A chronology for late prehistoric Madagascar.

PubMed

Burney, David A; Burney, Lida Pigott; Godfrey, Laurie R; Jungers, William L; Goodman, Steven M; Wright, Henry T; Jull, A J Timothy

2004-01-01

A database has been assembled with 278 age determinations for Madagascar. Materials 14C dated include pretreated sediments and plant macrofossils from cores and excavations throughout the island, and bones, teeth, or eggshells of most of the extinct megafaunal taxa, including the giant lemurs, hippopotami, and ratites. Additional measurements come from uranium-series dates on speleothems and thermoluminescence dating of pottery. Changes documented include late Pleistocene climatic events and, in the late Holocene, the apparently human-caused transformation of the environment. Multiple lines of evidence point to the earliest human presence at ca. 2300 14C yr BP (350 cal yr BC). A decline in megafauna, inferred from a drastic decrease in spores of the coprophilous fungus Sporormiella spp. in sediments at 1720+/-40 14C yr BP (230-410 cal yr AD), is followed by large increases in charcoal particles in sediment cores, beginning in the SW part of the island, and spreading to other coasts and the interior over the next millennium. The record of human occupation is initially sparse, but shows large human populations throughout the island by the beginning of the Second Millennium AD. Dating of the "subfossil" megafauna, including pygmy hippos, elephant birds, giant tortoises, and large lemurs, demonstrates that most if not all the extinct taxa were still present on the island when humans arrived. Many taxa overlapped chronologically with humans for a millennium or more. The extinct lemurs Hadropithecus stenognathus, Pachylemur insignis, Mesopropithecus pithecoides, and Daubentonia robusta, and the elephant birds Aepyornis spp. and Mullerornis spp., were still present near the end of the First Millennium AD. Palaeopropithecus ingens, Megaladapis edwardsi, and Archaeolemur sp. (cf. edwardsi) may have survived until the middle of the Second Millennium A.D. One specimen of Hippopotamus of unknown provenance dates to the period of European colonization.

Major Optical Depth Perturbations to the Stratosphere from Volcanic Eruptions: Stellar-Extinction Period, 1961-1978

NASA Technical Reports Server (NTRS)

Stothers, Richard B.; Hansen, James E. (Technical Monitor)

2001-01-01

A revised chronology of stratospheric aerosol extinction due to volcanic eruptions has been assembled for the period 1961-1978, which immediately precedes the era of dedicated satellite measurements. On the whole, the most accurate data consist of published observations of stellar extinction, supplemented in part by other kinds of observational data. The period covered encompasses the important eruptions of Agung (1963) and Fuego (1974), whose dust veils are discussed with respect to their transport, decay, and total mass. The effective (area-weighted mean) radii of the aerosols for both eruptions are found to be 0.3-0.4 microns. It is confirmed that, among known tropical eruptions, Agung's dust was unique for a low-latitude eruption in remaining almost entirely confined to the hemisphere of its production. A new table of homogeneous visual optical depth perturbations, listed by year and by hemisphere, is provided for the whole period 1881-1978, including the pyrheliometric period before 1961 that was investigated previously.

Tropical cloud forest climate variability and the demise of the Monteverde golden toad

PubMed Central

Anchukaitis, Kevin J.; Evans, Michael N.

2010-01-01

Widespread amphibian extinctions in the mountains of the American tropics have been blamed on the interaction of anthropogenic climate change and a lethal pathogen. However, limited meteorological records make it difficult to conclude whether current climate conditions at these sites are actually exceptional in the context of natural variability. We use stable oxygen isotope measurements from trees without annual rings to reconstruct a century of hydroclimatology in the Monteverde Cloud Forest of Costa Rica. High-resolution measurements reveal coherent isotope cycles that provide annual chronological control and paleoclimate information. Climate variability is dominated by interannual variance in dry season moisture associated with El Niño Southern Oscillation events. There is no evidence of a trend associated with global warming. Rather, the extinction of the Monteverde golden toad (Bufo periglenes) appears to have coincided with an exceptionally dry interval caused by the 1986–1987 El Niño event. PMID:20194772

Late Pleistocene Megafaunal Extinction Consistent With YDB Impact Hypothesis at Younger Dryas Onset

NASA Astrophysics Data System (ADS)

Kennett, J. P.; Kennett, D. J.

2008-12-01

At least 35 mammal and 19 bird genera became extinct across North America near the end of the Pleistocene. Modern increases in stratigraphic and dating resolution suggest that this extinction occurred relatively rapidly near 12.9 ka (11 radiocarbon kyrs). Within the context of a long-standing debate about its cause, Firestone et al., (2007) proposed that this extinction resulted from an extraterrestrial (ET) impact over North America at 12.9 ka. This hypothesis predicts that the extinction of most of these animals should have occurred abruptly at 12.9 ka. To test this hypothesis, we have critically examined radiocarbon ages and the extinction stratigraphy of these taxa. From a large data pool, we selected only radiocarbon dates with low error margins with a preference for directly dated biological materials (e.g., bone, dung, etc.) and modern chemical purification techniques. A relatively small number of acceptable dates indicate that at least 16 animal genera and several other species became extinct close to 12.9 ka. These taxa include the most common animals of the late Pleistocene such as horses, camels, and mammoths. Also, the remains of extinct taxa are reportedly found up to, but not above, the base of a widely distributed carbon-rich layer called the black mat. This stratum forms an abrupt, major biostratigraphic boundary at the Younger Dryas onset (12.9 ka), which also contains multiple ET markers comprising the impact layer (the YDB). Surviving animal populations were abruptly reduced at the YDB (e.g., Bison), with major range restrictions and apparent evolutionary bottlenecks. The abruptness of this major extinction is inconsistent with the hypotheses of human overkill and climatic change. We argue that extinction ages older than 12.9 ka for many less common species result from the Signor-Lipps effect, but the impact hypothesis predicts that as new dates are acquired, they will approach ever closer to 12.9 ka. The megafaunal extinction is strongly associated with abrupt and major vegetation changes, abrupt cooling, and widespread biomass burning at the onset of the Younger Dryas over North America. The stratigraphic and chronologic data are consistent with megafaunal extinction being caused by continental-scale ecosystem disruption due to an ET impact.

Double the dates and go for Bayes - Impacts of model choice, dating density and quality on chronologies

NASA Astrophysics Data System (ADS)

Blaauw, Maarten; Christen, J. Andrés; Bennett, K. D.; Reimer, Paula J.

2018-05-01

Reliable chronologies are essential for most Quaternary studies, but little is known about how age-depth model choice, as well as dating density and quality, affect the precision and accuracy of chronologies. A meta-analysis suggests that most existing late-Quaternary studies contain fewer than one date per millennium, and provide millennial-scale precision at best. We use existing and simulated sediment cores to estimate what dating density and quality are required to obtain accurate chronologies at a desired precision. For many sites, a doubling in dating density would significantly improve chronologies and thus their value for reconstructing and interpreting past environmental changes. Commonly used classical age-depth models stop becoming more precise after a minimum dating density is reached, but the precision of Bayesian age-depth models which take advantage of chronological ordering continues to improve with more dates. Our simulations show that classical age-depth models severely underestimate uncertainty and are inaccurate at low dating densities, and also perform poorly at high dating densities. On the other hand, Bayesian age-depth models provide more realistic precision estimates, including at low to average dating densities, and are much more robust against dating scatter and outliers. Indeed, Bayesian age-depth models outperform classical ones at all tested dating densities, qualities and time-scales. We recommend that chronologies should be produced using Bayesian age-depth models taking into account chronological ordering and based on a minimum of 2 dates per millennium.

Early History of the Moon: Zircon Perspective

NASA Technical Reports Server (NTRS)

Grange, M.L.; Nemchin, A.A.; Pidgeon, R.T.; Meyer, C.

2009-01-01

The Moon is believed to have formed from debris produced by a giant impact of a Mars sized body with the Earth (at around 4.51 Ga), forming a primitive body with a thick global layer of melt referred to as the Lunar Magma Ocean (LMO). The crystallization of LMO created internal stratification of the Moon forming main geochemical reservoirs. The surface features on the Moon were shaped by the subsequent collision with several large impactors during a short period of time (3.9-4.0 Ga). This process known as the Late Heavy Bombardment is supported by models of planetary motion, suggesting that rapid migration of giant planets could have triggered a massive delivery of planetesimals from the asteroid belt into the inner Solar System at about 3.9 Ga. Although, general chronology of LMO and LHB is well established using both long lived (U-Pb, Rb-Sr, Sm-147-Nd-143 and Ar-Ar) and extinct (Hf-182-W-182 and 146Sm-142Nd) isotope systems, some of these systems such as Ar-Ar are known to reset easily during secondary thermal overprints. As a result important details in the timing of LMO and LHB remain unresolved. In addition, the relative weakness of these systems under high T conditions can potentially bias the chronological information towards later events in the history of the Moon.

Modeling Variable Phanerozoic Oxygen Effects on Physiology and Evolution.

PubMed

Graham, Jeffrey B; Jew, Corey J; Wegner, Nicholas C

2016-01-01

Geochemical approximation of Earth's atmospheric O2 level over geologic time prompts hypotheses linking hyper- and hypoxic atmospheres to transformative events in the evolutionary history of the biosphere. Such correlations, however, remain problematic due to the relative imprecision of the timing and scope of oxygen change and the looseness of its overlay on the chronology of key biotic events such as radiations, evolutionary innovation, and extinctions. There are nevertheless general attributions of atmospheric oxygen concentration to key evolutionary changes among groups having a primary dependence upon oxygen diffusion for respiration. These include the occurrence of Devonian hypoxia and the accentuation of air-breathing dependence leading to the origin of vertebrate terrestriality, the occurrence of Carboniferous-Permian hyperoxia and the major radiation of early tetrapods and the origins of insect flight and gigantism, and the Mid-Late Permian oxygen decline accompanying the Permian extinction. However, because of variability between and error within different atmospheric models, there is little basis for postulating correlations outside the Late Paleozoic. Other problems arising in the correlation of paleo-oxygen with significant biological events include tendencies to ignore the role of blood pigment affinity modulation in maintaining homeostasis, the slow rates of O2 change that would have allowed for adaptation, and significant respiratory and circulatory modifications that can and do occur without changes in atmospheric oxygen. The purpose of this paper is thus to refocus thinking about basic questions central to the biological and physiological implications of O2 change over geological time.

Vegetation and Mammuthus primigenius extinction history on St Paul Island, Alaska

NASA Astrophysics Data System (ADS)

Wang, Y.; Newsom, L.; Belmecheri, S.; Culleton, B.; Williams, J. W.

2014-12-01

St. Paul Island, AK, part of the Pribilofs, is an island remnant of the Bering Land Bridge, a possible coastal Picea refugium at the last glacial maximum, and a Holocene refugium for Mammuthus primigenius. A prior pollen record from Lake Hill indicates that St. Paul was predominantly herb tundra during the last glacial maximum followed by a shrub tundra in the early Holocene (Colinvaux, 1980). Subsequently, three radiocarbon dates on bones from Qagnax Cave indicate a last appearance of Mammuthus primigenius of 6.5 ka on St. Paul (Veltre et al. 2008). In March 2013, our team retrieved a 13.5 m composite core from Lake Hill to refine the extinction timing chronology, assess environmental change during the extinction interval, and test hypotheses about vegetation-megafauna feedback. This paper reports the results from modern botanical survey and analyses of fossil pollen, Sporormiella and other coprophilous spores, anchored by a new radiocarbon chronology consisting of seven AMS dates. Presently, bryophytes, Equisetum, Poaceae, Juncaceae, Salix and Viola commonly occur at the lake margin, accompanied increasingly by sedge meadow taxa with greater distance from the water's edge, especially Cyperaceae, Asteraceae, Apiaceae, Lupinus, Rubus and Valeriana. Sporormiella is consistently present in low abundances (2%, ~700 grains/cm3) in the late glacial and early Holocene until a drop to zero at 6,050 yr BP, remaining absent during the middle and late Holocene when it reappears at 1904 AD. The timing of Sporormiella decline and reappearance match well to the youngest mammoth bone date and the historic reintroduction of reindeer (1911 AD) on St. Paul Island. After 11 ka, major pollen types include Apiaceae, Poaceae, Cyperaceae, Artemisia and Salix, with lower abundances of Betula, Alnus and Ericaceae, consistent with herb tundra with some shrubs. Degraded Picea pollen grains are found at 12,240 yr BP in very low concentrations (223 grains/cm3), indicating long-distance deposition from a distal source with no local refugium. Declines in Apiaceae and Poaceae, and increases in Artemisia and Salix between 8014 and 7605 yr BP suggest a gradual increase prevalence of shrub tundra. The establishment of shrub tundra precedes the Sporormiella decline, suggesting this vegetation change was not caused by the megafaunal extinction.

Integrating chronological uncertainties for annually laminated lake sediments using layer counting, independent chronologies and Bayesian age modelling (Lake Ohau, South Island, New Zealand)

NASA Astrophysics Data System (ADS)

Vandergoes, Marcus J.; Howarth, Jamie D.; Dunbar, Gavin B.; Turnbull, Jocelyn C.; Roop, Heidi A.; Levy, Richard H.; Li, Xun; Prior, Christine; Norris, Margaret; Keller, Liz D.; Baisden, W. Troy; Ditchburn, Robert; Fitzsimons, Sean J.; Bronk Ramsey, Christopher

2018-05-01

Annually resolved (varved) lake sequences are important palaeoenvironmental archives as they offer a direct incremental dating technique for high-frequency reconstruction of environmental and climate change. Despite the importance of these records, establishing a robust chronology and quantifying its precision and accuracy (estimations of error) remains an essential but challenging component of their development. We outline an approach for building reliable independent chronologies, testing the accuracy of layer counts and integrating all chronological uncertainties to provide quantitative age and error estimates for varved lake sequences. The approach incorporates (1) layer counts and estimates of counting precision; (2) radiometric and biostratigrapic dating techniques to derive independent chronology; and (3) the application of Bayesian age modelling to produce an integrated age model. This approach is applied to a case study of an annually resolved sediment record from Lake Ohau, New Zealand. The most robust age model provides an average error of 72 years across the whole depth range. This represents a fractional uncertainty of ∼5%, higher than the <3% quoted for most published varve records. However, the age model and reported uncertainty represent the best fit between layer counts and independent chronology and the uncertainties account for both layer counting precision and the chronological accuracy of the layer counts. This integrated approach provides a more representative estimate of age uncertainty and therefore represents a statistically more robust chronology.

A Chronology of Annual-Mean Effective Radii of Stratospheric Aerosols from Volcanic Eruptions During the Twentieth Century as Derived From Ground-based Spectral Extinction Measurements

NASA Technical Reports Server (NTRS)

Strothers, Richard B.; Hansen, James E. (Technical Monitor)

2001-01-01

Stratospheric extinction can be derived from ground-based spectral photometric observations of the Sun and other stars (as well as from satellite and aircraft measurements, available since 1979), and is found to increase after large volcanic eruptions. This increased extinction shows a characteristic wavelength dependence that gives information about the chemical composition and the effective (or area weighted mean) radius of the particles responsible for it. Known to be tiny aerosols constituted of sulfuric acid in a water solution, the stratospheric particles at midlatitudes exhibit a remarkable uniformity of their column-averaged effective radii r(sub eff) in the first few months after the eruption. Considering the seven largest eruptions of the twentieth century, r(sub eff) at this phase of peak aerosol abundance is approx. 0.3 micrometers in all cases. A year later, r(sub eff) either has remained about the same size (almost certainly in the case of the Katmai eruption of 1912) or has increased to approx. 0.5 micrometers (definitely so for the Pinatubo eruption of 1991). The reasons for this divergence in aerosol growth are unknown.

Revised age of late Neanderthal occupation and the end of the Middle Paleolithic in the northern Caucasus

PubMed Central

Pinhasi, Ron; Higham, Thomas F. G.; Golovanova, Liubov V.; Doronichev, Vladimir B.

2011-01-01

Advances in direct radiocarbon dating of Neanderthal and anatomically modern human (AMH) fossils and the development of archaeostratigraphic chronologies now allow refined regional models for Neanderthal–AMH coexistence. In addition, they allow us to explore the issue of late Neanderthal survival in regions of Western Eurasia located within early routes of AMH expansion such as the Caucasus. Here we report the direct radiocarbon (14C) dating of a late Neanderthal specimen from a Late Middle Paleolithic (LMP) layer in Mezmaiskaya Cave, northern Caucasus. Additionally, we provide a more accurate chronology for the timing of Neanderthal extinction in the region through a robust series of 16 ultrafiltered bone collagen radiocarbon dates from LMP layers and using Bayesian modeling to produce a boundary probability distribution function corresponding to the end of the LMP at Mezmaiskaya. The direct date of the fossil (39,700 ± 1,100 14C BP) is in good agreement with the probability distribution function, indicating at a high level of probability that Neanderthals did not survive at Mezmaiskaya Cave after 39 ka cal BP ("calendrical" age in kiloannum before present, based on IntCal09 calibration curve). This challenges previous claims for late Neanderthal survival in the northern Caucasus. We see striking and largely synchronous chronometric similarities between the Bayesian age modeling for the end of the LMP at Mezmaiskaya and chronometric data from Ortvale Klde for the end of the LMP in the southern Caucasus. Our results confirm the lack of reliably dated Neanderthal fossils younger than ∼40 ka cal BP in any other region of Western Eurasia, including the Caucasus. PMID:21555570

Mars chronology: Assessing techniques for quantifying surficial processes

USGS Publications Warehouse

Doran, P.T.; Clifford, S.M.; Forman, S.L.; Nyquist, Larry; Papanastassiou, D.A.; Stewart, B.W.; Sturchio, N.C.; Swindle, T.D.; Cerling, T.; Kargel, J.; McDonald, G.; Nishiizumi, K.; Poreda, R.; Rice, J.W.; Tanaka, K.

2004-01-01

Currently, the absolute chronology of Martian rocks, deposits and events is based mainly on crater counting and remains highly imprecise with epoch boundary uncertainties in excess of 2 billion years. Answers to key questions concerning the comparative origin and evolution of Mars and Earth will not be forthcoming without a rigid Martian chronology, enabling the construction of a time scale comparable to Earth's. Priorities for exploration include calibration of the cratering rate, dating major volcanic and fluvial events and establishing chronology of the polar layered deposits. If extinct and/or extant life is discovered, the chronology of the biosphere will be of paramount importance. Many radiometric and cosmogenic techniques applicable on Earth and the Moon will apply to Mars after certain baselines (e.g. composition of the atmosphere, trace species, chemical and physical characteristics of Martian dust) are established. The high radiation regime may pose a problem for dosimetry-based techniques (e.g. luminescence). The unique isotopic composition of nitrogen in the Martian atmosphere may permit a Mars-specific chronometer for tracing the time-evolution of the atmosphere and of lithic phases with trapped atmospheric gases. Other Mars-specific chronometers include measurement of gas fluxes and accumulation of platinum group elements (PGE) in the regolith. Putting collected samples into geologic context is deemed essential, as is using multiple techniques on multiple samples. If in situ measurements are restricted to a single technique it must be shown to give consistent results on multiple samples, but in all cases, using two or more techniques (e.g. on the same lander) will reduce error. While there is no question that returned samples will yield the best ages, in situ techniques have the potential to be flown on multiple missions providing a larger data set and broader context in which to place the more accurate dates. ?? 2004 Elsevier B.V. All rights reserved.

Late Quaternary cave bears and brown bears in Europe: implications for distribution, chronology, and extinction based on a multidisciplinary approach

NASA Astrophysics Data System (ADS)

Pacher, Martina

2010-05-01

Cave bear remains are one of the most numerous fossils found in European caves. Despite their frequency of occurrence, many aspects of cave bear palaeontology still remain poorly understood. New methodological approaches and ongoing studies led to controversial results and discussion about its taxonomy, palaeoecology, and final extinction. Are we dealing with one single or several species of cave bears? Was cave bear exclusively vegetarian or after all more omnivorous? Did he go extinct before or after the Late Glacial Maximum? Was cave bear restricted to Europe or did he also occur in Asia? Late Pleistocene brown bears, on the other hand, are often rare and little is known about the possible co-occurrence of cave and brown bears during the Late Pleistocene. Based on direct radiocarbon dates the distribution pattern of both, cave and brown bears is reconstructed during the Late Pleistocene in Europe. In addition, the reasons for the achieved pattern will be tested leading to the main question - why did cave bear become extinct while brown bears survived until today? To answer this question palaeobiological data of Late Pleistocene cave and brown bears will be tested against results from isotope analyses, while aDNA data may contribute to the question of distinct local population or even species of bears. The current state of evidence will be presented and on the basis of resulting pattern implications for further multi-disciplinary studies will be discussed.

Mid-Miocene cooling and the extinction of tundra in continental Antarctica

PubMed Central

Lewis, Adam R.; Marchant, David R.; Ashworth, Allan C.; Hedenäs, Lars; Hemming, Sidney R.; Johnson, Jesse V.; Leng, Melanie J.; Machlus, Malka L.; Newton, Angela E.; Raine, J. Ian; Willenbring, Jane K.; Williams, Mark; Wolfe, Alexander P.

2008-01-01

A major obstacle in understanding the evolution of Cenozoic climate has been the lack of well dated terrestrial evidence from high-latitude, glaciated regions. Here, we report the discovery of exceptionally well preserved fossils of lacustrine and terrestrial organisms from the McMurdo Dry Valleys sector of the Transantarctic Mountains for which we have established a precise radiometric chronology. The fossils, which include diatoms, palynomorphs, mosses, ostracodes, and insects, represent the last vestige of a tundra community that inhabited the mountains before stepped cooling that first brought a full polar climate to Antarctica. Paleoecological analyses, 40Ar/39Ar analyses of associated ash fall, and climate inferences from glaciological modeling together suggest that mean summer temperatures in the region cooled by at least 8°C between 14.07 ± 0.05 Ma and 13.85 ± 0.03 Ma. These results provide novel constraints for the timing and amplitude of middle-Miocene cooling in Antarctica and reveal the ecological legacy of this global climate transition. PMID:18678903

Astronomical timescale calibration for the Permian-Triassic boundary transition interval from global correlation of cyclic marine sequences

NASA Astrophysics Data System (ADS)

Huang, C.; Hinnov, L. A.; Tong, J.; Chen, Z.

2011-12-01

The mass extinctions near the Permian-Triassic boundary (PTB) resulted in the greatest dying of life on Earth. The cause of this catastrophe remains enigmatic. High-resolution chronology is crucial to understanding the recorded pattern of biotic evolution and possible causes for the extinctions. Magnetic susceptibility (MS) data from Shangsi, South China shows evidence for astronomical forcing through the PTB interval, with strong 405-kyr cycling. This allows development of an astrochronology for the PTB interval based on the 405-kyr orbital eccentricity metronome that has been proposed for the Mesozoic timescale. Radioisotope dating combined with the 405-kyr tuned MS series from Shangsi shows that the 405-kyr-cycle predominates throughout the PTB interval. In the Permian segment, ~100-kyr cyclicity dominates, and the 100-kyr-scale MS maxima correlate with high-amplitude precession-scale MS variations. Minima in the ~1.5-Myr, 405-kyr and ~100-kyr cycles converge at 252.6 Ma, approximately 200 kyr before the onset of the main mass extinction near the PTB. In the Triassic aftermath, the recorded astronomical signal is different, with predominant 405-kyr cycles and loss of 100 kyr cyclicity, and appearance of ~33 kyr (obliquity scale) cyclicity; 100-kyr cyclicity strengthens again 2 Myr later. This pattern indicates a change in the response of the depositional environment (or magnetic susceptibility) to astronomical forcing before and after the mass extinction interval. The astrochronology interpolates the timescale between the radioisotopically determined absolute dates; this facilitates estimation of ages for specific events in the PTB crisis, including magnetic reversals, biozone boundaries, and the mass extinctions. An estimated ~700 kyr duration for the Mass Extinction Interval (MEI) at Shangsi based on the 405-kyr tuning is supported by eccentricity-tuned estimates of three other sections in China (Meishan, Huangzhishan, and Heping), and two Alpine sections (Gartnerkofel, Austria and Bulla, Italy) from the eastern and western margins of the Palaeo-Tethys Ocean during PTB time. This suggests that the PTB mass extinctions were not the result of a single catastrophic event. Siberian trap volcanism was largely synchronous with the MEI and appears to be the most likely cause of the mass extinctions; astronomically paced climate change may also have played a role.

Predicting age by mining electronic medical records with deep learning characterizes differences between chronological and physiological age.

PubMed

Wang, Zichen; Li, Li; Glicksberg, Benjamin S; Israel, Ariel; Dudley, Joel T; Ma'ayan, Avi

2017-12-01

Determining the discrepancy between chronological and physiological age of patients is central to preventative and personalized care. Electronic medical records (EMR) provide rich information about the patient physiological state, but it is unclear whether such information can be predictive of chronological age. Here we present a deep learning model that uses vital signs and lab tests contained within the EMR of Mount Sinai Health System (MSHS) to predict chronological age. The model is trained on 377,686 EMR from patients of ages 18-85 years old. The discrepancy between the predicted and real chronological age is then used as a proxy to estimate physiological age. Overall, the model can predict the chronological age of patients with a standard deviation error of ∼7 years. The ages of the youngest and oldest patients were more accurately predicted, while patients of ages ranging between 40 and 60 years were the least accurately predicted. Patients with the largest discrepancy between their physiological and chronological age were further inspected. The patients predicted to be significantly older than their chronological age have higher systolic blood pressure, higher cholesterol, damaged liver, and anemia. In contrast, patients predicted to be younger than their chronological age have lower blood pressure and shorter stature among other indicators; both groups display lower weight than the population average. Using information from ∼10,000 patients from the entire cohort who have been also profiled with SNP arrays, genome-wide association study (GWAS) uncovers several novel genetic variants associated with aging. In particular, significant variants were mapped to genes known to be associated with inflammation, hypertension, lipid metabolism, height, and increased lifespan in mice. Several genes with missense mutations were identified as novel candidate aging genes. In conclusion, we demonstrate how EMR data can be used to assess overall health via a scale that is based on deviation from the patient's predicted chronological age. Copyright © 2017 Elsevier Inc. All rights reserved.

Modern U-Pb chronometry of meteorites: advancing to higher time resolution reveals new problems

USGS Publications Warehouse

Amelin, Y.; Connelly, J.; Zartman, R.E.; Chen, J.-H.; Gopel, C.; Neymark, L.A.

2009-01-01

In this paper, we evaluate the factors that influence the accuracy of lead (Pb)-isotopic ages of meteorites, and may possibly be responsible for inconsistencies between Pb-isotopic and extinct nuclide timescales of the early Solar System: instrumental mass fractionation and other possible analytical sources of error, presence of more than one component of non-radiogenic Pb, migration of ancient radiogenic Pb by diffusion and other mechanisms, possible heterogeneity of the isotopic composition of uranium (U), uncertainties in the decay constants of uranium isotopes, possible presence of "freshly synthesized" actinides with short half-life (e.g. 234U) in the early Solar System, possible initial disequilibrium in the uranium decay chains, and potential fractionation of radiogenic Pb isotopes and U isotopes caused by alpha-recoil and subsequent laboratory treatment. We review the use of 232Th/238U values to assist in making accurate interpretations of the U-Pb ages of meteorite components. We discuss recently published U-Pb dates of calcium-aluminum-rich inclusions (CAIs), and their apparent disagreement with the extinct nuclide dates, in the context of capability and common pitfalls in modern meteorite chronology. Finally, we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early Solar System, based on the combined use of the U-Pb system and extinct nuclide chronometers.

Hg concentrations from Late Triassic and Early Jurassic sedimentary rocks: first order similarities and second order depositional and diagenetic controls

NASA Astrophysics Data System (ADS)

Yager, J. A.; West, A. J.; Bergquist, B. A.; Thibodeau, A. M.; Corsetti, F. A.; Berelson, W.; Bottjer, D. J.; Rosas, S.

2016-12-01

Mercury concentrations in sediments have recently gained prominence as a potential tool for identifying large igneous province (LIP) volcanism in sedimentary records. LIP volcanism coincides with several mass extinctions during the Phanerozoic, but it is often difficult to directly tie LIP activity with the record of extinction in marine successions. Here, we build on mercury concentration data reported by Thibodeau et al. (Nature Communications, 7:11147, 2016) from the Late Triassic and Early Jurassic of New York Canyon, Nevada, USA. Increases in Hg concentrations in that record were attributed to Central Atlantic Magmatic Province (CAMP) activity in association with the end-Triassic mass extinction. We expand the measured section from New York Canyon and report new mercury concentrations from Levanto, Peru, where dated ash beds provide a discrete chronology, as well as St. Audrie's Bay, UK, a well-studied succession. We correlate these records using carbon isotopes and ammonites and find similarities in the onset of elevated Hg concentrations and Hg/TOC in association with changes in C isotopes. We also find second order patterns that differ between sections and may have depositional and diagenetic controls. We will discuss these changes within a sedimentological framework to further understand the controls on Hg concentrations in sedimentary records and their implications for past volcanism.

Condensation Time of the Solar Nebula from Extinct 129I in Primitive Meteorites

PubMed Central

Lewis, Roy S.; Anders, Edward

1975-01-01

Mineral separates from five carbonaceous chondrites were dated by extinct 16 million year 129I, in an attempt to establish the condensation time of the solar nebula. Two Fe3O4 or Fe3O4-FeS samples from the Murchison and Orgueil meteorites are older than any other material dated thus far, and apparently formed within 2 × 105 years of each other. The great age, close isochronism, and primitive nature of the samples suggest that the event recorded was the condensation stage of the solar nebula. It provides a suitable zero point for the chronology of the early solar system. The 129I/127I ratio during condensation of the nebula was (1.46 ± 0.04) × 10-4. The recrystallized C4 chondrite Karoonda began to retain 129Xe 1.8 ± 0.5 million years after the above event. This short cooling time implies rapid aceretion (≤1 million years) and a shallow origin (≤10 km) below the surface of its parent body. Images PMID:16592213

A comprehensive database of quality-rated fossil ages for Sahul's Quaternary vertebrates.

PubMed

Rodríguez-Rey, Marta; Herrando-Pérez, Salvador; Brook, Barry W; Saltré, Frédérik; Alroy, John; Beeton, Nicholas; Bird, Michael I; Cooper, Alan; Gillespie, Richard; Jacobs, Zenobia; Johnson, Christopher N; Miller, Gifford H; Prideaux, Gavin J; Roberts, Richard G; Turney, Chris S M; Bradshaw, Corey J A

2016-07-19

The study of palaeo-chronologies using fossil data provides evidence for past ecological and evolutionary processes, and is therefore useful for predicting patterns and impacts of future environmental change. However, the robustness of inferences made from fossil ages relies heavily on both the quantity and quality of available data. We compiled Quaternary non-human vertebrate fossil ages from Sahul published up to 2013. This, the FosSahul database, includes 9,302 fossil records from 363 deposits, for a total of 478 species within 215 genera, of which 27 are from extinct and extant megafaunal species (2,559 records). We also provide a rating of reliability of individual absolute age based on the dating protocols and association between the dated materials and the fossil remains. Our proposed rating system identified 2,422 records with high-quality ages (i.e., a reduction of 74%). There are many applications of the database, including disentangling the confounding influences of hypothetical extinction drivers, better spatial distribution estimates of species relative to palaeo-climates, and potentially identifying new areas for fossil discovery.

A comprehensive database of quality-rated fossil ages for Sahul’s Quaternary vertebrates

PubMed Central

Rodríguez-Rey, Marta; Herrando-Pérez, Salvador; Brook, Barry W.; Saltré, Frédérik; Alroy, John; Beeton, Nicholas; Bird, Michael I.; Cooper, Alan; Gillespie, Richard; Jacobs, Zenobia; Johnson, Christopher N.; Miller, Gifford H.; Prideaux, Gavin J.; Roberts, Richard G.; Turney, Chris S.M.; Bradshaw, Corey J.A.

2016-01-01

The study of palaeo-chronologies using fossil data provides evidence for past ecological and evolutionary processes, and is therefore useful for predicting patterns and impacts of future environmental change. However, the robustness of inferences made from fossil ages relies heavily on both the quantity and quality of available data. We compiled Quaternary non-human vertebrate fossil ages from Sahul published up to 2013. This, the FosSahul database, includes 9,302 fossil records from 363 deposits, for a total of 478 species within 215 genera, of which 27 are from extinct and extant megafaunal species (2,559 records). We also provide a rating of reliability of individual absolute age based on the dating protocols and association between the dated materials and the fossil remains. Our proposed rating system identified 2,422 records with high-quality ages (i.e., a reduction of 74%). There are many applications of the database, including disentangling the confounding influences of hypothetical extinction drivers, better spatial distribution estimates of species relative to palaeo-climates, and potentially identifying new areas for fossil discovery. PMID:27434208

Critical review of a new volcanic eruption chronology

NASA Astrophysics Data System (ADS)

Neuhäuser, Dagmar L.; Neuhäuser, Ralph

2016-04-01

Sigl. et al. (2015, Nature) present historical evidence for 32 volcanic eruptions to evaluate their new polar ice core 10-Be chronology - 24 are dated within three years of sulfur layers in polar ice. Most of them can be interpreted as weather phenomena (Babylonia: disk of sun like moon, reported for only one day, e.g. extinction due to clouds), Chinese sunspot reports (pellet, black vapor, etc.), solar eclipses, normal ice-halos and coronae (ring, bow, etc.), one aurora (redness), red suns due to mist drops in wet fog or fire-smoke, etc. Volcanic dust may facilitate detections of sunspots and formation of Bishop's ring, but tend to inhibit ice-halos, which are otherwise often reported in chronicles. We are left with three reports possibly indicating volcanic eruptions, namely fulfilling genuine criteria for atmospheric disturbances due to volcanic dust, e.g. bluish or faint sun, orange sky, or fainting of stars for months (BCE 208, 44-42, and 32). Among the volcanic eruptions used to fix the chronology (CE 536, 626, 939, 1257), the reports cited for the 930s deal only with 1-2 days, at least one reports an eclipse. In the new chronology, there is a sulfur detection eight years after the Vesuvius eruption, but none in CE 79. It may appear surprising that, from BCE 500 to 1, all five northern sulfur peaks labeled in figure 2 in Sigl et al. are systematically later by 2-4 years than the (corresponding?) southern peaks, while all five southern peaks from CE 100 to 600 labeled in figure 2 are systematically later by 1-4 years than the (corresponding?) northern peaks. Furthermore, in most of their six strongest volcanic eruptions, temperatures decreased years before their sulfur dating - correlated with weak solar activity as seen in radiocarbon, so that volcanic climate forcing appears dubious here. Also, their 10-Be peaks at CE 775 and 994 are neither significant nor certain in dating.

Paleo Data Assimilation of Pseudo-Tree-Ring-Width Chronologies in a Climate Model

NASA Astrophysics Data System (ADS)

Fallah Hassanabadi, B.; Acevedo, W.; Reich, S.; Cubasch, U.

2016-12-01

Using the Time-Averaged Ensemble Kalman Filter (EnKF) and a forward model, we assimilate the pseudo Tree-Ring-Width (TRW) chronologies into an Atmospheric Global Circulation model. This study investigates several aspects of Paleo-Data Assimilation (PDA) within a perfect-model set-up: (i) we test the performance of several forward operators in the framework of a PDA-based climate reconstruction, (ii) compare the PDA-based simulations' skill against the free ensemble runs and (iii) inverstigate the skill of the "online" (with cycling) DA and the "off-line" (no-cycling) DA. In our experiments, the "online" (with cycling) PDA approach did not outperform the "off-line" (no-cycling) one, despite its considerable additional implementation complexity. On the other hand, it was observed that the error reduction achieved by assimilating a particular pseudo-TRW chronology is modulated by the strength of the yearly internal variability of the model at the chronology site. This result might help the dendrochronology community to optimize their sampling efforts.

A comparison of chronologies from tree rings

Treesearch

Kurt H. Riitters

1990-01-01

Forty-five-year ring width index chronologies were estimated by five mean-value functions applied to 183 ring width series from four similar sites. The effects of autocorrelation on the comparisons among mean-value functions were explored by fitting box-Jenkins models to individual-tree index services prior to pooling (prewhitening), and to the pooled chronologies...

New ages for human occupation and climatic change at Lake Mungo, Australia.

PubMed

Bowler, James M; Johnston, Harvey; Olley, Jon M; Prescott, John R; Roberts, Richard G; Shawcross, Wilfred; Spooner, Nigel A

2003-02-20

Australia's oldest human remains, found at Lake Mungo, include the world's oldest ritual ochre burial (Mungo III) and the first recorded cremation (Mungo I). Until now, the importance of these finds has been constrained by limited chronologies and palaeoenvironmental information. Mungo III, the source of the world's oldest human mitochondrial DNA, has been variously estimated at 30 thousand years (kyr) old, 42-45 kyr old and 62 +/- 6 kyr old, while radiocarbon estimates placed the Mungo I cremation near 20-26 kyr ago. Here we report a new series of 25 optical ages showing that both burials occurred at 40 +/- 2 kyr ago and that humans were present at Lake Mungo by 50-46 kyr ago, synchronously with, or soon after, initial occupation of northern and western Australia. Stratigraphic evidence indicates fluctuations between lake-full and drier conditions from 50 to 40 kyr ago, simultaneously with increased dust deposition, human arrival and continent-wide extinction of the megafauna. This was followed by sustained aridity between 40 and 30 kyr ago. This new chronology corrects previous estimates for human burials at this important site and provides a new picture of Homo sapiens adapting to deteriorating climate in the world's driest inhabited continent.

Revised stratigraphy and chronology for Homo floresiensis at Liang Bua in Indonesia.

PubMed

Sutikna, Thomas; Tocheri, Matthew W; Morwood, Michael J; Saptomo, E Wahyu; Jatmiko; Awe, Rokus Due; Wasisto, Sri; Westaway, Kira E; Aubert, Maxime; Li, Bo; Zhao, Jian-xin; Storey, Michael; Alloway, Brent V; Morley, Mike W; Meijer, Hanneke J M; van den Bergh, Gerrit D; Grün, Rainer; Dosseto, Anthony; Brumm, Adam; Jungers, William L; Roberts, Richard G

2016-04-21

Homo floresiensis, a primitive hominin species discovered in Late Pleistocene sediments at Liang Bua (Flores, Indonesia), has generated wide interest and scientific debate. A major reason this taxon is controversial is because the H. floresiensis-bearing deposits, which include associated stone artefacts and remains of other extinct endemic fauna, were dated to between about 95 and 12 thousand calendar years (kyr) ago. These ages suggested that H. floresiensis survived until long after modern humans reached Australia by ~50 kyr ago. Here we report new stratigraphic and chronological evidence from Liang Bua that does not support the ages inferred previously for the H. floresiensis holotype (LB1), ~18 thousand calibrated radiocarbon years before present (kyr cal. BP), or the time of last appearance of this species (about 17 or 13-11 kyr cal. BP). Instead, the skeletal remains of H. floresiensis and the deposits containing them are dated to between about 100 and 60 kyr ago, whereas stone artefacts attributable to this species range from about 190 to 50 kyr in age. Whether H. floresiensis survived after 50 kyr ago--potentially encountering modern humans on Flores or other hominins dispersing through southeast Asia, such as Denisovans--is an open question.

Quantity of dates trumps quality of dates for dense Bayesian radiocarbon sediment chronologies - Gas ion source 14C dating instructed by simultaneous Bayesian accumulation rate modeling

NASA Astrophysics Data System (ADS)

Rosenheim, B. E.; Firesinger, D.; Roberts, M. L.; Burton, J. R.; Khan, N.; Moyer, R. P.

2016-12-01

Radiocarbon (14C) sediment core chronologies benefit from a high density of dates, even when precision of individual dates is sacrificed. This is demonstrated by a combined approach of rapid 14C analysis of CO2 gas generated from carbonates and organic material coupled with Bayesian statistical modeling. Analysis of 14C is facilitated by the gas ion source on the Continuous Flow Accelerator Mass Spectrometry (CFAMS) system at the Woods Hole Oceanographic Institution's National Ocean Sciences Accelerator Mass Spectrometry facility. This instrument is capable of producing a 14C determination of +/- 100 14C y precision every 4-5 minutes, with limited sample handling (dissolution of carbonates and/or combustion of organic carbon in evacuated containers). Rapid analysis allows over-preparation of samples to include replicates at each depth and/or comparison of different sample types at particular depths in a sediment or peat core. Analysis priority is given to depths that have the least chronologic precision as determined by Bayesian modeling of the chronology of calibrated ages. Use of such a statistical approach to determine the order in which samples are run ensures that the chronology constantly improves so long as material is available for the analysis of chronologic weak points. Ultimately, accuracy of the chronology is determined by the material that is actually being dated, and our combined approach allows testing of different constituents of the organic carbon pool and the carbonate minerals within a core. We will present preliminary results from a deep-sea sediment core abundant in deep-sea foraminifera as well as coastal wetland peat cores to demonstrate statistical improvements in sediment- and peat-core chronologies obtained by increasing the quantity and decreasing the quality of individual dates.

West Coast volcanic ashes provide a new continental-scale Lateglacial isochron

NASA Astrophysics Data System (ADS)

Pyne-O'Donnell, Sean D. F.; Cwynar, Les C.; Jensen, Britta J. L.; Vincent, Jessie H.; Kuehn, Stephen C.; Spear, Ray; Froese, Duane G.

2016-06-01

The 'Lateglacial' period (∼14.7-11.7 cal ka BP) eruptions of Mount St Helens and Glacier Peak in the Cascade Range deposited ash layers (tephras) within a short time span across much of western North America where they form event-stratigraphic marker layers or isochrons. They were deposited at a time which has long been of interest because it represents the transition between two fundamental states of the climate system: the late Pleistocene glacial world when ice sheets were widespread, and the modern interglacial Holocene world. This transition was marked by rapid changes in the distribution of plants, animals and humans on the landscape, and is characterised by short, rapid climate reversals in the warming trend. Yet despite the importance of understanding this period for many areas of palaeoclimatology, palaeobotany and archaeology it remains one of the most difficult for which to develop accurate chronologies because of fluctuations in atmospheric radiocarbon concentration. Hence, the occurrences of distinctive tephra isochrons are valuable for chronological control. Here, we report the first detection of the Mount St Helens set J and Glacier Peak tephras as closely-spaced 'cryptotephra' layers (not visible in stratigraphy to the naked eye) in three eastern seaboard lakes and dated to 13.74-13.45 cal ka BP. The presence of these tephras >4000 km from their sources affords an opportunity for continent-wide correlations by providing a high-precision chronological benchmark that is otherwise often lacking in North American studies of palaeoenvironmental change and deglaciation, megafaunal extinction and palaeoindian colonisation.

Extinction debt from climate change for frogs in the wet tropics

PubMed Central

Brook, Barry W.; Hoskin, Conrad J.; Pressey, Robert L.; VanDerWal, Jeremy; Williams, Stephen E.

2016-01-01

The effect of twenty-first-century climate change on biodiversity is commonly forecast based on modelled shifts in species ranges, linked to habitat suitability. These projections have been coupled with species–area relationships (SAR) to infer extinction rates indirectly as a result of the loss of climatically suitable areas and associated habitat. This approach does not model population dynamics explicitly, and so accepts that extinctions might occur after substantial (but unknown) delays—an extinction debt. Here we explicitly couple bioclimatic envelope models of climate and habitat suitability with generic life-history models for 24 species of frogs found in the Australian Wet Tropics (AWT). We show that (i) as many as four species of frogs face imminent extinction by 2080, due primarily to climate change; (ii) three frogs face delayed extinctions; and (iii) this extinction debt will take at least a century to be realized in full. Furthermore, we find congruence between forecast rates of extinction using SARs, and demographic models with an extinction lag of 120 years. We conclude that SAR approaches can provide useful advice to conservation on climate change impacts, provided there is a good understanding of the time lags over which delayed extinctions are likely to occur. PMID:27729484

Middle Pleistocene protein sequences from the rhinoceros genus Stephanorhinus and the phylogeny of extant and extinct Middle/Late Pleistocene Rhinocerotidae

PubMed Central

Smith, Geoff M.; Hutson, Jarod M.; Kindler, Lutz; Garcia-Moreno, Alejandro; Villaluenga, Aritza; Turner, Elaine

2017-01-01

Background Ancient protein sequences are increasingly used to elucidate the phylogenetic relationships between extinct and extant mammalian taxa. Here, we apply these recent developments to Middle Pleistocene bone specimens of the rhinoceros genus Stephanorhinus. No biomolecular sequence data is currently available for this genus, leaving phylogenetic hypotheses on its evolutionary relationships to extant and extinct rhinoceroses untested. Furthermore, recent phylogenies based on Rhinocerotidae (partial or complete) mitochondrial DNA sequences differ in the placement of the Sumatran rhinoceros (Dicerorhinus sumatrensis). Therefore, studies utilising ancient protein sequences from Middle Pleistocene contexts have the potential to provide further insights into the phylogenetic relationships between extant and extinct species, including Stephanorhinus and Dicerorhinus. Methods ZooMS screening (zooarchaeology by mass spectrometry) was performed on several Late and Middle Pleistocene specimens from the genus Stephanorhinus, subsequently followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to obtain ancient protein sequences from a Middle Pleistocene Stephanorhinus specimen. We performed parallel analysis on a Late Pleistocene woolly rhinoceros specimen and extant species of rhinoceroses, resulting in the availability of protein sequence data for five extant species and two extinct genera. Phylogenetic analysis additionally included all extant Perissodactyla genera (Equus, Tapirus), and was conducted using Bayesian (MrBayes) and maximum-likelihood (RAxML) methods. Results Various ancient proteins were identified in both the Middle and Late Pleistocene rhinoceros samples. Protein degradation and proteome complexity are consistent with an endogenous origin of the identified proteins. Phylogenetic analysis of informative proteins resolved the Perissodactyla phylogeny in agreement with previous studies in regards to the placement of the families Equidae, Tapiridae, and Rhinocerotidae. Stephanorhinus is shown to be most closely related to the genera Coelodonta and Dicerorhinus. The protein sequence data further places the Sumatran rhino in a clade together with the genus Rhinoceros, opposed to forming a clade with the black and white rhinoceros species. Discussion The first biomolecular dataset available for Stephanorhinus places this genus together with the extinct genus Coelodonta and the extant genus Dicerorhinus. This is in agreement with morphological studies, although we are unable to resolve the order of divergence between these genera based on the protein sequences available. Our data supports the placement of the genus Dicerorhinus in a clade together with extant Rhinoceros species. Finally, the availability of protein sequence data for both extinct European rhinoceros genera allows future investigations into their geographic distribution and extinction chronologies. PMID:28316883

Middle Pleistocene protein sequences from the rhinoceros genus Stephanorhinus and the phylogeny of extant and extinct Middle/Late Pleistocene Rhinocerotidae.

PubMed

Welker, Frido; Smith, Geoff M; Hutson, Jarod M; Kindler, Lutz; Garcia-Moreno, Alejandro; Villaluenga, Aritza; Turner, Elaine; Gaudzinski-Windheuser, Sabine

2017-01-01

Ancient protein sequences are increasingly used to elucidate the phylogenetic relationships between extinct and extant mammalian taxa. Here, we apply these recent developments to Middle Pleistocene bone specimens of the rhinoceros genus Stephanorhinus . No biomolecular sequence data is currently available for this genus, leaving phylogenetic hypotheses on its evolutionary relationships to extant and extinct rhinoceroses untested. Furthermore, recent phylogenies based on Rhinocerotidae (partial or complete) mitochondrial DNA sequences differ in the placement of the Sumatran rhinoceros ( Dicerorhinus sumatrensis ). Therefore, studies utilising ancient protein sequences from Middle Pleistocene contexts have the potential to provide further insights into the phylogenetic relationships between extant and extinct species, including Stephanorhinus and Dicerorhinus . ZooMS screening (zooarchaeology by mass spectrometry) was performed on several Late and Middle Pleistocene specimens from the genus Stephanorhinus , subsequently followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to obtain ancient protein sequences from a Middle Pleistocene Stephanorhinus specimen. We performed parallel analysis on a Late Pleistocene woolly rhinoceros specimen and extant species of rhinoceroses, resulting in the availability of protein sequence data for five extant species and two extinct genera. Phylogenetic analysis additionally included all extant Perissodactyla genera ( Equus , Tapirus ), and was conducted using Bayesian (MrBayes) and maximum-likelihood (RAxML) methods. Various ancient proteins were identified in both the Middle and Late Pleistocene rhinoceros samples. Protein degradation and proteome complexity are consistent with an endogenous origin of the identified proteins. Phylogenetic analysis of informative proteins resolved the Perissodactyla phylogeny in agreement with previous studies in regards to the placement of the families Equidae, Tapiridae, and Rhinocerotidae. Stephanorhinus is shown to be most closely related to the genera Coelodonta and Dicerorhinus . The protein sequence data further places the Sumatran rhino in a clade together with the genus Rhinoceros , opposed to forming a clade with the black and white rhinoceros species. The first biomolecular dataset available for Stephanorhinus places this genus together with the extinct genus Coelodonta and the extant genus Dicerorhinus . This is in agreement with morphological studies, although we are unable to resolve the order of divergence between these genera based on the protein sequences available. Our data supports the placement of the genus Dicerorhinus in a clade together with extant Rhinoceros species. Finally, the availability of protein sequence data for both extinct European rhinoceros genera allows future investigations into their geographic distribution and extinction chronologies.

Uncertainty-Dependent Extinction of Fear Memory in an Amygdala-mPFC Neural Circuit Model

PubMed Central

Li, Yuzhe; Nakae, Ken; Ishii, Shin; Naoki, Honda

2016-01-01

Uncertainty of fear conditioning is crucial for the acquisition and extinction of fear memory. Fear memory acquired through partial pairings of a conditioned stimulus (CS) and an unconditioned stimulus (US) is more resistant to extinction than that acquired through full pairings; this effect is known as the partial reinforcement extinction effect (PREE). Although the PREE has been explained by psychological theories, the neural mechanisms underlying the PREE remain largely unclear. Here, we developed a neural circuit model based on three distinct types of neurons (fear, persistent and extinction neurons) in the amygdala and medial prefrontal cortex (mPFC). In the model, the fear, persistent and extinction neurons encode predictions of net severity, of unconditioned stimulus (US) intensity, and of net safety, respectively. Our simulation successfully reproduces the PREE. We revealed that unpredictability of the US during extinction was represented by the combined responses of the three types of neurons, which are critical for the PREE. In addition, we extended the model to include amygdala subregions and the mPFC to address a recent finding that the ventral mPFC (vmPFC) is required for consolidating extinction memory but not for memory retrieval. Furthermore, model simulations led us to propose a novel procedure to enhance extinction learning through re-conditioning with a stronger US; strengthened fear memory up-regulates the extinction neuron, which, in turn, further inhibits the fear neuron during re-extinction. Thus, our models increased the understanding of the functional roles of the amygdala and vmPFC in the processing of uncertainty in fear conditioning and extinction. PMID:27617747

Uncertainty-Dependent Extinction of Fear Memory in an Amygdala-mPFC Neural Circuit Model.

PubMed

Li, Yuzhe; Nakae, Ken; Ishii, Shin; Naoki, Honda

2016-09-01

Uncertainty of fear conditioning is crucial for the acquisition and extinction of fear memory. Fear memory acquired through partial pairings of a conditioned stimulus (CS) and an unconditioned stimulus (US) is more resistant to extinction than that acquired through full pairings; this effect is known as the partial reinforcement extinction effect (PREE). Although the PREE has been explained by psychological theories, the neural mechanisms underlying the PREE remain largely unclear. Here, we developed a neural circuit model based on three distinct types of neurons (fear, persistent and extinction neurons) in the amygdala and medial prefrontal cortex (mPFC). In the model, the fear, persistent and extinction neurons encode predictions of net severity, of unconditioned stimulus (US) intensity, and of net safety, respectively. Our simulation successfully reproduces the PREE. We revealed that unpredictability of the US during extinction was represented by the combined responses of the three types of neurons, which are critical for the PREE. In addition, we extended the model to include amygdala subregions and the mPFC to address a recent finding that the ventral mPFC (vmPFC) is required for consolidating extinction memory but not for memory retrieval. Furthermore, model simulations led us to propose a novel procedure to enhance extinction learning through re-conditioning with a stronger US; strengthened fear memory up-regulates the extinction neuron, which, in turn, further inhibits the fear neuron during re-extinction. Thus, our models increased the understanding of the functional roles of the amygdala and vmPFC in the processing of uncertainty in fear conditioning and extinction.

Reconciling Reinforcement Learning Models with Behavioral Extinction and Renewal: Implications for Addiction, Relapse, and Problem Gambling

ERIC Educational Resources Information Center

Redish, A. David; Jensen, Steve; Johnson, Adam; Kurth-Nelson, Zeb

2007-01-01

Because learned associations are quickly renewed following extinction, the extinction process must include processes other than unlearning. However, reinforcement learning models, such as the temporal difference reinforcement learning (TDRL) model, treat extinction as an unlearning of associated value and are thus unable to capture renewal. TDRL…

Stone tools and foraging in northern Madagascar challenge Holocene extinction models.

PubMed

Dewar, Robert E; Radimilahy, Chantal; Wright, Henry T; Jacobs, Zenobia; Kelly, Gwendolyn O; Berna, Francesco

2013-07-30

Past research on Madagascar indicates that village communities were established about AD 500 by people of both Indonesian and East African heritage. Evidence of earlier visits is scattered and contentious. Recent archaeological excavations in northern Madagascar provide evidence of occupational sites with microlithic stone technologies related to foraging for forest and coastal resources. A forager occupation of one site dates to earlier than 2000 B.C., doubling the length of Madagascar's known occupational history, and thus the time during which people exploited Madagascar's environments. We detail stratigraphy, chronology, and artifacts from two rock shelters. Ambohiposa near Iharana (Vohémar) on the northeast coast, yielded a stratified assemblage with small flakes, microblades, and retouched crescentic and trapezoidal tools, probably projectile elements, made on cherts and obsidian, some brought more that 200 km. (14)C dates are contemporary with the earliest villages. No food remains are preserved. Lakaton'i Anja near Antsiranana in the north yielded several stratified assemblages. The latest assemblage is well dated to A.D. 1050-1350, by (14)C and optically stimulated luminescence dating and pottery imported from the Near East and China. Below is a series of stratified assemblages similar to Ambohiposa. (14)C and optically stimulated luminescence dates indicate occupation from at least 2000 B.C. Faunal remains indicate a foraging pattern. Our evidence shows that foragers with a microlithic technology were active in Madagascar long before the arrival of farmers and herders and before many Late Holocene faunal extinctions. The differing effects of historically distinct economies must be identified and understood to reconstruct Holocene histories of human environmental impact.

Cranial morphology of Javanese Homo erectus: new evidence for continuous evolution, specialization, and terminal extinction.

PubMed

Kaifu, Yousuke; Aziz, Fachroel; Indriati, Etty; Jacob, Teuku; Kurniawan, Iwan; Baba, Hisao

2008-10-01

Our current knowledge of the evolution of Homo during the early to middle Pleistocene is far from complete. This is not only because of the small number of fossil samples available, but also due to the scarcity of standardized datasets which are reliable in terms of landmark identification, interobserver error, and other distorting factors. This study aims to accurately describe the cranial morphological changes of H. erectus in Java using a standardized set of measurements taken by the authors from 18 adult crania from Sangiran, Trinil, Sambungmacan, and Ngandong. The identification of some obscure landmarks was aided by the use of micro-CT imaging. While recent studies tend to emphasize evolutionary conservatism in Javanese H. erectus, our results reinforce the theory that chronologically later groups experienced distinct morphological changes in a number of cranial traits. Some of these changes, particularly those related to brain size expansion, are similar to those observed for the genus Homo as a whole, whereas others are apparently unique specializations restricted to Javanese H. erectus. Such morphological specializations in Java include previously undescribed anteroposterior lengthening of the midcranial base and an anterior shift of the posterior temporal muscle, which might have influenced the morphology of the angular torus and supramastoid sulcus. Analyses of morphological variation indicate that the three crania from Sambungmacan variously fill the morphological gap between the chronologically earlier (Bapang-AG, Bapang Formation above the Grenzbank zone in Sangiran) and later (Ngandong) morphotypes of Java. At least one of the Bapang-AG crania, Sangiran 17, also exhibits a few characteristics which potentially indicate evolution toward the Ngandong condition. These strongly suggest the continuous, gradual morphological evolution of Javanese H. erectus from the Bapang-AG to Ngandong periods. The development of some unique features in later Javanese H. erectus supports the hypothesis that this Javanese lineage went extinct without making significant contributions to the ancestry of modern humans.

Mercury anomalies as a proxy for large igneous province volicanism and effects on the carbon cycle in a U-Pb age-constrained section spanning the end-Triassic mass extinction, Levanto, Peru

NASA Astrophysics Data System (ADS)

Yager, J. A.; West, A. J.; Bergquist, B. A.; Thibodeau, A. M.; Corsetti, F. A.; Berelson, W.; Rosas, S.; Bottjer, D. J.

2017-12-01

Understanding the causes of the end-Triassic extinction and their potential relationship to Central Atlantic Magmatic Province (CAMP) volcanism necessitates careful correlation of carbon cycle records (largely from marine sections) and volcanism (largely from terrestrial successions) in a robust chronological framework. Here, we report stable carbon isotopes and mercury concentrations and isotopes from the Levanto section in Northern Peru as a putative proxy for CAMP (a large igneous province) in a marine section. Levanto represents deposition well below storm wave base and is lithologically homogenous before, during, and after the end-Triassic extinction interval, making it ideal for detailed chemostratigraphy. Furthermore, abundant intercalated ash beds allow us to correlate mercury concentrations in the marine record directly with CAMP basalt ages, providing a test of the correspondence of mercury anomalies with the eruption of CAMP volcanics. Age dating and C isotope analyses provide an opportunity to explore orbital tuning of the carbon isotope record and ground truth it with existing U-Pb ages from the section, a feature not available in any other marine sections examined to date. The abundance of U-Pb dated ashes in the Levanto section allows us to correlate orbital tuning with other basins, which lack absolute age control, providing a better understanding for the C cycle changes associated with the Triassic-Jurassic boundary.

Extinction debt from climate change for frogs in the wet tropics.

PubMed

Fordham, Damien A; Brook, Barry W; Hoskin, Conrad J; Pressey, Robert L; VanDerWal, Jeremy; Williams, Stephen E

2016-10-01

The effect of twenty-first-century climate change on biodiversity is commonly forecast based on modelled shifts in species ranges, linked to habitat suitability. These projections have been coupled with species-area relationships (SAR) to infer extinction rates indirectly as a result of the loss of climatically suitable areas and associated habitat. This approach does not model population dynamics explicitly, and so accepts that extinctions might occur after substantial (but unknown) delays-an extinction debt. Here we explicitly couple bioclimatic envelope models of climate and habitat suitability with generic life-history models for 24 species of frogs found in the Australian Wet Tropics (AWT). We show that (i) as many as four species of frogs face imminent extinction by 2080, due primarily to climate change; (ii) three frogs face delayed extinctions; and (iii) this extinction debt will take at least a century to be realized in full. Furthermore, we find congruence between forecast rates of extinction using SARs, and demographic models with an extinction lag of 120 years. We conclude that SAR approaches can provide useful advice to conservation on climate change impacts, provided there is a good understanding of the time lags over which delayed extinctions are likely to occur. © 2016 The Author(s).

Animal models of extinction-induced depression: loss of reward and its consequences.

PubMed

Huston, Joseph P; Silva, Maria A de Souza; Komorowski, Mara; Schulz, Daniela; Topic, Bianca

2013-11-01

The absence or loss of rewards or reinforcers holds a major role in the development of depression in humans. In spite of the prevalence of extinction-induced depression (EID) in humans, few attempts have been made to establish animal models thereof. Here we present the concept of extinction-related depression and summarize the results of two sets of studies in our attempt to create animal models of EID, one set based on extinction after positive reinforcement in the Skinner-box, the other on extinction after negative reinforcement - escape from water. We found various behaviors emitted during the extinction trials that responded to treatment with antidepressant drugs: Accordingly, the important behavioral marker for EID during extinction of escape from the water was immobility. During extinction after positive reinforcement the important indices for extinction-induced depression are the withdrawal from the former site of reward, biting behavior and rearing up on the hind legs. Avoidance behavior and biting may model aspects of human depressive behavior, which may include withdrawal or avoidance as well as aggressive-like behaviors. Copyright © 2013 Elsevier Ltd. All rights reserved.

Radiocarbon evidence for the presence of mice on Madeira Island (North Atlantic) one millennium ago.

PubMed

Rando, Juan Carlos; Pieper, Harald; Alcover, Josep Antoni

2014-04-07

Owing to the catastrophic extinction events that occurred following the Holocene arrival of alien species, extant oceanic island biotas are a mixture of recently incorporated alien fauna and remnants of the original fauna. Knowledge of the Late Quaternary pristine island faunas and a reliable chronology of the earliest presence of alien species on each archipelago are critical in understanding the magnitude and tempo of Quaternary island extinctions. Until now, two successive waves of human arrivals have been identified in the North Atlantic Macaronesian archipelagos (Azores, Madeira, Selvagens, Canary and Cape Verde Islands): 'aboriginal', which is limited to the Canary Islands around two millennia ago, and 'colonial', from the fourteenth century onwards. New surveys in Ponta de São Lourenço (Madeira Island) have allowed us to obtain and date ancient bones of mice. The date obtained (1033 ± 28 BP) documents the earliest evidence for the presence of mice on the island. This date extends the time frame in which the most significant ecological changes occurred on the island. It also suggests that humans could have reached Madeira before 1036 cal AD, around four centuries before Portugal officially took possession of the island.

A tree-ring based reconstruction of Logan River streamflow, northern Utah

Treesearch

Eric B. Allen; Tammy M. Rittenour; R. Justin DeRose; Matthew F. Bekker; Roger Kjelgren; Brendan M. Buckley

2013-01-01

We created six new tree-ring chronologies in northern Utah, which were used with preexisting chronologies from Utah and western Wyoming to reconstruct mean annual flow for the Logan River, the largest tributary of the regionally important Bear River. Two reconstruction models were developed, a ''Local'' model that incorporated two Rocky Mountain...

Disturbances in the Isotopic Record of Asuka 881394

NASA Technical Reports Server (NTRS)

Nyquist, L. E.; Bogard, D. D.

2011-01-01

Asuka 881394 is a unique achondrite with a granulitic texture, very calcic approximately An(sub 98) plagioclase, and pigeonite that has not inverted to orthopyroxene. First thought to be a eucrite, recent Oisotopic studies show it has a closer affinity to angrites . Initial isotopic studies provided evidence for now extinct A-26, Mn-53, and Sm-146. A recent study confirmed an early chronology with an absolute Pb-207 - Pb-206 age of 4566.5 +/- 0.2 Ma, a new measurement of the Al-Mg formation interval as 3.7 +/- 0.1 Ma since Al-26/Al-27 = approximately 4.63 x 10(exp -5) for the E60 CAI, and a Mn-Cr formation interval of -6.0 +/- 0.2 Ma relative to LEW86010 ("LEW"). Absolute ages relative to age anchors presented by were 4563.4 +/- 0.2 Ma by Al- Mg and 4564.6 +/- 0.5 Ma by Mn-Cr. These ages are in good, but not perfect, agreement with the Pb-207 - Pb-206 age. Perhaps the most direct comparison of the early chronology of A881394 as determined by various workers is provided by reported Al-26/Al-27 values of 1.18 +/- 0.14, 1.28 +/- 0.07, and 2.1 +/- 0.4 x 10(exp -6). Analyses of mineral separates by TIMS and MC-ICPMS6] agree well, but the higher value obtained by in situ SIMS analysis is significant in light of the slight inconsistency between absolute ages inferred from the short-lived chronometers and the Pb-207 - Pb-206 age. We examine the possibility that inconsistencies in the earliest fine-scale chronology of Asuka 881394 may be related to isotopic "disturbances" observed in Ar-39 - Ar-40, Rb-97 - Sr-87, and Sm-147 - Nd-143 chronometers.

The association between chronological age, age at injury and employment: Is there a mediating effect of secondary health conditions?

PubMed

Marti, A; Boes, S; Lay, V; Escorpizo, R; Reuben Escorpizo, P T; Trezzini, B

2016-03-01

Cross-sectional observational study with data from the 2012 community-based survey of the Swiss Spinal Cord Injury Cohort Study. To examine the relationships between chronological age, age at injury, secondary health conditions (SHCs) and paid employment. Community setting in Switzerland. A total of 1159 individuals of working age (16-63 years for women and 64 years for men) with traumatic or non-traumatic spinal cord injury (SCI) were included in the study. Direct and indirect (via SHCs) effects of chronological age and age at injury on paid employment were tested using a decomposition method for logistic regression models. Both chronological age groups (age 35-49 and 50-63/64 years) and the group with age at injury beyond 40 years showed negative direct effects on employment status. A partial indirect effect (mediation) via chronic pain was found in the group with the highest chronological age (>50 years). Furthermore, pressure ulcer, pain and urinary tract infection were negatively related with employment in both models, that is, chronological age and employment and age at injury and employment. Being older and having a higher age at injury directly affects whether an individual is employed. Pain is mediating the relation between chronological age and employment. Furthermore, pressure ulcer, chronic pain and urinary tract infection directly reduce the likelihood to be employed and, therefore, represent important intervention targets in efforts to maintain or engage in employment of individuals with SCI.

Establishing endangered species recovery criteria using predictive simulation modeling

USGS Publications Warehouse

McGowan, Conor P.; Catlin, Daniel H.; Shaffer, Terry L.; Gratto-Trevor, Cheri L.; Aron, Carol

2014-01-01

Listing a species under the Endangered Species Act (ESA) and developing a recovery plan requires U.S. Fish and Wildlife Service to establish specific and measurable criteria for delisting. Generally, species are listed because they face (or are perceived to face) elevated risk of extinction due to issues such as habitat loss, invasive species, or other factors. Recovery plans identify recovery criteria that reduce extinction risk to an acceptable level. It logically follows that the recovery criteria, the defined conditions for removing a species from ESA protections, need to be closely related to extinction risk. Extinction probability is a population parameter estimated with a model that uses current demographic information to project the population into the future over a number of replicates, calculating the proportion of replicated populations that go extinct. We simulated extinction probabilities of piping plovers in the Great Plains and estimated the relationship between extinction probability and various demographic parameters. We tested the fit of regression models linking initial abundance, productivity, or population growth rate to extinction risk, and then, using the regression parameter estimates, determined the conditions required to reduce extinction probability to some pre-defined acceptable threshold. Binomial regression models with mean population growth rate and the natural log of initial abundance were the best predictors of extinction probability 50 years into the future. For example, based on our regression models, an initial abundance of approximately 2400 females with an expected mean population growth rate of 1.0 will limit extinction risk for piping plovers in the Great Plains to less than 0.048. Our method provides a straightforward way of developing specific and measurable recovery criteria linked directly to the core issue of extinction risk. Published by Elsevier Ltd.

A revised inoceramid biozonation for the Upper Cretaceous based on high-resolution carbon isotope stratigraphy in northwestern Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Hayakawa, Tatsuya; Hirano, Hiromichi

2013-06-01

Hayakawa, T., Hirano, H. 2013. A revised inoceramid biozonation for the Upper Cretaceous based on high-resolution carbon isotope stratigraphy in northwestern Hokkaido, Japan. Acta Geologica Polonica, 63 (2), 239-263. Warszawa. Biostratigraphic correlations of inoceramid bivalves between the North Pacific and Euramerican provinces have been difficult because the inoceramid biostratigraphy of the Japanese strata has been based on endemic species of the northwest Pacific. In this study, carbon stable isotope fluctuations of terrestrial organic matter are assembled for the Upper Cretaceous Yezo Group in the Haboro and Obira areas, Hokkaido, Japan, in order to revise the chronology of the inoceramid biozonation in Japan. The carbon isotope curves are correlated with those of marine carbonates in English and German sections with the aid of age-diagnostic taxa. According to the correlations of the carbon isotope curves, 11 isotope events are recognised in the sections studied. As a result of these correlations, the chronology of the inoceramid biozones of the Northwest Pacific has been considerably revised. The revised inoceramid biozones suggest that the timing of the origination and extinction of the inoceramids in the North Pacific biotic province is different from the stage/substage boundaries defined by inoceramids, as used in Europe and North America.

Goodness of fit of probability distributions for sightings as species approach extinction.

PubMed

Vogel, Richard M; Hosking, Jonathan R M; Elphick, Chris S; Roberts, David L; Reed, J Michael

2009-04-01

Estimating the probability that a species is extinct and the timing of extinctions is useful in biological fields ranging from paleoecology to conservation biology. Various statistical methods have been introduced to infer the time of extinction and extinction probability from a series of individual sightings. There is little evidence, however, as to which of these models provide adequate fit to actual sighting records. We use L-moment diagrams and probability plot correlation coefficient (PPCC) hypothesis tests to evaluate the goodness of fit of various probabilistic models to sighting data collected for a set of North American and Hawaiian bird populations that have either gone extinct, or are suspected of having gone extinct, during the past 150 years. For our data, the uniform, truncated exponential, and generalized Pareto models performed moderately well, but the Weibull model performed poorly. Of the acceptable models, the uniform distribution performed best based on PPCC goodness of fit comparisons and sequential Bonferroni-type tests. Further analyses using field significance tests suggest that although the uniform distribution is the best of those considered, additional work remains to evaluate the truncated exponential model more fully. The methods we present here provide a framework for evaluating subsequent models.

Deciphering the complete mitochondrial genome and phylogeny of the extinct cave bear in the Paleolithic painted cave of Chauvet.

PubMed

Bon, Céline; Caudy, Nicolas; de Dieuleveult, Maud; Fosse, Philippe; Philippe, Michel; Maksud, Frédéric; Beraud-Colomb, Eliane; Bouzaid, Eric; Kefi, Rym; Laugier, Christelle; Rousseau, Bernard; Casane, Didier; van der Plicht, Johannes; Elalouf, Jean-Marc

2008-11-11

Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost. To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome. Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago. With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA.

Deciphering the complete mitochondrial genome and phylogeny of the extinct cave bear in the Paleolithic painted cave of Chauvet

PubMed Central

Bon, Céline; Caudy, Nicolas; de Dieuleveult, Maud; Fosse, Philippe; Philippe, Michel; Maksud, Frédéric; Beraud-Colomb, Éliane; Bouzaid, Eric; Kefi, Rym; Laugier, Christelle; Rousseau, Bernard; Casane, Didier; van der Plicht, Johannes; Elalouf, Jean-Marc

2008-01-01

Retrieving a large amount of genetic information from extinct species was demonstrated feasible, but complete mitochondrial genome sequences have only been deciphered for the moa, a bird that became extinct a few hundred years ago, and for Pleistocene species, such as the woolly mammoth and the mastodon, both of which could be studied from animals embedded in permafrost. To enlarge the diversity of mitochondrial genomes available for Pleistocene species, we turned to the cave bear (Ursus spelaeus), whose only remains consist of skeletal elements. We collected bone samples from the Paleolithic painted cave of Chauvet-Pont d'Arc (France), which displays the earliest known human drawings, and contains thousands of bear remains. We selected a cave bear sternebra, radiocarbon dated to 32,000 years before present, from which we generated overlapping DNA fragments assembling into a 16,810-base pair mitochondrial genome. Together with the first mitochondrial genome for the brown bear western lineage, this study provides a statistically secured molecular phylogeny assessing the cave bear as a sister taxon to the brown bear and polar bear clade, with a divergence inferred to 1.6 million years ago. With the first mitochondrial genome for a Pleistocene carnivore to be delivered, our study establishes the Chauvet-Pont d'Arc Cave as a new reservoir for Paleogenetic studies. These molecular data enable establishing the chronology of bear speciation, and provide a helpful resource to rescue for genetic analysis archeological samples initially diagnosed as devoid of amplifiable DNA. PMID:18955696

Stone tools and foraging in northern Madagascar challenge Holocene extinction models

PubMed Central

Dewar, Robert E.; Radimilahy, Chantal; Wright, Henry T.; Jacobs, Zenobia; Kelly, Gwendolyn O.; Berna, Francesco

2013-01-01

Past research on Madagascar indicates that village communities were established about AD 500 by people of both Indonesian and East African heritage. Evidence of earlier visits is scattered and contentious. Recent archaeological excavations in northern Madagascar provide evidence of occupational sites with microlithic stone technologies related to foraging for forest and coastal resources. A forager occupation of one site dates to earlier than 2000 B.C., doubling the length of Madagascar’s known occupational history, and thus the time during which people exploited Madagascar’s environments. We detail stratigraphy, chronology, and artifacts from two rock shelters. Ambohiposa near Iharana (Vohémar) on the northeast coast, yielded a stratified assemblage with small flakes, microblades, and retouched crescentic and trapezoidal tools, probably projectile elements, made on cherts and obsidian, some brought more that 200 km. 14C dates are contemporary with the earliest villages. No food remains are preserved. Lakaton’i Anja near Antsiranana in the north yielded several stratified assemblages. The latest assemblage is well dated to A.D. 1050–1350, by 14C and optically stimulated luminescence dating and pottery imported from the Near East and China. Below is a series of stratified assemblages similar to Ambohiposa. 14C and optically stimulated luminescence dates indicate occupation from at least 2000 B.C. Faunal remains indicate a foraging pattern. Our evidence shows that foragers with a microlithic technology were active in Madagascar long before the arrival of farmers and herders and before many Late Holocene faunal extinctions. The differing effects of historically distinct economies must be identified and understood to reconstruct Holocene histories of human environmental impact. PMID:23858456

Toward unified ice core chronologies with the DatIce tool

NASA Astrophysics Data System (ADS)

Toye Mahamadou Kele, H.; Lemieux-Dudon, B.; Blayo, E.

2012-04-01

Antarctic and Greenland ice cores provide a means to study the phase relationships of climate changes in both hemispheres. They also enable to study the timing between climate, and greenhouse gases or orbital forcings. One key step for such studies is to improve the absolute and relative precisions of ice core age scales (for ice and trapped gas), and beyond that, to try to reach the best consistency between chronologies of paleo records of any kind. The DatIce tool is designed to increase the consistency between pre-existing (also called background) core chronologies. It formulates a variational inverse problem which aims at correcting three key quantities that uniquely define the core age scales: the accumulation rate, the total thinning function, and the close-off depth. For that purpose, it integrates paleo data constraints of many types among which age markers (with for instance documented volcanoes eruptions), and stratigraphic links (with for instance abrupt changes in methane concentration). A cost function is built that enables to calculate new chronologies by making a trade-off between all the constraints (background chronologies and paleo data). The method presented in Lemieux-Dudon et al (2010) has already been applied simultaneously to EPICA EDML and EDC, Vostok and NGRIP. Currently, on going works are conducted at LSCE Saclay and LGGE Grenoble laboratories to construct unified Antarctic chronologies by applying the DatIce tool with new ice cores and new sets of paleo measurements. We here present the DatIce tool, the underlying methodology, and its potential applications. We further show some improvements that have been made recently. We especially adress the issue related to the calibration of the error of pre-existing core chronologies. They are inputs that may have a strong impact on the results. However these uncertainties are uneasy to analyze, since prior chronologies are most of the time assessed on the basis of glaciological models (firn densification and ice flow models) which still face large uncertainties (forcing fields, model parameters, mechanic and physic formulation). For that reason, we chose to calibrate errors by applying consistency diagnostics, a classical method in data assimilation (Desrozier et al, 2009).

Bilateral Alternating Auditory Stimulations Facilitate Fear Extinction and Retrieval.

PubMed

Boukezzi, Sarah; Silva, Catarina; Nazarian, Bruno; Rousseau, Pierre-François; Guedj, Eric; Valenzuela-Moguillansky, Camila; Khalfa, Stéphanie

2017-01-01

Disruption of fear conditioning, its extinction and its retrieval are at the core of posttraumatic stress disorder (PTSD). Such deficits, especially fear extinction delay, disappear after alternating bilateral stimulations (BLS) during eye movement desensitization and reprocessing (EMDR) therapy. An animal model of fear recovery, based on auditory cued fear conditioning and extinction learning, recently showed that BLS facilitate fear extinction and fear extinction retrieval. Our goal was to determine if these previous results found in animals can be reproduced in humans. Twenty-two healthy participants took part in a classical fear conditioning, extinction, and extinction recall paradigm. Behavioral responses (fear expectations) as well as psychophysiological measures (skin conductance responses, SCRs) were recorded. The results showed a significant fear expectation decrease during fear extinction with BLS. Additionally, SCR for fear extinction retrieval were significantly lower with BLS. Our results demonstrate the importance of BLS to reduce negative emotions, and provide a successful model to further explore the neural mechanisms underlying the sole BLS effect in the EMDR.

Bilateral Alternating Auditory Stimulations Facilitate Fear Extinction and Retrieval

PubMed Central

Boukezzi, Sarah; Silva, Catarina; Nazarian, Bruno; Rousseau, Pierre-François; Guedj, Eric; Valenzuela-Moguillansky, Camila; Khalfa, Stéphanie

2017-01-01

Disruption of fear conditioning, its extinction and its retrieval are at the core of posttraumatic stress disorder (PTSD). Such deficits, especially fear extinction delay, disappear after alternating bilateral stimulations (BLS) during eye movement desensitization and reprocessing (EMDR) therapy. An animal model of fear recovery, based on auditory cued fear conditioning and extinction learning, recently showed that BLS facilitate fear extinction and fear extinction retrieval. Our goal was to determine if these previous results found in animals can be reproduced in humans. Twenty-two healthy participants took part in a classical fear conditioning, extinction, and extinction recall paradigm. Behavioral responses (fear expectations) as well as psychophysiological measures (skin conductance responses, SCRs) were recorded. The results showed a significant fear expectation decrease during fear extinction with BLS. Additionally, SCR for fear extinction retrieval were significantly lower with BLS. Our results demonstrate the importance of BLS to reduce negative emotions, and provide a successful model to further explore the neural mechanisms underlying the sole BLS effect in the EMDR. PMID:28659851

The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds

NASA Astrophysics Data System (ADS)

Chapman, Nicholas L.; Mundy, Lee G.; Lai, Shih-Ping; Evans, Neal J., II

2009-01-01

We compute the mid-IR extinction law from 3.6 to 24 μm in three molecular clouds—Ophiuchus, Perseus, and Serpens—by combining data from the "Cores to Disks" Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the χ2 deviation of the data from two extinction law models. Because our χ2 maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6-8 μm, we see evidence for grain growth. Below A_{K_s} = 0.5, our extinction law is well fitted by the Weingartner and Draine RV = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for A_{K_s} \\ge 1, the data are more consistent with the Weingartner and Draine RV = 5.5 model that uses larger maximum dust grain sizes. At 24 μm, our extinction law is 2-4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our χ2 maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.

