food web from the western Canadian Arctic. The animals studied and their relative trophic status in the food web, established using stable isotopes of nitrogen (delta15N), were beluga (Delphinapterus leucas) > ringed seal (Phoca hispida) > Arctic cod (Boreogadus saida) > Pacific herring (Clupea pallasi) approximately equal to Arctic cisco (Coregonus autumnalis) > pelagic amphipod (Themisto libellula) > Arctic copepod (Calanus hyperboreus). For the brominated diphenyl ethers, the lipid adjusted concentrations of the seven congeners analyzed (Sigma7BDEs: -47, -85, -99, -100, -153, -154, and -209) ranged from 205.4 +/- 52.7 ng/g in Arctic cod to 2.6 +/- 0.4 ng/g in ringed seals. Mean Sigma7BDEs concentrations in Arctic copepods, 16.4 ng/g (n = 2, composite sample), were greater than those in the top trophic level (TL) marine mammals and suggests that (i) Arctic copepods are an important dietary component that delivers BDEs to the food web and (ii) because these compounds are bioaccumulative, metabolism and depletion of BDE congeners in top TL mammals is an important biological process. There were differences in the concentration profiles of the isomers of hexabromocyclododecane (HBCD) in the food web. The most notable difference was observed for beluga, where the alpha-isomer was enriched (accounting for approximately 90% of the SigmaHBCD body burden), relative to its primary prey species, Arctic cod, where the alpha-isomer accounted for only 20% of the SigmaHBCD body burden (beta: 4% and gamma: 78%). For the C8-C11 perfluorinated carboxylic acids, the trophic magnification factors (TMFs) were all greater than unity and increased with increasing carbon chain length. PFOS and its neutral precursor, PFOSA, also had TMF values greater than one. There were also pronounced differences in the PFOSA to PFOS ratio in ringed seal (0.04) and in beluga (1.4) and suggests that, in part, there are differences in the efficacy of biotransforming PFOSA by whale and seal top predators that both preferentially feed on Arctic cod. PMID:19569333

Tomy, Gregg T; Pleskach, Kerri; Ferguson, Steve H; Hare, Jonathon; Stern, Gary; Macinnis, Gordia; Marvin, Chris H; Loseto, Lisa

2009-06-01

313

Disruption of the lower food web in Lake Ontario: Did it affect alewife growth or condition?  

USGS Publications Warehouse

From the early 1980s to the late 1990s, a succession of non-native invertebrates colonized Lake Ontario and the suite of consequences caused by their colonization became known as "food web disruption". For example, the native burrowing amphipod Diporeia spp., a key link in the profundal food web, declined to near absence, exotic predaceous cladocerans with long spines proliferated, altering the zooplankton community, and depth distributions of fishes shifted. These changes had the potential to affect growth and condition of planktivorous alewife Alosa pseudoharengus, the most abundant fish in the lake. To determine if food web disruption affected alewife, we used change-point analysis to examine alewife growth and adult alewife condition during 1976-2006 and analysis-of-variance to determine if values between change points differed significantly. There were no change points in growth during the first year of life. Of three change points in growth during the second year of life, one coincided with the shift in springtime distribution of alewife to deeper water but it was not associated with a significant change in growth. After the second year of life, no change points in growth were evident, although growth in the third year of life spiked in those years when Bythotrephes, the largest of the exotic cladocerans, was abundant suggesting that it was a profitable prey item for age-2 fish. We detected two change points in condition of adult alewife in fall, but the first occurred in 1981, well before disruption began. A second change point occurred in 2003, well after disruption began. After the springtime distribution of alewife shifted deeper during 1992-1994, growth in the first two years of life became more variable, and growth in years of life two and older became correlated (P < 0.05). In conclusion, food web disruption had no negative affect on growth and condition of alewife in Lake Ontario although it appears to have resulted in growth in the first two years of life becoming more variable, growth in years of life two and older becoming correlated (P < 0.05), and growth spurts in year of life three. Copyright ?? 2008 AEHMS.

O'Gorman, R.; Prindle, S. E.; Lantry, J. R.; Lantry, B. F.

2008-01-01

314

Perfluoroalkyl contaminants in an Arctic marine food web: trophic magnification and wildlife exposure.  

PubMed

To better understand the bioaccumulation behavior of perfluoroalkyl contaminants (PFCs), we conducted a comparative analysis of PFCs and lipophilic organohalogens in a Canadian Arctic marine food web. Concentrations of perfluorooctane sulfonic acid (PFOS), perfluorooctansulfoamide (PFOSA), and C7-C14 perfluorocarboxylic acids (PFCAs) ranged between 0.01 and 0.1 ng x g(-1) dry wt in sediments and 0.1 and 40 ng x g(-1) wet wt in biota, which was equivalent to or higher than levels of PCBs, PBDEs, and organochlorine pesticides. In beluga whales, PFOS and PFCA concentrations were higher (P < 0.05) in protein-rich compartments (liver and blood), compared to other tissues/fluids (milk, blubber, muscle, and fetus). In the marine mammalian food web, concentrations of PFOSA and lipophilic organochlorines (ng x g(-1) lipid equivalent) and proteinophilic substances (i.e., PFOS and C8-C14 PFCAs, ng x g(-1) protein) increased significantly (P < 0.05) with trophic level. Trophic magnification factors (TMFs) of organochlorines ranged between 5 and 14 and exhibited significant curvilinear relationships (P < 0.05) with octanol-water and octanol-air partition coefficients (KOW, KOA). TMFs of perfluorinated acids (PFAs) ranged between 2 and 11 and exhibited similar correlation (P < 0.05) with protein-water and protein-air partition coefficients (KPW, KPA). PFAs did not biomagnify in the aquatic piscivorous food web (TMF range: 0.3-2). This food web specific biomagnification behavior was attributed to the high aqueous solubility and low volatility of PFAs. Specifically, the anticipated phase-partitioning of these proteinophilic substances, represented by their protein-water (KPW) and protein-air (KPA) partition coefficients, likely results in efficient respiratory elimination in water-respiring organisms but very slow elimination and biomagnification in air-breathing animals. Lastly, the results indicate that PFOS exposure in nursing Hudson Bay beluga whale calves (CI95 range = 2.7 x 10(-5) to 1.8 x 10(-4) mg x kg bw(-1) x d(-1)), exceedsthe oral reference dose for PFOS (7.5 x 10(-5) mg x kg bw(-1) x d(-1)), which raises concern for potential biological effects in these and other sensitive Arctic marine wildlife species. PMID:19569327

Kelly, Barry C; Ikonomou, Michael G; Blair, Joel D; Surridge, Blair; Hoover, Dale; Grace, Richard; Gobas, Frank A P C

2009-06-01

315

Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling.  

PubMed

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem. PMID:22919916

Legagneux, P; Gauthier, G; Berteaux, D; Bêty, J; Cadieux, M C; Bilodeau, F; Bolduc, E; McKinnon, L; Tarroux, A; Therrien, J F; Morissette, L; Krebs, C J

2012-07-01

316

Dynamics of Leslie-Gower type generalist predator in a tri-trophic food web system  

NASA Astrophysics Data System (ADS)

In this paper, the dynamics of a tri-trophic food web system consists of Leslie-Gower type generalist predator has been explored. The system is bounded under certain conditions. The Hopf-bifurcation has been established in the phase planes. The bifurcation diagrams exhibit coexistence of all three species in the form of periodic/chaotic solutions. The "snail-shell" chaotic attractor has very high Lyapunov exponents. The coexistence in the form of stable equilibrium is also possible for lower values of parameters. The two-parameter bifurcation diagrams are drawn for critical parameters.

Priyadarshi, A.; Gakkhar, S.

2013-11-01

317

Food-web structure and ecosystem services: insights from the Serengeti.  

PubMed

The central organizing theme of this paper is to discuss the dynamics of the Serengeti grassland ecosystem from the perspective of recent developments in food-web theory. The seasonal rainfall patterns that characterize the East African climate create an annually oscillating, large-scale, spatial mosaic of feeding opportunities for the larger ungulates in the Serengeti; this in turn creates a significant annual variation in the food available for their predators. At a smaller spatial scale, periodic fires during the dry season create patches of highly nutritious grazing that are eaten in preference to the surrounding older patches of less palatable vegetation. The species interactions between herbivores and plants, and carnivores and herbivores, are hierarchically nested in the Serengeti food web, with the largest bodied consumers on each trophic level having the broadest diets that include species from a large variety of different habitats in the ecosystem. The different major habitats of the Serengeti are also used in a nested fashion; the highly nutritious forage of the short grass plains is available only to the larger migratory species for a few months each year. The longer grass areas, the woodlands and kopjes (large partially wooded rocky islands in the surrounding mosaic of grassland) contain species that are resident throughout the year; these species often have smaller body size and more specialized diets than the migratory species. Only the larger herbivores and carnivores obtain their nutrition from all the different major habitat types in the ecosystem. The net effect of this is to create a nested hierarchy of subchains of energy flow within the larger Serengeti food web; these flows are seasonally forced by rainfall and operate at different rates in different major branches of the web. The nested structure that couples sequential trophic levels together interacts with annual seasonal variation in the fast and slow chains of nutrient flow in a way that is likely to be central to the stability of the whole web. If the Serengeti is to be successfully conserved as a fully functioning ecosystem, then it is essential that the full diversity of natural habitats be maintained within the greater Serengeti ecosystem. The best way to do this is by controlling the external forces that threaten the boundaries of the ecosystem and by balancing the economic services the park provides between local, national and international needs. I conclude by discussing how the ecosystem services provided by the Serengeti are driven by species on different trophic levels. Tourism provides the largest financial revenue to the national economy, but it could be better organized to provide more sustained revenue to the park. Ultimately, ecotourism needs to be developed in ways that take lessons from the structure of the Serengeti food webs, and in ways that provide tangible benefits to people living around the park while also improving the experience of all visitors. PMID:19451118

Dobson, Andy

2009-06-27

318

Antarctic Fishes.  

ERIC Educational Resources Information Center

|Explains the adaptations to Antarctic waters that Notothenioidei, a group of advanced bony fishes, have exhibited. Discusses the fishes' mechanisms of production of antifreeze properties and their capacities for neutral buoyancy in water. (ML)|

Eastman, Joseph T.; DeVries, Arthur L.

1986-01-01

319

Antarctic Fishes.  

ERIC Educational Resources Information Center

Explains the adaptations to Antarctic waters that Notothenioidei, a group of advanced bony fishes, have exhibited. Discusses the fishes' mechanisms of production of antifreeze properties and their capacities for neutral buoyancy in water. (ML)

Eastman, Joseph T.; DeVries, Arthur L.

1986-01-01

320

Antarctic Ecosystem  

NSDL National Science Digital Library

In contrast with its largely lifeless interior, the Antarctic coastal marine environment supports a vibrant and diverse ecosystem. Explore the region's living bounty in this interactive activity adapted from the Woods Hole Oceanographic Institution.

Foundation, Wgbh E.

2008-01-17

321

Arthropod food webs become increasingly lipid-limited at higher trophic levels.  

PubMed

Understanding why food chains are relatively short in length has been an area of research and debate for decades. We tested if progressive changes in the nutritional content of arthropods with trophic position limit the availability of a key nutrient, lipid, for carnivores. Arthropods at higher trophic levels had progressively less lipid and more protein in their bodies compared with arthropods at lower trophic levels. The nutrients present in arthropod bodies were directly related to the nutrients that predators extracted when feeding on those arthropods. As a consequence, nutrient assimilation shifted from lipid-biased to protein-biased as arthropods ascended trophic levels from herbivores to secondary carnivores. Successive changes in the nutritional consequences of predation may ultimately set an upper limit on the number of trophic levels in arthropod communities. Further work is needed to examine the influence of lipid and other nutrients on food web traits in a range of ecosystems. PMID:23701046

Wilder, Shawn M; Norris, Michael; Lee, Raymond W; Raubenheimer, David; Simpson, Stephen J

2013-05-23

322

Entry of Oil to the Coastal Planktonic Food Web During the Deepwater Horizon Spill (Invited)  

NASA Astrophysics Data System (ADS)

After the explosion and subsequent sinking of the Deepwater Horizon (DWH) on 22 April 2010, an estimated 780,000 m3 of Sweet Louisiana Crude (SLC) and 205,000 mT of methane were released into the northern Gulf of Mexico over an 85 d period. A great deal of controversy ensued regarding the application of unprecedented volumes of chemical dispersants both at the surface and at depth. One of the consequences of dispersing such large volumes of oil into the water column was the difficulty of tracking its fate over distance and through the food web. Most of the attention to date has been on large underwater plumes of oil, and scant evidence exists for subsea oil in warm (>25 °C), shallow shelf waters due to rapid weathering and utilization by prokaryotes. A large pool of isotopically depleted carbon from released oil and methane is presumably available to zooplankton and zooplankton-eating fish and invertebrates via prokaryotic consumers. Thus, carbon isotopic depletion extending into marine zooplankton grazers, a pathway mediated by the microbial food web, is a good proxy for food web modification by the spill. We employed ?13C as a tracer of oil-derived carbon incorporation into the lower marine food web across the middle and inner continental shelf. During June-August 2010, we followed two particle size classes: the nominally 1 ?m - 0.2 mm “small suspended particulate” and the >0.2-2 mm “mesozooplankton” fractions, with the former considered likely food particle size for the latter. A clear pattern of ?13C depletion occurring in each fraction at middle and inner shelf stations was consistent with two sequential northward pulses of surface oil slicks from DWH. Relative to early June, an isotopic shift of -1 to -3 ‰ (toward weathered and fresh oil, -27.23 ± 0.03 ‰ and -27.34 ± 0.34 ‰, respectively) occurred during the peak of areal coverage of oil over the sites in late June 2010. Recovery of this depletion was 2-4 wks. A third pulse of residual oil occurred in late July, and depleted ?13C was observed in mid-August at the furthest offshore stations. Depletion and recovery cycles on the order of a few weeks are consistent with published warm water petroleum hydrocarbon decay time-scales. Carbon isotopic depletion in both surface and bottom samples suggests trophic transfer of oil carbon into the planktonic food web. A similar response found in benthic communities around natural seeps suggests that carbon isotopic shifts in the plankton fractions are likely due to the duration and magnitude of depleted carbon released into the system. These data provide strong evidence that labile fractions of the oil extended throughout the shallow water column during northward slick transport and that this carbon was processed at least two trophic levels beyond prokaryotic hydrocarbon consumers.

Graham, W. M.; Condon, R. H.; Carmichael, R. H.; D'Ambra, I.; Patterson, H. K.; Hernandez, F. J., Jr.

2010-12-01

323

Local adaptation to temperature conserves top-down control in a grassland food web  

PubMed Central

A fundamental limitation in many climate change experiments is that tests represent relatively short-term ‘shock’ experiments and so do not incorporate the phenotypic plasticity or evolutionary change that may occur during the gradual process of climate change. However, capturing this aspect of climate change effects in an experimental design is a difficult challenge that few studies have accomplished. I examined the effect of temperature and predator climate history in food webs composed of herbaceous plants, generalist grasshopper herbivores and spider predators across a natural 4.8°C temperature gradient spanning 500 km in northeastern USA. In these grasslands, the effects of rising temperatures on the plant community are indirect and arise via altered predator–herbivore interactions. Experimental warming had no direct effect on grasshoppers, but reduced predation risk effects by causing spiders from all study sites to seek thermal refuge lower in the plant canopy. However, spider thermal tolerance corresponded to spider origin such that spiders from warmer study sites tolerated higher temperatures than spiders from cooler study sites. As a consequence, the magnitude of the indirect effect of spiders on plants did not differ along the temperature gradient, although a reciprocal transplant experiment revealed significantly different effects of spider origin on the magnitude of top-down control. These results suggest that variation in predator response to warming may maintain species interactions and associated food web processes when faced with long term, chronic climate warming.

Barton, Brandon T.

2011-01-01

324

Soil acidity, ecological stoichiometry and allometric scaling in grassland food webs  

PubMed Central

The factors regulating the structure of food webs are a central focus of community and ecosystem ecology, as trophic interactions among species have important impacts on nutrient storage and cycling in many ecosystems. For soil invertebrates in grassland ecosystems in the Netherlands, the site-specific slopes of the faunal biomass to organism body mass relationships reflected basic biochemical and biogeochemical processes associated with soil acidity and soil C : N : P stoichiometry. That is, the higher the phosphorus availability in the soil, the higher, on average, the slope of the faunal biomass size spectrum (i.e., the higher the biomass of large-bodied invertebrates relative to the biomass of small invertebrates). While other factors may also be involved, these results are consistent with the growth rate hypothesis from biological stoichiometry that relates phosphorus demands to ribosomal RNA and protein production. Thus our data represent the first time that ecosystem phosphorus availability has been associated with allometry in soil food webs (supporting information available online). Our results have broad implications, as soil invertebrates of different size have different effects on soil processes.

MULDER, CHRISTIAN; ELSER, JAMES J

2009-01-01

325

Adaptive behaviour, tri-trophic food-web stability and damping of chaos  

PubMed Central

We examine the effect of adaptive foraging behaviour within a tri-trophic food web with intra-guild predation. The intra-guild prey is allowed to adjust its foraging effort so as to achieve an optimal per capita growth rate in the face of realized feeding, predation risk and foraging cost. Adaptive fitness-seeking behaviour of the intra-guild prey has a stabilizing effect on the tri-trophic food-web dynamics provided that (i) a finite optimal foraging effort exists and (ii) the trophic transfer efficiency from resource to predator via the intra-guild prey is greater than that from the resource directly. The latter condition is a general criterion for the feasibility of intra-guild predation as a trophic mode. Under these conditions, we demonstrate rigorously that adaptive behaviour will always promote stability of community dynamics in the sense that the region of parameter space in which stability is achieved is larger than for the non-adaptive counterpart of the system.

Visser, Andre W.; Mariani, Patrizio; Pigolotti, Simone

2012-01-01

326

Local adaptation to temperature conserves top-down control in a grassland food web.  

PubMed

A fundamental limitation in many climate change experiments is that tests represent relatively short-term 'shock' experiments and so do not incorporate the phenotypic plasticity or evolutionary change that may occur during the gradual process of climate change. However, capturing this aspect of climate change effects in an experimental design is a difficult challenge that few studies have accomplished. I examined the effect of temperature and predator climate history in food webs composed of herbaceous plants, generalist grasshopper herbivores and spider predators across a natural 4.8°C temperature gradient spanning 500 km in northeastern USA. In these grasslands, the effects of rising temperatures on the plant community are indirect and arise via altered predator-herbivore interactions. Experimental warming had no direct effect on grasshoppers, but reduced predation risk effects by causing spiders from all study sites to seek thermal refuge lower in the plant canopy. However, spider thermal tolerance corresponded to spider origin such that spiders from warmer study sites tolerated higher temperatures than spiders from cooler study sites. As a consequence, the magnitude of the indirect effect of spiders on plants did not differ along the temperature gradient, although a reciprocal transplant experiment revealed significantly different effects of spider origin on the magnitude of top-down control. These results suggest that variation in predator response to warming may maintain species interactions and associated food web processes when faced with long term, chronic climate warming. PMID:21367789

Barton, Brandon T

2011-03-02

327

Tracing Carbon Sources through Aquatic and Terrestrial Food Webs Using Amino Acid Stable Isotope Fingerprinting.  

PubMed

Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring ?(13)C patterns among amino acids (?(13)CAA) could distinguish between multiple aquatic and terrestrial primary production sources. We found that ?(13)CAA patterns in contrast to bulk ?(13)C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their ?(13)CAA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk ?(13)C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer ?(13)C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs. PMID:24069196

Larsen, Thomas; Ventura, Marc; Andersen, Nils; O'Brien, Diane M; Piatkowski, Uwe; McCarthy, Matthew D

2013-09-17

328

Insect-damaged fossil leaves record food web response to ancient climate change and extinction.  

PubMed

Plants and herbivorous insects have dominated terrestrial ecosystems for over 300 million years. Uniquely in the fossil record, foliage with well-preserved insect damage offers abundant and diverse information both about producers and about ecological and sometimes taxonomic groups of consumers. These data are ideally suited to investigate food web response to environmental perturbations, and they represent an invaluable deep-time complement to neoecological studies of global change. Correlations between feeding diversity and temperature, between herbivory and leaf traits that are modulated by climate, and between insect diversity and plant diversity can all be investigated in deep time. To illustrate, I emphasize recent work on the time interval from the latest Cretaceous through the middle Eocene (67-47 million years ago (Ma)), including two significant events that affected life: the end-Cretaceous mass extinction (65.5 Ma) and its ensuing recovery; and globally warming temperatures across the Paleocene-Eocene boundary (55.8 Ma). Climatic effects predicted from neoecology generally hold true in these deep-time settings. Rising temperature is associated with increased herbivory in multiple studies, a result with major predictive importance for current global warming. Diverse floras are usually associated with diverse insect damage; however, recovery from the end-Cretaceous extinction reveals uncorrelated plant and insect diversity as food webs rebuilt chaotically from a drastically simplified state. Calibration studies from living forests are needed to improve interpretation of the fossil data. PMID:18331425

Wilf, P

2008-03-03

329

Distribution of PCB congeners in seven lake systems: Interactions between sediment and food-web transport  

SciTech Connect

A study was conducted to examine the role of two processes, partitioning of PCBs between sediment and biota and food-web transport, in determining the concentration of PCB congeners in the biota of seven lakes. Biota PCB concentration (lipid)-to-sediment PCB concentration (organic carbon), or BSF, ratios were calculated as markers of the partitioning of PCBs between biota and sediment, and biota PCB concentration (lipid)-to-zooplankton PCB concentration (lipid), or BAS, ratios were calculated as markers of the transport of PCBs through food webs. The lakes ranged from a shallow, well-mixed lake with a historic input of Aroclor technical mixtures to deeper, oligotrophic systems in which atmospheric deposition was the only known source. BSF ratios ranged from approximately one in cyprinids and zooplankton in all lakes to 30 in yellow perch in one lake. A significant correlation between lake maximum depth and combined BSF ratios for all biota indicated that PCBs were generally more available for accumulation in the shallower lakes, regardless of the PCB source. Principal component analysis (PCA) showed that the biota in the shallower lakes had higher ratios of higher chlorinated congeners, suggesting that predictions of equal concentrations of hydrophobic contaminants on a lipid basis in sediment and lower trophic levels may significantly underestimate the accumulation of very hydrophobic compounds in the organisms of some lake systems. BAF ratios ranged from approximately one in the lower trophic levels to approximately 10 in lake trout.

MacDonald, C.R.; Metcalfe, C.D.; Balch, G.C.; Metcalfe, T.L. (Trent Univ., Peterborough, Ontario (Canada). Environmental and Resource Studies)

1993-11-01

330

Food webs in Mongolian grasslands: the analysis of 13C and 15N natural abundances.  

PubMed

Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the delta13C and delta15N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The delta13C and delta15N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 per thousand for delta13C and 2.1 per thousand for delta15N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment. PMID:19507080

Kohzu, Ayato; Iwata, T; Kato, M; Nishikawa, J; Wada, Eitaro; Amartuvshin, N; Namkhaidorj, B; Fujita, N

2009-09-01

331

Indirect food web interactions mediated by predator-rodent dynamics: relative roles of lemmings and voles.  

PubMed

Production cycles in birds are proposed as prime cases of indirect interactions in food webs. They are thought to be driven by predators switching from rodents to bird nests in the crash phase of rodent population cycles. Although rodent cycles are geographically widespread and found in different rodent taxa, bird production cycles appear to be most profound in the high Arctic where lemmings dominate. We hypothesized that this may be due to arctic lemmings inducing stronger predator responses than boreal voles. We tested this hypothesis by estimating predation rates in dummy bird nests during a rodent cycle in low-Arctic tundra. Here, the rodent community consists of a spatially variable mix of one lemming (Lemmus lemmus) and two vole species (Myodes rufocanus and Microtus oeconomus) with similar abundances. In consistence with our hypothesis, lemming peak abundances predicted well crash-phase nest predation rates, whereas the vole abundances had no predictive ability. Corvids were found to be the most important nest predators. Lemmings appear to be accessible to the whole predator community which makes them particularly powerful drivers of food web dynamics. PMID:24173526

Ims, Rolf A; Henden, John-André; Thingnes, Anders V; Killengreen, Siw T

2013-10-30

332

Food Webs in the Human Body: Linking Ecological Theory to Viral Dynamics  

PubMed Central

The dynamics of in-host infections are central to predicting the progression of natural infections and the effectiveness of drugs or vaccines, however, they are not well understood. Here, we apply food web theory to in-host disease networks of the human body that are structured similarly to food web models that treat both predation and competition simultaneously. We show that in-host trade-offs, an under-studied aspect of disease ecology, are fundamental to understanding the outcomes of competing viral strains under differential immune responses. Further, and importantly, our analysis shows that the outcome of competition between virulent and non-virulent strains can be highly contingent on the abiotic conditions prevailing in the human body. These results suggest the alarming idea that even subtle behavioral changes that alter the human body (e.g. weight gain, smoking) may switch the environmental conditions in a manner that suddenly allows a virulent strain to dominate and replace less virulent strains. These ecological results therefore cast new light on the control of disease in the human body, and highlight the importance of longitudinal empirical studies across host variation gradients, as well as, of studies focused on delineating life history trade-offs within hosts.

Murall, Carmen Lia; McCann, Kevin S.; Bauch, Chris T.

2012-01-01

333

Urbanization in a great plains river: Effects on fishes and food webs  

USGS Publications Warehouse

Spatial variation of habitat and food web structure of the fish community was investigated at three reaches in the Kansas River, USA to determine if ??13C variability and ??15N values differ longitudinally and are related to urbanization and instream habitat. Fish and macroinvertebrates were collected at three river reaches in the Kansas River classified as the less urbanized reach (no urban in riparian zone; 40% grass islands and sand bars, braided channel), intermediate (14% riparian zone as urban; 22% grass islands and sand bars) and urbanized (59% of riparian zone as urban; 6% grass islands and sand bars, highly channelized) reaches in June 2006. The less urbanized reach had higher variability in ??13C than the intermediate and urbanized reaches, suggesting fish from these reaches utilized a variety of carbon sources. The ??15N also indicated that omnivorous and detritivorous fish species tended to consume prey at higher trophic levels in the less urbanized reach. Channelization and reduction of habitat related to urbanization may be linked to homogenization of instream habitat, which was related to river food webs. ?? 2009.

Eitzmann, J. L.; Paukert, C. P.

2010-01-01

334

Hydrogen Isotope Fractionation in Aquatic Primary Producers: Implications for Food Web Studies  

NASA Astrophysics Data System (ADS)

Hydrogen in the organic matter of aquatic plants has a lower relative abundance of the deuterium isotope in comparison to hydrogen in the surrounding water due to a series of fractionation processes including photosynthesis and the biosynthesis of lipids. Expected differences between the deuterium values of different types of plant tissue have been used to observe terrestrial contributions to aquatic food webs and to discriminate organic matter sources in 3-isotope studies with more precision than in 2-isotope studies, however some values used in these studies are derived from an estimated fractionation value (?) between water and plant tissue. We found significant differences in fractionation values between different groups of aquatic plants sampled from three system types: lakes, river, and coastal lagoon. Fractionation values between water and plant tissue of macrophytes and marine macroalgae were more similar to those of terrestrial plants and distinctly different than those of benthic microalgae and phytoplankton. Incorporating the variability in fractionation values between plant types will improve models and experimental designs used in isotopic food web studies for aquatic systems.

Hondula, K. L.; Pace, M. L.; Cole, J. J.; Batt, R. D.

2011-12-01

335

Tracing Carbon Sources through Aquatic and Terrestrial Food Webs Using Amino Acid Stable Isotope Fingerprinting  

PubMed Central

Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring ?13C patterns among amino acids (?13CAA) could distinguish between multiple aquatic and terrestrial primary production sources. We found that ?13CAA patterns in contrast to bulk ?13C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their ?13CAA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk ?13C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer ?13C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

Larsen, Thomas; Ventura, Marc; Andersen, Nils; O'Brien, Diane M.; Piatkowski, Uwe; McCarthy, Matthew D.

2013-01-01

336

Contrasting Food Web Factor and Body Size Relationships with Hg and Se Concentrations in Marine Biota  

PubMed Central

Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by ?15N) and degree of pelagic feeding (measured by ?13C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans.

Karimi, Roxanne; Frisk, Michael; Fisher, Nicholas S.

2013-01-01

337

Contrasting food web factor and body size relationships with hg and se concentrations in marine biota.  

PubMed

Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by ?(15)N) and degree of pelagic feeding (measured by ?(13)C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans. PMID:24019976

Karimi, Roxanne; Frisk, Michael; Fisher, Nicholas S

2013-09-03

338

JCADM, new directions in Antarctic data management  

NASA Astrophysics Data System (ADS)

The Joint Committee on Antarctic Data Management (JCADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP), to assist in the fulfilment of the data management obligations imposed by the Antarctic Treaty (section III.1.c): "Scientific observations and results from Antarctica shall be exchanged and made freely available." JCADM comprises representatives of the National Antarctic Data Centres or national points of contact. Currently 31 nations around the world are represented in JCADM. So far, JCADM has been focussing on the coordination of the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. Currently, JCADM is in a transition phase, moving forward to provide data access. Existing systems and web services technology will be used as much as possible, to increase efficiency and prevent 're-inventing the wheel' This poster will give an overview of this process, the current status and the expected results.

Campbell, H.; de Bruin, T. F.