Extinction in Phylogenetics and Biogeography: From Timetrees to Patterns of Biotic Assemblage

PubMed Central

Meseguer, Andrea S.

2016-01-01

Global climate change and its impact on biodiversity levels have made extinction a relevant topic in biological research. Yet, until recently, extinction has received less attention in macroevolutionary studies than speciation; the reason is the difficulty to infer an event that actually eliminates rather than creates new taxa. For example, in biogeography, extinction has often been seen as noise, introducing homoplasy in biogeographic relationships, rather than a pattern-generating process. The molecular revolution and the possibility to integrate time into phylogenetic reconstructions have allowed studying extinction under different perspectives. Here, we review phylogenetic (temporal) and biogeographic (spatial) approaches to the inference of extinction and the challenges this process poses for reconstructing evolutionary history. Specifically, we focus on the problem of discriminating between alternative high extinction scenarios using time trees with only extant taxa, and on the confounding effect introduced by asymmetric spatial extinction – different rates of extinction across areas – in biogeographic inference. Finally, we identify the most promising avenues of research in both fields, which include the integration of additional sources of evidence such as the fossil record or environmental information in birth–death models and biogeographic reconstructions, the development of new models that tie extinction rates to phenotypic or environmental variation, or the implementation within a Bayesian framework of parametric non-stationary biogeographic models. PMID:27047538

Genetic disruptions of Drosophila Pavlovian learning leave extinction learning intact.

PubMed

Qin, H; Dubnau, J

2010-03-01

Individuals who experience traumatic events may develop persistent posttraumatic stress disorder. Patients with this disorder are commonly treated with exposure therapy, which has had limited long-term success. In experimental neurobiology, fear extinction is a model for exposure therapy. In this behavioral paradigm, animals are repeatedly exposed in a safe environment to the fearful stimulus, which leads to greatly reduced fear. Studying animal models of extinction already has lead to better therapeutic strategies and development of new candidate drugs. Lack of a powerful genetic model of extinction, however, has limited progress in identifying underlying molecular and genetic factors. In this study, we established a robust behavioral paradigm to study the short-term effect (acquisition) of extinction in Drosophila melanogaster. We focused on the extinction of olfactory aversive 1-day memory with a task that has been the main workhorse for genetics of memory in flies. Using this paradigm, we show that extinction can inhibit each of two genetically distinct forms of consolidated memory. We then used a series of single-gene mutants with known impact on associative learning to examine the effects on extinction. We find that extinction is intact in each of these mutants, suggesting that extinction learning relies on different molecular mechanisms than does Pavlovian learning.

Absolute ages from crater statistics: Using radiometric ages of Martian samples for determining the Martian cratering chronology

NASA Technical Reports Server (NTRS)

Neukum, G.

1988-01-01

In the absence of dates derived from rock samples, impact crater frequencies are commonly used to date Martian surface units. All models for absolute dating rely on the lunar cratering chronology and on the validity of its extrapolation to Martian conditions. Starting from somewhat different lunar chronologies, rather different Martian cratering chronologies are found in the literature. Currently favored models are compared. The differences at old ages are significant, the differences at younger ages are considerable and give absolute ages for the same crater frequencies as different as a factor of 3. The total uncertainty could be much higher, though, since the ratio of lunar to Martian cratering rate which is of basic importance in the models is believed to be known no better than within a factor of 2. Thus, it is of crucial importance for understanding the the evolution of Mars and determining the sequence of events to establish an unambiguous Martian cratering chronology from crater statistics in combination with clean radiometric ages of returned Martian samples. For the dating goal, rocks should be as pristine as possible from a geologically simple area with a one-stage emplacement history of the local formation. A minimum of at least one highland site for old ages, two intermediate-aged sites, and one very young site is needed.

Human demography and reserve size predict wildlife extinction in West Africa.

PubMed Central

Brashares, J S; Arcese, P; Sam, M K

2001-01-01

Species-area models have become the primary tool used to predict baseline extinction rates for species in isolated habitats, and have influenced conservation and land-use planning worldwide. In particular, these models have been used to predict extinction rates following the loss or fragmentation of natural habitats in the absence of direct human influence on species persistence. Thus, where direct human influences, such as hunting, put added pressure on species in remnant habitat patches, we should expect to observe extinction rates higher than those predicted by simple species-area models. Here, we show that extinction rates for 41 species of large mammals in six nature reserves in West Africa are 14-307 times higher than those predicted by models based on reserve size alone. Human population and reserve size accounted for 98% of the observed variation in extinction rates between reserves. Extinction occurred at higher rates than predicted by species-area models for carnivores, primates and ungulates, and at the highest rates overall near reserve borders. Our results indicate that, where the harvest of wildlife is common, conservation plans should focus on increasing the size of reserves and reducing the rate of hunting. PMID:11747566

Limits to biodiversity cycles from a unified model of mass-extinction events

NASA Astrophysics Data System (ADS)

Feulner, Georg

2011-04-01

Episodes of species mass extinction dramatically affected the evolution of life on Earth, but their causes remain a source of debate. Even more controversy surrounds the hypothesis of periodicity in the fossil record, with conflicting views still being published in the scientific literature, often even based on the same state-of-the-art datasets. From an empirical point of view, limitations of the currently available data on extinctions and possible causes remain an important issue. From a theoretical point of view, it is likely that a focus on single extinction causes and strong periodic forcings has strongly contributed to this controversy. Here I show that if there is a periodic extinction signal at all, it is much more likely to result from a combination of a comparatively weak periodic cause and various random factors. Tests of this unified model of mass extinctions on the available data show that the model is formally better than a model with random extinction causes only. However, the contribution of the periodic component is small compared to factors such as impacts or volcanic eruptions.

Is extinction age dependent?

USGS Publications Warehouse

Doran, N.A.; Arnold, A.J.; Parker, W.C.; Huffer, F.W.

2006-01-01

Age-dependent extinction is an observation with important biological implications. Van Valen's Red Queen hypothesis triggered three decades of research testing its primary implication: that age is independent of extinction. In contrast to this, later studies with species-level data have indicated the possible presence of age dependence. Since the formulation of the Red Queen hypothesis, more powerful tests of survivorship models have been developed. This is the first report of the application of the Cox Proportional Hazards model to paleontological data. Planktonic foraminiferal morphospecies allow the taxonomic and precise stratigraphic resolution necessary for the Cox model. As a whole, planktonic foraminiferal morphospecies clearly show age-dependent extinction. In particular, the effect is attributable to the presence of shorter-ranged species (range < 4 myr) following extinction events. These shorter-ranged species also possess tests with unique morphological architecture. The morphological differences are probably epiphenomena of underlying developmental and heterochronic processes of shorter-ranged species that survived various extinction events. Extinction survivors carry developmental and morphological characteristics into postextinction recovery times, and this sets them apart from species populations established independently of extinction events. Copyright ?? 2006, SEPM (Society for Sedimentary Geology).

Species extinction thresholds in the face of spatially correlated periodic disturbance.

PubMed

Liao, Jinbao; Ying, Zhixia; Hiebeler, David E; Wang, Yeqiao; Takada, Takenori; Nijs, Ivan

2015-10-20

The spatial correlation of disturbance is gaining attention in landscape ecology, but knowledge is still lacking on how species traits determine extinction thresholds under spatially correlated disturbance regimes. Here we develop a pair approximation model to explore species extinction risk in a lattice-structured landscape subject to aggregated periodic disturbance. Increasing disturbance extent and frequency accelerated population extinction irrespective of whether dispersal was local or global. Spatial correlation of disturbance likewise increased species extinction risk, but only for local dispersers. This indicates that models based on randomly simulated disturbances (e.g., mean-field or non-spatial models) may underestimate real extinction rates. Compared to local dispersal, species with global dispersal tolerated more severe disturbance, suggesting that the spatial correlation of disturbance favors long-range dispersal from an evolutionary perspective. Following disturbance, intraspecific competition greatly enhanced the extinction risk of distance-limited dispersers, while it surprisingly did not influence the extinction thresholds of global dispersers, apart from decreasing population density to some degree. As species respond differently to disturbance regimes with different spatiotemporal properties, different regimes may accommodate different species.

Fear Extinction as a Model for Translational Neuroscience: Ten Years of Progress

PubMed Central

Milad, Mohammed R.; Quirk, Gregory J.

2016-01-01

The psychology of extinction has been studied for decades. Approximately 10 years ago, however, there began a concerted effort to understand the neural circuits of extinction of fear conditioning, in both animals and humans. Progress during this period has been facilitated by an unusual degree of coordination between rodent and human researchers examining fear extinction. This successful research program could serve as a model for translational research in other areas of behavioral neuroscience. Here we review the major advances and highlight new approaches to understanding and exploiting fear extinction. PMID:22129456

Extinction of an instrumental response: a cognitive behavioral assay in Fmr1 knockout mice.

PubMed

Sidorov, M S; Krueger, D D; Taylor, M; Gisin, E; Osterweil, E K; Bear, M F

2014-06-01

Fragile X (FX) is the most common genetic cause of intellectual disability and autism. Previous studies have shown that partial inhibition of metabotropic glutamate receptor signaling is sufficient to correct behavioral phenotypes in a mouse model of FX, including audiogenic seizures, open-field hyperactivity and social behavior. These phenotypes model well the epilepsy (15%), hyperactivity (20%) and autism (30%) that are comorbid with FX in human patients. Identifying reliable and robust mouse phenotypes to model cognitive impairments is critical considering the 90% comorbidity of FX and intellectual disability. Recent work characterized a five-choice visuospatial discrimination assay testing cognitive flexibility, in which FX model mice show impairments associated with decreases in synaptic proteins in prefrontal cortex (PFC). In this study, we sought to determine whether instrumental extinction, another process requiring PFC, is altered in FX model mice, and whether downregulation of metabotropic glutamate receptor signaling pathways is sufficient to correct both visuospatial discrimination and extinction phenotypes. We report that instrumental extinction is consistently exaggerated in FX model mice. However, neither the extinction phenotype nor the visuospatial discrimination phenotype is corrected by approaches targeting metabotropic glutamate receptor signaling. This work describes a novel behavioral extinction assay to model impaired cognition in mouse models of neurodevelopmental disorders, provides evidence that extinction is exaggerated in the FX mouse model and suggests possible limitations of metabotropic glutamate receptor-based pharmacotherapy. © 2014 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.

Observational evidence of dust evolution in galactic extinction curves

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

Cecchi-Pestellini, Cesare; Casu, Silvia; Mulas, Giacomo

Although structural and optical properties of hydrogenated amorphous carbons are known to respond to varying physical conditions, most conventional extinction models are basically curve fits with modest predictive power. We compare an evolutionary model of the physical properties of carbonaceous grain mantles with their determination by homogeneously fitting observationally derived Galactic extinction curves with the same physically well-defined dust model. We find that a large sample of observed Galactic extinction curves are compatible with the evolutionary scenario underlying such a model, requiring physical conditions fully consistent with standard density, temperature, radiation field intensity, and average age of diffuse interstellar clouds.more » Hence, through the study of interstellar extinction we may, in principle, understand the evolutionary history of the diffuse interstellar clouds.« less

Forward modeling of tree-ring data: a case study with a global network

NASA Astrophysics Data System (ADS)

Breitenmoser, P. D.; Frank, D.; Brönnimann, S.

2012-04-01

Information derived from tree-rings is one of the most powerful tools presently available for studying past climatic variability as well as identifying fundamental relationships between tree-growth and climate. Climate reconstructions are typically performed by extending linear relationships, established during the overlapping period of instrumental and climate proxy archives into the past. Such analyses, however, are limited by methodological assumptions, including stationarity and linearity of the climate-proxy relationship. We investigate climate and tree-ring data using the Vaganov-Shashkin-Lite (VS-Lite) forward model of tree-ring width formation to examine the relations among actual tree growth and climate (as inferred from the simulated chronologies) to reconstruct past climate variability. The VS-lite model has been shown to produce skill comparable to that achieved using classical dendrochronological statistical modeling techniques when applied on simulations of a network of North American tree-ring chronologies. Although the detailed mechanistic processes such as photosynthesis, storage, or cell processes are not modeled directly, the net effect of the dominating nonlinear climatic controls on tree-growth are implemented into the model by the principle of limiting factors and threshold growth response functions. The VS-lite model requires as inputs only latitude, monthly mean temperature and monthly accumulated precipitation. Hence, this simple, process-based model enables ring-width simulation at any location where monthly climate records exist. In this study, we analyse the growth response of simulated tree-rings to monthly climate conditions obtained from the 20th century reanalysis project back to 1871. These simulated tree-ring chronologies are compared to the climate-driven variability in worldwide observed tree-ring chronologies from the International Tree Ring Database. Results point toward the suitability of the relationship among actual tree growth and climate (as inferred from the simulated chronologies) for use in global palaeoclimate reconstructions.

Drivers of extinction risk in African mammals: the interplay of distribution state, human pressure, conservation response and species biology

PubMed Central

Di Marco, Moreno; Buchanan, Graeme M.; Szantoi, Zoltan; Holmgren, Milena; Grottolo Marasini, Gabriele; Gross, Dorit; Tranquilli, Sandra; Boitani, Luigi; Rondinini, Carlo

2014-01-01

Although conservation intervention has reversed the decline of some species, our success is outweighed by a much larger number of species moving towards extinction. Extinction risk modelling can identify correlates of risk and species not yet recognized to be threatened. Here, we use machine learning models to identify correlates of extinction risk in African terrestrial mammals using a set of variables belonging to four classes: species distribution state, human pressures, conservation response and species biology. We derived information on distribution state and human pressure from satellite-borne imagery. Variables in all four classes were identified as important predictors of extinction risk, and interactions were observed among variables in different classes (e.g. level of protection, human threats, species distribution ranges). Species biology had a key role in mediating the effect of external variables. The model was 90% accurate in classifying extinction risk status of species, but in a few cases the observed and modelled extinction risk mismatched. Species in this condition might suffer from an incorrect classification of extinction risk (hence require reassessment). An increased availability of satellite imagery combined with improved resolution and classification accuracy of the resulting maps will play a progressively greater role in conservation monitoring. PMID:24733953

Drivers of extinction risk in African mammals: the interplay of distribution state, human pressure, conservation response and species biology.

PubMed

Di Marco, Moreno; Buchanan, Graeme M; Szantoi, Zoltan; Holmgren, Milena; Grottolo Marasini, Gabriele; Gross, Dorit; Tranquilli, Sandra; Boitani, Luigi; Rondinini, Carlo

2014-01-01

Although conservation intervention has reversed the decline of some species, our success is outweighed by a much larger number of species moving towards extinction. Extinction risk modelling can identify correlates of risk and species not yet recognized to be threatened. Here, we use machine learning models to identify correlates of extinction risk in African terrestrial mammals using a set of variables belonging to four classes: species distribution state, human pressures, conservation response and species biology. We derived information on distribution state and human pressure from satellite-borne imagery. Variables in all four classes were identified as important predictors of extinction risk, and interactions were observed among variables in different classes (e.g. level of protection, human threats, species distribution ranges). Species biology had a key role in mediating the effect of external variables. The model was 90% accurate in classifying extinction risk status of species, but in a few cases the observed and modelled extinction risk mismatched. Species in this condition might suffer from an incorrect classification of extinction risk (hence require reassessment). An increased availability of satellite imagery combined with improved resolution and classification accuracy of the resulting maps will play a progressively greater role in conservation monitoring.

Aligning and synchronization of MIS5 proxy records from Lake Ohrid (FYROM) with independently dated Mediterranean archives: implications for DEEP core chronology

NASA Astrophysics Data System (ADS)

Zanchetta, Giovanni; Regattieri, Eleonora; Giaccio, Biagio; Wagner, Bernd; Sulpizio, Roberto; Francke, Alex; Vogel, Hendrik; Sadori, Laura; Masi, Alessia; Sinopoli, Gaia; Lacey, Jack H.; Leng, Melanie J.; Leicher, Niklas

2016-05-01

The DEEP site sediment sequence obtained during the ICDP SCOPSCO project at Lake Ohrid was dated using tephrostratigraphic information, cyclostratigraphy, and orbital tuning through the marine isotope stages (MIS) 15-1. Although this approach is suitable for the generation of a general chronological framework of the long succession, it is insufficient to resolve more detailed palaeoclimatological questions, such as leads and lags of climate events between marine and terrestrial records or between different regions. Here, we demonstrate how the use of different tie points can affect cyclostratigraphy and orbital tuning for the period between ca. 140 and 70 ka and how the results can be correlated with directly/indirectly radiometrically dated Mediterranean marine and continental proxy records. The alternative age model presented here shows consistent differences with that initially proposed by Francke et al. (2015) for the same interval, in particular at the level of the MIS6-5e transition. According to this new age model, different proxies from the DEEP site sediment record support an increase of temperatures between glacial to interglacial conditions, which is almost synchronous with a rapid increase in sea surface temperature observed in the western Mediterranean. The results show how a detailed study of independent chronological tie points is important to align different records and to highlight asynchronisms of climate events. Moreover, Francke et al. (2016) have incorporated the new chronology proposed for tephra OH-DP-0499 in the final DEEP age model. This has reduced substantially the chronological discrepancies between the DEEP site age model and the model proposed here for the last glacial-interglacial transition.

Recreating the 1950’s Chesapeake Bay: Use of a Network Model to Guide the Application of a Eutrophication Model

DTIC Science & Technology

2009-08-01

14. Comparison of surface light extinction for base and 1950’ s RMB2 results in the upper, mid, and lower regions of the Chesapeake Bay...Lower Bay Light Extinction Surface 1950 Lower Bay Light Extinction Surface Figure 14. Comparison of surface light extinction for base and 1950’ s RMB2...ER D C/ EL T R -0 9 -9 System-Wide Water Resources Program Recreating the 1950’ s Chesapeake Bay: Use of a Network Model to Guide the

Timing of the Toarcian Ocean Anoxic Event (Early Jurassic) from correlation of astronomically forced global stratigraphic sections

NASA Astrophysics Data System (ADS)

Huang, C.; Hinnov, L. A.; Hesselbo, S. P.

2012-12-01

The Early Toarcian Oceanic Anoxic Event (OAE) in the Early Jurassic Period is associated with a major negative carbon isotope excursion (CIE), mass extinction, marine transgression and global warming. The Toarcian OAE is thought to have been caused by flood basalt magmatism, and may have been a trigger for mass extinction. However, these proposed causes of the Toarcian OAE and associated biotic crisis are not adequately resolved by a precise chronology. The duration of the Toarcian OAE has been estimated to be anywhere from ~0.12 to ~0.9 Myr, most recently 0.74 to 3.26 Myr from U-Pb dating. The CIE associated with the Toarcian OAE has a similar pattern at numerous localities, and there is evidence for astronomical forcing of marine carbon isotopes. Here we estimate a duration of ~625 kyr for the main negative CIE, ~860 kyr for the polymorphum zone and >1.58 Myr for the levisoni zone based on 405-kyr astronomical eccentricity tuning of the marine section at Peniche (Portugal). This 405-kyr tuned series provides a ~2.5 Myr continuous high-resolution chronology through the Early Toarcian. There are 6, or possibly 7 short eccentricity cycles in the main CIE interval at Peniche. To confirm this astronomically based estimate, we analyzed five other sections at Yorkshire (UK), Dotternhausen (Germany), Valdorbia (Italy), Mechowo (Poland) and Serrucho, Neuquén (Argentina), from marine and terrestrial carbon isotopic series. These six stratigraphic sections from Early Jurassic western Tethys and eastern Panthalassa record the Toarcian OAE with ~6 prominent carbon isotope cycles in the CIE that provide us a 600 ± 100 kyr duration. The Peniche 405 kyr-tuned series indicates that the pre- and post-CIE intervals experienced strong precession-eccentricity-forced climate change, whereas the CIE interval is marked by dominant obliquity forcing. These dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the Early Toarcian paleoclimate system that is directly linked to the global carbon cycle.

Trophic network models explain instability of Early Triassic terrestrial communities

PubMed Central

Roopnarine, Peter D; Angielczyk, Kenneth D; Wang, Steve C; Hertog, Rachel

2007-01-01

Studies of the end-Permian mass extinction have emphasized potential abiotic causes and their direct biotic effects. Less attention has been devoted to secondary extinctions resulting from ecological crises and the effect of community structure on such extinctions. Here we use a trophic network model that combines topological and dynamic approaches to simulate disruptions of primary productivity in palaeocommunities. We apply the model to Permian and Triassic communities of the Karoo Basin, South Africa, and show that while Permian communities bear no evidence of being especially susceptible to extinction, Early Triassic communities appear to have been inherently less stable. Much of the instability results from the faster post-extinction diversification of amphibian guilds relative to amniotes. The resulting communities differed fundamentally in structure from their Permian predecessors. Additionally, our results imply that changing community structures over time may explain long-term trends like declining rates of Phanerozoic background extinction PMID:17609191

Expansion or extinction: deterministic and stochastic two-patch models with Allee effects.

PubMed

Kang, Yun; Lanchier, Nicolas

2011-06-01

We investigate the impact of Allee effect and dispersal on the long-term evolution of a population in a patchy environment. Our main focus is on whether a population already established in one patch either successfully invades an adjacent empty patch or undergoes a global extinction. Our study is based on the combination of analytical and numerical results for both a deterministic two-patch model and a stochastic counterpart. The deterministic model has either two, three or four attractors. The existence of a regime with exactly three attractors only appears when patches have distinct Allee thresholds. In the presence of weak dispersal, the analysis of the deterministic model shows that a high-density and a low-density populations can coexist at equilibrium in nearby patches, whereas the analysis of the stochastic model indicates that this equilibrium is metastable, thus leading after a large random time to either a global expansion or a global extinction. Up to some critical dispersal, increasing the intensity of the interactions leads to an increase of both the basin of attraction of the global extinction and the basin of attraction of the global expansion. Above this threshold, for both the deterministic and the stochastic models, the patches tend to synchronize as the intensity of the dispersal increases. This results in either a global expansion or a global extinction. For the deterministic model, there are only two attractors, while the stochastic model no longer exhibits a metastable behavior. In the presence of strong dispersal, the limiting behavior is entirely determined by the value of the Allee thresholds as the global population size in the deterministic and the stochastic models evolves as dictated by their single-patch counterparts. For all values of the dispersal parameter, Allee effects promote global extinction in terms of an expansion of the basin of attraction of the extinction equilibrium for the deterministic model and an increase of the probability of extinction for the stochastic model.

Extinction, Reacquisition, and Rapid Forgetting of Eyeblink Conditioning in Developing Rats

ERIC Educational Resources Information Center

Brown, Kevin L.; Freeman, John H.

2014-01-01

Eyeblink conditioning is a well-established model for studying the developmental neurobiology of associative learning and memory. However, age differences in extinction and subsequent reacquisition have yet to be studied using this model. The present study examined extinction and reacquisition of eyeblink conditioning in developing rats. In…

Associative Accounts of Recovery-from-Extinction Effects

PubMed Central

McConnell, Bridget L.; Miller, Ralph R.

2014-01-01

Recovery-from-extinction effects (e.g., spontaneous recovery, renewal, reinstatement, and facilitated reacquisition) have become the focus of much research in recent years. However, despite a great deal of empirical data, there are few theoretical explanations for these effects. This paucity poses a severe limitation on our understanding of these behavioral effects, impedes advances in uncovering neural mechanisms of response recovery, and reduces our potential to prevent relapse after exposure therapy. Towards correcting this oversight, this review takes prominent models of associative learning that have been used in the past and continue to be used today to explain Pavlovian conditioning and extinction, and assesses how each model can be applied to account for recovery-from-extinction effects. The models include the Rescorla-Wagner (1972) model, Mackintosh's (1975) attentional model, Pearce and Hall's (1980) attentional model, Wagner's (1981) SOP model, Pearce's (1987) configural model, McLaren and Mackintosh's (2002) elemental model, and Stout and Miller's (2007) SOCR (comparator hypothesis) model. Each model is assessed for how well it explains or does not explain the various recovery-from-extinction phenomena. We offer some suggestions for how the models might be modified to account for these effects in those instances in which they initially fail. PMID:24707062

Atmospheric extinction in simulation tools for solar tower plants

NASA Astrophysics Data System (ADS)

Hanrieder, Natalie; Wilbert, Stefan; Schroedter-Homscheidt, Marion; Schnell, Franziska; Guevara, Diana Mancera; Buck, Reiner; Giuliano, Stefano; Pitz-Paal, Robert

2017-06-01

Atmospheric extinction causes significant radiation losses between the heliostat field and the receiver in a solar tower plants. These losses vary with site and time. State of the art is that in ray-tracing and plant optimization tools, atmospheric extinction is included by choosing between few constant standard atmospheric conditions. Even though some tools allow the consideration of site and time dependent extinction data, such data sets are nearly never available. This paper summarizes and compares the most common model equations implemented in several ray-tracing tools. There are already several methods developed and published to measure extinction on-site. An overview of the existing methods is also given here. Ray-tracing simulations of one exemplary tower plant at the Plataforma Solar de Almería (PSA) are presented to estimate the plant yield deviations between simulations using standard model equations instead of extinction time series. For PSA, the effect of atmospheric extinction accounts for losses between 1.6 and 7 %. This range is caused by considering overload dumping or not. Applying standard clear or hazy model equations instead of extinction time series lead to an underestimation of the annual plant yield at PSA. The discussion of the effect of extinction in tower plants has to include overload dumping. Situations in which overload dumping occurs are mostly connected to high radiation levels and low atmospheric extinction. Therefore it can be recommended that project developers should consider site and time dependent extinction data especially on hazy sites. A reduced uncertainty of the plant yield prediction can significantly reduce costs due to smaller risk margins for financing and EPCs. The generation of extinction data for several locations in form of representative yearly time series or geographical maps should be further elaborated.

Duration of and decoupling between carbon isotope excursions during the end-Triassic mass extinction and Central Atlantic Magmatic Province emplacement

NASA Astrophysics Data System (ADS)

Yager, Joyce A.; West, A. Joshua; Corsetti, Frank A.; Berelson, William M.; Rollins, Nick E.; Rosas, Silvia; Bottjer, David J.

2017-09-01

Changes in δ13Ccarb and δ13Corg from marine strata occur globally in association with the end-Triassic mass extinction and the emplacement of the Central Atlantic Magmatic Province (CAMP) during the break up of Pangea. As is typical in deep time, the timing and duration of these isotopic excursions has remained elusive, hampering attempts to link carbon cycle perturbations to specific processes. Here, we report δ13Ccarb and δ13Corg from Late Triassic and Early Jurassic strata near Levanto, Peru, where intercalated dated ash beds permit temporal calibration of the carbon isotope record. Both δ13Ccarb and δ13Corg exhibit a broad positive excursion through the latest Triassic into the earliest Jurassic. The first order positive excursion in δ13Corg is interrupted by a negative shift noted in many sections around the world coincident with the extinction horizon. Our data indicate that the negative excursion lasts 85 ± 25 kyrs, longer than inferred by previous studies based on cyclostratigraphy. A 260 ± 80 kyr positive δ13Corg shift follows, during which the first Jurassic ammonites appear. The overall excursion culminates in a return to pre-perturbation carbon isotopic values over the next 1090 ± 70 kyrs. Via chronologic, isotopic, and biostratigraphic correlation to other successions, we find that δ13Ccarb and δ13Corg return to pre-perturbation values as CAMP volcanism ceases and in association with the recovery of pelagic and benthic biota. However, the initiation of the carbon isotope excursion at Levanto predates the well-dated CAMP sills from North America, indicating that CAMP may have started earlier than thought based on these exposures, or that the onset of carbon cycle perturbations was not related to CAMP.

Unusual dynamics of extinction in a simple ecological model.

PubMed Central

Sinha, S; Parthasarathy, S

1996-01-01

Studies on natural populations and harvesting biological resources have led to the view, commonly held, that (i) populations exhibiting chaotic oscillations run a high risk of extinction; and (ii) a decrease in emigration/exploitation may reduce the risk of extinction. Here we describe a simple ecological model with emigration/depletion that shows behavior in contrast to this. This model displays unusual dynamics of extinction and survival, where populations growing beyond a critical rate can persist within a band of high depletion rates, whereas extinction occurs for lower depletion rates. Though prior to extinction at lower depletion rates the population exhibits chaotic dynamics with large amplitudes of variation and very low minima, at higher depletion rates the population persists at chaos but with reduced variation and increased minima. For still higher values, within the band of persistence, the dynamics show period reversal leading to stability. These results illustrate that chaos does not necessarily lead to population extinction. In addition, the persistence of populations at high depletion rates has important implications in the considerations of strategies for the management of biological resources. PMID:8643661

Direct and indirect effects of biological factors on extinction risk in fossil bivalves.

PubMed

Harnik, Paul G

2011-08-16

Biological factors, such as abundance and body size, may contribute directly to extinction risk and indirectly through their influence on other biological characteristics, such as geographic range size. Paleontological data can be used to explicitly test many of these hypothesized relationships, and general patterns revealed through analysis of the fossil record can help refine predictive models of extinction risk developed for extant species. Here, I use structural equation modeling to tease apart the contributions of three canonical predictors of extinction--abundance, body size, and geographic range size--to the duration of bivalve species in the early Cenozoic marine fossil record of the eastern United States. I find that geographic range size has a strong direct effect on extinction risk and that an apparent direct effect of abundance can be explained entirely by its covariation with geographic range. The influence of geographic range on extinction risk is manifest across three ecologically disparate bivalve clades. Body size also has strong direct effects on extinction risk but operates in opposing directions in different clades, and thus, it seems to be decoupled from extinction risk in bivalves as a whole. Although abundance does not directly predict extinction risk, I reveal weak indirect effects of both abundance and body size through their positive influence on geographic range size. Multivariate models that account for the pervasive covariation between biological factors and extinction are necessary for assessing causality in evolutionary processes and making informed predictions in applied conservation efforts.

Neighborhood and habitat effects on vital rates: expansion of the Barred Owl in the Oregon Coast Ranges

USGS Publications Warehouse

Yackulic, Charles B.; Reid, Janice; Davis, Raymond; Hines, James E.; Nichols, James D.; Forsman, Eric

2012-01-01

In this paper, we modify dynamic occupancy models developed for detection-nondetection data to allow for the dependence of local vital rates on neighborhood occupancy, where neighborhood is defined very flexibly. Such dependence of occupancy dynamics on the status of a relevant neighborhood is pervasive, yet frequently ignored. Our framework permits joint inference about the importance of neighborhood effects and habitat covariates in determining colonization and extinction rates. Our specific motivation is the recent expansion of the Barred Owl (Strix varia) in western Oregon, USA, over the period 1990-2010. Because the focal period was one of dramatic range expansion and local population increase, the use of models that incorporate regional occupancy (sources of colonists) as determinants of dynamic rate parameters is especially appropriate. We began our analysis of 21 years of Barred Owl presence/nondetection data in the Tyee Density Study Area (TDSA) by testing a suite of six models that varied only in the covariates included in the modeling of detection probability. We then tested whether models that used regional occupancy as a covariate for colonization and extinction outperformed models with constant or year-specific colonization or extinction rates. Finally we tested whether habitat covariates improved the AIC of our models, focusing on which habitat covariates performed best, and whether the signs of habitat effects are consistent with a priori hypotheses. We conclude that all covariates used to model detection probability lead to improved AIC, that regional occupancy influences colonization and extinction rates, and that habitat plays an important role in determining extinction and colonization rates. As occupancy increases from low levels toward equilibrium, colonization increases and extinction decreases, presumably because there are more and more dispersing juveniles. While both rates are affected, colonization increases more than extinction decreases. Colonization is higher and extinction is lower in survey polygons with more riparian forest. The effects of riparian forest on extinction rates are greater than on colonization rates. Model results have implications for management of the invading Barred Owl, both through habitat alteration and removal.

Preventing Return of Fear in an Animal Model of Anxiety: Additive Effects of Massive Extinction and Extinction in Multiple Contexts

PubMed Central

Laborda, Mario A.; Miller, Ralph R.

2013-01-01

Fear conditioning and experimental extinction have been presented as models of anxiety disorders and exposure therapy, respectively. Moreover, the return of fear serves as a model of relapse after exposure therapy. Here we present two experiments, with rats as subjects in a lick suppression preparation, in which we assessed the additive effects of two different treatments to attenuate the return of fear. First, we evaluated whether two phenomena known to generate return of fear (i.e., spontaneous recovery and renewal) summate to produce a stronger reappearance of extinguished fear. At test, rats evaluated outside the extinction context following a long delay after extinction (i.e., a delayed context shift) exhibited greater return of extinguished fear than rats evaluated outside the extinction context alone, but return of extinguished fear following a delayed context shift did not significantly differ from the return of fear elicited in rats tested following a long delay after extinction alone. Additionally, extinction in multiple contexts and a massive extinction treatment each attenuated the strong return of fear produced by a delayed context shift. Moreover, the conjoint action of these treatments was significantly more successful in preventing the reappearance of extinguished fear, suggesting that extensive cue exposure administered in several different therapeutic settings has the potential to reduce relapse after therapy for anxiety disorders, more than either manipulation alone. PMID:23611075

Toward a Last Interglacial Compilation Using a Tephra-based Chronology: a Future Reference For Model-data Comparison

NASA Astrophysics Data System (ADS)

Bazin, L.; Govin, A.; Capron, E.; Nomade, S.; Lemieux-Dudon, B.; Landais, A.

2017-12-01

The Last Interglacial (LIG, 129-116 ka) is a key period to decipher the interactions between the different components of the climate system under warmer-than-preindustrial conditions. Modelling the LIG climate is now part of the CMIP6/PMIP4 targeted simulations. As a result, recent efforts have been made to propose surface temperature compilations focusing on the spatio-temporal evolution of the LIG climate, and not only on its peak warmth as previously proposed. However, the major limitation of these compilations remains in the climatic alignment of records (e.g. temperature, foraminiferal δ18O) that is performed to define the sites' chronologies. Such methods prevent the proper discussion of phase relationship between the different sites. Thanks to recent developments of the Bayesian Datice dating tool, we are now able to build coherent multi-archive chronologies with a proper propagation of the associated uncertainties. We make the best use of common tephra layers identified in well-dated continental archives and marine sediment cores of the Mediterranean region to propose a coherent chronological framework for the LIG independent of any climatic assumption. We then extend this precise chronological context to the North Atlantic as a first step toward a global coherent compilation of surface temperature and stable isotope records. Based on this synthesis, we propose guidelines for the interpretation of different proxies measured from different archives that will be compared with climate model parameters. Finally, we present time-slices (e.g. 127 ka) of the preliminary regional synthesis of temperature reconstructions and stable isotopes to serve as reference for future model-data comparison of the up-coming CMIP6/PMIP4 LIG simulations.

A model of onshore-offshore change in faunal diversity

NASA Technical Reports Server (NTRS)

Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

1991-01-01

Onshore-offshore patterns of faunal change occurred at many taxonomic scales during the Paleozoic Era, ranging from replacement of the Cambrian evolutionary fauna by the Paleozoic fauna to the environmental expansion of many orders and classes. A simple mathematical model is constructed to investigate such change. The environmental gradient across the marine shelf-slope is treated as a linear array of discrete habitats, each of which holds a set number of species, as observed in the fossil record. During any interval of time, some portion of the species in each habitat becomes extinct by background processes, with rates of extinction varying among both clades and habitats, as also observed in the record. After extinction, species are replaced from within the habitat and from immediately adjacent habitats, with proportions dependent on surviving species. This model leads to the prediction that extinction-resistant clades will always diversify at the expense of extinction-prone clades. But if extinction intensity is highest in nearshore habitats, extinction-resistant clades will expand preferentially in the onshore direction, build up diversity there, and then diversify outward toward the offshore. Thus, onshore-offshore patterns of diversification may be the expectation for faunal change quite independently of whether or not clades originate onshore. When the model is parameterized for Paleozoic trilobites and brachiopods, numerical solutions exhibit both a pattern of faunal change and a time span for diversification similar to that seen in the fossil record. They also generate structure similar to that seen in global diversification, including logistic patterns of growth, declining origination but constant extinction within clades through time, and declining overall extinction across clades through time.

The wavelength dependent model of extinction in fog and haze for free space optical communication.

PubMed

Grabner, Martin; Kvicera, Vaclav

2011-02-14

The wavelength dependence of the extinction coefficient in fog and haze is investigated using Mie single scattering theory. It is shown that the effective radius of drop size distribution determines the slope of the log-log dependence of the extinction on wavelengths in the interval between 0.2 and 2 microns. The relation between the atmospheric visibility and the effective radius is derived from the empirical relationship of liquid water content and extinction. Based on these results, the model of the relationship between visibility and the extinction coefficient with different effective radii for fog and for haze conditions is proposed.

Conservation Risks: When Will Rhinos be Extinct?

PubMed

Haas, Timothy C; Ferreira, Sam M

2016-08-01

We develop a risk intelligence system for biodiversity enterprises. Such enterprises depend on a supply of endangered species for their revenue. Many of these enterprises, however, cannot purchase a supply of this resource and are largely unable to secure the resource against theft in the form of poaching. Because replacements are not available once a species becomes extinct, insurance products are not available to reduce the risk exposure of these enterprises to an extinction event. For many species, the dynamics of anthropogenic impacts driven by economic as well as noneconomic values of associated wildlife products along with their ecological stressors can help meaningfully predict extinction risks. We develop an agent/individual-based economic-ecological model that captures these effects and apply it to the case of South African rhinos. Our model uses observed rhino dynamics and poaching statistics. It seeks to predict rhino extinction under the present scenario. This scenario has no legal horn trade, but allows live African rhino trade and legal hunting. Present rhino populations are small and threatened by a rising onslaught of poaching. This present scenario and associated dynamics predicts continued decline in rhino population size with accelerated extinction risks of rhinos by 2036. Our model supports the computation of extinction risks at any future time point. This capability can be used to evaluate the effectiveness of proposed conservation strategies at reducing a species' extinction risk. Models used to compute risk predictions, however, need to be statistically estimated. We point out that statistically fitting such models to observations will involve massive numbers of observations on consumer behavior and time-stamped location observations on thousands of animals. Finally, we propose Big Data algorithms to perform such estimates and to interpret the fitted model's output.

Parameterization of the Extinction Coefficient in Ice and Mixed-Phase Arctic Clouds during the ISDAC Field Campaign

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

Korolev, A; Shashkov, A; Barker, H

This report documents the history of attempts to directly measure cloud extinction, the current measurement device known as the Cloud Extinction Probe (CEP), specific problems with direct measurement of extinction coefficient, and the attempts made here to address these problems. Extinction coefficient is one of the fundamental microphysical parameters characterizing bulk properties of clouds. Knowledge of extinction coefficient is of crucial importance for radiative transfer calculations in weather prediction and climate models given that Earth's radiation budget (ERB) is modulated much by clouds. In order for a large-scale model to properly account for ERB and perturbations to it, it mustmore » ultimately be able to simulate cloud extinction coefficient well. In turn this requires adequate and simultaneous simulation of profiles of cloud water content and particle habit and size. Similarly, remote inference of cloud properties requires assumptions to be made about cloud phase and associated single-scattering properties, of which extinction coefficient is crucial. Hence, extinction coefficient plays an important role in both application and validation of methods for remote inference of cloud properties from data obtained from both satellite and surface sensors (e.g., Barker et al. 2008). While estimation of extinction coefficient within large-scale models is relatively straightforward for pure water droplets, thanks to Mie theory, mixed-phase and ice clouds still present problems. This is because of the myriad forms and sizes that crystals can achieve, each having their own unique extinction properties. For the foreseeable future, large-scale models will have to be content with diagnostic parametrization of crystal size and type. However, before they are able to provide satisfactory values needed for calculation of radiative transfer, they require the intermediate step of assigning single-scattering properties to particles. The most basic of these is extinction coefficient, yet it is rarely measured directly, and therefore verification of parametrizations is difficult. The obvious solution is to be able to measure microphysical properties and extinction at the same time and for the same volume. This is best done by in situ sampling by instruments mounted on either balloon or aircraft. The latter is the usual route and the one employed here. Yet the problem of actually measuring extinction coefficient directly for arbitrarily complicated particles still remains unsolved.« less

Network-level reproduction number and extinction threshold for vector-borne diseases.

PubMed

Xue, Ling; Scoglio, Caterina

2015-06-01

The basic reproduction number of deterministic models is an essential quantity to predict whether an epidemic will spread or not. Thresholds for disease extinction contribute crucial knowledge of disease control, elimination, and mitigation of infectious diseases. Relationships between basic reproduction numbers of two deterministic network-based ordinary differential equation vector-host models, and extinction thresholds of corresponding stochastic continuous-time Markov chain models are derived under some assumptions. Numerical simulation results for malaria and Rift Valley fever transmission on heterogeneous networks are in agreement with analytical results without any assumptions, reinforcing that the relationships may always exist and proposing a mathematical problem for proving existence of the relationships in general. Moreover, numerical simulations show that the basic reproduction number does not monotonically increase or decrease with the extinction threshold. Consistent trends of extinction probability observed through numerical simulations provide novel insights into mitigation strategies to increase the disease extinction probability. Research findings may improve understandings of thresholds for disease persistence in order to control vector-borne diseases.

Chronology and ancient feeding ecology of two upper Pleistocene megamammals from the Brazilian Intertropical Region

NASA Astrophysics Data System (ADS)

de Melo França, Lucas; Trindade Dantas, Mário André; Bocchiglieri, Adriana; Cherckinsky, Alexander; de Souza Ribeiro, Adauto; Bocherens, Hervé

2014-09-01

In Brazilian Intertropical Region (BIR) fossil remains of the giant ground sloth Eremotherium laurillardi (Lund, 1842) and of the proboscidean Notiomastodon platensis (Ameghino, 1888) are the most abundant among megaherbivores. However, the paleoecology of both species needs to be better understood to enlighten why these species disappear in the end of the Pleistocene, an issue that is still debated. During the last decades, the carbon and oxygen stable isotopes have been increasingly being used to obtain paleoecological information about extinct animals, although this information is in most cases dissociated from chronological data. Thus, the main objective of this study is to contribute to the knowledge about feeding ecology and chronology of E. laurillardi and N. platensis within BIR. For each fossil sample we performed stable isotopes analyses (δ13C/δ18O) and radiocarbon dating (14C with AMS). The results showed that N. platensis occurred between 12,125 and 19,594 cal yr BP and exhibited a grazer diet (δ13C = -1.1‰-1.3‰), while E. laurillardi lived between 11,084 and 27,690 cal yr BP, with a mixed feeder diet (C3/C4 plants; values ratio δ13C = -7.7‰ to -3.3‰). The δ18O values of N. platensis ranged between 2.20‰ and 3.60‰, while the values of E. laurillardi ranged between -3.10‰ and -1.10‰. Neither species did exhibit differences in its diet through time, which suggests that the vegetational composition of this locality did not vary in the late Pleistocene. Both species were living in an open environment, rich in herbaceous plants (C4 plants) and with tree and shrub with disjoint distribution, maybe similar to some parts of recent Caatinga, where they have partitioned the spatial and feeding niches.

Erosion of lizard diversity by climate change and altered thermal niches.

PubMed

Sinervo, Barry; Méndez-de-la-Cruz, Fausto; Miles, Donald B; Heulin, Benoit; Bastiaans, Elizabeth; Villagrán-Santa Cruz, Maricela; Lara-Resendiz, Rafael; Martínez-Méndez, Norberto; Calderón-Espinosa, Martha Lucía; Meza-Lázaro, Rubi Nelsi; Gadsden, Héctor; Avila, Luciano Javier; Morando, Mariana; De la Riva, Ignacio J; Victoriano Sepulveda, Pedro; Rocha, Carlos Frederico Duarte; Ibargüengoytía, Nora; Aguilar Puntriano, César; Massot, Manuel; Lepetz, Virginie; Oksanen, Tuula A; Chapple, David G; Bauer, Aaron M; Branch, William R; Clobert, Jean; Sites, Jack W

2010-05-14

It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.

Towards a better preclinical model of PTSD: characterizing animals with weak extinction, maladaptive stress responses and low plasma corticosterone.

PubMed

Reznikov, Roman; Diwan, Mustansir; Nobrega, José N; Hamani, Clement

2015-02-01

Most of the available preclinical models of PTSD have focused on isolated behavioural aspects and have not considered individual variations in response to stress. We employed behavioural criteria to identify and characterize a subpopulation of rats that present several features analogous to PTSD-like states after exposure to classical fear conditioning. Outbred Sprague-Dawley rats were segregated into weak- and strong-extinction groups on the basis of behavioural scores during extinction of conditioned fear responses. Animals were subsequently tested for anxiety-like behaviour in the open-field test (OFT), novelty suppressed feeding (NSF) and elevated plus maze (EPM). Baseline plasma corticosterone was measured prior to any behavioural manipulation. In a second experiment, rats underwent OFT, NSF and EPM prior to being subjected to fear conditioning to ascertain whether or not pre-stress levels of anxiety-like behaviours could predict extinction scores. We found that 25% of rats exhibit low extinction rates of conditioned fear, a feature that was associated with increased anxiety-like behaviour across multiple tests in comparison to rats showing strong extinction. In addition, weak-extinction animals showed low levels of corticosterone prior to fear conditioning, a variable that seemed to predict extinction recall scores. In a separate experiment, anxiety measures taken prior to fear conditioning were not predictive of a weak-extinction phenotype, suggesting that weak-extinction animals do not show detectable traits of anxiety in the absence of a stressful experience. These findings suggest that extinction impairment may be used to identify stress-vulnerable rats, thus providing a useful model for elucidating mechanisms and investigating potential treatments for PTSD. Copyright © 2014 Elsevier Ltd. All rights reserved.

Acoustic Model Testing Chronology

NASA Technical Reports Server (NTRS)

Nesman, Tom

2017-01-01

Scale models have been used for decades to replicate liftoff environments and in particular acoustics for launch vehicles. It is assumed, and analyses supports, that the key characteristics of noise generation, propagation, and measurement can be scaled. Over time significant insight was gained not just towards understanding the effects of thruster details, pad geometry, and sound mitigation but also to the physical processes involved. An overview of a selected set of scale model tests are compiled here to illustrate the variety of configurations that have been tested and the fundamental knowledge gained. The selected scale model tests are presented chronologically.

MODELING GALACTIC EXTINCTION WITH DUST AND 'REAL' POLYCYCLIC AROMATIC HYDROCARBONS

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

Mulas, Giacomo; Casu, Silvia; Cecchi-Pestellini, Cesare

We investigate the remarkable apparent variety of galactic extinction curves by modeling extinction profiles with core-mantle grains and a collection of single polycyclic aromatic hydrocarbons. Our aim is to translate a synthetic description of dust into physically well-grounded building blocks through the analysis of a statistically relevant sample of different extinction curves. All different flavors of observed extinction curves, ranging from the average galactic extinction curve to virtually 'bumpless' profiles, can be described by the present model. We prove that a mixture of a relatively small number (54 species in 4 charge states each) of polycyclic aromatic hydrocarbons can reproducemore » the features of the extinction curve in the ultraviolet, dismissing an old objection to the contribution of polycyclic aromatic hydrocarbons to the interstellar extinction curve. Despite the large number of free parameters (at most the 54 Multiplication-Sign 4 column densities of each species in each ionization state included in the molecular ensemble plus the 9 parameters defining the physical properties of classical particles), we can strongly constrain some physically relevant properties such as the total number of C atoms in all species and the mean charge of the mixture. Such properties are found to be largely independent of the adopted dust model whose variation provides effects that are orthogonal to those brought about by the molecular component. Finally, the fitting procedure, together with some physical sense, suggests (but does not require) the presence of an additional component of chemically different very small carbonaceous grains.« less

Proxy system modeling of tree-ring isotope chronologies over the Common Era

NASA Astrophysics Data System (ADS)

Anchukaitis, K. J.; LeGrande, A. N.

2017-12-01

The Asian monsoon can be characterized in terms of both precipitation variability and atmospheric circulation across a range of spatial and temporal scales. While multicentury time series of tree-ring widths at hundreds of sites across Asia provide estimates of past rainfall, the oxygen isotope ratios of annual rings may reveal broader regional hydroclimate and atmosphere-ocean dynamics. Tree-ring oxygen isotope chronologies from Monsoon Asia have been interpreted to reflect a local 'amount effect', relative humidity, source water and seasonality, and winter snowfall. Here, we use an isotope-enabled general circulation model simulation from the NASA Goddard Institute for Space Science (GISS) Model E and a proxy system model of the oxygen isotope composition of tree-ring cellulose to interpret the large-scale and local climate controls on δ 18O chronologies. Broad-scale dominant signals are associated with a suite of covarying hydroclimate variables including growing season rainfall amounts, relative humidity, and vapor pressure deficit. Temperature and source water influences are region-dependent, as are the simulated tree-ring isotope signals associated with the El Nino Southern Oscillation (ENSO) and large-scale indices of the Asian monsoon circulation. At some locations, including southern coastal Viet Nam, local precipitation isotope ratios and the resulting simulated δ 18O tree-ring chronologies reflect upstream rainfall amounts and atmospheric circulation associated with monsoon strength and wind anomalies.

Hormonal Regulation of Extinction: Implications for Gender Differences in the Mechanisms of PTSD

DTIC Science & Technology

2010-03-01

Unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT This project investigates the role of gonadal hormones in the regulation of Pavlovian fear conditioning ...and its extinction. Pavlovian fear conditioning and its extinction serve as an animal model for the development of pathological fear in humans that...gonadal hormones in the regulation of Pavlovian fear conditioning and its extinction. Pavlovian fear conditioning and its extinction serve as an animal

Neural correlates of appetitive extinction in humans

PubMed Central

Tapia León, Isabell; Stark, Rudolf; Klucken, Tim

2017-01-01

Abstract Appetitive extinction receives attention as an important model for the treatment of psychiatric disorders. However, in humans, its underlying neural correlates remain unknown. To close this gap, we investigated appetitive acquisition and extinction with fMRI in a 2-day monetary incentive delay paradigm. During appetitive conditioning, one stimulus (CS+) was paired with monetary reward, while another stimulus (CS−) was never rewarded. Twenty-four hours later, subjects underwent extinction, in which neither CS was reinforced. Appetitive conditioning elicited stronger skin conductance responses to the CS+ as compared with the CS−. Regarding subjective ratings, the CS+ was rated more pleasant and arousing than the CS− after conditioning. Furthermore, fMRI-results (CS+ − CS−) showed activation of the reward circuitry including amygdala, midbrain and striatal areas. During extinction, conditioned responses were successfully extinguished. In the early phase of extinction, we found a significant activation of the caudate, the hippocampus, the dorsal and ventral anterior cingulate cortex (dACC and vACC). In the late phase, we found significant activation of the nucleus accumbens (NAcc) and the amygdala. Correlational analyses with subjective ratings linked extinction success to the vACC and the NAcc, while associating the dACC with reduced extinction. The results reveal neural correlates of appetitive extinction in humans and extend assumptions from models for human extinction learning. PMID:27803289

Dynamics of an eco-epidemiological model with saturated incidence rate

NASA Astrophysics Data System (ADS)

Suryanto, Agus

2017-03-01

In this paper we study the effect of prey infection on the modified Leslie-Gower predator-prey model with saturated incidence rate. The model will be analyzed dynamically to find the equilibria and their existence conditions as well as their local stability conditions. It is found that there are six type of equilibria, namely the extinction of both prey and predator point, the extinction of infective prey and predator point, the extinction of predator point, the extinction of prey point, the extinction of infective prey point and the interior point. The first four equilibrium points are always unstable, while the last two equilibria are conditionally stable. We also find that the system undergoes Hopf bifurcation around the interior point which is controlled by the rate of infection. To illustrate our analytical results, we show some numerical results.

Cross-correlation enhanced stability in a tumor cell growth model with immune surveillance driven by cross-correlated noises

NASA Astrophysics Data System (ADS)

Zeng, Chunhua; Zhou, Xiaofeng; Tao, Shufen

2009-12-01

The transient properties of a tumor cell growth model with immune surveillance driven by cross-correlated multiplicative and additive noises are investigated. The explicit expression of extinction rate from the state of a stable tumor to the state of extinction is obtained. Based on the numerical computations, we find the following: (i) the intensity of multiplicative noise D and the intensity of additive noise α enhance the extinction rate for the case of λ <= 0 (i.e. λ denotes cross-correlation intensity between two noises), but for the case of λ > 0, a critical noise intensity D or α exists at which the extinction rate is the smallest; D and α at first weaken the extinction rate and then enhance it. (ii) The immune rate β and the cross-correlation intensity λ play opposite roles on the extinction rate, i.e. β enhances the extinction rate of the tumor cell, while λ weakens the extinction rate of the tumor cell. Namely, the immune rate can enhance the extinction of the tumor cell and the cross-correlation between two noises can enhance stability of the cancer state.

Testing principle working mechanisms of the health action process approach for subjective physical age groups.

PubMed

Wienert, Julian; Kuhlmann, Tim; Fink, Sebastian; Hambrecht, Rainer; Lippke, Sonia

2016-01-01

This study investigated differences in social-cognitive predictors and self-regulatory planning, as proposed by the health action process approach (HAPA), across three different subjective physical age groups for physical activity. With a cross-sectional design, 521 participants across the chronological age span from 25 to 86 years (M = 48.79; SD = 12.66) were separated into three groups: those who feel physically younger than they are in terms of chronological age, the same perceived and chronological age, and feeling physically older compared to their chronological age. Participants were assessed regarding their perceived vulnerability, outcome expectancies, general intentions, planning, self-efficacy, and stages of physical activity (non-intenders, intenders, and actors). Data were analysed via mean comparison and multigroup structural equation modelling. Mean differences for all but one construct were eminent in all groups, generally showing that those feeling physically younger also report better social-cognitive predictors of physical activity (e.g. lower perceived vulnerability) in comparison to those who feel the same age or older. The model showed that basic working mechanisms of the HAPA can be applied to all groups. With that, the results provide for the first time evidence that principle working mechanism of the HAPA can be applied to all subjective physical age groups. These may be used to tailor health promoting interventions according to participants' needs as a more suitable proxy than chronological age.

The dendroclimatic proxies from the northern Quebec taiga in the PAGES 2K network: recent advances and future developments.

NASA Astrophysics Data System (ADS)

Gennaretti, Fabio; Naulier, Maud; Arseneault, Dominique; Savard, Martine; Bégin, Christian; Boucher, Etienne; Bégin, Yves; Guiot, Joël

2016-04-01

Northeastern North America was historically underrepresented in the network of climate proxies used for climate reconstructions over the last two millennia. Indeed, in North America most high-resolution climate proxies are long tree-ring chronologies but, in Northeastern North America, these chronologies are highly challenging due to short tree longevity, high frequency and severity of wildfires and remoteness of many areas. Here, we will present the efforts accomplished during the last decade by our team in developing millennial-long tree-ring chronologies in the northern Quebec taiga. We sampled black spruce [Picea mariana (Mill.) B.S.P] subfossil tree remains naturally fallen in the littoral zone of six lakes to build six site-specific ring-width chronologies as well as two chronologies of stable isotope ratios (δ18O and δ13C in tree-ring cellulose). These chronologies, which are now included in the PAGES 2K network, were independently used to reconstruct summer temperature variations showing a well-expressed Medieval Climate Anomaly and the impact of volcanic and solar forcings at regional scale. We will also discuss non-climatic influences on these chronologies (i.e. wildfires and sampling height inconsistency), as well as the ongoing effort to extend the reconstructions in time to cover the last 2500 years. Finally, a new European funded project called MAIDEN-SPRUCE will be introduced. Within MAIDEN-SPRUCE, we will use a data-model approach to improve our understanding of the links between forests and climate over the last millennium. More specifically, we will adapt the process-based ecophysiological model MAIDENiso to investigate factors influencing the growth and underlying biogeochemical processes of black spruce. One of our objectives is to provide the first multi-proxy (ring widths and δ18O and δ13C in tree-ring cellulose) regional climate reconstruction in Eastern North America over the last millennium taking into account mechanistic rules, including nonlinear or threshold relationships.

Stress-enhanced fear learning in rats is resistant to the effects of immediate massed extinction

PubMed Central

Long, Virginia A.; Fanselow, Michael S.

2014-01-01

Enhanced fear learning occurs subsequent to traumatic or stressful events and is a persistent challenge to the treatment of post-traumatic stress disorder (PTSD). Facilitation of learning produced by prior stress can elicit an exaggerated fear response to a minimally aversive event or stimulus. Stress-enhanced fear learning (SEFL) is a rat model of PTSD; rats previously exposed to the SEFL 15 electrical shocks procedure exhibit several behavioral responses similar to those seen in patients with PTSD. However, past reports found that SEFL is not mitigated by extinction (a model of exposure therapy) when the spaced extinction began 24 h after stress. Recent studies found that extinction from 10 min to 1 h subsequent to fear conditioning “erased” learning, whereas later extinction, occurring from 24 to 72 h after conditioning did not. Other studies indicate that massed extinction is more effective than spaced procedures. Therefore, we examined the time-dependent nature of extinction on the stress-induced enhancement of fear learning using a massed trial’s procedure. Experimental rats received 15 foot shocks and were given either no extinction or massed extinction 10 min or 72 h later. Our present data indicate that SEFL, following traumatic stress, is resistant to immediate massed extinction. Experimental rats showed exaggerated new fear learning regardless of when extinction training occurred. Thus, post-traumatic reactivity such as SEFL does not seem responsive to extinction treatments. PMID:22176467

THE IMPACT OF ACCURATE EXTINCTION MEASUREMENTS FOR X-RAY SPECTRAL MODELS

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

Smith, Randall K.; Valencic, Lynne A.; Corrales, Lia, E-mail: lynne.a.valencic@nasa.gov

Interstellar extinction includes both absorption and scattering of photons from interstellar gas and dust grains, and it has the effect of altering a source's spectrum and its total observed intensity. However, while multiple absorption models exist, there are no useful scattering models in standard X-ray spectrum fitting tools, such as XSPEC. Nonetheless, X-ray halos, created by scattering from dust grains, are detected around even moderately absorbed sources, and the impact on an observed source spectrum can be significant, if modest, compared to direct absorption. By convolving the scattering cross section with dust models, we have created a spectral model asmore » a function of energy, type of dust, and extraction region that can be used with models of direct absorption. This will ensure that the extinction model is consistent and enable direct connections to be made between a source's X-ray spectral fits and its UV/optical extinction.« less

Modeling Selection and Extinction Mechanisms of Biological Systems

NASA Astrophysics Data System (ADS)

Amirjanov, Adil

In this paper, the behavior of a genetic algorithm is modeled to enhance its applicability as a modeling tool of biological systems. A new description model for selection mechanism is introduced which operates on a portion of individuals of population. The extinction and recolonization mechanism is modeled, and solving the dynamics analytically shows that the genetic drift in the population with extinction/recolonization is doubled. The mathematical analysis of the interaction between selection and extinction/recolonization processes is carried out to assess the dynamics of motion of the macroscopic statistical properties of population. Computer simulations confirm that the theoretical predictions of described models are in good approximations. A mathematical model of GA dynamics was also examined, which describes the anti-predator vigilance in an animal group with respect to a known analytical solution of the problem, and showed a good agreement between them to find the evolutionarily stable strategies.

Selecting for extinction: nonrandom disease-associated extinction homogenizes amphibian biotas.

PubMed

Smith, Kevin G; Lips, Karen R; Chase, Jonathan M

2009-10-01

Studying the patterns in which local extinctions occur is critical to understanding how extinctions affect biodiversity at local, regional and global spatial scales. To understand the importance of patterns of extinction at a regional spatial scale, we use data from extirpations associated with a widespread pathogenic agent of amphibian decline, Batrachochytrium dendrobatidis (Bd) as a model system. We apply novel null model analyses to these data to determine whether recent extirpations associated with Bd have resulted in selective extinction and homogenization of diverse tropical American amphibian biotas. We find that Bd-associated extinctions in this region were nonrandom and disproportionately, but not exclusively, affected low-occupancy and endemic species, resulting in homogenization of the remnant amphibian fauna. The pattern of extirpations also resulted in phylogenetic homogenization at the family level and ecological homogenization of reproductive mode and habitat association. Additionally, many more species were extirpated from the region than would be expected if extirpations occurred randomly. Our results indicate that amphibian declines in this region are an extinction filter, reducing regional amphibian biodiversity to highly similar relict assemblages and ultimately causing amplified biodiversity loss at regional and global scales.

Extinction of drug- and withdrawal-paired cues in animal models: relevance to the treatment of addiction.

PubMed

Myers, Karyn M; Carlezon, William A

2010-11-01

Conditioned drug craving and withdrawal elicited by cues paired with drug use or acute withdrawal are among the many factors contributing to compulsive drug taking. Understanding how to stop these cues from having these effects is a major goal of addiction research. Extinction is a form of learning in which associations between cues and the events they predict are weakened by exposure to the cues in the absence of those events. Evidence from animal models suggests that conditioned responses to drug cues can be extinguished, although the degree to which this occurs in humans is controversial. Investigations into the neurobiological substrates of extinction of conditioned drug craving and withdrawal may facilitate the successful use of drug cue extinction within clinical contexts. While this work is still in the early stages, there are indications that extinction of drug- and withdrawal-paired cues shares neural mechanisms with extinction of conditioned fear. Using the fear extinction literature as a template, it is possible to organize the observations on drug cue extinction into a cohesive framework. Copyright © 2010 Elsevier Ltd. All rights reserved.

Predicting the process of extinction in experimental microcosms and accounting for interspecific interactions in single-species time series

PubMed Central

Ferguson, Jake M; Ponciano, José M

2014-01-01

Predicting population extinction risk is a fundamental application of ecological theory to the practice of conservation biology. Here, we compared the prediction performance of a wide array of stochastic, population dynamics models against direct observations of the extinction process from an extensive experimental data set. By varying a series of biological and statistical assumptions in the proposed models, we were able to identify the assumptions that affected predictions about population extinction. We also show how certain autocorrelation structures can emerge due to interspecific interactions, and that accounting for the stochastic effect of these interactions can improve predictions of the extinction process. We conclude that it is possible to account for the stochastic effects of community interactions on extinction when using single-species time series. PMID:24304946

Inhibiting corticosterone synthesis during fear memory formation exacerbates cued fear extinction memory deficits within the single prolonged stress model.

PubMed

Keller, Samantha M; Schreiber, William B; Stanfield, Briana R; Knox, Dayan

2015-01-01

Using the single prolonged stress (SPS) animal model of post-traumatic stress disorder (PTSD), previous studies suggest that enhanced glucocorticoid receptor (GR) expression leads to cued fear extinction retention deficits. However, it is unknown how the endogenous ligand of GRs, corticosterone (CORT), may contribute to extinction retention deficits in the SPS model. Given that CORT synthesis during fear learning is critical for fear memory consolidation and SPS enhances GR expression, CORT synthesis during fear memory formation could strengthen fear memory in SPS rats by enhancing GR activation during fear learning. In turn, this could lead to cued fear extinction retention deficits. We tested the hypothesis that CORT synthesis during fear learning leads to cued fear extinction retention deficits in SPS rats by administering the CORT synthesis inhibitor metyrapone to SPS and control rats prior to fear conditioning, and observed the effect this had on extinction memory. Inhibiting CORT synthesis during fear memory formation in control rats tended to decrease cued freezing, though this effect never reached statistical significance. Contrary to our hypothesis, inhibiting CORT synthesis during fear memory formation disrupted extinction retention in SPS rats. This finding suggests that even though SPS exposure leads to cued fear extinction memory deficits, CORT synthesis during fear memory formation enhances extinction retention in SPS rats. This suggests that stress-induced CORT synthesis in previously stressed rats can be beneficial. Copyright © 2015 Elsevier B.V. All rights reserved.

Direct and indirect effects of biological factors on extinction risk in fossil bivalves

PubMed Central

Harnik, Paul G.

2011-01-01

Biological factors, such as abundance and body size, may contribute directly to extinction risk and indirectly through their influence on other biological characteristics, such as geographic range size. Paleontological data can be used to explicitly test many of these hypothesized relationships, and general patterns revealed through analysis of the fossil record can help refine predictive models of extinction risk developed for extant species. Here, I use structural equation modeling to tease apart the contributions of three canonical predictors of extinction—abundance, body size, and geographic range size—to the duration of bivalve species in the early Cenozoic marine fossil record of the eastern United States. I find that geographic range size has a strong direct effect on extinction risk and that an apparent direct effect of abundance can be explained entirely by its covariation with geographic range. The influence of geographic range on extinction risk is manifest across three ecologically disparate bivalve clades. Body size also has strong direct effects on extinction risk but operates in opposing directions in different clades, and thus, it seems to be decoupled from extinction risk in bivalves as a whole. Although abundance does not directly predict extinction risk, I reveal weak indirect effects of both abundance and body size through their positive influence on geographic range size. Multivariate models that account for the pervasive covariation between biological factors and extinction are necessary for assessing causality in evolutionary processes and making informed predictions in applied conservation efforts. PMID:21808004

Dating the End of the Greek Bronze Age: A Robust Radiocarbon-Based Chronology from Assiros Toumba

PubMed Central

Wardle, Kenneth; Higham, Thomas; Kromer, Bernd

2014-01-01

Over 60 recent analyses of animal bones, plant remains, and building timbers from Assiros in northern Greece form an unique series from the 14th to the 10th century BC. With the exception of Thera, the number of 14C determinations from other Late Bronze Age sites in Greece has been small and their contribution to chronologies minimal. The absolute dates determined for Assiros through Bayesian modelling are both consistent and unexpected, since they are systematically earlier than the conventional chronologies of southern Greece by between 70 and 100 years. They have not been skewed by reference to assumed historical dates used as priors. They support high rather than low Iron Age chronologies from Spain to Israel where the merits of each are fiercely debated but remain unresolved. PMID:25222862

Fluctuations in epidemic modeling - disease extinction and control

NASA Astrophysics Data System (ADS)

Schwartz, Ira

2009-03-01

The analysis of infectious disease fluctuations has recently seen an increasing rise in the use of new tools and models from stochastic dynamics and statistical physics. Examples arise in modeling fluctuations of multi-strain diseases, in modeling adaptive social behavior and its impact on disease fluctuations, and in the analysis of disease extinction in finite population models. Proper stochastic model reduction [1] allows one to predict unobserved fluctuations from observed data in multi-strain models [2]. Degree alteration and power law behavior is predicted in adaptive network epidemic models [3,4]. And extinction rates derived from large fluctuation theory exhibit scaling with respect to distance to the bifurcation point of disease onset with an unusual exponent [5]. In addition to outbreak prediction, another main goal of epidemic modeling is one of eliminating the disease to extinction through various control mechanisms, such as vaccine implementation or quarantine. In this talk, a description will be presented of the fluctuational behavior of several epidemic models and their extinction rates. A general framework and analysis of the effect of non-Gaussian control actuations which enhance the rate to disease extinction will be described. In particular, in it is shown that even in the presence of a small Poisson distributed vaccination program, there is an exponentially enhanced rate to disease extinction. These ideas may lead to improved methods of controlling disease where random vaccinations are prevalent. [4pt] Recent papers:[0pt] [1] E. Forgoston and I. B. Schwartz, ``Escape Rates in a Stochastic Environment with Multiple Scales,'' arXiv:0809.1345 2008.[0pt] [2] L. B. Shaw, L. Billings, I. B. Schwartz, ``Using dimension reduction to improve outbreak predictability of multi-strain diseases,'' J. Math. Bio. 55, 1 2007.[0pt] [3] L. B. Shaw and I. B. Schwartz, ``Fluctuating epidemics on adaptive networks,'' Physical Review E 77, 066101 2008.[0pt] [4] L. B. Shaw and I. B. Schwartz, ``Noise induced dynamics in adaptivenetworks with applications to epidemiology,'' arXiv:0807.3455 2008.[0pt] [5] M. I. Dykman, I. B. Schwartz, A. S. Landsman, ``Disease Extinction in the Presence of Random Vaccination,'' Phys. Rev. Letts. 101, 078101 2008.

Optimal control of predator-prey mathematical model with infection and harvesting on prey

NASA Astrophysics Data System (ADS)

Diva Amalia, R. U.; Fatmawati; Windarto; Khusnul Arif, Didik

2018-03-01

This paper presents a predator-prey mathematical model with infection and harvesting on prey. The infection and harvesting only occur on the prey population and it assumed that the prey infection would not infect predator population. We analysed the mathematical model of predator-prey with infection and harvesting in prey. Optimal control, which is a prevention of the prey infection, also applied in the model and denoted as U. The purpose of the control is to increase the susceptible prey. The analytical result showed that the model has five equilibriums, namely the extinction equilibrium (E 0), the infection free and predator extinction equilibrium (E 1), the infection free equilibrium (E 2), the predator extinction equilibrium (E 3), and the coexistence equilibrium (E 4). The extinction equilibrium (E 0) is not stable. The infection free and predator extinction equilibrium (E 1), the infection free equilibrium (E 2), also the predator extinction equilibrium (E 3), are locally asymptotically stable with some certain conditions. The coexistence equilibrium (E 4) tends to be locally asymptotically stable. Afterwards, by using the Maximum Pontryagin Principle, we obtained the existence of optimal control U. From numerical simulation, we can conclude that the control could increase the population of susceptible prey and decrease the infected prey.

Climate modelling of mass-extinction events: a review

NASA Astrophysics Data System (ADS)

Feulner, Georg

2009-07-01

Despite tremendous interest in the topic and decades of research, the origins of the major losses of biodiversity in the history of life on Earth remain elusive. A variety of possible causes for these mass-extinction events have been investigated, including impacts of asteroids or comets, large-scale volcanic eruptions, effects from changes in the distribution of continents caused by plate tectonics, and biological factors, to name but a few. Many of these suggested drivers involve or indeed require changes of Earth's climate, which then affect the biosphere of our planet, causing a global reduction in the diversity of biological species. It can be argued, therefore, that a detailed understanding of these climatic variations and their effects on ecosystems are prerequisites for a solution to the enigma of biological extinctions. Apart from investigations of the paleoclimate data of the time periods of mass extinctions, climate-modelling experiments should be able to shed some light on these dramatic events. Somewhat surprisingly, however, only a few comprehensive modelling studies of the climate changes associated with extinction events have been undertaken. These studies will be reviewed in this paper. Furthermore, the role of modelling in extinction research in general and suggestions for future research are discussed.

Quantitative and qualitative approaches to identifying migration chronology in a continental migrant

USGS Publications Warehouse

Beatty, William S.; Kesler, Dylan C.; Webb, Elisabeth B.; Raedeke, Andrew H.; Naylor, Luke W.; Humburg, Dale D.

2013-01-01

The degree to which extrinsic factors influence migration chronology in North American waterfowl has not been quantified, particularly for dabbling ducks. Previous studies have examined waterfowl migration using various methods, however, quantitative approaches to define avian migration chronology over broad spatio-temporal scales are limited, and the implications for using different approaches have not been assessed. We used movement data from 19 female adult mallards (Anas platyrhynchos) equipped with solar-powered global positioning system satellite transmitters to evaluate two individual level approaches for quantifying migration chronology. The first approach defined migration based on individual movements among geopolitical boundaries (state, provincial, international), whereas the second method modeled net displacement as a function of time using nonlinear models. Differences in migration chronologies identified by each of the approaches were examined with analysis of variance. The geopolitical method identified mean autumn migration midpoints at 15 November 2010 and 13 November 2011, whereas the net displacement method identified midpoints at 15 November 2010 and 14 November 2011. The mean midpoints for spring migration were 3 April 2011 and 20 March 2012 using the geopolitical method and 31 March 2011 and 22 March 2012 using the net displacement method. The duration, initiation date, midpoint, and termination date for both autumn and spring migration did not differ between the two individual level approaches. Although we did not detect differences in migration parameters between the different approaches, the net displacement metric offers broad potential to address questions in movement ecology for migrating species. Ultimately, an objective definition of migration chronology will allow researchers to obtain a comprehensive understanding of the extrinsic factors that drive migration at the individual and population levels. As a result, targeted conservation plans can be developed to support planning for habitat management and evaluation of long-term climate effects.

Quantitative and qualitative approaches to identifying migration chronology in a continental migrant.

PubMed

Beatty, William S; Kesler, Dylan C; Webb, Elisabeth B; Raedeke, Andrew H; Naylor, Luke W; Humburg, Dale D

2013-01-01

The degree to which extrinsic factors influence migration chronology in North American waterfowl has not been quantified, particularly for dabbling ducks. Previous studies have examined waterfowl migration using various methods, however, quantitative approaches to define avian migration chronology over broad spatio-temporal scales are limited, and the implications for using different approaches have not been assessed. We used movement data from 19 female adult mallards (Anas platyrhynchos) equipped with solar-powered global positioning system satellite transmitters to evaluate two individual level approaches for quantifying migration chronology. The first approach defined migration based on individual movements among geopolitical boundaries (state, provincial, international), whereas the second method modeled net displacement as a function of time using nonlinear models. Differences in migration chronologies identified by each of the approaches were examined with analysis of variance. The geopolitical method identified mean autumn migration midpoints at 15 November 2010 and 13 November 2011, whereas the net displacement method identified midpoints at 15 November 2010 and 14 November 2011. The mean midpoints for spring migration were 3 April 2011 and 20 March 2012 using the geopolitical method and 31 March 2011 and 22 March 2012 using the net displacement method. The duration, initiation date, midpoint, and termination date for both autumn and spring migration did not differ between the two individual level approaches. Although we did not detect differences in migration parameters between the different approaches, the net displacement metric offers broad potential to address questions in movement ecology for migrating species. Ultimately, an objective definition of migration chronology will allow researchers to obtain a comprehensive understanding of the extrinsic factors that drive migration at the individual and population levels. As a result, targeted conservation plans can be developed to support planning for habitat management and evaluation of long-term climate effects.

High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling

NASA Astrophysics Data System (ADS)

Bendle, Jacob M.; Palmer, Adrian P.; Thorndycraft, Varyl R.; Matthews, Ian P.

2017-12-01

Glaciolacustrine varves offer the potential to construct continuous, annually-resolved chronologies for ice-sheet deglaciation, and improved understanding of glacier retreat dynamics. This paper investigates laminated glaciolacustrine sediments deposited around the waning margins of the Patagonian Ice Sheet, following the local Last Glacial Maximum (LGM). Detailed macro- and microfacies analyses confirm an annual (varve) structure within these sediments. The correlation of annual layers (varves) across five sites in eastern Lago Buenos Aires yields a 994 ± 36 varve-year (vyr) chronology and thickness record. The floating chronology has been anchored to the calendar-year timescale through identification of the Ho tephra (17,378 ± 118 cal a BP) in the varve sequences. Using a Bayesian age model to integrate the new varve chronology with published moraine ages, the onset of deglaciation at 46.5°S is dated to 18,086 ± 214 cal a BP. New age estimates for deglacial events are combined with high-resolution analysis of varve thickness trends, and new lithostratigraphic data on ice-margin position(s), to reconstruct ice-margin retreat rates for the earliest ca. 1000 years of ice-sheet demise. Glacier retreat rates were moderate (5.3-10.3 m yr-1) until 17,322 ± 115 cal a BP, but subsequently accelerated (15.4-18.0 m yr-1). Sustained influxes of ice-rafted debris (IRD) after 17,145 ± 122 cal a BP suggest retreat rates were enhanced by calving after ice contracted into deeper lake waters. Ice persisted in eastern Lago Buenos Aires until at least 16,934 ± 116 cal a BP, after which the glacier started to retreat towards the Patagonian mountains.

Persistence and extinction of a stochastic single-species model under regime switching in a polluted environment II.

PubMed

Liu, Meng; Wang, Ke

2010-12-07

This is a continuation of our paper [Liu, M., Wang, K., 2010. Persistence and extinction of a stochastic single-species model under regime switching in a polluted environment, J. Theor. Biol. 264, 934-944]. Taking both white noise and colored noise into account, a stochastic single-species model under regime switching in a polluted environment is studied. Sufficient conditions for extinction, stochastic nonpersistence in the mean, stochastic weak persistence and stochastic permanence are established. The threshold between stochastic weak persistence and extinction is obtained. The results show that a different type of noise has a different effect on the survival results. Copyright © 2010 Elsevier Ltd. All rights reserved.

A New Chronology of Late Quaternary Sequences From the Central Arctic Ocean Based on "Extinction Ages" of Their Excesses in 231Pa and 230Th

NASA Astrophysics Data System (ADS)

Hillaire-Marcel, C.; Ghaleb, B.; de Vernal, A.; Maccali, J.; Cuny, K.; Jacobel, A.; Le Duc, C.; McManus, J.

2017-12-01

Merging the late Quaternary Arctic paleoceanography into the Earth's global climate history remains challenging due to the lack of robust marine chronostratigraphies. Over ridges notably, low and variable sedimentation rates, scarce biogenic remains ensuing from low productivity and/or poor preservation, and oxygen isotope and paleomagnetic records differing from global stacks represent major impediments. However, as illustrate here based on consistent records from Mendeleev-Alpha and Lomonosov Ridges, disequilibria between U-series isotopes can provide benchmark ages. In such settings, fluxes of the particle-reactive U-daughter isotopes 230Th and 231Pa from the water column, are not unequivocally linked to sedimentation rates, but rather to sea-ice rafting and brine production histories, thus to the development of sea-ice factories over shelves during intervals of high relative sea level. The excesses in 230Th and 231Pa over fractions supported by their parent U-isotopes, collapse down sedimentary sequences, due to radioactive decay, and provide radiometric benchmark ages of approximately 300 and 140 ka, respectively. These "extinction ages" point to mean sedimentation rates of ˜4.3 and ˜1.7 mm/ka, respectively, over the Lomonosov and Mendeleev Ridges, which are significantly lower than assumed in most recent studies, thus highlighting the need for revisiting current interpretations of Arctic lithostratigraphies in relation to the global-scale late Quaternary climatostratigraphy.

Population viability analysis for endangered Roanoke logperch

USGS Publications Warehouse

Roberts, James H.; Angermeier, Paul; Anderson, Gregory B.