2008-12-01

339

Microbial food web structure in the Arabian Sea: a US JGOFS study  

NASA Astrophysics Data System (ADS)

One of the main objectives of the Joint Global Ocean Flux Studies (JGOFS) program is to develop an understanding of the factors controlling organic carbon production in the ocean and the time-varying vertical flux of carbon from surface waters (US JGOFS (1990) US JGOFS Planning Report Number 11; Sarmiento and Armstrong (1997) US JGOFS Synthesis and Modeling Project Implementation Plan). A considerable amount of evidence suggests that carbon cycling and the potential for exporting carbon from ocean systems is a function of food web structure. As part of the US JGOFS Arabian Sea Studies, the biomass of planktonic organisms, ranging from heterotrophic bacteria through microplankton-sized organisms, was estimated using a variety of methods including flow cytometry and microscopy. This is a first attempt to combine biomass data from a number of sources, evaluate the structure of the food web, examine changes in food web structure in relation to seasonal or spatial features of the study area, and look for indications of how changing structure affects carbon-cycling processes. Biomass in the upper 100 m of the water column ranged from approximately 1.5 to >5.2 gC m -2. Heterotrophic bacteria (Hbac) made up from 16 and 44% of the biomass; autotrophs comprised 43-64%; and the remainder was made up of nano- and microheterotrophs. Autotrophs and nano- and microheterotrophs showed a general pattern of higher values at coastal stations, with the lowest values offshore. Heterotrophic bacteria (Hbac) showed no significant spatial variations. The Spring Intermonsoon and early NE Monsoon were dominated by autotrophic picoplankton, Prochlorococcus and Synechococcus. The late NE Monsoon and late SW Monsoon periods showed an increase in the larger size fractions of the primary producers. At several stations during the SW Monsoon, autotrophic microplankton, primarily diatoms and Phaeocystis colonies, predominated. Increases in the size of autotrophs were also reflected in increasing sizes of nano- and microheterorophs. The biomass estimates based on cytometry and microscopy are consistent with measurement of pigments, POC and PON. Changes in community structure were assessed using the percent similarity index (PSI) in conjunction with multidimensional scaling (MDS) or single-linkage clustering analysis to show how assemblages differed among cruises and stations. Station clustering reflected environmental heterogeneity, and many of the conspicuous changes could be associated with changes in temperature, salinity and nutrient concentrations. Despite inherent problems in combining data from a variety of sources, the present community biomass estimates were well constrained by bulk measurements such as Chl a, POC and PON, and by comparisons with other quantitative and qualitative studies. The most striking correlation between food web structure and carbon cycling was the dominance of large phytoplankton, primarily diatoms, and the seasonal maxima of mass flux during the SW Monsoon. High nutrient conditions associated with upwelling during the SW Monsoon would explain the predominance of diatoms during this season. The sinking of large, ungrazed diatom cells is one possible explanation for the flux observations, but may not be consistent with the observation of concurrent increases in larger microzooplankton consumers (heterotrophic dinoflagellates and ciliates) and mesozooplankton during this season. Food-web structure during the early NE Monsoon and Intermonsoons suggests carbon cycling by the microbial community predominated.

Garrison, David L.; Gowing, Marcia M.; Hughes, Margaret P.; Campbell, Lisa; Caron, David A.; Dennett, Mark R.; Shalapyonok, Alexi; Olson, Robert J.; Landry, Michael R.; Brown, Susan L.; Liu, Hong-Bin; Azam, Farooq; Steward, Grieg F.; Ducklow, Hugh W.; Smith, David C.

340

Biomagnification of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls in a highly contaminated freshwater food web from South China.  

PubMed

To evaluate the biomagnification extent of polybrominated diphenyls ethers (PBDEs) and polychlorinated biphenyls (PCBs) in a highly contaminated freshwater food web from South China, trophic magnification factors (TMFs) for 18 PBDE congeners and 53 PCB congeners were calculated. The TMF values ranged 0.26-4.47 for PBDEs and 0.75-5.10 for PCBs. Forty-five of 53 PCBs and BDEs 47, 100 and 154 had TMFs greater than one, suggesting their biomagnification in the present food web. The TMFs for PBDEs were generally smaller than those for PCBs with the same degree of halogenation, indicating a lower biomagnification potential for PBDEs compared to PCBs. For PCBs, it followed a parabolic relationship between TMFs and logK(OW) (octanol-water partition coefficient). However, this relationship was not significant for PBDEs, possibly due to the more complex behaviors of PBDEs in the food web (e.g., metabolism), compared to that of PCBs. PMID:19062142

Wu, Jiang-Ping; Luo, Xiao-Jun; Zhang, Ying; Yu, Mei; Chen, She-Jun; Mai, Bi-Xian; Yang, Zhong-Yi

2008-12-05

341

Climate-driven warming during spring destabilises a Daphnia population: a mechanistic food web approach.  

PubMed

Temperature-driven changes in interactions between populations are crucial to the estimation of the impact of global warming on aquatic food webs. We analysed inter-annual variability in two data sets from Bautzen reservoir, Germany. In a long-term data set (1981-1999) we examined the pelagic phenology of Daphnia galeata, a keystone species, the invertebrate predator Leptodora kindtii, phytoplankton and Secchi depth in relation to water temperature and the North Atlantic Oscillation index. In a short-term data set (1995-1998) we examined food web relations, particularly the consumption of D. galeata by young-of-the-year (YOY) percids and L. kindtii and rates of population change of D. galeata (abundance, recruitment pattern and non-consumptive mortality). The start of the clear-water stage (CWS) was correlated with winter temperatures. It started 5.8 days earlier per degree warming after warm winters (mean January-March temperature>or=2.5 degrees C) compared to cold winters (mean temperature<2.5 degrees C). However, the end of the CWS remained relatively constant. Predation by L. kindtii and YOY percids on D. galeata started distinctly earlier, i.e. by 13.0 and 6.5 days per degree warming, respectively, in years when the average May temperature was high (>or=14 degrees C) compared to years when it was low (<14 degrees C). Significant reductions of Daphnia abundance in midsummer occurred only in years in which the mean May temperature exceeded 14 degrees C. This temperature regime resulted in a match of over-exploitation of food resources by Daphnia during the CWS and strong predation by YOY percids and L. kindtii. Consumptive mortality increased at higher rates with a rise in temperature than net recruitment, resulting in lower Daphnia densities at the end of the CWS. Our data suggest that even low warming by 1.7 degrees C during a short, but critical seasonal period, resulting in the coincidence of two or more factors adversely affecting a keystone species, such as Daphnia, may induce changes in whole lake food webs and thus alter entire ecosystems. PMID:17120058

Wagner, Annekatrin; Benndorf, Jürgen

2006-11-07

342

Ecosystem limits to food web fluxes and fisheries yields in the North Sea simulated with an end-to-end food web model  

NASA Astrophysics Data System (ADS)

Equilibrium yields from an exploited fish stock represent the surplus production remaining after accounting for losses due to predation. However, most estimates of maximum sustainable yield, upon which fisheries management targets are partly based, assume that productivity and predation rates are constant in time or at least stationary. This means that there is no recognition of the potential for interaction between different fishing sectors. Here, an end-to-end ecosystem model is developed to explore the possible scale and mechanisms of interactions between pelagic and demersal fishing in the North Sea. The model simulates fluxes of nitrogen between detritus, inorganic nutrient and guilds of taxa spanning phytoplankton to mammals. The structure strikes a balance between graininess in space, taxonomy and demography, and the need to constrain the parameter-count sufficiently to enable automatic parameter optimization. Simulated annealing is used to locate the maximum likelihood parameter set, given the model structure and a suite of observations of annual rates of production and fluxes between guilds. Simulations of the impact of fishery harvesting rates showed that equilibrium yields of pelagic and demersal fish were strongly interrelated due to a variety of top-down and bottom-up food web interactions. The results clearly show that management goals based on simultaneously achieving maximum sustainable biomass yields from all commercial fish stocks is simply unattainable. Trade-offs between, for example, pelagic and demersal fishery sectors and other properties of the ecosystem have to be considered in devising an overall harvesting strategy.

Heath, Michael R.

2012-09-01

343

Trophic relationships in an Arctic food web and implications for trace metal transfer.  

PubMed

Tissues of subsistence-harvested Arctic mammals were analyzed for silver (Ag), cadmium (Cd), and total mercury (THg). Muscle (or total body homogenates of potential fish and invertebrate prey) was analyzed for stable carbon (delta13C) and nitrogen (delta15N) isotopes to establish trophic interactions within the Arctic food chain. Food web magnification factors (FWMFs) and biomagnification factors for selected predator-prey scenarios (BMFs) were calculated to describe pathways of heavy metals in the Alaskan Arctic. FWMFs in this study indicate that magnification of selected heavy metals in the Arctic food web is not significant. Biomagnification of Cd occurs mainly in kidneys; calculated BMFs are higher for hepatic THg than renal THg for all predator-prey scenarios with the exception of polar bears (Ursus maritimus). In bears, the accumulation of renal THg is approximately 6 times higher than in liver. Magnification of hepatic Ag is minimal for all selected predator-prey scenarios. Though polar bears occupy a higher trophic level than belugas (Delphinapterus leucas), based on delta15N, the metal concentrations are either not statistically different between the two species or lower for bears. Similarly, concentrations of renal and hepatic Cd are significantly lower or not statistically different in polar bears compared to ringed (Phoca hispida) and bearded seals (Erignathus barbatus), their primary prey. THg, on the other hand, increased significantly from seal to polar bear tissues. Mean delta15N was lowest in muscle of Arctic fox (Alopex lagopus) and foxes also show the lowest levels of Hg, Cd and Ag in liver and kidney compared to the other species analyzed. These values are in good agreement with a diet dominated by terrestrial prey. Metal deposition in animal tissues is strongly dependent on biological factors such as diet, age, sex, body condition and health, and caution should be taken when interpreting magnification of dynamic and actively regulated trace metals. PMID:16387350

Dehn, Larissa-A; Follmann, Erich H; Thomas, Dana L; Sheffield, Gay G; Rosa, Cheryl; Duffy, Lawrence K; O'Hara, Todd M

2006-01-04

344

Increasing levels and biomagnification of persistent organic pollutants (POPs) in Antarctic biota.  

PubMed

Representatives of the Antarctic food web (krill, cephalopod, fish, penguin, seal) of the area around Elephant Island and from the Weddell Sea were analysed for the most recalcitrant organochlorine compounds. Due to sorption of the compounds to sinking particles and accumulation in sediments, two benthic fish species (Gobionotothen gibberifrons, Chaenocephalus aceratus) feeding on benthos invertebrates and fish reflected significantly increasing concentrations within a decade (1987-1996), while a benthopelagic species (Champsocephalus gunnari) feeding on krill did not. In the pelagic food chain, lipid normalised concentrations of all compounds increased from Antarctic krill to fish proving that biomagnification of highly lipophilic pollutants (log octanol-water partition coefficient>5) occurs in water-breathing animals. As top predators Weddell and southern elephant seals (Leptonychotes weddellii, Mirounga leonina) biomagnified the persistent organic pollutants relative to krill 30-160 fold with the exception of hexachlorobenzene, the levels of which were lower than in fish indicating its intense specific elimination. PMID:14972581

Goerke, Helmut; Weber, Kurt; Bornemann, Horst; Ramdohr, Sven; Plötz, Joachim

2004-02-01

345

The floodplain food web mosaic: a study of its importance to salmon and steelhead with implications for their recovery  

USGS Publications Warehouse

Although numerous studies have attempted to place species of interest within the context of food webs, such efforts have generally occurred at small scales or disregard potentially important spatial heterogeneity. If food web approaches are to be employed to manage species, studies are needed that evaluate the multiple habitats and associated webs of interactions in which these species participate. Here, we quantify the food webs that sustain rearing salmon and steelhead within a floodplain landscape of the Methow River, Washington, USA, a location where restoration has been proposed to restore side channels in an attempt to recover anadromous fishes. We combined year-long measures of production, food demand, and diet composition for the fish assemblage with estimates of invertebrate prey productivity to quantify food webs within the main channel and five different, intact, side channels; ranging from channels that remained connected to the main channel at low flow to those reduced to floodplain ponds. Although we found that habitats within the floodplain had similar invertebrate prey production, these habitats hosted different local food webs. In the main channel, 95% of total prey consumption flowed to fishes that are not the target of proposed restoration. These fishes consumed 64% and 47% of the prey resources that were found to be important to fueling chinook and steelhead production in the main channel, respectively. Conversely, in side channels, a greater proportion of prey was consumed by anadromous salmonids. As a result, carrying capacity estimates based on food were 251% higher, on average, for anadromous salmonids in side channels than the main channel. However, salmon and steelhead production was generally well below estimated capacity in both the main and side channels, suggesting these habitats are under-seeded with respect to food, and that much larger populations could be supported. Overall, this study demonstrates that floodplain heterogeneity is associated with the occurrence of a mosaic of food webs, all of which were utilized by anadromous salmonids, and all of which may be important to their recovery and persistence. In the long term, these and other fishes would likely benefit from restoring the processes that maintain floodplain complexity.

Bellmore, J. Ryan; Baxter, Colden V.; Martens, Kyle; Connolly, Patrick J.

2013-01-01

346

Trace metals in an urbanized estuarine sea turtle food web in San Diego Bay, CA.  