2016-01-01

A common strategy for recovering endangered species is ensuring that populations exceed the minimum viable population size (MVP), a demographic benchmark that theoretically ensures low long-term extinction risk. One method of establishing MVP is population viability analysis, a modeling technique that simulates population trajectories and forecasts extinction risk based on a series of biological, environmental, and management assumptions. Such models also help identify key uncertainties that have a large influence on extinction risk. We used stochastic count-based simulation models to explore extinction risk, MVP, and the possible benefits of alternative management strategies in populations of Roanoke logperch Percina rex, an endangered stream fish. Estimates of extinction risk were sensitive to the assumed population growth rate and model type, carrying capacity, and catastrophe regime (frequency and severity of anthropogenic fish kills), whereas demographic augmentation did little to reduce extinction risk. Under density-dependent growth, the estimated MVP for Roanoke logperch ranged from 200 to 4200 individuals, depending on the assumed severity of catastrophes. Thus, depending on the MVP threshold, anywhere from two to all five of the logperch populations we assessed were projected to be viable. Despite this uncertainty, these results help identify populations with the greatest relative extinction risk, as well as management strategies that might reduce this risk the most, such as increasing carrying capacity and reducing fish kills. Better estimates of population growth parameters and catastrophe regimes would facilitate the refinement of MVP and extinction-risk estimates, and they should be a high priority for future research on Roanoke logperch and other imperiled stream-fish species.

Effects of vagus nerve stimulation on extinction of conditioned fear and post-traumatic stress disorder symptoms in rats.

PubMed

Noble, L J; Gonzalez, I J; Meruva, V B; Callahan, K A; Belfort, B D; Ramanathan, K R; Meyers, E; Kilgard, M P; Rennaker, R L; McIntyre, C K

2017-08-22

Exposure-based therapies help patients with post-traumatic stress disorder (PTSD) to extinguish conditioned fear of trauma reminders. However, controlled laboratory studies indicate that PTSD patients do not extinguish conditioned fear as well as healthy controls, and exposure therapy has high failure and dropout rates. The present study examined whether vagus nerve stimulation (VNS) augments extinction of conditioned fear and attenuates PTSD-like symptoms in an animal model of PTSD. To model PTSD, rats were subjected to a single prolonged stress (SPS) protocol, which consisted of restraint, forced swim, loss of consciousness, and 1 week of social isolation. Like PTSD patients, rats subjected to SPS show impaired extinction of conditioned fear. The SPS procedure was followed, 1 week later, by auditory fear conditioning (AFC) and extinction. VNS or sham stimulation was administered during half of the extinction days, and was paired with presentations of the conditioned stimulus. One week after completion of extinction training, rats were given a battery of behavioral tests to assess anxiety, arousal and avoidance. Results indicated that rats given SPS 1 week prior to AFC (PTSD model) failed to extinguish the freezing response after eleven consecutive days of extinction. Administration of VNS reversed the extinction impairment and attenuated reinstatement of the conditioned fear response. Delivery of VNS during extinction also eliminated the PTSD-like symptoms, such as anxiety, hyperarousal and social avoidance for more than 1 week after VNS treatment. These results provide evidence that extinction paired with VNS treatment can lead to remission of fear and improvements in PTSD-like symptoms. Taken together, these findings suggest that VNS may be an effective adjunct to exposure therapy for the treatment of PTSD.

Predicting the process of extinction in experimental microcosms and accounting for interspecific interactions in single-species time series.

PubMed

Ferguson, Jake M; Ponciano, José M

2014-02-01

Predicting population extinction risk is a fundamental application of ecological theory to the practice of conservation biology. Here, we compared the prediction performance of a wide array of stochastic, population dynamics models against direct observations of the extinction process from an extensive experimental data set. By varying a series of biological and statistical assumptions in the proposed models, we were able to identify the assumptions that affected predictions about population extinction. We also show how certain autocorrelation structures can emerge due to interspecific interactions, and that accounting for the stochastic effect of these interactions can improve predictions of the extinction process. We conclude that it is possible to account for the stochastic effects of community interactions on extinction when using single-species time series. © 2013 The Authors. Ecology Letters published by John Wiley & Sons Ltd and CNRS.

Neural correlates of appetitive extinction in humans.

PubMed

Kruse, Onno; Tapia León, Isabell; Stark, Rudolf; Klucken, Tim

2017-01-01

Appetitive extinction receives attention as an important model for the treatment of psychiatric disorders. However, in humans, its underlying neural correlates remain unknown. To close this gap, we investigated appetitive acquisition and extinction with fMRI in a 2-day monetary incentive delay paradigm. During appetitive conditioning, one stimulus (CS+) was paired with monetary reward, while another stimulus (CS-) was never rewarded. Twenty-four hours later, subjects underwent extinction, in which neither CS was reinforced. Appetitive conditioning elicited stronger skin conductance responses to the CS+ as compared with the CS-. Regarding subjective ratings, the CS+ was rated more pleasant and arousing than the CS- after conditioning. Furthermore, fMRI-results (CS+ - CS-) showed activation of the reward circuitry including amygdala, midbrain and striatal areas. During extinction, conditioned responses were successfully extinguished. In the early phase of extinction, we found a significant activation of the caudate, the hippocampus, the dorsal and ventral anterior cingulate cortex (dACC and vACC). In the late phase, we found significant activation of the nucleus accumbens (NAcc) and the amygdala. Correlational analyses with subjective ratings linked extinction success to the vACC and the NAcc, while associating the dACC with reduced extinction. The results reveal neural correlates of appetitive extinction in humans and extend assumptions from models for human extinction learning. © The Author (2016). Published by Oxford University Press.

Reduced expression of conditioned fear in the R6/2 mouse model of Huntington’s disease is related to abnormal activity in prelimbic cortex

PubMed Central

Walker, Adam G.; Ummel, Jason R.; Rebec, George V.

2011-01-01

Prefrontal cortex (PFC) dysfunction is common in patients with Huntington’s disease (HD), a dominantly inherited neurological disorder, and has been linked to cognitive disruption. We previously reported alterations in neuronal firing patterns recorded from PFC of the R6/2 mouse model of HD. To determine if PFC dysfunction results in behavioral impairments, we evaluated performance of wild-type (WT) and R6/2 mice in a fear conditioning and extinction behavioral task. Fear conditioning and extinction retrieval were similar in both genotypes, but R6/2s exhibited less fear during extinction by freezing less than WTs. A fear reinstatement test after extinction retrieval indicated that faster extinction was not due to poor memory for conditioning. During initial extinction and extinction retrieval training, neuronal activity was recorded from prelimbic (PL) cortex, a subregion of PFC known to be important for fear expression. In WTs, a large number of neurons were activated by the conditioned stimulus during initial extinction and this activation was significantly impaired in R6/2s. Notably, there was no genotype difference in PFC activity during extinction retrieval. Thus, altered extinction is likely a result of reduced fear expression due to impairments in PL activation. Collectively, our results suggest that PFC dysfunction may play a key role in R6/2 cognitive impairments. PMID:21515374

Modeling Population Growth and Extinction

ERIC Educational Resources Information Center

Gordon, Sheldon P.

2009-01-01

The exponential growth model and the logistic model typically introduced in the mathematics curriculum presume that a population grows exclusively. In reality, species can also die out and more sophisticated models that take the possibility of extinction into account are needed. In this article, two extensions of the logistic model are considered,…

High-precision timeline for Earth’s most severe extinction

PubMed Central

Burgess, Seth D.; Bowring, Samuel; Shen, Shu-zhong

2014-01-01

The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms. PMID:24516148

High-precision timeline for Earth's most severe extinction.

PubMed

Burgess, Seth D; Bowring, Samuel; Shen, Shu-zhong

2014-03-04

The end-Permian mass extinction was the most severe loss of marine and terrestrial biota in the last 542 My. Understanding its cause and the controls on extinction/recovery dynamics depends on an accurate and precise age model. U-Pb zircon dates for five volcanic ash beds from the Global Stratotype Section and Point for the Permian-Triassic boundary at Meishan, China, define an age model for the extinction and allow exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales. The extinction occurred between 251.941 ± 0.037 and 251.880 ± 0.031 Mya, an interval of 60 ± 48 ka. Onset of a major reorganization of the carbon cycle immediately precedes the initiation of extinction and is punctuated by a sharp (3‰), short-lived negative spike in the isotopic composition of carbonate carbon. Carbon cycle volatility persists for ∼500 ka before a return to near preextinction values. Decamillenial to millennial level resolution of the mass extinction and its aftermath will permit a refined evaluation of the relative roles of rate-dependent processes contributing to the extinction, allowing insight into postextinction ecosystem expansion, and establish an accurate time point for evaluating the plausibility of trigger and kill mechanisms.

A MIS 15-MIS 12 record of environmental changes and Lower Palaeolithic occupation from Valle Giumentina, central Italy

NASA Astrophysics Data System (ADS)

Villa, Valentina; Pereira, Alison; Chaussé, Christine; Nomade, Sébastien; Giaccio, Biagio; Limondin-Lozouet, Nicole; Fusco, Fabio; Regattieri, Eleonora; Degeai, Jean-Philippe; Robert, Vincent; Kuzucuoglu, Catherine; Boschian, Giovanni; Agostini, Silvano; Aureli, Daniele; Pagli, Marina; Bahain, Jean Jacques; Nicoud, Elisa

2016-11-01

An integrated geological study, including sedimentology, stable isotope analysis (δ18O, δ13C), geochemistry, micromorphology, biomarker analysis, 40Ar/39Ar geochronology and tephrochronology, was undertaken on the Quaternary infill of the Valle Giumentina basin in Central Italy, which also includes an outstanding archaeological succession, composed of nine human occupation levels ascribed to the Lower and Middle Palaeolithic. 40Ar/39Ar dating, and other palaeoenvironmental and tephrochronological data, constrain the sedimentary history of the whole succession to the MIS 15-MIS 12 interval, between 618 ± 13 ka and 456 ± 2 ka. Palaeoenvironmental proxies suggest that over this time interval of about 150 ka, sedimentary and pedogenic processes were mainly influenced by climatic changes, in particular by the pulsing of local mountain glaciers of the Majella massif. Specifically, the Valle Giumentina succession records glacio-fluvial and lacustrine sedimentation during the colder glacial periods and pedogenesis and/or alluvial sedimentation during the warmer interglacial and/or interstadial periods. During this interval, tectonics played a negligible role as a driving factor of local morphogenesis and sedimentation, whereas the general regional uplift experienced in the Middle Pleistocene led to capture of the basin and its definitive extinction after MIS 12. These data substantially improve previous knowledge of the chronology and sedimentary evolution of the succession, providing for the first time, a well constrained chronological and palaeoenvironmental framework for the archaeological and human palaeoecological record of Valle Giumentina.

Approximate Bayesian estimation of extinction rate in the Finnish Daphnia magna metapopulation.

PubMed

Robinson, John D; Hall, David W; Wares, John P

2013-05-01

Approximate Bayesian computation (ABC) is useful for parameterizing complex models in population genetics. In this study, ABC was applied to simultaneously estimate parameter values for a model of metapopulation coalescence and test two alternatives to a strict metapopulation model in the well-studied network of Daphnia magna populations in Finland. The models shared four free parameters: the subpopulation genetic diversity (θS), the rate of gene flow among patches (4Nm), the founding population size (N0) and the metapopulation extinction rate (e) but differed in the distribution of extinction rates across habitat patches in the system. The three models had either a constant extinction rate in all populations (strict metapopulation), one population that was protected from local extinction (i.e. a persistent source), or habitat-specific extinction rates drawn from a distribution with specified mean and variance. Our model selection analysis favoured the model including a persistent source population over the two alternative models. Of the closest 750,000 data sets in Euclidean space, 78% were simulated under the persistent source model (estimated posterior probability = 0.769). This fraction increased to more than 85% when only the closest 150,000 data sets were considered (estimated posterior probability = 0.774). Approximate Bayesian computation was then used to estimate parameter values that might produce the observed set of summary statistics. Our analysis provided posterior distributions for e that included the point estimate obtained from previous data from the Finnish D. magna metapopulation. Our results support the use of ABC and population genetic data for testing the strict metapopulation model and parameterizing complex models of demography. © 2013 Blackwell Publishing Ltd.

Dynamics Analysis of Anti-predator Model on Intermediate Predator With Ratio Dependent Functional Responses

NASA Astrophysics Data System (ADS)

Savitri, D.

2018-01-01

This articel discusses a predator prey model with anti-predator on intermediate predator using ratio dependent functional responses. Dynamical analysis performed on the model includes determination of equilibrium point, stability and simulation. Three kinds of equilibrium points have been discussed, namely the extinction of prey point, the extinction of intermediate predator point and the extinction of predator point are exists under certain conditions. It can be shown that the result of numerical simulations are in accordance with analitical results

Ancient Egyptian chronology and the astronomical orientation of pyramids.

PubMed

Spence, K

2000-11-16

The ancient Egyptian pyramids at Giza have never been accurately dated, although we know that they were built approximately around the middle of the third millennium BC. The chronologies of this period have been reconstructed from surviving lists of kings and the lengths of their reigns, but the lists are rare, seldom complete and contain known inconsistencies and errors. As a result, the existing chronologies for that period (the Old Kingdom) can be considered accurate only to about +/-100 years, a figure that radiocarbon dating cannot at present improve. Here I use trends in the orientation of Old Kingdom pyramids to demonstrate that the Egyptians aligned them to north by using the simultaneous transit of two circumpolar stars. Modelling the precession of these stars yields a date for the start of construction of the Great Pyramid that is accurate to +/-5 yr, thereby providing an anchor for the Old Kingdom chronologies.

Ancient Egyptian chronology and the astronomical orientation of pyramids

NASA Astrophysics Data System (ADS)

Spence, Kate

2000-11-01

The ancient Egyptian pyramids at Giza have never been accurately dated, although we know that they were built approximately around the middle of the third millennium BC. The chronologies of this period have been reconstructed from surviving lists of kings and the lengths of their reigns, but the lists are rare, seldom complete and contain known inconsistencies and errors. As a result, the existing chronologies for that period (the Old Kingdom) can be considered accurate only to about +/-100 years, a figure that radiocarbon dating cannot at present improve. Here I use trends in the orientation of Old Kingdom pyramids to demonstrate that the Egyptians aligned them to north by using the simultaneous transit of two circumpolar stars. Modelling the precession of these stars yields a date for the start of construction of the Great Pyramid that is accurate to +/-5 yr, thereby providing an anchor for the Old Kingdom chronologies.

Detecting Hidden Diversification Shifts in Models of Trait-Dependent Speciation and Extinction.

PubMed

Beaulieu, Jeremy M; O'Meara, Brian C

2016-07-01

The distribution of diversity can vary considerably from clade to clade. Attempts to understand these patterns often employ state-dependent speciation and extinction models to determine whether the evolution of a particular novel trait has increased speciation rates and/or decreased extinction rates. It is still unclear, however, whether these models are uncovering important drivers of diversification, or whether they are simply pointing to more complex patterns involving many unmeasured and co-distributed factors. Here we describe an extension to the popular state-dependent speciation and extinction models that specifically accounts for the presence of unmeasured factors that could impact diversification rates estimated for the states of any observed trait, addressing at least one major criticism of BiSSE (Binary State Speciation and Extinction) methods. Specifically, our model, which we refer to as HiSSE (Hidden State Speciation and Extinction), assumes that related to each observed state in the model are "hidden" states that exhibit potentially distinct diversification dynamics and transition rates than the observed states in isolation. We also demonstrate how our model can be used as character-independent diversification models that allow for a complex diversification process that is independent of the evolution of a character. Under rigorous simulation tests and when applied to empirical data, we find that HiSSE performs reasonably well, and can at least detect net diversification rate differences between observed and hidden states and detect when diversification rate differences do not correlate with the observed states. We discuss the remaining issues with state-dependent speciation and extinction models in general, and the important ways in which HiSSE provides a more nuanced understanding of trait-dependent diversification. © The Author(s) 2016. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Dust models post-Planck: constraining the far-infrared opacity of dust in the diffuse interstellar medium

NASA Astrophysics Data System (ADS)

Fanciullo, L.; Guillet, V.; Aniano, G.; Jones, A. P.; Ysard, N.; Miville-Deschênes, M.-A.; Boulanger, F.; Köhler, M.

2015-08-01

Aims: We compare the performance of several dust models in reproducing the dust spectral energy distribution (SED) per unit extinction in the diffuse interstellar medium (ISM). We use our results to constrain the variability of the optical properties of big grains in the diffuse ISM, as published by the Planck collaboration. Methods: We use two different techniques to compare the predictions of dust models to data from the Planck HFI, IRAS, and SDSS surveys. First, we fit the far-infrared emission spectrum to recover the dust extinction and the intensity of the interstellar radiation field (ISRF). Second, we infer the ISRF intensity from the total power emitted by dust per unit extinction, and then predict the emission spectrum. In both cases, we test the ability of the models to reproduce dust emission and extinction at the same time. Results: We identify two issues. Not all models can reproduce the average dust emission per unit extinction: there are differences of up to a factor ~2 between models, and the best accord between model and observation is obtained with the more emissive grains derived from recent laboratory data on silicates and amorphous carbons. All models fail to reproduce the variations in the emission per unit extinction if the only variable parameter is the ISRF intensity: this confirms that the optical properties of dust are indeed variable in the diffuse ISM. Conclusions: Diffuse ISM observations are consistent with a scenario where both ISRF intensity and dust optical properties vary. The ratio of the far-infrared opacity to the V band extinction cross-section presents variations of the order of ~20% (40-50% in extreme cases), while ISRF intensity varies by ~30% (~60% in extreme cases). This must be accounted for in future modelling. Appendices are available in electronic form at http://www.aanda.org

Fossil Liposcelididae and the lice ages (Insecta: Psocodea)

PubMed Central

Grimaldi, David; Engel, Michael S

2005-01-01

Fossilized, winged adults belonging to the psocopteran family Liposcelididae are reported in amber from the mid-Cretaceous (ca 100 Myr) of Myanmar (described as Cretoscelis burmitica, gen. et sp. n.) and the Miocene (ca 20 Myr) of the Dominican Republic (Belaphopsocus dominicus sp. n.). Cretoscelis is an extinct sister group to all other Liposcelididae and the family is the free-living sister group to the true lice (order Phthiraptera, all of which are ectoparasites of birds and mammals). A phylogenetic hypothesis of relationships among genera of Liposcelididae, including fossils, reveals perfect correspondence between the chronology of fossils and cladistic rank of taxa. Lice and Liposcelididae minimally diverged 100 Myr, perhaps even in the earliest Cretaceous 145 Myr or earlier, in which case the hosts of lice would have been early mammals, early birds and possibly other feathered theropod dinosaurs, as well as haired pterosaurs. PMID:16537135

Quantifying bamboo coral growth rate nonlinearity with the radiocarbon bomb spike: A new model for paleoceanographic chronology development

NASA Astrophysics Data System (ADS)

Frenkel, M. M.; LaVigne, M.; Miller, H. R.; Hill, T. M.; McNichol, A.; Gaylord, M. Lardie

2017-07-01

Bamboo corals, long-lived cold water gorgonin octocorals, offer unique paleoceanographic archives of the intermediate ocean. These Isididae corals are characterized by alternating gorgonin nodes and high Mg-calcite internodes, which synchronously extend radially. Bamboo coral calcite internodes have been utilized to obtain geochemical proxy data, however, growth rate uncertainty has made it difficult to construct precise chronologies for these corals. Previous studies have relied upon a single tie point from records of the anthropogenic Δ14C bomb spike preserved in the gorgonin nodes of live-collected corals to calculate a mean radial extension rate for the outer 50 years of skeletal growth. Bamboo coral chronologies are typically constructed by applying this mean extension rate to the entire coral record, assuming constant radial extension with coral age. In this study, we aim to test this underlying assumption by analyzing the organic nodes of six California margin bamboo corals at high enough resolution (<0.5 mm) to identify the Δ14C bomb spike, including two tie points at 1957 and 1970, plus the coral collection date (2007.5) for four samples. Radial extension rates between tie points ranged from 10 to 204 μm/year, with a decrease in growth rate evident between the 1957-1970 and 1970-2007.5 periods for all four corals. A negative correlation between growth rate and coral radius (r =-0.7; p=0.04) was determined for multiple bamboo coral taxa and individuals from the California margin, demonstrating a decline in radial extension rate with specimen age and size. To provide a mechanistic basis for these observations, a simple mathematical model was developed based on the assumption of a constant increase in circular cross sectional area with time to quantify this decline in radial extension rate with coral size between chronological tie points. Applying the area-based model to our Δ14C bomb spike time series from individual corals improves chronology accuracy for all live-collected corals with complete Δ14C bomb spikes. Hence, this study provides paleoceanographers utilizing bamboo corals with a method for reducing age model uncertainty within the anthropogenic bomb spike era ( 1957-present). Chronological uncertainty is larger for the earliest portion of coral growth, particularly for skeleton precipitated prior to bomb spike tie points, meaning age estimations for samples living before 1957 remain uncertain. Combining this technique with additional chronological markers could improve age models for an entire bamboo coral. Finally, the relative consistency in growth rate in similarly-aged corals of the same depth and location supports the hypothesis that skeletal growth may be limited by local environmental conditions.

Early Extinction after Fear Conditioning Yields a Context-Independent and Short-Term Suppression of Conditional Freezing in Rats

ERIC Educational Resources Information Center

Chang, Chun-hui; Maren, Stephen

2009-01-01

Extinction of Pavlovian fear conditioning in rats is a useful model for therapeutic interventions in humans with anxiety disorders. Recently, we found that delivering extinction trials soon (15 min) after fear conditioning yields a short-term suppression of fear, but little long-term extinction. Here, we explored the possible mechanisms underlying…

The extinction differential induced virulence macroevolution

NASA Astrophysics Data System (ADS)

Zhang, Feng; Xu, Liufang; Wang, Jin

2014-04-01

We apply the potential-flux landscape theory to deal with the large fluctuation induced extinction phenomena. We quantify the most probable extinction pathway on the landscape and measure the extinction risk by the landscape topography. In this Letter, we investigate the disease extinction through an epidemic model described by a set of chemical reaction. We found the virulence-differential-dependent symbioses between mother and daughter pathogen species: mutualism and parasitism. The symbioses, whether mutualism or parasitism, benefit the higher virulence species. This implies that speciation towards lower virulence is an effective strategy for a pathogen species to reduce its extinction risk.

Stochastic modeling of unsteady extinction in turbulent non-premixed combustion

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

Lackmann, T.; Hewson, J. C.; Knaus, R. C.

Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. Furthermore, the magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve.

Stochastic modeling of unsteady extinction in turbulent non-premixed combustion

DOE PAGES

Lackmann, T.; Hewson, J. C.; Knaus, R. C.; ...

2016-07-19

Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. Furthermore, the magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve.

Axial cervical vertebrae-based multivariate regression model for the estimation of skeletal-maturation status.

PubMed

Yang, Y-M; Lee, J; Kim, Y-I; Cho, B-H; Park, S-B

2014-08-01

This study aimed to determine the viability of using axial cervical vertebrae (ACV) as biological indicators of skeletal maturation and to build models that estimate ossification level with improved explanatory power over models based only on chronological age. The study population comprised 74 female and 47 male patients with available hand-wrist radiographs and cone-beam computed tomography images. Generalized Procrustes analysis was used to analyze the shape, size, and form of the ACV regions of interest. The variabilities of these factors were analyzed by principal component analysis. Skeletal maturation was then estimated using a multiple regression model. Separate models were developed for male and female participants. For the female estimation model, the adjusted R(2) explained 84.8% of the variability of the Sempé maturation level (SML), representing a 7.9% increase in SML explanatory power over that using chronological age alone (76.9%). For the male estimation model, the adjusted R(2) was over 90%, representing a 1.7% increase relative to the reference model. The simplest possible ACV morphometric information provided a statistically significant explanation of the portion of skeletal-maturation variability not dependent on chronological age. These results verify that ACV is a strong biological indicator of ossification status. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, Frédéric; Bazin, Lucie; Capron, Emilie; Landais, Amaëlle; Lemieux-Dudon, Bénédicte; Masson-Delmotte, Valérie

2016-04-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age scale uncertainty are essential to interpret the climate and environmental records that they contain. It is however a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and air dated horizons, ice and air depth intervals with known durations, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 chronology for 4 Antarctic ice cores and 1 Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono is demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as gas intervals with known durations and observations as mixed ice-air stratigraphic links. IceChrono1 is freely available under the GPL v3 open source license.

IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, F.; Bazin, L.; Capron, E.; Landais, A.; Lemieux-Dudon, B.; Masson-Delmotte, V.

2015-05-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, depth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice-air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.

Does fear extinction in the laboratory predict outcomes of exposure therapy? A treatment analog study.

PubMed

Forcadell, Eduard; Torrents-Rodas, David; Vervliet, Bram; Leiva, David; Tortella-Feliu, Miquel; Fullana, Miquel A

2017-11-01

Fear extinction models have a key role in our understanding of anxiety disorders and their treatment with exposure therapy. Here, we tested whether individual differences in fear extinction learning and fear extinction recall in the laboratory were associated with the outcomes of an exposure therapy analog (ETA). Fifty adults with fear of spiders participated in a two-day fear-learning paradigm assessing fear extinction learning and fear extinction recall, and then underwent a brief ETA. Correlational analyses indicated that enhanced extinction learning was associated with better ETA outcome. Our results partially support the idea that individual differences in fear extinction learning may be associated with exposure therapy outcome, but suggest that further research in this area is needed. Copyright © 2017 Elsevier B.V. All rights reserved.

Persistence and extinction of an n-species mutualism model with random perturbations in a polluted environment

NASA Astrophysics Data System (ADS)

He, Xin; Shan, Meijing; Liu, Meng

2018-02-01

An n-species stochastic Lotka-Volterra cooperative model in a polluted environment is proposed and studied. For each species, sufficient conditions for extinction, non-persistence in the mean and weak persistence in the mean are established. The threshold between weak persistence in the mean and extinction is obtained. Several numerical figures are also worked out to validate the theoretical results.

A stochastic model for the probability of malaria extinction by mass drug administration.

PubMed

Pemberton-Ross, Peter; Chitnis, Nakul; Pothin, Emilie; Smith, Thomas A

2017-09-18

Mass drug administration (MDA) has been proposed as an intervention to achieve local extinction of malaria. Although its effect on the reproduction number is short lived, extinction may subsequently occur in a small population due to stochastic fluctuations. This paper examines how the probability of stochastic extinction depends on population size, MDA coverage and the reproduction number under control, R c . A simple compartmental model is developed which is used to compute the probability of extinction using probability generating functions. The expected time to extinction in small populations after MDA for various scenarios in this model is calculated analytically. The results indicate that mass drug administration (Firstly, R c must be sustained at R c  < 1.2 to avoid the rapid re-establishment of infections in the population. Secondly, the MDA must produce effective cure rates of >95% to have a non-negligible probability of successful elimination. Stochastic fluctuations only significantly affect the probability of extinction in populations of about 1000 individuals or less. The expected time to extinction via stochastic fluctuation is less than 10 years only in populations less than about 150 individuals. Clustering of secondary infections and of MDA distribution both contribute positively to the potential probability of success, indicating that MDA would most effectively be administered at the household level. There are very limited circumstances in which MDA will lead to local malaria elimination with a substantial probability.

Real fuel effects on flame extinction and re-ignition

NASA Astrophysics Data System (ADS)

Zhao, Xinyu; Wu, Bifen; Xu, Chao; Lu, Tianfeng; Chen, Jacqueline H.

2016-11-01

Flame-vortex interactions have significant implications in studying combustion in practical aeronautical engines, and can be used to facilitate the model development in capturing local extinction and re-ignition. To study the interactions between the complex fuel and the intense turbulence that are commonly encountered in engines, direct numerical simulations of the interactions between a flame and a vortex pair are carried out using a recently-developed 24-species reduced chemistry for n-dodecane. Both non-premixed and premixed flames with different initial and inlet thermochemical conditions are studied. Parametric studies of different vortex strengths and orientations are carried out to induce maximum local extinction and re-ignition. Chemical-explosive-mode-analysis based flame diagnostic tools are used to identify different modes of combustion, including auto-ignition and extinction. Results obtained from the reduced chemistry are compared with those obtained from one-step chemistry to quantify the effect of fuel pyrolysis on the extinction limit. Effects of flame curvature, heat loss and unsteadiness on flame extinction are also explored. Finally, the validity of current turbulent combustion models to capture the local extinction and re-ignition will be discussed.

Model for macroevolutionary dynamics.

PubMed

Maruvka, Yosef E; Shnerb, Nadav M; Kessler, David A; Ricklefs, Robert E

2013-07-02

The highly skewed distribution of species among genera, although challenging to macroevolutionists, provides an opportunity to understand the dynamics of diversification, including species formation, extinction, and morphological evolution. Early models were based on either the work by Yule [Yule GU (1925) Philos Trans R Soc Lond B Biol Sci 213:21-87], which neglects extinction, or a simple birth-death (speciation-extinction) process. Here, we extend the more recent development of a generic, neutral speciation-extinction (of species)-origination (of genera; SEO) model for macroevolutionary dynamics of taxon diversification. Simulations show that deviations from the homogeneity assumptions in the model can be detected in species-per-genus distributions. The SEO model fits observed species-per-genus distributions well for class-to-kingdom-sized taxonomic groups. The model's predictions for the appearance times (the time of the first existing species) of the taxonomic groups also approximately match estimates based on molecular inference and fossil records. Unlike estimates based on analyses of phylogenetic reconstruction, fitted extinction rates for large clades are close to speciation rates, consistent with high rates of species turnover and the relatively slow change in diversity observed in the fossil record. Finally, the SEO model generally supports the consistency of generic boundaries based on morphological differences between species and provides a comparator for rates of lineage splitting and morphological evolution.

Influence of habitat quality, population size, patch size, and connectivity on patch-occupancy dynamics of the middle spotted woodpecker.

PubMed

Robles, Hugo; Ciudad, Carlos

2012-04-01

Despite extensive research on the effects of habitat fragmentation, the ecological mechanisms underlying colonization and extinction processes are poorly known, but knowledge of these mechanisms is essential to understanding the distribution and persistence of populations in fragmented habitats. We examined these mechanisms through multiseason occupancy models that elucidated patch-occupancy dynamics of Middle Spotted Woodpeckers (Dendrocopos medius) in northwestern Spain. The number of occupied patches was relatively stable from 2000 to 2010 (15-24% of 101 patches occupied every year) because extinction was balanced by recolonization. Larger and higher quality patches (i.e., higher density of oaks >37 cm dbh [diameter at breast height]) were more likely to be occupied. Habitat quality (i.e., density of large oaks) explained more variation in patch colonization and extinction than did patch size and connectivity, which were both weakly associated with probabilities of turnover. Patches of higher quality were more likely to be colonized than patches of lower quality. Populations in high-quality patches were less likely to become extinct. In addition, extinction in a patch was strongly associated with local population size but not with patch size, which means the latter may not be a good surrogate of population size in assessments of extinction probability. Our results suggest that habitat quality may be a primary driver of patch-occupancy dynamics and may increase the accuracy of models of population survival. We encourage comparisons of competing models that assess occupancy, colonization, and extinction probabilities in a single analytical framework (e.g., dynamic occupancy models) so as to shed light on the association of habitat quality and patch geometry with colonization and extinction processes in different settings and species. ©2012 Society for Conservation Biology.

Dust in the small Magellanic Cloud. 2: Dust models from interstellar polarization and extinction data

NASA Technical Reports Server (NTRS)

Rodrigues, C. V.; Magalhaes, A. M.; Coyne, G. V.

1995-01-01

We study the dust in the Small Magellanic Cloud using our polarization and extinction data (Paper 1) and existing dust models. The data suggest that the monotonic SMC extinction curve is related to values of lambda(sub max), the wavelength of maximum polarization, which are on the average smaller than the mean for the Galaxy. On the other hand, AZV 456, a star with an extinction similar to that for the Galaxy, shows a value of lambda(sub max) similar to the mean for the Galaxy. We discuss simultaneous dust model fits to extinction and polarization. Fits to the wavelength dependent polarization data are possible for stars with small lambda(sub max). In general, they imply dust size distributions which are narrower and have smaller mean sizes compared to typical size distributions for the Galaxy. However, stars with lambda(sub max) close to the Galactic norm, which also have a narrower polarization curve, cannot be fit adequately. This holds true for all of the dust models considered. The best fits to the extinction curves are obtained with a power law size distribution by assuming that the cylindrical and spherical silicate grains have a volume distribution which is continuous from the smaller spheres to the larger cylinders. The size distribution for the cylinders is taken from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be fit well with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grain. However, amorphous carbon and silicate grains also fit the data well. AZV456, which has an extinction curve similar to that for the Galaxy, has a UV bump which is too blue to be fit by spherical graphite grains.

NMDA receptors in the avian amygdala and the premotor arcopallium mediate distinct aspects of appetitive extinction learning.

PubMed

Gao, Meng; Lengersdorf, Daniel; Stüttgen, Maik C; Güntürkün, Onur

2018-05-02

Extinction learning is an essential mechanism that enables constant adaptation to ever-changing environmental conditions. The underlying neural circuit is mostly studied with rodent models using auditory cued fear conditioning. In order to uncover the variant and the invariant neural properties of extinction learning, we adopted pigeons as an animal model in an appetitive sign-tracking paradigm. The animals firstly learned to respond to two conditioned stimuli in two different contexts (CS-1 in context A and CS-2 in context B), before conditioned responses to the stimuli were extinguished in the opposite contexts (CS-1 in context B and CS-2 in context A). Subsequently, responding to both stimuli was tested in both contexts. Prior to extinction training, we locally injected the N-methyl-d-aspartate receptor (NMDAR) antagonist 2-Amino-5-phosphonovaleric acid (APV) in either the amygdala or the (pre)motor arcopallium to investigate their involvement in extinction learning. Our findings suggest that the encoding of extinction memory required the activation of amygdala, as visible by an impairment of extinction acquisition by concurrent inactivation of local NMDARs. In contrast, consolidation and subsequent retrieval of extinction memory recruited the (pre)motor arcopallium. Also, the inactivation of arcopallial NMDARs induced a general motoric slowing during extinction training. Thus, our results reveal a double dissociation between arcopallium and amygdala with respect to acquisition and consolidation of extinction, respectively. Our study therefore provides new insights on the two key components of the avian extinction network and their resemblance to the data obtained from mammals, possibly indicating a shared neural mechanism underlying extinction learning shaped by evolution. Copyright © 2018 Elsevier B.V. All rights reserved.

Theoretical Study of near Neutrality. II. Effect of Subdivided Population Structure with Local Extinction and Recolonization

PubMed Central

Ohta, T.

1992-01-01

There are several unsolved problems concerning the model of nearly neutral mutations. One is the interaction of subdivided population structure and weak selection that spatially fluctuates. The model of nearly neutral mutations whose selection coefficient spatially fluctuates has been studied by adopting the island model with periodic extinction-recolonization. Both the number of colonies and the migration rate play significant roles in determining mutants' behavior, and selection is ineffective when the extinction-recolonization is frequent with low migration rate. In summary, the number of mutant substitutions decreases and the polymorphism increases by increasing the total population size, and/or decreasing the extinction-recolonization rate. However, by increasing the total size of the population, the mutant substitution rate does not become as low when compared with that in panmictic populations, because of the extinction-recolonization, especially when the migration rate is limited. It is also found that the model satisfactorily explains the contrasting patterns of molecular polymorphisms observed in sibling species of Drosophila, including heterozygosity, proportion of polymorphism and fixation index. PMID:1582566

Associative learning versus fear habituation as predictors of long-term extinction retention.

PubMed

Brown, Lily A; LeBeau, Richard T; Chat, Ka Yi; Craske, Michelle G

2017-06-01

Violation of unconditioned stimulus (US) expectancy during extinction training may enhance associative learning and result in improved long-term extinction retention compared to within-session habituation. This experiment examines variation in US expectancy (i.e., expectancy violation) as a predictor of long-term extinction retention. It also examines within-session habituation of fear-potentiated startle (electromyography, EMG) and fear of conditioned stimuli (CS) throughout extinction training as predictors of extinction retention. Participants (n = 63) underwent fear conditioning, extinction and retention and provided continuous ratings of US expectancy and EMG, as well as CS fear ratings before and after each phase. Variation in US expectancy throughout extinction and habituation of EMG and fear was entered into a regression as predictors of retention and reinstatement of levels of expectancy and fear. Greater variation in US expectancy throughout extinction training was significantly predictive of enhanced extinction performance measured at retention test, although not after reinstatement test. Slope of EMG and CS fear during extinction did not predict retention of extinction. Within-session habituation of EMG and self-reported fear is not sufficient for long-term retention of extinction learning, and models emphasizing expectation violation may result in enhanced outcomes.

Spatial variability in growth-increment chronologies of long-lived freshwater mussels: Implications for climate impacts and reconstructions

USGS Publications Warehouse

Black, Bryan A.; Dunham, Jason B.; Blundon, Brett W.; Raggon, Mark F.; Zima, Daniela

2010-01-01

Estimates of historical variability in river ecosystems are often lacking, but long-lived freshwater mussels could provide unique opportunities to understand past conditions in these environments. We applied dendrochronology techniques to quantify historical variability in growth-increment widths in valves (shells) of western pearlshell freshwater mussels (Margaritifera falcata). A total of 3 growth-increment chronologies, spanning 19 to 26 y in length, were developed. Growth was highly synchronous among individuals within each site, and to a lesser extent, chronologies were synchronous among sites. All 3 chronologies negatively related to instrumental records of stream discharge, while correlations with measures of water temperature were consistently positive but weaker. A reconstruction of stream discharge was performed using linear regressions based on a mussel growth chronology and the regional Palmer Drought Severity Index (PDSI). Models based on mussel growth and PDSI yielded similar coefficients of prediction (R2Pred) of 0.73 and 0.77, respectively, for predicting out-ofsample observations. From an ecological perspective, we found that mussel chronologies provided a rich source of information for understanding climate impacts. Responses of mussels to changes in climate and stream ecosystems can be very site- and process-specific, underscoring the complex nature of biotic responses to climate change and the need to understand both regional and local processes in projecting climate impacts on freshwater species.

A theoretical quantitative genetic study of negative ecological interactions and extinction times in changing environments.

PubMed

Jones, Adam G

2008-04-25

Rapid human-induced changes in the environment at local, regional and global scales appear to be contributing to population declines and extinctions, resulting in an unprecedented biodiversity crisis. Although in the short term populations can respond ecologically to environmental alterations, in the face of persistent change populations must evolve or become extinct. Existing models of evolution and extinction in changing environments focus only on single species, even though the dynamics of extinction almost certainly depend upon the nature of species interactions. Here, I use a model of quantitative trait evolution in a two-species community to show that negative ecological interactions, such as predation and competition, can produce unexpected results regarding time to extinction. Under some circumstances, negative interactions can be expected to hasten the extinction of species declining in numbers. However, under other circumstances, negative interactions can actually increase times to extinction. This effect occurs across a wide range of parameter values and can be substantial, in some cases allowing a population to persist for 40 percent longer than it would in the absence of the species interaction. This theoretical study indicates that negative species interactions can have unexpected positive effects on times to extinction. Consequently, detailed studies of selection and demographics will be necessary to predict the consequences of species interactions in changing environments for any particular ecological community.

Outbreak and Extinction Dynamics in a Stochastic Ebola Model

NASA Astrophysics Data System (ADS)

Nieddu, Garrett; Bianco, Simone; Billings, Lora; Forgoston, Eric; Kaufman, James

A zoonotic disease is a disease that can be passed between animals and humans. In many cases zoonotic diseases can persist in the animal population even if there are no infections in the human population. In this case we call the infected animal population the reservoir for the disease. Ebola virus disease (EVD) and SARS are both notable examples of such diseases. There is little work devoted to understanding stochastic disease extinction and reintroduction in the presence of a reservoir. Here we build a stochastic model for EVD and explicitly consider the presence of an animal reservoir. Using a master equation approach and a WKB ansatz, we determine the associated Hamiltonian of the system. Hamilton's equations are then used to numerically compute the 12-dimensional optimal path to extinction, which is then used to estimate mean extinction times. We also numerically investigate the behavior of the model for dynamic population size. Our results provide an improved understanding of outbreak and extinction dynamics in diseases like EVD.

On the extinction probability in models of within-host infection: the role of latency and immunity.

PubMed

Yan, Ada W C; Cao, Pengxing; McCaw, James M

2016-10-01

Not every exposure to virus establishes infection in the host; instead, the small amount of initial virus could become extinct due to stochastic events. Different diseases and routes of transmission have a different average number of exposures required to establish an infection. Furthermore, the host immune response and antiviral treatment affect not only the time course of the viral load provided infection occurs, but can prevent infection altogether by increasing the extinction probability. We show that the extinction probability when there is a time-dependent immune response depends on the chosen form of the model-specifically, on the presence or absence of a delay between infection of a cell and production of virus, and the distribution of latent and infectious periods of an infected cell. We hypothesise that experimentally measuring the extinction probability when the virus is introduced at different stages of the immune response, alongside the viral load which is usually measured, will improve parameter estimates and determine the most suitable mathematical form of the model.

Extinction events can accelerate evolution.

PubMed

Lehman, Joel; Miikkulainen, Risto

2015-01-01

Extinction events impact the trajectory of biological evolution significantly. They are often viewed as upheavals to the evolutionary process. In contrast, this paper supports the hypothesis that although they are unpredictably destructive, extinction events may in the long term accelerate evolution by increasing evolvability. In particular, if extinction events extinguish indiscriminately many ways of life, indirectly they may select for the ability to expand rapidly through vacated niches. Lineages with such an ability are more likely to persist through multiple extinctions. Lending computational support for this hypothesis, this paper shows how increased evolvability will result from simulated extinction events in two computational models of evolved behavior. The conclusion is that although they are destructive in the short term, extinction events may make evolution more prolific in the long term.

The threshold of a stochastic delayed SIR epidemic model with vaccination

NASA Astrophysics Data System (ADS)

Liu, Qun; Jiang, Daqing

2016-11-01

In this paper, we study the threshold dynamics of a stochastic delayed SIR epidemic model with vaccination. We obtain sufficient conditions for extinction and persistence in the mean of the epidemic. The threshold between persistence in the mean and extinction of the stochastic system is also obtained. Compared with the corresponding deterministic model, the threshold affected by the white noise is smaller than the basic reproduction number Rbar0 of the deterministic system. Results show that time delay has important effects on the persistence and extinction of the epidemic.

The role of the medial prefrontal cortex in trace fear extinction

PubMed Central

Kwapis, Janine L.; Jarome, Timothy J.

2015-01-01

The extinction of delay fear conditioning relies on a neural circuit that has received much attention and is relatively well defined. Whether this established circuit also supports the extinction of more complex associations, however, is unclear. Trace fear conditioning is a better model of complex relational learning, yet the circuit that supports extinction of this memory has received very little attention. Recent research has indicated that trace fear extinction requires a different neural circuit than delay extinction; trace extinction requires the participation of the retrosplenial cortex, but not the amygdala, as noted in a previous study. Here, we tested the roles of the prelimbic and infralimbic regions of the medial prefrontal cortex in trace and delay fear extinction by blocking NMDA receptors during extinction learning. We found that the prelimbic cortex is necessary for trace, but not for delay fear extinction, whereas the infralimbic cortex is involved in both types of extinction. These results are consistent with the idea that trace fear associations require plasticity in multiple cortical areas for successful extinction. Further, the infralimbic cortex appears to play a role in extinction regardless of whether the animal was initially trained in trace or delay conditioning. Together, our results provide new information about how the neural circuits supporting trace and delay fear extinction differ. PMID:25512576

Abrupt climate change and extinction events

NASA Technical Reports Server (NTRS)

Crowley, Thomas J.

1988-01-01

There is a growing body of theoretical and empirical support for the concept of instabilities in the climate system, and indications that abrupt climate change may in some cases contribute to abrupt extinctions. Theoretical indications of instabilities can be found in a broad spectrum of climate models (energy balance models, a thermohaline model of deep-water circulation, atmospheric general circulation models, and coupled ocean-atmosphere models). Abrupt transitions can be of several types and affect the environment in different ways. There is increasing evidence for abrupt climate change in the geologic record and involves both interglacial-glacial scale transitions and the longer-term evolution of climate over the last 100 million years. Records from the Cenozoic clearly show that the long-term trend is characterized by numerous abrupt steps where the system appears to be rapidly moving to a new equilibrium state. The long-term trend probably is due to changes associated with plate tectonic processes, but the abrupt steps most likely reflect instabilities in the climate system as the slowly changing boundary conditions caused the climate to reach some threshold critical point. A more detailed analysis of abrupt steps comes from high-resolution studies of glacial-interglacial fluctuations in the Pleistocene. Comparison of climate transitions with the extinction record indicates that many climate and biotic transitions coincide. The Cretaceous-Tertiary extinction is not a candidate for an extinction event due to instabilities in the climate system. It is quite possible that more detailed comparisons and analysis will indicate some flaws in the climate instability-extinction hypothesis, but at present it appears to be a viable candidate as an alternate mechanism for causing abrupt environmental changes and extinctions.

A stochastic model for transmission, extinction and outbreak of Escherichia coli O157:H7 in cattle as affected by ambient temperature and cleaning practices.

PubMed

Wang, Xueying; Gautam, Raju; Pinedo, Pablo J; Allen, Linda J S; Ivanek, Renata

2014-08-01

Many infectious agents transmitting through a contaminated environment are able to persist in the environment depending on the temperature and sanitation determined rates of their replication and clearance, respectively. There is a need to elucidate the effect of these factors on the infection transmission dynamics in terms of infection outbreaks and extinction while accounting for the random nature of the process. Also, it is important to distinguish between the true and apparent extinction, where the former means pathogen extinction in both the host and the environment while the latter means extinction only in the host population. This study proposes a stochastic-differential equation model as an approximation to a Markov jump process model, using Escherichia coli O157:H7 in cattle as a model system. In the model, the host population infection dynamics are described using the standard susceptible-infected-susceptible framework, and the E. coli O157:H7 population in the environment is represented by an additional variable. The backward Kolmogorov equations that determine the probability distribution and the expectation of the first passage time are provided in a general setting. The outbreak and apparent extinction of infection are investigated by numerically solving the Kolmogorov equations for the probability density function of the associated process and the expectation of the associated stopping time. The results provide insight into E. coli O157:H7 transmission and apparent extinction, and suggest ways for controlling the spread of infection in a cattle herd. Specifically, this study highlights the importance of ambient temperature and sanitation, especially during summer.

Monthly paleostreamflow reconstruction from annual tree-ring chronologies

NASA Astrophysics Data System (ADS)

Stagge, J. H.; Rosenberg, D. E.; DeRose, R. J.; Rittenour, T. M.

2018-02-01

Paleoclimate reconstructions are increasingly used to characterize annual climate variability prior to the instrumental record, to improve estimates of climate extremes, and to provide a baseline for climate-change projections. To date, paleoclimate records have seen limited engineering use to estimate hydrologic risks because water systems models and managers usually require streamflow input at the monthly scale. This study explores the hypothesis that monthly streamflows can be adequately modeled by statistically decomposing annual flow reconstructions. To test this hypothesis, a multiple linear regression model for monthly streamflow reconstruction is presented that expands the set of predictors to include annual streamflow reconstructions, reconstructions of global circulation, and potential differences among regional tree-ring chronologies related to tree species and geographic location. This approach is used to reconstruct 600 years of monthly streamflows at two sites on the Bear and Logan rivers in northern Utah. Nash-Sutcliffe Efficiencies remain above zero (0.26-0.60) for all months except April and Pearson's correlation coefficients (R) are 0.94 and 0.88 for the Bear and Logan rivers, respectively, confirming that the model can adequately reproduce monthly flows during the reference period (10/1942 to 9/2015). Incorporating a flexible transition between the previous and concurrent annual reconstructed flows was the most important factor for model skill. Expanding the model to include global climate indices and regional tree-ring chronologies produced smaller, but still significant improvements in model fit. The model presented here is the only approach currently available to reconstruct monthly streamflows directly from tree-ring chronologies and climate reconstructions, rather than using resampling of the observed record. With reasonable estimates of monthly flow that extend back in time many centuries, water managers can challenge systems models with a larger range of natural variability in drought and pluvial events and better evaluate extreme events with recurrence intervals longer than the observed record. Establishing this natural baseline is critical when estimating future hydrologic risks under conditions of a non-stationary climate.

Behavioral momentum and resurgence: Effects of time in extinction and repeated resurgence tests

PubMed Central

Shahan, Timothy A.

2014-01-01

Resurgence is an increase in a previously extinguished operant response that occurs if an alternative reinforcement introduced during extinction is removed. Shahan and Sweeney (2011) developed a quantitative model of resurgence based on behavioral momentum theory that captures existing data well and predicts that resurgence should decrease as time in extinction and exposure to the alternative reinforcement increases. Two experiments tested this prediction. The data from Experiment 1 suggested that without a return to baseline, resurgence decreases with increased exposure to alternative reinforcement and to extinction of the target response. Experiment 2 tested the predictions of the model across two conditions, one with constant alternative reinforcement for five sessions, and the other with alternative reinforcement removed three times. In both conditions, the alternative reinforcement was removed for the final test session. Experiment 2 again demonstrated a decrease in relapse across repeated resurgence tests. Furthermore, comparably little resurgence was observed at the same time point in extinction in the final test, despite dissimilar previous exposures to alternative reinforcement removal. The quantitative model provided a good description of the observed data in both experiments. More broadly, these data suggest that increased exposure to extinction may be a successful strategy to reduce resurgence. The relationship between these data and existing tests of the effect of time in extinction on resurgence is discussed. PMID:23982985

Forecasting extinction risk with nonstationary matrix models.

PubMed

Gotelli, Nicholas J; Ellison, Aaron M

2006-02-01

Matrix population growth models are standard tools for forecasting population change and for managing rare species, but they are less useful for predicting extinction risk in the face of changing environmental conditions. Deterministic models provide point estimates of lambda, the finite rate of increase, as well as measures of matrix sensitivity and elasticity. Stationary matrix models can be used to estimate extinction risk in a variable environment, but they assume that the matrix elements are randomly sampled from a stationary (i.e., non-changing) distribution. Here we outline a method for using nonstationary matrix models to construct realistic forecasts of population fluctuation in changing environments. Our method requires three pieces of data: (1) field estimates of transition matrix elements, (2) experimental data on the demographic responses of populations to altered environmental conditions, and (3) forecasting data on environmental drivers. These three pieces of data are combined to generate a series of sequential transition matrices that emulate a pattern of long-term change in environmental drivers. Realistic estimates of population persistence and extinction risk can be derived from stochastic permutations of such a model. We illustrate the steps of this analysis with data from two populations of Sarracenia purpurea growing in northern New England. Sarracenia purpurea is a perennial carnivorous plant that is potentially at risk of local extinction because of increased nitrogen deposition. Long-term monitoring records or models of environmental change can be used to generate time series of driver variables under different scenarios of changing environments. Both manipulative and natural experiments can be used to construct a linking function that describes how matrix parameters change as a function of the environmental driver. This synthetic modeling approach provides quantitative estimates of extinction probability that have an explicit mechanistic basis.

A NEW CHRONOLOGY FOR THE MOON AND MERCURY

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

Marchi, Simone; Mottola, Stefano; Cremonese, Gabriele

2009-06-15

In this paper, we present a new method for dating the surface of the Moon, obtained by modeling the incoming flux of impactors and converting it into a size distribution of resulting craters. We compare the results from this model with the standard chronology for the Moon showing their similarities and discrepancies. In particular, we find indications of a nonconstant impactor flux in the last 500 Myr and also discuss the implications of our findings for the Late Heavy Bombardment hypothesis. We also show the potential of our model for accurate dating of other inner solar system bodies, by applyingmore » it to Mercury.« less

Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction.

PubMed

Finnegan, Seth; Rasmussen, Christian M Ø; Harper, David A T

2016-04-27

The Late Ordovician mass extinction (LOME) coincided with dramatic climate changes, but there are numerous ways in which these changes could have driven marine extinctions. We use a palaeobiogeographic database of rhynchonelliform brachiopods to examine the selectivity of Late Ordovician-Early Silurian genus extinctions and evaluate which extinction drivers are best supported by the data. The first (latest Katian) pulse of the LOME preferentially affected genera restricted to deeper waters or to relatively narrow (less than 35°) palaeolatitudinal ranges. This pattern is only observed in the latest Katian, suggesting that it reflects drivers unique to this interval. Extinction of exclusively deeper-water genera implies that changes in water mass properties such as dissolved oxygen content played an important role. Extinction of genera with narrow latitudinal ranges suggests that interactions between shifting climate zones and palaeobiogeography may also have been important. We test the latter hypothesis by estimating whether each genus would have been able to track habitats within its thermal tolerance range during the greenhouse-icehouse climate transition. Models including these estimates are favoured over alternative models. We argue that the LOME, long regarded as non-selective, is highly selective along biogeographic and bathymetric axes that are not closely correlated with taxonomic identity. © 2016 The Author(s).

Biogeographic and bathymetric determinants of brachiopod extinction and survival during the Late Ordovician mass extinction

PubMed Central

Finnegan, Seth; Rasmussen, Christian M. Ø.; Harper, David A. T.

2016-01-01

The Late Ordovician mass extinction (LOME) coincided with dramatic climate changes, but there are numerous ways in which these changes could have driven marine extinctions. We use a palaeobiogeographic database of rhynchonelliform brachiopods to examine the selectivity of Late Ordovician–Early Silurian genus extinctions and evaluate which extinction drivers are best supported by the data. The first (latest Katian) pulse of the LOME preferentially affected genera restricted to deeper waters or to relatively narrow (less than 35°) palaeolatitudinal ranges. This pattern is only observed in the latest Katian, suggesting that it reflects drivers unique to this interval. Extinction of exclusively deeper-water genera implies that changes in water mass properties such as dissolved oxygen content played an important role. Extinction of genera with narrow latitudinal ranges suggests that interactions between shifting climate zones and palaeobiogeography may also have been important. We test the latter hypothesis by estimating whether each genus would have been able to track habitats within its thermal tolerance range during the greenhouse–icehouse climate transition. Models including these estimates are favoured over alternative models. We argue that the LOME, long regarded as non-selective, is highly selective along biogeographic and bathymetric axes that are not closely correlated with taxonomic identity. PMID:27122567

Large Diameter, Radiative Extinction Experiments with Decane Droplets in Microgravity

NASA Technical Reports Server (NTRS)

Easton, John; Tien, James; Dietrich, Daniel

1999-01-01

The extinction of a diffusion flame is of fundamental interest in combustion science. Linan, Law, and Chung and Law analytically and experimentally determined an extinction boundary in terms of droplet diameter and pressure for a single droplet due to Damkohler, or blowoff, extinction. More recently, other researchers demonstrated extinction due to finite rate kinetics in reduced gravity for free droplets of heptane. Chao modeled the effect of radiative heat loss on a quasi-steady spherically symmetric single droplet burning in the absence of buoyancy. They determined that for increasing droplet diameter, a second limit can be reached such that combustion is no longer possible. This second, larger droplet diameter limit arises due to radiative heat loss, which increases with increasing droplet and flame diameter. This increase in radiative heat loss arises due to an increase in the surface area of the flame. Recently, Marchese modeled fuel droplets with detailed chemistry and radiative effects, and compared the results to other work. The modeling also showed the importance of radiative loss and radiative extinction Experiments examined the behavior of a large droplet of decane burning in reduced gravity onboard the NASA Lewis DC-9 aircraft, but did not show a radiative extinction boundary due to g-jitter (Variations in gravitational level and direction) effects. Dietrich conducted experiments in the reduced gravity environment of the Space Shuttle. This work showed that the extinction diameter of methanol droplets increased when the initial diameter of the droplets was large (in this case, approximately 5 mm). Theoretical results agreed with these experimental results only when the theory included radiative effects . Radiative extinction was experimentally verified by Nayagam in a later Shuttle mission. The following work focuses on the combustion and extinction of a single fuel droplet. The goal is to experimentally determine a large droplet diameter limit that arises due to radiative heat loss from the flame to the surroundings.

Individual differences in learning predict the return of fear.

PubMed

Gershman, Samuel J; Hartley, Catherine A

2015-09-01

Using a laboratory analogue of learned fear (Pavlovian fear conditioning), we show that there is substantial heterogeneity across individuals in spontaneous recovery of fear following extinction training. We propose that this heterogeneity might stem from qualitative individual differences in the nature of extinction learning. Whereas some individuals tend to form a new memory during extinction, leaving their fear memory intact, others update the original threat association with new safety information, effectively unlearning the fear memory. We formalize this account in a computational model of fear learning and show that individuals who, according to the model, are more likely to form new extinction memories tend to show greater spontaneous recovery compared to individuals who appear to only update a single memory. This qualitative variation in fear and extinction learning may have important implications for understanding vulnerability and resilience to fear-related psychiatric disorders.

Glucocorticoid receptors and extinction retention deficits in the single prolonged stress model.

PubMed

Knox, D; Nault, T; Henderson, C; Liberzon, I

2012-10-25

Single prolonged stress (SPS) is a rodent model of post traumatic stress disorder that is comprised of serial application of restraint (r), forced swim (fs), and ether (eth) followed by a 7-day quiescent period. SPS induces extinction retention deficits and it is believed that these deficits are caused by the combined stressful effect of serial exposure to r, fs, and eth. However, this hypothesis remains untested. Neurobiological mechanisms by which SPS induces extinction retention deficits are unknown, but SPS enhances glucocorticoid receptor (GR) expression in the hippocampus, which is critical for contextual modulation of extinction retrieval. Upregulation of GRs in extinction circuits may be a mechanism by which SPS induces extinction retention deficits, but this hypothesis has not been examined. In this study, we systematically altered the stressors that constitute SPS (i.e. r, fs, eth), generating a number of partial SPS (p-SPS) groups, and observed the effects SPS and p-SPSs had on extinction retention and GR levels in the hippocampus and prefrontal cortex (PFC). PFC GRs were assayed, because regions of the PFC are critical for maintaining extinction. We predicted that only exposure to full SPS would result in extinction retention deficits and enhance hippocampal and PFC GR levels. Only exposure to full SPS induced extinction retention deficits. Hippocampal and PFC GR expression was enhanced by SPS and most p-SPSs, however hippocampal GR expression was significantly larger following the full SPS exposure than all other conditions. Our findings suggest that the combined stressful effect of serial exposure to r, fs, and eth results in extinction retention deficits. The results also suggest that simple enhancements in GR expression in the hippocampus and PFC are insufficient to result in extinction retention deficits, but raise the possibility that a threshold-enhancement in hippocampal GR expression contributes to SPS-induced extinction retention deficits. Copyright © 2012 IBRO. Published by Elsevier Ltd. All rights reserved.

Contextualising primate origins--an ecomorphological framework.

PubMed

Soligo, Christophe; Smaers, Jeroen B

2016-04-01

Ecomorphology - the characterisation of the adaptive relationship between an organism's morphology and its ecological role - has long been central to theories of the origin and early evolution of the primate order. This is exemplified by two of the most influential theories of primate origins: Matt Cartmill's Visual Predation Hypothesis, and Bob Sussman's Angiosperm Co-Evolution Hypothesis. However, the study of primate origins is constrained by the absence of data directly documenting the events under investigation, and has to rely instead on a fragmentary fossil record and the methodological assumptions inherent in phylogenetic comparative analyses of extant species. These constraints introduce particular challenges for inferring the ecomorphology of primate origins, as morphology and environmental context must first be inferred before the relationship between the two can be considered. Fossils can be integrated in comparative analyses and observations of extant model species and laboratory experiments of form-function relationships are critical for the functional interpretation of the morphology of extinct species. Recent developments have led to important advancements, including phylogenetic comparative methods based on more realistic models of evolution, and improved methods for the inference of clade divergence times, as well as an improved fossil record. This contribution will review current perspectives on the origin and early evolution of primates, paying particular attention to their phylogenetic (including cladistic relationships and character evolution) and environmental (including chronology, geography, and physical environments) contextualisation, before attempting an up-to-date ecomorphological synthesis of primate origins. © 2016 Anatomical Society.

Metapopulation extinction risk: dispersal's duplicity.

PubMed

Higgins, Kevin

2009-09-01

Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation's extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation's extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation's extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation's extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation's extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation's extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.

Thermoregulation of two sympatric species of horned lizards in the Chihuahuan Desert and their local extinction risk.

PubMed

Lara-Reséndiz, Rafael A; Gadsden, Héctor; Rosen, Philip C; Sinervo, Barry; Méndez-De la Cruz, Fausto R

2015-02-01

Thermoregulatory studies of ectothermic organisms are an important tool for ecological physiology, evolutionary ecology and behavior, and recently have become central for evaluating and predicting global climate change impacts. Here, we present a novel combination of field, laboratory, and modeling approaches to examine body temperature regulation, habitat thermal quality, and hours of thermal restriction on the activity of two sympatric, aridlands horned lizards (Phrynosoma cornutum and Phrynosoma modestum) at three contrasting Chihuahuan Desert sites in Mexico. Using these physiological data, we estimate local extinction risk under predicted climate change within their current geographical distribution. We followed the Hertz et al. (1993, Am. Nat., 142, 796-818) protocol for evaluating thermoregulation and the Sinervo et al. (2010, Science, 328, 894-899) eco-physiological model of extinction under climatic warming. Thermoregulatory indices suggest that both species thermoregulate effectively despite living in habitats of low thermal quality, although high environmental temperatures restrict the activity period of both species. Based on our measurements, if air temperature rises as predicted by climate models, the extinction model projects that P. cornutum will become locally extinct at 6% of sites by 2050 and 18% by 2080 and P. modestum will become extinct at 32% of sites by 2050 and 60% by 2080. The method we apply, using widely available or readily acquired thermal data, along with the modeling, appeared to identify several unique ecological traits that seemingly exacerbate climate sensitivity of P. modestum. Copyright © 2014 Elsevier Ltd. All rights reserved.

Computational search for hypotheses concerning the endocannabinoid contribution to the extinction of fear conditioning.

PubMed

Anastasio, Thomas J

2013-01-01

Fear conditioning, in which a cue is conditioned to elicit a fear response, and extinction, in which a previously conditioned cue no longer elicits a fear response, depend on neural plasticity occurring within the amygdala. Projection neurons in the basolateral amygdala (BLA) learn to respond to the cue during fear conditioning, and they mediate fear responding by transferring cue signals to the output stage of the amygdala. Some BLA projection neurons retain their cue responses after extinction. Recent work shows that activation of the endocannabinoid system is necessary for extinction, and it leads to long-term depression (LTD) of the GABAergic synapses that inhibitory interneurons make onto BLA projection neurons. Such GABAergic LTD would enhance the responses of the BLA projection neurons that mediate fear responding, so it would seem to oppose, rather than promote, extinction. To address this paradox, a computational analysis of two well-known conceptual models of amygdaloid plasticity was undertaken. The analysis employed exhaustive state-space search conducted within a declarative programming environment. The analysis reveals that GABAergic LTD actually increases the number of synaptic strength configurations that achieve extinction while preserving the cue responses of some BLA projection neurons in both models. The results suggest that GABAergic LTD helps the amygdala retain cue memory during extinction even as the amygdala learns to suppress the previously conditioned response. The analysis also reveals which features of both models are essential for their ability to achieve extinction with some cue memory preservation, and suggests experimental tests of those features.

Computational search for hypotheses concerning the endocannabinoid contribution to the extinction of fear conditioning

PubMed Central

Anastasio, Thomas J.

2013-01-01

Fear conditioning, in which a cue is conditioned to elicit a fear response, and extinction, in which a previously conditioned cue no longer elicits a fear response, depend on neural plasticity occurring within the amygdala. Projection neurons in the basolateral amygdala (BLA) learn to respond to the cue during fear conditioning, and they mediate fear responding by transferring cue signals to the output stage of the amygdala. Some BLA projection neurons retain their cue responses after extinction. Recent work shows that activation of the endocannabinoid system is necessary for extinction, and it leads to long-term depression (LTD) of the GABAergic synapses that inhibitory interneurons make onto BLA projection neurons. Such GABAergic LTD would enhance the responses of the BLA projection neurons that mediate fear responding, so it would seem to oppose, rather than promote, extinction. To address this paradox, a computational analysis of two well-known conceptual models of amygdaloid plasticity was undertaken. The analysis employed exhaustive state-space search conducted within a declarative programming environment. The analysis reveals that GABAergic LTD actually increases the number of synaptic strength configurations that achieve extinction while preserving the cue responses of some BLA projection neurons in both models. The results suggest that GABAergic LTD helps the amygdala retain cue memory during extinction even as the amygdala learns to suppress the previously conditioned response. The analysis also reveals which features of both models are essential for their ability to achieve extinction with some cue memory preservation, and suggests experimental tests of those features. PMID:23761759

Vorinostat ameliorates impaired fear extinction possibly via the hippocampal NMDA-CaMKII pathway in an animal model of posttraumatic stress disorder.

PubMed

Matsumoto, Yasutaka; Morinobu, Shigeru; Yamamoto, Shigeto; Matsumoto, Tomoya; Takei, Shiro; Fujita, Yosuke; Yamawaki, Shigeto

2013-09-01

Given that impairment of fear extinction plays a pivotal role in the pathophysiology of posttraumatic stress disorder (PTSD), drugs that facilitate fear extinction may be useful as novel treatments for PTSD. Histone deacetylase (HDAC) inhibitors have recently been shown to enhance fear extinction in animal studies. Using a single prolonged stress (SPS) paradigm, an animal model of PTSD, we examined whether the HDAC inhibitor vorinostat can facilitate fear extinction in rats, and elucidated the mechanism by which vorinostat enhanced fear extinction, focusing on the N-methyl-D-aspartate (NMDA) receptor signals in the hippocampus. Seven days after SPS, rats received contextual fear conditioning, followed by 2-day extinction training. Vorinostat was intraperitoneally injected immediately after second extinction training session. Contextual fear response was assessed 24 h after vorinostat injection. Hippocampal tissues were dissected 2 h after vorinostat injection. The levels of mRNA and protein tested were measured by RT-PCR or western blotting, respectively. Systemic administration of vorinostat with extinction training significantly enhanced fear extinction in SPS rats as compared with the controls. Furthermore, vorinostat enhanced the hippocampal levels of NR2B and calcium/calmodulin kinase II (CaMKII) α and β proteins, accompanied by increases in the levels of acetylated histone H3 and H4. These findings suggest that vorinostat ameliorated the impaired fear extinction in SPS rats, and this effect was associated with an increase in histone acetylation and thereby enhancement of NR2B and CaMKII in the hippocampus. Our results may provide new insight into the molecular and therapeutic mechanisms of PTSD.

Extinction, reacquisition, and rapid forgetting of eyeblink conditioning in developing rats

PubMed Central

Freeman, John H.

2014-01-01

Eyeblink conditioning is a well-established model for studying the developmental neurobiology of associative learning and memory. However, age differences in extinction and subsequent reacquisition have yet to be studied using this model. The present study examined extinction and reacquisition of eyeblink conditioning in developing rats. In Experiment 1, post-natal day (P) 17 and 24 rats were trained to a criterion of 80% conditioned responses (CRs) using stimulation of the middle cerebellar peduncle (MCP) as a conditioned stimulus (CS). Stimulation CS-alone extinction training commenced 24 h later, followed by reacquisition training after the fourth extinction session. Contrary to expected results, rats trained starting on P17 showed significantly fewer CRs to stimulation CS-alone presentations relative to P24s, including fewer CRs as early as the first block of extinction session 1. Furthermore, the P17 group was slower to reacquire following extinction. Experiment 2 was run to determine the extent to which the low CR percentage observed in P17s early in extinction reflected rapid forgetting versus rapid extinction. Twenty-four hours after reaching criterion, subjects were trained in a session split into 50 stimulation CS-unconditioned stimulus paired trials followed immediately by 50 stimulation CS-alone trials. With this “immediate” extinction protocol, CR percentages during the first block of stimulation CS-alone presentations were equivalent to terminal acquisition levels at both ages but extinction was more rapid in the P17 group. These findings indicate that forgetting is observed in P17 relative to P24 rats 24 h following acquisition. The forgetting in P17 rats has important implications for the neurobiological mechanisms of memory in the developing cerebellum. PMID:25403458

Breeding chronology and social interactions affect ungulate foraging behavior at a concentrated food resource

PubMed Central

Cohen, Bradley S.; Miller, Karl V.

2017-01-01

Prey species must balance predator avoidance behavior with other essential activities including foraging, breeding, and social interactions. Anti-predator behaviors such as vigilance can impede resource acquisition rates by altering foraging behavior. However, in addition to predation risk, foraging behavior may also be affected by socio-sexual factors including breeding chronology and social interactions. Therefore, we investigated how time-of-day, distance-to-forest, group size, social interactions (presence of different sex-age class), and breeding chronology (pre-breeding, breeding, post-breeding seasons) affected probability of feeding (hereafter: feeding) for different sex and age-classes (mature males, immature males, adult females, and juveniles) of white-tailed deer at feed sites. We developed a set of candidate models consisting of social, habitat, reproductive, and abiotic factors and combinations of these factors. We then used generalized linear mixed models (GLMMs) to estimate the probability of feeding and used model averaging of competing models for multimodel inference. Each adult sex-age class’ feeding was influenced by breeding chronology. Juveniles were more likely to be feeding than adults in all seasons. Feeding increased with group size for all sex-age classes. The presence of a mature male negatively influenced the feeding of immature males and juveniles were more likely to be feeding when an adult female was present. Feeding decreased with increasing distance-to-forest for mature males but not for other sex-age classes. Our results indicate that each sex-age class modulates vigilance levels in response to socio-sexual factors according to the unique pressures placed upon them by their reproductive status and social rank. PMID:28591136

IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores

NASA Astrophysics Data System (ADS)

Parrenin, Frédéric

2015-04-01

Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores is essential to interpret the paleo records that they contain, but it is a complicated problem since it involves different dating methods. Here I present IceChrono v1, a new probabilistic model to combine different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its uncertainty. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. The chronological information used are: models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice and gas dated horizons, ice and gas dated depth intervals, Δdepth observations (depth shift between synchronous events recorded in the ice and in the air), stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air and air-ice links). The optimization problem is formulated as a least squares problems, that is, all densities of probabilities are assumed gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono is similar in scope to the Datice model, but has differences from the mathematical, numerical and programming point of views. I apply IceChrono on an AICC2012-like experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. IceChrono v1 is freely available under the GPL v3 open source license.

Severe environmental effects of Chicxulub impact imply key role in end-Cretaceous mass extinction

NASA Astrophysics Data System (ADS)

Brugger, Julia; Feulner, Georg; Petri, Stefan

2017-04-01

66 million years ago, during the most recent of the five severe mass extinctions in Earth's history, non-avian dinosaurs and many other organisms became extinct. The cause of this end-Cretaceous mass extinction is seen in either flood-basalt eruptions or an asteroid impact. Modeling the climatic changes after the Chicxulub asteroid impact allow to assess its contribution to the extinction event and to analyze the short-term and long-term response of the climate and the biosphere to the impact. Existing studies either investigated the effect of dust, which is now believed to play a minor role, or used one-dimensional, non-coupled models. In contrast, we use a coupled climate model to explore the longer lasting cooling due to sulfate aerosols. Based on data from geophysical impact modeling, we set up simulations with different stratospheric residence times for sulfate aerosols. Depending on this residence time, global surface air temperature decreased by at least 26°C, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. Vigorous ocean mixing, caused by the fast cooling of the surface ocean, might have perturbed marine ecosystems by the upwelling of nutrients. The dramatic climatic changes seen in our simulations imply severe environmental effects and therefore a significant contribution of the impact in the end-Cretaceous mass extinction.

Extinction Events Can Accelerate Evolution

PubMed Central

Lehman, Joel; Miikkulainen, Risto

2015-01-01

Extinction events impact the trajectory of biological evolution significantly. They are often viewed as upheavals to the evolutionary process. In contrast, this paper supports the hypothesis that although they are unpredictably destructive, extinction events may in the long term accelerate evolution by increasing evolvability. In particular, if extinction events extinguish indiscriminately many ways of life, indirectly they may select for the ability to expand rapidly through vacated niches. Lineages with such an ability are more likely to persist through multiple extinctions. Lending computational support for this hypothesis, this paper shows how increased evolvability will result from simulated extinction events in two computational models of evolved behavior. The conclusion is that although they are destructive in the short term, extinction events may make evolution more prolific in the long term. PMID:26266804

A requirement for memory retrieval during and after long-term extinction learning

PubMed Central

Ouyang, Ming; Thomas, Steven A.

2005-01-01

Current learning theories are based on the idea that learning is driven by the difference between expectations and experience (the delta rule). In extinction, one learns that certain expectations no longer apply. Here, we test the potential validity of the delta rule by manipulating memory retrieval (and thus expectations) during extinction learning. Adrenergic signaling is critical for the time-limited retrieval (but not acquisition or consolidation) of contextual fear. Using genetic and pharmacologic approaches to manipulate adrenergic signaling, we find that long-term extinction requires memory retrieval but not conditioned responding. Identical manipulations of the adrenergic system that do not affect memory retrieval do not alter extinction. The results provide substantial support for the delta rule of learning theory. In addition, the timing over which extinction is sensitive to adrenergic manipulation suggests a model whereby memory retrieval occurs during, and several hours after, extinction learning to consolidate long-term extinction memory. PMID:15947076

VISION - Vienna Survey in Orion. II. Infrared extinction in Orion A

NASA Astrophysics Data System (ADS)

Meingast, Stefan; Alves, João; Lombardi, Marco

2018-06-01

We have investigated the shape of the extinction curve in the infrared up to 25μm for the Orion A star-forming complex. The basis of this work is near-infrared data acquired with the Visual and Infrared Survey Telescope for Astronomy, in combination with Pan-STARRS and mid-infrared Spitzer photometry. We obtain colour excess ratios for eight passbands by fitting a series of colour-colour diagrams. The fits are performed using Markov chain Monte Carlo methods, together with a linear model under a Bayesian formalism. The resulting colour excess ratios are directly interpreted as a measure of the extinction law. We show that the Orion A molecular cloud is characterized by flat mid-infrared extinction, similar to many other recently studied sightlines. Moreover, we find statistically significant evidence that the extinction law from 1μm to at least 6μm varies across the cloud. In particular, we find a gradient along galactic longitude, where regions near the Orion Nebula Cluster show a different extinction law compared to L1641 and L1647, the low-mass star-forming sites in the cloud complex. These variations are of the order of only 3% and are most likely caused by the influence of the massive stars on their surrounding medium. While the observed general trends in our measurements are in agreement with model predictions, both well-established and new dust grain models are not able to fully reproduce our infrared extinction curve. We also present a new extinction map featuring a resolution of 1' and revisit the correlation between extinction and dust optical depth. This analysis shows that cloud substructure, which is not sampled by background sources, affects the conversion factor between these two measures. In conclusion, we argue that specific characteristics of the infrared extinction law are still not well understood, but Orion A can serve as an unbiased template for future studies. The extinction map (FITS file) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A65

AN ANALYSIS OF THE SHAPES OF INTERSTELLAR EXTINCTION CURVES. VI. THE NEAR-IR EXTINCTION LAW

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

Fitzpatrick, E. L.; Massa, D.

We combine new observations from the Hubble Space Telescope's Advanced Camera of Survey with existing data to investigate the wavelength dependence of near-IR (NIR) extinction. Previous studies suggest a power law form for NIR extinction, with a 'universal' value of the exponent, although some recent observations indicate that significant sight line-to-sight line variability may exist. We show that a power-law model for the NIR extinction provides an excellent fit to most extinction curves, but that the value of the power, {beta}, varies significantly from sight line to sight line. Therefore, it seems that a 'universal NIR extinction law' is notmore » possible. Instead, we find that as {beta} decreases, R(V) {identical_to} A(V)/E(B - V) tends to increase, suggesting that NIR extinction curves which have been considered 'peculiar' may, in fact, be typical for different R(V) values. We show that the power-law parameters can depend on the wavelength interval used to derive them, with the {beta} increasing as longer wavelengths are included. This result implies that extrapolating power-law fits to determine R(V) is unreliable. To avoid this problem, we adopt a different functional form for NIR extinction. This new form mimics a power law whose exponent increases with wavelength, has only two free parameters, can fit all of our curves over a longer wavelength baseline and to higher precision, and produces R(V) values which are consistent with independent estimates and commonly used methods for estimating R(V). Furthermore, unlike the power-law model, it gives R(V)s that are independent of the wavelength interval used to derive them. It also suggests that the relation R(V) = -1.36 E(K-V)/(E(B-V)) - 0.79 can estimate R(V) to {+-}0.12. Finally, we use model extinction curves to show that our extinction curves are in accord with theoretical expectations, and demonstrate how large samples of observational quantities can provide useful constraints on the grain properties.« less

The role of climate and vegetation on woolly mammoth extinction on St. Paul Island, Alaska and megafauna extinction in North America in the late Quaternary

NASA Astrophysics Data System (ADS)

Wang, Y.; Porter, W.; Miller, P. A.; Graham, R. W.; Williams, J. W.

2016-12-01

Estimate of megafauna behaviors dynamically under associated environmental factors is important to understand the mechanisms and causes of the late Quaternary megafaunal extinctions. On St. Paul Island, an isolated remnant of the Bering Land Bridge, a late-surviving population of woolly mammoth (Mammuthus primigenius) persisted until 5,600 cal BP, while 37 out of 54 megafauna species in the continent of North America, all herbivores, went extinct at the end of Pleistocene between 13,800 and 11,500 cal BP. Proposed natural drivers of the extinction events include abrupt temperature changes, food resource loss and freshwater shortage. Here we tested these three hypothesized mechanisms, using a physiological model (Niche Mapper) to estimate individual megafauna behaviors from the perspectives of metabolic rate, individual vegetation and freshwater requirement under simulated climates from Community Climate System Model version 3 (CCSM3), vegetation reconstructions based on dynamic LPJ-GUESS model and woolly mammoth and megafauna species trait data reconstructed based on mammal fossils. Preliminary simulations of woolly mammoth on St. Paul Island point to the importance of net vegetation primary productivity and freshwater availability as limits on the carrying capacity of St. Paul for mammoth populations, with a low carrying capacity in the middle Holocene making this population highly vulnerable to extinction. Results also indicate that the abrupt warming based around 14,000 cal BP in Bering land bridge on CCSM3 simulations causes woolly mammoth extinction, by driving metabolic rate high up beyond the active basic metabolic rate. Analysis suggests a positive relationship between temperature and metabolic rate, and woolly mammoth would go extinct when summer temperature is up to 12 °C or higher. However the temperature reconstructed based on regional proxies is relatively stable compared to CCSM3 simulations, and leads to stable metabolic rate of woolly mammoth and no extinction events. Proposed simulations of megafauna species in North America indicate the role of ice sheets in limiting habitats. This work helps resolve the drivers of extinction for a small island surviving woolly mammoth population and worldwide megafauna extinctions in the late Quaternary.

A (210)Pb-based chronological model for recent sediments with random entries of mass and activities: Model development.

PubMed

Abril Hernández, José-María

2016-01-01

Unsupported (210)Pb ((210)Pbexc) vs. mass depth profiles do not contain enough information as to extract a unique chronology when both, (210)Pbexc fluxes and mass sediment accumulation rates (SAR) independently vary with time. Restrictive assumptions are needed to develop a suitable dating tool. A statistical correlation between fluxes and SAR seems to be a quite general rule. This paper builds up a new (210)Pb-based dating tool by using such a statistical correlation. It operates with SAR and initial activities that closely follow normal distributions, what leads to the expected correlation between fluxes and SAR. An intelligent algorithm solves their best arrangement downcore to fit the experimental (210)Pbexc vs. mass depth profile, generating then solutions for the chronological line, and for the histories of SAR and fluxes. Parametric maps of a χ-function serve to find out the solution and to support error estimates. Optionally, the model's answers can be better constrained through the use of time markers. The performance of the model is illustrated with a synthetic core, and with real cases using published data for varved sediment cores. Copyright © 2015 Elsevier Ltd. All rights reserved.

A Time Scale for Major Events in Early Mars Crustal Evolution

NASA Technical Reports Server (NTRS)

Frey, Herbert V.

2004-01-01

The population of visible and buried impact basins > 200 km diameter revealed by high resolution gridded MOLA data and the cumulative frequency curves derived for these pvide a basis for a chronology of major events in early martian history. The relative chronology can be given in terms of N(200) crater retention ages; 'absolute ages' can be assigued using the Hartmann-Neukum (H&N) model chronology. In terms of billions of H&N years, the crustal dichotomy formed by large impact basins at 4.12 +/- 0.08 BYA (N(200) = 3.0-3.2) and the global magnetic field died at about or slightly before the same time (4.15 +/- 0.08 BYA (N(200) = 3.5). In this chronology, the buried lowlands are approx. 120 my younger than the buried highlands, approx. 160 my younger than the highlands overall and approx. 340 my younger than the oldest crater retention surface we see, defined by the largest impact basins.

Organic Model of Interstellar Grains

NASA Astrophysics Data System (ADS)

Yabushita, S.; Inagaki, T.; Kawabe, T.; Wada, K.

1987-04-01

Extinction efficiency of grains is calculated from the Mie formula on the premise that the grains are of organic composition. The optical constants adopted for the calculations are those of E. coli, polystyrene and bovine albumin. The grain radius a is assumed to obey a distribution of the form N(a) ∝ a-α and the value of α is chosen so as to make the calculated extinction curve match the observed interstellar extinction curve. Although the calculated curve gives a reasonably good fit to the observed extinction curve for wavelengths less than 2100 Å, at longer wavelength regions, agreement is poor. It is concluded that another component is required for the organic model to be viable.

How partial reinforcement of food cues affects the extinction and reacquisition of appetitive responses. A new model for dieting success?

PubMed

van den Akker, Karolien; Havermans, Remco C; Bouton, Mark E; Jansen, Anita

2014-10-01

Animals and humans can easily learn to associate an initially neutral cue with food intake through classical conditioning, but extinction of learned appetitive responses can be more difficult. Intermittent or partial reinforcement of food cues causes especially persistent behaviour in animals: after exposure to such learning schedules, the decline in responding that occurs during extinction is slow. After extinction, increases in responding with renewed reinforcement of food cues (reacquisition) might be less rapid after acquisition with partial reinforcement. In humans, it may be that the eating behaviour of some individuals resembles partial reinforcement schedules to a greater extent, possibly affecting dieting success by interacting with extinction and reacquisition. Furthermore, impulsivity has been associated with less successful dieting, and this association might be explained by impulsivity affecting the learning and extinction of appetitive responses. In the present two studies, the effects of different reinforcement schedules and impulsivity on the acquisition, extinction, and reacquisition of appetitive responses were investigated in a conditioning paradigm involving food rewards in healthy humans. Overall, the results indicate both partial reinforcement schedules and, possibly, impulsivity to be associated with worse extinction performance. A new model of dieting success is proposed: learning histories and, perhaps, certain personality traits (impulsivity) can interfere with the extinction and reacquisition of appetitive responses to food cues and they may be causally related to unsuccessful dieting. Copyright © 2014 Elsevier Ltd. All rights reserved.

An analytical prediction of the oscillation and extinction thresholds of a clarinet

NASA Astrophysics Data System (ADS)

Dalmont, Jean-Pierre; Gilbert, Joël; Kergomard, Jean; Ollivier, Sébastien

2005-11-01

This paper investigates the dynamic range of the clarinet from the oscillation threshold to the extinction at high pressure level. The use of an elementary model for the reed-mouthpiece valve effect combined with a simplified model of the pipe assuming frequency independent losses (Raman's model) allows an analytical calculation of the oscillations and their stability analysis. The different thresholds are shown to depend on parameters related to embouchure parameters and to the absorption coefficient in the pipe. Their values determine the dynamic range of the fundamental oscillations and the bifurcation scheme at the extinction.

Resonant activation of population extinctions

NASA Astrophysics Data System (ADS)

Spalding, Christopher; Doering, Charles R.; Flierl, Glenn R.

2017-10-01

Understanding the mechanisms governing population extinctions is of key importance to many problems in ecology and evolution. Stochastic factors are known to play a central role in extinction, but the interactions between a population's demographic stochasticity and environmental noise remain poorly understood. Here we model environmental forcing as a stochastic fluctuation between two states, one with a higher death rate than the other. We find that, in general, there exists a rate of fluctuations that minimizes the mean time to extinction, a phenomenon previously dubbed "resonant activation." We develop a heuristic description of the phenomenon, together with a criterion for the existence of resonant activation. Specifically, the minimum extinction time arises as a result of the system approaching a scenario wherein the severity of rare events is balanced by the time interval between them. We discuss our findings within the context of more general forms of environmental noise and suggest potential applications to evolutionary models.

Electromagnetic wave extinction within a forested canopy

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.

1989-01-01

A forested canopy is modeled by a collection of randomly oriented finite-length cylinders shaded by randomly oriented and distributed disk- or needle-shaped leaves. For a plane wave exciting the forested canopy, the extinction coefficient is formulated in terms of the extinction cross sections (ECSs) in the local frame of each forest component and the Eulerian angles of orientation (used to describe the orientation of each component). The ECSs in the local frame for the finite-length cylinders used to model the branches are obtained by using the forward-scattering theorem. ECSs in the local frame for the disk- and needle-shaped leaves are obtained by the summation of the absorption and scattering cross-sections. The behavior of the extinction coefficients with the incidence angle is investigated numerically for both deciduous and coniferous forest. The dependencies of the extinction coefficients on the orientation of the leaves are illustrated numerically.

The influence of environmental forcing on biodiversity and extinction in a resource competition model

NASA Astrophysics Data System (ADS)

Vakulenko, Sergey A.; Sudakov, Ivan; Mander, Luke

2018-03-01

In this paper, we study a model of many species that compete, directly or indirectly, for a pool of common resources under the influence of periodic, stochastic, and/or chaotic environmental forcing. Using numerical simulations, we find the number and sequence of species going extinct when the community is initially packed with a large number of species of random initial densities. Thereby, any species with a density below a given threshold is regarded to be extinct.

The influence of environmental forcing on biodiversity and extinction in a resource competition model.

PubMed

Vakulenko, Sergey A; Sudakov, Ivan; Mander, Luke

2018-03-01

In this paper, we study a model of many species that compete, directly or indirectly, for a pool of common resources under the influence of periodic, stochastic, and/or chaotic environmental forcing. Using numerical simulations, we find the number and sequence of species going extinct when the community is initially packed with a large number of species of random initial densities. Thereby, any species with a density below a given threshold is regarded to be extinct.

Open-path, closed-path and reconstructed aerosol extinction at a rural site.

PubMed

Gordon, Timothy D; Prenni, Anthony J; Renfro, James R; McClure, Ethan; Hicks, Bill; Onasch, Timothy B; Freedman, Andrew; McMeeking, Gavin R; Chen, Ping

2018-04-09

The Handix Scientific Open-Path Cavity Ringdown Spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne's Cavity Attenuated Phase Shift Particulate Matter Extinction Monitor, CAPS PMex). Derived hygroscopicity (RH < 95%) from this campaign agreed with data from 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern U.S. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016-possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high time resolution OPCRDS+CAPS PMex data, and the K ext model was more accurate than the γ model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of the IMPROVE reconstructed extinction.

Extragalactic interstellar extinction curves: Indicators of local physical conditions

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

Cecchi-Pestellini, Cesare; Viti, Serena; Williams, David A., E-mail: cecchi-pestellini@astropa.unipa.it, E-mail: sv@star.ucl.ac.uk, E-mail: daw@star.ucl.ac.uk

Normalized interstellar extinction curves (ISECs) in the Milky Way and other galaxies show a variety of shapes. This variety is attributed to differences along different sight lines in the abundances of the several dust and gas components contributing to extinction. In this paper we propose that these abundance differences are not arbitrary but are a specific consequence of the physical conditions on those sight lines. If this proposal is correct, then it implies that ISECs contain information about physical conditions in the regions generating extinction. This may be particularly important for high redshift galaxies where information on the conditions maymore » be difficult to obtain. We adopt a model of extinction carriers in which the solid and gaseous components are not immutable but respond time-dependently to the local physics. We validate this model by fitting extinction curves measured on sight lines in the Magellanic Clouds and obtained for the gamma-ray burst afterglow GRB 080605. We present results for this model as follows: (1) we show that computed ISECs are controlled by a small number of physical parameters, (2) we demonstrate the sensitivity of computed ISECs to these parameters, (3) we compute as examples ISECs for particular galaxy types, and (4) we note that different galaxy types have different shapes of ISEC.« less

Application of the CALIOP Layer Product to Evaluate the Vertical Distribution of Aerosols Estimated by Global Models: AeroCom Phase I Results

NASA Technical Reports Server (NTRS)

Koffi, Brigitte; Schulz, Michael; Breon, Francois-Marie; Griesfeller, Jan; Winker, David; Balkanski, Yves; Bauer, Susanne; Berntsen, Terje; Chin, Mian; Collins, William D.;

Dust models compatible with Planck intensity and polarization data in translucent lines of sight

NASA Astrophysics Data System (ADS)

Guillet, V.; Fanciullo, L.; Verstraete, L.; Boulanger, F.; Jones, A. P.; Miville-Deschênes, M.-A.; Ysard, N.; Levrier, F.; Alves, M.

2018-02-01

Context. Current dust models are challenged by the dust properties inferred from the analysis of Planck observations in total and polarized emission. Aims: We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight (0.5 < AV < 2.5). Methods: We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, total and polarized spectral energy distributions (SEDs) with polycyclic aromatic hydrocarbons, astrosilicate and amorphous carbon (a-C) grains. The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. Results: With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio P353/pV derived with Planck data. Successful models are those using prolate astrosilicate grains with an elongation a/b = 3 and an inclusion of 20% porosity. The spectral dependence of the polarized SED is steeper in our models than in the data. Models perform slightly better when a-C grains are aligned. A small (6%) volume inclusion of a-C in the astrosilicate matrix removes the need for porosity and perfect grain alignment, and improves the fit to the polarized SED. Conclusions: Dust models based on astrosilicates can be reconciled with data by adapting the shape of grains and adding inclusions of porosity or a-C in the astrosilicate matrix.

Body size reductions in nonmammalian eutheriodont therapsids (Synapsida) during the end-Permian mass extinction.

PubMed

Huttenlocker, Adam K

2014-01-01

The extent to which mass extinctions influence body size evolution in major tetrapod clades is inadequately understood. For example, the 'Lilliput effect,' a common feature of mass extinctions, describes a temporary decrease in body sizes of survivor taxa in post-extinction faunas. However, its signature on existing patterns of body size evolution in tetrapods and the persistence of its impacts during post-extinction recoveries are virtually unknown, and rarely compared in both geologic and phylogenetic contexts. Here, I evaluate temporal and phylogenetic distributions of body size in Permo-Triassic therocephalian and cynodont therapsids (eutheriodonts) using a museum collections-based approach and time series model fitting on a regional stratigraphic sequence from the Karoo Basin, South Africa. I further employed rank order correlation tests on global age and clade rank data from an expanded phylogenetic dataset, and performed evolutionary model testing using Brownian (passive diffusion) models. Results support significant size reductions in the immediate aftermath of the end-Permian mass extinction (ca. 252.3 Ma) consistent with some definitions of Lilliput effects. However, this temporal succession reflects a pattern that was underscored largely by Brownian processes and constructive selectivity. Results also support two recent contentions about body size evolution and mass extinctions: 1) active, directional evolution in size traits is rare over macroevolutionary time scales and 2) geologically brief size reductions may be accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns.

The mineralogical, chemical, and chronological characteristics of the crystalline Apollo 16 impact melt rocks

NASA Technical Reports Server (NTRS)

Reimold, W. U.; Reimold, J. N.

1984-01-01

A comparative review of mineralogical, chemical, and chronological data on crystalline Apollo 16 impact melt rocks is presented. The use of such data to identify distinct impact melt complex is discussed, and 22 distinct impact melt bodies are identified. The recently detected group of feldspathic microporphyritic (FM) melt rocks was tested for chemical and isotopic homogeneity; instrumental neutron activation analysis and new Rb-Sr isotopic whole rock data indicate that FMs were probably not derived from a single impact melt sheet, but might be representative of the Descartes basement. Stratigraphical and chronological concepts for the geological development of the landing site are discussed, and a model is presented for the formation of the Cayley Plains and the Descartes formation.

The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Thermal histories of Mercury and the Moon. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Leake, M. A.

1982-01-01

To determine a planet's thermal history, a wide range of data is necessary. These data include remote sensing results, photogeologic evidence, magnetic field and remanent magnetization data, composition and ages of samples, and physical parameters of the planet and its orbit. Few of these data form unambiguous constraints for thermal models of Mercury. Igneous Chronology as the time history of the differentiation and igneous activity, is defined. Igneous Chronology is used here in the sense of the apparent igneous or relative chronology of geologic events, such as plains formation (through whatever mechanism) relative to the crater production and tectonic history (lineament and scarp formation).

Mathematical Modeling of Extinction of Inhomogeneous Populations

PubMed Central

Karev, G.P.; Kareva, I.

2016-01-01

Mathematical models of population extinction have a variety of applications in such areas as ecology, paleontology and conservation biology. Here we propose and investigate two types of sub-exponential models of population extinction. Unlike the more traditional exponential models, the life duration of sub-exponential models is finite. In the first model, the population is assumed to be composed clones that are independent from each other. In the second model, we assume that the size of the population as a whole decreases according to the sub-exponential equation. We then investigate the “unobserved heterogeneity”, i.e. the underlying inhomogeneous population model, and calculate the distribution of frequencies of clones for both models. We show that the dynamics of frequencies in the first model is governed by the principle of minimum of Tsallis information loss. In the second model, the notion of “internal population time” is proposed; with respect to the internal time, the dynamics of frequencies is governed by the principle of minimum of Shannon information loss. The results of this analysis show that the principle of minimum of information loss is the underlying law for the evolution of a broad class of models of population extinction. Finally, we propose a possible application of this modeling framework to mechanisms underlying time perception. PMID:27090117

Extinction of Pavlovian conditioning: The influence of trial number and reinforcement history.

PubMed

Chan, C K J; Harris, Justin A

2017-08-01

Pavlovian conditioning is sensitive to the temporal relationship between the conditioned stimulus (CS) and the unconditioned stimulus (US). This has motivated models that describe learning as a process that continuously updates associative strength during the trial or specifically encodes the CS-US interval. These models predict that extinction of responding is also continuous, such that response loss is proportional to the cumulative duration of exposure to the CS without the US. We review evidence showing that this prediction is incorrect, and that extinction is trial-based rather than time-based. We also present two experiments that test the importance of trials versus time on the Partial Reinforcement Extinction Effect (PREE), in which responding extinguishes more slowly for a CS that was inconsistently reinforced with the US than for a consistently reinforced one. We show that increasing the number of extinction trials of the partially reinforced CS, relative to the consistently reinforced CS, overcomes the PREE. However, increasing the duration of extinction trials by the same amount does not overcome the PREE. We conclude that animals learn about the likelihood of the US per trial during conditioning, and learn trial-by-trial about the absence of the US during extinction. Moreover, what they learn about the likelihood of the US during conditioning affects how sensitive they are to the absence of the US during extinction. Copyright © 2017 Elsevier B.V. All rights reserved.

Dynamics of Droplet Extinction in Slow Convective Flows

NASA Technical Reports Server (NTRS)

Nayagam, V.; Haggard, J. B., Jr.; Williams, F. A.

1999-01-01

The classical model for droplet combustion predicts that the square of the droplet diameter decreases linearly with time. It also predicts that a droplet of any size will burn to completion over a period of time. However, it has been known for some time that under certain conditions flames surrounding a droplet, in a quiescent environment, could extinguish because of insufficient residence time for the chemistry to proceed to completion. This type of extinction that occurs for smaller droplets has been studied extensively in the past. Large droplets, on the other hand, exhibit a different type of extinction where excessive radiative heat loss from the flame zone leads to extinction. This mode of "radiative extinction" was theoretically predicted for droplet burning by Chao et al. and was observed in recent space experiments in a quiescent environment. Thus far, the fundamental flammability limit prescribed by radiative extinction of liquid droplets has been measured only under quiescent environmental conditions. In many space platforms, however, ventilation systems produce small convective flows and understanding of the influences of this convection on the extinction process will help better define the radiative extinction flammability boundaries. Boundaries defined by experiments and captured using theoretical models could provide enhanced fire safety margin in space explor1999063d investigation of convective effects will help in interpretations of burning-rate data obtained during free-floated droplet combustion experiments with small residual velocities.

Infrared Extinction and Stellar Populations in the Milky Way Midplane

NASA Astrophysics Data System (ADS)

Zasowski, Gail; Majewski, S. R.; Benjamin, R. A.; Nidever, D. L.; Skrutskie, M. F.; Indebetouw, R.; Patterson, R. J.; Meade, M. R.; Whitney, B. A.; Babler, B.; Churchwell, E.; Watson, C.

2012-01-01

The primary laboratory for developing and testing models of galaxy formation, structure, and evolution is our own Milky Way, the closest large galaxy and the only one in which we can resolve large numbers of individual stars. The recent availability of extensive stellar surveys, particularly infrared ones, has enabled precise, contiguous measurement of large-scale Galactic properties, a major improvement over inferences based on selected, but scattered, sightlines. However, our ability to fully exploit the Milky Way as a galactic laboratory is severely hampered by the fact that its midplane and central bulge -- where most of the Galactic stellar mass lies -- is heavily obscured by interstellar dust. Therefore, proper consideration of the interstellar extinction is crucial. This thesis describes a new extinction-correction method (the RJCE method) that measures the foreground extinction towards each star and, in many cases, enables recovery of its intrinsic stellar type. We have demonstrated the RJCE Method's validity and used it to produce new, reliable extinction maps of the heavily-reddened Galactic midplane. Taking advantage of the recovered stellar type information, we have generated maps probing the extinction at different heliocentric distances, thus yielding information on the elusive three-dimensional distribution of the interstellar dust. We also performed a study of the interstellar extinction law itself which revealed variations previously undetected in the diffuse ISM and established constraints on models of ISM grain formation and evolution. Furthermore, we undertook a study of large-scale stellar structure in the inner Galaxy -- the bar(s), bulge(s), and inner spiral arms. We used observed and extinction-corrected infrared photometry to map the coherent stellar features in these heavily-obscured parts of the Galaxy, placing constraints on models of the central stellar mass distribution.

Therapeutic Effects of Extinction Learning as a Model of Exposure Therapy in Rats.

PubMed

Fucich, Elizabeth A; Paredes, Denisse; Morilak, David A

2016-12-01

Current treatments for stress-related psychiatric disorders, such as depression and posttraumatic stress disorder (PTSD), are inadequate. Cognitive behavioral psychotherapies, including exposure therapy, are an alternative to pharmacotherapy, but the neurobiological mechanisms are unknown. Preclinical models demonstrating therapeutic effects of behavioral interventions are required to investigate such mechanisms. Exposure therapy bears similarity to extinction learning. Thus, we investigated the therapeutic effects of extinction learning as a behavioral intervention to model exposure therapy in rats, testing its effectiveness in reversing chronic stress-induced deficits in cognitive flexibility and coping behavior that resemble dimensions of depression and PTSD. Rats were fear-conditioned by pairing a tone with footshock, and then exposed to chronic unpredictable stress (CUS) that induces deficits in cognitive set-shifting and active coping behavior. They then received an extinction learning session as a therapeutic intervention by repeated exposure to the tone with no shock. Effects on cognitive flexibility and coping behavior were assessed 24 h later on the attentional set-shifting test or shock-probe defensive burying test, respectively. Extinction reversed the CUS-induced deficits in cognitive flexibility and coping behavior, and increased phosphorylation of ribosomal protein S6 in the medial prefrontal cortex (mPFC) of stress-compromised rats, suggesting a role for activity-dependent protein synthesis in the therapeutic effect. Inhibiting protein synthesis by microinjecting anisomycin into mPFC blocked the therapeutic effect of extinction on cognitive flexibility. These results demonstrate the utility of extinction as a model by which to study mechanisms underlying exposure therapy, and suggest these mechanisms involve protein synthesis in the mPFC, the further study of which may identify novel therapeutic targets.

Therapeutic Effects of Extinction Learning as a Model of Exposure Therapy in Rats

PubMed Central

Fucich, Elizabeth A; Paredes, Denisse; Morilak, David A

2016-01-01

Current treatments for stress-related psychiatric disorders, such as depression and posttraumatic stress disorder (PTSD), are inadequate. Cognitive behavioral psychotherapies, including exposure therapy, are an alternative to pharmacotherapy, but the neurobiological mechanisms are unknown. Preclinical models demonstrating therapeutic effects of behavioral interventions are required to investigate such mechanisms. Exposure therapy bears similarity to extinction learning. Thus, we investigated the therapeutic effects of extinction learning as a behavioral intervention to model exposure therapy in rats, testing its effectiveness in reversing chronic stress-induced deficits in cognitive flexibility and coping behavior that resemble dimensions of depression and PTSD. Rats were fear-conditioned by pairing a tone with footshock, and then exposed to chronic unpredictable stress (CUS) that induces deficits in cognitive set-shifting and active coping behavior. They then received an extinction learning session as a therapeutic intervention by repeated exposure to the tone with no shock. Effects on cognitive flexibility and coping behavior were assessed 24 h later on the attentional set-shifting test or shock-probe defensive burying test, respectively. Extinction reversed the CUS-induced deficits in cognitive flexibility and coping behavior, and increased phosphorylation of ribosomal protein S6 in the medial prefrontal cortex (mPFC) of stress-compromised rats, suggesting a role for activity-dependent protein synthesis in the therapeutic effect. Inhibiting protein synthesis by microinjecting anisomycin into mPFC blocked the therapeutic effect of extinction on cognitive flexibility. These results demonstrate the utility of extinction as a model by which to study mechanisms underlying exposure therapy, and suggest these mechanisms involve protein synthesis in the mPFC, the further study of which may identify novel therapeutic targets. PMID:27417516

The Role of the Medial Prefrontal Cortex in Trace Fear Extinction

ERIC Educational Resources Information Center

Kwapis, Janine L.; Jarome, Timothy J.; Helmstetter, Fred J.

2015-01-01

The extinction of delay fear conditioning relies on a neural circuit that has received much attention and is relatively well defined. Whether this established circuit also supports the extinction of more complex associations, however, is unclear. Trace fear conditioning is a better model of complex relational learning, yet the circuit that…

Predicting extinctions as a result of climate change

Treesearch

Mark W. Schwartz; Louis R. Iverson; Anantha M. Prasad; Stephen N. Matthews; Raymond J. O' Connor; Raymond J. O' Connor

2006-01-01

Widespread extinction is a predicted ecological consequence of global warming. Extinction risk under climate change scenarios is a function of distribution breadth. Focusing on trees and birds of the eastern United States, we used joint climate and environment models to examine fit and climate change vulnerability as a function of distribution breadth. We found that...

Quantification of habitat fragmentation reveals extinction risk in terrestrial mammals

PubMed Central

Crooks, Kevin R.; Burdett, Christopher L.; Theobald, David M.; King, Sarah R. B.; Rondinini, Carlo; Boitani, Luigi

2017-01-01

Although habitat fragmentation is often assumed to be a primary driver of extinction, global patterns of fragmentation and its relationship to extinction risk have not been consistently quantified for any major animal taxon. We developed high-resolution habitat fragmentation models and used phylogenetic comparative methods to quantify the effects of habitat fragmentation on the world’s terrestrial mammals, including 4,018 species across 26 taxonomic Orders. Results demonstrate that species with more fragmentation are at greater risk of extinction, even after accounting for the effects of key macroecological predictors, such as body size and geographic range size. Species with higher fragmentation had smaller ranges and a lower proportion of high-suitability habitat within their range, and most high-suitability habitat occurred outside of protected areas, further elevating extinction risk. Our models provide a quantitative evaluation of extinction risk assessments for species, allow for identification of emerging threats in species not classified as threatened, and provide maps of global hotspots of fragmentation for the world’s terrestrial mammals. Quantification of habitat fragmentation will help guide threat assessment and strategic priorities for global mammal conservation. PMID:28673992

Quantification of habitat fragmentation reveals extinction risk in terrestrial mammals.

PubMed

Crooks, Kevin R; Burdett, Christopher L; Theobald, David M; King, Sarah R B; Di Marco, Moreno; Rondinini, Carlo; Boitani, Luigi

2017-07-18

Although habitat fragmentation is often assumed to be a primary driver of extinction, global patterns of fragmentation and its relationship to extinction risk have not been consistently quantified for any major animal taxon. We developed high-resolution habitat fragmentation models and used phylogenetic comparative methods to quantify the effects of habitat fragmentation on the world's terrestrial mammals, including 4,018 species across 26 taxonomic Orders. Results demonstrate that species with more fragmentation are at greater risk of extinction, even after accounting for the effects of key macroecological predictors, such as body size and geographic range size. Species with higher fragmentation had smaller ranges and a lower proportion of high-suitability habitat within their range, and most high-suitability habitat occurred outside of protected areas, further elevating extinction risk. Our models provide a quantitative evaluation of extinction risk assessments for species, allow for identification of emerging threats in species not classified as threatened, and provide maps of global hotspots of fragmentation for the world's terrestrial mammals. Quantification of habitat fragmentation will help guide threat assessment and strategic priorities for global mammal conservation.

Parasite biodiversity faces extinction and redistribution in a changing climate.

PubMed

Carlson, Colin J; Burgio, Kevin R; Dougherty, Eric R; Phillips, Anna J; Bueno, Veronica M; Clements, Christopher F; Castaldo, Giovanni; Dallas, Tad A; Cizauskas, Carrie A; Cumming, Graeme S; Doña, Jorge; Harris, Nyeema C; Jovani, Roger; Mironov, Sergey; Muellerklein, Oliver C; Proctor, Heather C; Getz, Wayne M

2017-09-01

Climate change is a well-documented driver of both wildlife extinction and disease emergence, but the negative impacts of climate change on parasite diversity are undocumented. We compiled the most comprehensive spatially explicit data set available for parasites, projected range shifts in a changing climate, and estimated extinction rates for eight major parasite clades. On the basis of 53,133 occurrences capturing the geographic ranges of 457 parasite species, conservative model projections suggest that 5 to 10% of these species are committed to extinction by 2070 from climate-driven habitat loss alone. We find no evidence that parasites with zoonotic potential have a significantly higher potential to gain range in a changing climate, but we do find that ectoparasites (especially ticks) fare disproportionately worse than endoparasites. Accounting for host-driven coextinctions, models predict that up to 30% of parasitic worms are committed to extinction, driven by a combination of direct and indirect pressures. Despite high local extinction rates, parasite richness could still increase by an order of magnitude in some places, because species successfully tracking climate change invade temperate ecosystems and replace native species with unpredictable ecological consequences.

The transcriptional landscape of age in human peripheral blood

PubMed Central

Peters, Marjolein J.; Joehanes, Roby; Pilling, Luke C.; Schurmann, Claudia; Conneely, Karen N.; Powell, Joseph; Reinmaa, Eva; Sutphin, George L.; Zhernakova, Alexandra; Schramm, Katharina; Wilson, Yana A.; Kobes, Sayuko; Tukiainen, Taru; Nalls, Michael A.; Hernandez, Dena G.; Cookson, Mark R.; Gibbs, Raphael J.; Hardy, John; Ramasamy, Adaikalavan; Zonderman, Alan B.; Dillman, Allissa; Traynor, Bryan; Smith, Colin; Longo, Dan L.; Trabzuni, Daniah; Troncoso, Juan; van der Brug, Marcel; Weale, Michael E.; O'Brien, Richard; Johnson, Robert; Walker, Robert; Zielke, Ronald H.; Arepalli, Sampath; Ryten, Mina; Singleton, Andrew B.; Ramos, Yolande F.; Göring, Harald H. H.; Fornage, Myriam; Liu, Yongmei; Gharib, Sina A.; Stranger, Barbara E.; De Jager, Philip L.; Aviv, Abraham; Levy, Daniel; Murabito, Joanne M.; Munson, Peter J.; Huan, Tianxiao; Hofman, Albert; Uitterlinden, André G.; Rivadeneira, Fernando; van Rooij, Jeroen; Stolk, Lisette; Broer, Linda; Verbiest, Michael M. P. J.; Jhamai, Mila; Arp, Pascal; Metspalu, Andres; Tserel, Liina; Milani, Lili; Samani, Nilesh J.; Peterson, Pärt; Kasela, Silva; Codd, Veryan; Peters, Annette; Ward-Caviness, Cavin K.; Herder, Christian; Waldenberger, Melanie; Roden, Michael; Singmann, Paula; Zeilinger, Sonja; Illig, Thomas; Homuth, Georg; Grabe, Hans-Jörgen; Völzke, Henry; Steil, Leif; Kocher, Thomas; Murray, Anna; Melzer, David; Yaghootkar, Hanieh; Bandinelli, Stefania; Moses, Eric K.; Kent, Jack W.; Curran, Joanne E.; Johnson, Matthew P.; Williams-Blangero, Sarah; Westra, Harm-Jan; McRae, Allan F.; Smith, Jennifer A.; Kardia, Sharon L. R.; Hovatta, Iiris; Perola, Markus; Ripatti, Samuli; Salomaa, Veikko; Henders, Anjali K.; Martin, Nicholas G.; Smith, Alicia K.; Mehta, Divya; Binder, Elisabeth B.; Nylocks, K Maria; Kennedy, Elizabeth M.; Klengel, Torsten; Ding, Jingzhong; Suchy-Dicey, Astrid M.; Enquobahrie, Daniel A.; Brody, Jennifer; Rotter, Jerome I.; Chen, Yii-Der I.; Houwing-Duistermaat, Jeanine; Kloppenburg, Margreet; Slagboom, P. Eline; Helmer, Quinta; den Hollander, Wouter; Bean, Shannon; Raj, Towfique; Bakhshi, Noman; Wang, Qiao Ping; Oyston, Lisa J.; Psaty, Bruce M.; Tracy, Russell P.; Montgomery, Grant W.; Turner, Stephen T.; Blangero, John; Meulenbelt, Ingrid; Ressler, Kerry J.; Yang, Jian; Franke, Lude; Kettunen, Johannes; Visscher, Peter M.; Neely, G. Gregory; Korstanje, Ron; Hanson, Robert L.; Prokisch, Holger; Ferrucci, Luigi; Esko, Tonu; Teumer, Alexander; van Meurs, Joyce B. J.; Johnson, Andrew D.

2015-01-01

Disease incidences increase with age, but the molecular characteristics of ageing that lead to increased disease susceptibility remain inadequately understood. Here we perform a whole-blood gene expression meta-analysis in 14,983 individuals of European ancestry (including replication) and identify 1,497 genes that are differentially expressed with chronological age. The age-associated genes do not harbor more age-associated CpG-methylation sites than other genes, but are instead enriched for the presence of potentially functional CpG-methylation sites in enhancer and insulator regions that associate with both chronological age and gene expression levels. We further used the gene expression profiles to calculate the ‘transcriptomic age' of an individual, and show that differences between transcriptomic age and chronological age are associated with biological features linked to ageing, such as blood pressure, cholesterol levels, fasting glucose, and body mass index. The transcriptomic prediction model adds biological relevance and complements existing epigenetic prediction models, and can be used by others to calculate transcriptomic age in external cohorts. PMID:26490707

Extinguishing trace fear engages the retrosplenial cortex rather than the amygdala

PubMed Central

Kwapis, Janine L.; Jarome, Timothy J.; Lee, Jonathan L.; Gilmartin, Marieke R.; Helmstetter, Fred J.

2013-01-01

Extinction learning underlies the treatment for a variety of anxiety disorders. Most of what is known about the neurobiology of extinction is based on standard “delay” fear conditioning, in which awareness is not required for learning. Little is known about how complex, explicit associations extinguish, however. “Trace” conditioning is considered to be a rodent model of explicit fear because it relies on both the cortex and hippocampus and requires explicit contingency awareness in humans. Here, we explore the neural circuit supporting trace fear extinction in order to better understand how complex memories extinguish. We first show that the amygdala is selectively involved in delay fear extinction; blocking intra-amygdala glutamate receptors disrupted delay, but not trace extinction. Further, ERK phosphorylation was increased in the amygdala after delay, but not trace extinction. We then identify the retrosplenial cortex (RSC) as a key structure supporting trace extinction. ERK phosphorylation was selectively increased in the RSC following trace extinction and blocking intra-RSC NMDA receptors impaired trace, but not delay extinction. These findings indicate that delay and trace extinction require different neural circuits; delay extinction requires plasticity in the amygdala whereas trace extinction requires the RSC. Anxiety disorders linked to explicit memory may therefore depend on cortical processes that have not been traditionally targeted by extinction studies based on delay fear. PMID:24055593

Using c-Jun to identify fear extinction learning-specific patterns of neural activity that are affected by single prolonged stress.

PubMed

Knox, Dayan; Stanfield, Briana R; Staib, Jennifer M; David, Nina P; DePietro, Thomas; Chamness, Marisa; Schneider, Elizabeth K; Keller, Samantha M; Lawless, Caroline

2018-04-02

Neural circuits via which stress leads to disruptions in fear extinction is often explored in animal stress models. Using the single prolonged stress (SPS) model of post traumatic stress disorder and the immediate early gene (IEG) c-Fos as a measure of neural activity, we previously identified patterns of neural activity through which SPS disrupts extinction retention. However, none of these stress effects were specific to fear or extinction learning and memory. C-Jun is another IEG that is sometimes regulated in a different manner to c-Fos and could be used to identify emotional learning/memory specific patterns of neural activity that are sensitive to SPS. Animals were either fear conditioned (CS-fear) or presented with CSs only (CS-only) then subjected to extinction training and testing. C-Jun was then assayed within neural substrates critical for extinction memory. Inhibited c-Jun levels in the hippocampus (Hipp) and enhanced functional connectivity between the ventromedial prefrontal cortex (vmPFC) and basolateral amygdala (BLA) during extinction training was disrupted by SPS in the CS-fear group only. As a result, these effects were specific to emotional learning/memory. SPS also disrupted inhibited Hipp c-Jun levels, enhanced BLA c-Jun levels, and altered functional connectivity among the vmPFC, BLA, and Hipp during extinction testing in SPS rats in the CS-fear and CS-only groups. As a result, these effects were not specific to emotional learning/memory. Our findings suggest that SPS disrupts neural activity specific to extinction memory, but may also disrupt the retention of fear extinction by mechanisms that do not involve emotional learning/memory. Copyright © 2017 Elsevier B.V. All rights reserved.

Inhibition of serotonin transporters disrupts the enhancement of fear memory extinction by 3,4-methylenedioxymethamphetamine (MDMA).

PubMed

Young, Matthew B; Norrholm, Seth D; Khoury, Lara M; Jovanovic, Tanja; Rauch, Sheila A M; Reiff, Collin M; Dunlop, Boadie W; Rothbaum, Barbara O; Howell, Leonard L

2017-10-01

3,4-Methylenedioxymethamphetamine (MDMA) persistently improves symptoms of post-traumatic stress disorder (PTSD) when combined with psychotherapy. Studies in rodents suggest that these effects can be attributed to enhancement of fear memory extinction. Therefore, MDMA may improve the effects of exposure-based therapy for PTSD, particularly in treatment-resistant patients. However, given MDMA's broad pharmacological profile, further investigation is warranted before moving to a complex clinical population. We aimed to inform clinical research by providing a translational model of MDMA's effect, and elucidating monoaminergic mechanisms through which MDMA enhances fear extinction. We explored the importance of monoamine transporters targeted by MDMA to fear memory extinction, as measured by reductions in conditioned freezing and fear-potentiated startle (FPS) in mice. Mice were treated with selective inhibitors of individual monoamine transporters prior to combined MDMA treatment and fear extinction training. MDMA enhanced the lasting extinction of FPS. Acute and chronic treatment with a 5-HT transporter (5-HTT) inhibitor blocked MDMA's effect on fear memory extinction. Acute inhibition of dopamine (DA) and norepinephrine (NE) transporters had no effect. 5-HT release alone did not enhance extinction. Blockade of MDMA's effect by 5-HTT inhibition also downregulated 5-HT 2A -mediated behavior, and 5-HT 2A antagonism disrupted MDMA's effect on extinction. We validate enhancement of fear memory extinction by MDMA in a translational behavioral model, and reveal the importance of 5-HTT and 5-HT 2A receptors to this effect. These observations support future clinical research of MDMA as an adjunct to exposure therapy, and provide important pharmacological considerations for clinical use in a population frequently treated with 5-HTT inhibitors.

Stochastic foundations in nonlinear density-regulation growth

NASA Astrophysics Data System (ADS)

Méndez, Vicenç; Assaf, Michael; Horsthemke, Werner; Campos, Daniel

2017-08-01

In this work we construct individual-based models that give rise to the generalized logistic model at the mean-field deterministic level and that allow us to interpret the parameters of these models in terms of individual interactions. We also study the effect of internal fluctuations on the long-time dynamics for the different models that have been widely used in the literature, such as the theta-logistic and Savageau models. In particular, we determine the conditions for population extinction and calculate the mean time to extinction. If the population does not become extinct, we obtain analytical expressions for the population abundance distribution. Our theoretical results are based on WKB theory and the probability generating function formalism and are verified by numerical simulations.

Local extinction and recolonization, species effective population size, and modern human origins.

PubMed

Eller, Elise; Hawks, John; Relethford, John H

2004-10-01

A primary objection from a population genetics perspective to a multiregional model of modern human origins is that the model posits a large census size, whereas genetic data suggest a small effective population size. The relationship between census size and effective size is complex, but arguments based on an island model of migration show that if the effective population size reflects the number of breeding individuals and the effects of population subdivision, then an effective population size of 10,000 is inconsistent with the census size of 500,000 to 1,000,000 that has been suggested by archeological evidence. However, these models have ignored the effects of population extinction and recolonization, which increase the expected variance among demes and reduce the inbreeding effective population size. Using models developed for population extinction and recolonization, we show that a large census size consistent with the multiregional model can be reconciled with an effective population size of 10,000, but genetic variation among demes must be high, reflecting low interdeme migration rates and a colonization process that involves a small number of colonists or kin-structured colonization. Ethnographic and archeological evidence is insufficient to determine whether such demographic conditions existed among Pleistocene human populations, and further work needs to be done. More realistic models that incorporate isolation by distance and heterogeneity in extinction rates and effective deme sizes also need to be developed. However, if true, a process of population extinction and recolonization has interesting implications for human demographic history.

Search for jet extinction in the inclusive jet-pt spectrum from proton-proton collisions at sqrt(s) = 8 TeV

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

Khachatryan, Vardan; et al.,

The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To testmore » this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale.« less

Search for jet extinction in the inclusive jet-pT spectrum from proton-proton collisions at √s =8 TeV

NASA Astrophysics Data System (ADS)

Khachatryan, V.; Sirunyan, A. M.; Tumasyan, A.; Adam, W.; Bergauer, T.; Dragicevic, M.; Erö, J.; Fabjan, C.; Friedl, M.; Frühwirth, R.; Ghete, V. M.; Hartl, C.; Hörmann, N.; Hrubec, J.; Jeitler, M.; Kiesenhofer, W.; Knünz, V.; Krammer, M.; Krätschmer, I.; Liko, D.; Mikulec, I.; Rabady, D.; Rahbaran, B.; Rohringer, H.; Schöfbeck, R.; Strauss, J.; Taurok, A.; Treberer-Treberspurg, W.; Waltenberger, W.; Wulz, C.-E.; Mossolov, V.; Shumeiko, N.; Suarez Gonzalez, J.; Alderweireldt, S.; Bansal, M.; Bansal, S.; Cornelis, T.; De Wolf, E. A.; Janssen, X.; Knutsson, A.; Luyckx, S.; Ochesanu, S.; Roland, B.; Rougny, R.; Van De Klundert, M.; Van Haevermaet, H.; Van Mechelen, P.; Van Remortel, N.; Van Spilbeeck, A.; Blekman, F.; Blyweert, S.; D'Hondt, J.; Daci, N.; Heracleous, N.; Kalogeropoulos, A.; Keaveney, J.; Kim, T. J.; Lowette, S.; Maes, M.; Olbrechts, A.; Python, Q.; Strom, D.; Tavernier, S.; Van Doninck, W.; Van Mulders, P.; Van Onsem, G. P.; Villella, I.; Caillol, C.; Clerbaux, B.; De Lentdecker, G.; Dobur, D.; Favart, L.; Gay, A. P. R.; Grebenyuk, A.; Léonard, A.; Mohammadi, A.; Perniè, L.; Reis, T.; Seva, T.; Thomas, L.; Vander Velde, C.; Vanlaer, P.; Wang, J.; Adler, V.; Beernaert, K.; Benucci, L.; Cimmino, A.; Costantini, S.; Crucy, S.; Dildick, S.; Fagot, A.; Garcia, G.; Klein, B.; Mccartin, J.; Ocampo Rios, A. A.; Ryckbosch, D.; Salva Diblen, S.; Sigamani, M.; Strobbe, N.; Thyssen, F.; Tytgat, M.; Yazgan, E.; Zaganidis, N.; Basegmez, S.; Beluffi, C.; Bruno, G.; Castello, R.; Caudron, A.; Ceard, L.; Da Silveira, G. G.; Delaere, C.; du Pree, T.; Favart, D.; Forthomme, L.; Giammanco, A.; Hollar, J.; Jez, P.; Komm, M.; Lemaitre, V.; Liao, J.; Nuttens, C.; Pagano, D.; Pin, A.; Piotrzkowski, K.; Popov, A.; Quertenmont, L.; Selvaggi, M.; Vidal Marono, M.; Vizan Garcia, J. M.; Beliy, N.; Caebergs, T.; Daubie, E.; Hammad, G. H.; Alves, G. A.; Correa Martins Junior, M.; Dos Reis Martins, T.; Pol, M. E.; Aldá Júnior, W. L.; Carvalho, W.; Chinellato, J.; Custódio, A.; Da Costa, E. M.; De Jesus Damiao, D.; De Oliveira Martins, C.; Fonseca De Souza, S.; Malbouisson, H.; Malek, M.; Matos Figueiredo, D.; Mundim, L.; Nogima, H.; Prado Da Silva, W. L.; Santaolalla, J.; Santoro, A.; Sznajder, A.; Tonelli Manganote, E. J.; Vilela Pereira, A.; Bernardes, C. A.; Dias, F. A.; Fernandez Perez Tomei, T. R.; Gregores, E. M.; Mercadante, P. G.; Novaes, S. F.; Padula, Sandra S.; Aleksandrov, A.; Genchev, V.; Iaydjiev, P.; Marinov, A.; Piperov, S.; Rodozov, M.; Sultanov, G.; Vutova, M.; Dimitrov, A.; Glushkov, I.; Hadjiiska, R.; Kozhuharov, V.; Litov, L.; Pavlov, B.; Petkov, P.; Bian, J. G.; Chen, G. M.; Chen, H. S.; Chen, M.; Du, R.; Jiang, C. H.; Liang, D.; Liang, S.; Plestina, R.; Tao, J.; Wang, X.; Wang, Z.; Asawatangtrakuldee, C.; Ban, Y.; Guo, Y.; Li, Q.; Li, W.; Liu, S.; Mao, Y.; Qian, S. J.; Wang, D.; Zhang, L.; Zou, W.; Avila, C.; Chaparro Sierra, L. F.; Florez, C.; Gomez, J. P.; Gomez Moreno, B.; Sanabria, J. C.; Godinovic, N.; Lelas, D.; Polic, D.; Puljak, I.; Antunovic, Z.; Kovac, M.; Brigljevic, V.; Kadija, K.; Luetic, J.; Mekterovic, D.; Sudic, L.; Attikis, A.; Mavromanolakis, G.; Mousa, J.; Nicolaou, C.; Ptochos, F.; Razis, P. A.; Bodlak, M.; Finger, M.; Finger, M.; Assran, Y.; Elgammal, S.; Mahmoud, M. A.; Radi, A.; Kadastik, M.; Murumaa, M.; Raidal, M.; Tiko, A.; Eerola, P.; Fedi, G.; Voutilainen, M.; Härkönen, J.; Karimäki, V.; Kinnunen, R.; Kortelainen, M. J.; Lampén, T.; Lassila-Perini, K.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Peltola, T.; Tuominen, E.; Tuominiemi, J.; Tuovinen, E.; Wendland, L.; Tuuva, T.; Besancon, M.; Couderc, F.; Dejardin, M.; Denegri, D.; Fabbro, B.; Faure, J. L.; Favaro, C.; Ferri, F.; Ganjour, S.; Givernaud, A.; Gras, P.; Hamel de Monchenault, G.; Jarry, P.; Locci, E.; Malcles, J.; Nayak, A.; Rander, J.; Rosowsky, A.; Titov, M.; Baffioni, S.; Beaudette, F.; Busson, P.; Charlot, C.; Dahms, T.; Dalchenko, M.; Dobrzynski, L.; Filipovic, N.; Florent, A.; Granier de Cassagnac, R.; Mastrolorenzo, L.; Miné, P.; Mironov, C.; Naranjo, I. N.; Nguyen, M.; Ochando, C.; Paganini, P.; Salerno, R.; Sauvan, J. B.; Sirois, Y.; Veelken, C.; Yilmaz, Y.; Zabi, A.; Agram, J.-L.; Andrea, J.; Aubin, A.; Bloch, D.; Brom, J.-M.; Chabert, E. C.; Collard, C.; Conte, E.; Fontaine, J.-C.; Gelé, D.; Goerlach, U.; Goetzmann, C.; Le Bihan, A.-C.; Van Hove, P.; Gadrat, S.; Beauceron, S.; Beaupere, N.; Boudoul, G.; Brochet, S.; Carrillo Montoya, C. A.; Chasserat, J.; Chierici, R.; Contardo, D.; Depasse, P.; El Mamouni, H.; Fan, J.; Fay, J.; Gascon, S.; Gouzevitch, M.; Ille, B.; Kurca, T.; Lethuillier, M.; Mirabito, L.; Perries, S.; Ruiz Alvarez, J. D.; Sabes, D.; Sgandurra, L.; Sordini, V.; Vander Donckt, M.; Verdier, P.; Viret, S.; Xiao, H.; Tsamalaidze, Z.; Autermann, C.; Beranek, S.; Bontenackels, M.; Calpas, B.; Edelhoff, M.; Feld, L.; Hindrichs, O.; Klein, K.; Ostapchuk, A.; Perieanu, A.; Raupach, F.; Sammet, J.; Schael, S.; Sprenger, D.; Weber, H.; Wittmer, B.; Zhukov, V.; Ata, M.; Caudron, J.; Dietz-Laursonn, E.; Duchardt, D.; Erdmann, M.; Fischer, R.; Güth, A.; Hebbeker, T.; Heidemann, C.; Hoepfner, K.; Klingebiel, D.; Knutzen, S.; Kreuzer, P.; Merschmeyer, M.; Meyer, A.; Olschewski, M.; Padeken, K.; Papacz, P.; Reithler, H.; Schmitz, S. A.; Sonnenschein, L.; Teyssier, D.; Thüer, S.; Weber, M.; Cherepanov, V.; Erdogan, Y.; Flügge, G.; Geenen, H.; Geisler, M.; Haj Ahmad, W.; Hoehle, F.; Kargoll, B.; Kress, T.; Kuessel, Y.; Lingemann, J.; Nowack, A.; Nugent, I. M.; Perchalla, L.; Pooth, O.; Stahl, A.; Asin, I.; Bartosik, N.; Behr, J.; Behrenhoff, W.; Behrens, U.; Bell, A. J.; Bergholz, M.; Bethani, A.; Borras, K.; Burgmeier, A.; Cakir, A.; Calligaris, L.; Campbell, A.; Choudhury, S.; Costanza, F.; Diez Pardos, C.; Dooling, S.; Dorland, T.; Eckerlin, G.; Eckstein, D.; Eichhorn, T.; Flucke, G.; Garay Garcia, J.; Geiser, A.; Gunnellini, P.; Hauk, J.; Hellwig, G.; Hempel, M.; Horton, D.; Jung, H.; Kasemann, M.; Katsas, P.; Kieseler, J.; Kleinwort, C.; Krücker, D.; Lange, W.; Leonard, J.; Lipka, K.; Lobanov, A.; Lohmann, W.; Lutz, B.; Mankel, R.; Marfin, I.; Melzer-Pellmann, I.-A.; Meyer, A. B.; Mnich, J.; Mussgiller, A.; Naumann-Emme, S.; Novgorodova, O.; Nowak, F.; Ntomari, E.; Perrey, H.; Pitzl, D.; Placakyte, R.; Raspereza, A.; Ribeiro Cipriano, P. M.; Ron, E.; Sahin, M. Ö.; Salfeld-Nebgen, J.; Saxena, P.; Schmidt, R.; Schoerner-Sadenius, T.; Schröder, M.; Spannagel, S.; Vargas Trevino, A. D. R.; Walsh, R.; Wissing, C.; Aldaya Martin, M.; Blobel, V.; Centis Vignali, M.; Erfle, J.; Garutti, E.; Goebel, K.; Görner, M.; Gosselink, M.; Haller, J.; Höing, R. S.; Kirschenmann, H.; Klanner, R.; Kogler, R.; Lange, J.; Lapsien, T.; Lenz, T.; Marchesini, I.; Ott, J.; Peiffer, T.; Pietsch, N.; Rathjens, D.; Sander, C.; Schettler, H.; Schleper, P.; Schlieckau, E.; Schmidt, A.; Seidel, M.; Sibille, J.; Sola, V.; Stadie, H.; Steinbrück, G.; Troendle, D.; Usai, E.; Vanelderen, L.; Barth, C.; Baus, C.; Berger, J.; Böser, C.; Butz, E.; Chwalek, T.; De Boer, W.; Descroix, A.; Dierlamm, A.; Feindt, M.; Hartmann, F.; Hauth, T.; Husemann, U.; Katkov, I.; Kornmayer, A.; Kuznetsova, E.; Lobelle Pardo, P.; Mozer, M. U.; Müller, Th.; Nürnberg, A.; Quast, G.; Rabbertz, K.; Ratnikov, F.; Röcker, S.; Simonis, H. J.; Stober, F. M.; Ulrich, R.; Wagner-Kuhr, J.; Wayand, S.; Weiler, T.; Wolf, R.; Anagnostou, G.; Daskalakis, G.; Geralis, T.; Giakoumopoulou, V. A.; Kyriakis, A.; Loukas, D.; Markou, A.; Markou, C.; Psallidas, A.; Topsis-Giotis, I.; Gouskos, L.; Panagiotou, A.; Saoulidou, N.; Stiliaris, E.; Aslanoglou, X.; Evangelou, I.; Flouris, G.; Foudas, C.; Kokkas, P.; Manthos, N.; Papadopoulos, I.; Paradas, E.; Bencze, G.; Hajdu, C.; Hidas, P.; Horvath, D.; Sikler, F.; Veszpremi, V.; Vesztergombi, G.; Zsigmond, A. J.; Beni, N.; Czellar, S.; Karancsi, J.; Molnar, J.; Palinkas, J.; Szillasi, Z.; Raics, P.; Trocsanyi, Z. L.; Ujvari, B.; Swain, S. K.; Beri, S. B.; Bhatnagar, V.; Dhingra, N.; Gupta, R.; Kalsi, A. K.; Kaur, M.; Mittal, M.; Nishu, N.; Singh, J. B.; Kumar, Ashok; Kumar, Arun; Ahuja, S.; Bhardwaj, A.; Choudhary, B. C.; Kumar, A.; Malhotra, S.; Naimuddin, M.; Ranjan, K.; Sharma, V.; Banerjee, S.; Bhattacharya, S.; Chatterjee, K.; Dutta, S.; Gomber, B.; Jain, Sa.; Jain, Sh.; Khurana, R.; Modak, A.; Mukherjee, S.; Roy, D.; Sarkar, S.; Sharan, M.; Abdulsalam, A.; Dutta, D.; Kailas, S.; Kumar, V.; Mohanty, A. K.; Pant, L. M.; Shukla, P.; Topkar, A.; Aziz, T.; Banerjee, S.; Chatterjee, R. M.; Dewanjee, R. K.; Dugad, S.; Ganguly, S.; Ghosh, S.; Guchait, M.; Gurtu, A.; Kole, G.; Kumar, S.; Maity, M.; Majumder, G.; Mazumdar, K.; Mohanty, G. B.; Parida, B.; Sudhakar, K.; Wickramage, N.; Bakhshiansohi, H.; Behnamian, H.; Etesami, S. M.; Fahim, A.; Goldouzian, R.; Jafari, A.; Khakzad, M.; Mohammadi Najafabadi, M.; Naseri, M.; Paktinat Mehdiabadi, S.; Safarzadeh, B.; Zeinali, M.; Felcini, M.; Grunewald, M.; Abbrescia, M.; Barbone, L.; Calabria, C.; Chhibra, S. S.; Colaleo, A.; Creanza, D.; De Filippis, N.; De Palma, M.; Fiore, L.; Iaselli, G.; Maggi, G.; Maggi, M.; My, S.; Nuzzo, S.; Pompili, A.; Pugliese, G.; Radogna, R.; Selvaggi, G.; Silvestris, L.; Singh, G.; Venditti, R.; Verwilligen, P.; Zito, G.; Abbiendi, G.; Benvenuti, A. C.; Bonacorsi, D.; Braibant-Giacomelli, S.; Brigliadori, L.; Campanini, R.; Capiluppi, P.; Castro, A.; Cavallo, F. R.; Codispoti, G.; Cuffiani, M.; Dallavalle, G. M.; Fabbri, F.; Fanfani, A.; Fasanella, D.; Giacomelli, P.; Grandi, C.; Guiducci, L.; Marcellini, S.; Masetti, G.; Montanari, A.; Navarria, F. L.; Perrotta, A.; Primavera, F.; Rossi, A. M.; Rovelli, T.; Siroli, G. P.; Tosi, N.; Travaglini, R.; Albergo, S.; Cappello, G.; Chiorboli, M.; Costa, S.; Giordano, F.; Potenza, R.; Tricomi, A.; Tuve, C.; Barbagli, G.; Ciulli, V.; Civinini, C.; D'Alessandro, R.; Focardi, E.; Gallo, E.; Gonzi, S.; Gori, V.; Lenzi, P.; Meschini, M.; Paoletti, S.; Sguazzoni, G.; Tropiano, A.; Benussi, L.; Bianco, S.; Fabbri, F.; Piccolo, D.; Ferro, F.; Lo Vetere, M.; Robutti, E.; Tosi, S.; Dinardo, M. E.; Fiorendi, S.; Gennai, S.; Gerosa, R.; Ghezzi, A.; Govoni, P.; Lucchini, M. T.; Malvezzi, S.; Manzoni, R. A.; Martelli, A.; Marzocchi, B.; Menasce, D.; Moroni, L.; Paganoni, M.; Pedrini, D.; Ragazzi, S.; Redaelli, N.; Tabarelli de Fatis, T.; Buontempo, S.; Cavallo, N.; Di Guida, S.; Fabozzi, F.; Iorio, A. O. M.; Lista, L.; Meola, S.; Merola, M.; Paolucci, P.; Azzi, P.; Bacchetta, N.; Bisello, D.; Branca, A.; Carlin, R.; Dall'Osso, M.; Dorigo, T.; Galanti, M.; Gasparini, F.; Giubilato, P.; Gozzelino, A.; Kanishchev, K.; Lacaprara, S.; Margoni, M.; Meneguzzo, A. T.; Montecassiano, F.; Passaseo, M.; Pazzini, J.; Pozzobon, N.; Ronchese, P.; Simonetto, F.; Torassa, E.; Tosi, M.; Vanini, S.; Zotto, P.; Zucchetta, A.; Zumerle, G.; Gabusi, M.; Ratti, S. P.; Riccardi, C.; Salvini, P.; Vitulo, P.; Biasini, M.; Bilei, G. M.; Ciangottini, D.; Fanò, L.; Lariccia, P.; Mantovani, G.; Menichelli, M.; Romeo, F.; Saha, A.; Santocchia, A.; Spiezia, A.; Androsov, K.; Azzurri, P.; Bagliesi, G.; Bernardini, J.; Boccali, T.; Broccolo, G.; Castaldi, R.; Ciocci, M. A.; Dell'Orso, R.; Donato, S.; Fiori, F.; Foà, L.; Giassi, A.; Grippo, M. T.; Ligabue, F.; Lomtadze, T.; Martini, L.; Messineo, A.; Moon, C. S.; Palla, F.; Rizzi, A.; Savoy-Navarro, A.; Serban, A. T.; Spagnolo, P.; Squillacioti, P.; Tenchini, R.; Tonelli, G.; Venturi, A.; Verdini, P. G.; Vernieri, C.; Barone, L.; Cavallari, F.; Del Re, D.; Diemoz, M.; Grassi, M.; Jorda, C.; Longo, E.; Margaroli, F.; Meridiani, P.; Micheli, F.; Nourbakhsh, S.; Organtini, G.; Paramatti, R.; Rahatlou, S.; Rovelli, C.; Santanastasio, F.; Soffi, L.; Traczyk, P.; Amapane, N.; Arcidiacono, R.; Argiro, S.; Arneodo, M.; Bellan, R.; Biino, C.; Cartiglia, N.; Casasso, S.; Costa, M.; Degano, A.; Demaria, N.; Finco, L.; Mariotti, C.; Maselli, S.; Migliore, E.; Monaco, V.; Musich, M.; Obertino, M. M.; Ortona, G.; Pacher, L.; Pastrone, N.; Pelliccioni, M.; Pinna Angioni, G. L.; Potenza, A.; Romero, A.; Ruspa, M.; Sacchi, R.; Solano, A.; Staiano, A.; Tamponi, U.; Belforte, S.; Candelise, V.; Casarsa, M.; Cossutti, F.; Della Ricca, G.; Gobbo, B.; La Licata, C.; Marone, M.; Montanino, D.; Schizzi, A.; Umer, T.; Zanetti, A.; Chang, S.; Kropivnitskaya, A.; Nam, S. K.; Kim, D. H.; Kim, G. N.; Kim, M. S.; Kong, D. J.; Lee, S.; Oh, Y. D.; Park, H.; Sakharov, A.; Son, D. C.; Kim, J. Y.; Song, S.; Choi, S.; Gyun, D.; Hong, B.; Jo, M.; Kim, H.; Kim, Y.; Lee, B.; Lee, K. S.; Park, S. K.; Roh, Y.; Choi, M.; Kim, J. H.; Park, I. C.; Park, S.; Ryu, G.; Ryu, M. S.; Choi, Y.; Choi, Y. K.; Goh, J.; Kwon, E.; Lee, J.; Seo, H.; Yu, I.; Juodagalvis, A.; Komaragiri, J. R.; Castilla-Valdez, H.; De La Cruz-Burelo, E.; Heredia-de La Cruz, I.; Lopez-Fernandez, R.; Sanchez-Hernandez, A.; Carrillo Moreno, S.; Vazquez Valencia, F.; Pedraza, I.; Salazar Ibarguen, H. A.; Casimiro Linares, E.; Morelos Pineda, A.; Krofcheck, D.; Butler, P. H.; Reucroft, S.; Ahmad, A.; Ahmad, M.; Hassan, Q.; Hoorani, H. R.; Khalid, S.; Khan, W. A.; Khurshid, T.; Shah, M. A.; Shoaib, M.; Bialkowska, H.; Bluj, M.; Boimska, B.; Frueboes, T.; Górski, M.; Kazana, M.; Nawrocki, K.; Romanowska-Rybinska, K.; Szleper, M.; Zalewski, P.; Brona, G.; Bunkowski, K.; Cwiok, M.; Dominik, W.; Doroba, K.; Kalinowski, A.; Konecki, M.; Krolikowski, J.; Misiura, M.; Olszewski, M.; Wolszczak, W.; Bargassa, P.; Beirão Da Cruz E Silva, C.; Faccioli, P.; Ferreira Parracho, P. 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V.; Vinogradov, A.; Belyaev, A.; Boos, E.; Dubinin, M.; Dudko, L.; Ershov, A.; Gribushin, A.; Klyukhin, V.; Kodolova, O.; Lokhtin, I.; Obraztsov, S.; Petrushanko, S.; Savrin, V.; Snigirev, A.; Azhgirey, I.; Bayshev, I.; Bitioukov, S.; Kachanov, V.; Kalinin, A.; Konstantinov, D.; Krychkine, V.; Petrov, V.; Ryutin, R.; Sobol, A.; Tourtchanovitch, L.; Troshin, S.; Tyurin, N.; Uzunian, A.; Volkov, A.; Adzic, P.; Dordevic, M.; Ekmedzic, M.; Milosevic, J.; Alcaraz Maestre, J.; Battilana, C.; Calvo, E.; Cerrada, M.; Chamizo Llatas, M.; Colino, N.; De La Cruz, B.; Delgado Peris, A.; Domínguez Vázquez, D.; Escalante Del Valle, A.; Fernandez Bedoya, C.; Fernández Ramos, J. P.; Flix, J.; Fouz, M. C.; Garcia-Abia, P.; Gonzalez Lopez, O.; Goy Lopez, S.; Hernandez, J. M.; Josa, M. I.; Merino, G.; Navarro De Martino, E.; Pérez-Calero Yzquierdo, A.; Puerta Pelayo, J.; Quintario Olmeda, A.; Redondo, I.; Romero, L.; Soares, M. S.; Albajar, C.; de Trocóniz, J. 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I.; Vlimant, J. R.; Wardle, N.; Wöhri, H. K.; Zeuner, W. D.; Bertl, W.; Deiters, K.; Erdmann, W.; Horisberger, R.; Ingram, Q.; Kaestli, H. C.; König, S.; Kotlinski, D.; Langenegger, U.; Renker, D.; Rohe, T.; Bachmair, F.; Bäni, L.; Bianchini, L.; Bortignon, P.; Buchmann, M. A.; Casal, B.; Chanon, N.; Deisher, A.; Dissertori, G.; Dittmar, M.; Donegà, M.; Dünser, M.; Eller, P.; Grab, C.; Hits, D.; Lustermann, W.; Mangano, B.; Marini, A. C.; Martinez Ruiz del Arbol, P.; Meister, D.; Mohr, N.; Nägeli, C.; Nef, P.; Nessi-Tedaldi, F.; Pandolfi, F.; Pauss, F.; Peruzzi, M.; Quittnat, M.; Rebane, L.; Ronga, F. J.; Rossini, M.; Starodumov, A.; Takahashi, M.; Theofilatos, K.; Wallny, R.; Weber, H. A.; Amsler, C.; Canelli, M. F.; Chiochia, V.; De Cosa, A.; Hinzmann, A.; Hreus, T.; Ivova Rikova, M.; Kilminster, B.; Millan Mejias, B.; Ngadiuba, J.; Robmann, P.; Snoek, H.; Taroni, S.; Verzetti, M.; Yang, Y.; Cardaci, M.; Chen, K. H.; Ferro, C.; Kuo, C. M.; Lin, W.; Lu, Y. J.; Volpe, R.; Yu, S. 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D.; Symonds, P.; Teodorescu, L.; Turner, M.; Dittmann, J.; Hatakeyama, K.; Kasmi, A.; Liu, H.; Scarborough, T.; Charaf, O.; Cooper, S. I.; Henderson, C.; Rumerio, P.; Avetisyan, A.; Bose, T.; Fantasia, C.; Heister, A.; Lawson, P.; Richardson, C.; Rohlf, J.; Sperka, D.; St. John, J.; Sulak, L.; Alimena, J.; Bhattacharya, S.; Christopher, G.; Cutts, D.; Demiragli, Z.; Ferapontov, A.; Garabedian, A.; Heintz, U.; Jabeen, S.; Kukartsev, G.; Laird, E.; Landsberg, G.; Luk, M.; Narain, M.; Segala, M.; Sinthuprasith, T.; Speer, T.; Swanson, J.; Breedon, R.; Breto, G.; Calderon De La Barca Sanchez, M.; Chauhan, S.; Chertok, M.; Conway, J.; Conway, R.; Cox, P. T.; Erbacher, R.; Gardner, M.; Ko, W.; Lander, R.; Miceli, T.; Mulhearn, M.; Pellett, D.; Pilot, J.; Ricci-Tam, F.; Searle, M.; Shalhout, S.; Smith, J.; Squires, M.; Stolp, D.; Tripathi, M.; Wilbur, S.; Yohay, R.; Cousins, R.; Everaerts, P.; Farrell, C.; Hauser, J.; Ignatenko, M.; Rakness, G.; Takasugi, E.; Valuev, V.; Weber, M.; Babb, J.; Clare, R.; Ellison, J.; Gary, J. W.; Hanson, G.; Heilman, J.; Jandir, P.; Kennedy, E.; Lacroix, F.; Liu, H.; Long, O. R.; Luthra, A.; Malberti, M.; Nguyen, H.; Shrinivas, A.; Sturdy, J.; Sumowidagdo, S.; Wimpenny, S.; Andrews, W.; Branson, J. G.; Cerati, G. B.; Cittolin, S.; D'Agnolo, R. 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I.; Maruyama, S.; Mason, D.; McBride, P.; Mishra, K.; Mrenna, S.; Musienko, Y.; Nahn, S.; Newman-Holmes, C.; O'Dell, V.; Prokofyev, O.; Sexton-Kennedy, E.; Sharma, S.; Soha, A.; Spalding, W. J.; Spiegel, L.; Taylor, L.; Tkaczyk, S.; Tran, N. V.; Uplegger, L.; Vaandering, E. W.; Vidal, R.; Whitbeck, A.; Whitmore, J.; Yang, F.; Acosta, D.; Avery, P.; Bourilkov, D.; Carver, M.; Cheng, T.; Curry, D.; Das, S.; De Gruttola, M.; Di Giovanni, G. P.; Field, R. D.; Fisher, M.; Furic, I. K.; Hugon, J.; Konigsberg, J.; Korytov, A.; Kypreos, T.; Low, J. F.; Matchev, K.; Milenovic, P.; Mitselmakher, G.; Muniz, L.; Rinkevicius, A.; Shchutska, L.; Skhirtladze, N.; Snowball, M.; Yelton, J.; Zakaria, M.; Gaultney, V.; Hewamanage, S.; Linn, S.; Markowitz, P.; Martinez, G.; Rodriguez, J. L.; Adams, T.; Askew, A.; Bochenek, J.; Diamond, B.; Haas, J.; Hagopian, S.; Hagopian, V.; Johnson, K. F.; Prosper, H.; Veeraraghavan, V.; Weinberg, M.; Baarmand, M. M.; Hohlmann, M.; Kalakhety, H.; Yumiceva, F.; Adams, M. R.; Apanasevich, L.; Bazterra, V. E.; Berry, D.; Betts, R. R.; Bucinskaite, I.; Cavanaugh, R.; Evdokimov, O.; Gauthier, L.; Gerber, C. E.; Hofman, D. J.; Khalatyan, S.; Kurt, P.; Moon, D. H.; O'Brien, C.; Silkworth, C.; Turner, P.; Varelas, N.; Albayrak, E. A.; Bilki, B.; Clarida, W.; Dilsiz, K.; Duru, F.; Haytmyradov, M.; Merlo, J.-P.; Mermerkaya, H.; Mestvirishvili, A.; Moeller, A.; Nachtman, J.; Ogul, H.; Onel, Y.; Ozok, F.; Penzo, A.; Rahmat, R.; Sen, S.; Tan, P.; Tiras, E.; Wetzel, J.; Yetkin, T.; Yi, K.; Barnett, B. A.; Blumenfeld, B.; Bolognesi, S.; Fehling, D.; Gritsan, A. V.; Maksimovic, P.; Martin, C.; Swartz, M.; Baringer, P.; Bean, A.; Benelli, G.; Bruner, C.; Gray, J.; Kenny, R. P.; Murray, M.; Noonan, D.; Sanders, S.; Sekaric, J.; Stringer, R.; Wang, Q.; Wood, J. S.; Barfuss, A. F.; Chakaberia, I.; Ivanov, A.; Khalil, S.; Makouski, M.; Maravin, Y.; Saini, L. K.; Shrestha, S.; Svintradze, I.; Gronberg, J.; Lange, D.; Rebassoo, F.; Wright, D.; Baden, A.; Calvert, B.; Eno, S. C.; Gomez, J. A.; Hadley, N. J.; Kellogg, R. G.; Kolberg, T.; Lu, Y.; Marionneau, M.; Mignerey, A. C.; Pedro, K.; Skuja, A.; Tonjes, M. B.; Tonwar, S. C.; Apyan, A.; Barbieri, R.; Bauer, G.; Busza, W.; Cali, I. A.; Chan, M.; Di Matteo, L.; Dutta, V.; Gomez Ceballos, G.; Goncharov, M.; Gulhan, D.; Klute, M.; Lai, Y. S.; Lee, Y.-J.; Levin, A.; Luckey, P. D.; Ma, T.; Paus, C.; Ralph, D.; Roland, C.; Roland, G.; Stephans, G. S. F.; Stöckli, F.; Sumorok, K.; Velicanu, D.; Veverka, J.; Wyslouch, B.; Yang, M.; Zanetti, M.; Zhukova, V.; Dahmes, B.; De Benedetti, A.; Gude, A.; Kao, S. C.; Klapoetke, K.; Kubota, Y.; Mans, J.; Pastika, N.; Rusack, R.; Singovsky, A.; Tambe, N.; Turkewitz, J.; Acosta, J. G.; Oliveros, S.; Avdeeva, E.; Bloom, K.; Bose, S.; Claes, D. R.; Dominguez, A.; Gonzalez Suarez, R.; Keller, J.; Knowlton, D.; Kravchenko, I.; Lazo-Flores, J.; Malik, S.; Meier, F.; Snow, G. R.; Dolen, J.; Godshalk, A.; Iashvili, I.; Kharchilava, A.; Kumar, A.; Rappoccio, S.; Alverson, G.; Barberis, E.; Baumgartel, D.; Chasco, M.; Haley, J.; Massironi, A.; Morse, D. M.; Nash, D.; Orimoto, T.; Trocino, D.; Wood, D.; Zhang, J.; Hahn, K. A.; Kubik, A.; Mucia, N.; Odell, N.; Pollack, B.; Pozdnyakov, A.; Schmitt, M.; Stoynev, S.; Sung, K.; Velasco, M.; Won, S.; Brinkerhoff, A.; Chan, K. M.; Drozdetskiy, A.; Hildreth, M.; Jessop, C.; Karmgard, D. J.; Kellams, N.; Lannon, K.; Luo, W.; Lynch, S.; Marinelli, N.; Pearson, T.; Planer, M.; Ruchti, R.; Valls, N.; Wayne, M.; Wolf, M.; Woodard, A.; Antonelli, L.; Brinson, J.; Bylsma, B.; Durkin, L. S.; Flowers, S.; Hill, C.; Hughes, R.; Kotov, K.; Ling, T. Y.; Puigh, D.; Rodenburg, M.; Smith, G.; Vuosalo, C.; Winer, B. L.; Wolfe, H.; Wulsin, H. W.; Berry, E.; Driga, O.; Elmer, P.; Hebda, P.; Hunt, A.; Koay, S. A.; Lujan, P.; Marlow, D.; Medvedeva, T.; Mooney, M.; Olsen, J.; Piroué, P.; Quan, X.; Saka, H.; Stickland, D.; Tully, C.; Werner, J. S.; Zenz, S. C.; Zuranski, A.; Brownson, E.; Mendez, H.; Ramirez Vargas, J. E.; Alagoz, E.; Barnes, V. E.; Benedetti, D.; Bolla, G.; Bortoletto, D.; De Mattia, M.; Everett, A.; Hu, Z.; Jha, M. K.; Jones, M.; Jung, K.; Kress, M.; Leonardo, N.; Lopes Pegna, D.; Maroussov, V.; Merkel, P.; Miller, D. H.; Neumeister, N.; Radburn-Smith, B. C.; Shipsey, I.; Silvers, D.; Svyatkovskiy, A.; Wang, F.; Xie, W.; Xu, L.; Yoo, H. D.; Zablocki, J.; Zheng, Y.; Parashar, N.; Stupak, J.; Adair, A.; Akgun, B.; Ecklund, K. M.; Geurts, F. J. M.; Li, W.; Michlin, B.; Padley, B. P.; Redjimi, R.; Roberts, J.; Zabel, J.; Betchart, B.; Bodek, A.; Covarelli, R.; de Barbaro, P.; Demina, R.; Eshaq, Y.; Ferbel, T.; Garcia-Bellido, A.; Goldenzweig, P.; Han, J.; Harel, A.; Khukhunaishvili, A.; Miner, D. C.; Petrillo, G.; Vishnevskiy, D.; Ciesielski, R.; Demortier, L.; Goulianos, K.; Lungu, G.; Mesropian, C.; Arora, S.; Barker, A.; Chou, J. P.; Contreras-Campana, C.; Contreras-Campana, E.; Duggan, D.; Ferencek, D.; Gershtein, Y.; Gray, R.; Halkiadakis, E.; Hidas, D.; Lath, A.; Panwalkar, S.; Park, M.; Patel, R.; Rekovic, V.; Salur, S.; Schnetzer, S.; Seitz, C.; Somalwar, S.; Stone, R.; Thomas, S.; Thomassen, P.; Walker, M.; Rose, K.; Spanier, S.; York, A.; Bouhali, O.; Eusebi, R.; Flanagan, W.; Gilmore, J.; Kamon, T.; Khotilovich, V.; Krutelyov, V.; Montalvo, R.; Osipenkov, I.; Pakhotin, Y.; Perloff, A.; Roe, J.; Rose, A.; Safonov, A.; Sakuma, T.; Suarez, I.; Tatarinov, A.; Akchurin, N.; Cowden, C.; Damgov, J.; Dragoiu, C.; Dudero, P. R.; Faulkner, J.; Kovitanggoon, K.; Kunori, S.; Lee, S. W.; Libeiro, T.; Volobouev, I.; Appelt, E.; Delannoy, A. G.; Greene, S.; Gurrola, A.; Johns, W.; Maguire, C.; Mao, Y.; Melo, A.; Sharma, M.; Sheldon, P.; Snook, B.; Tuo, S.; Velkovska, J.; Arenton, M. W.; Boutle, S.; Cox, B.; Francis, B.; Goodell, J.; Hirosky, R.; Ledovskoy, A.; Li, H.; Lin, C.; Neu, C.; Wood, J.; Gollapinni, S.; Harr, R.; Karchin, P. E.; Kottachchi Kankanamge Don, C.; Lamichhane, P.; Belknap, D. A.; Carlsmith, D.; Cepeda, M.; Dasu, S.; Duric, S.; Friis, E.; Hall-Wilton, R.; Herndon, M.; Hervé, A.; Klabbers, P.; Klukas, J.; Lanaro, A.; Lazaridis, C.; Levine, A.; Loveless, R.; Mohapatra, A.; Ojalvo, I.; Perry, T.; Pierro, G. A.; Polese, G.; Ross, I.; Sarangi, T.; Savin, A.; Smith, W. H.; Woods, N.; CMS Collaboration

2014-08-01

The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7 fb-1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale.

Extinction in neutrally stable stochastic Lotka-Volterra models

NASA Astrophysics Data System (ADS)

Dobrinevski, Alexander; Frey, Erwin

2012-05-01

Populations of competing biological species exhibit a fascinating interplay between the nonlinear dynamics of evolutionary selection forces and random fluctuations arising from the stochastic nature of the interactions. The processes leading to extinction of species, whose understanding is a key component in the study of evolution and biodiversity, are influenced by both of these factors. Here, we investigate a class of stochastic population dynamics models based on generalized Lotka-Volterra systems. In the case of neutral stability of the underlying deterministic model, the impact of intrinsic noise on the survival of species is dramatic: It destroys coexistence of interacting species on a time scale proportional to the population size. We introduce a new method based on stochastic averaging which allows one to understand this extinction process quantitatively by reduction to a lower-dimensional effective dynamics. This is performed analytically for two highly symmetrical models and can be generalized numerically to more complex situations. The extinction probability distributions and other quantities of interest we obtain show excellent agreement with simulations.

Extinction in neutrally stable stochastic Lotka-Volterra models.

PubMed

Dobrinevski, Alexander; Frey, Erwin

2012-05-01

Populations of competing biological species exhibit a fascinating interplay between the nonlinear dynamics of evolutionary selection forces and random fluctuations arising from the stochastic nature of the interactions. The processes leading to extinction of species, whose understanding is a key component in the study of evolution and biodiversity, are influenced by both of these factors. Here, we investigate a class of stochastic population dynamics models based on generalized Lotka-Volterra systems. In the case of neutral stability of the underlying deterministic model, the impact of intrinsic noise on the survival of species is dramatic: It destroys coexistence of interacting species on a time scale proportional to the population size. We introduce a new method based on stochastic averaging which allows one to understand this extinction process quantitatively by reduction to a lower-dimensional effective dynamics. This is performed analytically for two highly symmetrical models and can be generalized numerically to more complex situations. The extinction probability distributions and other quantities of interest we obtain show excellent agreement with simulations.