PubMed

San Diego Bay is an anthropogenically impacted waterway that is also a critical habitat for many sensitive species such as the green sea turtle (Chelonia mydas). In this study, we quantified trace metal concentrations in sediment and organisms composing the green sea turtle diet, and identified bioaccumulation patterns for a suite of trace metals. We found Ag, Cd, Cu, Mn, Se, and Zn exhibited the highest bioaccumulation levels in this food web. Cu and Mn concentrations in resident biota displayed a strong spatial gradient from the mouth to the head of the Bay, which was different from the patterns found in the sediment itself. Sediment median concentrations followed a general pattern across the bay of Al>Mn>Cu?Zn>Pb>As>Cd>Ag>Se>Hg. In contrast, eelgrass displayed differential patterns in the mouth versus the back of the Bay (three front Bay sites: Al>Mn>Zn>Cu>Pb>Se>Cd?Ag>As; five back Bay sites: Mn>Al>Zn>Cu>Pb?Se>Cd>Ag>Hg>As) with the exception of Shelter Island where levels of Zn and Cu were elevated as a result of anti-fouling paint pollution. Observed differences between sediment and biota metal patterns are likely due to complex processes related to trace metals input and bioavailability, habitat characteristics and specific metabolic functioning of the trace metals for each member of the food web. These data highlight the fact that for the San Diego Bay ecosystem, the current use of toxicity reference values scaled up from sediment and invertebrate testing ex-situ is likely to be inaccurate when transposed to the green sea turtle. Here, we illustrate how identifying spatial variability in metal exposure can improve our understanding of habitat utilization by sea turtles in highly urbanized estuaries. Monitoring contaminants directly in food webs of sensitive vertebrates may greatly improve our understanding of their direct and indirect exposure to potentially deleterious contamination, and should be considered in the future to improve traditional risk assessment approaches. PMID:22261404

Komoroske, Lisa M; Lewison, Rebecca L; Seminoff, Jeffrey A; Deustchman, Douglas D; Deheyn, Dimitri D

2012-01-20

347

Simulating the response to phosphate additions in the oligotrophic eastern Mediterranean using an idealized four-member microbial food web model  

Microsoft Academic Search

Elsewhere in this volume, observations of the natural microbial food web in the Cyprus Gyre, eastern Mediterranean, and its transient responses both to phosphate additions in situ and to phosphate and ammonium additions when enclosed in microcosm bottles, are reported. We here explore an idealized four-population model of the microbial part of the food web, containing features suggested in these

T. Frede Thingstad

2005-01-01

348

A new computational system, DOVE (Digital Organisms in a Virtual Ecosystem), to study phenotypic plasticity and its effects in food webs  

Microsoft Academic Search

Food webs are abstract models that represent who eats whom relationships in ecosystems. Classical food web representations do not typically include phenotypic plasticity, in which one species responds to changes in density of other species by modifying traits such as behavior and morphology. Such changes, which are presumably adaptive, will affect the magnitude of both direct and indirect effects on

Scott D. Peacor; Stefano Allesina; Rick L. Riolo; Tim S. Hunter

2007-01-01

349

Impact of changing ice cover on pelagic productivity and food web structure in Disko Bay, West Greenland: a dynamic model approach  

Microsoft Academic Search

A rise in global temperatures could potentially lead to less ice in the Arctic, including a reduction in the ice-covered period. The consequence of a changing ice cover on the food web structure and production in Disko Bay, Western Greenland, is analysed through application of a dynamical model for the planktonic food web. The model is successfully calibrated and tested

Anja Skjoldborg Hansen; Torkel Gissel Nielsen; Henrik Levinsen; Siz D. Madsen; T. Frede Thingstad; Benni Winding Hansen

2003-01-01

350

Changes in food web structure under scenarios of overfishing in the southern Benguela: Comparison of the Ecosim and OSMOSE modelling approaches  

Microsoft Academic Search

Ecosystem models provide a platform allowing exploration into the possible responses of marine food webs to fishing pressure and various potential management decisions. In this study we investigate the particular effects of overfishing on the structure and function of the southern Benguela food web, using two models with different underlying assumptions: the spatialized, size-based individual-based model, OSMOSE, and the trophic

M. Travers; K. Watermeyer; L. J. Shannon; Y.-J. Shin

2010-01-01

351

Establishment of trophic continuum in the food web of the Yellow Sea and East China Sea ecosystem: insight from carbon and nitrogen stable isotopes.  

PubMed

Stable carbon and nitrogen isotope ratios (delta (13)C and delta (15)N) are used to study the trophic structure of food web in the Yellow Sea and East China Sea ecosystem. The trophic continuum of pelagic food web from phytoplankton to top preyer was elementarily established, and a trophic structure diagram in the Yellow Sea and East China Sea was outlined in combination with carbon isotopic data of benthic organisms, which is basically consistent with and makes some improvements on the simplified Yellow Sea food web and the trophic structure diagram drawn based on the biomass of main resource population during 1985-1986. This result indicates that the stable isotope method is a potential useful means for further studying the complete marine food web trophic continuum from viruses to top predators and food web stability. PMID:16483132

Cai, Deling; Li, Hongyan; Tang, Qisheng; Sun, Yao

2005-12-01

352

Evolutionary ecology in silico: evolving food webs, migrating population and speciation  

NASA Astrophysics Data System (ADS)

After a brief review of our recent works on “unified” models of evolutionary ecology, we have generalized our “unified” model by taking into account spatial variations from one “patch” to another. We model the spatial extension of the ecosystem (i.e., the geography) by a square lattice where each site corresponds to a distinct “patch”. A distinct self-organizing hierarchical food web describes the prey predator relations at each patch in the ecosystem. By carrying out computer simulations up to 10 time steps, we found that, depending on the values of the set of parameters, the distribution of the lifetimes of the species can be fitted to power laws, but only over a very restricted regime of lifetimes. We also interpret our model in terms of taxonomy and present results to elucidate some evolutionary trends in genus, family, order, class, phylum, etc.

Stauffer, Dietrich; Kunwar, Ambarish; Chowdhury, Debashish

2005-07-01

353

Combined impacts of global warming and pollution: impacts on food web structure and ecosystem function.  

NASA Astrophysics Data System (ADS)

Effects of global species loss on ecosystem function have traditionally been extrapolated from studies which investigate the effect of random species loss or addition. Real species loss is highly patterned and clumped according to trophic position, taxonomic relatedness and interconnectedness with the remainder of the food web. Using pond microcosms, I evoked a realistic pattern of species loss using toxins and warming. Species loss was predictably highly patterned. Influences on ecosystem functions ranged from simple and linear in the case of algal productivity, through to complex and step-like in the case of bacterial decomposition. Impacts on algal productivity were mediated by effects on the rate of grazing by invertebrates. There is strong evidence from the bacterial decomposition results of an `insurance effect' whereby the presence of multiple stressors has a strong, non-additive effect on function. These results clearly show that the traditional ecotoxicological practice of studying effects of single toxins on single species may be highly misleading.

Thompson, R. M.

2005-05-01

354

Identification of bacterial micropredators distinctively active in a soil microbial food web.  

PubMed

The understanding of microbial interactions and trophic networks is a prerequisite for the elucidation of the turnover and transformation of organic materials in soils. To elucidate the incorporation of biomass carbon into a soil microbial food web, we added 13C-labeled Escherichia coli biomass to an agricultural soil and identified those indigenous microbes that were specifically active in its mineralization and carbon sequestration. rRNA stable isotope probing (SIP) revealed that uncultivated relatives of distinct groups of gliding bacterial micropredators (Lysobacter spp., Myxococcales, and the Bacteroidetes) lead carbon sequestration and mineralization from the added biomass. In addition, fungal populations within the Microascaceae were shown to respond to the added biomass after only 1 h of incubation and were thus surprisingly reactive to degradable labile carbon. This RNA-SIP study identifies indigenous microbes specifically active in the transformation of a nondefined complex carbon source, bacterial biomass, directly in a soil ecosystem. PMID:16885285

Lueders, Tillmann; Kindler, Reimo; Miltner, Anja; Friedrich, Michael W; Kaestner, Matthias

2006-08-01

355

Food web structure and vulnerability of a deep-sea ecosystem in the NW Mediterranean Sea  

NASA Astrophysics Data System (ADS)

There is increasing fishing pressure on the continental margins of the oceans, and this raises concerns about the vulnerability of the ecosystems thriving there. The current knowledge of the biology of deep-water fish species identifies potential reduced resilience to anthropogenic disturbance. However, there are extreme difficulties in sampling the deep sea, resulting in poorly resolved and indirectly obtained food-web relationships. Here, we modelled the flows and biomasses of a Mediterranean deep-sea ecosystem, the Catalan Sea continental slope at depths of 1000-1400 m. This is the first model of a deep-water ecosystem in the Mediterranean Sea. The objectives were to (a) quantitatively describe the food web structure of the ecosystem, (b) examine the role of key species in the ecosystem, and (c) explore the vulnerability of this deep-sea ecosystem to potential future fishing exploitation. We used the Ecopath with Ecosim (EwE) modelling approach and software to model the ecosystem. The trophic model included 18 consumers, a marine snow group, and a sediment detritus group. Trophic network analysis identified low levels of consumer biomass cycling and low system omnivory index when compared with expected values of marine ecosystems, and higher cycling and omnivory when compared with available EwE models of shallower areas of the Mediterranean Sea. The majority of flows in the ecosystem were concentrated at the trophic level of first-order consumers (TL 2). Benthic invertebrates and demersal sharks were identified to have key ecological roles in the ecosystem. We used the dynamic temporal model Ecosim to simulate expansion of the red-shrimp benthic trawl fishery that currently operates at shallower depths, down to 800 m depth. The simulations showed reductions in fish biomass and that the state of the deep continental slope ecosystem in the western Mediterranean seems to be the result of a long-term succession process, which has reached ecological stability, and is particularly vulnerable to human impact and, specifically, to fisheries exploitation.

Tecchio, Samuele; Coll, Marta; Christensen, Villy; Company, Joan B.; Ramírez-Llodra, Eva; Sardà, Francisco

2013-05-01

356

Infiltration by alien predators into invertebrate food webs in Hawaii: a molecular approach.  

PubMed

Abstract Alien invertebrate predators have been introduced to Hawaii to control pests, particularly in lowland areas where most crops are grown. We developed techniques for assessing the impact of these predators on native food webs in relatively pristine upland areas where, it was hypothesized, few lowland predators might be found. Predator densities were assessed along transects within the Alakaii Swamp on Kaua'i. The most numerous alien biocontrol agents found were Halmus chalybeus (Coccinellidae), a species known to feed on Lepidoptera eggs. Laboratory experiments were conducted using two genera of endemic Lepidoptera, Scotorythra and Eupithecia (Geometridae), that are of considerable conservation value, the former because of its recent speciation across Hawaii, the latter for its unique predatory larvae. Techniques were developed for detecting Lepidoptera DNA within the guts of alien predators using prey-specific PCR primers. General primers amplified fragments of the mitochondrial cytochrome oxidase I gene from beetles and Lepidoptera. The sequences were aligned and used successfully to design target-specific primers for general detection of the remains of Geometridae and for particular species, including Scotorythra rara and Eupithecia monticolans. DNA fragments amplified were short [140-170 base pairs (bp)], optimizing detection periods following prey ingestion. Trials using the introduced biocontrol agent Curinus coeruleus (Coccinellidae) demonstrated detection of Lepidoptera DNA fragments = 151 bp in 85-100% of beetles after 24 h digestion of an early instar larva. This study provides a framework for future use of molecular gut analysis in arthropod conservation ecology and food web research with considerable potential for quantifying threats to endemic species in Hawaii and elsewhere. PMID:15189227

Sheppard, S K; Henneman, M L; Memmott, J; Symondson, W O C

2004-07-01

357

Combined effects of global climate change and regional ecosystem drivers on an exploited marine food web.  

PubMed

Changes in climate, in combination with intensive exploitation of marine resources, have caused large-scale reorganizations in many of the world's marine ecosystems during the past decades. The Baltic Sea in Northern Europe is one of the systems most affected. In addition to being exposed to persistent eutrophication, intensive fishing, and one of the world's fastest rates of warming in the last two decades of the 20th century, accelerated climate change including atmospheric warming and changes in precipitation is projected for this region during the 21st century. Here, we used a new multimodel approach to project how the interaction of climate, nutrient loads, and cod fishing may affect the future of the open Central Baltic Sea food web. Regionally downscaled global climate scenarios were, in combination with three nutrient load scenarios, used to drive an ensemble of three regional biogeochemical models (BGMs). An Ecopath with Ecosim food web model was then forced with the BGM results from different nutrient-climate scenarios in combination with two different cod fishing scenarios. The results showed that regional management is likely to play a major role in determining the future of the Baltic Sea ecosystem. By the end of the 21st century, for example, the combination of intensive cod fishing and high nutrient loads projected a strongly eutrophicated and sprat-dominated ecosystem, whereas low cod fishing in combination with low nutrient loads resulted in a cod-dominated ecosystem with eutrophication levels close to present. Also, nonlinearities were observed in the sensitivity of different trophic groups to nutrient loads or fishing depending on the combination of the two. Finally, many climate variables and species biomasses were projected to levels unseen in the past. Hence, the risk for ecological surprises needs to be addressed, particularly when the results are discussed in the ecosystem-based management context. PMID:23818413

Niiranen, Susa; Yletyinen, Johanna; Tomczak, Maciej T; Blenckner, Thorsten; Hjerne, Olle; Mackenzie, Brian R; Müller-Karulis, Bärbel; Neumann, Thomas; Meier, H E Markus

2013-08-23

358

Bioaccumulation and biomagnification of organochlorines in a marine food web at a pristine site in Iceland.  

PubMed

Organochlorine (OC) bioaccumulation and biomagnification were studied in a marine food web at a pristine site in Iceland. The species studied were the gastropod and grazer chink shell (Lacuna vincta), the filter feeding bivalve blue mussel (Mytilus edulis), the predators butterfish (Pholis gunnellus), and the seabird black guillemot (Cepphus grylle), all sampled and analysed in 1996-1997. Individual OC levels were generally low in chink shell and blue mussels, somewhat elevated in the fish, and an order of a magnitude higher in the top predator black guillemot, except for Sigma HCH (hexachlorocyclohexane isomers) and Sigma chlordane levels, which were similar in all organisms, ranging from 10 to 36 ng/g lipid weight (lw). In the molluscs and fish, mean concentrations of Sigma PCB (polychlorinated biphenyl) ranged from 111 to 377 ng/g lw, Sigma DDT (dichlorodiphenyltrichloroethane) ranged from 19 to 65 ng/g lw, and HCB (hexachlorobenzene) ranged from 21 to 30 ng/g lw. The levels of same OCs in the black guillemot were on average 2352, 361, and 283 ng/g lw, respectively. The OC tissue concentrations in blue mussel and black guillemot are comparable to levels in Arctic and sub-Arctic regions, but OC levels in blue mussel tissue were an order of magnitude lower than found in the North Sea and the Baltic Sea. The relative composition of OCs were generally similar among species with the PCB congeners emerging as the most abundant compounds with levels an order of magnitude higher than the other compounds in all species. Food web magnification factors (FWMFs) were determined for the OCs by using trophic levels determined from delta(15)N. FWMFs >1, indicating biomagnification, were found for Sigma PCB, penta- or higher chlorinated PCBs (e.g., PCB 101, 118, 138, 153, 180), beta-HCH, HCB, Sigma DDT, p,p-DDE, and transnonachlor. The highest FWMF was observed for PCB 180 at FWMF = 5.8. PMID:19711125

Skarphedinsdottir, Halldora; Gunnarsson, Karl; Gudmundsson, Gudmundur A; Nfon, Erick

2009-08-27

359

Intermediate-consumer identity and resources alter a food web with omnivory.  