Extinction time of a stochastic predator-prey model by the generalized cell mapping method

NASA Astrophysics Data System (ADS)

Han, Qun; Xu, Wei; Hu, Bing; Huang, Dongmei; Sun, Jian-Qiao

2018-03-01

The stochastic response and extinction time of a predator-prey model with Gaussian white noise excitations are studied by the generalized cell mapping (GCM) method based on the short-time Gaussian approximation (STGA). The methods for stochastic response probability density functions (PDFs) and extinction time statistics are developed. The Taylor expansion is used to deal with non-polynomial nonlinear terms of the model for deriving the moment equations with Gaussian closure, which are needed for the STGA in order to compute the one-step transition probabilities. The work is validated with direct Monte Carlo simulations. We have presented the transient responses showing the evolution from a Gaussian initial distribution to a non-Gaussian steady-state one. The effects of the model parameter and noise intensities on the steady-state PDFs are discussed. It is also found that the effects of noise intensities on the extinction time statistics are opposite to the effects on the limit probability distributions of the survival species.

Macroecological analyses support an overkill scenario for late Pleistocene extinctions.

PubMed

Diniz-Filho, J A F

2004-08-01

The extinction of megafauna at the end of Pleistocene has been traditionally explained by environmental changes or overexploitation by human hunting (overkill). Despite difficulties in choosing between these alternative (and not mutually exclusive) scenarios, the plausibility of the overkill hypothesis can be established by ecological models of predator-prey interactions. In this paper, I have developed a macroecological model for the overkill hypothesis, in which prey population dynamic parameters, including abundance, geographic extent, and food supply for hunters, were derived from empirical allometric relationships with body mass. The last output correctly predicts the final destiny (survival or extinction) for 73% of the species considered, a value only slightly smaller than those obtained by more complex models based on detailed archaeological and ecological data for each species. This illustrates the high selectivity of Pleistocene extinction in relation to body mass and confers more plausibility on the overkill scenario.

Looking beyond fear: the extinction of other emotions implicated in anxiety disorders.

PubMed

Mason, Elizabeth C; Richardson, Rick

2010-01-01

Previous research examining anxiety has traditionally focused on models of fear. More recently, attention has been directed to the role of disgust as an important emotion in the context of certain anxiety disorders. Further, it has been suggested that disgust, a form of evaluative responding, may be resistant to extinction and may contribute to relapse. However, previous work on this has largely relied on self-report ratings. In the current experiment, using a disgust conditioning and extinction procedure, disgust reactions were indeed shown to be resistant to extinction, as indexed by both self-report and an objective behavioral measure (visual avoidance). Furthermore, our research shows that individuals with greater levels of disgust sensitivity exhibit heightened resistance to extinction. In addition, expectancy of the disgusting US during extinction was dissociated from measures of disgust responding. Given that the treatment of choice for anxiety disorders (exposure therapy) is based on models of extinction, this research suggests that current treatments for anxiety disorders may not be adequately targeting disgust reactions, a crucial maintaining factor in certain anxiety disorders. As such, this inattention to disgust reactions may reduce the effectiveness of treatment in the short-term or may leave the patient vulnerable to relapse in the long-term.

A reminder of extinction reduces relapse in an animal model of voluntary behavior.

PubMed

Nieto, Javier; Uengoer, Metin; Bernal-Gamboa, Rodolfo

2017-02-01

One experiment with rats explored whether an extinction-cue prevents the recovery of extinguished lever-pressing responses. Initially, rats were trained to perform one instrumental response (R1) for food in Context A, and a different instrumental response (R2) in Context B. Then, responses were extinguished each in the alternate context (R1 in Context B; R2 in Context A). For one group, extinction of both responses was conducted in the presence of an extinction-cue, whereas in a second group, the extinction-cue only accompanied extinction of R1. During a final test, we observed that returning the rats to the initial acquisition context renewed performance and that response recovery was attenuated in the presence of the cue that accompanied extinction of the response. The impact of the extinction-cue, however, was not transferred to the response that has been extinguished without the cue. Our results are consistent with the idea that extinction established an inhibitory cue-response association. © 2017 Nieto et al.; Published by Cold Spring Harbor Laboratory Press.

Postretrieval Extinction Attenuates Alcohol Cue Reactivity in Rats.

PubMed

Cofresí, Roberto U; Lewis, Suzanne M; Chaudhri, Nadia; Lee, Hongjoo J; Monfils, Marie-H; Gonzales, Rueben A

2017-03-01

Conditioned responses to alcohol-associated cues can hinder recovery from alcohol use disorder (AUD). Cue exposure (extinction) therapy (CET) can reduce reactivity to alcohol cues, but its efficacy is limited by phenomena such as spontaneous recovery and reinstatement that can cause a return of conditioned responding after extinction. Using a preclinical model of alcohol cue reactivity in rats, we evaluated whether the efficacy of alcohol CET could be improved by conducting CET during the memory reconsolidation window after retrieval of cue-alcohol associations. Rats were provided with intermittent access to unsweetened alcohol. Rats were then trained to predict alcohol access based on a visual cue. Next, rats were treated with either standard extinction (n = 14) or postretrieval extinction (n = 13). Rats were then tested for long-term memory of extinction and susceptibility to spontaneous recovery and reinstatement. Despite equivalent extinction, rats treated with postretrieval extinction exhibited reduced spontaneous recovery and reinstatement relative to rats treated with standard extinction. Postretrieval CET shows promise for persistently attenuating the risk to relapse posed by alcohol cues in individuals with AUD. Copyright © 2017 by the Research Society on Alcoholism.

POST-RETRIEVAL EXTINCTION ATTENUATES ALCOHOL CUE REACTIVITY IN RATS

PubMed Central

Cofresí, Roberto U.; Lewis, Suzanne M.; Chaudhri, Nadia; Lee, Hongjoo J.; Monfils, Marie-H.; Gonzales, Rueben A.

2017-01-01

BACKGROUND Conditioned responses to alcohol-associated cues can hinder recovery from alcohol use disorder (AUD). Cue exposure (extinction) therapy (CET) can reduce reactivity to alcohol cues, but its efficacy is limited by phenomena such as spontaneous recovery and reinstatement that can cause a return of conditioned responding after extinction. Using a preclinical model of alcohol cue reactivity in rats, we evaluated whether the efficacy of alcohol CET could be improved by conducting CET during the memory reconsolidation window after retrieval of a cue-alcohol association. METHODS Rats were provided with intermittent access to unsweetened alcohol. Rats were then trained to predict alcohol access based on a visual cue. Next, rats were treated with either standard extinction (n=14) or post-retrieval extinction (n=13). Rats were then tested for long-term memory of extinction and susceptibility to spontaneous recovery and reinstatement. RESULTS Despite equivalent extinction, rats treated with post-retrieval extinction exhibited reduced spontaneous recovery and reinstatement relative to rats treated with standard extinction. CONCLUSIONS Post-retrieval CET shows promise for persistently attenuating the risk to relapse posed by alcohol cues in individuals with AUD. PMID:28169439

Exposing extinction risk analysis to pathogens: Is disease just another form of density dependence?

USGS Publications Warehouse

Gerber, L.R.; McCallum, H.; Lafferty, K.D.; Sabo, J.L.; Dobson, A.

2005-01-01

In the United States and several other countries, the development of population viability analyses (PVA) is a legal requirement of any species survival plan developed for threatened and endangered species. Despite the importance of pathogens in natural populations, little attention has been given to host-pathogen dynamics in PVA. To study the effect of infectious pathogens on extinction risk estimates generated from PVA, we review and synthesize the relevance of host-pathogen dynamics in analyses of extinction risk. We then develop a stochastic, density-dependent host-parasite model to investigate the effects of disease on the persistence of endangered populations. We show that this model converges on a Ricker model of density dependence under a suite of limiting assumptions, including a high probability that epidemics will arrive and occur. Using this modeling framework, we then quantify: (1) dynamic differences between time series generated by disease and Ricker processes with the same parameters; (2) observed probabilities of quasi-extinction for populations exposed to disease or self-limitation; and (3) bias in probabilities of quasi-extinction estimated by density-independent PVAs when populations experience either form of density dependence. Our results suggest two generalities about the relationships among disease, PVA, and the management of endangered species. First, disease more strongly increases variability in host abundance and, thus, the probability of quasi-extinction, than does self-limitation. This result stems from the fact that the effects and the probability of occurrence of disease are both density dependent. Second, estimates of quasi-extinction are more often overly optimistic for populations experiencing disease than for those subject to self-limitation. Thus, although the results of density-independent PVAs may be relatively robust to some particular assumptions about density dependence, they are less robust when endangered populations are known to be susceptible to disease. If potential management actions involve manipulating pathogens, then it may be useful to model disease explicitly. ?? 2005 by the Ecological Society of America.

Assessing regional and interspecific variation in threshold responses of forest breeding birds through broad scale analyses.

PubMed

van der Hoek, Yntze; Renfrew, Rosalind; Manne, Lisa L

2013-01-01

Identifying persistence and extinction thresholds in species-habitat relationships is a major focal point of ecological research and conservation. However, one major concern regarding the incorporation of threshold analyses in conservation is the lack of knowledge on the generality and transferability of results across species and regions. We present a multi-region, multi-species approach of modeling threshold responses, which we use to investigate whether threshold effects are similar across species and regions. We modeled local persistence and extinction dynamics of 25 forest-associated breeding birds based on detection/non-detection data, which were derived from repeated breeding bird atlases for the state of Vermont. We did not find threshold responses to be particularly well-supported, with 9 species supporting extinction thresholds and 5 supporting persistence thresholds. This contrasts with a previous study based on breeding bird atlas data from adjacent New York State, which showed that most species support persistence and extinction threshold models (15 and 22 of 25 study species respectively). In addition, species that supported a threshold model in both states had associated average threshold estimates of 61.41% (SE = 6.11, persistence) and 66.45% (SE = 9.15, extinction) in New York, compared to 51.08% (SE = 10.60, persistence) and 73.67% (SE = 5.70, extinction) in Vermont. Across species, thresholds were found at 19.45-87.96% forest cover for persistence and 50.82-91.02% for extinction dynamics. Through an approach that allows for broad-scale comparisons of threshold responses, we show that species vary in their threshold responses with regard to habitat amount, and that differences between even nearby regions can be pronounced. We present both ecological and methodological factors that may contribute to the different model results, but propose that regardless of the reasons behind these differences, our results merit a warning that threshold values cannot simply be transferred across regions or interpreted as clear-cut targets for ecosystem management and conservation.

Testing for variation in taxonomic extinction probabilities: a suggested methodology and some results

USGS Publications Warehouse

Conroy, M.J.; Nichols, J.D.

1984-01-01

Several important questions in evolutionary biology and paleobiology involve sources of variation in extinction rates. In all cases of which we are aware, extinction rates have been estimated from data in which the probability that an observation (e.g., a fossil taxon) will occur is related both to extinction rates and to what we term encounter probabilities. Any statistical method for analyzing fossil data should at a minimum permit separate inferences on these two components. We develop a method for estimating taxonomic extinction rates from stratigraphic range data and for testing hypotheses about variability in these rates. We use this method to estimate extinction rates and to test the hypothesis of constant extinction rates for several sets of stratigraphic range data. The results of our tests support the hypothesis that extinction rates varied over the geologic time periods examined. We also present a test that can be used to identify periods of high or low extinction probabilities and provide an example using Phanerozoic invertebrate data. Extinction rates should be analyzed using stochastic models, in which it is recognized that stratigraphic samples are random varlates and that sampling is imperfect

Dust in the Small Magellanic Cloud

NASA Technical Reports Server (NTRS)

Rodrigues, C. V.; Coyne, G. V.; Magalhaes, A. M.

1995-01-01

We discuss simultaneous dust model fits to our extinction and polarization data for the Small Magellanic Cloud (SMC) using existing dust models. Dust model fits to the wavelength dependent polarization are possible for stars with small lambda(sub max). They generally imply size distributions which are narrower and have smaller average sizes compared to those in the Galaxy. The best fits for the extinction curves are obtained with a power law size distribution. The typical, monotonic SMC extinction curve can be well fit with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grains. Amorphous carbon and silicate grains also fit the data well.

Extinctions. Paleontological baselines for evaluating extinction risk in the modern oceans.

PubMed

Finnegan, Seth; Anderson, Sean C; Harnik, Paul G; Simpson, Carl; Tittensor, Derek P; Byrnes, Jarrett E; Finkel, Zoe V; Lindberg, David R; Liow, Lee Hsiang; Lockwood, Rowan; Lotze, Heike K; McClain, Craig R; McGuire, Jenny L; O'Dea, Aaron; Pandolfi, John M

2015-05-01

Marine taxa are threatened by anthropogenic impacts, but knowledge of their extinction vulnerabilities is limited. The fossil record provides rich information on past extinctions that can help predict biotic responses. We show that over 23 million years, taxonomic membership and geographic range size consistently explain a large proportion of extinction risk variation in six major taxonomic groups. We assess intrinsic risk-extinction risk predicted by paleontologically calibrated models-for modern genera in these groups. Mapping the geographic distribution of these genera identifies coastal biogeographic provinces where fauna with high intrinsic risk are strongly affected by human activity or climate change. Such regions are disproportionately in the tropics, raising the possibility that these ecosystems may be particularly vulnerable to future extinctions. Intrinsic risk provides a prehuman baseline for considering current threats to marine biodiversity. Copyright © 2015, American Association for the Advancement of Science.

Rescuing Ecosystems from Extinction Cascades

NASA Astrophysics Data System (ADS)

Sahasrabudhe, Sagar; Motter, Adilson

2010-03-01

Food web perturbations stemming from climate change, overexploitation, invasive species, and natural disasters often cause an initial loss of species that results in a cascade of secondary extinctions. Using a predictive modeling framework, here we will present a systematic network-based approach to reduce the number of secondary extinctions. We will show that the extinction of one species can often be compensated by the concurrent removal of a second specific species, which is a counter-intuitive effect not previously tested in complex food webs. These compensatory perturbations frequently involve long-range interactions that are not a priori evident from local predator-prey relationships. Strikingly, in numerous cases even the early removal of a species that would eventually be extinct by the cascade is found to significantly reduce the number of cascading extinctions. Other nondestructive interventions based on partial removals and growth suppression and/or mortality increase are shown to sometimes prevent all secondary extinctions.

Rethinking Extinction

PubMed Central

Dunsmoor, Joseph E.; Niv, Yael; Daw, Nathaniel; Phelps, Elizabeth A.

2015-01-01

Extinction serves as the leading theoretical framework and experimental model to describe how learned behaviors diminish through absence of anticipated reinforcement. In the past decade, extinction has moved beyond the realm of associative learning theory and behavioral experimentation in animals and has become a topic of considerable interest in the neuroscience of learning, memory, and emotion. Here, we review research and theories of extinction, both as a learning process and as a behavioral technique, and consider whether traditional understandings warrant a re-examination. We discuss the neurobiology, cognitive factors, and major computational theories, and revisit the predominant view that extinction results in new learning that interferes with expression of the original memory. Additionally, we reconsider the limitations of extinction as a technique to prevent the relapse of maladaptive behavior, and discuss novel approaches, informed by contemporary theoretical advances, that augment traditional extinction methods to target and potentially alter maladaptive memories. PMID:26447572

Chemical antipredator defence is linked to higher extinction risk

PubMed Central

2016-01-01

Many attributes of species may be linked to contemporary extinction risk, though some such traits remain untested despite suggestions that they may be important. Here, I test whether a trait associated with higher background extinction rates, chemical antipredator defence, is also associated with current extinction risk, using amphibians as a model system—a group facing global population declines. I find that chemically defended species are approximately 60% more likely to be threatened than species without chemical defence, although the severity of the contemporary extinction risk may not relate to chemical defence. The results confirm that background and contemporary extinction rates can be predicted from the same traits, at least in certain cases. This suggests that associations between extinction risk and phenotypic traits can be temporally stable over long periods. The results also provide novel insights into the relevance of antipredator defences for species subject to conservation concerns. PMID:28018657

17ß-Estradiol Is Necessary for Extinction of Cocaine Seeking in Female Rats

ERIC Educational Resources Information Center

Twining, Robert C.; Tuscher, Jennifer J.; Doncheck, Elizabeth M.; Frick, Karyn M.; Mueller, Devin

2013-01-01

Human and preclinical models of addiction demonstrate that gonadal hormones modulate acquisition of drug seeking. Little is known, however, about the effects of these hormones on extinction of drug-seeking behavior. Here, we investigated how 17ß-estradiol (E[subscript 2]) affects expression and extinction of cocaine seeking in female rats. Using a…

Systemic Blockade of D2-Like Dopamine Receptors Facilitates Extinction of Conditioned Fear in Mice

ERIC Educational Resources Information Center

Ponnusamy, Ravikumar; Nissim, Helen A.; Barad, Mark

2005-01-01

Extinction of conditioned fear in animals is the explicit model of behavior therapy for human anxiety disorders, including panic disorder, obsessive-compulsive disorder, and post-traumatic stress disorder. Based on previous data indicating that fear extinction in rats is blocked by quinpirole, an agonist of dopamine D2 receptors, we hypothesized…

Histone Modifications around Individual BDNF Gene Promoters in Prefrontal Cortex Are Associated with Extinction of Conditioned Fear

ERIC Educational Resources Information Center

Bredy, Timothy W.; Wu, Hao; Crego, Cortney; Zellhoefer, Jessica; Sun, Yi E.; Barad, Mark

2007-01-01

Extinction of conditioned fear is an important model both of inhibitory learning and of behavior therapy for human anxiety disorders. Like other forms of learning, extinction learning is long-lasting and depends on regulated gene expression. Epigenetic mechanisms make an important contribution to persistent changes in gene expression; therefore,…

Neurocircuitry models of posttraumatic stress disorder and extinction: human neuroimaging research--past, present, and future.

PubMed

Rauch, Scott L; Shin, Lisa M; Phelps, Elizabeth A

2006-08-15

The prevailing neurocircuitry models of anxiety disorders have been amygdalocentric in form. The bases for such models have progressed from theoretical considerations, extrapolated from research in animals, to in vivo human imaging data. For example, one current model of posttraumatic stress disorder (PTSD) has been highly influenced by knowledge from rodent fear conditioning research. Given the phenomenological parallels between fear conditioning and the pathogenesis of PTSD, we have proposed that PTSD is characterized by exaggerated amygdala responses (subserving exaggerated acquisition of fear associations and expression of fear responses) and deficient frontal cortical function (mediating deficits in extinction and the capacity to suppress attention/response to trauma-related stimuli), as well as deficient hippocampal function (mediating deficits in appreciation of safe contexts and explicit learning/memory). Neuroimaging studies have yielded convergent findings in support of this model. However, to date, neuroimaging investigations of PTSD have not principally employed conditioning and extinction paradigms per se. The recent development of such imaging probes now sets the stage for directly testing hypotheses regarding the neural substrates of fear conditioning and extinction abnormalities in PTSD.

Can Transcranial Direct Current Stimulation Augment Extinction of Conditioned Fear?

PubMed Central

van ’t Wout, Mascha; Mariano, Timothy Y.; Garnaat, Sarah L.; Reddy, Madhavi K.; Rasmussen, Steven A.; Greenberg, Benjamin D.

2016-01-01

Background Exposure-based therapy parallels extinction learning of conditioned fear. Prior research points to the ventromedial prefrontal cortex as a potential site for the consolidation of extinction learning and subsequent retention of extinction memory. Objective/hypothesis The present study aimed to evaluate whether the application of non-invasive transcranial direct current stimulation (tDCS) during extinction learning enhances late extinction and early recall in human participants. Methods Forty-four healthy volunteers completed a 2-day Pavlovian fear conditioning, extinction, and recall paradigm while skin conductance activity was continuously measured. Twenty-six participants received 2 mA anodal tDCS over EEG coordinate AF3 during extinction of a first conditioned stimulus. The remaining 18 participants received similar tDCS during extinction of a second conditioned stimulus. Sham stimulation was applied for the balance of extinction trials in both groups. Normalized skin conductance changes were analyzed using linear mixed models to evaluate effects of tDCS over late extinction and early recall trials. Results We observed a significant interaction between timing of tDCS during extinction blocks and changes in skin conductance reactivity over late extinction trials. These data indicate that tDCS was associated with accelerated late extinction learning of a second conditioned stimulus after tDCS was combined with extinction learning of a previous conditioned stimulus. No significant effects of tDCS timing were observed on early extinction recall. Conclusions Results could be explained by an anxiolytic aftereffect of tDCS and extend previous studies on tDCS-induced modulation of fear and threat related learning processes. These findings support further exploration of the clinical use of tDCS. PMID:27037186

Thermal Transgressions and Phanerozoic Extinctions

NASA Astrophysics Data System (ADS)

Worsley, T. R.; Kidder, D. L.

2007-12-01

A number of significant Phanerozoic extinctions are associated with marine transgressions that were probably driven by rapid ocean warming. The conditions associated with what we call thermal transgressions are extremely stressful to life on Earth. The Earth system setting associated with end-Permian extinction exemplifies an end-member case of our model. The conditions favoring extreme warmth and sea-level increases driven by thermal expansion are also conducive to changes in ocean circulation that foster widespread anoxia and sulfidic subsurface ocean waters. Equable climates are characterized by reduced wind shear and weak surface ocean circulation. Late Permian and Early Triassic thermohaline circulation differs considerably from today's world, with minimal polar sinking and intensified mid-latitude sinking that delivers sulfate from shallow evaporative areas to deeper water where it is reduced to sulfide. Reduced nutrient input to oceans from land at many of the extinction intervals results from diminished silicate weathering and weakened delivery of iron via eolian dust. The falloff in iron-bearing dust leads to minimal nitrate production, weakening food webs and rendering faunas and floras more susceptible to extinction when stressed. Factors such as heat, anoxia, ocean acidification, hypercapnia, and hydrogen sulfide poisoning would significantly affect these biotas. Intervals of tectonic quiescence set up preconditions favoring extinctions. Reductions in chemical silicate weathering lead to carbon dioxide buildup, oxygen drawdown, nutrient depletion, wind and ocean current abatement, long-term global warming, and ocean acidification. The effects of extinction triggers such as large igneous provinces, bolide impacts, and episodes of sudden methane release are more potent against the backdrop of our proposed preconditions. Extinctions that have characteristics we call for in the thermal transgressions include the Early Cambrian Sinsk event, as well as extinction events at the Frasnian-Famennian, end-Devonian, end Permian, Early Toarcian, Cenomanian-Turonian, and end Cretaceous. The Late Paleocene and end Triassic extinctions are still under evaluation. The extinctions associated with the glacio-eustatic sea-level change in the Late Ordovician are not consistent with the conditions of our model.

Biodiversity loss decreases parasite diversity: theory and patterns

USGS Publications Warehouse

Lafferty, Kevin D.

2012-01-01

Past models have suggested host–parasite coextinction could lead to linear, or concave down relationships between free-living species richness and parasite richness. I explored several models for the relationship between parasite richness and biodiversity loss. Life cycle complexity, low generality of parasites and sensitivity of hosts reduced the robustness of parasite species to the loss of free-living species diversity. Food-web complexity and the ordering of extinctions altered these relationships in unpredictable ways. Each disassembly of a food web resulted in a unique relationship between parasite richness and the richness of free-living species, because the extinction trajectory of parasites was sensitive to the order of extinctions of free-living species. However, the average of many disassemblies tended to approximate an analytical model. Parasites of specialist hosts and hosts higher on food chains were more likely to go extinct in food-web models. Furthermore, correlated extinctions between hosts and parasites (e.g. if parasites share a host with a specialist predator) led to steeper declines in parasite richness with biodiversity loss. In empirical food webs with random removals of free-living species, the relationship between free-living species richness and parasite richness was, on average, quasi-linear, suggesting biodiversity loss reduces parasite diversity more than previously thought.

Recent developments in the behavioural and pharmacological enhancement of extinction of drug seeking.

PubMed

Chesworth, Rose; Corbit, Laura H

2017-01-01

One of the principal barriers to overcoming addiction is the propensity to relapse, even after months or years of abstinence. Relapse can be precipitated by cues and contexts associated with drug use; thus, decreasing the conditioned properties of these cues and contexts may assist in preventing relapse. The predictive power of drug cues and contexts can be reduced by repeatedly presenting them in the absence of the drug reinforcer, a process known as extinction. The potential of extinction to limit relapse has generated considerable interest and research over the past few decades. While pre-clinical animal models suggest extinction learning assists relapse prevention, treatment efficacy is often lacking when extinction learning principles are translated into clinical trials. Conklin and Tiffany (Addiction, 2002) suggest the lack of efficacy in clinical practice may be due to limited translation of procedures demonstrated through animal research and propose several methodological improvements to enhance extinction learning for drug addiction. This review will examine recent advances in the behavioural and pharmacological manipulation of extinction learning, based on research from pre-clinical models. In addition, the translation of pre-clinical findings-both those suggested by Conklin and Tiffany () and novel demonstrations from the past 13 years-into clinical trials and the efficacy of these methods in reducing craving and relapse, where available, will be discussed. Finally, we highlight areas where promising pre-clinical models have not yet been integrated into current clinical practice but, if applied, could improve upon existing behavioural and pharmacological methods. © 2015 Society for the Study of Addiction.

Body Size Reductions in Nonmammalian Eutheriodont Therapsids (Synapsida) during the End-Permian Mass Extinction

PubMed Central

Huttenlocker, Adam K.

2014-01-01

The extent to which mass extinctions influence body size evolution in major tetrapod clades is inadequately understood. For example, the ‘Lilliput effect,’ a common feature of mass extinctions, describes a temporary decrease in body sizes of survivor taxa in post-extinction faunas. However, its signature on existing patterns of body size evolution in tetrapods and the persistence of its impacts during post-extinction recoveries are virtually unknown, and rarely compared in both geologic and phylogenetic contexts. Here, I evaluate temporal and phylogenetic distributions of body size in Permo-Triassic therocephalian and cynodont therapsids (eutheriodonts) using a museum collections-based approach and time series model fitting on a regional stratigraphic sequence from the Karoo Basin, South Africa. I further employed rank order correlation tests on global age and clade rank data from an expanded phylogenetic dataset, and performed evolutionary model testing using Brownian (passive diffusion) models. Results support significant size reductions in the immediate aftermath of the end-Permian mass extinction (ca. 252.3 Ma) consistent with some definitions of Lilliput effects. However, this temporal succession reflects a pattern that was underscored largely by Brownian processes and constructive selectivity. Results also support two recent contentions about body size evolution and mass extinctions: 1) active, directional evolution in size traits is rare over macroevolutionary time scales and 2) geologically brief size reductions may be accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns. PMID:24498335

Chronic psychosocial stress causes delayed extinction and exacerbates reinstatement of ethanol-induced conditioned place preference in mice.

PubMed

Bahi, Amine; Dreyer, Jean-Luc

2014-01-01

We have shown previously, using an animal model of voluntary ethanol intake and ethanol-conditioned place preference (EtOH-CPP), that exposure to chronic psychosocial stress induces increased ethanol intake and EtOH-CPP acquisition in mice. Here, we examined the impact of chronic subordinate colony (CSC) exposure on EtOH-CPP extinction, as well as ethanol-induced reinstatement of CPP. Mice were conditioned with saline or 1.5 g/kg ethanol and were tested in the EtOH-CPP model. In the first experiment, the mice were subjected to 19 days of chronic stress, and EtOH-CPP extinction was assessed during seven daily trials without ethanol injection. In the second experiment and after the EtOH-CPP test, the mice were subjected to 7 days of extinction trials before the 19 days of chronic stress. Drug-induced EtOH-CPP reinstatement was induced by a priming injection of 0.5 g/kg ethanol. Compared to the single-housed colony mice, CSC mice exhibited increased anxiety-like behavior in the elevated plus maze (EPM) and the open field tests. Interestingly, the CSC mice showed delayed EtOH-CPP extinction. More importantly, CSC mice showed increased alcohol-induced reinstatement of the EtOH-CPP behavior. Taken together, this study indicates that chronic psychosocial stress can have long-term effects on EtOH-CPP extinction as well as drug-induced reinstatement behavior and may provide a suitable model to study the latent effects of chronic psychosocial stress on extinction and relapse to drug abuse.

Unravelling the structure of species extinction risk for predictive conservation science.

PubMed

Lee, Tien Ming; Jetz, Walter

2011-05-07

Extinction risk varies across species and space owing to the combined and interactive effects of ecology/life history and geography. For predictive conservation science to be effective, large datasets and integrative models that quantify the relative importance of potential factors and separate rapidly changing from relatively static threat drivers are urgently required. Here, we integrate and map in space the relative and joint effects of key correlates of The International Union for Conservation of Nature-assessed extinction risk for 8700 living birds. Extinction risk varies significantly with species' broad-scale environmental niche, geographical range size, and life-history and ecological traits such as body size, developmental mode, primary diet and foraging height. Even at this broad scale, simple quantifications of past human encroachment across species' ranges emerge as key in predicting extinction risk, supporting the use of land-cover change projections for estimating future threat in an integrative setting. A final joint model explains much of the interspecific variation in extinction risk and provides a remarkably strong prediction of its observed global geography. Our approach unravels the species-level structure underlying geographical gradients in extinction risk and offers a means of disentangling static from changing components of current and future threat. This reconciliation of intrinsic and extrinsic, and of past and future extinction risk factors may offer a critical step towards a more continuous, forward-looking assessment of species' threat status based on geographically explicit environmental change projections, potentially advancing global predictive conservation science.

Muscarinic receptors modulate the intrinsic excitability of infralimbic neurons and consolidation of fear extinction.

PubMed

Santini, Edwin; Sepulveda-Orengo, Marian; Porter, James T

2012-08-01

There is considerable interest in identifying pharmacological compounds that could be used to facilitate fear extinction. Recently, we showed that the modulation of M-type K(+) channels regulates the intrinsic excitability of infralimbic (IL) neurons and fear expression. As muscarinic acetylcholine receptors inhibit M-type K(+) channels, cholinergic inputs to IL may have an important role in controlling IL excitability and, thereby, fear expression and extinction. To test this model, we combined whole-cell patch-clamp electrophysiology and auditory fear conditioning. In prefrontal brain slices, muscarine enhanced the intrinsic excitability of IL neurons by reducing the M-current and the slow afterhyperpolarization, resulting in an increased number of spikes with shorter inter-spike intervals. Next, we examined the role of endogenous activation of muscarinic receptors in fear extinction. Systemic injected scopolamine (Scop) (muscarinic receptor antagonist) before or immediately after extinction training impaired recall of extinction 24-h later, suggesting that muscarinic receptors are critically involved in consolidation of extinction memory. Similarly, infusion of Scop into IL before extinction training also impaired recall of extinction 24-h later. Finally, we demonstrated that systemic injections of the muscarinic agonist, cevimeline (Cev), given before or immediately after extinction training facilitated recall of extinction the following day. Taken together, these findings suggest that cholinergic inputs to IL have a critical role in modulating consolidation of fear extinction and that muscarinic agonists such as Cev might be useful for facilitating extinction memory in patients suffering from anxiety disorders.

Muscarinic Receptors Modulate the Intrinsic Excitability of Infralimbic Neurons and Consolidation of Fear Extinction

PubMed Central

Santini, Edwin; Sepulveda-Orengo, Marian; Porter, James T

2012-01-01

There is considerable interest in identifying pharmacological compounds that could be used to facilitate fear extinction. Recently, we showed that the modulation of M-type K+ channels regulates the intrinsic excitability of infralimbic (IL) neurons and fear expression. As muscarinic acetylcholine receptors inhibit M-type K+ channels, cholinergic inputs to IL may have an important role in controlling IL excitability and, thereby, fear expression and extinction. To test this model, we combined whole-cell patch-clamp electrophysiology and auditory fear conditioning. In prefrontal brain slices, muscarine enhanced the intrinsic excitability of IL neurons by reducing the M-current and the slow afterhyperpolarization, resulting in an increased number of spikes with shorter inter-spike intervals. Next, we examined the role of endogenous activation of muscarinic receptors in fear extinction. Systemic injected scopolamine (Scop) (muscarinic receptor antagonist) before or immediately after extinction training impaired recall of extinction 24-h later, suggesting that muscarinic receptors are critically involved in consolidation of extinction memory. Similarly, infusion of Scop into IL before extinction training also impaired recall of extinction 24-h later. Finally, we demonstrated that systemic injections of the muscarinic agonist, cevimeline (Cev), given before or immediately after extinction training facilitated recall of extinction the following day. Taken together, these findings suggest that cholinergic inputs to IL have a critical role in modulating consolidation of fear extinction and that muscarinic agonists such as Cev might be useful for facilitating extinction memory in patients suffering from anxiety disorders. PMID:22510723

Building physiological toughness: Some aversive events during extinction may attenuate return of fear.

PubMed

Culver, Najwa C; Stevens, Stephan; Fanselow, Michael S; Craske, Michelle G

2018-03-01

Although exposure therapy is an effective treatment for anxiety disorders, fear sometimes returns following successful therapy. Recent literature in animal models indicates that incorporating some aversive events into extinction training may offset these return of fear effects. The effect of occasional reinforced extinction trials was investigated in a sample of thirty-nine participants using a fear conditioning and extinction paradigm. Participants either underwent traditional extinction procedures during which the conditional stimulus which had been paired with the unconditional stimulus (US) during acquisition training (CS+) was presented alone with no presentations of the US or partially reinforced extinction during which there were several unpredicted CS+/US pairings. As measured by skin conductance responses, physiological fear responding remained elevated during extinction for participants who experienced partially reinforced extinction; however, these participants demonstrated protection from rapid reacquisition effects. Results from the subjective US-expectancy ratings did not provide evidence of protection against rapid reacquisition in the partially reinforced extinction group; however, there was evidence of protection from spontaneous recovery effects. Lastly, as measured by valence ratings, it was unclear whether partially reinforced extinction provided protection from fear recovery effects. Although participants who experienced partially reinforced extinction demonstrated protection from rapid reacquisition as measured by skin conductance responses, they also demonstrated significantly higher levels of physiological fear responding during extinction which made the results of the spontaneous recovery test more difficult to interpret. Occasional CS-US pairings during extinction may protect against return of fear effects. Clinical implications are discussed. Published by Elsevier Ltd.

IMPAIRED FEAR EXTINCTION ASSOCIATED WITH PTSD INCREASES WITH HOURS-SINCE-WAKING.

PubMed

Zuj, Daniel V; Palmer, Matthew A; Hsu, Chia-Ming K; Nicholson, Emma L; Cushing, Pippa J; Gray, Kate E; Felmingham, Kim L

2016-03-01

Prior research has demonstrated that time-of-day may play an important role in the extinction of conditioned fear, with extinction better learned earlier in the day rather than later. Impaired fear extinction memory is widely considered a key mechanism of posttraumatic stress disorder (PTSD). The relationship between fear extinction and PTSD symptoms may be moderated by hours-since-waking. In the present experiment, we examined whether hours-since-waking would moderate fear extinction learning ability in a clinical PTSD sample (n = 15), compared to trauma-exposed (n = 33) and nonexposed controls (n = 22). Participants completed a standardized differential fear conditioning and extinction paradigm, providing skin conductance response measures to quantify conditioned responding. Mixed-model analysis of variance revealed a PTSD-specific impairment in extinction learning ability in the late extinction phase. A moderation analysis showed that hours-since-waking was a significant moderator of the relationship between impaired late extinction and PTSD symptoms. Specifically, we found that participants with higher PTSD symptoms demonstrated poorer fear extinction learning ability as they were awake for longer. The results of the current study add to a growing literature indicating deficits in fear extinction learning in PTSD samples, compared to trauma-exposed and nonexposed controls. These results support previous findings that fear extinction is impaired later in the day, and extends this to a clinical sample, suggesting that exposure-therapy may be optimized by scheduling sessions in the morning. © 2016 Wiley Periodicals, Inc.

Chronology of Postglacial Eruptive Activity and Calculation of Eruption Probabilities for Medicine Lake Volcano, Northern California

USGS Publications Warehouse

Nathenson, Manuel; Donnelly-Nolan, Julie M.; Champion, Duane E.; Lowenstern, Jacob B.

2007-01-01

Medicine Lake volcano has had 4 eruptive episodes in its postglacial history (since 13,000 years ago) comprising 16 eruptions. Time intervals between events within the episodes are relatively short, whereas time intervals between the episodes are much longer. An updated radiocarbon chronology for these eruptions is presented that uses paleomagnetic data to constrain the choice of calibrated ages. This chronology is used with exponential, Weibull, and mixed-exponential probability distributions to model the data for time intervals between eruptions. The mixed exponential distribution is the best match to the data and provides estimates for the conditional probability of a future eruption given the time since the last eruption. The probability of an eruption at Medicine Lake volcano in the next year from today is 0.00028.

THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. VIII. A WIDE-AREA, HIGH-RESOLUTION MAP OF DUST EXTINCTION IN M31

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

Dalcanton, Julianne J.; Fouesneau, Morgan; Weisz, Daniel R.

We map the distribution of dust in M31 at 25 pc resolution using stellar photometry from the Panchromatic Hubble Andromeda Treasury survey. The map is derived with a new technique that models the near-infrared color–magnitude diagram (CMD) of red giant branch (RGB) stars. The model CMDs combine an unreddened foreground of RGB stars with a reddened background population viewed through a log-normal column density distribution of dust. Fits to the model constrain the median extinction, the width of the extinction distribution, and the fraction of reddened stars in each 25 pc cell. The resulting extinction map has a factor ofmore » ≳4 times better resolution than maps of dust emission, while providing a more direct measurement of the dust column. There is superb morphological agreement between the new map and maps of the extinction inferred from dust emission by Draine et al. However, the widely used Draine and Li dust models overpredict the observed extinction by a factor of ∼2.5, suggesting that M31's true dust mass is lower and that dust grains are significantly more emissive than assumed in Draine et al. The observed factor of ∼2.5 discrepancy is consistent with similar findings in the Milky Way by the Plank Collaboration et al., but we find a more complex dependence on parameters from the Draine and Li dust models. We also show that the the discrepancy with the Draine et al. map is lowest where the current interstellar radiation field has a harder spectrum than average. We discuss possible improvements to the CMD dust mapping technique, and explore further applications in both M31 and other galaxies.« less

Life history trade-off moderates model predictions of diversity loss from climate change.

PubMed

Moor, Helen

2017-01-01

Climate change can trigger species range shifts, local extinctions and changes in diversity. Species interactions and dispersal capacity are important mediators of community responses to climate change. The interaction between multispecies competition and variation in dispersal capacity has recently been shown to exacerbate the effects of climate change on diversity and to increase predictions of extinction risk dramatically. Dispersal capacity, however, is part of a species' overall ecological strategy and are likely to trade off with other aspects of its life history that influence population growth and persistence. In plants, a well-known example is the trade-off between seed mass and seed number. The presence of such a trade-off might buffer the diversity loss predicted by models with random but neutral (i.e. not impacting fitness otherwise) differences in dispersal capacity. Using a trait-based metacommunity model along a warming climatic gradient the effect of three different dispersal scenarios on model predictions of diversity change were compared. Adding random variation in species dispersal capacity caused extinctions by the introduction of strong fitness differences due an inherent property of the dispersal kernel. Simulations including a fitness-equalising trade-off based on empirical relationships between seed mass (here affecting dispersal distance, establishment probability, and seedling biomass) and seed number (fecundity) maintained higher initial species diversity and predicted lower extinction risk and diversity loss during climate change than simulations with variable dispersal capacity. Large seeded species persisted during climate change, but developed lags behind their climate niche that may cause extinction debts. Small seeded species were more extinction-prone during climate change but tracked their niches through dispersal and colonisation, despite competitive resistance from residents. Life history trade-offs involved in coexistence mechanisms may increase community resilience to future climate change and are useful guides for model development.

Cumulative frequency distribution of past species extinctions

NASA Technical Reports Server (NTRS)

Raup, D. M.

1991-01-01

Analysis of Sepkoski's compendium of the time ranges of 30,000+ taxa yields a mean duration of 28.4 ma for genera of fossil invertebrates. This converts to an average extinction rate of 3.5 percent per million years or about one percent every 286,000 years. Using survivorship techniques, these estimates can be converted to the species level, yielding a Phanerozoic average of one percent species extinction every 40,000 years. Variation in extinction rates through time is far greater than the null expectation of a homogeneous birth-death model and this reflects the well-known episodicity of extinction ranging from a few large mass extinctions to so-called background extinction. The observed variation in rates can be used to construct a cumulative frequency distribution of extinction intensity, and this distribution, in the form of a kill curve for species, shows the expected waiting times between extinction events of a given intensity. The kill curve is an average description of the extinction events of a given intensity. The kill curve is an average description of the extinction record and does not imply any cause or causes of extinction. The kill curve shows, among other things, that only about five percent of total species extinctions in the Phanerozoic were involved in the five largest mass extinctions. The other 95 percent were distributed among large and small events not normally called mass extinctions. As an exploration of the possibly absurd proposition that most past extinctions were produced by the effects of large-body impact, the kill curve for species was mapped on the comparable distribution for comet and asteroid impacts. The result is a curve predicting the species kill for a given size of impacting object (expressed as crater size). The results are reasonable in that impacts producing craters less than 30 km (diameter) cause negligible extinction but those producing craters 100-150 km (diameter) cause extinction of species in the range of 45-60 percent.

Population control methods in stochastic extinction and outbreak scenarios.

PubMed

Segura, Juan; Hilker, Frank M; Franco, Daniel

2017-01-01

Adaptive limiter control (ALC) and adaptive threshold harvesting (ATH) are two related control methods that have been shown to stabilize fluctuating populations. Large variations in population abundance can threaten the constancy and the persistence stability of ecological populations, which may impede the success and efficiency of managing natural resources. Here, we consider population models that include biological mechanisms characteristic for causing extinctions on the one hand and pest outbreaks on the other hand. These models include Allee effects and the impact of natural enemies (as is typical of forest defoliating insects). We study the impacts of noise and different levels of biological parameters in three extinction and two outbreak scenarios. Our results show that ALC and ATH have an effect on extinction and outbreak risks only for sufficiently large control intensities. Moreover, there is a clear disparity between the two control methods: in the extinction scenarios, ALC can be effective and ATH can be counterproductive, whereas in the outbreak scenarios the situation is reversed, with ATH being effective and ALC being potentially counterproductive.

Stochastic models for the Trojan Y-Chromosome eradication strategy of an invasive species.

PubMed

Wang, Xueying; Walton, Jay R; Parshad, Rana D

2016-01-01

The Trojan Y-Chromosome (TYC) strategy, an autocidal genetic biocontrol method, has been proposed to eliminate invasive alien species. In this work, we develop a Markov jump process model for this strategy, and we verify that there is a positive probability for wild-type females going extinct within a finite time. Moreover, when sex-reversed Trojan females are introduced at a constant population size, we formulate a stochastic differential equation (SDE) model as an approximation to the proposed Markov jump process model. Using the SDE model, we investigate the probability distribution and expectation of the extinction time of wild-type females by solving Kolmogorov equations associated with these statistics. The results indicate how the probability distribution and expectation of the extinction time are shaped by the initial conditions and the model parameters.

The sweet taste of death: glucose triggers apoptosis during yeast chronological aging.

PubMed

Ruckenstuhl, Christoph; Carmona-Gutierrez, Didac; Madeo, Frank

2010-10-01

As time goes by, a postmitotic cell ages following a degeneration process ultimately ending in cell death. This phenomenon is evolutionary conserved and present in unicellular eukaryotes as well, making the yeast chronological aging system an appreciated model. Here, single cells die in a programmed fashion (both by apoptosis and necrosis) for the benefit of the whole population. Besides its meaning for aging and cell death research, age-induced programmed cell death represents the first experimental proof for the so-called group selection theory: Apoptotic genes became selected during evolution because of the benefits they might render to the whole cell culture and not to the individual cell. Many anti‐aging stimuli have been discovered in the yeast chronological aging system and have afterwards been confirmed in higher cells or organisms. New work from the Burhans group (this issue) now demonstrates that glucose signaling has a progeriatric effect on chronologically aged yeast cells: Glucose administration results in a diminished efficacy of cells to enter quiescence, finally causing superoxide‐mediated replication stress and apoptosis.

Estimation of species extinction: what are the consequences when total species number is unknown?

PubMed

Chen, Youhua

2014-12-01

The species-area relationship (SAR) is known to overestimate species extinction but the underlying mechanisms remain unclear to a great extent. Here, I show that when total species number in an area is unknown, the SAR model exaggerates the estimation of species extinction. It is proposed that to accurately estimate species extinction caused by habitat destruction, one of the principal prerequisites is to accurately total the species numbers presented in the whole study area. One can better evaluate and compare alternative theoretical SAR models on the accurate estimation of species loss only when the exact total species number for the whole area is clear. This presents an opportunity for ecologists to simulate more research on accurately estimating Whittaker's gamma diversity for the purpose of better predicting species loss.

Extinction risk and structure of a food web model

NASA Astrophysics Data System (ADS)

Pękalski, Andrzej; Szwabiński, Janusz; Bena, Ioana; Droz, Michel

2008-03-01

We investigate in detail the model of a trophic web proposed by Amaral and Meyer [Phys. Rev. Lett. 82, 652 (1999)]. We focus on small-size systems that are relevant for real biological food webs and for which the fluctuations play an important role. We show, using Monte Carlo simulations, that such webs can be nonviable, leading to extinction of all species in small and/or weakly coupled systems. Estimations of the extinction times and survival chances are also given. We show that before the extinction the fraction of highly connected species (“omnivores”) is increasing. Viable food webs exhibit a pyramidal structure, where the density of occupied niches is higher at lower trophic levels, and moreover the occupations of adjacent levels are closely correlated. We also demonstrate that the distribution of the lengths of food chains has an exponential character and changes weakly with the parameters of the model. On the contrary, the distribution of avalanche sizes of the extinct species depends strongly on the connectedness of the web. For rather loosely connected systems, we recover the power-law type of behavior with the same exponent as found in earlier studies, while for densely connected webs the distribution is not of a power-law type.

Context-Dependent Encoding of Fear and Extinction Memories in a Large-Scale Network Model of the Basal Amygdala

PubMed Central

Vlachos, Ioannis; Herry, Cyril; Lüthi, Andreas; Aertsen, Ad; Kumar, Arvind

2011-01-01

The basal nucleus of the amygdala (BA) is involved in the formation of context-dependent conditioned fear and extinction memories. To understand the underlying neural mechanisms we developed a large-scale neuron network model of the BA, composed of excitatory and inhibitory leaky-integrate-and-fire neurons. Excitatory BA neurons received conditioned stimulus (CS)-related input from the adjacent lateral nucleus (LA) and contextual input from the hippocampus or medial prefrontal cortex (mPFC). We implemented a plasticity mechanism according to which CS and contextual synapses were potentiated if CS and contextual inputs temporally coincided on the afferents of the excitatory neurons. Our simulations revealed a differential recruitment of two distinct subpopulations of BA neurons during conditioning and extinction, mimicking the activation of experimentally observed cell populations. We propose that these two subgroups encode contextual specificity of fear and extinction memories, respectively. Mutual competition between them, mediated by feedback inhibition and driven by contextual inputs, regulates the activity in the central amygdala (CEA) thereby controlling amygdala output and fear behavior. The model makes multiple testable predictions that may advance our understanding of fear and extinction memories. PMID:21437238

Deep brain stimulation, histone deacetylase inhibitors and glutamatergic drugs rescue resistance to fear extinction in a genetic mouse model

PubMed Central

Whittle, Nigel; Schmuckermair, Claudia; Gunduz Cinar, Ozge; Hauschild, Markus; Ferraguti, Francesco; Holmes, Andrew; Singewald, Nicolas

2013-01-01

Anxiety disorders are characterized by persistent, excessive fear. Therapeutic interventions that reverse deficits in fear extinction represent a tractable approach to treating these disorders. We previously reported that 129S1/SvImJ (S1) mice show no extinction learning following normal fear conditioning. We now demonstrate that weak fear conditioning does permit fear reduction during massed extinction training in S1 mice, but reveals specific deficiency in extinction memory consolidation/retrieval. Rescue of this impaired extinction consolidation/retrieval was achieved with d-cycloserine (N-methly-d-aspartate partial agonist) or MS-275 (histone deacetylase (HDAC) inhibitor), applied after extinction training. We next examined the ability of different drugs and non-pharmacological manipulations to rescue the extreme fear extinction deficit in S1 following normal fear conditioning with the ultimate aim to produce low fear levels in extinction retrieval tests. Results showed that deep brain stimulation (DBS) by applying high frequency stimulation to the nucleus accumbens (ventral striatum) during extinction training, indeed significantly reduced fear during extinction retrieval compared to sham stimulation controls. Rescue of both impaired extinction acquisition and deficient extinction consolidation/retrieval was achieved with prior extinction training administration of valproic acid (a GABAergic enhancer and HDAC inhibitor) or AMN082 [metabotropic glutamate receptor 7 (mGlu7) agonist], while MS-275 or PEPA (AMPA receptor potentiator) failed to affect extinction acquisition in S1 mice. Collectively, these data identify potential beneficial effects of DBS and various drug treatments, including those with HDAC inhibiting or mGlu7 agonism properties, as adjuncts to overcome treatment resistance in exposure-based therapies. This article is part of a Special Issue entitled ‘Cognitive Enhancers’. PMID:22722028

Confounding environmental colour and distribution shape leads to underestimation of population extinction risk.

PubMed

Fowler, Mike S; Ruokolainen, Lasse

2013-01-01

The colour of environmental variability influences the size of population fluctuations when filtered through density dependent dynamics, driving extinction risk through dynamical resonance. Slow fluctuations (low frequencies) dominate in red environments, rapid fluctuations (high frequencies) in blue environments and white environments are purely random (no frequencies dominate). Two methods are commonly employed to generate the coloured spatial and/or temporal stochastic (environmental) series used in combination with population (dynamical feedback) models: autoregressive [AR(1)] and sinusoidal (1/f) models. We show that changing environmental colour from white to red with 1/f models, and from white to red or blue with AR(1) models, generates coloured environmental series that are not normally distributed at finite time-scales, potentially confounding comparison with normally distributed white noise models. Increasing variability of sample Skewness and Kurtosis and decreasing mean Kurtosis of these series alter the frequency distribution shape of the realised values of the coloured stochastic processes. These changes in distribution shape alter patterns in the probability of single and series of extreme conditions. We show that the reduced extinction risk for undercompensating (slow growing) populations in red environments previously predicted with traditional 1/f methods is an artefact of changes in the distribution shapes of the environmental series. This is demonstrated by comparison with coloured series controlled to be normally distributed using spectral mimicry. Changes in the distribution shape that arise using traditional methods lead to underestimation of extinction risk in normally distributed, red 1/f environments. AR(1) methods also underestimate extinction risks in traditionally generated red environments. This work synthesises previous results and provides further insight into the processes driving extinction risk in model populations. We must let the characteristics of known natural environmental covariates (e.g., colour and distribution shape) guide us in our choice of how to best model the impact of coloured environmental variation on population dynamics.

A statistical approach to quasi-extinction forecasting.

PubMed

Holmes, Elizabeth Eli; Sabo, John L; Viscido, Steven Vincent; Fagan, William Fredric

2007-12-01

Forecasting population decline to a certain critical threshold (the quasi-extinction risk) is one of the central objectives of population viability analysis (PVA), and such predictions figure prominently in the decisions of major conservation organizations. In this paper, we argue that accurate forecasting of a population's quasi-extinction risk does not necessarily require knowledge of the underlying biological mechanisms. Because of the stochastic and multiplicative nature of population growth, the ensemble behaviour of population trajectories converges to common statistical forms across a wide variety of stochastic population processes. This paper provides a theoretical basis for this argument. We show that the quasi-extinction surfaces of a variety of complex stochastic population processes (including age-structured, density-dependent and spatially structured populations) can be modelled by a simple stochastic approximation: the stochastic exponential growth process overlaid with Gaussian errors. Using simulated and real data, we show that this model can be estimated with 20-30 years of data and can provide relatively unbiased quasi-extinction risk with confidence intervals considerably smaller than (0,1). This was found to be true even for simulated data derived from some of the noisiest population processes (density-dependent feedback, species interactions and strong age-structure cycling). A key advantage of statistical models is that their parameters and the uncertainty of those parameters can be estimated from time series data using standard statistical methods. In contrast for most species of conservation concern, biologically realistic models must often be specified rather than estimated because of the limited data available for all the various parameters. Biologically realistic models will always have a prominent place in PVA for evaluating specific management options which affect a single segment of a population, a single demographic rate, or different geographic areas. However, for forecasting quasi-extinction risk, statistical models that are based on the convergent statistical properties of population processes offer many advantages over biologically realistic models.

Parasite biodiversity faces extinction and redistribution in a changing climate

PubMed Central

Carlson, Colin J.; Burgio, Kevin R.; Dougherty, Eric R.; Phillips, Anna J.; Bueno, Veronica M.; Clements, Christopher F.; Castaldo, Giovanni; Dallas, Tad A.; Cizauskas, Carrie A.; Cumming, Graeme S.; Doña, Jorge; Harris, Nyeema C.; Jovani, Roger; Mironov, Sergey; Muellerklein, Oliver C.; Proctor, Heather C.; Getz, Wayne M.

2017-01-01

Climate change is a well-documented driver of both wildlife extinction and disease emergence, but the negative impacts of climate change on parasite diversity are undocumented. We compiled the most comprehensive spatially explicit data set available for parasites, projected range shifts in a changing climate, and estimated extinction rates for eight major parasite clades. On the basis of 53,133 occurrences capturing the geographic ranges of 457 parasite species, conservative model projections suggest that 5 to 10% of these species are committed to extinction by 2070 from climate-driven habitat loss alone. We find no evidence that parasites with zoonotic potential have a significantly higher potential to gain range in a changing climate, but we do find that ectoparasites (especially ticks) fare disproportionately worse than endoparasites. Accounting for host-driven coextinctions, models predict that up to 30% of parasitic worms are committed to extinction, driven by a combination of direct and indirect pressures. Despite high local extinction rates, parasite richness could still increase by an order of magnitude in some places, because species successfully tracking climate change invade temperate ecosystems and replace native species with unpredictable ecological consequences. PMID:28913417

Raman Lidar Profiling of Aerosols Over the Central US; Diurnal Variability and Comparisons with the GOCART Model

NASA Technical Reports Server (NTRS)

Ferrare, R. A.; Chin, M.; Clayton, M.; Turner, D.

2002-01-01

We use profiles of aerosol extinction, water vapor mixing ratio, and relative humidity measured by the ARM SGP Raman lidar in northern Oklahoma to show how the vertical distributions of aerosol extinction and water vapor vary throughout the diurnal cycle. While significant (20-30%) variations in aerosol extinction occurred near the surface as well as aloft, smaller (approximately 10%) variations were observed in the diurnal variability of aerosol optical thickness (AOT). The diurnal variations in aerosol extinction profiles are well correlated with corresponding variations in the average relative humidity profiles. The water vapor mixing ratio profiles and integrated water vapor amounts generally show less diurnal variability. The Raman lidar profiles are also used to evaluate the aerosol optical thickness and aerosol extinction profiles simulated by the GOCART global aerosol model. Initial comparisons show that the AOT simulated by GOCART was in closer agreement with the AOT derived from the Raman lidar and Sun photometer measurements during November 2000 than during September 2000. For both months, the vertical variability in average aerosol extinction profiles simulated by GOCART is less than the variability in the corresponding Raman lidar profiles.

Rising synchrony controls western North American ecosystems.

PubMed

Black, Bryan A; van der Sleen, Peter; Di Lorenzo, Emanuele; Griffin, Daniel; Sydeman, William J; Dunham, Jason B; Rykaczewski, Ryan R; García-Reyes, Marisol; Safeeq, Mohammad; Arismendi, Ivan; Bograd, Steven J

2018-06-01

Along the western margin of North America, the winter expression of the North Pacific High (NPH) strongly influences interannual variability in coastal upwelling, storm track position, precipitation, and river discharge. Coherence among these factors induces covariance among physical and biological processes across adjacent marine and terrestrial ecosystems. Here, we show that over the past century the degree and spatial extent of this covariance (synchrony) has substantially increased, and is coincident with rising variance in the winter NPH. Furthermore, centuries-long blue oak (Quercus douglasii) growth chronologies sensitive to the winter NPH provide robust evidence that modern levels of synchrony are among the highest observed in the context of the last 250 years. These trends may ultimately be linked to changing impacts of the El Niño Southern Oscillation on midlatitude ecosystems of North America. Such a rise in synchrony may destabilize ecosystems, expose populations to higher risks of extinction, and is thus a concern given the broad biological relevance of winter climate to biological systems. © 2018 John Wiley & Sons Ltd.

Rising synchrony controls western North American ecosystems

USGS Publications Warehouse

Black, Bryan A.; van der Sleen, Peter; Di Lorenzo, Emanuele; Griffin, Daniel; Sydeman, William J.; Dunham, Jason B.; Rykaczewski, Ryan R.; Garcia-Reyes, Marisol; Safeeq, Mohammad; Arismendi, Ivan; Bograd, Steven J.

2018-01-01

Along the western margin of North America, the winter expression of the North Pacific High (NPH) strongly influences interannual variability in coastal upwelling, storm track position, precipitation, and river discharge. Coherence among these factors induces covariance among physical and biological processes across adjacent marine and terrestrial ecosystems. Here, we show that over the past century the degree and spatial extent of this covariance (synchrony) has substantially increased, and is coincident with rising variance in the winter NPH. Furthermore, centuries‐long blue oak (Quercus douglasii) growth chronologies sensitive to the winter NPH provide robust evidence that modern levels of synchrony are among the highest observed in the context of the last 250 years. These trends may ultimately be linked to changing impacts of the El Niño Southern Oscillation on mid‐latitude ecosystems of North America. Such a rise in synchrony may destabilize ecosystems, expose populations to higher risks of extinction, and is thus a concern given the broad biological relevance of winter climate to biological systems.

Birth-death models and coalescent point processes: the shape and probability of reconstructed phylogenies.

PubMed

Lambert, Amaury; Stadler, Tanja

2013-12-01

Forward-in-time models of diversification (i.e., speciation and extinction) produce phylogenetic trees that grow "vertically" as time goes by. Pruning the extinct lineages out of such trees leads to natural models for reconstructed trees (i.e., phylogenies of extant species). Alternatively, reconstructed trees can be modelled by coalescent point processes (CPPs), where trees grow "horizontally" by the sequential addition of vertical edges. Each new edge starts at some random speciation time and ends at the present time; speciation times are drawn from the same distribution independently. CPPs lead to extremely fast computation of tree likelihoods and simulation of reconstructed trees. Their topology always follows the uniform distribution on ranked tree shapes (URT). We characterize which forward-in-time models lead to URT reconstructed trees and among these, which lead to CPP reconstructed trees. We show that for any "asymmetric" diversification model in which speciation rates only depend on time and extinction rates only depend on time and on a non-heritable trait (e.g., age), the reconstructed tree is CPP, even if extant species are incompletely sampled. If rates additionally depend on the number of species, the reconstructed tree is (only) URT (but not CPP). We characterize the common distribution of speciation times in the CPP description, and discuss incomplete species sampling as well as three special model cases in detail: (1) the extinction rate does not depend on a trait; (2) rates do not depend on time; (3) mass extinctions may happen additionally at certain points in the past. Copyright © 2013 Elsevier Inc. All rights reserved.

Palaeoecology: Megafauna as a nutrient pump

NASA Astrophysics Data System (ADS)

Daufresne, Tanguy

2013-09-01

The end of the Pleistocene epoch saw the extinction of large-bodied herbivores around the world. Numerical modelling suggests that continental-scale effects of this extinction on nutrient transport are ongoing.

Community stability and selective extinction during the Permian-Triassic mass extinction

NASA Astrophysics Data System (ADS)

Roopnarine, Peter D.; Angielczyk, Kenneth D.

2015-10-01

The fossil record contains exemplars of extreme biodiversity crises. Here, we examined the stability of terrestrial paleocommunities from South Africa during Earth's most severe mass extinction, the Permian-Triassic. We show that stability depended critically on functional diversity and patterns of guild interaction, regardless of species richness. Paleocommunities exhibited less transient instability—relative to model communities with alternative community organization—and significantly greater probabilities of being locally stable during the mass extinction. Functional patterns that have evolved during an ecosystem's history support significantly more stable communities than hypothetical alternatives.

H2 spectroscopy as an agent for extinction determinations The near-infrared curve for the Orion molecular cloud

NASA Technical Reports Server (NTRS)

Davis, D. S.; Larson, H. P.; Hofmann, R.

1986-01-01

A near-infrared (1.8 to 3.5) microns extinction curve for the Orion molecular cloud is presented. The curve is derived from high-resolution spectra of the Orion H2 source recorded from the Kuiper Airborne Observatory. The data reveal that the Orion extinction law is indistinguishable from a 1/lambda form in the near-infrared, except for strongly enhanced extinction near a wavelength of about 3 microns. The implications of these results, in the context of current interstellar grain models, are discussed.

Spatially Synchronous Extinction of Species under External Forcing

NASA Astrophysics Data System (ADS)

Amritkar, R. E.; Rangarajan, Govindan

2006-06-01

More than 99% of the species that ever existed on the surface of the Earth are now extinct and their extinction on a global scale has been a puzzle. One may think that a species under an external threat may survive in some isolated locations leading to the revival of the species. Using a general model we show that, under a common external forcing, the species with a quadratic saturation term first undergoes spatial synchronization and then extinction. The effect can be observed even when the external forcing acts only on some locations provided the dynamics contains a synchronizing term. Absence of the quadratic saturation term can help the species to avoid extinction.

NLC Past Workshops & Conferences

Science.gov Websites

NLC Technical SLAC Meeting Schedule Web Comments 2004 Calendar Year 2003 Calendar Year 2003 Chronological listing 2002 Calendar Year 2002 Chronological listing 2001 Calendar Year 2001 Chronological listing 2000 Calendar Year 2000 Chronological listing 1999 Calendar Year 1999 Chronological listing This

Threshold for extinction and survival in stochastic tumor immune system

NASA Astrophysics Data System (ADS)

Li, Dongxi; Cheng, Fangjuan

2017-10-01

This paper mainly investigates the stochastic character of tumor growth and extinction in the presence of immune response of a host organism. Firstly, the mathematical model describing the interaction and competition between the tumor cells and immune system is established based on the Michaelis-Menten enzyme kinetics. Then, the threshold conditions for extinction, weak persistence and stochastic persistence of tumor cells are derived by the rigorous theoretical proofs. Finally, stochastic simulation are taken to substantiate and illustrate the conclusion we have derived. The modeling results will be beneficial to understand to concept of immunoediting, and develop the cancer immunotherapy. Besides, our simple theoretical model can help to obtain new insight into the complexity of tumor growth.

The Perils of Picky Eating: Dietary Breadth Is Related to Extinction Risk in Insectivorous Bats

PubMed Central

Boyles, Justin G.; Storm, Jonathan J.

2007-01-01

Several recent papers evaluate the relationship between ecological characteristics and extinction risk in bats. These studies report that extinction risk is negatively related to geographic range size and positively related to habitat specialization. Here, we evaluate the hypothesis that extinction risk is also related to dietary specialization in insectivorous vespertilionid bats using both traditional and phylogenetically-controlled analysis of variance. We collected dietary data and The World Conservation Union (IUCN) rankings for 44 Australian, European, and North American bat species. Our results indicate that species of conservation concern (IUCN ranking near threatened or above) are more likely to have a specialized diet than are species of least concern. Additional analyses show that dietary breadth is not correlated to geographic range size or wing morphology, characteristics previously found to correlate with extinction risk. Therefore, there is likely a direct relationship between dietary specialization and extinction risk; however, the large variation in dietary breadth within species of least concern suggests that diet alone cannot explain extinction risk. Our results may have important implications for the development of predictive models of extinction risk and for the assignment of extinction risk to insectivorous bat species. Similar analyses should be conducted on additional bat families to assess the generality of this relationship between niche breadth and extinction risk. PMID:17653286

Evaluating differences in Pavlovian fear acquisition and extinction as predictors of outcome from cognitive behavioural therapy for anxious children.

PubMed

Waters, Allison M; Pine, Daniel S

2016-07-01

Extinction is a key theoretical model of exposure-based treatments, such as cognitive behavioural therapy (CBT). This study examined whether individual differences in physiological responses and subjective stimulus evaluations as indices of fear extinction predicted response to CBT. Thirty-two nonanxious comparisons and 44 anxious, 7-to-13-year-old children completed a Pavlovian conditioning and extinction task. Anxious children then completed group-based CBT. Skin conductance responses (SCRs) as well as subjective arousal and valence evaluations were measured in response to a conditioned stimulus paired with an aversive tone (CS+) and another conditioned stimulus presented alone (CS-). Both stimuli were presented alone during extinction. Diagnostic and symptom measures were completed before and after treatment. Like nonanxious comparisons, treatment responders did not acquire conditioned negative stimulus evaluations and displayed elevated SCRs that declined significantly across extinction trials. Nonresponders, by contrast, showed elevated negative stimulus evaluations of both CSs that were sensitive to extinction trials but showed no change in SCRs during extinction. Change in physiological but not evaluative indices of fear extinction predicted better treatment outcomes. Individual differences in evaluative and physiological indices of fear extinction might moderate response to CBT. © 2016 Association for Child and Adolescent Mental Health.

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120-800 ka

NASA Astrophysics Data System (ADS)

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Veres, D.; Parrenin, F.; Martinerie, P.; Ritz, C.; Capron, E.; Lipenkov, V.; Loutre, M.-F.; Raynaud, D.; Vinther, B.; Svensson, A.; Rasmussen, S. O.; Severi, M.; Blunier, T.; Leuenberger, M.; Fischer, H.; Masson-Delmotte, V.; Chappellaz, J.; Wolff, E.

2013-08-01

An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale had been developed based on an inverse dating method (Datice), combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousands of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2013), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120-800 ka. In this framework, new measurements of δ18Oatm over Marine Isotope Stage (MIS) 11-12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive additional orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content) has been verified before implementation in AICC2012. The new chronology is now independent of other archives and shows only small differences, most of the time within the original uncertainty range calculated by Datice, when compared with the previous ice core reference age scale EDC3, the Dome F chronology, or using a comparison between speleothems and methane. For instance, the largest deviation between AICC2012 and EDC3 (5.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

Climate change and the selective signature of the Late Ordovician mass extinction.

PubMed

Finnegan, Seth; Heim, Noel A; Peters, Shanan E; Fischer, Woodward W

2012-05-01

Selectivity patterns provide insights into the causes of ancient extinction events. The Late Ordovician mass extinction was related to Gondwanan glaciation; however, it is still unclear whether elevated extinction rates were attributable to record failure, habitat loss, or climatic cooling. We examined Middle Ordovician-Early Silurian North American fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per-taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk. Genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the Katian stage were particularly hard hit. The duration of the subsequent sampling gaps had little effect on extinction risk, suggesting that this extinction pulse cannot be entirely attributed to rock record failure; rather, it was caused, in part, by habitat loss. Extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled, a macroecological trait linked to thermal tolerance. A model trained on the relationship between 16 explanatory variables and extinction patterns during the early Katian interval substantially underestimates the extinction of exclusively tropical taxa during the late Katian interval. These results indicate that glacioeustatic sea-level fall and tropical ocean cooling played important roles in the first pulse of the Late Ordovician mass extinction in Laurentia.

Deepened extinction following compound stimulus presentation: Noradrenergic modulation

PubMed Central

Janak, Patricia H.; Corbit, Laura H.

2011-01-01

Behavioral extinction is an active form of new learning involving the prediction of nonreward where reward has previously been present. The expression of extinction learning can be disrupted by the presentation of reward itself or reward-predictive stimuli (reinstatement) as well as the passage of time (spontaneous recovery) or contextual changes (renewal). The following experiments replicated the demonstration that presenting multiple previously rewarded stimuli in compound during extinction enhances extinction learning. To explore the pharmacological basis for this we next examined the effects of pharmacological treatments that either facilitated or blocked noradrenergic activity to test the hypothesis that increased noradrenergic activity at the time of extinction training would improve, whereas blockade of noradrenergic activity would impair the extinction of appetitive stimulus–reward memories. Different groups of rats were trained in a discriminative stimulus paradigm to lever-press for food reward. Once stable responding was achieved, responding was extinguished for 2 d. Prior to a third extinction session, rats received systemic administration of either saline, yohimbine (α2 antagonist), atomoxetine (norepinephrine reuptake inhibitor), or propranolol (β-receptor antagonist). Spontaneous recovery of responding to the stimuli was tested 4 wk later. Our results indicate that increasing noradrenergic activity during extinction augments extinction learning resulting in less recovery of responding at test. These results have important implications for models of relapse to drug seeking and the development of extinction-based therapies. PMID:21224211

Orbital Debris: A Chronology

NASA Technical Reports Server (NTRS)

Portree, Davis S. F. (Editor); Loftus, Joseph P., Jr. (Editor)

1999-01-01

This chronology covers the 37-year history of orbital debris concerns. It tracks orbital debris hazard creation, research, observation, experimentation, management, mitigation, protection, and policy. Included are debris-producing, events; U.N. orbital debris treaties, Space Shuttle and space station orbital debris issues; ASAT tests; milestones in theory and modeling; uncontrolled reentries; detection system development; shielding development; geosynchronous debris issues, including reboost policies: returned surfaces studies, seminar papers reports, conferences, and studies; the increasing effect of space activities on astronomy; and growing international awareness of the near-Earth environment.

Nicotinamide supplementation phenocopies SIR2 inactivation by modulating carbon metabolism and respiration during yeast chronological aging.

PubMed

Orlandi, Ivan; Pellegrino Coppola, Damiano; Strippoli, Maurizio; Ronzulli, Rossella; Vai, Marina

2017-01-01

Nicotinamide (NAM), a form of vitamin B 3 , is a byproduct and noncompetitive inhibitor of the deacetylation reaction catalyzed by Sirtuins. These represent a family of evolutionarily conserved NAD + -dependent deacetylases that are well-known critical regulators of metabolism and aging and whose founding member is Sir2 of Saccharomyces cerevisiae. Here, we investigated the effects of NAM supplementation in the context of yeast chronological aging, the established model for studying aging of postmitotic quiescent mammalian cells. Our data show that NAM supplementation at the diauxic shift results in a phenocopy of chronologically aging sir2Δ cells. In fact, NAM-supplemented cells display the same chronological lifespan extension both in expired medium and extreme Calorie Restriction. Furthermore, NAM allows the cells to push their metabolism toward the same outcomes of sir2Δ cells by elevating the level of the acetylated Pck1. Both these cells have the same metabolic changes that concern not only anabolic pathways such as an increased gluconeogenesis but also respiratory activity in terms both of respiratory rate and state of respiration. In particular, they have a higher respiratory reserve capacity and a lower non-phosphorylating respiration that in concert with a low burden of superoxide anions can affect positively chronological aging. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

The shrinking ark: patterns of large mammal extinctions in India

PubMed Central

Karanth, Krithi K.; Nichols, James D.; Karanth, K. Ullas; Hines, James E.; Christensen, Norman L.

2010-01-01

Mammal extinctions are widespread globally, with South Asian species being most threatened. We examine local extinctions of 25 mammals in India. We use historical records to obtain a set of locations at which each species was known to have been present at some time in the last 200 years. We then use occupancy estimation models to draw inferences about current presence at these same locations based on field observations of local experts. We examine predictions about the influence of key factors such as protected areas, forest cover, elevation, human population density and cultural tolerance on species extinction. For all 25 species, estimated local extinction probabilities (referenced to a 100 year time frame) range between 0.14 and 0.96. Time elapsed since the historical occurrence record was an important determinant of extinction probability for 14 species. Protected areas are positively associated with lower extinction of 18 species, although many species occur outside them. We find evidence that higher proportion of forest cover is associated with lower extinction probabilities for seven species. However, for species that prefer open habitats (which have experienced intensive land-use change), forest cover alone appears insufficient to ensure persistence (the complement of extinction). We find that higher altitude is positively associated with lower extinction for eight species. Human population density is positively associated with extinction of 13 species. We find that ‘culturally tolerated’ species do exhibit higher persistence. Overall, large-bodied, rare and habitat specialist mammals tend to have higher extinction probabilities. PMID:20219736

Effects of Extinction Context and Retrieval Cues on Renewal of Alcohol-Cue Reactivity Among Alcohol-Dependent Outpatients

PubMed Central

Stasiewicz, Paul R.; Brandon, Thomas H.; Bradizza, Clara M.

2013-01-01

Pavlovian conditioning models have led to cue-exposure treatments for drug abuse. However, conditioned responding to drug stimuli can return (be renewed) following treatment. Animal research and a previous study of social drinkers indicated that extinction is highly context dependent but that renewal could be reduced by the inclusion of a cue from the extinction context. This study extends this research to a clinical sample. Alcohol-dependent outpatients (N = 143) completed an extinction trial to reduce craving and salivation responses to alcohol cues. They were then randomized to renewal tests in either the same context as extinction, a different context, the different context containing an extinction cue, or the different context with cue plus a manipulation to increase the salience of the cue. Contrary to predictions, the different context did not produce the expected renewal effect. Although the generalization of extinction effects beyond the cue-exposure context is a positive clinical finding, it is inconsistent with basic research findings on the context dependence of extinction. Possible explanations for this inconsistency are discussed. PMID:17563145

Effects of extinction context and retrieval cues on renewal of alcohol-cue reactivity among alcohol-dependent outpatients.

PubMed

Stasiewicz, Paul R; Brandon, Thomas H; Bradizza, Clara M

2007-06-01

Pavlovian conditioning models have led to cue-exposure treatments for drug abuse. However, conditioned responding to drug stimuli can return (be renewed) following treatment. Animal research and a previous study of social drinkers indicated that extinction is highly context dependent but that renewal could be reduced by the inclusion of a cue from the extinction context. This study extends this research to a clinical sample. Alcohol-dependent outpatients (N = 143) completed an extinction trial to reduce craving and salivation responses to alcohol cues. They were then randomized to renewal tests in either the same context as extinction, a different context, the different context containing an extinction cue, or the different context with cue plus a manipulation to increase the salience of the cue. Contrary to predictions, the different context did not produce the expected renewal effect. Although the generalization of extinction effects beyond the cue-exposure context is a positive clinical finding, it is inconsistent with basic research findings on the context dependence of extinction. Possible explanations for this inconsistency are discussed.

Social buffering enhances extinction of conditioned fear responses in male rats.

PubMed

Mikami, Kaori; Kiyokawa, Yasushi; Takeuchi, Yukari; Mori, Yuji

2016-09-01

In social species, the phenomenon in which the presence of conspecific animals mitigates stress responses is called social buffering. We previously reported that social buffering in male rats ameliorated behavioral fear responses, as well as hypothalamic-pituitary-adrenal axis activation, elicited by an auditory conditioned stimulus (CS). However, after social buffering, it is not clear whether rats exhibit fear responses when they are re-exposed to the same CS in the absence of another rat. In the present study, we addressed this issue using an experimental model of extinction. High stress levels during extinction training impaired extinction, suggesting that extinction is enhanced when stress levels during extinction training are low. Therefore, we hypothesized that rats that had received social buffering during extinction training would not show fear responses to a CS, even in the absence of another rat, because social buffering had enhanced the extinction of conditioned fear responses. To test this, we subjected male fear-conditioned rats to extinction training either alone or with a non-conditioned male rat. The subjects were then individually re-exposed to the CS in a recall test. When the subjects individually underwent extinction training, no responses were suppressed in the recall test. Conversely, when the subjects received social buffering during extinction training, freezing and Fos expression in the paraventricular nucleus of the hypothalamus and lateral amygdala were suppressed. Additionally, the effects of social buffering were absent when the recall test was conducted in a different context from the extinction training. The present results suggest that social buffering enhances extinction of conditioned fear responses. Copyright © 2016 Elsevier Inc. All rights reserved.

Numerical experiments with model monophyletic and paraphyletic taxa

NASA Technical Reports Server (NTRS)

Sepkoski, J. J. Jr; Kendrick, D. C.; Sepkoski JJ, J. r. (Principal Investigator)

1993-01-01

The problem of how accurately paraphyletic taxa versus monophyletic (i.e., holophyletic) groups (clades) capture underlying species patterns of diversity and extinction is explored with Monte Carlo simulations. Phylogenies are modeled as stochastic trees. Paraphyletic taxa are defined in an arbitrary manner by randomly choosing progenitors and clustering all descendants not belonging to other taxa. These taxa are then examined to determine which are clades, and the remaining paraphyletic groups are dissected to discover monophyletic subgroups. Comparisons of diversity patterns and extinction rates between modeled taxa and lineages indicate that paraphyletic groups can adequately capture lineage information under a variety of conditions of diversification and mass extinction. This suggests that these groups constitute more than mere "taxonomic noise" in this context. But, strictly monophyletic groups perform somewhat better, especially with regard to mass extinctions. However, when low levels of paleontologic sampling are simulated, the veracity of clades deteriorates, especially with respect to diversity, and modeled paraphyletic taxa often capture more information about underlying lineages. Thus, for studies of diversity and taxic evolution in the fossil record, traditional paleontologic genera and families need not be rejected in favor of cladistically-defined taxa.

Candesartan ameliorates impaired fear extinction induced by innate immune activation.

PubMed

Quiñones, María M; Maldonado, Lizette; Velazquez, Bethzaly; Porter, James T

2016-02-01

Patients with post-traumatic stress disorder (PTSD) tend to show signs of a relatively increased inflammatory state suggesting that activation of the immune system may contribute to the development of PTSD. In the present study, we tested whether activation of the innate immune system can disrupt acquisition or recall of auditory fear extinction using an animal model of PTSD. Male adolescent rats received auditory fear conditioning in context A. The next day, an intraperitoneal injection of lipopolysaccharide (LPS; 100 μg/kg) prior to auditory fear extinction in context B impaired acquisition and recall of extinction. LPS (100 μg/kg) given after extinction training did not impair extinction recall suggesting that LPS did not affect consolidation of extinction. In contrast to cued fear extinction, contextual fear extinction was not affected by prior injection of LPS (100 μg/kg). Although LPS also reduced locomotion, we could dissociate the effects of LPS on extinction and locomotion by using a lower dose of LPS (50 μg/kg) which impaired locomotion without affecting extinction. In addition, 15 h after an injection of 250 μg/kg LPS in adult rats, extinction learning and recall were impaired without affecting locomotion. A sub-chronic treatment with candesartan, an angiotensin II type 1 receptor blocker, prevented the LPS-induced impairment of extinction in adult rats. Our results demonstrate that activation of the innate immune system can disrupt auditory fear extinction in adolescent and adult animals. These findings also provide direction for clinical studies of novel treatments that modulate the innate immune system for stress-related disorders like PTSD. Copyright © 2015 Elsevier Inc. All rights reserved.