PubMed

1. Omnivory is an important interaction that has been the centre of numerous theoretical and empirical studies in recent years. Most of these studies examine the conditions necessary for coexistence between an omnivore and an intermediate consumer. Trait variation in ecological interactions (competition and predator tolerance) among intermediate consumers has not been considered in previous empirical studies despite the evidence that variation in species-specific traits can have important community-level effects. 2. I conducted a multifactorial microcosm experiment using species from the Sarracenia purpurea phytotelmata community, organisms that inhabit the water collected within its modified leaves. The basal trophic level consisted of bacterial decomposers, the second trophic level (intermediate consumers) consisted of protozoa and rotifers, and the third trophic level (omnivore) were larvae of the pitcher plant mosquito Wyeomyia smithii. Trophic level number (1, 2 and 3), resources (low and high), omnivore density (low and high) and intermediate consumer (monoculture of five protozoa and rotifers) identity were manipulated. Abundance of the basal trophic level, intermediate consumers, and growth of the omnivore were measured, as well as time to extinction (intermediate consumers) and time to pupation (mosquito larvae). 3. The presence of different intermediate consumers affected both bacteria abundance and omnivore growth. At high resource levels, Poteriochromonas, Colpidium and Habrotrocha rosa reduced bacteria densities greater than omnivore reduction of bacteria. Mosquito larvae did not pupate at low resource levels except when Poteriochromonas and Colopoda were present as intermediate consumers. Communities with H. rosa were the only ones consistent with the prediction that omnivores should exclude intermediate consumers at high resources. 4. These results had mixed support for predictions from omnivory food web theory. Intermediate consumers responded and affected this community differently under different community structures and resource levels. Consequently, variation in species-specific traits can have important population- and community-level effects and needs to be considered in food webs with omnivory. PMID:17584370

Kneitel, Jamie M

2007-07-01

360

A vigorous specialized microbial food web in the suboxic waters of a shallow subtropical coastal lagoon.  

PubMed

To examine the extent of the microbial food web in suboxic waters of a shallow subtropical coastal lagoon, the density and biomass of bacteria and protozooplankton were quantified under different dissolved oxygen (DO) levels. In addition, bottom waters of a stratified site were compared with bottom waters of a homogeneous site under periods of high and low biological oxygen production/consumption in the lagoon. At the stratified site, microbial biomass decreased with oxygen decline, from oxia to suboxia, with a recovery of the initial total biomass after a 20-day period of persistent suboxia. A peak in density and biomass of purple sulfur bacteria (PSB) (90 ?g C L(-1)) occurred in the suboxic waters 20 days prior to the peak in biomass of ciliates >50 ?m (Loxophyllum sp. of 150 ?m) (160 ?g C L(-1)), demonstrating a top down biomass control. Ciliates >50 ?m were positively correlated with PSB and bacteriochlorophyll a (photosynthetic pigment of PSB). Total protozoan biomass reached 430 ?g C L(-1) in the suboxic waters of the stratified site, with ciliates >50 ?m accounting for 90% of the total ciliate biomass and of 55 % of biomass of protozoa. At the homogeneous site, total protozoan biomass was only 66 ?g C L(-1), where flagellates and ciliates <25 ?m were the dominant microorganisms. Therefore, as light is available for primary producers in the bottom waters of shallow stratified coastal lagoons or estuaries, one can expect that high primary production of PSB may favor a specialized microbial food web composed by larger microorganisms, accessible to zooplankton that tolerate low DO levels. PMID:22450511

Fontes, Maria Luiza S; Abreu, Paulo C

2012-03-27

361

Spider web  

NSDL National Science Digital Library

Spiders build webs as a way to catch food. Flying and crawling insects can easily be caught in this sticky web and eaten if they aren't careful. Spiders also live on these webs and store their eggs cases on webs.

N/A N/A (U.S. Fish and Wildlife Service;)

2005-07-25

362

Nitrogen-stable isotope signatures in estuarine food webs: A record of increasing urbanization in coastal watersheds  

Microsoft Academic Search

Nutrient enrichment as a result of anthropogenic activity concentrated along the land-sea margin is increasing eutrophication of near-shore waters across the globe. Management of eutrophication in the coastal zone has been ' hampered by the lack of a direct method to trace nitrogen sources from land into coastal food webs. Stable isotope data from a series of estuaries receiving nitrogen

James W. McClelland; Ivan Valiela; Robert H. Michener

363

Effects of fish and nutrient additions on food-web stability in a charophyte-dominated lake  

Microsoft Academic Search

1. The response of major food-web constituents to combinations of nutrient addition and zooplanktivorous fish abundance was tested during two subsequent years in the shallow charophyte-dominated lake Naardermeer in the Netherlands, using in situ enclosures. 2. Treatment effects differed sharply between study years. In 1998, when the summer temperature was low (1721 °C), high algal biomass only developed at high

Wouter J. Van De Bund; Ellen Van Donk

2004-01-01

364

Stable isotope assessment of water quality, primary productivity, nutrient sources, and food web structure in Lake Winnipeg  

Microsoft Academic Search

Lake Winnipeg (Canada) is a shallow great lake currently undergoing extensive eutrophication. A 4-year stable isotope project is currently underway to examine water quality, primary productivity, nutrient sources, and food web structure in the lake. The isotope hydrology (18O, 2H) of Lake Winnipeg is needed in order to gain a picture of spatial isotopic patterns in the lake that can

L. I. Wassenaar

2008-01-01

365

What sources of organic carbon drive food webs in billabongs? A study based on stable isotope analysis  

Microsoft Academic Search

We used the stable isotopes of carbon and nitrogen to examine the food webs of three small flood-plain lakes (billabongs) in south-eastern Australia. With few exceptions, stable carbon isotope analysis could not be used to discriminate among the conspicuous potential sources of fringing, emergent or floating vegetation or benthic detritus. These primary sources showed little spatial or temporal variation in

Stuart E. Bunn; Paul I. Boon

1993-01-01

366

Biomagnification of PBDEs and PCBs in food webs from the Baltic Sea and the northern Atlantic Ocean  

Microsoft Academic Search

Biomagnification of polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs) in food webs from the Baltic Sea and the northern Atlantic Sea was investigated. For this, we used PCB and PBDE concentration data, together with data on fish body weight and ?15N of fish and zooplankton as a measure of trophic position. In the Baltic Sea material, consisting of zooplankton, sprat,

Sven Burreau; Yngve Zebühr; Dag Broman; Rasha Ishaq

2006-01-01

367

Bacterial traits, organism mass, and numerical abundance in the detrital soil food web of Dutch agricultural grasslands  

Microsoft Academic Search

This paper compares responses to environmental stress of the ecophysiological traits of organisms in the detrital soil food webs of grasslands in the Netherlands, using the relationship between average body mass M and numerical abundance N. The microbial biomass and biodiversity of belowground fauna were measured in 110 grasslands on sand, 85 of them farmed under organic, conventional and intensive

Christian Mulder; Joel E. Cohen; Heikki Setala

368

Impacts of changing food webs in Lake Ontario: Implications of dietary fatty acids on growth of Alewives  

Microsoft Academic Search

Declines in the abundance and condition of Great Lakes Alewives have been reported periodically during the last two decades, and the reasons for these declines remain unclear. To better understand how food web changes may influence Alewife growth and Wisconsin growth model predictions, we fed Alewives isocaloric diets high in omega-6 fatty acids (corn oil) or high in omega-3 fatty

Randal J. Snyder; Chad J. DeMarche; Dale C. Honeyfield

2011-01-01

369

Food web reliance on allochthonous carbon in two high mountain lakes with contrasting catchments: a stable isotope approach  

Microsoft Academic Search

The carbon isotopic signature (?13C) of dissolved inorganic carbon and food web components was examined in two high mountain lakes. Río Seco Lake is partially surrounded by alpine meadows and has temporal inlets, whereas La Caldera Lake is located on rocky terrain and does not receive inputs from runoff. We assessed whether these con- trasting catchments involve differences in the

Elvira Pulido-Villena; Isabel Reche; Rafael Morales-Baquero

2005-01-01

370

Biomagnification profiles of tributyltin (TBT) and triphenyltin (TPT) in Japanese coastal food webs elucidated by stable nitrogen isotope ratios.  

PubMed

The measurement of organotins in the various biotas of coastal food webs with stable nitrogen isotope ratios (delta(15)N), which increase 3.4 per thousand per trophic level, can provide a biomagnification profile of organotins through food web. In this study, various biological samples were collected from three localities in Western Japan between 2002 and 2003 for analyses. Tributyltin (TBT) and triphenyltin (TPT) were still detected with a maximum of 99.5 and 8.7 ng wet weight g(-1), respectively. Unlike TBT, significant biomagnification of TPT through the food web (expressed by delta(15)N) was found in all three localities. The log transformed octanol-water partition coefficient (log K(ow)) of TPT of 2.11-3.43 was overlapped by, but was slightly lower than, that of TBT of 3.70-4.70. Thus, this study demonstrates that although these chemicals have a log K(ow) lower than 5, at least TPT undergoes significant biomagnification through the food web. PMID:18950832

Murai, Ryota; Sugimoto, Atsuko; Tanabe, Shinsuke; Takeuchi, Ichiro

2008-10-23

371

Using Stable Isotope Mixing in a Great Lakes Coastal Tributary to Determine Food Web Linkages in Young Fishes  

EPA Science Inventory

Our objectives were to determine whether we can detect a stable isotope gradient along the river-Great Lake hydrologic continuum in a coastal river and use it to identify changes across this gradient in the food web supporting young-of-year (YOY) and juvenile fish production. We ...

372

COASTAL WETLAND-NEARSHORE FOOD WEB LINKAGES ALONG A TROPHIC GRADIENT IN GREEN BAY: A FISH-EYE VIEW  

EPA Science Inventory

To identify ecological interactions among Green Bay coastal wetlands and lake habitats we analyzed stable isotope signatures of organismsa from wetland and adjacent nearshore food webs in Green Bay, Lake Michigan. We were interested in the influence of nutrient loading/trophic st...

373

Agricultural intensification and cereal aphid-parasitoid-hyperparasitoid food webs: network complexity, temporal variability and parasitism rates.  

PubMed

Agricultural intensification (AI) is currently a major driver of biodiversity loss and related ecosystem functioning decline. However, spatio-temporal changes in community structure induced by AI, and their relation to ecosystem functioning, remain largely unexplored. Here, we analysed 16 quantitative cereal aphid-parasitoid and parasitoid-hyperparasitoid food webs, replicated four times during the season, under contrasting AI regimes (organic farming in complex landscapes vs. conventional farming in simple landscapes). High AI increased food web complexity but also temporal variability in aphid-parasitoid food webs and in the dominant parasitoid species identity. Enhanced complexity and variability appeared to be controlled bottom-up by changes in aphid dominance structure and evenness. Contrary to the common expectations of positive biodiversity-ecosystem functioning relationships, community complexity (food-web complexity, species richness and evenness) was negatively related to primary parasitism rates. However, this relationship was positive for secondary parasitoids. Despite differences in community structures among different trophic levels, ecosystem services (parasitism rates) and disservices (aphid abundances and hyperparasitism rates) were always higher in fields with low AI. Hence, community structure and ecosystem functioning appear to be differently influenced by AI, and change differently over time and among trophic levels. In conclusion, intensified agriculture can support diverse albeit highly variable parasitoid-host communities, but ecosystem functioning might not be easy to predict from observed changes in community structure and composition. PMID:22644050

Gagic, Vesna; Hänke, Sebastian; Thies, Carsten; Scherber, Christoph; Tomanovi?, Zeljko; Tscharntke, Teja

2012-05-30

374

Carbon and nitrogen stable isotopes and metal concentration in food webs from a mining-impacted coastal lagoon  

Microsoft Academic Search

Two food webs from the Mar Menor coastal lagoon, differing in the distance from the desert-stream through which mining wastes were discharged, were examined by reference to essential (Zn and Cu) and non-essential (Pb and Cd) metal concentrations and stable isotopes content (C and N). The partial extraction technique applied, which reflects the availability of metals to organisms after sediment

Lázaro Marín-Guirao; Javier Lloret; Arnaldo Marin

2008-01-01

375

Food Web Relationships of Northern Puget Sound and the Strait of Juan de Fuca. A Synthesis of the Available Knowledge.  

National Technical Information Service (NTIS)

This report resulted from the need to synthesize existing knowledge of the structure of food webs in nearshore marine habitats of northern Puget Sound and the Strait of Juan de Fuca, in order to identify the potential transfer processes of petroleum hydro...

B. S. Miller C. A. Simenstad C. F. Nyblade K. Thornburgh L. J. Bledsoe

1979-01-01

376

The toxic effects of rubber contaminants on microbial food webs and zooplankton of two lakes of different trophic status  

Microsoft Academic Search

Rubber is commonly used in recreational equipment and devicesforsampling in lakes, but there have been few studies of theeffectsof rubber on planktonic organisms. We investigated the toxiceffects of rubber on the microbial food webs of a mesotrophiclakeand a eutrophic lake. Lake water was collected by pumping via,(i) a polyvinylchloride hose and, (ii) a rubber hose. Samplesoflake water collected by each

Lisa Galbraith; Carolyn W. Burns

1997-01-01

377

Insects from the grazing food web favoured the evolutionary habitat shift to bright environments in araneoid spiders  

PubMed Central

The Araneoidea comprises a diverse group of web-building spiders, and part of this diversity is believed attributable to habitat expansion to bright environments. We clarified the fitness-related advantages of living in such environments by examining prey availability and the growth rates of 10 species in three families inhabiting grassland (bright) and forest understory (dim) habitats. Spiders in the grassland habitat captured more prey, derived mainly from the grazing food web, than those in the forest-floor environment, and this difference was manifested in their growth rate. Independent contrasts indicated that increased utilization of insects from the grazing food web led to an evolutionary increase in adult body size. These results suggest that the shift to bright environments enabled araneoid spiders to evolve diverse life-history traits, including rapid growth and large size, which were not possible in dim environments.

Miyashita, Tadashi; Shimazaki, Aya

2006-01-01

378

The SCAR Standing Committee on Antarctic Data Management - new directions in access to Antarctic research data  

NASA Astrophysics Data System (ADS)

The SCAR Standing Committee on Antarctic Data Management (SC-ADM) was established by the Scientific Committee on Antarctic Research (SCAR) and the Council of Managers of National Antarctic Programs (COMNAP), to assist in the fulfillment of the data management obligations imposed by the Antarctic Treaty (section III.1.c): "Scientific observations and results from Antarctica shall be exchanged and made freely available." SC-ADM comprises representatives of the National Antarctic Data Centres or national points of contact. Currently 31 nations around the world are represented in SC-ADM. So far, SC-ADM has been focussing on the coordination of the Antarctic Master Directory (AMD), the internationally accessible, web-based, searchable record of Antarctic and Southern Ocean data set descriptions. The AMD is directly integrated into the international Global Change Master Directory (GCMD) to help further merge Antarctic science into global science. The AMD is a resource for scientists to advertise the data they have collected and to search for data they may need. Currently, SC-ADM is in a transition phase, moving forward to provide data access. Existing systems and web services technology will be used as much as possible, to increase efficiency and prevent 're-inventing the wheel' This poster will give an overview of this process, the current status and the expected results.

de Bruin, T.

2009-04-01

379

Simulating climate change-induced alterations in bioaccumulation of organic contaminants in an Arctic marine food web.  