Persistence and extinction of a stochastic single-specie model under regime switching in a polluted environment.

PubMed

Liu, Meng; Wang, Ke

2010-06-07

A new single-species model disturbed by both white noise and colored noise in a polluted environment is developed and analyzed. Sufficient criteria for extinction, stochastic nonpersistence in the mean, stochastic weak persistence in the mean, stochastic strong persistence in the mean and stochastic permanence of the species are established. The threshold between stochastic weak persistence in the mean and extinction is obtained. The results show that both white and colored environmental noises have sufficient effect to the survival results. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Quantifying the severity of hurricanes on extinction probabilities of a primate population: Insights into "Island" extirpations.

PubMed

Ameca y Juárez, Eric I; Ellis, Edward A; Rodríguez-Luna, Ernesto

2015-07-01

Long-term studies quantifying impacts of hurricane activity on growth and trajectory of primate populations are rare. Using a 14-year monitored population of Alouatta palliata mexicana as a study system, we developed a modeling framework to assess the relative contribution of hurricane disturbance and two types of human impacts, habitat loss, and hunting, on quasi-extinction risk. We found that the scenario with the highest level of disturbance generated a 21% increase in quasi-extinction risk by 40 years compared to scenarios of intermediate disturbance, and around 67% increase relative to that found in low disturbance scenarios. We also found that the probability of reaching quasi-extinction due to human disturbance alone was below 1% by 40 years, although such scenarios reduced population size by 70%, whereas the risk of quasi-extinction ranged between 3% and 65% for different scenarios of hurricane severity alone, in absence of human impacts. Our analysis moreover found that the quasi-extinction risk driven by hunting and hurricane disturbance was significantly lower than the quasi-extinction risk posed by human-driven habitat loss and hurricane disturbance. These models suggest that hurricane disturbance has the potential to exceed the risk posed by human impacts, and, in particular, to substantially increase the speed of the extinction vortex driven by habitat loss relative to that driven by hunting. Early mitigation of habitat loss constituted the best method for reducing quasi-extinction risk: the earlier habitat loss is halted, the less vulnerable the population becomes to hurricane disturbance. By using a well-studied population of A. p. mexicana, we help understand the demographic impacts that extreme environmental disturbance can trigger on isolated populations of taxa already endangered in other systems where long-term demographic data are not available. For those experiencing heavy anthropogenic pressure and lacking sufficiently evolved coping strategies against unpredictable environmental disturbance, the risk of population extinction can be exacerbated. © 2015 Wiley Periodicals, Inc.

Challenging process to make the Lateglacial tree-ring chronologies from Europe absolute - an inventory

NASA Astrophysics Data System (ADS)

Kaiser, Klaus Felix; Friedrich, Michael; Miramont, Cécile; Kromer, Bernd; Sgier, Mario; Schaub, Matthias; Boeren, Ilse; Remmele, Sabine; Talamo, Sahra; Guibal, Frédéric; Sivan, Olivier

2012-03-01

Here we present the entire range of Lateglacial tree-ring chronologies from Switzerland, Germany, France, covering the Lateglacial north and west of the Alps without interruption as well as finds from northern Italy, complemented by a 14C data set of the Swiss chronologies. Geographical expansion of cross-matched European Lateglacial chronologies, limits and prospects of teleconnection between remote sites and extension of the absolute tree-ring chronology are discussed. High frequency signals and long-term fluctuations are revealed by the ring-width data sets of the newly constructed Swiss Late-glacial Master Chronology (SWILM) as well as the Central European Lateglacial Master Chronology (CELM) spanning 1606 years. They agree well with the characteristics of Boelling/Alleroed (GI-1) and the transition into Younger Dryas (GS-1). The regional chronologies of Central Europe may provide improved interconnection to other terrestrial or marine high-resolution archives. Nevertheless the breakthrough to a continuous absolute chronology back to Boelling (GI-1e) has not yet been achieved. A gap remains, even though it is covered by several floating chronologies from France and Switzerland.

Dry Chemical Development - A Model for the Extinction of Hydrocarbon Flames.

DTIC Science & Technology

1984-02-08

and predicts the suppression effectiveness of a wide variety of gaseous, liquid, and solid agents . The flame extinguishment model is based on the...generalized by consideration of all endothermic reaction sinks, eg., vaporization, dissociation, and decomposition. The general equation correlates...CHEMICAL DEVELOPMENT - A MODEL FOR THE EXTINCTION OF HYDROCARBON FLAMES Various fire-extinguishing agents are carried on board Navy ships to control

EXTINCTION AND DUST GEOMETRY IN M83 H II REGIONS: AN HUBBLE SPACE TELESCOPE/WFC3 STUDY

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

Liu, Guilin; Calzetti, Daniela; Hong, Sungryong

We present Hubble Space Telescope/WFC3 narrow-band imaging of the starburst galaxy M83 targeting the hydrogen recombination lines (Hβ, Hα, and Paβ), which we use to investigate the dust extinction in the H II regions. We derive extinction maps with 6 pc spatial resolution from two combinations of hydrogen lines (Hα/Hβ and Hα/Paβ), and show that the longer wavelengths probe larger optical depths, with A{sub V} values larger by ≳1 mag than those derived from the shorter wavelengths. This difference leads to a factor ≳2 discrepancy in the extinction-corrected Hα luminosity, a significant effect when studying extragalactic H II regions. By comparing thesemore » observations to a series of simple models, we conclude that a large diversity of absorber/emitter geometric configurations can account for the data, implying a more complex physical structure than the classical foreground ''dust screen'' assumption. However, most data points are bracketed by the foreground screen and a model where dust and emitters are uniformly mixed. When averaged over large (≳100-200 pc) scales, the extinction becomes consistent with a ''dust screen'', suggesting that other geometries tend to be restricted to more local scales. Moreover, the extinction in any region can be described by a combination of the foreground screen and the uniform mixture model with weights of 1/3 and 2/3 in the center (≲2 kpc), respectively, and 2/3 and 1/3 for the rest of the disk. This simple prescription significantly improves the accuracy of the dust extinction corrections and can be especially useful for pixel-based analyses of galaxies similar to M83.« less

Food web structure and the evolution of ecological communities

NASA Astrophysics Data System (ADS)

Quince, Christopher; Higgs, Paul G.; McKane, Alan J.

Simulations of the coevolution of many interacting species are performed using the Webworld model. The model has a realistic set of predator-prey equations that describe the population dynamics of the species for any structure of the food web. The equations account for competition between species for the same resources, and for the diet choice of predators between alternative prey according to an evolutionarily stable strategy. The set of species present undergoes long-term evolution d ue to speciation and extinction events. We summarize results obtained on the macro-evolutionary dynamics of speciations and extinctions, and on the statistical properties of the food webs that are generated by the model. Simulations begin from small numbers of species and build up to larger webs with relatively constant species number on average. The rate of origination and extinction of species are relatively high, but remain roughly balanced throughout the simulations. When a 'parent' species undergoes sp eciation, the 'child' species usually adds to the same trophic level as the parent. The chance of the child species surviving is significantly higher if the parent is on the second or third trophic level than if it is on the first level, most likely due to a wider choice of possible prey for species on higher levels. Addition of a new species sometimes causes extinction of existing species. The parent species has a high probability of extinction because it has strong competition with the new species. Non-pa rental competitors of the new species also have a significantly higher extinction probability than average, as do prey of the new species. Predators of the new species are less likely than average to become extinct.

Temporal factors in the extinction of fear in inbred mouse strains differing in extinction efficacy.

PubMed

MacPherson, Kathryn; Whittle, Nigel; Camp, Marguerite; Gunduz-Cinar, Ozge; Singewald, Nicolas; Holmes, Andrew

2013-07-05

Various neuropsychiatric conditions, including posttraumatic stress disorder (PTSD), are characterized by deficient fear extinction, but individuals differ greatly in risk for these. While there is growing evidence that fear extinction is influenced by certain procedural variables, it is unclear how these influences might vary across individuals and subpopulations. To model individual differences in fear extinction, prior studies identified a strain of inbred mouse, 129S1/SvImJ (S1), which exhibits a profound deficit in fear extinction, as compared to other inbred strains, such as C57BL/6J (B6). Here, we assessed the effects of procedural variables on the impaired extinction phenotype of the S1 strain and, by comparison, the extinction-intact B6 strain. The variables studied were 1) the interval between conditioning and extinction, 2) the interval between cues during extinction training, 3) single-cue exposure before extinction training, and 4) extinction of a second-order conditioned cue. Conducting extinction training soon after ('immediately') conditioning attenuated fear retrieval in S1 mice and impaired extinction in B6 mice. Spacing cue presentations with long inter-trial intervals during extinction training augmented fear in S1 and B6 mice. The effect of spacing was lost with one-trial fear conditioning in B6, but not S1 mice. A single exposure to a conditioned cue before extinction training did not alter extinction retrieval, either in B6 or S1 mice. Both the S1 and B6 strains exhibited robust second-order fear conditioning, in which a cue associated with footshock was sufficient to serve as a conditioned exciter to condition a fear association to a second cue. B6 mice extinguished the fear response to the second-order conditioned cue, but S1 mice failed to do so. These data provide further evidence that fear extinction is strongly influenced by multiple procedural variables and is so in a highly strain-dependent manner. This suggests that the efficacy of extinction-based behavioral interventions, such as exposure therapy, for trauma-related anxiety disorders will be determined by the procedural parameters employed and the degree to which the patient can extinguish.

MODELING EXTRAGALACTIC EXTINCTION THROUGH GAMMA-RAY BURST AFTERGLOWS

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

Zonca, Alberto; Mulas, Giacomo; Casu, Silvia

We analyze extragalactic extinction profiles derived through gamma-ray burst afterglows, using a dust model specifically constructed on the assumption that dust grains are not immutable but respond, time-dependently, to the local physics. Such a model includes core-mantle spherical particles of mixed chemical composition (silicate core, sp{sup 2}, and sp{sup 3} carbonaceous layers), and an additional molecular component in the form of free-flying polycyclic aromatic hydrocarbons. We fit most of the observed extinction profiles. Failures occur for lines of sight, presenting remarkable rises blueward of the bump. We find a tendency for the carbon chemical structure to become more aliphatic withmore » the galactic activity, and to some extent with increasing redshifts. Moreover, the contribution of the molecular component to the total extinction is more important in younger objects. The results of the fitting procedure (either successes and failures) may be naturally interpreted through an evolutionary prescription based on the carbon cycle in the interstellar medium of galaxies.« less

Modeling Effects of Local Extinctions on Culture Change and Diversity in the Paleolithic

PubMed Central

Premo, L. S.; Kuhn, Steven L.

2010-01-01

The persistence of early stone tool technologies has puzzled archaeologists for decades. Cognitively based explanations, which presume either lack of ability to innovate or extreme conformism, do not account for the totality of the empirical patterns. Following recent research, this study explores the effects of demographic factors on rates of culture change and diversification. We investigate whether the appearance of stability in early Paleolithic technologies could result from frequent extinctions of local subpopulations within a persistent metapopulation. A spatially explicit agent-based model was constructed to test the influence of local extinction rate on three general cultural patterns that archaeologists might observe in the material record: total diversity, differentiation among spatially defined groups, and the rate of cumulative change. The model shows that diversity, differentiation, and the rate of cumulative cultural change would be strongly affected by local extinction rates, in some cases mimicking the results of conformist cultural transmission. The results have implications for understanding spatial and temporal patterning in ancient material culture. PMID:21179418

Examining the relationship between local extinction risk and position in range.

PubMed

Boakes, Elizabeth H; Isaac, Nicholas J B; Fuller, Richard A; Mace, Georgina M; McGowan, Philip J K

2018-02-01

Over half of globally threatened animal species have experienced rapid geographic range loss. Identifying the parts of species' distributions most vulnerable to local extinction would benefit conservation planning. However, previous studies give little consensus on whether ranges decline to the core or edge. We built on previous work by using empirical data to examine the position of recent local extinctions within species' geographic ranges, address range position as a continuum, and explore the influence of environmental factors. We aggregated point-locality data for 125 Galliform species from across the Palearctic and Indo-Malaya into equal-area half-degree grid cells and used a multispecies dynamic Bayesian occupancy model to estimate rates of local extinctions. Our model provides a novel approach to identify loss of populations from within species ranges. We investigated the relationship between extinction rates and distance from range edge by examining whether patterns were consistent across biogeographic realm and different categories of land use. In the Palearctic, local extinctions occurred closer to the range edge than range core in both unconverted and human-dominated landscapes. In Indo-Malaya, no pattern was found for unconverted landscapes, but in human-dominated landscapes extinctions tended to occur closer to the core than the edge. Our results suggest that local and regional factors override general spatial patterns of recent local extinction within species' ranges and highlight the difficulty of predicting the parts of a species' distribution most vulnerable to threat. © 2017 The Authors. Conservation Biology published by Wiley Periodicals, Inc. on behalf of Society for Conservation Biology.

Fear extinction and BDNF: Translating animal models of PTSD to the clinic

PubMed Central

Andero, Raül; Ressler, Kerry J

2012-01-01

Brain-derived neurotrophic factor (BDNF) is the most studied neurotrophin involved in synaptic plasticity processes that are required for long-term learning and memory. Specifically, BDNF gene expression and activation of its high-affinity TrkB receptor are necessary in the amygdala, hippocampus and prefrontal cortex for the formation of emotional memories, including fear memories. Among the psychiatric disorders with altered fear processing there is Post-traumatic Stress Disorder (PTSD) which is characterized by an inability to extinguish fear memories. Since BDNF appears to enhance extinction of fear, targeting impaired extinction in anxiety disorders such as PTSD via BDNF signalling may be an important and novel way to enhance treatment efficacy. The aim of this review is to provide a translational point of view that stems from findings in the BDNF regulation of synaptic plasticity and fear extinction. In addition, there are different systems that seem to alter fear extinction through BDNF modulation like the endocannabionoid system and the hypothalamic-pituitary adrenal axis (HPA). Recent work also finds that the pituitary adenylate cyclase-activating polypeptide (PACAP) and PAC1 receptor, which are upstream of BDNF activation, may be implicated in PTSD. Especially interesting are data that exogenous fear extinction enhancers such as antidepressants, histone deacetylases inhibitors (HDACi) and D-cycloserine, a partial NMDA agonist, may act through or in concert with the BDNF-TrkB system. Finally, we review studies where recombinant BDNF and a putative TrkB agonist, 7,8-DHF, may enhance extinction of fear. These approaches may lead to novel agents that improve extinction in animal models and eventually humans. PMID:22530815

PHIBSS: MOLECULAR GAS, EXTINCTION, STAR FORMATION, AND KINEMATICS IN THE z = 1.5 STAR-FORMING GALAXY EGS13011166

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

Genzel, R.; Tacconi, L. J.; Kurk, J.

We report matched resolution imaging spectroscopy of the CO 3-2 line (with the IRAM Plateau de Bure millimeter interferometer) and of the H{alpha} line (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the ''Plateau de Bure high-z, blue-sequence survey'' (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similarmore » and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a ''mixed'' extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlog{Sigma}{sub starform}/dlog{Sigma}{sub molgas}, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 {+-} 0.1.« less

The Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP) Version 1 aerosol extinction retrieval algorithm: theoretical basis

NASA Astrophysics Data System (ADS)

Loughman, Robert; Bhartia, Pawan K.; Chen, Zhong; Xu, Philippe; Nyaku, Ernest; Taha, Ghassan

2018-05-01

The theoretical basis of the Ozone Mapping and Profiler Suite (OMPS) Limb Profiler (LP) Version 1 aerosol extinction retrieval algorithm is presented. The algorithm uses an assumed bimodal lognormal aerosol size distribution to retrieve aerosol extinction profiles at 675 nm from OMPS LP radiance measurements. A first-guess aerosol extinction profile is updated by iteration using the Chahine nonlinear relaxation method, based on comparisons between the measured radiance profile at 675 nm and the radiance profile calculated by the Gauss-Seidel limb-scattering (GSLS) radiative transfer model for a spherical-shell atmosphere. This algorithm is discussed in the context of previous limb-scattering aerosol extinction retrieval algorithms, and the most significant error sources are enumerated. The retrieval algorithm is limited primarily by uncertainty about the aerosol phase function. Horizontal variations in aerosol extinction, which violate the spherical-shell atmosphere assumed in the version 1 algorithm, may also limit the quality of the retrieved aerosol extinction profiles significantly.

Mutation load and the extinction of large populations

NASA Astrophysics Data System (ADS)

Bernardes, A. T.

1996-02-01

In the time evolution of finite populations, the accumulation of harmful mutations in further generations might lead to a temporal decay in the mean fitness of the whole population that, after sufficient time, would reduce population size and so lead to extinction. This joint action of mutation load and population reduction is called Mutational Meltdown and is usually considered only to occur in small asexual or very small sexual populations. However, the problem of extinction cannot be discussed in a proper way if one previously assumes the existence of an equilibrium state, as initially discussed in this paper. By performing simulations in a genetically inspired model for time-changing populations, we show that mutational meltdown also occurs in large asexual populations and that the mean time to extinction is a nonmonotonic function of the selection coefficient. The stochasticity of the extinction process is also discussed. The extinction of small sexual N ∼ 700 populations is shown and our results confirm the assumption that the existence of recombination might be a powerful mechanism to avoid extinction.

Climate-driven extinctions shape the phylogenetic structure of temperate tree floras.

PubMed

Eiserhardt, Wolf L; Borchsenius, Finn; Plum, Christoffer M; Ordonez, Alejandro; Svenning, Jens-Christian

2015-03-01

When taxa go extinct, unique evolutionary history is lost. If extinction is selective, and the intrinsic vulnerabilities of taxa show phylogenetic signal, more evolutionary history may be lost than expected under random extinction. Under what conditions this occurs is insufficiently known. We show that late Cenozoic climate change induced phylogenetically selective regional extinction of northern temperate trees because of phylogenetic signal in cold tolerance, leading to significantly and substantially larger than random losses of phylogenetic diversity (PD). The surviving floras in regions that experienced stronger extinction are phylogenetically more clustered, indicating that non-random losses of PD are of increasing concern with increasing extinction severity. Using simulations, we show that a simple threshold model of survival given a physiological trait with phylogenetic signal reproduces our findings. Our results send a strong warning that we may expect future assemblages to be phylogenetically and possibly functionally depauperate if anthropogenic climate change affects taxa similarly. © 2015 John Wiley & Sons Ltd/CNRS.

A mathematical model of interaction among humans, vampires and werewolves populations

NASA Astrophysics Data System (ADS)

Sumarti, Novriana; Nurrizky, Insan; Nuraini, Nuning

2018-03-01

In every country there are many fictional creatures depicting evil. In the western world, fictional creatures who often appear in horror stories are vampires and werewolves. Many released movies expose the conflict between humans with one or both creatures. In this paper, the interaction among humans, vampires and werewolves is modeled using a system of differential equations. We consider the stability of equilibrium points of the system that represent four situations; only humans remain or a disease-free condition, either vampires or werewolves are going to extinction, and no population goes extinct. The derived model is implemented for depicting some scenarios in the movie series of Underworld. The model can describe the fluctuation of vampires and werewolves population from the beginning to their extinction at 1500 years since the story started.

A stable isotope-based approach to tropical dendroclimatology

NASA Astrophysics Data System (ADS)

Evans, Michael N.; Schrag, Daniel P.

2004-08-01

We describe a strategy for development of chronological control in tropical trees lacking demonstrably annual ring formation, using high resolution δ 18O measurements in tropical wood. The approach applies existing models of the oxygen isotopic composition of alpha-cellulose (Roden et al., 2000), a rapid method for cellulose extraction from raw wood (Brendel et al., 2000), and continuous flow isotope ratio mass spectrometry (Brenna et al., 1998) to develop proxy chronological, rainfall and growth rate estimates from tropical trees lacking visible annual ring structure. Consistent with model predictions, pilot datasets from the temperate US and Costa Rica having independent chronological control suggest that observed cyclic isotopic signatures of several permil (SMOW) represent the annual cycle of local rainfall and relative humidity. Additional data from a plantation tree of known age from ENSO-sensitive northwestern coastal Peru suggests that the 1997-8 ENSO warm phase event was recorded as an 8‰ anomaly in the δ 18O of α-cellulose. The results demonstrate reproducibility of the stable isotopic chronometer over decades, two different climatic zones, and three tropical tree genera, and point to future applications in paleoclimatology.

An empirical test of the relative and combined effects of land-cover and climate change on local colonization and extinction.

PubMed

Yalcin, Semra; Leroux, Shawn James

2018-04-14

Land-cover and climate change are two main drivers of changes in species ranges. Yet, the majority of studies investigating the impacts of global change on biodiversity focus on one global change driver and usually use simulations to project biodiversity responses to future conditions. We conduct an empirical test of the relative and combined effects of land-cover and climate change on species occurrence changes. Specifically, we examine whether observed local colonization and extinctions of North American birds between 1981-1985 and 2001-2005 are correlated with land-cover and climate change and whether bird life history and ecological traits explain interspecific variation in observed occurrence changes. We fit logistic regression models to test the impact of physical land-cover change, changes in net primary productivity, winter precipitation, mean summer temperature, and mean winter temperature on the probability of Ontario breeding bird local colonization and extinction. Models with climate change, land-cover change, and the combination of these two drivers were the top ranked models of local colonization for 30%, 27%, and 29% of species, respectively. Conversely, models with climate change, land-cover change, and the combination of these two drivers were the top ranked models of local extinction for 61%, 7%, and 9% of species, respectively. The quantitative impacts of land-cover and climate change variables also vary among bird species. We then fit linear regression models to test whether the variation in regional colonization and extinction rate could be explained by mean body mass, migratory strategy, and habitat preference of birds. Overall, species traits were weakly correlated with heterogeneity in species occurrence changes. We provide empirical evidence showing that land-cover change, climate change, and the combination of multiple global change drivers can differentially explain observed species local colonization and extinction. © 2018 John Wiley & Sons Ltd.

Persistence of black-tailed prairie-dog populations affected by plague in northern Colorado, USA.

PubMed

George, Dylan B; Webb, Colleen T; Pepin, Kim M; Savage, Lisa T; Antolini, Michael F

2013-07-01

The spatial distribution of prairie dog (Cynomys ludovicianus) colonies in North America has changed from large, contiguous populations to small, isolated colonies in metapopulations. One factor responsible for this drastic change in prairie-dog population structure is plague (caused by the bacterium Yersinia pestis). We fit stochastic patch occupancy models to 20 years of prairie-dog colony occupancy data from two discrete metapopulations (west and east) in the Pawnee National Grassland in Colorado, USA, that differ in connectivity among suitable habitat patches. We conducted model selection between two hypothesized modes of plague movement: independent of prairie-dog dispersal (colony-area) vs. plague movement consistent with prairie-dog dispersal (connectivity to extinct colonies). The best model, which fit the data well (area under the curve [AUC]: 0.94 west area; 0.79 east area), revealed that over time the proportion of extant colonies was better explained by colony size than by connectivity to extinct (plagued) colonies. The idea that prairie dogs are not likely to be the main vector that spreads Y. pestis across the landscape is supported by the observation that colony extinctions are primarily caused by plague, prairie-dog dispersal is short range, and connectivity to extinct colonies was not selected as a factor in the models. We also conducted simulations with the best model to examine long-term patterns of colony occupancy and persistence of prairie-dog metapopulations. In the case where the metapopulations persist, our model predicted that the western metapopulation would have a colony occupancy rate approximately 2.5 times higher than that of the eastern metapopulation (-50% occupied colonies vs. 20%) in 50 years, but that the western metapopulation has -80% chance of extinction in 100 years while the eastern metapopulation has a less than 25% chance. Extinction probability of individual colonies depended on the frequency with which colonies of the same size class occurred in the metapopulation. Thus, the long-term persistence of prairie-dog metapopulations depended on specific details of the metapopulation.

The Cretaceous/Tertiary Extinction Controversy Reconsidered.

ERIC Educational Resources Information Center

McCartney, Kevin; Nienstedt, Jeffrey

1986-01-01

Reviews varying positions taken in the Cretaceous/Tertiary (K/Y) extinction controversy. Analyzes and contests the meteoritic impact theory known as the Alvarez Model. Presents an alternative working hypothesis explaining the K/T transition. (ML)

Modeling The Atmosphere In The Era Of Big Data From Extremely Wide Field-Of-View Telescopes

NASA Astrophysics Data System (ADS)

Gonzalez Quiles, Junellie; Nordin, Jakob

2018-01-01

Surveys like the Sloan Digital Sky Survey (SDSS), Pan-STARRS and the Palomar Transient Factory Survey (PTF) receive large amounts of data, which need to be processed and calibrated in order to correct for various factors. One of the limiting factors in obtaining high quality data is the atmosphere, and it is therefore essential to find the appropriate calibration for the atmospheric extinction. It is to be expected that a physical atmospheric model, compared to a photometric calibration used currently by PTF, is more effective in calibrating for the atmospheric extinction due to its ability to account for rapid atmospheric fluctuation and objects of different colors. We focused on creating tools to model the atmospheric extinction for the upcoming Zwicky Transient Factory Survey (ZTF). In order to model the atmosphere, we created a program that combines input data and catalogue values, and efficiently handles them. Then, using PTF data and the SDSS catalogue, we created several models to fit the data, and tested the quality of the fits by chi-square minimization. This will allow us to optimize atmospheric extinction for the upcoming ZTF in the near future.

Fatal disease and demographic Allee effect: population persistence and extinction.

PubMed

Friedman, Avner; Yakubu, Abdul-Aziz

2012-01-01

If a healthy stable host population at the disease-free equilibrium is subject to the Allee effect, can a small number of infected individuals with a fatal disease cause the host population to go extinct? That is, does the Allee effect matter at high densities? To answer this question, we use a susceptible-infected epidemic model to obtain model parameters that lead to host population persistence (with or without infected individuals) and to host extinction. We prove that the presence of an Allee effect in host demographics matters even at large population densities. We show that a small perturbation to the disease-free equilibrium can eventually lead to host population extinction. In addition, we prove that additional deaths due to a fatal infectious disease effectively increase the Allee threshold of the host population demographics.

EMPIRICALLY ESTIMATED FAR-UV EXTINCTION CURVES FOR CLASSICAL T TAURI STARS

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

McJunkin, Matthew; France, Kevin; Schindhelm, Eric

Measurements of extinction curves toward young stars are essential for calculating the intrinsic stellar spectrophotometric radiation. This flux determines the chemical properties and evolution of the circumstellar region, including the environment in which planets form. We develop a new technique using H{sub 2} emission lines pumped by stellar Ly α photons to characterize the extinction curve by comparing the measured far-ultraviolet H{sub 2} line fluxes with model H{sub 2} line fluxes. The difference between model and observed fluxes can be attributed to the dust attenuation along the line of sight through both the interstellar and circumstellar material. The extinction curvesmore » are fit by a Cardelli et al. (1989) model and the A {sub V} (H{sub 2}) for the 10 targets studied with good extinction fits range from 0.5 to 1.5 mag, with R {sub V} values ranging from 2.0 to 4.7. A {sub V} and R {sub V} are found to be highly degenerate, suggesting that one or the other needs to be calculated independently. Column densities and temperatures for the fluorescent H{sub 2} populations are also determined, with averages of log{sub 10}( N (H{sub 2})) = 19.0 and T = 1500 K. This paper explores the strengths and limitations of the newly developed extinction curve technique in order to assess the reliability of the results and improve the method in the future.« less

Spectroscopic Infrared Extinction Mapping as a Probe of Grain Growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

2015-11-01

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3-8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14-38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffuse Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR-FIR opacity laws that lack the ˜12 and ˜35 μm features associated with the thick water ice mantle models of Ossenkopf & Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

SPECTROSCOPIC INFRARED EXTINCTION MAPPING AS A PROBE OF GRAIN GROWTH IN IRDCs

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

Lim, Wanggi; Carey, Sean J.; Tan, Jonathan C.

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim and Tan developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 μm and Herschel-PACS 70 μm images, and by comparing to MIR Spitzer-IRAC 3–8 μm extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction mapping using Spitzer-IRS (14–38 μm) data of the same Infrared dark cloud (IRDC). These methods allow us to first measure the SED of the diffusemore » Galactic interstellar medium that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR–FIR opacity laws that lack the ∼12 and ∼35 μm features associated with the thick water ice mantle models of Ossenkopf and Henning. Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.« less

Combined Neuropeptide S and D-Cycloserine Augmentation Prevents the Return of Fear in Extinction-Impaired Rodents: Advantage of Dual versus Single Drug Approaches

PubMed Central

Maurer, Verena; Murphy, Conor; Schmuckermair, Claudia; Muigg, Patrick; Neumann, Inga D.; Whittle, Nigel

2016-01-01

Background: Despite its success in treating specific anxiety disorders, the effect of exposure therapy is limited by problems with tolerability, treatment resistance, and fear relapse after initial response. The identification of novel drug targets facilitating fear extinction in clinically relevant animal models may guide improved treatment strategies for these disorders in terms of efficacy, acceleration of fear extinction, and return of fear. Methods: The extinction-facilitating potential of neuropeptide S, D-cycloserine, and a benzodiazepine was investigated in extinction-impaired high anxiety HAB rats and 129S1/SvImJ mice using a classical cued fear conditioning paradigm followed by extinction training and several extinction test sessions to study fear relapse. Results: Administration of D-cycloserine improved fear extinction in extinction-limited, but not in extinction-deficient, rodents compared with controls. Preextinction neuropeptide S caused attenuated fear responses in extinction-deficient 129S1/SvImJ mice at extinction training onset and further reduced freezing during this session. While the positive effects of either D-cycloserine or neuropeptide S were not persistent in 129S1/SvImJ mice after 10 days, the combination of preextinction neuropeptide S with postextinction D-cycloserine rendered the extinction memory persistent and context independent up to 5 weeks after extinction training. This dual pharmacological adjunct to extinction learning also protected against fear reinstatement in 129S1/SvImJ mice. Conclusions: By using the potentially nonsedative anxiolytic neuropeptide S and the cognitive enhancer D-cycloserine to facilitate deficient fear extinction, we provide here the first evidence of a purported efficacy of a dual over a single drug approach. This approach may render exposure sessions less aversive and more efficacious for patients, leading to enhanced protection from fear relapse in the long term. PMID:26625894

Combined Neuropeptide S and D-Cycloserine Augmentation Prevents the Return of Fear in Extinction-Impaired Rodents: Advantage of Dual versus Single Drug Approaches.

PubMed

Sartori, Simone B; Maurer, Verena; Murphy, Conor; Schmuckermair, Claudia; Muigg, Patrick; Neumann, Inga D; Whittle, Nigel; Singewald, Nicolas

2016-06-01

Despite its success in treating specific anxiety disorders, the effect of exposure therapy is limited by problems with tolerability, treatment resistance, and fear relapse after initial response. The identification of novel drug targets facilitating fear extinction in clinically relevant animal models may guide improved treatment strategies for these disorders in terms of efficacy, acceleration of fear extinction, and return of fear. The extinction-facilitating potential of neuropeptide S, D-cycloserine, and a benzodiazepine was investigated in extinction-impaired high anxiety HAB rats and 129S1/SvImJ mice using a classical cued fear conditioning paradigm followed by extinction training and several extinction test sessions to study fear relapse. Administration of D-cycloserine improved fear extinction in extinction-limited, but not in extinction-deficient, rodents compared with controls. Preextinction neuropeptide S caused attenuated fear responses in extinction-deficient 129S1/SvImJ mice at extinction training onset and further reduced freezing during this session. While the positive effects of either D-cycloserine or neuropeptide S were not persistent in 129S1/SvImJ mice after 10 days, the combination of preextinction neuropeptide S with postextinction D-cycloserine rendered the extinction memory persistent and context independent up to 5 weeks after extinction training. This dual pharmacological adjunct to extinction learning also protected against fear reinstatement in 129S1/SvImJ mice. By using the potentially nonsedative anxiolytic neuropeptide S and the cognitive enhancer D-cycloserine to facilitate deficient fear extinction, we provide here the first evidence of a purported efficacy of a dual over a single drug approach. This approach may render exposure sessions less aversive and more efficacious for patients, leading to enhanced protection from fear relapse in the long term. © The Author 2015. Published by Oxford University Press on behalf of CINP.

Versions of the Waste Reduction Model (WARM)

EPA Pesticide Factsheets

This page provides a brief chronology of changes made to EPA’s Waste Reduction Model (WARM), organized by WARM version number. The page includes brief summaries of changes and updates since the previous version.

Versions of the Waste Reduction Model (WARM)

EPA Pesticide Factsheets

2017-02-14

This page provides a brief chronology of changes made to EPA’s Waste Reduction Model (WARM), organized by WARM version number. The page includes brief summaries of changes and updates since the previous version.

Coincident mass extirpation of neotropical amphibians with the emergence of the infectious fungal pathogen Batrachochytrium dendrobatidis

PubMed Central

Cheng, Tina L.; Rovito, Sean M.; Wake, David B.; Vredenburg, Vance T.

2011-01-01

Amphibians highlight the global biodiversity crisis because ∼40% of all amphibian species are currently in decline. Species have disappeared even in protected habitats (e.g., the enigmatic extinction of the golden toad, Bufo periglenes, from Costa Rica). The emergence of a fungal pathogen, Batrachochytrium dendrobatidis (Bd), has been implicated in a number of declines that have occurred in the last decade, but few studies have been able to test retroactively whether Bd emergence was linked to earlier declines and extinctions. We describe a noninvasive PCR sampling technique that detects Bd in formalin-preserved museum specimens. We detected Bd by PCR in 83–90% (n = 38) of samples that were identified as positive by histology. We examined specimens collected before, during, and after major amphibian decline events at established study sites in southern Mexico, Guatemala, and Costa Rica. A pattern of Bd emergence coincident with decline at these localities is revealed—the absence of Bd over multiple years at all localities followed by the concurrent emergence of Bd in various species at each locality during a period of population decline. The geographical and chronological emergence of Bd at these localities also indicates a southbound spread from southern Mexico in the early 1970s to western Guatemala in the 1980s/1990s and to Monteverde, Costa Rica by 1987. We find evidence of a historical “Bd epidemic wave” that began in Mexico and subsequently spread to Central America. We describe a technique that can be used to screen museum specimens from other amphibian decline sites around the world. PMID:21543713

Coincident mass extirpation of neotropical amphibians with the emergence of the infectious fungal pathogen Batrachochytrium dendrobatidis.

PubMed

Cheng, Tina L; Rovito, Sean M; Wake, David B; Vredenburg, Vance T

2011-06-07

Amphibians highlight the global biodiversity crisis because ∼40% of all amphibian species are currently in decline. Species have disappeared even in protected habitats (e.g., the enigmatic extinction of the golden toad, Bufo periglenes, from Costa Rica). The emergence of a fungal pathogen, Batrachochytrium dendrobatidis (Bd), has been implicated in a number of declines that have occurred in the last decade, but few studies have been able to test retroactively whether Bd emergence was linked to earlier declines and extinctions. We describe a noninvasive PCR sampling technique that detects Bd in formalin-preserved museum specimens. We detected Bd by PCR in 83-90% (n = 38) of samples that were identified as positive by histology. We examined specimens collected before, during, and after major amphibian decline events at established study sites in southern Mexico, Guatemala, and Costa Rica. A pattern of Bd emergence coincident with decline at these localities is revealed-the absence of Bd over multiple years at all localities followed by the concurrent emergence of Bd in various species at each locality during a period of population decline. The geographical and chronological emergence of Bd at these localities also indicates a southbound spread from southern Mexico in the early 1970s to western Guatemala in the 1980s/1990s and to Monteverde, Costa Rica by 1987. We find evidence of a historical "Bd epidemic wave" that began in Mexico and subsequently spread to Central America. We describe a technique that can be used to screen museum specimens from other amphibian decline sites around the world.

Assessing Regional and Interspecific Variation in Threshold Responses of Forest Breeding Birds through Broad Scale Analyses

PubMed Central

van der Hoek, Yntze; Renfrew, Rosalind; Manne, Lisa L.

2013-01-01

Background Identifying persistence and extinction thresholds in species-habitat relationships is a major focal point of ecological research and conservation. However, one major concern regarding the incorporation of threshold analyses in conservation is the lack of knowledge on the generality and transferability of results across species and regions. We present a multi-region, multi-species approach of modeling threshold responses, which we use to investigate whether threshold effects are similar across species and regions. Methodology/Principal Findings We modeled local persistence and extinction dynamics of 25 forest-associated breeding birds based on detection/non-detection data, which were derived from repeated breeding bird atlases for the state of Vermont. We did not find threshold responses to be particularly well-supported, with 9 species supporting extinction thresholds and 5 supporting persistence thresholds. This contrasts with a previous study based on breeding bird atlas data from adjacent New York State, which showed that most species support persistence and extinction threshold models (15 and 22 of 25 study species respectively). In addition, species that supported a threshold model in both states had associated average threshold estimates of 61.41% (SE = 6.11, persistence) and 66.45% (SE = 9.15, extinction) in New York, compared to 51.08% (SE = 10.60, persistence) and 73.67% (SE = 5.70, extinction) in Vermont. Across species, thresholds were found at 19.45–87.96% forest cover for persistence and 50.82–91.02% for extinction dynamics. Conclusions/Significance Through an approach that allows for broad-scale comparisons of threshold responses, we show that species vary in their threshold responses with regard to habitat amount, and that differences between even nearby regions can be pronounced. We present both ecological and methodological factors that may contribute to the different model results, but propose that regardless of the reasons behind these differences, our results merit a warning that threshold values cannot simply be transferred across regions or interpreted as clear-cut targets for ecosystem management and conservation. PMID:23409106

Ultraviolet photometry from the Orbiting Astronomical Observatory. II Interstellar extinction.

NASA Technical Reports Server (NTRS)

Bless, R. C.; Savage, B. D.

1972-01-01

Evaluation of interstellar extinction curves over the region from 3600 to 1100 A for 17 stars. The observations were made by the two Wisconsin spectrometers on board the Orbiting Astronomical Observatory 2, with spectral resolutions of 10 and 20 A. The extinction curves generally show a pronounced maximum at 2175 plus or minus 25 A, a broad minimum in the region from 1800 to 1350 A, and finally a rapid rise to the far-ultraviolet. Large extinction variations from star to star are found, especially in the far-ultraviolet; however, with only two possible exceptions in this sample, the wavelength at the maximum of the extinction bump is essentially constant. These data are combined with visual and infrared observations to display the extinction behavior over a range in wavelength of about a factor of 20. The observations appear to require a multicomponent model of the interstellar dust.

How global extinctions impact regional biodiversity in mammals.

PubMed

Huang, Shan; Davies, T Jonathan; Gittleman, John L

2012-04-23

Phylogenetic diversity (PD) represents the evolutionary history of a species assemblage and is a valuable measure of biodiversity because it captures not only species richness but potentially also genetic and functional diversity. Preserving PD could be critical for maintaining the functional integrity of the world's ecosystems, and species extinction will have a large impact on ecosystems in areas where the ecosystem cost per species extinction is high. Here, we show that impacts from global extinctions are linked to spatial location. Using a phylogeny of all mammals, we compare regional losses of PD against a model of random extinction. At regional scales, losses differ dramatically: several biodiversity hotspots in southern Asia and Amazonia will lose an unexpectedly large proportion of PD. Global analyses may therefore underestimate the impacts of extinction on ecosystem processes and function because they occur at finer spatial scales within the context of natural biogeography.

Laser measurement of the spectral extinction coefficients of fluorescent, highly absorbing liquids. [crude petroleum oils

NASA Technical Reports Server (NTRS)

Hoge, F. E.

1982-01-01

A conceptual method is developed to deduce rapidly the spectral extinction coefficient of fluorescent, highly absorbing liquids, such as crude or refined petroleum oils. The technique offers the advantage of only requiring one laser wavelength and a single experimental assembly and execution for any specific fluorescent liquid. The liquid is inserted into an extremely thin wedge-shaped cavity for stimulation by a laser from one side and flurescence measurement on the other side by a monochromator system. For each arbitrarily selected extinction wavelength, the wedge is driven slowly to increasing thicknesses until the fluorescence extinguishes. The fluorescence as a function of wedge thickness permits a determination of the extinction coefficient using an included theoretical model. When the monochromator is set to the laser emission wavelength, the extinction coefficient is determined using the usual on-wavelength signal extinction procedure.

Expected time-invariant effects of biological traits on mammal species duration.

PubMed

Smits, Peter D

2015-10-20

Determining which biological traits influence differences in extinction risk is vital for understanding the differential diversification of life and for making predictions about species' vulnerability to anthropogenic impacts. Here I present a hierarchical Bayesian survival model of North American Cenozoic mammal species durations in relation to species-level ecological factors, time of origination, and phylogenetic relationships. I find support for the survival of the unspecialized as a time-invariant generalization of trait-based extinction risk. Furthermore, I find that phylogenetic and temporal effects are both substantial factors associated with differences in species durations. Finally, I find that the estimated effects of these factors are partially incongruous with how these factors are correlated with extinction risk of the extant species. These findings parallel previous observations that background extinction is a poor predictor of mass extinction events and suggest that attention should be focused on mass extinctions to gain insight into modern species loss.

Compound Stimulus Presentation Does Not Deepen Extinction in Human Causal Learning

PubMed Central

Griffiths, Oren; Holmes, Nathan; Westbrook, R. Fred

2017-01-01

Models of associative learning have proposed that cue-outcome learning critically depends on the degree of prediction error encountered during training. Two experiments examined the role of error-driven extinction learning in a human causal learning task. Target cues underwent extinction in the presence of additional cues, which differed in the degree to which they predicted the outcome, thereby manipulating outcome expectancy and, in the absence of any change in reinforcement, prediction error. These prediction error manipulations have each been shown to modulate extinction learning in aversive conditioning studies. While both manipulations resulted in increased prediction error during training, neither enhanced extinction in the present human learning task (one manipulation resulted in less extinction at test). The results are discussed with reference to the types of associations that are regulated by prediction error, the types of error terms involved in their regulation, and how these interact with parameters involved in training. PMID:28232809

Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

NASA Astrophysics Data System (ADS)

Dissanayake, P.; Brown, J.; Karunarathna, H.

2015-07-01

Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/2014 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper-beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

Impacts of storm chronology on the morphological changes of the Formby beach and dune system, UK

NASA Astrophysics Data System (ADS)

Dissanayake, P.; Brown, J.; Karunarathna, H.

2015-04-01

Impacts of storm chronology within a storm cluster on beach/dune erosion are investigated by applying the state-of-the-art numerical model XBeach to the Sefton coast, northwest England. Six temporal storm clusters of different storm chronologies were formulated using three storms observed during the 2013/14 winter. The storm power values of these three events nearly halve from the first to second event and from the second to third event. Cross-shore profile evolution was simulated in response to the tide, surge and wave forcing during these storms. The model was first calibrated against the available post-storm survey profiles. Cumulative impacts of beach/dune erosion during each storm cluster were simulated by using the post-storm profile of an event as the pre-storm profile for each subsequent event. For the largest event the water levels caused noticeable retreat of the dune toe due to the high water elevation. For the other events the greatest evolution occurs over the bar formations (erosion) and within the corresponding troughs (deposition) of the upper beach profile. The sequence of events impacting the size of this ridge-runnel feature is important as it consequently changes the resilience of the system to the most extreme event that causes dune retreat. The highest erosion during each single storm event was always observed when that storm initialised the storm cluster. The most severe storm always resulted in the most erosion during each cluster, no matter when it occurred within the chronology, although the erosion volume due to this storm was reduced when it was not the primary event. The greatest cumulative cluster erosion occurred with increasing storm severity; however, the variability in cumulative cluster impact over a beach/dune cross-section due to storm chronology is minimal. Initial storm impact can act to enhance or reduce the system resilience to subsequent impact, but overall the cumulative impact is controlled by the magnitude and number of the storms. This model application provides inter-survey information about morphological response to repeated storm impact. This will inform local managers of the potential beach response and dune vulnerability to variable storm configurations.

Measurements of Aerosol Vertical Profiles and Optical Properties during INDOEX 1999 Using Micro-Pulse Lidars

NASA Technical Reports Server (NTRS)

Welton, Ellsworth J.; Voss, Kenneth J.; Quinn, Patricia K.; Flatau, Piotr J.; Markowicz, Krzysztof; Campbell, James R.; Spinhirne, James D.; Gordon, Howard R.; Johnson, James E.; Starr, David OC. (Technical Monitor)

2001-01-01

Micro-pulse lidar systems (MPL) were used to measure aerosol properties during the Indian Ocean Experiment (INDOEX) 1999 field phase. Measurements were made from two platforms: the NOAA ship RN Ronald H. Brown, and the Kaashidhoo Climate Observatory (KCO) in the Maldives. Sunphotometers were used to provide aerosol optical depths (AOD) needed to calibrate the MPL. This study focuses on the height distribution and optical properties (at 523 nm) of aerosols observed during the campaign. The height of the highest aerosols (top height) was calculated and found to be below 4 km for most of the cruise. The marine boundary layer (MBL) top was calculated and found to be less than 1 km. MPL results were combined with air mass trajectories, radiosonde profiles of temperature and humidity, and aerosol concentration and optical measurements. Humidity varied from approximately 80% near the surface to 50% near the top height during the entire cruise. The average value and standard deviation of aerosol optical parameters were determined for characteristic air mass regimes. Marine aerosols in the absence of any continental influence were found to have an AOD of 0.05 +/- 0.03, an extinction-to-backscatter ratio (S-ratio) of 33 +/- 6 sr, and peak extinction values around 0.05/km (near the MBL top). The marine results are shown to be in agreement with previously measured and expected values. Polluted marine areas over the Indian Ocean, influenced by continental aerosols, had AOD values in excess of 0.2, S-ratios well above 40 sr, and peak extinction values approximately 0.20/km (near the MBL top). The polluted marine results are shown to be similar to previously published values for continental aerosols. Comparisons between MPL derived extinction near the ship (75 m) and extinction calculated at ship-level using scattering measured by a nephelometer and absorption using a PSAP were conducted. The comparisons indicated that the MPL algorithm (using a constant S-ratio throughout the lower troposphere) calculates extinction near the surface in agreement with the ship-level measurements only when the MBL aerosols are well mixed with aerosols above. Finally, a review of the MPL extinction profiles showed that the model of aerosol vertical extinction developed during an earlier INDOEX field campaign (at the Maldives) did not correctly describe the true vertical distribution over the greater Indian Ocean region. Using the average extinction profile and AOD obtained during marine conditions, a new model of aerosol vertical extinction was determined for marine atmospheres over the Indian Ocean. A new model of aerosol vertical extinction for polluted marine atmospheres was also developed using the average extinction profile and AOD obtained during marine conditions influenced by continental aerosols.

Characterizing the Vertical Distribution of Aerosols Over the ARM SGP Site

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

Richard Ferrare, Connor Flynn, David Turner

This project focused on: 1) evaluating the performance of the DOE ARM SGP Raman lidar system in measuring profiles of water vapor and aerosols, and 2) the use of the Raman lidar measurements of aerosol and water vapor profiles for assessing the vertical distribution of aerosols and water vapor simulated by global transport models and examining diurnal variability of aerosols and water vapor. The highest aerosol extinction was generally observed close to the surface during the nighttime just prior to sunrise. The high values of aerosol extinction are most likely associated with increased scattering by hygroscopic aerosols, since the correspondingmore » average relative humidity values were above 70%. After sunrise, relative humidity and aerosol extinction below 500 m decreased with the growth in the daytime convective boundary layer. The largest aerosol extinction for altitudes above 1 km occurred during the early afternoon most likely as a result of the increase in relative humidity. The water vapor mixing ratio profiles generally showed smaller variations with altitude between day and night. We also compared simultaneous measurements of relative humidity, aerosol extinction, and aerosol optical thickness derived from the ARM SGP Raman lidar and in situ instruments on board a small aircraft flown routinely over the ARM SGP site. In contrast, the differences between the CARL and IAP aerosol extinction measurements are considerably larger. Aerosol extinction derived from the IAP measurements is, on average, about 30-40% less than values derived from the Raman lidar. The reasons for this difference are not clear, but may be related to the corrections for supermicron scattering and relative humidity that were applied to the IAP data. The investigators on this project helped to set up a major field mission (2003 Aerosol IOP) over the DOE ARM SGP site. One of the goals of the mission was to further evaluate the aerosol and water vapor retrievals from this lidar system. Analysis of the aerosol and water vapor data collected by the Raman lidar during the 2003 Aerosol IOP indicated that the sensitivity of the lidar was significantly lower than when the lidar was initially deployed. A detailed analysis after the IOP of the long-term dataset demonstrated that the lidar began degrading in early 2002, and that it lost approximately a factor of 4 in sensitivity between 2002 and 2004. We participated in the development of the remediation plan for the system to restore its initial performance. We conducted this refurbishment and upgrade from May- September 2004. This remediation lead to an increase in the signal-to-noise ratio of 10 and 30 for the Raman lidar's water vapor mixing ratio and aerosol backscatter coefficient data, respectively as compared to the signal strengths when the system was first deployed. The DOE ARM Aerosol Lidar Validation Experiment (ALIVE), which was conducted during September 2005, evaluated the impact of these modifications and upgrades on the SGP Raman lidar measurements of aerosol extinction and optical thickness. The CARL modifications significantly improved the accuracy and temporal resolution of the aerosol measurements. Aerosol extinction profiles measured by the Raman lidar were also used to evaluate aerosol extinction profiles and aerosol optical thickness (AOT) simulated by aerosol models as part of the Aerosol module inter-Comparison in global models (AEROCOM) (http://nansen.ipsl.jussieu.fr/AEROCOM/aerocomhome.html) project. There was a wide range in how the models represent the aerosol extinction profiles over the ARM SGP site, even though the average annual AOT represented by the various models and measured by CARL and the Sun photometer were in general agreement, at least within the standard deviations of the averages. There were considerable differences in the average vertical distributions among the models, even among models that had similar average aerosol optical thickness. Deviations between mean aerosol extinction profiles were generally small (~20-30%) for altitudes above 2 km, and grew considerably larger below 2 km.« less

Paleomagnetism of a well-dated marine succession in South China: A possible Late Cambrian true polar wander (TPW)

NASA Astrophysics Data System (ADS)

Jiao, Wen-Jun; Li, Yong-Xiang; Yang, Zhen-Yu

2018-04-01

The Cambrian true polar wander (TPW) hypothesis remains controversial largely because of the uncertainties in the quality and/or fidelity of the paleomagnetic data as well as their chronological control. Testing the TPW hypothesis requires high-quality paleomagnetic data of sufficient spatial and temporal resolutions. Here, we present paleomagnetic results of a continuous Cambrian shallow marine succession from South China where available detailed biostratigraphy provides exceptional chronological constraints. Forty-three sites of paleomagnetic samples were collected from this limestone-dominated succession. Stepwise thermal demagnetization generally reveals three-component magnetizations. Low- and intermediate-temperature components can be cleaned by ∼330 °C, and the high-temperature component (HTC) was isolated typically from ∼350 to ∼450 °C. A positive fold test and the presence of reversed polarity in the strata, together with rock magnetic data as well as the scanning electron microscopic (SEM) and transmission electron microscopic (TEM) results, collectively suggest that the HTCs are likely primary. A directional shift of the HTCs occurs between the lower-middle Cambrian and the upper Cambrian strata in the succession and is tentatively interpreted to indicate a ∼57° polar wander from ∼500.5 to 494 Ma. Because the rate of polar wander is too fast to be a tectonic origin, this polar wander is interpreted to represent a Late Cambrian TPW. This TPW appears coeval with the Steptoean positive carbon isotope excursion (SPICE) and the major trilobite mass extinctions, suggesting a potential link between the TPW and the Late Cambrian biotic and climatic changes. Because the proposed TPW event is exceptionally well-dated, it should be testable through examination of other worldwide sections.

A model of amygdala-hippocampal-prefrontal interaction in fear conditioning and extinction in animals

PubMed Central

Moustafa, Ahmed A.; Gilbertson, Mark W.; Orr, Scott P.; Herzallah, Mohammad M.; Servatius, Richard. J.; Myers, Catherine E.

2012-01-01

Empirical research has shown that the amygdala, hippocampus, and ventromedial prefrontal cortex (vmPFC) are involved in fear conditioning. However, the functional contribution of each brain area and the nature of their interactions are not clearly understood. Here, we extend existing neural network models of the functional roles of the hippocampus in classical conditioning to include interactions with the amygdala and prefrontal cortex. We apply the model to fear conditioning, in which animals learn physiological (e.g. heart rate) and behavioral (e.g. freezing) responses to stimuli that have been paired with a highly aversive event (e.g. electrical shock). The key feature of our model is that learning of these conditioned responses in the central nucleus of the amygdala is modulated by two separate processes, one from basolateral amygdala and signaling a positive prediction error, and one from the vmPFC, via the intercalated cells of the amygdala, and signaling a negative prediction error. In addition, we propose that hippocampal input to both vmPFC and basolateral amygdala is essential for contextual modulation of fear acquisition and extinction. The model is sufficient to account for a body of data from various animal fear conditioning paradigms, including acquisition, extinction, reacquisition, and context specificity effects. Consistent with studies on lesioned animals, our model shows that damage to the vmPFC impairs extinction, while damage to the hippocampus impairs extinction in a different context (e.g., a different conditioning chamber from that used in initial training in animal experiments). We also discuss model limitations and predictions, including the effects of number of training trials on fear conditioning. PMID:23164732

Loss in species caused by tropical deforestation and their recovery through management

Treesearch

Ariel E. Lugo; John A. Parrotta; Sandra Brown

1993-01-01

The loss of species as a result of deforestation and degradation of tropical forest lands is widely discussed. Models based on island biogeography theory are used to evaluate the relationship between extinctions of species and deforestation. The analysis shows that natural resiliency causes the models to overestimate the rates of species extinctions for given...

Extinction maps toward the Milky Way bulge: Two-dimensional and three-dimensional tests with apogee

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

Schultheis, M.; Zasowski, G.; Allende Prieto, C.

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmosphericmore » parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.« less

When Local Extinction and Colonization of River Fishes Can Be Predicted by Regional Occupancy: the Role of Spatial Scales

PubMed Central

Bergerot, Benjamin; Hugueny, Bernard; Belliard, Jérôme

2013-01-01

Background Predicting which species are likely to go extinct is perhaps one of the most fundamental yet challenging tasks for conservation biologists. This is particularly relevant for freshwater ecosystems which tend to have the highest proportion of species threatened with extinction. According to metapopulation theories, local extinction and colonization rates of freshwater subpopulations can depend on the degree of regional occupancy, notably due to rescue effects. However, relationships between extinction, colonization, regional occupancy and the spatial scales at which they operate are currently poorly known. Methods And Findings: We used a large dataset of freshwater fish annual censuses in 325 stream reaches to analyse how annual extinction/colonization rates of subpopulations depend on the regional occupancy of species. For this purpose, we modelled the regional occupancy of 34 fish species over the whole French river network and we tested how extinction/colonization rates could be predicted by regional occupancy described at five nested spatial scales. Results show that extinction and colonization rates depend on regional occupancy, revealing existence a rescue effect. We also find that these effects are scale dependent and their absolute contribution to colonization and extinction tends to decrease from river section to larger basin scales. Conclusions In terms of management, we show that regional occupancy quantification allows the evaluation of local species extinction/colonization dynamics and reduction of local extinction risks for freshwater fish species implies the preservation of suitable habitats at both local and drainage basin scales. PMID:24367636

Trophic redundancy reduces vulnerability to extinction cascades

PubMed Central

Sanders, Dirk; Thébault, Elisa; Kehoe, Rachel; Frank van Veen, F. J.

2018-01-01

Current species extinction rates are at unprecedentedly high levels. While human activities can be the direct cause of some extinctions, it is becoming increasingly clear that species extinctions themselves can be the cause of further extinctions, since species affect each other through the network of ecological interactions among them. There is concern that the simplification of ecosystems, due to the loss of species and ecological interactions, increases their vulnerability to such secondary extinctions. It is predicted that more complex food webs will be less vulnerable to secondary extinctions due to greater trophic redundancy that can buffer against the effects of species loss. Here, we demonstrate in a field experiment with replicated plant-insect communities, that the probability of secondary extinctions is indeed smaller in food webs that include trophic redundancy. Harvesting one species of parasitoid wasp led to secondary extinctions of other, indirectly linked, species at the same trophic level. This effect was markedly stronger in simple communities than for the same species within a more complex food web. We show that this is due to functional redundancy in the more complex food webs and confirm this mechanism with a food web simulation model by highlighting the importance of the presence and strength of trophic links providing redundancy to those links that were lost. Our results demonstrate that biodiversity loss, leading to a reduction in redundant interactions, can increase the vulnerability of ecosystems to secondary extinctions, which, when they occur, can then lead to further simplification and run-away extinction cascades. PMID:29467292

When local extinction and colonization of river fishes can be predicted by regional occupancy: the role of spatial scales.

PubMed

Bergerot, Benjamin; Hugueny, Bernard; Belliard, Jérôme

2013-01-01

Predicting which species are likely to go extinct is perhaps one of the most fundamental yet challenging tasks for conservation biologists. This is particularly relevant for freshwater ecosystems which tend to have the highest proportion of species threatened with extinction. According to metapopulation theories, local extinction and colonization rates of freshwater subpopulations can depend on the degree of regional occupancy, notably due to rescue effects. However, relationships between extinction, colonization, regional occupancy and the spatial scales at which they operate are currently poorly known. And Findings: We used a large dataset of freshwater fish annual censuses in 325 stream reaches to analyse how annual extinction/colonization rates of subpopulations depend on the regional occupancy of species. For this purpose, we modelled the regional occupancy of 34 fish species over the whole French river network and we tested how extinction/colonization rates could be predicted by regional occupancy described at five nested spatial scales. Results show that extinction and colonization rates depend on regional occupancy, revealing existence a rescue effect. We also find that these effects are scale dependent and their absolute contribution to colonization and extinction tends to decrease from river section to larger basin scales. In terms of management, we show that regional occupancy quantification allows the evaluation of local species extinction/colonization dynamics and reduction of local extinction risks for freshwater fish species implies the preservation of suitable habitats at both local and drainage basin scales.

Dynamics of a Stochastic Predator-Prey Model with Stage Structure for Predator and Holling Type II Functional Response

NASA Astrophysics Data System (ADS)

Liu, Qun; Jiang, Daqing; Hayat, Tasawar; Alsaedi, Ahmed

2018-01-01

In this paper, we develop and study a stochastic predator-prey model with stage structure for predator and Holling type II functional response. First of all, by constructing a suitable stochastic Lyapunov function, we establish sufficient conditions for the existence and uniqueness of an ergodic stationary distribution of the positive solutions to the model. Then, we obtain sufficient conditions for extinction of the predator populations in two cases, that is, the first case is that the prey population survival and the predator populations extinction; the second case is that all the prey and predator populations extinction. The existence of a stationary distribution implies stochastic weak stability. Numerical simulations are carried out to demonstrate the analytical results.

Extinction properties of single-walled carbon nanotubes: Two-fluid model

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

Moradi, Afshin, E-mail: a.moradi@kut.ac.ir

The extinction spectra of a single-walled carbon nanotube are investigated, within the framework of the vector wave function method in conjunction with the hydrodynamic model. Both polarizations of the incident plane wave (TE and TM with respect to the x-z plane) are treated. Electronic excitations on the nanotube surface are modeled by an infinitesimally thin layer of a two-dimensional electron gas represented by two interacting fluids, which takes into account the different nature of the σ and π electrons. Numerical results show that strong interaction between the fluids gives rise to the splitting of the extinction spectra into two peaksmore » in quantitative agreement with the π and σ + π plasmon energies.« less

Dynamics of a Stochastic Predator-Prey Model with Stage Structure for Predator and Holling Type II Functional Response

NASA Astrophysics Data System (ADS)

Liu, Qun; Jiang, Daqing; Hayat, Tasawar; Alsaedi, Ahmed

2018-06-01

In this paper, we develop and study a stochastic predator-prey model with stage structure for predator and Holling type II functional response. First of all, by constructing a suitable stochastic Lyapunov function, we establish sufficient conditions for the existence and uniqueness of an ergodic stationary distribution of the positive solutions to the model. Then, we obtain sufficient conditions for extinction of the predator populations in two cases, that is, the first case is that the prey population survival and the predator populations extinction; the second case is that all the prey and predator populations extinction. The existence of a stationary distribution implies stochastic weak stability. Numerical simulations are carried out to demonstrate the analytical results.

Noise-induced extinction for a ratio-dependent predator-prey model with strong Allee effect in prey

NASA Astrophysics Data System (ADS)

Mandal, Partha Sarathi

2018-04-01

In this paper, we study a stochastically forced ratio-dependent predator-prey model with strong Allee effect in prey population. In the deterministic case, we show that the model exhibits the stable interior equilibrium point or limit cycle corresponding to the co-existence of both species. We investigate a probabilistic mechanism of the noise-induced extinction in a zone of stable interior equilibrium point. Computational methods based on the stochastic sensitivity function technique are applied for the analysis of the dispersion of random states near stable interior equilibrium point. This method allows to construct a confidence domain and estimate the threshold value of the noise intensity for a transition from the coexistence to the extinction.

VLT/X-shooter GRBs: Individual extinction curves of star-forming regions★

NASA Astrophysics Data System (ADS)

Zafar, T.; Watson, D.; Møller, P.; Selsing, J.; Fynbo, J. PU; Schady, P.; Wiersema, K.; Levan, A. J.; Heintz, K. E.; Postigo, A. de Ugarte; D'Elia, V.; Jakobsson, P.; Bolmer, J.; Japelj, J.; Covino, S.; Gomboc, A.; Cano, Z.

2018-05-01

The extinction profiles in Gamma-Ray Burst (GRB) afterglow spectral energy distributions (SEDs) are usually described by the Small Magellanic Cloud (SMC)-type extinction curve. In different empirical extinction laws, the total-to-selective extinction, RV, is an important quantity because of its relation to dust grain sizes and compositions. We here analyse a sample of 17 GRBs (0.34

Role of hippocampal β-adrenergic and glucocorticoid receptors in the novelty-induced enhancement of fear extinction.

PubMed

Liu, Jian-Feng; Yang, Chang; Deng, Jia-Hui; Yan, Wei; Wang, Hui-Min; Luo, Yi-Xiao; Shi, Hai-Shui; Meng, Shi-Qiu; Chai, Bai-Sheng; Fang, Qin; Chai, Ning; Xue, Yan-Xue; Sun, Jia; Chen, Chen; Wang, Xue-Yi; Wang, Ji-Shi; Lu, Lin

2015-05-27

Fear extinction forms a new memory but does not erase the original fear memory. Exposure to novelty facilitates transfer of short-term extinction memory to long-lasting memory. However, the underlying cellular and molecular mechanisms are still unclear. Using a classical contextual fear-conditioning model, we investigated the effect of novelty on long-lasting extinction memory in rats. We found that exposure to a novel environment but not familiar environment 1 h before or after extinction enhanced extinction long-term memory (LTM) and reduced fear reinstatement. However, exploring novelty 6 h before or after extinction had no such effect. Infusion of the β-adrenergic receptor (βAR) inhibitor propranolol and glucocorticoid receptor (GR) inhibitor RU486 into the CA1 area of the dorsal hippocampus before novelty exposure blocked the effect of novelty on extinction memory. Propranolol prevented activation of the hippocampal PKA-CREB pathway, and RU486 prevented activation of the hippocampal extracellular signal-regulated kinase 1/2 (Erk1/2)-CREB pathway induced by novelty exposure. These results indicate that the hippocampal βAR-PKA-CREB and GR-Erk1/2-CREB pathways mediate the extinction-enhancing effect of novelty exposure. Infusion of RU486 or the Erk1/2 inhibitor U0126, but not propranolol or the PKA inhibitor Rp-cAMPS, into the CA1 before extinction disrupted the formation of extinction LTM, suggesting that hippocampal GR and Erk1/2 but not βAR or PKA play critical roles in this process. These results indicate that novelty promotes extinction memory via hippocampal βAR- and GR-dependent pathways, and Erk1/2 may serve as a behavioral tag of extinction. Copyright © 2015 the authors 0270-6474/15/358308-14$15.00/0.

[On the extinction of populations with several types in a random environment].

PubMed

Bacaër, Nicolas

2018-03-01

This study focuses on the extinction rate of a population that follows a continuous-time multi-type branching process in a random environment. Numerical computations in a particular example inspired by an epidemic model suggest an explicit formula for this extinction rate, but only for certain parameter values. Copyright © 2018 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.

A Mismatch-Based Model for Memory Reconsolidation and Extinction in Attractor Networks

PubMed Central

Amaral, Olavo B.

2011-01-01

The processes of memory reconsolidation and extinction have received increasing attention in recent experimental research, as their potential clinical applications begin to be uncovered. A number of studies suggest that amnestic drugs injected after reexposure to a learning context can disrupt either of the two processes, depending on the behavioral protocol employed. Hypothesizing that reconsolidation represents updating of a memory trace in the hippocampus, while extinction represents formation of a new trace, we have built a neural network model in which either simple retrieval, reconsolidation or extinction of a stored attractor can occur upon contextual reexposure, depending on the similarity between the representations of the original learning and reexposure sessions. This is achieved by assuming that independent mechanisms mediate Hebbian-like synaptic strengthening and mismatch-driven labilization of synaptic changes, with protein synthesis inhibition preferentially affecting the former. Our framework provides a unified mechanistic explanation for experimental data showing (a) the effect of reexposure duration on the occurrence of reconsolidation or extinction and (b) the requirement of memory updating during reexposure to drive reconsolidation. PMID:21826231

Stressor controllability modulates fear extinction in humans

PubMed Central

Hartley, Catherine A.; Gorun, Alyson; Reddan, Marianne C.; Ramirez, Franchesca; Phelps, Elizabeth A.

2014-01-01

Traumatic events are proposed to play a role in the development of anxiety disorders, however not all individuals exposed to extreme stress experience a pathological increase in fear. Recent studies in animal models suggest that the degree to which one is able to control an aversive experience is a critical factor determining its behavioral consequences. In this study, we examined whether stressor controllability modulates subsequent conditioned fear expression in humans. Participants were randomly assigned to an escapable stressor condition, a yoked inescapable stressor condition, or a control condition involving no stress exposure. One week later, all participants underwent fear conditioning, fear extinction, and a test of extinction retrieval the following day. Participants exposed to inescapable stress showed impaired fear extinction learning and increased fear expression the following day. In contrast, escapable stress improved fear extinction and prevented the spontaneous recovery of fear. Consistent with the bidirectional controllability effects previously reported in animal models, these results suggest that one's degree of control over aversive experiences may be an important factor influencing the development of psychological resilience or vulnerability in humans. PMID:24333646

Blockade of estrogen by hormonal contraceptives impairs fear extinction in female rats and women.

PubMed

Graham, Bronwyn M; Milad, Mohammed R

2013-02-15

Fear extinction is a laboratory model of fear inhibition and is the basis of exposure therapy for anxiety disorders. Emerging evidence from naturally cycling female rodents and women indicates that estrogens are necessary to the consolidation of fear extinction. Hormonal contraceptives (HCs) inhibit estrogen production; yet, their effects on fear extinction are unknown. We used a cross-species translational approach to investigate the impact of HCs and estradiol supplementation on fear extinction in healthy women (n=76) and female rats (n = 140). Women using HCs exhibited significantly poorer extinction recall compared with naturally cycling women. The extinction impairment was also apparent in HC-treated female rats and was associated with reduced serum estradiol levels. The impairment could be rescued in HC-treated rats either by terminating HC treatment after fear learning or by systemic injection of estrogen-receptor agonists before fear extinction, all of which restored serum estradiol levels. Finally, a single administration of estradiol to naturally cycling women significantly enhanced their ability to recall extinction memories. Together, these findings suggest that HCs may impact women's ability to inhibit fear but that this impairment is not permanent and could potentially be alleviated with estrogen treatment. Copyright © 2013 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Probing Cosmic Dust of the Early Universe through High-Redshift Gamma-Ray Bursts

NASA Astrophysics Data System (ADS)

Liang, S. L.; Li, Aigen

2009-01-01

We explore the extinction properties of the dust in the distant universe through the afterglows of high-redshifted gamma-ray bursts (GRBs) based on the "Drude" model which, unlike previous studies, does not require a prior assumption of template extinction laws. We select GRB 070802 at z ≈ 2.45 (which shows clear evidence for the 2175 Å extinction bump) and GRB 050904 at z ≈ 6.29, the second most distant GRB observed to date. We fit their afterglow spectra to determine the extinction of their host galaxies. We find that (1) their extinction curves differ substantially from that of the Milky Way and the Small and Large Magellanic Clouds (which were widely adopted as template extinction laws in the literature); (2) the 2175 Å extinction feature appears to be also present in GRB 050904 at z ≈ 6.29; and (3) there does not appear to be strong evidence for the dependence of dust extinction on redshifts. The inferred extinction curves are closely reproduced in terms of a mixture of amorphous silicate and graphite, both of which are expected supernova condensates and have been identified in primitive meteorites as presolar grains originating from supernovae (which are considered as the main source of dust at high-z).

Genetic variability and effective population size when local extinction and recolonization of subpopulations are frequent

PubMed Central

Maruyama, Takeo; Kimura, Motoo

1980-01-01

If a population (species) consists of n haploid lines (subpopulations) which reproduce asexually and each of which is subject to random extinction and subsequent replacement, it is shown that, at equilibrium in which mutational production of new alleles and their random extinction balance each other, the genetic diversity (1 minus the sum of squares of allelic frequencies) is given by 2Nev/(1 + 2Nev), where [Formula: see text] in which Ñ is the harmonic mean of the population size per line, n is the number of lines (assumed to be large), λ is the rate of line extinction, and v is the mutation rate (assuming the infinite neutral allele model). In a diploid population (species) consisting of n colonies, if migration takes place between colonies at the rate m (the island model) in addition to extinction and recolonization of colonies, it is shown that effective population size is [Formula: see text] If the rate of colony extinction (λ) is much larger than the migration rate of individuals, the effective population size is greatly reduced compared with the case in which no colony extinctions occur (in which case Ne = nÑ). The stepping-stone type of recolonization scheme is also considered. Bearing of these results on the interpretation of the level of genetic variability at the enzyme level observed in natural populations is discussed from the standpoint of the neutral mutation-random drift hypothesis. PMID:16592920

A cross-immunization model for the extinction of old influenza strains.

PubMed

Uekermann, Florian; Sneppen, Kim

2016-05-13

Given the frequent mutation of antigenic features, the constancy of genetic and antigenic diversity of influenza within a subtype is surprising. While the emergence of new strains and antigenic features is commonly attributed to selection by the human immune system, the mechanism that ensures the extinction of older strains remains controversial. To replicate this dynamics of replacement current models utilize mechanisms such as short-lived strain-transcending immunity, a direct competition for hosts, stochastic extinction or constrained antigenic evolution. Building on the idea of short-lived immunity we introduce a minimal model that exhibits the aforementioned dynamics of replacement. Our model relies only on competition due to an antigen specific immune-response in an unconstrained antigenic space. Furthermore the model explains the size of typical influenza epidemics as well as the tendency that new epidemics are associated with mutations of old antigens.

The timing and cause of megafauna mass deaths at Lancefield Swamp, south-eastern Australia

NASA Astrophysics Data System (ADS)

Dortch, Joe; Cupper, Matt; Grün, Rainer; Harpley, Bernice; Lee, Kerrie; Field, Judith

2016-08-01

Lancefield Swamp, south-eastern Australia, was one of the earliest sites to provoke interest in Pleistocene faunal extinctions in Sahul (Pleistocene Australia-New Guinea). The systematic investigation of the deposit in the early 1970s identified megafaunal remains dominated by the 100-200 kg kangaroo Macropus giganteus titan. Associated radiocarbon ages indicated that the species was extant until c.30,000 BP, suggesting significant overlap with human settlement of Sahul. This evidence was inconsistent with contemporary models of rapid human-driven extinctions. Instead, researchers inferred ecological tethering of fauna at Lancefield Swamp due to intense drought precipitated localised mass deaths, consistent with Late Pleistocene climatic variability. Later investigations in another part of the swamp, the Mayne Site, remote to the initial investigations, concluded that mass flow disturbed this area, and Electron Spin Resonance (ESR) analyses on megafauna teeth returned wide-ranging ages. To clarify site formation processes and dating of Lancefield Swamp, we excavated new test-pits next to previous trenches in the Classic and Mayne Sites. We compared absolute chronologies for sediments and teeth, sedimentology, palaeo-topography, taphonomy, and macropod age at death across the swamp. Luminescence dating of sediments and ESR analysis of teeth returned ages between c.80,000 and 45,000 years ago. We found no archaeological remains in the bone beds, and evidence of carnivore activity and fluvial action, in the form of reactivated spring flow. The latter disturbed limited parts of the site and substantial areas of the bone beds remained intact. The faunal assemblage is dominated by megafaunal adult Macropus, consistent with mass die-offs due to severe drought. Such droughts appear to have recurred over millennia during the climatic variability of Marine Isotope Stages 4 and 3. These events began tens of millennia before the first appearance of Aboriginal people in Sahul and only the very youngest fossil deposits could be coeval with the earliest human arrivals. Therefore, anthropogenic causes cannot be implicated in most if not all of mass deaths at the site. Climatic and environmental changes were the main factors in site formation and megafauna deaths at Lancefield Swamp.

Food web structure and interaction strength pave the way for vulnerability to extinction.

PubMed

Karlsson, Patrik; Jonsson, Tomas; Jonsson, Annie

2007-11-07

This paper focuses on how food web structure and interactions among species affects the vulnerability, due to environmental variability, to extinction of species at different positions in model food webs. Vulnerability is here not measured by a traditional extinction threshold but is instead inspired by the IUCN criteria for endangered species: an observed rapid decline in population abundance. Using model webs influenced by stochasticity with zero autocorrelation, we investigate the ecological determinants of species vulnerability, i.e. the trophic interactions between species and food web structure and how these interact with the risk of sudden drops in abundance of species. We find that (i) producers fulfil the criterion of vulnerable species more frequently than other species, (ii) food web structure is related to vulnerability, and (iii) the vulnerability of species is greater when involved in a strong trophic interaction than when not. We note that our result on the relationship between extinction risk and trophic position of species contradict previous suggestions and argue that the main reason for the discrepancy probably is due to the fact that we study the vulnerability to environmental stochasticity and not extinction risk due to overexploitation, habitat destruction or interactions with introduced species. Thus, we suggest that the vulnerability of species to environmental stochasticity may be differently related to trophic position than the vulnerability of species to other factors. Earlier research on species extinctions has looked for intrinsic traits of species that correlate with increased vulnerability to extinction. However, to fully understand the extinction process we must also consider that species interactions may affect vulnerability and that not all extinctions are the result of long, gradual reductions in species abundances. Under environmental stochasticity (which importance frequently is assumed to increase as a result of climate change) and direct and indirect interactions with other species some extinctions may occur rapidly and apparently unexpectedly. To identify the first declines of population abundances that may escalate and lead to extinctions as early as possible, we need to recognize which species are at greatest risk of entering such dangerous routes and under what circumstances. This new perspective may contribute to our understanding of the processes leading to extinction of populations and eventually species. This is especially urgent in the light of the current biodiversity crisis where a large fraction of the world's biodiversity is threatened.

A NMDA Receptor Antagonist, MK-801 Impairs Consolidating Extinction of Auditory Conditioned Fear Responses in a Pavlovian Model

PubMed Central

Wang, Zheng-Hong; Rao, Zhi-Ren; Wu, Sheng-Xi; Li, Yun-Qing; Wang, Wen

2009-01-01

Background In auditory fear conditioning, repeated presentation of the tone in the absence of shock leads to extinction of the acquired fear responses. The glutamate N-methyl-D-aspartate receptor (NMDAR) is thought to be involved in the extinction of the conditioned fear responses, but its detailed role in initiating and consolidating or maintaining the fear extinction memory is unclear. Here we investigated this issue by using a NMDAR antagonist, MK-801. Methods/Main Findings The effects of immediate (beginning at 10 min after the conditioning) and delayed (beginning at 24 h after conditioning) extinctions were first compared with the finding that delayed extinction caused a better and long-lasting (still significant on the 20th day after extinction) depression on the conditioned fear responses. In a second experiment, MK-801 was intraperitoneally (i.p.) injected at 40 min before, 4 h or 12 h after the delayed extinction, corresponding to critical time points for initiating, consolidating or maintaining the fear extinction memory. i.p. injection of MK-801 at either 40 min before or 4 h after delayed extinction resulted in an impairment of initiating and consolidating fear extinction memory, which caused a long lasting increased freezing score that was still significant on the 7th day after extinction, compared with extinction group. However, MK-801 administered at 12 h after the delayed extinction, when robust consolidation has been occurred and stabilized, did not affect the established extinction memory. Furthermore, the changed freezing behaviors was not due to an alteration in general anxiety levels, since MK-801 treatment had no effect on the percentage of open-arm time or open-arm entries in an Elevated Plus Maze (EPM) task. Conclusions/Significance Our data suggested that the activation of NMDARs plays important role in initiation and consolidation but not maintenance of fear extinction memory. Together with the fact that NMDA receptor is very important for memory, our data added experimental evidence to the concept that the extinction of conditioned fear responses is a procedure of initiating and consolidating new memory other than simply “erasing” the fear memory. PMID:19855841

A NMDA receptor antagonist, MK-801 impairs consolidating extinction of auditory conditioned fear responses in a Pavlovian model.

PubMed

Liu, Jun-Li; Li, Min; Dang, Xiao-Rong; Wang, Zheng-Hong; Rao, Zhi-Ren; Wu, Sheng-Xi; Li, Yun-Qing; Wang, Wen

2009-10-26

In auditory fear conditioning, repeated presentation of the tone in the absence of shock leads to extinction of the acquired fear responses. The glutamate N-methyl-D-aspartate receptor (NMDAR) is thought to be involved in the extinction of the conditioned fear responses, but its detailed role in initiating and consolidating or maintaining the fear extinction memory is unclear. Here we investigated this issue by using a NMDAR antagonist, MK-801. The effects of immediate (beginning at 10 min after the conditioning) and delayed (beginning at 24 h after conditioning) extinctions were first compared with the finding that delayed extinction caused a better and long-lasting (still significant on the 20(th) day after extinction) depression on the conditioned fear responses. In a second experiment, MK-801 was intraperitoneally (i.p.) injected at 40 min before, 4 h or 12 h after the delayed extinction, corresponding to critical time points for initiating, consolidating or maintaining the fear extinction memory. i.p. injection of MK-801 at either 40 min before or 4 h after delayed extinction resulted in an impairment of initiating and consolidating fear extinction memory, which caused a long lasting increased freezing score that was still significant on the 7th day after extinction, compared with extinction group. However, MK-801 administered at 12 h after the delayed extinction, when robust consolidation has been occurred and stabilized, did not affect the established extinction memory. Furthermore, the changed freezing behaviors was not due to an alteration in general anxiety levels, since MK-801 treatment had no effect on the percentage of open-arm time or open-arm entries in an Elevated Plus Maze (EPM) task. Our data suggested that the activation of NMDARs plays important role in initiation and consolidation but not maintenance of fear extinction memory. Together with the fact that NMDA receptor is very important for memory, our data added experimental evidence to the concept that the extinction of conditioned fear responses is a procedure of initiating and consolidating new memory other than simply "erasing" the fear memory.