PubMed

Climate change is expected to alter environmental distribution of contaminants and their bioaccumulation due to changes in transport, partitioning, carbon pathways, and bioaccumulation process rates. Magnitude and direction of these changes and resulting overall bioaccumulation in food webs is currently not known. The present study investigates and quantifies the effect of climate change in terms of increased temperature and primary production (i.e., concentrations of particulate organic carbon, C(POC)), on bioaccumulation of organic contaminants in biota at various trophic levels. The present study covers only parts of the contaminant behavior that is influenced by climate change, and it was assumed that there were no changes in food web structure and in total air and water concentrations of organic contaminants. Therefore, other climate change-induced effects on net bioaccumulation, such as altered contaminant transport and food web structure, should be addressed in future studies. To determine the effect of climate change, a bioaccumulation model was used on the pelagic marine food web of the Arctic, where climate change is expected to occur fastest and to the largest magnitude. The effect of climate change on model parameters and processes, and on net bioaccumulation, were quantified for three modeling substances (gamma-hexachlorocyclohexane [HCH], polychlorinated biphenyl [PCB]-52, and PCB-153) for two possible climate scenarios. In conclusion, increased temperature and C(POC) reduced the overall bioaccumulation of organic contaminants in the Arctic marine food web, with the largest change being for PCB-52 and PCB-153. Reduced bioavailability, due to increased C(POC), was the most influential parameter for the less water soluble compounds. Increase in temperature resulted in an overall reduction in net bioaccumulation. PMID:20821579

Borgå, Katrine; Saloranta, Tuomo M; Ruus, Anders

2010-06-01

380

Fatty acid transfer in the food web of a coastal Mediterranean lagoon: Evidence for high arachidonic acid retention in fish  

NASA Astrophysics Data System (ADS)

The transfer of fatty acids (FAs) in the food web of a Mediterranean lagoon was studied using FA compositional patterns across several trophic levels. The structure of the food web was inferred from C and N stable isotopes values and an isotope mixing model was used in order to estimate the relative contribution of the different potential food sources to the biomass of consumers. Bidimensional plots of FA composition of food web components against their ? 15N values indicated a general trend of increasing proportions of highly unsaturated fatty acids (HUFAs) with increasing trophic levels while the proportions of saturated fatty acids (SAFAs) and 18-carbon polyunsaturated fatty acids (PUFAs) decreased. Using the relative contributions of food sources to consumers and their FA compositions, a model was built in order to estimate the PUFA composition of consumer mixed diets which was compared to consumer PUFA profiles. The latter allowed the identification of the PUFAs which were mostly enriched/retained in consumer lipids. There was a surprisingly high retention of arachidonic acid (ARA), a trend which challenges the idea of low ARA needs in marine fish and suggests the important physiological role of this essential FA for fish in estuarine environments.

Koussoroplis, Apostolos-Manuel; Bec, Alexandre; Perga, Marie-Elodie; Koutrakis, Emmanuil; Bourdier, Gilles; Desvilettes, Christian

2011-02-01

381

Transformation of chiral polychlorinated biphenyls (PCBs) in a stream food web  

USGS Publications Warehouse

The enantiomeric composition of chiral PCB congeners was determined in Twelvemile Creek (Clemson, SC) to examine potential mechanisms of biotransformation in a stream food web. We measured enantiomeric fractions (EFs) of six PCB atropisomers (PCBs 84, 91, 95, 136, 149, and 174) in surface sediment, fine benthic organic matter (FBOM), coarse particulate organic matter (CPOM), periphyton, Asian clam, mayflies, yellowfin shiner, and semipermeable membrane devices (SPMDs) using gas chromatography (GC-ECD). Nonracemic EFs of PCBs 91, 95, 136, and 149 were measured in almost all samples. Enantiomeric compositions of PCBs 84 and 174 were infrequently detected with racemic EFs measured in samples except for a nonracemic EF of PCB 84 in clams. Nonracemic EFs of PCBs 91, 136, and 149 in SPMDs may be due to desorption of nonracemic residues from FBOM. EFs for some atropisomers were significantly different among FBOM, CPOM, and periphyton, suggesting that their microbial communities have different biotransformation processes. Nonracemic EFs in clams and fish suggest both in vivo biotransformation and uptake of nonracemic residues from their food sources. Longitudinal variability in EFs was generally low among congeners observed in matrices. ?? 2010 American Chemical Society.

Dang, V. D.; Walters, D. M.; Lee, C. M.

2010-01-01

382

Changes in food web structure affect rate of PCB decline in herring gull (Larus argentatus) eggs  

SciTech Connect

Biological monitors provide important information regarding temporal trends in levels of persistent organic pollutants. Correct interpretation of these trends is critical if one is to accurately assess his progress in eliminating these contaminants from the environment. In the Laurentian Great Lakes, polychlorinated biphenyl concentrations in herring gull eggs declined during the 1970s and early 1980s. By the mid-1980s, further declines were not as obvious. An exception to this trend was observed in eggs from Lake Erie. On that lake, egg PCB concentrations continued to decline rapidly during the 1980s/1990s. Evidence from stable isotope analysis indicated that temporal changes in the composition of the herring gull diet occurred on Lake Erie. In the eastern basin, declines in fish availability may have forced the gulls to incorporate a greater proportion of terrestrial food into their diets. Decreases in the proportion of fish in the gull diet would have resulted in reduced PCB exposure. This may be partially responsible for the continuing rapid rate of decline in egg PCB concentrations. This decline should be interpreted with caution. These trends may not be indicative of lake-wide declines in PCB bioavailability but only reflect changes in dietary exposure brought about by alterations in food web structure.

Hebert, C.E.; Hobson, K.A.; Shutt, J.L.

2000-05-01

383

Antarctic Krill 454 Pyrosequencing Reveals Chaperone and Stress Transcriptome  

Microsoft Academic Search

BackgroundThe Antarctic krill Euphausia superba is a keystone species in the Antarctic food chain. Not only is it a significant grazer of phytoplankton, but it is also a major food item for charismatic megafauna such as whales and seals and an important Southern Ocean fisheries crop. Ecological data suggest that this species is being affected by climate change and this

Melody S. Clark; Michael A. S. Thorne; Jean-Yves Toullec; Yan Meng; Le Luo Guan; Lloyd S. Peck; Stephen Moore; Jack Anthony Gilbert

2011-01-01

384

The Antarctic Cruise Industry  

Microsoft Academic Search

This chapter outlines the growth of cruise tourism in Antarctica. It describes the highly concentrated spatial distribution of Antarctic tourism, examines the background of Antarctic cruise tourists, and discusses the environmental impacts of Antarctic tourism

Ross Dowling; Thomas Bauer

2006-01-01

385

Trophic structure and mercury distribution in a Gulf of St. Lawrence (Canada) food web using stable isotope analysis.  

PubMed

Even at low concentrations in the environment, mercury has the potential to biomagnify in food chains and reaches levels of concern in apex predators. The aim of this study was to relate the transfer of total mercury (THg) and methylmercury (MeHg) in a Gulf of St. Lawrence food web to the trophic structure, from primary consumers to seabirds, using stable nitrogen (?(15)N) and carbon (?(13)C) isotope analysis and physical environmental parameters. The energy reaching upper trophic level species was principally derived from pelagic primary production, with particulate organic matter (POM) at the base of the food chain. We developed a biomagnification factor (BMF) taking into account the various prey items consumed by a given predator using stable isotope mixing models. This BMF provides a more realistic estimation than when using a single prey. Lipid content, body weight, trophic level and benthic connection explained 77.4 and 80.7% of the variation in THg and MeHg concentrations, respectively in this food web. When other values were held constant, relationships with lipid and benthic connection were negative whereas relationships with trophic level and body weight were positive. Total Hg and MeHg biomagnified in this food web with biomagnification power values (slope of the relationship with ?(15)N) of 0.170 and 0.235, respectively on wet weight and 0.134 and 0.201, respectively on dry weight. Values of biomagnification power were greater for pelagic and benthopelagic species compared to benthic species whereas the opposite trend was observed for levels at the base of the food chain. This suggests that Hg would be readily bioavailable to organisms at the base of the benthic food chain, but trophic transfer would be more efficient in each trophic level of pelagic and benthopelagic food chains. PMID:20810146

Lavoie, Raphael A; Hebert, Craig E; Rail, Jean-François; Braune, Birgit M; Yumvihoze, Emmanuel; Hill, Laura G; Lean, David R S

2010-10-15

386

Effects of Seasonal and Spatial Differences in Food Webs on Mercury Concentrations in Fish in the Everglades  

NASA Astrophysics Data System (ADS)

A clear understanding of the aquatic food web is essential for determining the entry points and subsequent biomagnification pathways of contaminants such as methyl-mercury (MeHg) in the Everglades. Anthropogenic changes in nutrients can significantly affect the entry points of MeHg by changing food web structure from one dominated by algal productivity to one dominated by macrophytes and associated microbial activity. These changes in the base of the food web can also influence the distribution of animals within the ecosystem, and subsequently the bioaccumulation of MeHg up the food chain. As part of several collaborations with local and other federal agencies, more than 7000 Everglades samples were collected in 1995-99, and analysed for d13C and d15N. Many organisms were also analysed for d34S, gut contents, total Hg, and MeHg. Carbon isotopes effectively distinguish between two main types of food webs: ones where algae is the dominant base of the food web, which are characteristic of relatively pristine marsh sites with long hydroperiods, and ones where macrophyte debris appears to be a significant source of nutrients, which are apparently characteristic of shorter hydroperiod sites, and nutrient-impacted marshes and canals. Many organisms show significant (5-12%) spatial and temporal differences in d13C and d15N values across the Everglades. These differences may reflect site and season-specific differences in the relative importance of algae vs. macrophyte debris to the food web. However, there is a lack of evidence that these sites otherwise differ in food chain length (as determined by d15N values). This conclusion is generally supported by gut contents and mercury data. Furthermore, there are no statistically significant differences between the Delta d15N (predator-algae) values at pristine marsh, nutrient-impacted marsh, or canal sites. The main conclusions from this preliminary comparison of gut contents, stable isotope, and Hg data are: (1) there is little evidence for spatial variations in food chain length - hence, this does not appear to be the dominant explanation for spatial variations in Hg in predators, (2) the poor correlation of d15N and Hg for many organisms, reflective of the heterogeneous and dynamic nature of the ecosystem, makes it difficult to account for changes in Hg with trophic position, and (3) seasonal and spatial variations in hydrology and nutrient conditions, which are often reflected in changes in the base of the food web, appear to be the dominant controls on the isotopic compositions of organisms in the Everglades. Hence, biota isotopes provide a tool for monitoring how future ecosystem changes affect the distribution of algae vs. macrophyte-dominated food webs across the Everglades.

Kendall, C.; Bemis, B. E.; Wankel, S. D.; Rawlik, P. S.; Lange, T.; Krabbenhoft, D. P.

2002-05-01

387

Bioaccumulation and trophic transfer of polybrominated diphenyl ethers (PBDEs) in a marine food web from Liaodong Bay, North China.  

PubMed

The concentrations of 21 polybrominated diphenyl ethers (PBDEs) congeners were analyzed in organisms within a marine food web collected from the Liaodong Bay, North China. The total concentrations of PBDEs in all samples ranged from 0.87 to 91.4 ng g(-1) lipid weight (lw). BDE-47 was the predominant congener and had a concentration ranging from 0.30 to 36.1 ng g(-1) lw. The trophic magnification factors (TMF) of the PBDEs were calculated using the trophic levels obtained from the stable nitrogen isotope ratios. The TMF value of ?PBDEs was 3.50 for the entire food web and 2.21 for the food web excluding seabirds. Four concentration ratios, BDE-99/BDE-100, BDE-99/BDE-47, BDE-153/BDE-154 and BDE-183/BDE-154, decreased linearly with the increase of the trophic levels in the invertebrates and the fishes (p<0.01). The results suggested that the PBDEs were steadily metabolized in the trophic transfer process along the food chain. PMID:23906472

Ma, Xindong; Zhang, Haijun; Yao, Ziwei; Zhao, Xiaofeng; Wang, Longxing; Wang, Zhen; Chen, Jiping; Chen, Jingwen

2013-07-29

388

Predator identity and the nature and strength of food web interactions.  

PubMed

1. Most trophic interaction theory assumes that all predators are an abstract form of risk to which prey respond in a quantitatively similar manner. This conceptualization can be problematic because recent empirical work demonstrates that variation in the responses of prey to different predators can play a key role in structuring communities and regulating ecosystem function. 2. Predator identity - the species specific response of prey to a predator - has been proposed as an ultimate mechanism driving the relative contribution of indirect effects in food webs; however few studies have explicitly tested this hypothesis. 3. This study explores the impact of predator identity on direct consumptive (CE) and non-consumptive effects (NCEs), and on the relative contribution of indirect, density and trait-mediated effects in trophic cascades within host-parasitoid communities. 4. We systematically compared the individual, host-parasitoid-plant interactions of two actively foraging parasitoid species with disparate foraging styles, one aggressive and one furtive, a common aphid host and plant. Our results demonstrate that the degree of risk aversion by prey to each particular predator species (i.e. predator identity) is a key factor driving the nature and strength of direct and indirect transmission pathways. 5. Both parasitoid species, in general, had a negative impact on plants. The magnitude of the aphid anti-predator dispersal response was positively correlated with plant infestation and plant damage. The qualitative effect of predator-induced infestation of new plants superseded the quantitative effects of predator-mediated reductions in aphid numbers. 6. The greatest indirect impact on plants was generated by the aggressively foraging parasitoid, and the strength of the aphids anti-predator response (a NCE) antagonistically traded-off with CEs due to an increased investment in attempting to capture risk-sensitized prey. In contrast, the furtive parasitoid did not elicit a strong anti-predator response, had little indirect impact on plants, but generated very high CEs due to the advantage of ovipositing into a sedentary prey population. 7. Our data suggest the responses of prey to different predatory cues may be an important mechanism driving the relative contribution of transmission pathways in trophic cascades. We conclude that predator identity is a key factor influencing the nature and strength of food web interactions. PMID:20646124

Henry, Lee M; Bannerman, Jordan A; Gillespie, David R; Roitberg, Bernard D

2010-11-01

389

Regulation of intertidal food webs by avian predators on New England rocky shores.  