Retrieving chronological age from dental remains of early fossil hominins to reconstruct human growth in the past.

PubMed

Dean, M Christopher

2010-10-27

A chronology of dental development in Pan troglodytes is arguably the best available model with which to compare and contrast reconstructed dental chronologies of the earliest fossil hominins. Establishing a time scale for growth is a requirement for being able to make further comparative observations about timing and rate during both dento-skeletal growth and brain growth. The absolute timing of anterior tooth crown and root formation appears not to reflect the period of somatic growth. In contrast, the molar dentition best reflects changes to the total growth period. Earlier initiation of molar mineralization, shorter crown formation times, less root length formed at gingival emergence into functional occlusion are cumulatively expressed as earlier ages at molar eruption. Things that are similar in modern humans and Pan, such as the total length of time taken to form individual teeth, raise expectations that these would also have been the same in fossil hominins. The best evidence there is from the youngest fossil hominin specimens suggests a close resemblance to the model for Pan but also hints that Gorilla may be a better developmental model for some. A mosaic of great ape-like features currently best describes the timing of early hominin dental development.

Retrieving chronological age from dental remains of early fossil hominins to reconstruct human growth in the past

PubMed Central

Dean, M. Christopher

2010-01-01

A chronology of dental development in Pan troglodytes is arguably the best available model with which to compare and contrast reconstructed dental chronologies of the earliest fossil hominins. Establishing a time scale for growth is a requirement for being able to make further comparative observations about timing and rate during both dento-skeletal growth and brain growth. The absolute timing of anterior tooth crown and root formation appears not to reflect the period of somatic growth. In contrast, the molar dentition best reflects changes to the total growth period. Earlier initiation of molar mineralization, shorter crown formation times, less root length formed at gingival emergence into functional occlusion are cumulatively expressed as earlier ages at molar eruption. Things that are similar in modern humans and Pan, such as the total length of time taken to form individual teeth, raise expectations that these would also have been the same in fossil hominins. The best evidence there is from the youngest fossil hominin specimens suggests a close resemblance to the model for Pan but also hints that Gorilla may be a better developmental model for some. A mosaic of great ape-like features currently best describes the timing of early hominin dental development. PMID:20855313

Evaluation of third molar development in the estimation of chronological age.

PubMed

Soares, Caio Belém Rodrigues Barros; Figueiroa, José Natal; Dantas, Renata Moura Xavier; Kurita, Lúcio Mitsuo; Pontual, Andréa dos Anjos; Ramos-Perez, Flávia Maria de Moraes; Perez, Danyel Elias da Cruz; Pontual, Maria Luiza dos Anjos

2015-09-01

The purpose of this study was to evaluate the correlation between chronological age and the degree of third molar mineralization by Demirjian's developmental stages (Demirjian et al., 1973) using panoramic radiography. From a total of 11.396 digital panoramic radiographs of patients from three oral radiology private clinics from the northeast region of Brazil, obtained from January to June 2009, 2097 radiographic images from patients aged between 6 and 22 years were selected. The images were analyzed individually by two obsevers using a 21-inch computer screen and Windows Picture and Fax Viewer. Reliability was achieved by intra- and interobserver evaluation, using the Kappa test. Chronological age, calcification stage, gender and third molar were interrelated using a multiple linear regression model, considering age as a response variable. There was reliability with Demirjian et al.'s developmental stage assesment, displaying a significant relationship between mineralization stages and patients' age (P<0.05). There was no significant difference between the average age and the calcification stage taking gender and localization of the third molar into consideration. It is possible to estimate chronological age based on Demirjian's stage of a third molar, regardless of gender and location. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Characterizing Facial Skin Ageing in Humans: Disentangling Extrinsic from Intrinsic Biological Phenomena

PubMed Central

Trojahn, Carina; Dobos, Gabor; Lichterfeld, Andrea; Blume-Peytavi, Ulrike; Kottner, Jan

2015-01-01

Facial skin ageing is caused by intrinsic and extrinsic mechanisms. Intrinsic ageing is highly related to chronological age. Age related skin changes can be measured using clinical and biophysical methods. The aim of this study was to evaluate whether and how clinical characteristics and biophysical parameters are associated with each other with and without adjustment for chronological age. Twenty-four female subjects of three age groups were enrolled. Clinical assessments (global facial skin ageing, wrinkling, and sagging), and biophysical measurements (roughness, colour, skin elasticity, and barrier function) were conducted at both upper cheeks. Pearson's correlations and linear regression models adjusted for age were calculated. Most of the measured parameters were correlated with chronological age (e.g., association with wrinkle score, r = 0.901) and with each other (e.g., residual skin deformation and wrinkle score, r = 0.606). After statistical adjustment for age, only few associations remained (e.g., mean roughness (R z) and luminance (L *),  β = −0.507, R 2 = 0.377). Chronological age as surrogate marker for intrinsic ageing has the most important influence on most facial skin ageing signs. Changes in skin elasticity, wrinkling, sagging, and yellowness seem to be caused by additional extrinsic ageing. PMID:25767806

Extinction phase transitions in a model of ecological and evolutionary dynamics

NASA Astrophysics Data System (ADS)

Barghathi, Hatem; Tackkett, Skye; Vojta, Thomas

2017-07-01

We study the non-equilibrium phase transition between survival and extinction of spatially extended biological populations using an agent-based model. We especially focus on the effects of global temporal fluctuations of the environmental conditions, i.e., temporal disorder. Using large-scale Monte-Carlo simulations of up to 3 × 107 organisms and 105 generations, we find the extinction transition in time-independent environments to be in the well-known directed percolation universality class. In contrast, temporal disorder leads to a highly unusual extinction transition characterized by logarithmically slow population decay and enormous fluctuations even for large populations. The simulations provide strong evidence for this transition to be of exotic infinite-noise type, as recently predicted by a renormalization group theory. The transition is accompanied by temporal Griffiths phases featuring a power-law dependence of the life time on the population size.

Behavioral techniques for attenuating the expression of fear associations in an animal model of anxiety.

PubMed

Laborda, Mario A; Polack, Cody W; Miguez, Gonzalo; Miller, Ralph R

2014-09-01

Recent data indicate that extinguished fear often returns when the testing conditions differ from those of treatment. Several manipulations including extensive extinction training, extinction in multiple contexts, and spacing the extinction trials and sessions reduce the return of fear. Moreover, extensive extinction and extinction in multiple contexts summate in reducing return of fear, and the spacing of the extinction trials and the spacing of extinction sessions summate in reducing return of fear. Here we evaluated whether these techniques also attenuate the context specificity of latent inhibition, and whether they summate to further decrease fear responding at test. In two experiments, with rats as subjects in a lick suppression preparation, we assessed the effects of massive CS preexposure, CS preexposure in multiple contexts, and of spacing the CS-preexposure trials and sessions, in reducing the context specificity of latent inhibition. Fear responding was attenuated by all four manipulations. Moreover, extensive CS preexposure in multiple contexts, and conjoint spacing of the CS-preexposure trials and sessions, were more effective in reducing the context specificity of latent inhibition than each manipulation alone. Our experimental designs evaluated degrees of context specificity of latent inhibition but omitted groups in which latent inhibition was assessed without a context shift away from the context of latent inhibition treatment. This precluded us from drawing conclusions concerning absolute (as opposed to relative) levels of recovery from latent inhibition. Techniques effective in decreasing the return of conditioned fear following extinction are also effective in decreasing the context specificity of latent inhibition in an animal model of anxiety. Fear and anxiety disorders might be prevented in anxious human participants with the same techniques used here, but that is still an empirical question. Copyright © 2014 Elsevier Ltd. All rights reserved.

Integrated multi-site U-Th chronology of the last glacial Lake Lisan

NASA Astrophysics Data System (ADS)

Torfstein, Adi; Goldstein, Steven L.; Kagan, Elisa J.; Stein, Mordechai

2013-03-01

We present a new integrated multi-site chronology for Lake Lisan, which occupied the Dead Sea basin and Jordan Valley during the last glacial period (70-14 kka, Marine Isotope Stages 4, 3, 2). The Dead Sea basin lacustrine deposits are unique among closed basin sediments in that they formed in a deep, hypersaline water body that precipitated primary aragonite which is amenable to radiometric dating by U-series, providing a solid basis for studies of the relationship of Middle East climate to other changes in the high latitudes or the tropics. The application of U-Th dating for lacustrine carbonates requires corrections for detrital U and Th and hydrogenous ("initial") 230Th. Here we followed an iterative approach, in which we evaluate the composition of the detrital contamination independently for every set of coeval samples to determine the corrected ages. These were further filtered and combined with lithological-limnological considerations, which were used to construct age-height models for all studied stratigraphic sections. Finally, the ages of stratigraphic tie-points were used to integrate the individual age-height models into a unified chronology. The resulting chronological framework indicates that the ages of several primary gypsum units associated with catastrophic lake level drops correspond with the timing of Heinrich events in the North Atlantic. Thus, a final iterative step involves refining the ages of "Lisan-gypsum events" based on the ages of Heinrich events 6, 5, 5a, 4, and 1. This approach yields an unprecedented basin-wide, unified, event-anchored chronology for the Lisan Formation, with typical age uncertainties ca. 1000-2000 years (95% confidence limit) across the entire last glacial, well below those typically related to individual U-Th and radiocarbon dating of "dirty" carbonates from similar time intervals. The results can be further extrapolated to new sites and serve as a geochronometric reference for the reconstruction of the limnological history of Lake Lisan.

A System Computational Model of Implicit Emotional Learning

PubMed Central

Puviani, Luca; Rama, Sidita

2016-01-01

Nowadays, the experimental study of emotional learning is commonly based on classical conditioning paradigms and models, which have been thoroughly investigated in the last century. Unluckily, models based on classical conditioning are unable to explain or predict important psychophysiological phenomena, such as the failure of the extinction of emotional responses in certain circumstances (for instance, those observed in evaluative conditioning, in post-traumatic stress disorders and in panic attacks). In this manuscript, starting from the experimental results available from the literature, a computational model of implicit emotional learning based both on prediction errors computation and on statistical inference is developed. The model quantitatively predicts (a) the occurrence of evaluative conditioning, (b) the dynamics and the resistance-to-extinction of the traumatic emotional responses, (c) the mathematical relation between classical conditioning and unconditioned stimulus revaluation. Moreover, we discuss how the derived computational model can lead to the development of new animal models for resistant-to-extinction emotional reactions and novel methodologies of emotions modulation. PMID:27378898

A System Computational Model of Implicit Emotional Learning.

PubMed

Puviani, Luca; Rama, Sidita

2016-01-01

Nowadays, the experimental study of emotional learning is commonly based on classical conditioning paradigms and models, which have been thoroughly investigated in the last century. Unluckily, models based on classical conditioning are unable to explain or predict important psychophysiological phenomena, such as the failure of the extinction of emotional responses in certain circumstances (for instance, those observed in evaluative conditioning, in post-traumatic stress disorders and in panic attacks). In this manuscript, starting from the experimental results available from the literature, a computational model of implicit emotional learning based both on prediction errors computation and on statistical inference is developed. The model quantitatively predicts (a) the occurrence of evaluative conditioning, (b) the dynamics and the resistance-to-extinction of the traumatic emotional responses, (c) the mathematical relation between classical conditioning and unconditioned stimulus revaluation. Moreover, we discuss how the derived computational model can lead to the development of new animal models for resistant-to-extinction emotional reactions and novel methodologies of emotions modulation.

Temporal factors in the extinction of fear in inbred mouse strains differing in extinction efficacy

PubMed Central

2013-01-01

Background Various neuropsychiatric conditions, including posttraumatic stress disorder (PTSD), are characterized by deficient fear extinction, but individuals differ greatly in risk for these. While there is growing evidence that fear extinction is influenced by certain procedural variables, it is unclear how these influences might vary across individuals and subpopulations. To model individual differences in fear extinction, prior studies identified a strain of inbred mouse, 129S1/SvImJ (S1), which exhibits a profound deficit in fear extinction, as compared to other inbred strains, such as C57BL/6J (B6). Methods Here, we assessed the effects of procedural variables on the impaired extinction phenotype of the S1 strain and, by comparison, the extinction-intact B6 strain. The variables studied were 1) the interval between conditioning and extinction, 2) the interval between cues during extinction training, 3) single-cue exposure before extinction training, and 4) extinction of a second-order conditioned cue. Results Conducting extinction training soon after (‘immediately’) conditioning attenuated fear retrieval in S1 mice and impaired extinction in B6 mice. Spacing cue presentations with long inter-trial intervals during extinction training augmented fear in S1 and B6 mice. The effect of spacing was lost with one-trial fear conditioning in B6, but not S1 mice. A single exposure to a conditioned cue before extinction training did not alter extinction retrieval, either in B6 or S1 mice. Both the S1 and B6 strains exhibited robust second-order fear conditioning, in which a cue associated with footshock was sufficient to serve as a conditioned exciter to condition a fear association to a second cue. B6 mice extinguished the fear response to the second-order conditioned cue, but S1 mice failed to do so. Conclusions These data provide further evidence that fear extinction is strongly influenced by multiple procedural variables and is so in a highly strain-dependent manner. This suggests that the efficacy of extinction-based behavioral interventions, such as exposure therapy, for trauma-related anxiety disorders will be determined by the procedural parameters employed and the degree to which the patient can extinguish. PMID:23830244

Life history trade-off moderates model predictions of diversity loss from climate change

PubMed Central

2017-01-01

Climate change can trigger species range shifts, local extinctions and changes in diversity. Species interactions and dispersal capacity are important mediators of community responses to climate change. The interaction between multispecies competition and variation in dispersal capacity has recently been shown to exacerbate the effects of climate change on diversity and to increase predictions of extinction risk dramatically. Dispersal capacity, however, is part of a species’ overall ecological strategy and are likely to trade off with other aspects of its life history that influence population growth and persistence. In plants, a well-known example is the trade-off between seed mass and seed number. The presence of such a trade-off might buffer the diversity loss predicted by models with random but neutral (i.e. not impacting fitness otherwise) differences in dispersal capacity. Using a trait-based metacommunity model along a warming climatic gradient the effect of three different dispersal scenarios on model predictions of diversity change were compared. Adding random variation in species dispersal capacity caused extinctions by the introduction of strong fitness differences due an inherent property of the dispersal kernel. Simulations including a fitness-equalising trade-off based on empirical relationships between seed mass (here affecting dispersal distance, establishment probability, and seedling biomass) and seed number (fecundity) maintained higher initial species diversity and predicted lower extinction risk and diversity loss during climate change than simulations with variable dispersal capacity. Large seeded species persisted during climate change, but developed lags behind their climate niche that may cause extinction debts. Small seeded species were more extinction-prone during climate change but tracked their niches through dispersal and colonisation, despite competitive resistance from residents. Life history trade-offs involved in coexistence mechanisms may increase community resilience to future climate change and are useful guides for model development. PMID:28520770

Using population viability analysis to predict the effects of climate change on the extinction risk of an endangered limestone endemic shrub, Arizona cliffrose.

PubMed

Maschinski, Joyce; Baggs, Joanne E; Quintana-Ascencio, Pedro F; Menges, Eric S

2006-02-01

The threat of global warming to rare species is a growing concern, yet few studies have predicted its effects on rare populations. Using demographic data gathered in both drought and nondrought years between 1996-2003 in central Arizona upper Sonoran Desert, we modeled population viability for the federally endangered Purshia subintegra (Kearney) Henrickson (Arizona cliffrose). We used deterministic matrix projection models and stochastic models simulating weather conditions during our study, given historical weather variation and under scenarios of increased aridity. Our models suggest that the P. subintegra population in Verde Valley is slowly declining and will be at greater risk of extinction with increased aridity. Across patches at a fine spatial scale, demographic performance was associated with environmental factors. Moist sites (patches with the highest soil moisture, lowest sand content, and most northern aspects) had the highest densities, highest seedling recruitment, and highest risk of extinction over the shortest time span. Extinction risk in moist sites was exacerbated by higher variance in recruitment and mortality. Dry sites had higher cumulative adult survival and lower extinction risk but negative growth rates. Steps necessary for the conservation of the species include introductions at more northern latitudes and in situ manipulations to enhance seedling recruitment and plant survival. We demonstrate that fine spatial-scale modeling is necessary to predict where patches with highest extinction risk or potential refugia for rare species may occur Because current climate projections for the 21st century imply range shifts at rates of 300 to 500 km/century, which are beyond even exceptional examples of shifts in the fossil record of 100-150 km, it is likely that preservation of many rare species will require human intervention and a long-term commitment. Global warming conditions are likely to reduce the carrying capacity of many rare species' habitats.

Retrieval method of aerosol extinction coefficient profile by an integral lidar system and case study

NASA Astrophysics Data System (ADS)

Shan, Huihui; Zhang, Hui; Liu, Junjian; Wang, Shenhao; Ma, Xiaomin; Zhang, Lianqing; Liu, Dong; Xie, Chenbo; Tao, Zongming

2018-02-01

Aerosol extinction coefficient profile is an essential parameter for atmospheric radiation model. But it is difficult to get the full aerosol extinction profile from the ground to the tropopause especially in near ground precisely using backscattering lidar. A combined measurement of side-scattering, backscattering and Raman-scattering lidar is proposed to retrieve the aerosol extinction coefficient profile from the surface to the tropopause which covered a dynamic range of 5 orders. The side-scattering technique solves the dead zone and the overlap problem caused by the traditional lidar in the near range. Using the Raman-scattering the aerosol lidar ratio (extinction to backscatter ratio) can be obtained. The cases studies in this paper show the proposed method is reasonable and feasible.

Modeling ecological traps for the control of feral pigs

PubMed Central

Dexter, Nick; McLeod, Steven R

2015-01-01

Ecological traps are habitat sinks that are preferred by dispersing animals but have higher mortality or reduced fecundity compared to source habitats. Theory suggests that if mortality rates are sufficiently high, then ecological traps can result in extinction. An ecological trap may be created when pest animals are controlled in one area, but not in another area of equal habitat quality, and when there is density-dependent immigration from the high-density uncontrolled area to the low-density controlled area. We used a logistic population model to explore how varying the proportion of habitat controlled, control mortality rate, and strength of density-dependent immigration for feral pigs could affect the long-term population abundance and time to extinction. Increasing control mortality, the proportion of habitat controlled and the strength of density-dependent immigration decreased abundance both within and outside the area controlled. At higher levels of these parameters, extinction was achieved for feral pigs. We extended the analysis with a more complex stochastic, interactive model of feral pig dynamics in the Australian rangelands to examine how the same variables as the logistic model affected long-term abundance in the controlled and uncontrolled area and time to extinction. Compared to the logistic model of feral pig dynamics, the stochastic interactive model predicted lower abundances and extinction at lower control mortalities and proportions of habitat controlled. To improve the realism of the stochastic interactive model, we substituted fixed mortality rates with a density-dependent control mortality function, empirically derived from helicopter shooting exercises in Australia. Compared to the stochastic interactive model with fixed mortality rates, the model with the density-dependent control mortality function did not predict as substantial decline in abundance in controlled or uncontrolled areas or extinction for any combination of variables. These models demonstrate that pest eradication is theoretically possible without the pest being controlled throughout its range because of density-dependent immigration into the area controlled. The stronger the density-dependent immigration, the better the overall control in controlled and uncontrolled habitat combined. However, the stronger the density-dependent immigration, the poorer the control in the area controlled. For feral pigs, incorporating environmental stochasticity improves the prospects for eradication, but adding a realistic density-dependent control function eliminates these prospects. PMID:26045954

Cerebral aneurysms: Formation, progression and developmental chronology

PubMed Central

Etminan, Nima; Buchholz, Bruce A.; Dreier, Rita; Bruckner, Peter; Torner, James C.; Steiger, Hans-Jakob; Hänggi, Daniel; Macdonald, R. Loch

2015-01-01

The prevalence of unruptured intracranial aneurysms (UAIs) in the general population is up to 3%. Existing epidemiological data suggests that only a small fraction of UIAs progress towards rupture over the lifetime of an individual, but the surrogates for subsequent rupture and the natural history of UIAs are discussed very controversially at present. In case of rupture of an UIA, the case-fatality is up to 50%, which therefore continues to stimulate interest in the pathogenesis of cerebral aneurysm formation and progression. Actual data on the chronological development of cerebral aneurysm has been especially difficult to obtain and, until recently, the existing knowledge in this respect is mainly derived from animal or mathematical models or short-term observational studies. Here, we highlight the current data on cerebral aneurysm formation and progression as well as a novel approach to investigate the developmental chronology of cerebral aneurysms. PMID:24323717

Genetic and phylogenetic consequences of island biogeography.

PubMed

Johnson, K P; Adler, F R; Cherry, J L

2000-04-01

Island biogeography theory predicts that the number of species on an island should increase with island size and decrease with island distance to the mainland. These predictions are generally well supported in comparative and experimental studies. These ecological, equilibrium predictions arise as a result of colonization and extinction processes. Because colonization and extinction are also important processes in evolution, we develop methods to test evolutionary predictions of island biogeography. We derive a population genetic model of island biogeography that incorporates island colonization, migration of individuals from the mainland, and extinction of island populations. The model provides a means of estimating the rates of migration and extinction from population genetic data. This model predicts that within an island population the distribution of genetic divergences with respect to the mainland source population should be bimodal, with much of the divergence dating to the colonization event. Across islands, this model predicts that populations on large islands should be on average more genetically divergent from mainland source populations than those on small islands. Likewise, populations on distant islands should be more divergent than those on close islands. Published observations of a larger proportion of endemic species on large and distant islands support these predictions.

Experimental demonstration of a two-phase population extinction hazard

PubMed Central

Drake, John M.; Shapiro, Jeff; Griffen, Blaine D.

2011-01-01

Population extinction is a fundamental biological process with applications to ecology, epidemiology, immunology, conservation biology and genetics. Although a monotonic relationship between initial population size and mean extinction time is predicted by virtually all theoretical models, attempts at empirical demonstration have been equivocal. We suggest that this anomaly is best explained with reference to the transient properties of ensembles of populations. Specifically, we submit that under experimental conditions, many populations escape their initially vulnerable state to reach quasi-stationarity, where effects of initial conditions are erased. Thus, extinction of populations initialized far from quasi-stationarity may be exposed to a two-phase extinction hazard. An empirical prediction of this theory is that the fit Cox proportional hazards regression model for the observed survival time distribution of a group of populations will be shown to violate the proportional hazards assumption early in the experiment, but not at later times. We report results of two experiments with the cladoceran zooplankton Daphnia magna designed to exhibit this phenomenon. In one experiment, habitat size was also varied. Statistical analysis showed that in one of these experiments a transformation occurred so that very early in the experiment there existed a transient phase during which the extinction hazard was primarily owing to the initial population size, and that this was gradually replaced by a more stable quasi-stationary phase. In the second experiment, only habitat size unambiguously displayed an effect. Analysis of data pooled from both experiments suggests that the overall extinction time distribution in this system results from the mixture of extinctions during the initial rapid phase, during which the effects of initial population size can be considerable, and a longer quasi-stationary phase, during which only habitat size has an effect. These are the first results, to our knowledge, of a two-phase population extinction process. PMID:21429907

Long-Distance Rescue and Slow Extinction Dynamics Govern Multiscale Metapopulations.

PubMed

Huth, Géraldine; Haegeman, Bart; Pitard, Estelle; Munoz, François

2015-10-01

Rare long-distance dispersal is known to be critical for species dynamics, but how the interplay between short- and long-distance colonization influences regional persistence in a fragmented habitat remains poorly understood. We propose a metapopulation model that combines local colonization within habitat islands and long-distance colonization between islands. We study how regional occupancy dynamics are affected by the multiscale colonization process. We find that the island size distribution (ISD) is a key driver of the long-term occupancy dynamics. When the ISD is heterogeneous-that is, when the size of islands is variable-we show that extinction dynamics become very slow. We demonstrate that this behavior is unrelated to the well-known extinction debt near the critical extinction threshold. Hence, this finding questions the equivalence between extinction debt and critical transitions in the context of metapopulation collapse. Furthermore, we show that long-distance colonization can rescue small islands from extinction and sustain a steady regional occupancy. These results provide novel theoretical and practical insights into extinction dynamics and persistence in fragmented habitats and are thus relevant for the design of conservation strategies.

Extinction with multiple excitors

PubMed Central

McConnell, Bridget L.; Miguez, Gonzalo; Miller, Ralph R.

2012-01-01

Four conditioned suppression experiments with rats, using an ABC renewal design, investigated the effects of compounding the target conditioned excitor with additional, nontarget conditioned excitors during extinction. Experiment 1 showed stronger extinction, as evidenced by less renewal, when the target excitor was extinguished in compound with a second excitor, relative to when it was extinguished with associatively neutral stimuli. Critically, this deepened extinction effect was attenuated (i.e., more renewal occurred) when a third excitor was added during extinction training. This novel demonstration contradicts the predictions of associative learning models based on total error reduction, but it is explicable in terms of a counteraction effect within the framework of the extended comparator hypothesis. The attenuated deepened extinction effect was replicated in Experiments 2a and 3, which also showed that pretraining consisting of weakening the association between the two additional excitors (Experiments 2a and 2b) or weakening the association between one of the additional excitors and the unconditioned stimulus (Experiment 3) attenuated the counteraction effect, thereby resulting in a decrease in responding to the target excitor. These results suggest that more than simple total error reduction determines responding after extinction. PMID:23055103

Extinction of opiate reward reduces dendritic arborization and c-Fos expression in the nucleus accumbens core.

PubMed

Leite-Morris, Kimberly A; Kobrin, Kendra L; Guy, Marsha D; Young, Angela J; Heinrichs, Stephen C; Kaplan, Gary B

2014-04-15

Recurrent opiate use combined with environmental cues, in which the drug was administered, provokes cue-induced drug craving and conditioned drug reward. Drug abuse craving is frequently linked with stimuli from a prior drug-taking environment via classical conditioning and associative learning. We modeled the conditioned morphine reward process by using acquisition and extinction of conditioned place preference (CPP) in C57BL/6 mice. Mice were trained to associate a morphine injection with a drug context using a classical conditioning paradigm. In morphine conditioning (0, 0.25, 0.5, 1, 5, or 10 mg/kg) experimental mice acquired a morphine CPP dose response with 10mg/kg as most effective. During morphine CPP extinction experiments, mice were divided into three test groups: morphine CPP followed by extinction training, morphine CPP followed by sham extinction, and saline controls. Extinction of morphine CPP developed within one extinction experiment (4 days) that lasted over two more trials (another 8 days). However, the morphine CPP/sham extinction group retained a place preference that endured through all three extinction trials. Brains were harvested following CPP extinction and processed using Golgi-Cox impregnation. Changes in dendritic morphology and spine quantity were examined in the nucleus accumbens (NAc) Core and Shell neurons. In the NAcCore only, morphine CPP/extinguished mice produced less dendritic arborization, and a decrease in neuronal activity marker c-Fos compared to the morphine CPP/sham extinction group. Extinction of morphine CPP is associated with decreased structural complexity of dendrites in the NAcCore and may represent a substrate for learning induced structural plasticity relevant to addiction. Published by Elsevier B.V.

A cross species study of heterogeneity in fear extinction learning in relation to FKBP5 variation and expression: Implications for the acute treatment of posttraumatic stress disorder.

PubMed

Galatzer-Levy, Isaac R; Andero, Raül; Sawamura, Takehito; Jovanovic, Tanja; Papini, Santiago; Ressler, Kerry J; Norrholm, Seth Davin

2017-04-01

Deficits in fear extinction learning are hypothesized to underlie the development of posttraumatic stress disorder (PTSD). Such deficits may, in part, be due to genetic and epigenetic variation in the stress related gene FKBP5. Conversely, altering FKBP5 epigenetic responses during memory consolidation may rescue extinction deficits making it a target for acute intervention to prevent the development of PTSD. Study 1 (Humans) examines if FKBP5 single nucleotide polymorphisms (SNPs) and PTSD symptom domains (re-experiencing, avoidance/numbing, hyperarousal) are associated with abnormal fear extinction phenotypes identified using latent growth mixture modeling (LGMM). Study 2 (Mice) tests if increasing doses of dexamethasone administered prior to extinction alters Fkbp5 mRNA production in the amygdala after extinction and recall and prevents the development of abnormal extinction phenotypes. In humans, abnormal extinction was associated with the TT homozygous genotype of FKBP5 SNPs RS9470080 and RS1360780, and hyperarousal symptoms. In mice, dexamethasone 300 μg/kg was associated with increased amygdala Fkbp5 mRNA following extinction and robust extinction learning while lower doses were not associated with amygdala Fkbp5 mRNA or differences in extinction learning. Further, mice that extinguished on dexamethasone 300 μg/kg maintained low levels of freezing behavior during recall training while mRNA levels were no longer elevated. Together, findings indicate that FKBP5 confers risk for fear extinction deficits. However, this risk may be ameliorated by increasing fkbp5 mRNA expression in the amygdala during memory consolidation making this mechanism a plausible point of acute intervention to prevent the development of PTSD. Copyright © 2016 Elsevier Ltd. All rights reserved.

Body Size Preference of Marine Animals in Relation to Extinction Selectivity

NASA Astrophysics Data System (ADS)

Sriram, A.; Idgunji, S.; Heim, N. A.; Payne, J.

2014-12-01

Our project encompasses an extremely specific aspect in relation to the five mass extinctions in geologic history. We asked ourselves whether larger or smaller body sizes would be better suited for surviving a mass extinction. To conduct research for our project, we used the body sizes of 17,172 marine animal genera as our primary data. These animals include echinoderms, arthropods, chordates, mollusks, and brachiopods. These creatures are perfect model organisms in terms of finding data on them because they have an excellent fossil record, and are well documented. We focused on the mean body size of these animals before and after each of the five mass extinctions (end-Ordovician, Late Devonian, end-Permian, end-Triassic, and end-Cretaceous). Our hypothesis was that the average biovolume of animals increased after each of the extinctions, with the mean size being greater after than it was before. Our size data is from the Ellis & Messina Catalogue of Ostracoda and the Treatise on Invertebrate Paleontology. We obtained stratigraphic range data The Treatise and Sepkoski (2002). In our analyses, we compared the mean size of the different animal genera before and after each extinction event. We further partitioned size change across mass extinction boundaries into three categories: the surviving genera, the extinct genera, and the newly originating genera that came about after the extinction. According to our analyses, the mean sizes did not change significantly from the genera living during the stages before the extinctions and after the extinctions. From our results, we can assume that there were not enough major increases in the overall volume of the organisms to warrant a definite conclusion that extinctions lead to larger body sizes. Further support for our findings came from the T-tests in our R code. Only the Cretaceous period showed true evidence for size changing because of the extinction; in this case, the mean size decreased. T-tests for the Cretaceous comparisons showed that mean size decreased across the extinction boundary. This was due to the fact that new originating genera were smaller than the genera that survived. Our results show that there is variability in the relationship between body size and extinction selectivity in various mass extinctions.

Effects of uncertainty and variability on population declines and IUCN Red List classifications.

PubMed

Rueda-Cediel, Pamela; Anderson, Kurt E; Regan, Tracey J; Regan, Helen M

2018-01-22

The International Union for Conservation of Nature (IUCN) Red List Categories and Criteria is a quantitative framework for classifying species according to extinction risk. Population models may be used to estimate extinction risk or population declines. Uncertainty and variability arise in threat classifications through measurement and process error in empirical data and uncertainty in the models used to estimate extinction risk and population declines. Furthermore, species traits are known to affect extinction risk. We investigated the effects of measurement and process error, model type, population growth rate, and age at first reproduction on the reliability of risk classifications based on projected population declines on IUCN Red List classifications. We used an age-structured population model to simulate true population trajectories with different growth rates, reproductive ages and levels of variation, and subjected them to measurement error. We evaluated the ability of scalar and matrix models parameterized with these simulated time series to accurately capture the IUCN Red List classification generated with true population declines. Under all levels of measurement error tested and low process error, classifications were reasonably accurate; scalar and matrix models yielded roughly the same rate of misclassifications, but the distribution of errors differed; matrix models led to greater overestimation of extinction risk than underestimations; process error tended to contribute to misclassifications to a greater extent than measurement error; and more misclassifications occurred for fast, rather than slow, life histories. These results indicate that classifications of highly threatened taxa (i.e., taxa with low growth rates) under criterion A are more likely to be reliable than for less threatened taxa when assessed with population models. Greater scrutiny needs to be placed on data used to parameterize population models for species with high growth rates, particularly when available evidence indicates a potential transition to higher risk categories. © 2018 Society for Conservation Biology.

Murine GRPR and Stathmin Control in Opposite Directions both Cued Fear Extinction and Neural Activities of the Amygdala and Prefrontal Cortex

PubMed Central

Martel, Guillaume; Hevi, Charles; Wong, Alexandra; Zushida, Ko; Uchida, Shusaku; Shumyatsky, Gleb P.

2012-01-01

Extinction is an integral part of normal healthy fear responses, while it is compromised in several fear-related mental conditions in humans, such as post-traumatic stress disorder (PTSD). Although much research has recently been focused on fear extinction, its molecular and cellular underpinnings are still unclear. The development of animal models for extinction will greatly enhance our approaches to studying its neural circuits and the mechanisms involved. Here, we describe two gene-knockout mouse lines, one with impaired and another with enhanced extinction of learned fear. These mutant mice are based on fear memory-related genes, stathmin and gastrin-releasing peptide receptor (GRPR). Remarkably, both mutant lines showed changes in fear extinction to the cue but not to the context. We performed indirect imaging of neuronal activity on the second day of cued extinction, using immediate-early gene c-Fos. GRPR knockout mice extinguished slower (impaired extinction) than wildtype mice, which was accompanied by an increase in c-Fos activity in the basolateral amygdala and a decrease in the prefrontal cortex. By contrast, stathmin knockout mice extinguished faster (enhanced extinction) and showed a decrease in c-Fos activity in the basolateral amygdala and an increase in the prefrontal cortex. At the same time, c-Fos activity in the dentate gyrus was increased in both mutant lines. These experiments provide genetic evidence that the balance between neuronal activities of the amygdala and prefrontal cortex defines an impairment or facilitation of extinction to the cue while the hippocampus is involved in the context-specificity of extinction. PMID:22312434

Murine GRPR and stathmin control in opposite directions both cued fear extinction and neural activities of the amygdala and prefrontal cortex.

PubMed

Martel, Guillaume; Hevi, Charles; Wong, Alexandra; Zushida, Ko; Uchida, Shusaku; Shumyatsky, Gleb P

2012-01-01

Extinction is an integral part of normal healthy fear responses, while it is compromised in several fear-related mental conditions in humans, such as post-traumatic stress disorder (PTSD). Although much research has recently been focused on fear extinction, its molecular and cellular underpinnings are still unclear. The development of animal models for extinction will greatly enhance our approaches to studying its neural circuits and the mechanisms involved. Here, we describe two gene-knockout mouse lines, one with impaired and another with enhanced extinction of learned fear. These mutant mice are based on fear memory-related genes, stathmin and gastrin-releasing peptide receptor (GRPR). Remarkably, both mutant lines showed changes in fear extinction to the cue but not to the context. We performed indirect imaging of neuronal activity on the second day of cued extinction, using immediate-early gene c-Fos. GRPR knockout mice extinguished slower (impaired extinction) than wildtype mice, which was accompanied by an increase in c-Fos activity in the basolateral amygdala and a decrease in the prefrontal cortex. By contrast, stathmin knockout mice extinguished faster (enhanced extinction) and showed a decrease in c-Fos activity in the basolateral amygdala and an increase in the prefrontal cortex. At the same time, c-Fos activity in the dentate gyrus was increased in both mutant lines. These experiments provide genetic evidence that the balance between neuronal activities of the amygdala and prefrontal cortex defines an impairment or facilitation of extinction to the cue while the hippocampus is involved in the context-specificity of extinction.

Extinguishment of a Diffusion Flame Over a PMMA Cylinder by Depressurization in Reduced-Gravity

NASA Technical Reports Server (NTRS)

Goldmeer, Jeffrey Scott

1996-01-01

Extinction of a diffusion flame burning over horizontal PMMA (Polymethyl methacrylate) cylinders in low-gravity was examined experimentally and via numerical simulations. Low-gravity conditions were obtained using the NASA Lewis Research Center's reduced-gravity aircraft. The effects of velocity and pressure on the visible flame were examined. The flammability of the burning solid was examined as a function of pressure and the solid-phase centerline temperature. As the solid temperature increased, the extinction pressure decreased, and with a centerline temperature of 525 K, the flame was sustained to 0.1 atmospheres before extinguishing. The numerical simulation iteratively coupled a two-dimensional quasi-steady, gas-phase model with a transient solid-phase model which included conductive heat transfer and surface regression. This model employed an energy balance at the gas/solid interface that included the energy conducted by the gas-phase to the gas/solid interface, Arrhenius pyrolysis kinetics, surface radiation, and the energy conducted into the solid. The ratio of the solid and gas-phase conductive fluxes Phi was a boundary condition for the gas-phase model at the solid-surface. Initial simulations modeled conditions similar to the low-gravity experiments and predicted low-pressure extinction limits consistent with the experimental limits. Other simulations examined the effects of velocity, depressurization rate and Phi on extinction.

Species sorting and patch dynamics in harlequin metacommunities affect the relative importance of environment and space.

PubMed

Leibold, Mathew A; Loeuille, Nicolas

2015-12-01

Metacommunity theory indicates that variation in local community structure can be partitioned into components including those related to local environmental conditions vs. spatial effects and that these can be quantified using statistical methods based on variation partitioning. It has been hypothesized that joint associations of community composition with environment and space could be due to patch dynamics involving colonization-extinction processes in environmentally heterogeneous landscapes but this has yet to be theoretically shown. We develop a two-patch, type-two, species competition model in such a "harlequin" landscape (where different patches have different environments) to evaluate how composition is related to environmental and spatial effects as a function of background extinction rate. Using spatially implicit analytical models, we find that the environmental association of community composition declines with extinction rate as expected. Using spatially explicit simulation models, we further find that there is an increase in the spatial structure with extinction due to spatial patterning into clusters that are not related to environmental conditions but that this increase is limited. Natural metacommunities often show both environment and spatial determination even under conditions of relatively high isolation and these could be more easily explained by our model than alternative metacommunity models.

Mass Extinction and the Structure of the Milky Way

NASA Astrophysics Data System (ADS)

Filipovic, M. D.; Horner, J.; Crawford, E. J.; Tothill, N. F. H.; White, G. L.

2013-12-01

We use the most up-to-date Milky Way model and solar orbit data in order to test the hypothesis that the Sun's galactic spiral arm crossings cause mass extinction events on Earth. To do this, we created a new model of the Milky Way's spiral arms by combining a large quantity of data from several surveys. We then combined this model with a recently derived solution for the solar orbit to determine the timing of the Sun's historical passages through the Galaxy's spiral arms. Our new model was designed with a symmetrical appearance, with the major alteration being the addition of a spur at the far side of the Galaxy. A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33~Myr ago. Our simulations indicate that the Sun has spent ˜60 per cent of its time passing through our Galaxy's various spiral arms. Also, we briefly discuss and combine previous work on the Galactic Habitable Zone with the new Milky Way model.

DO PERIODICITIES IN EXTINCTION-WITH POSSIBLE ASTRONOMICAL CONNECTIONS-SURVIVE A REVISION OF THE GEOLOGICAL TIMESCALE?

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

Melott, Adrian L.; Bambach, Richard K.

A major revision of the geological timescale was published in 2012. We re-examine our past finding of a 27 Myr periodicity in marine extinction rates by re-assigning dates to the extinction data used previously. We find that the spectral power in this period is somewhat increased, and persists at a narrow bandwidth, which supports our previous contention that the Nemesis hypothesis is untenable as an explanation for the periodicity that was first noted by Raup and Sepkoski in the 1980s. We enumerate a number of problems in a recent study comparing extinction rates with time series models.

Star clusters: age, metallicity and extinction from integrated spectra

NASA Astrophysics Data System (ADS)

González Delgado, Rosa M.; Cid Fernandes, Roberto

2010-01-01

Integrated optical spectra of star clusters in the Magellanic Clouds and a few Galactic globular clusters are fitted using high-resolution spectral models for single stellar populations. The goal is to estimate the age, metallicity and extinction of the clusters, and evaluate the degeneracies among these parameters. Several sets of evolutionary models that were computed with recent high-spectral-resolution stellar libraries (MILES, GRANADA, STELIB), are used as inputs to the starlight code to perform the fits. The comparison of the results derived from this method and previous estimates available in the literature allow us to evaluate the pros and cons of each set of models to determine star cluster properties. In addition, we quantify the uncertainties associated with the age, metallicity and extinction determinations resulting from variance in the ingredients for the analysis.

Effect of lethality on the extinction and on the error threshold of quasispecies.

PubMed

Tejero, Hector; Marín, Arturo; Montero, Francisco

2010-02-21

In this paper the effect of lethality on error threshold and extinction has been studied in a population of error-prone self-replicating molecules. For given lethality and a simple fitness landscape, three dynamic regimes can be obtained: quasispecies, error catastrophe, and extinction. Using a simple model in which molecules are classified as master, lethal and non-lethal mutants, it is possible to obtain the mutation rates of the transitions between the three regimes analytically. The numerical resolution of the extended model, in which molecules are classified depending on their Hamming distance to the master sequence, confirms the results obtained in the simple model and shows how an error catastrophe regime changes when lethality is taken in account. (c) 2009 Elsevier Ltd. All rights reserved.

System Models and Aging: A Driving Example.

ERIC Educational Resources Information Center

Melichar, Joseph F.

Chronological age is a marker in time but it fails to measure accurately the performance or behavioral characteristics of individuals. This paper models the complexity of aging by using a system model and a human function paradigm. These models help facilitate representation of older adults, integrate research agendas, and enhance remediative…

EXTINCTION LAWS TOWARD STELLAR SOURCES WITHIN A DUSTY CIRCUMSTELLAR MEDIUM AND IMPLICATIONS FOR TYPE IA SUPERNOVAE

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

Nagao, Takashi; Maeda, Keiichi; Nozawa, Takaya, E-mail: nagao@kusastro.kyoto-u.ac.jp

Many astronomical objects are surrounded by dusty environments. In such dusty objects, multiple scattering processes of photons by circumstellar (CS) dust grains can effectively alter extinction properties. In this paper, we systematically investigate the effects of multiple scattering on extinction laws for steady-emission sources surrounded by the dusty CS medium using a radiation transfer simulation based on the Monte Carlo technique. In particular, we focus on whether and how the extinction properties are affected by properties of CS dust grains by adopting various dust grain models. We confirm that behaviors of the (effective) extinction laws are highly dependent on themore » properties of CS grains, especially the total-to-selective extinction ratio R{sub V}, which characterizes the extinction law and can be either increased or decreased and compared with the case without multiple scattering. We find that the criterion for this behavior is given by a ratio of albedos in the B and V bands. We also find that either small silicate grains or polycyclic aromatic hydrocarbons are necessary for realizing a low value of R{sub V} as often measured toward SNe Ia if the multiple scattering by CS dust is responsible for their non-standard extinction laws. Using the derived relations between the properties of dust grains and the resulting effective extinction laws, we propose that the extinction laws toward dusty objects could be used to constrain the properties of dust grains in CS environments.« less

Interstellar Dust Models Consistent with Extinction, Emission, and Abundance Constraints

NASA Technical Reports Server (NTRS)

Zubko, Viktor; Dwek, Eli; Arendt, Richard G.

2004-01-01

We present new interstellar dust models which have been derived by simultaneously fitting the far ultraviolet to near infrared extinction, the diffuse infrared emission, and, unlike previous models, the elemental abundances in dust for the diffuse interstellar medium. We found that dust models consisting of a mixture of spherical graphite and silicate grains, polycyclic aromatic hydrocarbon (PAH) molecules, in addition to porous composite particles containing silicate, organic refractory, and water ice, provide an improved .t to the UV-to-infrared extinction and infrared emission measurements, while consuming the amounts of elements well within the uncertainties of adopted interstellar abundances, including B star abundances. These models are a signi.cant improvement over the recent Li & Draine (2001, ApJ, 554, 778) model which requires an excessive amount of silicon to be locked up in dust: 48 ppm (atoms per million of H atoms), considerably more than the solar abundance of 34 ppm or the B star abundance of 19 ppm.

Periodic mass extinctions and the Planet X model reconsidered

NASA Astrophysics Data System (ADS)

Whitmire, Daniel P.

2016-01-01

The 27 Myr period in the fossil extinction record has been confirmed in modern data bases dating back 500 Myr, which is twice the time interval of the original analysis from 30 years ago. The surprising regularity of this period has been used to reject the Nemesis model. A second model based on the Sun's vertical Galactic oscillations has been challenged on the basis of an inconsistency in period and phasing. The third astronomical model originally proposed to explain the periodicity is the Planet X model in which the period is associated with the perihelion precession of the inclined orbit of a trans-Neptunian planet. Recently, and unrelated to mass extinctions, a trans-Neptunian super-Earth planet has been proposed to explain the observation that the inner Oort cloud objects Sedna and 2012VP113 have perihelia that lie near the ecliptic plane. In this Letter, we reconsider the Planet X model in light of the confluence of the modern palaeontological and outer Solar system dynamical evidence.

Population turnover and adaptation in heterogeneous environments

NASA Astrophysics Data System (ADS)

Campos, Paulo R. A.; de Oliveira, Viviane M.

2012-02-01

We study adaptive dynamics in a structured population model of asexual individuals which takes into account environmental heterogeneity among the subpopulations. The key purpose of the present work is to address how population turnovers, i.e. extinction events followed by recolonization, affect the rate of fixation of advantageous mutations. This model is a generalization of our previous model to address the interplay between environmental correlation and evolutionary forces on the adaptive process. The incorporation of population turnovers into the model enables us to make a direct correspondence between the model and host-parasite dynamics (epidemiological models). Strikingly, contrary to the intuitive and usual deleterious effect associated to extinction events, it is observed that population turnovers can in fact speed up adaptation as heterogeneity rises. On the other side, in nearly homogeneous population turnovers have a neutral effect on fixation rates, but a detrimental outcome is also achieved when extinction events become very common. In resume, population turnover outcomes on fixation rates of advantageous mutations are strongly influenced by the selective correlation among the subpopulations (demes).

Compound stimulus presentation and the norepinephrine reuptake inhibitor atomoxetine enhance long-term extinction of cocaine-seeking behavior.

PubMed

Janak, Patricia H; Bowers, M Scott; Corbit, Laura H

2012-03-01

Drug abstinence is frequently compromised when addicted individuals are re-exposed to environmental stimuli previously associated with drug use. Research with human addicts and in animal models has demonstrated that extinction learning (non-reinforced cue-exposure) can reduce the capacity of such stimuli to induce relapse, yet extinction therapies have limited long-term success under real-world conditions (Bouton, 2002; O'Brien, 2008). We hypothesized that enhancing extinction would reduce the later ability of drug-predictive cues to precipitate drug-seeking behavior. We, therefore, tested whether compound stimulus presentation and pharmacological treatments that augment noradrenergic activity (atomoxetine; norepinephrine reuptake inhibitor) during extinction training would facilitate the extinction of drug-seeking behaviors, thus reducing relapse. Rats were trained that the presentation of a discrete cue signaled that a lever press response would result in cocaine reinforcement. Rats were subsequently extinguished and spontaneous recovery of drug-seeking behavior following presentation of previously drug-predictive cues was tested 4 weeks later. We find that compound stimulus presentations or pharmacologically increasing noradrenergic activity during extinction training results in less future recovery of responding, whereas propranolol treatment reduced the benefit seen with compound stimulus presentation. These data may have important implications for understanding the biological basis of extinction learning, as well as for improving the outcome of extinction-based therapies.

A discrete Markov metapopulation model for persistence and extinction of species.

PubMed

Thompson, Colin J; Shtilerman, Elad; Stone, Lewi

2016-09-07

A simple discrete generation Markov metapopulation model is formulated for studying the persistence and extinction dynamics of a species in a given region which is divided into a large number of sites or patches. Assuming a linear site occupancy probability from one generation to the next we obtain exact expressions for the time evolution of the expected number of occupied sites and the mean-time to extinction (MTE). Under quite general conditions we show that the MTE, to leading order, is proportional to the logarithm of the initial number of occupied sites and in precise agreement with similar expressions for continuous time-dependent stochastic models. Our key contribution is a novel application of generating function techniques and simple asymptotic methods to obtain a second order asymptotic expression for the MTE which is extremely accurate over the entire range of model parameter values. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dust extinction of the stellar continua in starburst galaxies: The ultraviolet and optical extinction law

NASA Technical Reports Server (NTRS)

Calzetti, Daniela; Kinney, Anne L.; Storchi-Bergmann, Thaisa

1994-01-01

We analyze the International Ultraviolet Explorer (IUE) UV and the optical spectra of 39 starburst and blue compact galaxies in order to study the average properties of dust extinction in extended regions of galaxies. The optical spectra have been obtained using an aperture which matches that of IUE, so comparable regions within each galaxy are sampled. The data from the 39 galaxies are compared with five models for the geometrical distribution of dust, adopting as extinction laws both the Milky Way and the Large Magellanic Cloud laws. The commonly used uniform dust screen is included among the models. We find that none of the five models is in satisfactory agreement with the data. In order to understand the discrepancy between the data and the models, we have derived an extinction law directly from the data in the UV and optical wavelength range. The resulting curve is characterized by an overall slope which is more gray than the Milky Way extinction law's slope, and by the absence of the 2175 A dust feature. Remarkably, the difference in optical depth between the Balmer emission lines H(sub alpha) and H(sub beta) is about a factor of 2 larger than the difference in the optical depth between the continuum underlying the two Balmer lines. We interpret this discrepancy as a consequence of the fact that the hot ionizing stars are associated with dustier regions than the cold stellar population is. The absence of the 2175 A dust feature can be due either to the effects of the scattering and clumpiness of the dust or to a chemical composition different from that of the Milky Way dust grains. Disentangling the two interpretations is not easy because of the complexity of the spatial distribution of the emitting regions. The extinction law of the UV and optical spectral continua of extended regions can be applied to the spectra of medium- and high-redshift galaxies, where extended regions of a galaxy are, by necessity, sampled.

Influence of Subpixel Scale Cloud Top Structure on Reflectances from Overcast Stratiform Cloud Layers

NASA Technical Reports Server (NTRS)

Loeb, N. G.; Varnai, Tamas; Winker, David M.

1998-01-01

Recent observational studies have shown that satellite retrievals of cloud optical depth based on plane-parallel model theory suffer from systematic biases that depend on viewing geometry, even when observations are restricted to overcast marine stratus layers, arguably the closest to plane parallel in nature. At moderate to low sun elevations, the plane-parallel model significantly overestimates the reflectance dependence on view angle in the forward-scattering direction but shows a similar dependence in the backscattering direction. Theoretical simulations are performed that show that the likely cause for this discrepancy is because the plane-parallel model assumption does not account for subpixel, scale variations in cloud-top height (i.e., "cloud bumps"). Monte Carlo simulation, comparing ID model radiances to radiances from overcast cloud field with 1) cloud-top height variation, but constant cloud volume extinction; 2) flat tops but horizontal variations in cloud volume extinction; and 3) variations in both cloud top height and cloud extinction are performed over a approximately equal to 4 km x 4 km domain (roughly the size of an individual GAC AVHRR pixel). The comparisons show that when cloud-top height variations are included, departures from 1D theory are remarkably similar (qualitatively) to those obtained observationally. In contrast, when clouds are assumed flat and only cloud extinction is variable, reflectance differences are much smaller and do not show any view-angle dependence. When both cloud-top height and cloud extinction variations are included, however, large increases in cloud extinction variability can enhance reflectance difference. The reason 3D-1D reflectance differences are more sensitive to cloud-top height variations in the forward-scattering direction (at moderate to low, sun elevations) is because photons leaving the cloud field in that direction experience fewer scattering events (low-order scattering) and are restricted to the topmost portions of the cloud. While reflectance deviations from 1D theory are much larger for bumpy clouds than for flat clouds with variable cloud extinction, differences in cloud albedo are comparable for these two cases.

A spectroscopic study of the microorganism model of interstellar grains

NASA Astrophysics Data System (ADS)

Yabushita, S.; Wada, K.; Takai, T.; Inagaki, T.; Young, D.; Arakawa, E. T.

1986-07-01

The microorganism model of interstellar grains is investigated by spectroscopy from the infrared, visible to the ultraviolet (UV) wave regions. E. coli, yeast and spores of Bacillus subtilis exhibit absorption bands at lambda = 3.1 and 9.7 microns; they also exhibit several absorptions at 6 to about 8 microns which are in agreement with the observed IS extinction curves. To obtain the extinction curves in the visible and UV regions, dry films of microorganism are prepared on a MgF2 plate or synthesized quartz plate and their spectra measured. In the wavelength region 190 to about 400 nm, conventional spectrophotometers are adopted for the measurement. The extinction curve of the film of E. coli is similar to the observed IS curve. For the wave-range lambda of between 100 and 400 nm, a vacuum UV spectrometer is adopted to avoid absorptions due to O2 in the atmosphere. The extinction spectra by this method are in agreement with the result obtained by the conventional method where comparison is possible. The extinction curves of E. coli and yeast are such that they increase towards the short wavelength and exhibit a peak at lambda = 190 nm, which is different from the well-known IS peak at lambda = 220 nm. It remains to be seen whether interstellar low temperatures (10 to about 40 K) can shift the peak position in the extinction curve of biochemical materials.

Targeting extinction and reconsolidation mechanisms to combat the impact of drug cues on addiction.

PubMed

Taylor, Jane R; Olausson, Peter; Quinn, Jennifer J; Torregrossa, Mary M

2009-01-01

Drug addiction is a progressive and compulsive disorder, where recurrent craving and relapse to drug-seeking occur even after long periods of abstinence. A major contributing factor to relapse is drug-associated cues. Here we review behavioral and pharmacological studies outlining novel methods of effective and persistent reductions in cue-induced relapse behavior in animal models. We focus on extinction and reconsolidation of cue-drug associations as the memory processes that are the most likely targets for interventions. Extinction involves the formation of new inhibitory memories rather than memory erasure; thus, it should be possible to facilitate the extinction of cue-drug memories to reduce relapse. We propose that context-dependency of extinction might be altered by mnemonic agents, thereby enhancing the efficacy of cue-exposure therapy as treatment strategy. In contrast, interfering with memory reconsolidation processes can disrupt the integrity or strength of specific cue-drug memories. Reconsolidation is argued to be a distinct process that occurs over a brief time period after memory is reactivated/retrieved - when the memory becomes labile and vulnerable to disruption. Reconsolidation is thought to be an independent, perhaps opposing, process to extinction and disruption of reconsolidation has recently been shown to directly affect subsequent cue-drug memory retrieval in an animal model of relapse. We hypothesize that a combined approach aimed at both enhancing the consolidation of cue-drug extinction and interfering with the reconsolidation of cue-drug memories will have a greater potential for persistently inhibiting cue-induced relapse than either treatment alone.

Optical extinction of highly porous aerosol following atmospheric freeze drying

NASA Astrophysics Data System (ADS)

Adler, Gabriela; Haspel, Carynelisa; Moise, Tamar; Rudich, Yinon

2014-06-01

Porous glassy particles are a potentially significant but unexplored component of atmospheric aerosol that can form by aerosol processing through the ice phase of high convective clouds. The optical properties of porous glassy aerosols formed from a freeze-dry cycle simulating freezing and sublimation of ice particles were measured using a cavity ring down aerosol spectrometer (CRD-AS) at 532 nm and 355 nm wavelength. The measured extinction efficiency was significantly reduced for porous organic and mixed organic-ammonium sulfate particles as compared to the extinction efficiency of the homogeneous aerosol of the same composition prior to the freeze-drying process. A number of theoretical approaches for modeling the optical extinction of porous aerosols were explored. These include effective medium approximations, extended effective medium approximations, multilayer concentric sphere models, Rayleigh-Debye-Gans theory, and the discrete dipole approximation. Though such approaches are commonly used to describe porous particles in astrophysical and atmospheric contexts, in the current study, these approaches predicted an even lower extinction than the measured one. Rather, the best representation of the measured extinction was obtained with an effective refractive index retrieved from a fit to Mie scattering theory assuming spherical particles with a fixed void content. The single-scattering albedo of the porous glassy aerosols was derived using this effective refractive index and was found to be lower than that of the corresponding homogeneous aerosol, indicating stronger relative absorption at the wavelengths measured. The reduced extinction and increased absorption may be of significance in assessing direct, indirect, and semidirect forcing in regions where porous aerosols are expected to be prevalent.

"Despair" induced by extinction trials in the water maze: relationship with measures of anxiety in aged and adult rats.

PubMed

Schulz, Daniela; Huston, Joseph P; Buddenberg, Tim; Topic, Bianca

2007-03-01

We have previously reported that extinction of escape behavior in the water maze due to the removal of the platform coincided with the development of behavioral "despair" in aged and adult rats, as assessed by immobility. The present study examines further predictions derived from the hypothesis that the withholding of reinforcement induces behaviors akin to depression. We tested for correlations between extinction performance and immobility, as well as between immobility and measures of anxiety in aged and adult rats. Age comparisons were also performed on these variables. Forty aged and 29 adult male Wistar rats (24 and 3 months old, respectively) were examined in the open field, black/white box and elevated-plus maze followed by 6 days of training in the water maze hidden platform task and 8 days of extinction without the platform. Indices of immobility increased over trials of extinction, with the aged showing higher levels, earlier onsets and larger slope increases of immobility than the adults. A lower resistance-to-extinction was predictive of more "despair" in both age groups. Between-group differences in the open field, black/white box and elevated-plus maze indicated that the aged showed more anxiety-like behavior than the adults and/or explored these environments less. Within the aged group, indicators of fearfulness in the three tests were predictive of higher levels of "despair". The extinction-despair model is held to provide the promise of a conceptual and empirical model of human depression that is the consequence of withdrawal of reinforcement.

Effects of systemic glutamatergic manipulations on conditioned eyeblink responses and hyperarousal in a rabbit model of post-traumatic stress disorder.

PubMed

Burhans, Lauren B; Smith-Bell, Carrie A; Schreurs, Bernard G

2017-10-01

Glutamatergic dysfunction is implicated in many neuropsychiatric conditions, including post-traumatic stress disorder (PTSD). Glutamate antagonists have shown some utility in treating PTSD symptoms, whereas glutamate agonists may facilitate cognitive behavioral therapy outcomes. We have developed an animal model of PTSD, based on conditioning of the rabbit's eyeblink response, that addresses two key features: conditioned responses (CRs) to cues associated with an aversive event and a form of conditioned hyperarousal referred to as conditioning-specific reflex modification (CRM). The optimal treatment to reduce both CRs and CRM is unpaired extinction. The goals of the study were to examine whether treatment with the N-methyl-D-aspartate glutamate receptor antagonist ketamine could reduce CRs and CRM, and whether the N-methyl-D-aspartate agonist D-cycloserine combined with unpaired extinction treatment could enhance the extinction of both. Administration of a single dose of subanesthetic ketamine had no significant immediate or delayed effect on CRs or CRM. Combining D-cycloserine with a single day of unpaired extinction facilitated extinction of CRs in the short term while having no impact on CRM. These results caution that treatments may improve one aspect of the PTSD symptomology while having no significant effects on other symptoms, stressing the importance of a multiple-treatment approach to PTSD and of animal models that address multiple symptoms.

Estimating the ecology of extinct species with paleoecological data assimilation

NASA Astrophysics Data System (ADS)

Raiho, A.; McLachlan, J. S.; Dietze, M.

2017-12-01

In order to understand long term, unobservable ecosystem processes, ecologists must use both paleoecoloigcal data and ecosystem models. Models parameterize species competitive interactions using modern data. But, modern ecological or physiological observations are not available for extinct species, making it difficult for models to conceptualize their ecology. For instance, American chestnut (Castanea dentata), who played a large role in forests of northeastern US, was decimated by disease to virtual extinction. Since chestnut's demise, defining its ecology has been controversial. Models typically assume that chestnut's ecology was very similar to oak; They parameterize chestnut like oak species. These assumptions are drawn from paleoecological data, but these data are often reported without uncertainty. Since the paleoecological data are often reported without uncertainty, paleoecological data has never been directly incorporated with ecosystem models. We developed a Bayesian statistical model to estimate fractional composition from paleoecological data with uncertainty. Then, we assimilated this data product into an ecosystem model for long term forest succession using a generalized ensemble adjustment filter to determine which species demographic parameters lead to changes in species composition over the last 2,000 years at Harvard Forest. We found that chestnut was strongly negatively correlated with white pine (Pinus strobus) and red oak (Quercus rubra) in the process covariance matrix, suggesting a strong competitive interaction that is not currently understood by models for forest succession. These findings provide support for utilizing a data assimilation framework to ecologically interpret paleoecological data or data products to learn about the ecology of extinct species.

Context-induced relapse after extinction versus punishment: similarities and differences.

PubMed

Marchant, Nathan J; Campbell, Erin J; Pelloux, Yann; Bossert, Jennifer M; Shaham, Yavin

2018-05-24

Results from clinical studies suggest that drug relapse and craving are often provoked by exposure to drug-associated contexts. Since 2002, this phenomenon has been modeled in laboratory animals using the ABA renewal model. In the classical version of this model, rats with a history of drug self-administration in one context (A) undergo extinction in a different context (B) and reinstate (or relapse to) drug seeking after exposure to the original drug-associated context (A). In a more recent version of the model introduced in 2013, the experimental conditions in context A are identical to those used in the classical model, but drug-reinforced responding in context B is suppressed by probabilistic punishment. The punishment-based ABA renewal model is proposed to resemble abstinence in humans, which is often initiated by the desire to avoid the negative consequences of drug use. The goal of our review is to discuss similarities and differences in mechanisms that play a role in suppression of drug seeking in context B and context-induced relapse to drug seeking in context A in the two models. We first describe psychological mechanisms that mediate extinction and punishment of drug-reinforced responding in context B. We then summarize recent findings on brain mechanisms of context-induced relapse of drug seeking after extinction, or punishment-imposed abstinence. These findings demonstrate both similarities and differences in brain mechanisms underlying relapse in the two variations of the ABA renewal model. We conclude by briefly discussing clinical implications of the preclinical studies.

A Memory Retrieval-Extinction Procedure to Prevent Drug Craving and Relapse

PubMed Central

Xue, Yan-Xue; Luo, Yi-Xiao; Wu, Ping; Shi, Hai-Shui; Xue, Li-Fen; Chen, Chen; Zhu, Wei-Li; Ding, Zeng-Bo; Bao, Yan-ping; Shi, Jie; Epstein, David H.; Shaham, Yavin; Lu, Lin

2013-01-01

Drug use and relapse involve learned associations between drug-associated environmental cues and drug effects. Extinction procedures in the clinic can suppress conditioned responses to drug cues, but the extinguished responses typically reemerge after exposure to the drug itself (reinstatement), the drug-associated environment (renewal), or the passage of time (spontaneous recovery). We describe a memory retrieval-extinction procedure that decreases conditioned drug effects and drug seeking in rat models of relapse, and drug craving in abstinent heroin addicts. In rats, daily retrieval of drug-associated memories 10 minutes or 1 hour but not 6 hours before extinction sessions attenuated drug-induced reinstatement, spontaneous recovery, and renewal of conditioned drug effects and drug seeking. In heroin addicts, retrieval of drug-associated memories 10 minutes before extinction sessions attenuated cue-induced heroin craving 1, 30, and 180 days later. The memory retrieval-extinction procedure is a promising nonpharmacological method for decreasing drug craving and relapse during abstinence. PMID:22499948

The threshold of a stochastic delayed SIR epidemic model with temporary immunity

NASA Astrophysics Data System (ADS)

Liu, Qun; Chen, Qingmei; Jiang, Daqing

2016-05-01

This paper is concerned with the asymptotic properties of a stochastic delayed SIR epidemic model with temporary immunity. Sufficient conditions for extinction and persistence in the mean of the epidemic are established. The threshold between persistence in the mean and extinction of the epidemic is obtained. Compared with the corresponding deterministic model, the threshold affected by the white noise is smaller than the basic reproduction number R0 of the deterministic system.

Millennia-long tree-ring records from Tasmania and New Zealand: a basis for modelling climate variability and forcing, past, present and future

NASA Astrophysics Data System (ADS)

Cook, Edward R.; Buckley, Brendan M.; Palmer, Jonathan G.; Fenwick, Pavla; Peterson, Michael J.; Boswijk, Gretel; Fowler, Anthony

2006-10-01

Progress in the development of millennia-long tree-ring chronologies from Australia and New Zealand is reviewed from the perspective of modelling long-term climate variability there. Three tree species have proved successful in this regard: Huon pine (Lagarostrobos franklinii) from Tasmania, silver pine (L. colensoi) from the South Island of New Zealand, and kauri (Agathis australis) from the North Island of New Zealand. Each of these species is very long-lived and produces abundant quantities of well-preserved wood for extending their tree-ring chronologies back several millennia into the past. The growth patterns on these chronologies strongly correlate with both local and regional warm-season temperature changes over significant areas of the Southern Hemisphere (especially Huon and silver pine) and to ENSO variability emanating from the equatorial Pacific region (especially kauri). In addition, there is evidence for significant, band-limited, multi-decadal and centennial timescale variability in the warm-season temperature reconstruction based on Huon pine tree rings that may be related to slowly varying changes in ocean circulation dynamics in the southern Indian Ocean. This suggests the possibility of long-term climate predictability there. Copyright

A multispecies tree ring reconstruction of Potomac River streamflow (950-2001)

NASA Astrophysics Data System (ADS)

Maxwell, R. Stockton; Hessl, Amy E.; Cook, Edward R.; Pederson, Neil

2011-05-01

Mean May-September Potomac River streamflow was reconstructed from 950-2001 using a network of tree ring chronologies (n = 27) representing multiple species. We chose a nested principal components reconstruction method to maximize use of available chronologies backward in time. Explained variance during the period of calibration ranged from 20% to 53% depending on the number and species of chronologies available in each 25 year time step. The model was verified by two goodness of fit tests, the coefficient of efficiency (CE) and the reduction of error statistic (RE). The RE and CE never fell below zero, suggesting the model had explanatory power over the entire period of reconstruction. Beta weights indicated a loss of explained variance during the 1550-1700 period that we hypothesize was caused by the reduction in total number of predictor chronologies and loss of important predictor species. Thus, the reconstruction is strongest from 1700-2001. Frequency, intensity, and duration of drought and pluvial events were examined to aid water resource managers. We found that the instrumental period did not represent adequately the full range of annual to multidecadal variability present in the reconstruction. Our reconstruction of mean May-September Potomac River streamflow was a significant improvement over the Cook and Jacoby (1983) reconstruction because it expanded the seasonal window, lengthened the record by 780 years, and better replicated the mean and variance of the instrumental record. By capitalizing on variable phenologies and tree growth responses to climate, multispecies reconstructions may provide significantly more information about past hydroclimate, especially in regions with low aridity and high tree species diversity.

A numerical study of mixing in stationary, nonpremixed, turbulent reacting flows

NASA Astrophysics Data System (ADS)

Overholt, Matthew Ryan

1998-10-01

In this work a detailed numerical study is made of a statistically-stationary, non-premixed, turbulent reacting model flow known as Periodic Reaction Zones. The mixture fraction-progress variable approach is used, with a mean gradient in the mixture fraction and a model, single-step, reversible, finite-rate thermochemistry, yielding both stationary and local extinction behavior. The passive scalar is studied first, using a statistical forcing scheme to achieve stationarity of the velocity field. Multiple independent direct numerical simulations (DNS) are performed for a wide range of Reynolds numbers with a number of results including a bilinear model for scalar mixing jointly conditioned on the scalar and x2-component of velocity, Gaussian scalar probability density function tails which were anticipated to be exponential, and the quantification of the dissipation of scalar flux. A new deterministic forcing scheme for DNS is then developed which yields reduced fluctuations in many quantities and a more natural evolution of the velocity fields. This forcing method is used for the final portion of this work. DNS results for Periodic Reaction Zones are compared with the Conditional Moment Closure (CMC) model, the Quasi-Equilibrium Distributed Reaction (QEDR) model, and full probability density function (PDF) simulations using the Euclidean Minimum Spanning Tree (EMST) and the Interaction by Exchange with the Mean (IEM) mixing models. It is shown that CMC and QEDR results based on the local scalar dissipation match DNS wherever local extinction is not present. However, due to the large spatial variations of scalar dissipation, and hence local Damkohler number, local extinction is present even when the global Damkohler number is twenty-five times the critical value for extinction. Finally, in the PDF simulations the EMST mixing model closely reproduces CMC and DNS results when local extinction is not present, whereas the IEM model results in large error.

Endolithic microbial model for Martian exobiology: The road to extinction

NASA Technical Reports Server (NTRS)

Oscampo-Friedmann, R.; Friedmann, E. I.

1991-01-01

Martian exobiology is based on the assumption that on early Mars, liquid water was present and that conditions were suitable for the evolution of life. The cause for life to disappear from the surface and the recognizable fingerprints of past microbial activity preserved on Mars are addressed. The Antarctic cryptoendolithic microbial ecosystem as a model for extinction in the deteriorating Martian environment is discussed.

Integrating copper toxicity and climate change to understand extinction risk to two species of pond-breeding anurans.

PubMed

Weir, Scott M; Scott, David E; Salice, Christopher J; Lance, Stacey L

2016-09-01

Chemical contamination is often suggested as an important contributing factor to amphibian population declines, but direct links are rarely reported. Population modeling provides a quantitative method to integrate toxicity data with demographic data to understand the long-term effects of contaminants on population persistence. In this study we use laboratory-derived embryo and larval toxicity data for two anuran species to investigate the potential for toxicity to contribute to population declines. We use the southern toad (Anaxyrus terrestris) and the southern leopard frog (Lithobates sphenocephalus) as model species to investigate copper (Cu) toxicity. We use matrix models to project populations through time and quantify extinction risk (the probability of quasi-extinction in 35 yr). Life-history parameters for toads and frogs were obtained from previously published literature or unpublished data from a long-term (>35 yr) data set. In addition to Cu toxicity, we investigate the role of climate change on amphibian populations by including the probability of early pond drying that results in catastrophic reproductive failure (CRF, i.e., complete mortality of all larval individuals). Our models indicate that CRF is an important parameter for both species as both were unable to persist when CRF probability was >50% for toads or 40% for frogs. Copper toxicity alone did not result in significant effects on extinction risk unless toxicity was very high (>50% reduction in survival parameters). For toads, Cu toxicity and high probability of CRF both resulted in high extinction risk but no synergistic (or greater than additive) effects between the two stressors occurred. For leopard frogs, in the absence of CRF survival was high even under Cu toxicity, but with CRF Cu toxicity increased extinction risk. Our analyses highlight the importance of considering multiple stressors as well as species differences in response to those stressors. Our models were consistently most sensitive to juvenile and adult survival, further suggesting the importance of terrestrial stages to population persistence. Future models will incorporate multiple wetlands with different combinations of stressors to understand if our results for a single wetland result in a population sink within the landscape. © 2016 by the Ecological Society of America.

The extinction properties of forest components

NASA Technical Reports Server (NTRS)

Karam, M. A.; Fung, A. K.; Blanchard, A. J.; Nance, C. E.

1988-01-01

The effect of each forest component on the extinction of electromagnetic waves is investigated by modeling the branches with finite cylinders, deciduous leaves with elliptic disks, and coniferous leaves with needles. The inner field is estimated by the field inside an infinitely long cylinder of similar properties for the branches, and by the Shifrin approximation for the leaves. For each forest component analytic expressions were derived for the extinction cross section via the forward scattering theorem and for ohmic and scattered losses. For branches, the variation of the extinction cross section obtained via the forward scattering theorem is illustrated numerically as a function of the branch radius and the imaginery part of its dielectric constant. It is compared with the measurements from a single branch. For the leaves, the forward scattering theorem gives value for the extinction cross section equal to the ohmic cross section.

Phase function, backscatter, extinction, and absorption for standard radiation atmosphere and El Chichon aerosol models at visible and near-infrared wavelengths

NASA Technical Reports Server (NTRS)

Whitlock, C. H.; Suttles, J. T.; Lecroy, S. R.

1985-01-01

Tabular values of phase function, Legendre polynominal coefficients, 180 deg backscatter, and extinction cross section are given for eight wavelengths in the atmospheric windows between 0.4 and 2.2 microns. Also included are single scattering albedo, asymmetry factor, and refractive indices. These values are based on Mie theory calculations for the standard rediation atmospheres (continental, maritime, urban, unperturbed stratospheric, volcanic, upper atmospheric, soot, oceanic, dust, and water-soluble) assest measured volcanic aerosols at several time intervals following the El Chichon eruption. Comparisons of extinction to 180 deg backscatter for different aerosol models are presented and related to lidar data.

A model describing the effect of sex-reversed YY fish in an established wild population: The use of a Trojan Y chromosome to cause extinction of an introduced exotic species.

PubMed

Gutierrez, Juan B; Teem, John L

2006-07-21

A novel means of inducing extinction of an exotic fish population is proposed using a genetic approach to shift the ratio of male to females within a population. In the proposed strategy, sex-reversed fish containing two Y chromosomes are introduced into a normal fish population. These YY fish result in the production of a disproportionate number of male fish in subsequent generations. Mathematical modeling of the system following introduction of YY fish at a constant rate reveals that female fish decline in numbers over time, leading to eventual extinction of the population.

Quantitative traits and diversification.

PubMed

FitzJohn, Richard G

2010-12-01

Quantitative traits have long been hypothesized to affect speciation and extinction rates. For example, smaller body size or increased specialization may be associated with increased rates of diversification. Here, I present a phylogenetic likelihood-based method (quantitative state speciation and extinction [QuaSSE]) that can be used to test such hypotheses using extant character distributions. This approach assumes that diversification follows a birth-death process where speciation and extinction rates may vary with one or more traits that evolve under a diffusion model. Speciation and extinction rates may be arbitrary functions of the character state, allowing much flexibility in testing models of trait-dependent diversification. I test the approach using simulated phylogenies and show that a known relationship between speciation and a quantitative character could be recovered in up to 80% of the cases on large trees (500 species). Consistent with other approaches, detecting shifts in diversification due to differences in extinction rates was harder than when due to differences in speciation rates. Finally, I demonstrate the application of QuaSSE to investigate the correlation between body size and diversification in primates, concluding that clade-specific differences in diversification may be more important than size-dependent diversification in shaping the patterns of diversity within this group.

Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

NASA Astrophysics Data System (ADS)

Lim, Wanggi; Carey, Sean J.

2014-07-01

We present photometric and spectroscopic tests of MIR to FIR extinction laws toward IRDC G028.36+00.07, a potential site of massive star formation. Lim & Tan (2014, hereafter LT14) developed methods of FIR extinction mapping of this source using Spitzer-MIPS 24 micron and Herschel-PACS 70 micron images, and extending the MIR 8 micron mapping methods of (Butler & Tan 2012, hereafter BT12), finding evidence for grain growth in the highest mass surface density regions. Here we present initial results of spectroscopic infrared extinction (SIREX) mapping using Spitzer-IRS (14 to 38 micron) data of the same IRDC. These methods allow us to measure the SED of the diffuse Galactic ISM, which we compare to theoretical models of Draine & Li (2007), as well as to search for opacity law variations with mass surface density within the IRDC. By comparison with theoretical dust models, e.g., Ossenkopf & Henning (1994) and Ormel et al. (2011), we are able to search for compositional signatures of the grain ices, such as water and methanol. We find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

Cognitive Enhancers for Facilitating Drug Cue Extinction: Insights from Animal Models

PubMed Central

Nic Dhonnchadha, Bríd Áine; Kantak, Kathleen M.

2011-01-01

Given the success of cue exposure (extinction) therapy combined with a cognitive enhancer for reducing anxiety, it is anticipated that this approach will prove more efficacious than exposure therapy alone in preventing relapse in individuals with substance use disorders. Several factors may undermine the efficacy of exposure therapy for substance use disorders, but we suspect that neurocognitive impairments associated with chronic drug use are an important contributing factor. Numerous insights on these issues are gained from research using animal models of addiction. In this review, the relationship between brain sites whose learning, memory and executive functions are impaired by chronic drug use and brain sites that are important for effective drug cue extinction learning is explored first. This is followed by an overview of animal research showing improved treatment outcome for drug addiction (e.g. alcohol, amphetamine, cocaine, heroin) when explicit extinction training is conducted in combination with acute dosing of a cognitive-enhancing drug. The mechanism by which cognitive enhancers are thought to exert their benefits is by facilitating consolidation of drug cue extinction memory after activation of glutamatergic receptors. Based on the encouraging work in animals, factors that may be important for the treatment of drug addiction are considered. PMID:21295059

On Galactic Density Modeling in the Presence of Dust Extinction

NASA Astrophysics Data System (ADS)

Bovy, Jo; Rix, Hans-Walter; Green, Gregory M.; Schlafly, Edward F.; Finkbeiner, Douglas P.

2016-02-01

Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic midplane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of small-scale structure in the extinction. This formalism demonstrates that the spatially complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a low-pass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical and efficient method for properly taking the effect of extinction into account in analyses of Galactic structure through an effective selection function. We illustrate its use with the selection function of red-clump stars in APOGEE using and comparing a variety of current 3D extinction maps.

[Analysis of visible extinction spectrum of particle system and selection of optimal wavelength].