PubMed

Although there is a large body of research on food webs in rocky intertidal communities, most of the emphasis has been on the marine benthic components. Effects of avian predation on highly mobile predators such as crabs, remains practically unstudied in rocky shore ecosystems. The crab, Cancer borealis, is an important component of the diet of gulls (Larus marinus, L. argentatus) at the Isles of Shoals, Maine, USA. C. borealis prey include the predatory gastropod Nucella lapillus L., the herbivore Littorina littorea, and mussels Mytilus edulis L. We hypothesized that gulls reduce abundance of C. borealis in the low intertidal and shallow subtidal, thereby allowing C. borealis prey to persist in high numbers. A study of crab tidal migration showed that C. borealis density nearly doubled at high tide compared to low tide; thus, crabs from a large subtidal source population migrate into the intertidal zone during high tides and either emigrate or are removed by gulls during low tides. Results from a small-scale (1 m2) predator caging experiment in the low intertidal zone indicated that enclosed crabs significantly reduced L. littorea abundance when protected from gull predation. In a much larger-scale gull exclusion experiment, densities of C. borealis increased significantly during low and high tides in exclosures relative to the controls. C. borealis density was inversely correlated with changes in the abundance of two mesopredators Carcinus maenas and Nucella lapillus, and with the space-occupier M. edulis. There was a similar negative correlation between abundance of C. borealis and the change in abundance of the herbivore L. littorea, but the trend was not significant. Mortality of tethered L. littorea was associated with C. borealis density across sites. However, preferred algae did not change in response to L. littorea density during the experiment. Thus, we found suggestive, but not conclusive, evidence for a three-level cascade involving gulls, crabs, and L. littorea. Our studies strongly suggest that gulls, as apex predators, generate three-level trophic cascades in rocky intertidal food webs by preventing the highly mobile subtidal predator, C. borealis, from establishing substantial populations in the low-mid intertidal zone thereby indirectly enhancing densities of two key mesopredators (N. lapillus, Carcinus) and blue mussels (M. edulis). PMID:17536702

Ellis, Julie C; Shulman, Myra J; Wood, Megan; Witman, Jon D; Lozyniak, Sara

2007-04-01

390

USDA Food and Nutrient Database for Dietary Studies: Released on the web  

Microsoft Academic Search

The USDA Survey Nutrient Database and other technical files used to code foods and calculate nutrient values for national food consumption surveys were updated, redesigned, and renamed the USDA Food and Nutrient Database for Dietary Studies (FNDDS). This new database is now available over the internet from the Food Surveys Research Group (FSRG). Code numbers, food descriptions and food portion

Janice Bodner-Montville; Jaspreet K. C. Ahuja; Linda A. Ingwersen; Etta Susanne Haggerty; Cecilia Wilkinson Enns; Betty P. Perloff

2006-01-01

391

Antarctic macrozooplankton of the southwest Atlantic sector and Bellingshausen Sea: Baseline historical distributions ( Discovery Investigations, 1928-1935) related to temperature and food, with projections for subsequent ocean warming  

NASA Astrophysics Data System (ADS)

Since the Discovery Investigations of the 1920s and 1930s, seawater temperatures have increased in the Atlantic sector by ˜1 °C; greater than the global mean rise. The aims of this paper were first to rescue the Discovery macrozooplankton data, second to provide quantitative "baseline" distribution maps, relating these to indices of temperature and food. Our third aim was to use the relationships we derived between abundance and temperature to project the potential affect of a 1 °C warming on the Discovery era distribution patterns. Based on the 1 m ringnet data retrieved from 615 stations (Nov-March), four taxa comprised >90% of the Antarctic macrozooplankton abundance: Rhincalanus gigas, Thysanoessa spp., Euphausia superba, and Chaetognaths. Most of the taxa, especially the more abundant ones, were warm water species penetrating into Antarctica and thus total macrozooplankton abundance decreased about 100-fold from 50°S to 70°S. While temperature correlated best with distribution at this large scale, food availability (proxied by a present-day satellite-based Chlorophyll a climatology) had a secondary effect, with the major euphausiids Euphausia superba and Thysanoessa spp. concentrated in high chl a areas. A modelled uniform 1 °C temperature rise produced a poleward shift for all taxa, but the Antarctic continent blocked this re-adjustment for the high latitude species, constricting their predicted range. More widespread polar/sub-polar species were predicted to increase their penetration into Antarctica by 4-12° in latitude, whereas the poleward shift in potential range of sub-Antarctic taxa were limited by the steep temperature gradient across the Antarctic Polar Front (APF). However, within the Scotia Sea the relatively warm temperatures of the northern Antarctic Zone, abundant food due to iron fertilisation and intense eddy activity provide a "gateway" for northern species to penetrate south of the APF. Our model predictions, based on measured distributional ranges and observed temperature increases, provide a yardstick with which to compare modern day data compilations and assess the potential effects of future temperature increases.

Mackey, A. P.; Atkinson, A.; Hill, S. L.; Ward, P.; Cunningham, N. J.; Johnston, N. M.; Murphy, E. J.

2012-01-01

392

Effects of temperature on isotopic enrichment in Daphnia magna: implications for aquatic food-web studies.  

PubMed

Laboratory experiments were conducted with Daphnia magna and Hyalella sp. grown on a single food source of known isotopic composition at a range of temperatures spanning the physiological optima for each species. Daphnia raised at 26.5 degrees C were enriched in delta(13)C and delta(15)N by 3.1 and 2.8 per thousand, respectively, relative to diet. Daphnia raised at 12.8 degrees C were enriched 1.7 and 5.0 per thousand in delta(13)C and delta(15)N, respectively. Results imply a significant negative relationship between the delta(13)C and delta(15)N of primary consumers when a temperature gradient exists. Similar responses were observed for Hyalella. Results indicate a general increase in delta(13)C enrichment and decrease in delta(15)N enrichment as temperature rises. Deviations from the commonly applied isotopic enrichment values used in aquatic ecology were attributed to changes in temperature-mediated physiological rates. Field data from a variety of sources also showed a general trend toward delta(13)C enrichment with increasing temperature in marine and lacustrine zooplankton. Multivariate regression models demonstrated that, in oligotrophic and mesotrophic lakes, zooplankton delta(13)C was related to lake-specific POM delta(13)C, lake surface temperature and latitude. Temperature-dependent isotopic separation (enrichment) between predator and prey should be taken into consideration when interpreting the significance of isotopic differences within and among aquatic organisms and ecosystems, and when assigning organisms to food-web positions on the basis of observed isotope values. PMID:12845588

Power, M; Guiguer, K R R A; Barton, D R

2003-01-01

393

Methylmercury levels and bioaccumulation in the aquatic food web of a highly mercury-contaminated reservoir.  

PubMed

The low Ebro River basin (NE Spain) represents a particular case of chronic and long-term mercury pollution due to the presence of an industrial waste (up to 436 ?g/g of Hg) coming from a chlor-alkali plant Albeit high total mercury (THg) levels have been previously described in several aquatic species from the surveyed area, methylmercury (MeHg) values in fish individuals have never been reported. Accordingly, in order to investigate bioaccumulation patterns at different levels of the aquatic food web of such polluted area, crayfish and various fish species, were analysed for THg and MeHg content. At the hot spot, THg mean values of crayfish muscle tissue and hepatopancreas were 10 and 15 times, respectively, greater than the local background level. Higher mean THg concentrations were detected in piscivorous (THg=0.848 ± 0.476 ?g/g wet weight (ww); MeHg=0.672 ± 0.364 ?g/g ww) than in non-piscivorous fish (THg=0.305 ± 0.163 ?g/g ww; MeHg=0.278 ± 0.239 ?g/g ww). Although these results indicated that THg in fish increased significantly with increasing trophic position, the percentage of the methylated form of Hg was not strongly influenced by differences in relative trophic position. This is an important finding, since the fraction of THg as MeHg in the top fish predator was unexpectedly lower than for other species of the aquatic food chain. Moreover, mean THg concentrations in piscivorous fish exceed the maximum level recommended for human consumption. From our findings, it is clear that for this specific polluted system, speciation becomes almost mandatory when risk assessment is based on MeHg, since single measurements of THg are inadequate and could lead to an over- or under-estimation of contamination levels. PMID:21658770

Carrasco, Luis; Benejam, Lluís; Benito, Josep; Bayona, Josep M; Díez, Sergi

2011-06-11

394

Organic matter flow in the food web at a temperate heath under multifactorial climate change.  

PubMed

The rising atmospheric CO(2) concentration, increasing temperature and changed patterns of precipitation currently expose terrestrial ecosystems to altered environmental conditions. This may affect belowground nutrient cycling through its intimate relationship with the belowground decomposers. Three climate change factors (elevated CO(2), increased temperature and drought) were investigated in a full factorial field experiment at a temperate heathland location. The combined effect of biotic and abiotic factors on nitrogen and carbon flows was traced in plant root ? litter ? microbe ? detritivore/omnivore ? predator food-web for one year after amendment with (15)N(13)C(2)-glycine. Isotope ratio mass spectrometry (IRMS) measurement of (15)N/(14)N and (13)C/(12)C in soil extracts and functional ecosystem compartments revealed that the recovery of (15)N sometimes decreased through the chain of consumption, with the largest amount of bioactive (15)N label pool accumulated in the microbial biomass. The elevated CO(2) concentration at the site for 2 years increased the biomass, the (15)N enrichment and the (15)N recovery in detritivores. This suggests that detritivore consumption was controlled by both the availability of the microbial biomass, a likely major food source, and the climatic factors. Furthermore, the natural abundance ?(13)C of enchytraeids was significantly altered in CO(2)-fumigated plots, showing that even small changes in ?(13)C-CO(2) can be used to detect transfer of carbon from primary producers to detritivores. We conclude that, in the short term, the climate change treatments affected soil organism activity, possibly with labile carbohydrate production controlling the microbial and detritivore biomass, with potential consequences for the decomposition of detritus and nutrient cycling. Hence, there appears to be a strong coupling of responses in carbon and nitrogen cycling at this temperate heath. PMID:21594921

Andresen, Louise C; Konestabo, Heidi S; Maraldo, Kristine; Holmstrup, Martin; Ambus, Per; Beier, Claus; Michelsen, Anders

2011-06-15

395

Food-web dynamics and trophic-level interactions in a multispecies community of freshwater unionids  

USGS Publications Warehouse

We compared feeding habits and trophic-level relationships of unionid species in a detritus-dominated river and an alga-dominated lake using biochemical analyses, gut contents, and stable-isotope ratios. The ??13C ratios for algae and other food-web components show that all unionids from both the river and the lake used bacterial carbons, not algal carbons, as their main dietary source, in spite of positive selection and concentration of diatoms and green algae from the water column in the gut and mantle cavity. Algae did provide key nutrients such as vitamins A and D and phytosterols that were bioaccumulated in the tissues of all species. The ??15N ratios for the multispecies unionid community in the Huron River indicated some differences in nitrogen enrichment between species, the greatest enrichment being found in Pyganadon grandis. These ??15N ratios indicate that unionids may not always feed as primary consumers or omnivores. Stable-isotope data were critical for delineating diets and trophic-level interactions of this group of filter-feeders. Further refinements in identifying bacterial and picoplankton components of the fine particulate organic matter are needed to complete our understanding of resource partitioning between multispecies unionid populations.

Nichols, S. J.; Garling, D.

2000-01-01

396

Anomalous rise in algal production linked to lakewater calcium decline through food web interactions  

PubMed Central

Increased algal blooms are a threat to aquatic ecosystems worldwide, although the combined effects of multiple stressors make it difficult to determine the underlying causes. We explore whether changes in trophic interactions in response to declining calcium (Ca) concentrations, a water quality issue only recently recognized in Europe and North America, can be linked with unexplained bloom production. Using a palaeolimnological approach analysing the remains of Cladocera (herbivorous grazers) and visual reflectance spectroscopically inferred chlorophyll a from the sediments of a Nova Scotia (Canada) lake, we show that a keystone grazer, Daphnia, declined in the early 1990s and was replaced by a less effective grazer, Bosmina, while inferred chlorophyll a levels tripled at constant total phosphorus (TP) concentrations. The decline in Daphnia cannot be attributed to changes in pH, thermal stratification or predation, but instead is linked to declining lakewater [Ca]. The consistency in the timing of changes in Daphnia and inferred chlorophyll a suggests top-down control on algal production, providing, to our knowledge, the first evidence of a link between lakewater [Ca] decline and elevated algal production mediated through the effects of [Ca] decline on Daphnia. [Ca] decline has severe implications for whole-lake food webs, and presents yet another mechanism for potential increases in algal blooms.

Korosi, Jennifer B.; Burke, Samantha M.; Thienpont, Joshua R.; Smol, John P.

2012-01-01

397

Ecological versus phylogenetic determinants of trophic associations in a plant-leafminer-parasitoid food web.  

PubMed

Specialized trophic interactions in plant-herbivore-parasitoid food webs can spur "bottom-up" diversification if speciation in plants leads to host-shift driven divergence in insect herbivores, and if the effect then cascades up to the third trophic level. Conversely, parasitoids that search for victims on certain plant taxa may trigger "top-down" diversification by pushing herbivores into "enemy-free space" on novel hosts. We used phylogenetic regression methods to compare the relative importance of ecology versus phylogeny on associations between Heterarthrinae leafmining sawflies and their parasitoids. We found that: (1) the origin of leafmining led to escape from most parasitoids attacking external-feeding sawflies; (2) the current enemies mainly consist of generalists that are shared with other leafmining taxa, and of more specialized lineages that may have diversified by shifting among heterarthrines; and (3) parasitoid-leafminer associations are influenced more by the phylogeny of the miners' host plants than by relationships among miner species. Our results suggest that vertical diversifying forces have a significant-but not ubiquitous-role in speciation: many of the parasitoids have remained polyphagous despite niche diversification in the miners, and heterarthrine host shifts also seem to be strongly affected by host availability. PMID:23617924

Leppänen, Sanna A; Altenhofer, Ewald; Liston, Andrew D; Nyman, Tommi

2013-01-04

398

Selenium in San Francisco Bay zooplankton: Potential effects of hydrodynamics and food web interactions  

USGS Publications Warehouse

The potential toxicity of elevated selenium (Se) concentrations in aquatic ecosystems has stimulated efforts to measure Se concentrations in benthos, nekton, and waterfowl in San Francisco Bay (SF Bay). In September 1998, we initiated a 14 mo field study to determine the concentration of Se in SF Bay zooplankton, which play a major role in the Bay food web, but which have not previously been studied with respect to Se. Monthly vertical plankton tows were collected at several stations throughout SF Bay, and zooplankton were separated into two operationally defined size classes for Se analyses: 73-2,000 ??m, and ???2,000 ??m. Selenium values ranged 1.02-6.07 ??g Se g-1 dry weight. No spatial differences in zooplankton Se concentrations were found. However, there were inter- and intra-annual differences. Zooplankton Se concentrations were enriched in the North Bay in Fall 1999 when compared to other seasons and locations within and outside SF Bay. The abundance and biovolume of the zooplankton community varied spatially between stations, but not seasonally within each station. Smaller herbivorous-omnivorous zooplankton had higher Se concentrations than larger omnivorous-carnivorous zooplankton. Selenium concentrations in zooplankton were negatively correlated with the proportion of total copepod biovolume comprising the large carnivorous copepod Tortanus dextrilobatus, but positively correlated with the proportion of copepod biovolume comprising smaller copepods of the family Oithonidae, suggesting an important role of trophic level and size in regulating zooplankton Se concentrations.

Purkerson, D. G.; Doblin, M. A.; Bollens, S. M.; Luoma, S. N.; Cutter, G. A.

2003-01-01

399

A screening level probabilistic risk assessment of mercury in Florida Everglades food webs.  

PubMed

A screening level probabilistic assessment of risks was performed on three species of piscivorous wildlife at the top of Everglades aquatic food webs: the American alligator (Alligator mississippiensis), the great egret (Egretta alba), and the raccoon (Procyon lotor varius). Ranges of dietary exposure concentrations (and probability distribution functions) were derived for two general areas of the Everglades: Shark Slough and the southcentral Everglades (highly contaminated with Hg), and the northern Everglades (a lower Hg contaminated area in and near Water Conservation Area 1). Ranges of toxicity reference values and probability distribution functions were derived from literature on the toxicity of dietary methyl Hg to birds and mammals. Probability distributions of risk estimates for each receptor were generated using Monte Carlo simulations and indicated that piscivorous wildlife feeding in the south-central region of the Everglades are at high risk from consumption of Hg-contaminated prey. Alligators had 100% exceedences of chronic risk thresholds, and great egrets had 99% exceedences. In the northern Everglades, exceedences of chronic risk thresholds were substantially lower but were still present (6-34% exceedences). Results support previous studies suggesting that top predators of the Everglades may be at risk from Hg contamination and indicate that Hg risks are location-dependent. PMID:11139184

Duvall, S E; Barron, M G

2000-11-01

400

Paratenic hosts as regular transmission route in the acanthocephalan Pomphorhynchus laevis: potential implications for food webs  

NASA Astrophysics Data System (ADS)

Although trophically transmitted parasites are recognized to strongly influence food-web dynamics through their ability to manipulate host phenotype, our knowledge of their host spectrum is often imperfect. This is particularly true for the facultative paratenic hosts, which receive little interest. We investigated the occurrence and significance both in terms of ecology and evolution of paratenic hosts in the life cycle of the fish acanthocephalan Pomphorhynchus laevis. This freshwater parasite uses amphipods as intermediate hosts and cyprinids and salmonids as definitive hosts. Within a cohort of parasite larvae, usually reported in amphipod intermediate hosts, more than 90% were actually hosted by small-sized fish. We demonstrated experimentally, using one of these fish, that they get infected through the consumption of parasitized amphipods and contribute to the parasite's transmission to a definitive host, hence confirming their paratenic host status. A better knowledge of paratenic host spectrums could help us to understand the fine tuning of transmission strategies, to better estimate parasite biomass, and could improve our perception of parasite subwebs in terms of host-parasite and predator-parasite links.

Médoc, Vincent; Rigaud, Thierry; Motreuil, Sébastien; Perrot-Minnot, Marie-Jeanne; Bollache, Loïc

2011-10-01

401

The impact of climate change on the structure of Pleistocene food webs across the mammoth steppe.  

PubMed

Species interactions form food webs, impacting community structure and, potentially, ecological dynamics. It is likely that global climatic perturbations that occur over long periods of time have a significant influence on species interaction patterns. Here, we integrate stable isotope analysis and network theory to reconstruct patterns of trophic interactions for six independent mammalian communities that inhabited mammoth steppe environments spanning western Europe to eastern Alaska (Beringia) during the Late Pleistocene. We use a Bayesian mixing model to quantify the contribution of prey to the diets of local predators, and assess how the structure of trophic interactions changed across space and the Last Glacial Maximum (LGM), a global climatic event that severely impacted mammoth steppe communities. We find that large felids had diets that were more constrained than those of co-occurring predators, and largely influenced by an increase in Rangifer abundance after the LGM. Moreover, the structural organization of Beringian and European communities strongly differed: compared with Europe, species interactions in Beringian communities before--and possibly after--the LGM were highly modular. We suggest that this difference in modularity may have been driven by the geographical insularity of Beringian communities. PMID:23658198

Yeakel, Justin D; Guimarães, Paulo R; Bocherens, Hervé; Koch, Paul L

2013-05-08

402

Fractal-like aspects of the microbial part of the pelagic food web?.  

NASA Astrophysics Data System (ADS)

From many perspectives, most of the biological activity in pelagic systems is in the microbial part, invisible to the naked eye. Conceptual perceptions of this system vary from the overly simplistic in nutrient-phytoplankton-zooplankton models, to one of "unmanageably complexity" in the large sets of data recently collected by metagenomic techniques. The interacting members of this microbial community range in size from viruses to large diatoms and ciliates and cover a linear size range around 3 orders of magnitude (9 orders of magnitude in volume). One pattern-generating mechanism in this system is what has been termed "killing-the-winner" where the biomass-controlling effect of a predator or parasite allows the co-existence of organisms classified as competition and defense strategists. Since this mechanism can be seen to repeat itself at many levels of resolution, it is suggested to have a resemblance to the concept of self-similarity in fractal theory. On a higher level, the outcome of these interactions is size-abundance curves that are known to follow power-law relationships and therefore also allows one to draw an analogy to fractal dimensions. This perspective is suggested to allow another entrance to the problem of connecting phenomena at different scales in the pelagic food web, compared to the more traditional attempts to build plankton functional type model of ever-increasing complexity.

Frede Thingstad, Tron

2010-05-01

403

Long-term variation of link strength in a simple benthic food web.  

PubMed

1. The predatory isopod Saduria entomon (L.) and its amphipod prey Monoporeia affinis (Lindström) are key components of the food web in the northern Baltic Sea, together representing 80-90% of the macrobenthic biomass. We use 20 years of stomach content data for Saduria to investigate how diet dynamics affect the stability of the interaction between Saduria and Monoporeia. 2. Consumption of the main prey, Monoporeia, fitted a type III functional response. Consumption rates of the most important alternative prey, mysids, were found to be unrelated to mysid densities but negatively related to the density of Monoporeia. The fit of consumption data to a model that assumes passive prey selection was poor. Thus we conclude that some form of active choice is involved. 3. The effect of consumption of mysids, the alternative prey, on the stability of this system was investigated using a 'one predator-two prey' model with stochastic environmental variation. Analysis of the model suggests that feeding on mysids leads to a decreased extinction risk for the predator, Saduria, and reduced density oscillations for both Saduria and its main prey, Monoporeia. PMID:18507696

Englund, G; Rydberg, C; Leonardsson, K

2008-05-27

404

A Quantitative Food Web Model for the Macroinvertebrate Community of a Northern German Lowland Stream  

NASA Astrophysics Data System (ADS)

Trophic interactions and cycling of organic carbon within the macroinvertebrate community of a Northern German lowland stream were analyzed based on a compartment model. The network model describes the structure of the food web quantifying biomass, production, and consumption of their elements, of the entire system and between trophic levels. System primary production is 153.7 g C m-2 yr-1 and invertebrate production 53.3 g C m-2 yr-1. Invertebrate consumption amounts to 702.6 g C m-2 yr-1. Main flows are identified between trophic level 1 and 2 and are connected with highly productive compartments. Anodonta and Pseudanodonta and Dreissena polymorpha show the highest consumption of all groups with 269.9 g C m-2 yr-1 and 114.1 g C m-2 yr-1, respectively. System consumption is highest on the import from the upstream lake with 532.5 g C m-2 yr-1, sediment detritus with 135.5 g C m-2 yr-1, and primary producers with 25.7 g C m-2 yr-1. The lowest predation pressure is observed for Bivalvia with an ecotrophic efficiency of <10% and highest for Chironomidae with 91%. Approximately 20% of organic matter entering the detritus pool are recycled to the living groups of the system. Transfer efficiencies between discrete trophic levels are generally low except for transfer of detrital material between level I and II.

Poepperl, Rainer

2003-09-01

405

Extinction cascades partially estimate herbivore losses in a complete Lepidoptera--plant food web.  

PubMed

The loss of species from an ecological community can have cascading effects leading to the extinction of other species. Specialist herbivores are highly diverse and may be particularly susceptible to extinction due to host plant loss. We used a bipartite food web of 900 Lepidoptera (butterfly and moth) herbivores and 2403 plant species from Central Europe to simulate the cascading effect of plant extinctions on Lepidoptera extinctions. Realistic extinction sequences of plants, incorporating red-list status, range size, and native status, altered subsequent Lepidoptera extinctions. We compared simulated Lepidoptera extinctions to the number of actual regional Lepidoptera extinctions and found that all predicted scenarios underestimated total observed extinctions but accurately predicted observed extinctions attributed to host loss (n = 8, 14%). Likely, many regional Lepidoptera extinctions occurred for reasons other than loss of host plant alone, such as climate change and habitat loss. Ecological networks can be useful in assessing a component of extinction risk to herbivores based on host loss, but further factors may be equally important. PMID:24015522

Pearse, Ian S; Altermatt, Florian

2013-08-01

406

Examination of the bioaccumulation of halogenated dimethyl bipyrroles in an Arctic marine food web using stable nitrogen isotope analysis  

Microsoft Academic Search

Concentrations of four possibly naturally produced organohalogens — 1,1?-dimethyl-3,3?,4-tribromo-4,5,5?-trichloro-2,2?-bipyrrole (DBP-Br3Cl3), 1,1?-dimethyl-3,3?,4,4?-tetrabromo-5,5?-dichloro-2,2?-bipyrrole (DBP-Br4Cl2), 1,1?-dimethyl-3,3?,4,4?,5-pentabromo-5?-chloro-2,2?-bipyrrole (DBP-Br5Cl) and 1,1?-dimethyl-3,3?,4,4?,5,5?-hexabromo-2,2?-bipyrrole (DBP-Br6) — were quantitated and the extent of their magnification through an entire Arctic marine food web [measured as integrated trophic magnification factors (TMFs)] were calculated. The food web consisted of three zooplankton species (Calanus hyperboreus, Mysis oculata, and Sagitta sp.), one fish species [Arctic cod

Sheryl A Tittlemier; Aaron T Fisk; Keith A Hobson; Ross J Norstrom

2002-01-01

407

Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets  

NASA Astrophysics Data System (ADS)

The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27-1218 m d -1 (median 304 m d -1), being governed mainly by pellet diameter (80-600 ?m, mean 183 ?m) and density (1.038-1.391 g cm -3, mean 1.121 g cm -3). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such "superfluous feeding" probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2-10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter that tend to prevail in sediment traps. We suggest that this is because krill schools are more compact, producing "rain showers" of pellets that exceed the capacity of pelagic scavengers to reprocess them.

Atkinson, A.; Schmidt, K.; Fielding, S.; Kawaguchi, S.; Geissler, P. A.

2012-01-01

408

Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets  

NASA Astrophysics Data System (ADS)

The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27-1218 m d-1 (median 304 m d-1), being governed mainly by pellet diameter (80-600 ?m, mean 183 ?m) and density (1.038-1.391 g cm-3, mean 1.121 g cm-3). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such “superfluous feeding” probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2-10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter that tend to prevail in sediment traps. We suggest that this is because krill schools are more compact, producing “rain showers” of pellets that exceed the capacity of pelagic scavengers to reprocess them.

Atkinson, A.; Schmidt, K.; Fielding, S.; Kawaguchi, S.; Geissler, P. A.

2012-01-01

409

Grazer traits, competition, and carbon sources to a headwater-stream food web.  

PubMed

We investigated the effect of grazing by a dominant invertebrate grazer (the caddisfly Glossosoma penitum) on the energy sources used by other consumers in a headwater-stream food web. Stable isotope studies in small, forested streams in northern California have shown that G. penitum larvae derive most of their carbon from algae, despite low algal standing crops. We hypothesized that the caddisfly competes with other primary consumers (including mayflies) for algal food and increases their reliance on terrestrial detritus. Because Glossosoma are abundant and defended from predators by stone cases, their consumption of algal energy may reduce its transfer up the food chain. We removed Glossosoma (natural densities >1000 caddisflies/m2) from five approximately 4 m2) stream sections during the summer of 2000 and measured responses of algae, invertebrate primary consumers, and invertebrate predators. The treatment reduced Glossosoma biomass by 80-90%. We observed a doubling in chlorophyll a per area in sections with reduced Glossosoma abundance and aggregative increases in the biomass of undefended primary consumers. Heptageniid mayfly larvae consumed more algae (as measured by stable carbon isotope ratios and gut content analysis) in caddisfly removal plots at the end of the 60-day experiment, although not after one month. We did not see isotopic evidence of increased algal carbon in invertebrate predators, however. Patterns of caddisfly and mayfly diets in the surrounding watershed suggested that mayfly diets are variable and include algae and detrital carbon in variable proportions, but scraping caddisflies consume primarily algae. Caddisfly and mayfly diets are more similar in larger, more productive streams where the mayflies assimilate more algae. Isotopic analysis, in combination with measurements of macroinvertebrate abundance and biomass in unmanipulated plots, suggested that a substantial portion of the invertebrate community (>50% of biomass) was supported, at least partially, by local algal carbon during midsummer. These data suggest that algae may be more important to community dynamics in headwater streams than their relatively low productivity would suggest. Through their high densities and relative invulnerability to predation, armored grazers may also affect community structure and flow of algal and detrital carbon in headwater streams. PMID:17479757

McNeely, Camille; Finlay, Jacques C; Power, Mary E

2007-02-01

410

Differential mercury transfer in the aquatic food web of a double basined lake associated with selenium and habitat  

USGS Publications Warehouse

Food web trophodynamics of total mercury (THg) and selenium (Se) were assessed for the double-basined ultraoligotrophic system of Lake Moreno, Patagonia. Each basin has differing proportions of littoral and pelagic habitats, thereby providing an opportunity to assess the importance of habitat (e.g. food web structure or benthic MeHg production) in the transfer of Hg and Se to top trophic fish species. Pelagic plankton, analyzed in three size classes (10–53, 53–200, and > 200 ?m), had very high [THg], exceeding 200 ?g g? 1 dry weight (DW) in the smallest, and a low ratio of MeHg to THg (0.1 to 3%). In contrast, [THg] in littoral macroinvertebrates showed lower values (0.3 to 1.8 ?g g? 1 DW). Juvenile and small fish species feeding upon plankton had higher [THg] (0.2 to 8 ?g g? 1 muscle DW) compared to large piscivore fish species (0.1 to 1.6 ?g g? 1 muscle DW). Selenium concentrations exhibited a much narrower variation range than THg in the food web, varying from 0.5 to 2.7 ?g g? 1 DW. Molar Se:Hg ratios exceeded 1 for the majority of organisms in both basins, with most ratios exceeding 10. Using stable nitrogen isotopes as indicator of trophic level, no significant correlations were found with [THg], [Se] or Se:Hg. The apparent lack of biomagnification trends was attributed to elevated [THg] in plankton in the inorganic form mostly, as well as the possibility of consistent Se supply reducing the biomagnification in the food web of the organic portion of THg.

Arcagni, Marina; Campbell, Linda; Arribére, María A.; Marvin-DiPasquale, Mark; Rizzo, Andrea; Guevara, Sergio Ribeiro