PubMed

Sun, Xiao-gang; Tang, Hong; Yuan, Gui-bin

2008-09-01

In the total light scattering particle sizing technique, the extinction spectrum of particle system contains some information about the particle size and refractive index. The visible extinction spectra of the common monomodal and biomodal R-R particle size distribution were computed, and the variation in the visible extinction spectrum with the particle size and refractive index was analyzed. The corresponding wavelengths were selected as the measurement wavelengths at which the second order differential extinction spectrum was discontinuous. Furthermore, the minimum and the maximum wavelengths in the visible region were also selected as the measurement wavelengths. The genetic algorithm was used as the inversion method under the dependent model The computer simulation and experiments illustrate that it is feasible to make an analysis of the extinction spectrum and use this selection method of the optimal wavelength in the total light scattering particle sizing. The rough contour of the particle size distribution can be determined after the analysis of visible extinction spectrum, so the search range of the particle size parameter is reduced in the optimal algorithm, and then a more accurate inversion result can be obtained using the selection method. The inversion results of monomodal and biomodal distribution are all still satisfactory when 1% stochastic noise is put in the transmission extinction measurement values.

An allometric approach to quantify the extinction vulnerability of birds and mammals.

PubMed

Hilbers, J P; Schipper, A M; Hendriks, A J; Verones, F; Pereira, H M; Huijbregts, M A J

2016-03-01

Methods to quantify the vulnerability of species to extinction are typically limited by the availability of species-specific input data pertaining to life-history characteristics and population dynamics. This lack of data hampers global biodiversity assessments and conservation planning. Here, we developed a new framework that systematically quantifies extinction risk based on allometric relationships between various wildlife demographic parameters and body size. These allometric relationships have a solid theoretical and ecological foundation. Extinction risk indicators included are (1) the probability of extinction, (2) the mean time to extinction, and (3) the critical patch size. We applied our framework to assess the global extinction vulnerability of terrestrial carnivorous and non-carnivorous birds and mammals. Irrespective of the indicator used, large-bodied species were found to be more vulnerable to extinction than their smaller counterparts. The patterns with body size were confirmed for all species groups by a comparison with IUCN data on the proportion of extant threatened species: the models correctly predicted a multimodal distribution with body size for carnivorous birds and a monotonic distribution for mammals and non-carnivorous birds. Carnivorous mammals were found to have higher extinction risks than non-carnivores, while birds were more prone to extinction than mammals. These results are explained by the allometric relationships, predicting the vulnerable species groups to have lower intrinsic population growth rates, smaller population sizes, lower carrying capacities, or larger dispersal distances, which, in turn, increase the importance of losses due to environmental stochastic effects and dispersal activities. Our study is the first to integrate population viability analysis and allometry into a novel, process-based framework that is able to quantify extinction risk of a large number of species without requiring data-intensive, species-specific information. The framework facilitates the estimation of extinction vulnerabilities of data-deficient species. It may be applied to forecast extinction vulnerability in response to a changing environment, by incorporating quantitative relationships between wildlife demographic parameters and environmental drivers like habitat alteration, climate change, or hunting.

Extinction Risk and Diversification Are Linked in a Plant Biodiversity Hotspot

PubMed Central

Davies, T. Jonathan; Smith, Gideon F.; Bellstedt, Dirk U.; Boatwright, James S.; Bytebier, Benny; Cowling, Richard M.; Forest, Félix; Harmon, Luke J.; Muasya, A. Muthama; Schrire, Brian D.; Steenkamp, Yolande; van der Bank, Michelle; Savolainen, Vincent

2011-01-01

It is widely recognized that we are entering an extinction event on a scale approaching the mass extinctions seen in the fossil record. Present-day rates of extinction are estimated to be several orders of magnitude greater than background rates and are projected to increase further if current trends continue. In vertebrates, species traits, such as body size, fecundity, and geographic range, are important predictors of vulnerability. Although plants are the basis for life on Earth, our knowledge of plant extinctions and vulnerabilities is lagging. Here, we disentangle the underlying drivers of extinction risk in plants, focusing on the Cape of South Africa, a global biodiversity hotspot. By comparing Red List data for the British and South African floras, we demonstrate that the taxonomic distribution of extinction risk differs significantly between regions, inconsistent with a simple, trait-based model of extinction. Using a comprehensive phylogenetic tree for the Cape, we reveal a phylogenetic signal in the distribution of plant extinction risks but show that the most threatened species cluster within short branches at the tips of the phylogeny—opposite to trends in mammals. From analyzing the distribution of threatened species across 11 exemplar clades, we suggest that mode of speciation best explains the unusual phylogenetic structure of extinction risks in plants of the Cape. Our results demonstrate that explanations for elevated extinction risk in plants of the Cape flora differ dramatically from those recognized for vertebrates. In the Cape, extinction risk is higher for young and fast-evolving plant lineages and cannot be explained by correlations with simple biological traits. Critically, we find that the most vulnerable plant species are nonetheless marching towards extinction at a more rapid pace but, surprisingly, independently from anthropogenic effects. Our results have important implications for conservation priorities and cast doubts on the utility of current Red List criteria for plants in regions such as the Cape, where speciation has been rapid, if our aim is to maximize the preservation of the tree-of-life. PMID:21629678

Fossil biogeography: a new model to infer dispersal, extinction and sampling from palaeontological data.

PubMed

Silvestro, Daniele; Zizka, Alexander; Bacon, Christine D; Cascales-Miñana, Borja; Salamin, Nicolas; Antonelli, Alexandre

2016-04-05

Methods in historical biogeography have revolutionized our ability to infer the evolution of ancestral geographical ranges from phylogenies of extant taxa, the rates of dispersals, and biotic connectivity among areas. However, extant taxa are likely to provide limited and potentially biased information about past biogeographic processes, due to extinction, asymmetrical dispersals and variable connectivity among areas. Fossil data hold considerable information about past distribution of lineages, but suffer from largely incomplete sampling. Here we present a new dispersal-extinction-sampling (DES) model, which estimates biogeographic parameters using fossil occurrences instead of phylogenetic trees. The model estimates dispersal and extinction rates while explicitly accounting for the incompleteness of the fossil record. Rates can vary between areas and through time, thus providing the opportunity to assess complex scenarios of biogeographic evolution. We implement the DES model in a Bayesian framework and demonstrate through simulations that it can accurately infer all the relevant parameters. We demonstrate the use of our model by analysing the Cenozoic fossil record of land plants and inferring dispersal and extinction rates across Eurasia and North America. Our results show that biogeographic range evolution is not a time-homogeneous process, as assumed in most phylogenetic analyses, but varies through time and between areas. In our empirical assessment, this is shown by the striking predominance of plant dispersals from Eurasia into North America during the Eocene climatic cooling, followed by a shift in the opposite direction, and finally, a balance in biotic interchange since the middle Miocene. We conclude by discussing the potential of fossil-based analyses to test biogeographic hypotheses and improve phylogenetic methods in historical biogeography. © 2016 The Author(s).

Association of extinction risk of saproxylic beetles with ecological degradation of forests in Europe.

PubMed

Seibold, Sebastian; Brandl, Roland; Buse, Jörn; Hothorn, Torsten; Schmidl, Jürgen; Thorn, Simon; Müller, Jörg

2015-04-01

To reduce future loss of biodiversity and to allocate conservation funds effectively, the major drivers behind large-scale extinction processes must be identified. A promising approach is to link the red-list status of species and specific traits that connect species of functionally important taxa or guilds to resources they rely on. Such traits can be used to detect the influence of anthropogenic ecosystem changes and conservation efforts on species, which allows for practical recommendations for conservation. We modeled the German Red List categories as an ordinal index of extinction risk of 1025 saproxylic beetles with a proportional-odds linear mixed-effects model for ordered categorical responses. In this model, we estimated fixed effects for intrinsic traits characterizing species biology, required resources, and distribution with phylogenetically correlated random intercepts. The model also allowed predictions of extinction risk for species with no red-list category. Our model revealed a higher extinction risk for lowland and large species as well as for species that rely on wood of large diameter, broad-leaved trees, or open canopy. These results mirror well the ecological degradation of European forests over the last centuries caused by modern forestry, that is the conversion of natural broad-leaved forests to dense conifer-dominated forests and the loss of old growth and dead wood. Therefore, conservation activities aimed at saproxylic beetles in all types of forests in Central and Western Europe should focus on lowlands, and habitat management of forest stands should aim at increasing the amount of dead wood of large diameter, dead wood of broad-leaved trees, and dead wood in sunny areas. © 2014 Society for Conservation Biology.

MODELING THE ANOMALY OF SURFACE NUMBER DENSITIES OF GALAXIES ON THE GALACTIC EXTINCTION MAP DUE TO THEIR FIR EMISSION CONTAMINATION

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

Kashiwagi, Toshiya; Suto, Yasushi; Taruya, Atsushi

The most widely used Galactic extinction map is constructed assuming that the observed far-infrared (FIR) fluxes come entirely from Galactic dust. According to the earlier suggestion by Yahata et al., we consider how FIR emission of galaxies affects the SFD map. We first compute the surface number density of Sloan Digital Sky Survey (SDSS) DR7 galaxies as a function of the r-band extinction, A {sub r,} {sub SFD}. We confirm that the surface densities of those galaxies positively correlate with A {sub r,} {sub SFD} for A {sub r,} {sub SFD} < 0.1, as first discovered by Yahata et al.more » for SDSS DR4 galaxies. Next we construct an analytical model to compute the surface density of galaxies, taking into account the contamination of their FIR emission. We adopt a log-normal probability distribution for the ratio of 100 μm and r-band luminosities of each galaxy, y ≡ (νL){sub 100} {sub μm}/(νL) {sub r}. Then we search for the mean and rms values of y that fit the observed anomaly, using the analytical model. The required values to reproduce the anomaly are roughly consistent with those measured from the stacking analysis of SDSS galaxies. Due to the limitation of our statistical modeling, we are not yet able to remove the FIR contamination of galaxies from the extinction map. Nevertheless, the agreement with the model prediction suggests that the FIR emission of galaxies is mainly responsible for the observed anomaly. Whereas the corresponding systematic error in the Galactic extinction map is 0.1-1 mmag, it is directly correlated with galaxy clustering and thus needs to be carefully examined in precision cosmology.« less

Human impacts on the rates of recent, present, and future bird extinctions.

PubMed

Pimm, Stuart; Raven, Peter; Peterson, Alan; Sekercioglu, Cagan H; Ehrlich, Paul R

2006-07-18

Unqualified, the statement that approximately 1.3% of the approximately 10,000 presently known bird species have become extinct since A.D. 1500 yields an estimate of approximately 26 extinctions per million species per year (or 26 E/MSY). This is higher than the benchmark rate of approximately 1 E/MSY before human impacts, but is a serious underestimate. First, Polynesian expansion across the Pacific also exterminated many species well before European explorations. Second, three factors increase the rate: (i) The number of known extinctions before 1800 is increasing as taxonomists describe new species from skeletal remains. (ii) One should calculate extinction rates over the years since taxonomists described the species. Most bird species were described only after 1850. (iii) Some species are probably extinct; there is reluctance to declare them so prematurely. Thus corrected, recent extinction rates are approximately 100 E/MSY. In the last decades, the rate is <50 E/MSY, but would be 150 E/MSY were it not for conservation efforts. Increasing numbers of extinctions are on continents, whereas previously most were on islands. We predict a 21st century rate of approximately 1,000 E/MSY. Extinction threatens 12% of bird species; another 12% have small geographical ranges and live where human actions rapidly destroy their habitats. If present forest losses continue, extinction rates will reach 1,500 E/MSY by the century's end. Invasive species, expanding human technologies, and global change will harm additional species. Birds are poor models for predicting extinction rates for other taxa. Human actions threaten higher fractions of other well known taxa than they do birds. Moreover, people take special efforts to protect birds.

High frequency of functional extinctions in ecological networks.

PubMed

Säterberg, Torbjörn; Sellman, Stefan; Ebenman, Bo

2013-07-25

Intensified exploitation of natural populations and habitats has led to increased mortality rates and decreased abundances of many species. There is a growing concern that this might cause critical abundance thresholds of species to be crossed, with extinction cascades and state shifts in ecosystems as a consequence. When increased mortality rate and decreased abundance of a given species lead to extinction of other species, this species can be characterized as functionally extinct even though it still exists. Although such functional extinctions have been observed in some ecosystems, their frequency is largely unknown. Here we use a new modelling approach to explore the frequency and pattern of functional extinctions in ecological networks. Specifically, we analytically derive critical abundance thresholds of species by increasing their mortality rates until an extinction occurs in the network. Applying this approach on natural and theoretical food webs, we show that the species most likely to go extinct first is not the one whose mortality rate is increased but instead another species. Indeed, up to 80% of all first extinctions are of another species, suggesting that a species' ecological functionality is often lost before its own existence is threatened. Furthermore, we find that large-bodied species at the top of the food chains can only be exposed to small increases in mortality rate and small decreases in abundance before going functionally extinct compared to small-bodied species lower in the food chains. These results illustrate the potential importance of functional extinctions in ecological networks and lend strong support to arguments advocating a more community-oriented approach in conservation biology, with target levels for populations based on ecological functionality rather than on mere persistence.

Extinction of conditioned opiate withdrawal in rats is blocked by intracerebroventricular infusion of an NMDA receptor antagonist.

PubMed

Coleman, Brian R; Carlezon, William A; Myers, Karyn M

2013-04-29

Maladaptive conditioned responses (CRs) contribute to psychiatric disorders including anxiety disorders and addiction. Methods of reducing these CRs have been considered as possible therapeutic approaches. One such method is extinction, which involves exposure to CR-eliciting cues in the absence of the event they once predicted. In animal models, extinction reduces both fear and addiction-related CRs, and in humans, extinction-based cue exposure therapy (CET) reduces fear CRs. However, CET is less effective in drug addicts, for reasons that are not clear. Increased understanding of the neurobiology of extinction of drug-related CRs as compared to fear CRs may help illuminate this issue. Here, we examine the N-methyl-d-aspartate (NMDA) receptor-dependence of extinction of conditioned opiate withdrawal in rats. Using a place conditioning paradigm, we trained morphine-dependent rats to associate an environment with naloxone-precipitated withdrawal. We then extinguished that association by returning the rats repeatedly to the environment in the absence of acute withdrawal. In some rats we administered the NMDA receptor antagonist d,l-2-amino-5-phosphovaleric acid (AP5) intracerebroventricularly immediately prior to extinction training. In a subsequent test session, these rats avoided the formerly naloxone-paired environment, similar to rats that had not undergone extinction training. By contrast, rats that received vehicle prior to extinction training did not avoid the formerly naloxone-paired environment. This finding indicates that extinction of a drug-related CR (conditioned opiate withdrawal) is dependent on NMDA receptors, similar to extinction of conditioned fear. The locus of the critical NMDA receptors is unclear but may include basolateral amygdala and/or medial prefrontal cortex. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

Stress exposure prior to fear acquisition interacts with estradiol status to alter recall of fear extinction in humans.

PubMed

Antov, Martin I; Stockhorst, Ursula

2014-11-01

Classical fear acquisition and extinction are important models for the etiology and treatment of anxiety disorders such as posttraumatic stress disorder (PTSD). Women are at a higher risk for PTSD than men. Levels of circulating 17-β estradiol (E2) in women have been linked to deficits in fear extinction and extinction recall. In PTSD, fear learning coincides with acute traumatic stress. However, little is known about the possible interaction between stress exposure and hormone status on fear acquisition and extinction learning. In a 2-day, 2×3 between-subjects design with healthy participants, we examined the effects of stress (psychosocial stressor vs. control, placed 45 min prior to conditioning) and natural E2-status on differential fear conditioning, covering fear acquisition, immediate extinction (Day 1), and 24h-delayed extinction recall (Day 2). To operationalize E2-status, we compared women in the early follicular phase (EF) of their menstrual cycle (low E2, low progesterone plasma levels), women in the midcycle phase (MC, high E2, low progesterone), and men. Conditioning was indicated by differential skin conductance responses. We found an interaction between stress exposure and natural E2-status in women only: In MC-women, extinction recall on Day 2 (24h after initial extinction training) was better when fear acquisition had been preceded by stress. In EF-women, the inverse was true. We show that extinction recall of conditioned fear acquired after stress depends on estrogen status in women. Therefore, extinction-based exposure therapy in free-cycling female anxiety patients should take cycle status into account. Copyright © 2014 Elsevier Ltd. All rights reserved.

Enhanced extinction of cocaine seeking in brain-derived neurotrophic factor Val66Met knock-in mice.

PubMed

Briand, Lisa A; Lee, Francis S; Blendy, Julie A; Pierce, R Christopher

2012-03-01

The Val66Met polymorphism in the brain-derived neurotropic factor (BDNF) gene results in alterations in fear extinction behavior in both human populations and mouse models. However, it is not clear whether this polymorphism plays a similar role in extinction of appetitive behaviors. Therefore, we examined operant learning and extinction of both food and cocaine self-administration behavior in an inbred genetic knock-in mouse strain expressing the variant Bdnf. These mice provide a unique opportunity to relate alterations in aversive and appetitive extinction learning as well as provide insight into how human genetic variation can lead to differences in behavior. BDNF(Met/Met) mice exhibited a severe deficit in operant learning as demonstrated by an inability to learn the food self-administration task. Therefore, extinction experiments were performed comparing wildtype (BDNF(Val/Val) ) animals to mice heterozygous for the Met allele (BDNF(Val/Met) ), which did not differ in food or cocaine self-administration behavior. In contrast to the deficit in fear extinction previously demonstrated in these mice, we found that BDNF(Val/Met) mice exhibited more rapid extinction of cocaine responding compared to wildtype mice. No differences were found between the genotypes in the extinction of food self-administration behavior or the reinstatement of cocaine seeking, indicating that the effect is specific to extinction of cocaine responding. These results suggest that the molecular mechanisms underlying aversive and appetitive extinction are distinct from one another and BDNF may play opposing roles in the two phenomena. © 2012 The Authors. European Journal of Neuroscience © 2012 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.

Human impacts on the rates of recent, present, and future bird extinctions

PubMed Central

Pimm, Stuart; Raven, Peter; Peterson, Alan; Şekercioğlu, Çağan H.; Ehrlich, Paul R.

2006-01-01

Unqualified, the statement that ≈1.3% of the ≈10,000 presently known bird species have become extinct since A.D. 1500 yields an estimate of ≈26 extinctions per million species per year (or 26 E/MSY). This is higher than the benchmark rate of ≈1 E/MSY before human impacts, but is a serious underestimate. First, Polynesian expansion across the Pacific also exterminated many species well before European explorations. Second, three factors increase the rate: (i) The number of known extinctions before 1800 is increasing as taxonomists describe new species from skeletal remains. (ii) One should calculate extinction rates over the years since taxonomists described the species. Most bird species were described only after 1850. (iii) Some species are probably extinct; there is reluctance to declare them so prematurely. Thus corrected, recent extinction rates are ≈100 E/MSY. In the last decades, the rate is <50 E/MSY, but would be 150 E/MSY were it not for conservation efforts. Increasing numbers of extinctions are on continents, whereas previously most were on islands. We predict a 21st century rate of ≈1,000 E/MSY. Extinction threatens 12% of bird species; another 12% have small geographical ranges and live where human actions rapidly destroy their habitats. If present forest losses continue, extinction rates will reach 1,500 E/MSY by the century’s end. Invasive species, expanding human technologies, and global change will harm additional species. Birds are poor models for predicting extinction rates for other taxa. Human actions threaten higher fractions of other well known taxa than they do birds. Moreover, people take special efforts to protect birds. PMID:16829570

Extinction of conditioned opiate withdrawal in rats is blocked by intracerebroventricular infusion of an NMDA receptor antagonist

PubMed Central

Coleman, Brian R.; Carlezon, William A.; Myers, Karyn M.

2015-01-01

Maladaptive conditioned responses (CRs) contribute to psychiatric disorders including anxiety disorders and addiction. Methods of reducing these CRs have been considered as possible therapeutic approaches. One such method is extinction, which involves exposure to CR-eliciting cues in the absence of the event they once predicted. In animal models, extinction reduces both fear and addiction-related CRs, and in humans, extinction-based cue exposure therapy (CET) reduces fear CRs. However, CET is less effective in drug addicts, for reasons that are not clear. Increased understanding of the neurobiology of extinction of drug-related CRs as compared to fear CRs may help illuminate this issue. Here, we examine the N-methyl-D-aspartate (NMDA) receptor-dependence of extinction of conditioned opiate withdrawal in rats. Using a place conditioning paradigm, we trained morphine-dependent rats to associate an environment with naloxone-precipitated withdrawal. We then extinguished that association by returning the rats repeatedly to the environment in the absence of acute withdrawal. In some rats we administered the NMDA receptor antagonist D,L-2-amino-5-phosphovaleric acid (AP5) intracerebroventricularly immediately prior to extinction training. In a subsequent test session, these rats avoided the formerly naloxone-paired environment, similar to rats that had not undergone extinction training. By contrast, rats that received vehicle prior to extinction training did not avoid the formerly naloxone-paired environment. This finding indicates that extinction of a drug-related CR (conditioned opiate withdrawal) is dependent on NMDA receptors, similar to extinction of conditioned fear. The locus of the critical NMDA receptors is unclear but may include basolateral amygdala and/or medial prefrontal cortex. PMID:23416323

Colonization and extinction in dynamic habitats: an occupancy approach for a Great Plains stream fish assemblage.

PubMed

Falke, Jeffrey A; Bailey, Larissa L; Fausch, Kurt D; Bestgen, Kevin R

2012-04-01

Despite the importance of habitat in determining species distribution and persistence, habitat dynamics are rarely modeled in studies of metapopulations. We used an integrated habitat-occupancy model to simultaneously quantify habitat change, site fidelity, and local colonization and extinction rates for larvae of a suite of Great Plains stream fishes in the Arikaree River, eastern Colorado, USA, across three years. Sites were located along a gradient of flow intermittency and groundwater connectivity. Hydrology varied across years: the first and third being relatively wet and the second dry. Despite hydrologic variation, our results indicated that site suitability was random from one year to the next. Occupancy probabilities were also independent of previous habitat and occupancy state for most species, indicating little site fidelity. Climate and groundwater connectivity were important drivers of local extinction and colonization, but the importance of groundwater differed between periods. Across species, site extinction probabilities were highest during the transition from wet to dry conditions (range: 0.52-0.98), and the effect of groundwater was apparent with higher extinction probabilities for sites not fed by groundwater. Colonization probabilities during this period were relatively low for both previously dry sites (range: 0.02-0.38) and previously wet sites (range: 0.02-0.43). In contrast, no sites dried or remained dry during the transition from dry to wet conditions, yielding lower but still substantial extinction probabilities (range: 0.16-0.63) and higher colonization probabilities (range: 0.06-0.86), with little difference among sites with and without groundwater. This approach of jointly modeling both habitat change and species occupancy will likely be useful to incorporate effects of dynamic habitat on metapopulation processes and to better inform appropriate conservation actions.

Competitive displacement among post-Paleozoic cyclostome and cheilostome bryozoans

NASA Technical Reports Server (NTRS)

Sepkoski, J. J. Jr; McKinney, F. K.; Lidgard, S.; Sepkoski JJ, J. r. (Principal Investigator)

2000-01-01

Encrusting bryozoans provide one of the few systems in the fossil record in which ecological competition can be observed directly at local scales. The macroevolutionary history of diversity of cyclostome and cheilostome bryozoans is consistent with a coupled-logistic model of clade displacement predicated on species within clades interacting competitively. The model matches observed diversity history if the model is perturbed by a mass extinction with a position and magnitude analogous to the Cretaceous/Tertiary boundary event, Although it is difficult to measure all parameters in the model from fossil data, critical factors are intrinsic rates of extinction, which can be measured. Cyclostomes maintained a rather low rate of extinction, and the model solutions predict that they would lose diversity only slowly as competitively superior species of cheilostomes diversified into their environment. Thus, the microecological record of preserved competitive interactions between cyclostome and cheilostome bryozoans and the macroevolutionary record of global diversity are consistent in regard to competition as a significant influence on diversity histories of post-Paleozoic bryozoans.

On the choice of statistical models for estimating occurrence and extinction from animal surveys

USGS Publications Warehouse

Dorazio, R.M.

2007-01-01

In surveys of natural animal populations the number of animals that are present and available to be detected at a sample location is often low, resulting in few or no detections. Low detection frequencies are especially common in surveys of imperiled species; however, the choice of sampling method and protocol also may influence the size of the population that is vulnerable to detection. In these circumstances, probabilities of animal occurrence and extinction will generally be estimated more accurately if the models used in data analysis account for differences in abundance among sample locations and for the dependence between site-specific abundance and detection. Simulation experiments are used to illustrate conditions wherein these types of models can be expected to outperform alternative estimators of population site occupancy and extinction. ?? 2007 by the Ecological Society of America.

Extinction threshold for spatial forest dynamics with height structure.

PubMed

Garcia-Domingo, Josep L; Saldaña, Joan

2011-05-07

We present a pair-approximation model for spatial forest dynamics defined on a regular lattice. The model assumes three possible states for a lattice site: empty (gap site), occupied by an immature tree, and occupied by a mature tree, and considers three nonlinearities in the dynamics associated to the processes of light interference, gap expansion, and recruitment. We obtain an expression of the basic reproduction number R(0) which, in contrast to the one obtained under the mean-field approach, uses information about the spatial arrangement of individuals close to extinction. Moreover, we analyze the corresponding survival-extinction transition of the forest and the spatial correlations among gaps, immature and mature trees close to this critical point. Predictions of the pair-approximation model are compared with those of a cellular automaton. Copyright © 2011 Elsevier Ltd. All rights reserved.

Drivers and hotspots of extinction risk in marine mammals.

PubMed

Davidson, Ana D; Boyer, Alison G; Kim, Hwahwan; Pompa-Mansilla, Sandra; Hamilton, Marcus J; Costa, Daniel P; Ceballos, Gerardo; Brown, James H

2012-02-28

The world's oceans are undergoing profound changes as a result of human activities. However, the consequences of escalating human impacts on marine mammal biodiversity remain poorly understood. The International Union for the Conservation of Nature (IUCN) identifies 25% of marine mammals as at risk of extinction, but the conservation status of nearly 40% of marine mammals remains unknown due to insufficient data. Predictive models of extinction risk are crucial to informing present and future conservation needs, yet such models have not been developed for marine mammals. In this paper, we: (i) used powerful machine-learning and spatial-modeling approaches to understand the intrinsic and extrinsic drivers of marine mammal extinction risk; (ii) used this information to predict risk across all marine mammals, including IUCN "Data Deficient" species; and (iii) conducted a spatially explicit assessment of these results to understand how risk is distributed across the world's oceans. Rate of offspring production was the most important predictor of risk. Additional predictors included taxonomic group, small geographic range area, and small social group size. Although the interaction of both intrinsic and extrinsic variables was important in predicting risk, overall, intrinsic traits were more important than extrinsic variables. In addition to the 32 species already on the IUCN Red List, our model identified 15 more species, suggesting that 37% of all marine mammals are at risk of extinction. Most at-risk species occur in coastal areas and in productive regions of the high seas. We identify 13 global hotspots of risk and show how they overlap with human impacts and Marine Protected Areas.

Testing metapopulation concepts: effects of patch characteristics and neighborhood occupancy on the dynamics of an endangered lagomorph

USGS Publications Warehouse

Eaton, Mitchell J.; Hughes, Phillip T.; Hines, James E.; Nichols, James D.

2014-01-01

Metapopulation ecology is a field that is richer in theory than in empirical results. Many existing empirical studies use an incidence function approach based on spatial patterns and key assumptions about extinction and colonization rates. Here we recast these assumptions as hypotheses to be tested using 18 years of historic detection survey data combined with four years of data from a new monitoring program for the Lower Keys marsh rabbit. We developed a new model to estimate probabilities of local extinction and colonization in the presence of nondetection, while accounting for estimated occupancy levels of neighboring patches. We used model selection to identify important drivers of population turnover and estimate the effective neighborhood size for this system. Several key relationships related to patch size and isolation that are often assumed in metapopulation models were supported: patch size was negatively related to the probability of extinction and positively related to colonization, and estimated occupancy of neighboring patches was positively related to colonization and negatively related to extinction probabilities. This latter relationship suggested the existence of rescue effects. In our study system, we inferred that coastal patches experienced higher probabilities of extinction and colonization than interior patches. Interior patches exhibited higher occupancy probabilities and may serve as refugia, permitting colonization of coastal patches following disturbances such as hurricanes and storm surges. Our modeling approach should be useful for incorporating neighbor occupancy into future metapopulation analyses and in dealing with other historic occupancy surveys that may not include the recommended levels of sampling replication.

Enhanced THz extinction in arrays of resonant semiconductor particles.

PubMed

Schaafsma, Martijn C; Georgiou, Giorgos; Rivas, Jaime Gómez

2015-09-21

We demonstrate experimentally the enhanced THz extinction by periodic arrays of resonant semiconductor particles. This phenomenon is explained in terms of the radiative coupling of localized resonances with diffractive orders in the plane of the array (Rayleigh anomalies). The experimental results are described by numerical calculations using a coupled dipole model and by Finite-Difference in Time-Domain simulations. An optimum particle size for enhancing the extinction efficiency of the array is found. This optimum is determined by the frequency detuning between the localized resonances in the individual particles and the Rayleigh anomaly. The extinction calculations and measurements are also compared to near-field simulations illustrating the optimum particle size for the enhancement of the near-field.

Extinction times of epidemic outbreaks in networks.

PubMed

Holme, Petter

2013-01-01

In the Susceptible-Infectious-Recovered (SIR) model of disease spreading, the time to extinction of the epidemics happens at an intermediate value of the per-contact transmission probability. Too contagious infections burn out fast in the population. Infections that are not contagious enough die out before they spread to a large fraction of people. We characterize how the maximal extinction time in SIR simulations on networks depend on the network structure. For example we find that the average distances in isolated components, weighted by the component size, is a good predictor of the maximal time to extinction. Furthermore, the transmission probability giving the longest outbreaks is larger than, but otherwise seemingly independent of, the epidemic threshold.

Fear conditioning and extinction across development: evidence from human studies and animal models.

PubMed

Shechner, Tomer; Hong, Melanie; Britton, Jennifer C; Pine, Daniel S; Fox, Nathan A

2014-07-01

The ability to differentiate danger and safety through associative processes emerges early in life. Understanding the mechanisms underlying associative learning of threat and safety can clarify the processes that shape development of normative fears and pathological anxiety. Considerable research has used fear conditioning and extinction paradigms to delineate underlying mechanisms in animals and human adults; however, little is known about these mechanisms in children and adolescents. The current paper summarizes the empirical data on the development of fear conditioning and extinction. It reviews methodological considerations and future directions for research on fear conditioning and extinction in pediatric populations. Copyright © 2014 Elsevier B.V. All rights reserved.

Biological age and sex-related declines in physical activity during adolescence.

PubMed

Cairney, John; Veldhuizen, Scott; Kwan, Matthew; Hay, John; Faught, Brent E

2014-04-01

Sex differences in the rate of decline in physical activity (PA) are most pronounced during adolescence. However, once boys and girls are aligned on biological age, sex differences in the patterns of PA become attenuated. The aim of this study was to test whether biological maturation can account for sex differences in participation in PA over time from late childhood to early adolescence. A prospective cohort of children (N = 2100; 1064 boys) was followed from ages 11 to 14 yr, with repeated assessments of PA and anthropometry. Self-reported participation in organized and free play activities was used to track participation in PA. Biological age was measured using an estimate of years to attainment of peak height velocity. Mixed-effects models were used to test whether controlling for biological age attenuates the effect of chronological age and sex on PA. As expected, the rate of decline in participation in PA was greater for girls than for boys (B = -1.18, P < 0.01). In multivariable analyses, adjusting for biological age completely attenuated the effect of sex and chronological age for participation in free play activities, but not for participation in organized play. Overall, biological age was a stronger predictor of participation than chronological age. The effect of biological age on sex by chronological age differences may be specific to certain types of PA participation. Given the importance of maturation to participation in activity, it is suggested that public health strategies target biological not chronological age to prevent declines in PA during adolescence particularly when promoting habitual or lifestyle activity.

Extinction of Conditioned Responses to Methamphetamine-Associated Stimuli in Healthy Humans.

PubMed

Cavallo, Joel S; Ruiz, Nicholas A; de Wit, Harriet

2016-07-01

Contextual stimuli present during drug experiences become associated with the drug through Pavlovian conditioning and are thought to sustain drug-seeking behavior. Thus, extinction of conditioned responses is an important target for treatment. To date, acquisition and extinction to drug-paired cues have been studied in animal models or drug-dependent individuals, but rarely in non-drug users. We have recently developed a procedure to study acquisition of conditioned responses after single doses of methamphetamine (MA) in healthy volunteers. Here, we examined extinction of these responses and their persistence after conditioning. Healthy adults (18-35 years; N = 20) received two pairings of audio-visual stimuli with MA (20 mg oral) or placebo. Responses to stimuli were assessed before and after conditioning, using three tasks: behavioral preference, attentional bias, and subjective "liking." Subjects exhibited behavioral preference for the drug-paired stimuli at the first post-conditioning test, but this declined rapidly on subsequent extinction tests. They also exhibited a bias to initially look towards the drug-paired stimuli at the first post-test session, but not thereafter. Subjects who experienced more positive subjective drug effects during conditioning exhibited a smaller decline in preference during the extinction phase. Further, longer inter-session intervals during the extinction phase were associated with less extinction of the behavioral preference measure. Conditioned responses after two pairings with MA extinguish quickly, and are influenced by both subjective drug effects and the extinction interval. Characterizing and refining this conditioning procedure will aid in understanding the acquisition and extinction processes of drug-related conditioned responses in humans.

Extinction of Conditioned Responses to Methamphetamine-Associated Stimuli in Healthy Humans

PubMed Central

Cavallo, Joel S.; Ruiz, Nicholas A.; de Wit, Harriet

2016-01-01

Rationale Contextual stimuli present during drug experiences become associated with the drug through Pavlovian conditioning, and are thought to sustain drug-seeking behavior. Thus, extinction of conditioned responses is an important target for treatment. To date, acquisition and extinction to drug-paired cues have been studied in animal models or drug-dependent individuals, but rarely in non drug-users. Objective We have recently developed a procedure to study acquisition of conditioned responses after single doses of methamphetamine (MA) in healthy volunteers. Here we examined extinction of these responses and their persistence after conditioning. Methods Healthy adults (18–35 yrs; N=20) received two pairings of audio-visual stimuli with MA (20 mg oral) or placebo. Responses to stimuli were assessed before and after conditioning, using three tasks: behavioral preference, attentional bias, and subjective ‘liking.’ Results Subjects exhibited behavioral preference for the drug-paired stimuli at the first post-conditioning test, but this declined rapidly on subsequent extinction tests. They also exhibited a bias to initially look towards the drug-paired stimuli at the first post-test session, but not thereafter. Subjects who experienced more positive subjective drug effects during conditioning exhibited a smaller decline in preference during the extinction phase. Further, longer inter-session intervals during the extinction phase were associated with less extinction of the behavioral preference measure. Conclusions Conditioned responses after two pairings with MA extinguish quickly, and are influenced by both subjective drug effects and the extinction interval. Characterizing and refining this conditioning procedure will aid in understanding the acquisition and extinction processes of drug-related conditioned responses in humans. PMID:27113223

Ketamine accelerates fear extinction via mTORC1 signaling

PubMed Central

Girgenti, Matthew J.; Ghosal, Sriparna; LoPresto, Dora; Taylor, Jane R.; Duman, Ronald S.

2018-01-01

Impaired fear extinction contributes to the persistence of post-traumatic stress disorder (PTSD), and can be utilized for the study of novel therapeutic agents. Glutamate plays an important role in the formation of traumatic memories, and in the pathophysiology and treatment of PTSD, highlighting several possible drug targets. Recent clinical studies demonstrate that infusion of ketamine, a glutamate NMDA receptor antagonist, rapidly and significantly reduces symptom severity in PTSD patients. In the present study, we examine the mechanisms underlying the actions of ketamine in a rodent model of fear conditioning, extinction, and renewal. Rats received ketamine or saline 24 h after fear conditioning and were then subjected to extinction-training on each of the following three days. Ketamine administration enhanced extinction on the second day of training (i.e., reduced freezing behavior to cue) and produced a long-lasting reduction in freezing on exposure to cue plus context 8 days later. Additionally, ketamine and extinction exposure increased levels of mTORC1 in the medial prefrontal cortex (mPFC), a region involved in the acquisition and retrieval of extinction, and infusion of the selective mTORC1 inhibitor rapamycin into the mPFC blocked the effects of ketamine on extinction. Ketamine plus extinction also increased cFos in the mPFC and administration of a glutamate-AMPA receptor antagonist blocked the effects of ketamine. These results support the hypothesis that ketamine produces long-lasting mTORC1/protein synthesis and activity dependent effects on neuronal circuits that enhance the expression of extinction and could represent a novel approach for the treatment of PTSD. PMID:28043916

A Study of Correlation of Various Growth Indicators with Chronological Age.

PubMed

Singh, Sarabjeet; Sandhu, Navreet; Puri, Taruna; Gulati, Ritika; Kashyap, Rita

2015-01-01

The aim of this study was to assess the relationship of chronological age with cervical vertebrae skeletal maturation, frontal sinus width and antegonial notch depth and a correlation, if any, among the three variables. The samples were derived from lateral cephalometric radiographs of 80 subjects (40 males, 40 females; age range: 10 to 19 years). Cervical vertebral development was evaluated by the method of Hassel and Farman, frontal sinus width was measured by the method described by Ertürk and antegonial notch depth as described by Singer et al. The Pearson's correlation coefficients were estimated to assess the relationship of chronological age with cervical vertebrae skeletal maturation, frontal sinus width and antegonial notch depth. The Pearson's correlation coefficient were 0.855 (p < 0.001) between chronological age and cervical vertebrae skeletal maturation, and 0.333 (p < 0.001) between chronological age and frontal sinus width. A highly significant positive correlation was found between chronological age and cervical vertebrae skeletal maturation, and between chronological age and frontal sinus width. Nonsignificant correlation was found between chronological age and antegonial notch depth. How to cite this article: Singh S, Sandhu N, Puri T, Gulati R, Kashyap R. A Study of Correlation of Various Growth Indicators with Chronological Age. Int J Clin Pediatr Dent 2015;8(3): 190-195.

Dynamic analysis of a stochastic rumor propagation model

NASA Astrophysics Data System (ADS)

Jia, Fangju; Lv, Guangying

2018-01-01

The rapid development of the Internet, especially the emergence of the social networks, leads rumor propagation into a new media era. In this paper, we are concerned with a stochastic rumor propagation model. Sufficient conditions for extinction and persistence in the mean of the rumor are established. The threshold between persistence in the mean and extinction of the rumor is obtained. Compared with the corresponding deterministic model, the threshold affected by the white noise is smaller than the basic reproduction number R0 of the deterministic system.

A global three-dimensional model of the stratospheric sulfuric acid layer

NASA Technical Reports Server (NTRS)

Golombek, Amram; Prinn, Ronald G.

1993-01-01

A 3D model which encompasses SO2 production from OCS, followed by its oxidation to gaseous H2SO4, the condensation-evaporation equilibrium of gaseous and particulate H2SO4, and finally particle condensation and rainout, is presently used to study processes maintaining the nonvolcanically-perturbed stratosphere's sulfuric acid layer. A comparison of the results thus obtained with remotely sensed stratospheric aerosol extinction data shows the model to simulate the general behavior of stratospheric aerosol extinction.

Periodicity of mass extinctions without an extraterrestrial cause.

PubMed

Lipowski, Adam

2005-05-01

We study a lattice model of a multispecies prey-predator system. Numerical results show that for a small mutation rate the model develops irregular long-period oscillatory behavior with sizeable changes in a number of species. The periodicity of extinctions on Earth was suggested by Raup and Sepkoski [Proc. Natl. Acad. Sci. 81, 801 (1984)], but thus far is lacking a satisfactory explanation. Our model indicates that this might be a natural consequence of the ecosystem dynamics and not the result of any extraterrestrial cause.

Unraveling the drivers of community dissimilarity and species extinction in fragmented landscapes.

PubMed

Banks-Leite, Cristina; Ewers, Robert M; Metzger, Jean Paul

2012-12-01

Communities in fragmented landscapes are often assumed to be structured by species extinction due to habitat loss, which has led to extensive use of the species-area relationship (SAR) in fragmentation studies. However, the use of the SAR presupposes that habitat loss leads species to extinction but does not allow for extinction to be offset by colonization of disturbed-habitat specialists. Moreover, the use of SAR assumes that species richness is a good proxy of community changes in fragmented landscapes. Here, we assessed how communities dwelling in fragmented landscapes are influenced by habitat loss at multiple scales; then we estimated the ability of models ruled by SAR and by species turnover in successfully predicting changes in community composition, and asked whether species richness is indeed an informative community metric. To address these issues, we used a data set consisting of 140 bird species sampled in 65 patches, from six landscapes with different proportions of forest cover in the Atlantic Forest of Brazil. We compared empirical patterns against simulations of over 8 million communities structured by different magnitudes of the power-law SAR and with species-specific rules to assign species to sites. Empirical results showed that, while bird community composition was strongly influenced by habitat loss at the patch and landscape scale, species richness remained largely unaffected. Modeling results revealed that the compositional changes observed in the Atlantic Forest bird metacommunity were only matched by models with either unrealistic magnitudes of the SAR or by models ruled by species turnover, akin to what would be observed along natural gradients. We show that, in the presence of such compositional turnover, species richness is poorly correlated with species extinction, and z values of the SAR strongly underestimate the effects of habitat loss. We suggest that the observed compositional changes are driven by each species reaching its individual extinction threshold: either a threshold of forest cover for species that disappear with habitat loss, or of matrix cover for species that benefit from habitat loss.

Extinction models for cancer stem cell therapy

PubMed Central

Sehl, Mary; Zhou, Hua; Sinsheimer, Janet S.; Lange, Kenneth L.

2012-01-01

Cells with stem cell-like properties are now viewed as initiating and sustaining many cancers. This suggests that cancer can be cured by driving these cancer stem cells to extinction. The problem with this strategy is that ordinary stem cells are apt to be killed in the process. This paper sets bounds on the killing differential (difference between death rates of cancer stem cells and normal stem cells) that must exist for the survival of an adequate number of normal stem cells. Our main tools are birth–death Markov chains in continuous time. In this framework, we investigate the extinction times of cancer stem cells and normal stem cells. Application of extreme value theory from mathematical statistics yields an accurate asymptotic distribution and corresponding moments for both extinction times. We compare these distributions for the two cell populations as a function of the killing rates. Perhaps a more telling comparison involves the number of normal stem cells NH at the extinction time of the cancer stem cells. Conditioning on the asymptotic time to extinction of the cancer stem cells allows us to calculate the asymptotic mean and variance of NH. The full distribution of NH can be retrieved by the finite Fourier transform and, in some parameter regimes, by an eigenfunction expansion. Finally, we discuss the impact of quiescence (the resting state) on stem cell dynamics. Quiescence can act as a sanctuary for cancer stem cells and imperils the proposed therapy. We approach the complication of quiescence via multitype branching process models and stochastic simulation. Improvements to the τ-leaping method of stochastic simulation make it a versatile tool in this context. We conclude that the proposed therapy must target quiescent cancer stem cells as well as actively dividing cancer stem cells. The current cancer models demonstrate the virtue of attacking the same quantitative questions from a variety of modeling, mathematical, and computational perspectives. PMID:22001354

Extinction models for cancer stem cell therapy.

PubMed

Sehl, Mary; Zhou, Hua; Sinsheimer, Janet S; Lange, Kenneth L

2011-12-01

Cells with stem cell-like properties are now viewed as initiating and sustaining many cancers. This suggests that cancer can be cured by driving these cancer stem cells to extinction. The problem with this strategy is that ordinary stem cells are apt to be killed in the process. This paper sets bounds on the killing differential (difference between death rates of cancer stem cells and normal stem cells) that must exist for the survival of an adequate number of normal stem cells. Our main tools are birth-death Markov chains in continuous time. In this framework, we investigate the extinction times of cancer stem cells and normal stem cells. Application of extreme value theory from mathematical statistics yields an accurate asymptotic distribution and corresponding moments for both extinction times. We compare these distributions for the two cell populations as a function of the killing rates. Perhaps a more telling comparison involves the number of normal stem cells NH at the extinction time of the cancer stem cells. Conditioning on the asymptotic time to extinction of the cancer stem cells allows us to calculate the asymptotic mean and variance of NH. The full distribution of NH can be retrieved by the finite Fourier transform and, in some parameter regimes, by an eigenfunction expansion. Finally, we discuss the impact of quiescence (the resting state) on stem cell dynamics. Quiescence can act as a sanctuary for cancer stem cells and imperils the proposed therapy. We approach the complication of quiescence via multitype branching process models and stochastic simulation. Improvements to the τ-leaping method of stochastic simulation make it a versatile tool in this context. We conclude that the proposed therapy must target quiescent cancer stem cells as well as actively dividing cancer stem cells. The current cancer models demonstrate the virtue of attacking the same quantitative questions from a variety of modeling, mathematical, and computational perspectives. Copyright © 2011 Elsevier Inc. All rights reserved.

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120-800 ka

NASA Astrophysics Data System (ADS)

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Veres, D.; Parrenin, F.; Martinerie, P.; Ritz, C.; Capron, E.; Lipenkov, V.; Loutre, M.-F.; Raynaud, D.; Vinther, B.; Svensson, A.; Rasmussen, S. O.; Severi, M.; Blunier, T.; Leuenberger, M.; Fischer, H.; Masson-Delmotte, V.; Chappellaz, J.; Wolff, E.

2012-11-01

An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale has been developed based on an inverse dating method (Datice) combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousand of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2012), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120-800 ka. In this frame, new measurements of δ18Oatm over Marine Isotope Stage (MIS) 11-12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive new orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content) has been verified before implementation in AICC2012. The new chronology shows only small differences, well within the original uncertainty range, when compared with the previous ice core reference age scale EDC3. For instance, the duration of the last four interglacial periods is not affected by more than 5%. The largest deviation between AICC2012 and EDC3 (4.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

Skeletal and chronological ages in American adolescents: current findings in skeletal maturation.

PubMed

Calfee, Ryan P; Sutter, Melanie; Steffen, Jennifer A; Goldfarb, Charles A

2010-10-01

This study was designed to assess the relationship between skeletal and chronological ages among current American adolescents using the Greulich and Pyle atlas for skeletal age determination. We used the Greulich and Pyle atlas to prospectively determine skeletal age in a group of 138 otherwise healthy American adolescents from 12 to 18 years of age. 62 males and 76 females were enrolled in this cohort. Paired Student t-tests were used to statistically compare the skeletal and chronological ages in this population. Subgroup analysis examined the effect of gender on differences between chronologic age and skeletal age. For the entire cohort, mean skeletal age was significantly greater than chronological age (mean 0.80 years, P < 0.01). In 29 cases (21%) the skeletal age was at least 2 years greater than the chronologic age. Among females, such cases with marked discrepancy occurred exclusively in those chronologically between 12 and 15 years of age (P < 0.01). Males demonstrated a 2-year or greater discrepancy more commonly than females (26 vs. 17%). In males, 2-year discrepancies were equally likely across chronologic ages (P = 0.82). Current American adolescents are significantly more mature by skeletal age, as determined by the Greulich and Pyle method, than their chronological age would suggest. The skeletal ages of females are most likely to markedly exceed chronologic age between the ages of 12-15 years.

A General Class of Test Statistics for Van Valen’s Red Queen Hypothesis

PubMed Central

Wiltshire, Jelani; Huffer, Fred W.; Parker, William C.

2014-01-01

Van Valen’s Red Queen hypothesis states that within a homogeneous taxonomic group the age is statistically independent of the rate of extinction. The case of the Red Queen hypothesis being addressed here is when the homogeneous taxonomic group is a group of similar species. Since Van Valen’s work, various statistical approaches have been used to address the relationship between taxon age and the rate of extinction. We propose a general class of test statistics that can be used to test for the effect of age on the rate of extinction. These test statistics allow for a varying background rate of extinction and attempt to remove the effects of other covariates when assessing the effect of age on extinction. No model is assumed for the covariate effects. Instead we control for covariate effects by pairing or grouping together similar species. Simulations are used to compare the power of the statistics. We apply the test statistics to data on Foram extinctions and find that age has a positive effect on the rate of extinction. A derivation of the null distribution of one of the test statistics is provided in the supplementary material. PMID:24910489

Fear extinction in the human brain: A meta-analysis of fMRI studies in healthy participants.

PubMed

Fullana, Miquel A; Albajes-Eizagirre, Anton; Soriano-Mas, Carles; Vervliet, Bram; Cardoner, Narcís; Benet, Olívia; Radua, Joaquim; Harrison, Ben J

2018-05-01

The study of fear extinction represents an important example of translational neuroscience in psychiatry and promises to improve the understanding and treatment of anxiety and fear-related disorders. We present the results of a set of meta-analyses of human fear extinction studies in healthy participants, conducted with functional magnetic resonance imaging (fMRI) and reporting whole-brain results. Meta-analyses of fear extinction learning primarily implicate consistent activation of brain regions linked to threat appraisal and experience, including the dorsal anterior cingulate and anterior insular cortices. An overlapping anatomical result was obtained from the meta-analysis of extinction recall studies, except when studies directly compared an extinguished threat stimulus to an unextinguished threat stimulus (instead of a safety stimulus). In this latter instance, more consistent activation was observed in dorsolateral and ventromedial prefrontal cortex regions, together with other areas including the hippocampus. While our results partially support the notion of a shared neuroanatomy between human and rodent models of extinction processes, they also encourage an expanded account of the neural basis of human fear extinction. Copyright © 2018 Elsevier Ltd. All rights reserved.

A General Class of Test Statistics for Van Valen's Red Queen Hypothesis.

PubMed

Wiltshire, Jelani; Huffer, Fred W; Parker, William C

2014-09-01

Van Valen's Red Queen hypothesis states that within a homogeneous taxonomic group the age is statistically independent of the rate of extinction. The case of the Red Queen hypothesis being addressed here is when the homogeneous taxonomic group is a group of similar species. Since Van Valen's work, various statistical approaches have been used to address the relationship between taxon age and the rate of extinction. We propose a general class of test statistics that can be used to test for the effect of age on the rate of extinction. These test statistics allow for a varying background rate of extinction and attempt to remove the effects of other covariates when assessing the effect of age on extinction. No model is assumed for the covariate effects. Instead we control for covariate effects by pairing or grouping together similar species. Simulations are used to compare the power of the statistics. We apply the test statistics to data on Foram extinctions and find that age has a positive effect on the rate of extinction. A derivation of the null distribution of one of the test statistics is provided in the supplementary material.

Stratigraphy, U-Th chronology, and paleoenvironments at Gladysvale Cave: insights into the climatic control of South African hominin-bearing cave deposits.

PubMed

Pickering, Robyn; Hancox, Phillip J; Lee-Thorp, Julia A; Grün, Rainer; Mortimer, Graham E; McCulloch, Malcolm; Berger, Lee R

2007-11-01

Gladysvale Cave is one of the few Plio-Pleistocene hominin-bearing cave sites in South Africa that contains a well-stratified cave fill with clastic sediments interspersed with flowstones. The clastic sediments can be divided into units based on the presence of intercalated flowstones, forming flowstone bounded units (FBU). Ten MC-ICP-MS uranium-series dates on several flowstone horizons in the Gladysvale Internal Deposit fan indicate deposition from the late mid-Pleistocene ( approximately 570 ka) to Holocene ( approximately 7 ka) during limited periods of higher effective moisture. Clastic sedimentation occurred during the interceding, presumably more arid, periods. This sequence is not consistent with earlier models for South African caves that simply assumed interglacial sedimentation and glacial erosion. (13)C/(12)C data suggest that flowstone tended to form during periods with higher proportions of C(3) plants in the local vegetation, while clastic sediments reflect higher proportions of C(4) grasses, although this is not always the case. We argue that flowstones are precipitated during periods of higher effective precipitation and restricted cave entrances, while clastic sediments accumulated during periods with more open vegetation. The sedimentary fill of the fossiliferous deposits are, therefore, highly episodic in nature, with large periods of time unlikely to be represented. This has serious implications for the other hominin-bearing caves close by, as these deposits are likely to be similarly episodic. This is especially pertinent when addressing extinction events and reconstructions of paleoenvironments, as large periods of time may be unrecorded. The Gladysvale Cave fill sediments may serve as a climatically forced chronostratigraphic model for these less well-stratified and well-dated Plio-Pleistocene sites.

Regional tree growth and inferred summer climate in the Winnipeg River basin, Canada, since AD 1783

NASA Astrophysics Data System (ADS)

St. George, Scott; Meko, David M.; Evans, Michael N.

2008-09-01

A network of 54 ring-width chronologies is used to estimate changes in summer climate within the Winnipeg River basin, Canada, since AD 1783. The basin drains parts of northwestern Ontario, northern Minnesota and southeastern Manitoba, and is a key area for hydroelectric power production. Most chronologies were developed from Pinus resinosa and P. strobus, with a limited number of Thuja occidentalis, Picea glauca and Pinus banksiana. The dominant pattern of regional tree growth can be recovered using only the nine longest chronologies, and is not affected by the method used to remove variability related to age or stand dynamics from individual trees. Tree growth is significantly, but weakly, correlated with both temperature (negatively) and precipitation (positively) during summer. Simulated ring-width chronologies produced by a process model of tree-ring growth exhibit similar relationships with summer climate. High and low growth across the region is associated with cool/wet and warm/dry summers, respectively; this relationship is supported by comparisons with archival records from early 19th century fur-trading posts. The tree-ring record indicates that summer droughts were more persistent in the 19th and late 18th century, but there is no evidence that drought was more extreme prior to the onset of direct monitoring.

Attentional, Associative, and Configural Mechanisms in Extinction

ERIC Educational Resources Information Center

Larrauri, Jose A.; Schmajuk, Nestor A.

2008-01-01

The participation of attentional and associative mechanisms in extinction, spontaneous recovery, external disinhibition, renewal, reinstatement, and reacquisition was evaluated through computer simulations with an extant computational model of classical conditioning (N. A. Schmajuk, Y. Lam, & J. A. Gray, 1996; N. A. Schmajuk & J. A. Larrauri,…

Extinction Dynamics and Control in Adaptive Networks

NASA Astrophysics Data System (ADS)

Schwartz, Ira; Shaw, Leah; Hindes, Jason

Disease control is of paramount importance in public health. Moreover, models of disease spread are an important component in implementing effective vaccination and treatment campaigns. However, human behavior in response to an outbreak has only recently been included in epidemic models on networks. Here we develop the mathematical machinery to describe the dynamics of extinction in finite populations that include human adaptive behavior. The formalism enables us to compute the optimal, fluctuation-induced path to extinction, and predict the average extinction time in adaptive networks as a function of the adaptation rate. We find that both observables have several unique scalings depending on the relative speed of infection and adaptivity. Finally, we discuss how the theory can be used to design optimal control programs in general networks, by coupling the effective force of noise with treatment and human behavior. Research supported by U.S. Naval Research Laboratory funding (Grant No. N0001414WX00023) and the Office of Naval Research (Grant No. N0001414WX20610).

Risk of population extinction from fixation of deleterious and reverse mutations.

PubMed

Lande, R

1998-01-01

A model is developed for alternate fixations of mildly deleterious and wild-type alleles arising by forward and reverse mutation in a finite population. For almost all parameter values, this gives an equilibrium load that agrees closely with the general expression derived from diffusion theory. Nearly neutral mutations with selection coefficient a few times larger than 1/(2N(e)) do the most damage by increasing the equilibrium load. The model of alternate fixations facilitates dynamical analysis of the expected load and the mean time to extinction in a population that has been suddenly reduced from a very large size to a small size. Reverse mutation can substantially improve population viability, increasing the mean time to extinction by an order of magnitude or more, but because many mutations are irreversible the effects may not be large. Populations with initially high mean fitness and small effective size, N(e) below a few hundred individuals, may be at serious risk of extinction from fixation of deleterious mutations within 10(3) to 10(4) generations.

Quantifying variation in speciation and extinction rates with clade data.

PubMed

Paradis, Emmanuel; Tedesco, Pablo A; Hugueny, Bernard

2013-12-01

High-level phylogenies are very common in evolutionary analyses, although they are often treated as incomplete data. Here, we provide statistical tools to analyze what we name "clade data," which are the ages of clades together with their numbers of species. We develop a general approach for the statistical modeling of variation in speciation and extinction rates, including temporal variation, unknown variation, and linear and nonlinear modeling. We show how this approach can be generalized to a wide range of situations, including testing the effects of life-history traits and environmental variables on diversification rates. We report the results of an extensive simulation study to assess the performance of some statistical tests presented here as well as of the estimators of speciation and extinction rates. These latter results suggest the possibility to estimate correctly extinction rate in the absence of fossils. An example with data on fish is presented. © 2013 The Author(s). Evolution © 2013 The Society for the Study of Evolution.

Prefrontal single-unit firing associated with deficient extinction in mice

PubMed Central

Fitzgerald, Paul J; Whittle, Nigel; Flynn, Shaun M; Graybeal, Carolyn; Pinard, Courtney; Gunduz-Cinar, Ozge; Kravitz, Alexxai; Singewald, Nicolas; Holmes, Andrew

2014-01-01

The neural circuitry mediating fear extinction has been increasingly well studied and delineated. The rodent infralimbic subregion (IL) of the ventromedial prefrontal cortex (vmPFC) has been found to promote extinction, whereas the prelimbic cortex (PL) demonstrates an opposing, pro-fear, function. Studies employing in vivo electrophysiological recordings have observed that while increased IL single-unit firing and bursting predicts robust extinction retrieval, increased PL firing can correlate with sustained fear and poor extinction. These relationships between single-unit firing and extinction do not hold under all experimental conditions, however. In the current study, we further investigated the relationship between vmPFC and PL single-unit firing and extinction using inbred mouse models of intact (C57BL/6J, B6) and deficient (129S1/SvImJ, S1) extinction strains. Simultaneous single-unit recordings were made in the PL and vmPFC (encompassing IL) as B6 and S1 mice performed extinction training and retrieval. Impaired extinction retrieval in S1 mice was associated with elevated PL single-unit firing, as compared to firing in extinguishing B6 mice, consistent with the hypothesized pro-fear contribution of PL. Analysis of local field potentials also revealed significantly higher gamma power in the PL of Sthan B6 mice during extinction training and retrieval. In the vmPFC, impaired extinction in S1 mice was also associated with exaggerated single-unit firing, relative to B6 mice. This is in apparent contradiction to evidence that IL activity promotes extinction, but could reflect a (failed) compensatory effort by the vmPFC to mitigate fear-promoting activity in other regions, such as the PL or amygdala. In support of this hypothesis, augmenting IL activity via direct infusion of the GABAA receptor antagonist picrotoxin rescued impaired extinction retrieval in S1 mice. Chronic fluoxetine treatment produced modest reductions in fear during extinction retrieval and increased the number of Zif268-labeled cells in layer II of IL, but failed to increase vmPFC single-unit firing. Collectively, these findings further support the important contribution these cortical regions play in determining the balance between robust extinction on the one hand, and sustained fear on the other. Elucidating the precise nature of these roles could help inform understanding of the pathophysiology of fear-related anxiety disorders. PMID:24231425

American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change.

PubMed

Zazula, Grant D; MacPhee, Ross D E; Metcalfe, Jessica Z; Reyes, Alberto V; Brock, Fiona; Druckenmiller, Patrick S; Groves, Pamela; Harington, C Richard; Hodgins, Gregory W L; Kunz, Michael L; Longstaffe, Fred J; Mann, Daniel H; McDonald, H Gregory; Nalawade-Chavan, Shweta; Southon, John R

2014-12-30

Existing radiocarbon ((14)C) dates on American mastodon (Mammut americanum) fossils from eastern Beringia (Alaska and Yukon) have been interpreted as evidence they inhabited the Arctic and Subarctic during Pleistocene full-glacial times (∼ 18,000 (14)C years B.P.). However, this chronology is inconsistent with inferred habitat preferences of mastodons and correlative paleoecological evidence. To establish a last appearance date (LAD) for M. americanum regionally, we obtained 53 new (14)C dates on 36 fossils, including specimens with previously published dates. Using collagen ultrafiltration and single amino acid (hydroxyproline) methods, these specimens consistently date to beyond or near the ∼ 50,000 y B.P. limit of (14)C dating. Some erroneously "young" (14)C dates are due to contamination by exogenous carbon from natural sources and conservation treatments used in museums. We suggest mastodons inhabited the high latitudes only during warm intervals, particularly the Last Interglacial [Marine Isotope Stage (MIS) 5] when boreal forests existed regionally. Our (14)C dataset suggests that mastodons were extirpated from eastern Beringia during the MIS 4 glacial interval (∼ 75,000 y ago), following the ecological shift from boreal forest to steppe tundra. Mastodons thereafter became restricted to areas south of the continental ice sheets, where they suffered complete extinction ∼ 10,000 (14)C years B.P. Mastodons were already absent from eastern Beringia several tens of millennia before the first humans crossed the Bering Isthmus or the onset of climate changes during the terminal Pleistocene. Local extirpations of mastodons and other megafaunal populations in eastern Beringia were asynchrononous and independent of their final extinction south of the continental ice sheets.

American mastodon extirpation in the Arctic and Subarctic predates human colonization and terminal Pleistocene climate change

PubMed Central

Zazula, Grant D.; MacPhee, Ross D. E.; Metcalfe, Jessica Z.; Reyes, Alberto V.; Brock, Fiona; Druckenmiller, Patrick S.; Groves, Pamela; Harington, C. Richard; Hodgins, Gregory W. L.; Kunz, Michael L.; Longstaffe, Fred J.; Mann, Daniel H.; McDonald, H. Gregory; Nalawade-Chavan, Shweta; Southon, John R.

2014-01-01

Existing radiocarbon (14C) dates on American mastodon (Mammut americanum) fossils from eastern Beringia (Alaska and Yukon) have been interpreted as evidence they inhabited the Arctic and Subarctic during Pleistocene full-glacial times (∼18,000 14C years B.P.). However, this chronology is inconsistent with inferred habitat preferences of mastodons and correlative paleoecological evidence. To establish a last appearance date (LAD) for M. americanum regionally, we obtained 53 new 14C dates on 36 fossils, including specimens with previously published dates. Using collagen ultrafiltration and single amino acid (hydroxyproline) methods, these specimens consistently date to beyond or near the ∼50,000 y B.P. limit of 14C dating. Some erroneously “young” 14C dates are due to contamination by exogenous carbon from natural sources and conservation treatments used in museums. We suggest mastodons inhabited the high latitudes only during warm intervals, particularly the Last Interglacial [Marine Isotope Stage (MIS) 5] when boreal forests existed regionally. Our 14C dataset suggests that mastodons were extirpated from eastern Beringia during the MIS 4 glacial interval (∼75,000 y ago), following the ecological shift from boreal forest to steppe tundra. Mastodons thereafter became restricted to areas south of the continental ice sheets, where they suffered complete extinction ∼10,000 14C years B.P. Mastodons were already absent from eastern Beringia several tens of millennia before the first humans crossed the Bering Isthmus or the onset of climate changes during the terminal Pleistocene. Local extirpations of mastodons and other megafaunal populations in eastern Beringia were asynchrononous and independent of their final extinction south of the continental ice sheets. PMID:25453065

Dental development in Megaladapis edwardsi (Primates, Lemuriformes): implications for understanding life history variation in subfossil lemurs.

PubMed

Schwartz, Gary T; Mahoney, Patrick; Godfrey, Laurie R; Cuozzo, Frank P; Jungers, William L; Randria, Gisèle F N

2005-12-01

Teeth grow incrementally and preserve within them a record of that incremental growth in the form of microscopic growth lines. Studying dental development in extinct and extant primates, and its relationship to adult brain and body size as well as other life history and ecological parameters (e.g., diet, somatic growth rates, gestation length, age at weaning), holds the potential to yield unparalleled insights into the life history profiles of fossil primates. Here, we address the absolute pace of dental development in Megaladapis edwardsi, a giant extinct lemur of Madagascar. By examining the microstructure of the first and developing second molars in a juvenile individual, we establish a chronology of molar crown development for this specimen (M1 CFT = 1.04 years; M2 CFT = 1.42 years) and determine its age at death (1.39 years). Microstructural data on prenatal M1 crown formation time allow us to calculate a minimum gestation length of 0.54 years for this species. Postnatal crown and root formation data allow us to estimate its age at M1 emergence (approximately 0.9 years) and to establish a minimum age for M2 emergence (>1.39 years). Finally, using reconstructions or estimates (drawn elsewhere) of adult body mass, brain size, and diet in Megaladapis, as well as the eruption sequence of its permanent teeth, we explore the efficacy of these variables in predicting the absolute pace of dental development in this fossil species. We test competing explanations of variation in crown formation timing across the order Primates. Brain size is the best single predictor of crown formation time in primates, but other variables help to explain the variation.

High resolution chronology of late Cretaceous-early Tertiary events determined from 21,000 yr orbital-climatic cycles in marine sediments

NASA Technical Reports Server (NTRS)

Herbert, Timothy D.; Dhondt, Steven

1988-01-01

A number of South Atlantic sites cored by the Deep Sea Drilling Project (DSDP) recovered late Cretaceous and early Tertiary sediments with alternating light-dark, high-low carbonate content. The sedimentary oscillations were turned into time series by digitizing color photographs of core segments at a resolution of about 5 points/cm. Spectral analysis of these records indicates prominent periodicity at 25 to 35 cm in the Cretaceous intervals, and about 15 cm in the early Tertiary sediments. The absolute period of the cycles that is determined from paleomagnetic calibration at two sites is 20,000 to 25,000 yr, and almost certainly corresponds to the period of the earth's precessional cycle. These sequences therefore contain an internal chronometer to measure events across the K/T extinction boundary at this scale of resolution. The orbital metronome was used to address several related questions: the position of the K/T boundary within magnetic chron 29R, the fluxes of biogenic and detrital material to the deep sea immediately before and after the K/T event, the duration of the Sr anomaly, and the level of background climatic variability in the latest Cretaceous time. The carbonate/color cycles that were analyzed contain primary records of ocean carbonate productivity and chemistry, as evidenced by bioturbational mixing of adjacent beds and the weak lithification of the rhythmic sequences. It was concluded that sedimentary sequences that contain orbital cyclicity are capable of providing resolution of dramatic events in earth history with much greater precision than obtainable through radiometric methods. The data show no evidence for a gradual climatic deterioration prior to the K/T extinction event, and argue for a geologically rapid revolution at this horizon.

Fear of cultural extinction and psychopathology among Mandaean refugees: an exploratory path analysis.

PubMed

Nickerson, Angela; Bryant, Richard A; Brooks, Robert; Steel, Zachary; Silove, Derrick

2009-01-01

The Mandaeans are a small religious community originating from Iraq and Iran who are facing the possibility of cultural extinction within the next few generations. This study aimed to examine the relationships between life experiences, psychopathology and fear of cultural extinction in Mandaean refugees. A survey was conducted of 315 adult Iraqi Mandaean refugees living in Australia. Past traumatic experiences and current resettlement difficulties were assessed. Mental health outcomes were also examined, including measures of posttraumatic stress disorder (PTSD) and depression. Fear of cultural extinction was measured by items developed in consultation with the Mandaean community. A path analysis was employed to investigate the relationship between trauma, living difficulties, PTSD, depression, and fear of cultural extinction. Results indicated that trauma and living difficulties impacted indirectly on fear of cultural extinction, while PTSD (and not depression) directly predicted levels of anxiety about the Mandaean culture ceasing to exist. The current findings indicate that past trauma and symptoms of posttraumatic stress contribute to fear of cultural extinction. Exposure to human rights violations enacted on the basis of religion has significant mental health consequences that extend beyond PTSD. The relationship between perception of threat, PTSD, and fear of cultural extinction is considered in the context of cognitive models of traumatic stress. Government immigration policy must prioritize the reunification of small, endangered groups to sustain cultural traditions. Treatment interventions implemented with cultural groups facing extinction should take into consideration anxiety about loss of culture.

Timing and causes of mid-Holocene mammoth extinction on St. Paul Island, Alaska

PubMed Central

Graham, Russell W.; Belmecheri, Soumaya; Choy, Kyungcheol; Culleton, Brendan J.; Davies, Lauren J.; Hritz, Carrie; Kapp, Joshua D.; Newsom, Lee A.; Rawcliffe, Ruth; Saulnier-Talbot, Émilie; Wang, Yue; Williams, John W.; Wooller, Matthew J.

2016-01-01

Relict woolly mammoth (Mammuthus primigenius) populations survived on several small Beringian islands for thousands of years after mainland populations went extinct. Here we present multiproxy paleoenvironmental records to investigate the timing, causes, and consequences of mammoth disappearance from St. Paul Island, Alaska. Five independent indicators of extinction show that mammoths survived on St. Paul until 5,600 ± 100 y ago. Vegetation composition remained stable during the extinction window, and there is no evidence of human presence on the island before 1787 CE, suggesting that these factors were not extinction drivers. Instead, the extinction coincided with declining freshwater resources and drier climates between 7,850 and 5,600 y ago, as inferred from sedimentary magnetic susceptibility, oxygen isotopes, and diatom and cladoceran assemblages in a sediment core from a freshwater lake on the island, and stable nitrogen isotopes from mammoth remains. Contrary to other extinction models for the St. Paul mammoth population, this evidence indicates that this mammoth population died out because of the synergistic effects of shrinking island area and freshwater scarcity caused by rising sea levels and regional climate change. Degradation of water quality by intensified mammoth activity around the lake likely exacerbated the situation. The St. Paul mammoth demise is now one of the best-dated prehistoric extinctions, highlighting freshwater limitation as an overlooked extinction driver and underscoring the vulnerability of small island populations to environmental change, even in the absence of human influence. PMID:27482085

Effects of prenatal chronic mild stress exposure on hippocampal cell proliferation, expression of GSK-3α, β and NR2B in adult offspring during fear extinction in rats.

PubMed

Li, Min; Li, Xiaobai; Zhang, Xinxin; Ren, Jintao; Jiang, Han; Wang, Yan; Ma, Yuchao; Cheng, Wenwen

2014-06-01

Stress during pregnancy has been implicated as a risk factor for the development of many mental disorders; however, the influence of prenatal stress on the fear or anxiety-related behaviors, especially the fear extinction in adult offspring has been little investigated. In order to investigate how prenatal stress affects fear extinction, which is regarded as a form of new learning that counteracts the expression of Pavlovian's conditioned fear, a rat model of prenatal chronic mild stress (PNS) was used to evaluate the effects of PNS on fear extinction in adult offspring. The expression of hippocampal glycogen synthase kinase-3s (GSK-3α, β), N-methyl-d-aspartic acid receptors (NMDARs)-2B and the hippocampal cell proliferation in dentate gyrus in the adult offspring during fear extinction were studied. Our results showed that PNS significantly reduced body weight of pups, indicating PNS might induce growth retardation in offspring. Moreover, PNS significantly enhanced the freezing behavior of offspring at the phase of extinction, suggesting PNS impaired the abilities of fear extinction learning. In addition, PNS significantly increased the levels of GSK-3α, β and NR2B, but reduced hippocampal cell proliferation during fear extinction. Taken together, our findings suggest that maternal stress during pregnancy can impair the fear extinction of adult offspring, probably by affecting the neural plasticity of brain. Copyright © 2014 ISDN. Published by Elsevier Ltd. All rights reserved.

Extinction risk and eco-evolutionary dynamics in a variable environment with increasing frequency of extreme events

PubMed Central

Vincenzi, Simone

2014-01-01

One of the most dramatic consequences of climate change will be the intensification and increased frequency of extreme events. I used numerical simulations to understand and predict the consequences of directional trend (i.e. mean state) and increased variability of a climate variable (e.g. temperature), increased probability of occurrence of point extreme events (e.g. floods), selection pressure and effect size of mutations on a quantitative trait determining individual fitness, as well as the their effects on the population and genetic dynamics of a population of moderate size. The interaction among climate trend, variability and probability of point extremes had a minor effect on risk of extinction, time to extinction and distribution of the trait after accounting for their independent effects. The survival chances of a population strongly and linearly decreased with increasing strength of selection, as well as with increasing climate trend and variability. Mutation amplitude had no effects on extinction risk, time to extinction or genetic adaptation to the new climate. Climate trend and strength of selection largely determined the shift of the mean phenotype in the population. The extinction or persistence of the populations in an ‘extinction window’ of 10 years was well predicted by a simple model including mean population size and mean genetic variance over a 10-year time frame preceding the ‘extinction window’, although genetic variance had a smaller role than population size in predicting contemporary risk of extinction. PMID:24920116

A counterflow diffusion flame study of branched octane isomers

DOE PAGES

Sarathy, S. Mani; Niemann, Ulrich; Yeung, Coleman; ...

2012-09-25

Conventional petroleum, Fischer–Tropsch (FT), and other alternative hydrocarbon fuels typically contain a high concentration of lightly methylated iso-alkanes. However, until recently little work has been done on this important class of hydrocarbon components. In order to better understand the combustion characteristics of real fuels, this study presents new experimental data for 3-methylheptane and 2,5-dimethylhexane in counterflow diffusion flames. This new dataset includes flame ignition, extinction, and speciation profiles. The high temperature oxidation of these fuels has been modeled using an extended transport database and a high temperature skeletal chemical kinetic model. The skeletal model is generated from a detailed modelmore » reduced using the directed relation graph with expert knowledge (DRG-X) methodology. The proposed skeletal model contains sufficient chemical fidelity to accurately predict the experimental speciation data in flames. The predictions are compared to elucidate the effects of number and location of the methyl substitutions. The location is found to have little effect on ignition and extinction in these counterflow diffusion flames. However, increasing the number of methyl substitutions was found to inhibit ignition and promote extinction. Chemical kinetic modelling simulations were used to correlate a fuel’s extinction propensity with its ability to populate the H radical concentration. In conclusion, species composition measurements indicate that the location and number of methyl substitutions was found to particularly affect the amount and type of alkenes observed.« less

What killed the dinosaurs?

USGS Publications Warehouse

Glen, W.

1990-01-01

Out of a number of earlier attempts to explain mass extinctions, only the volcanism alternative to the impact hypothesis remains under serious consideration. The evidence for an impact is reviewed, and the mechanisms which might have brought about the apocalyptic series of extinctions at the Cretaceous-Tertiary (K-T) boundary are reviewed, referring to Alvarez's and other research teams working on the problem. As suggested by the patterns of extinctions and the periodicity of this and other mass extinctions, the "volcanist alternative' is introduced. This would produce a series of selective extinctions spread over a considerable length of time, and which is similar to what the fossil record shows, and could account for the iridium anomaly at the K-T boundary. More support for this theory comes from models put forward by volcanist exponents, but it is concluded that the debate is far from ended. -J.W.Cooper

Evolution and Extinction Dynamics in Rugged Fitness Landscapes

NASA Astrophysics Data System (ADS)

Sibani, Paolo; Brandt, Michael; Alstrøm, Preben

After an introductory section summarizing the paleontological data and some of their theoretical descriptions, we describe the "reset" model and its (in part analytically soluble) mean field version, which have been briefly introduced in Letters.1,2 Macroevolution is considered as a problem of stochastic dynamics in a system with many competing agents. Evolutionary events (speciations and extinctions) are triggered by fitness records found by random exploration of the agents' fitness landscapes. As a consequence, the average fitness in the system increases logarithmically with time, while the rate of extinction steadily decreases. This non-stationary dynamics is studied by numerical simulations and, in a simpler mean field version, analytically. We also consider the effect of externally added "mass" extinctions. The predictions for various quantities of paleontological interest (life-time distribution, distribution of event sizes and behavior of the rate of extinction) are robust and in good agreement with available data.

Population collapse to extinction: the catastrophic combination of parasitism and Allee effect.

PubMed

Hilker, Frank M

2010-01-01

Infectious diseases are responsible for the extinction of a number of species. In conventional epidemic models, the transition from endemic population persistence to extirpation takes place gradually. However, if host demographics exhibits a strong Allee effect (AE) (population decline at low densities), extinction can occur abruptly in a catastrophic population crash. This might explain why species suddenly disappear even when they used to persist at high endemic population levels. Mathematically, the tipping point towards population collapse is associated with a saddle-node bifurcation. The underlying mechanism is the simultaneous population size depression and the increase of the extinction threshold due to parasite pathogenicity and Allee effect. Since highly pathogenic parasites cause their own extinction but not that of their host, there can be another saddle-node bifurcation with the re-emergence of two endemic equilibria. The implications for control interventions are discussed, suggesting that effective management may be possible for ℛ(0)≫1.

Method of confidence domains in the analysis of noise-induced extinction for tritrophic population system

NASA Astrophysics Data System (ADS)

Bashkirtseva, Irina; Ryashko, Lev; Ryazanova, Tatyana

2017-09-01

A problem of the analysis of the noise-induced extinction in multidimensional population systems is considered. For the investigation of conditions of the extinction caused by random disturbances, a new approach based on the stochastic sensitivity function technique and confidence domains is suggested, and applied to tritrophic population model of interacting prey, predator and top predator. This approach allows us to analyze constructively the probabilistic mechanisms of the transition to the noise-induced extinction from both equilibrium and oscillatory regimes of coexistence. In this analysis, a method of principal directions for the reducing of the dimension of confidence domains is suggested. In the dispersion of random states, the principal subspace is defined by the ratio of eigenvalues of the stochastic sensitivity matrix. A detailed analysis of two scenarios of the noise-induced extinction in dependence on parameters of considered tritrophic system is carried out.

Can stable isotopes and radiocarbon dating provide a forensic solution for curbing illegal harvesting of threatened cycads?

PubMed

Retief, Kirsten; West, Adam G; Pfab, Michèle F

2014-11-01

Cycads in South Africa are facing an extinction crisis due to the illegal extraction of plants from the wild. Proving wild origin of suspect ex situ cycads to the satisfaction of a court of law is difficult, limiting law enforcement efforts. We investigated the feasibility of using multiple stable isotopes to identify specimens removed from the wild. Relocated and wild specimens from two species in the African genus Encephalartos (E. lebomboensis and E. arenarius) were sampled. (14) C analysis indicated that a ± 30-year chronology could be reliably obtained from the cycads. For E. arenarius, pre-relocation tissue was consistent with a wild origin, whereas tissue grown post-relocation was isotopically distinct from the wild for (87) Sr/(86) Sr and δ(15) N. For E. lebomboensis, δ(34) S, δ(18) O, and (87) Sr/(86) Sr were different between relocated and control plants, consistent with the >30 years since relocation. Our findings demonstrate the potential for a forensic isotope approach to identify illegal ex situ cycads. © 2014 American Academy of Forensic Sciences.

Human Response to Climatic Shifts during MIS3 in Northern Iberia

NASA Astrophysics Data System (ADS)

Marin-Arroyo, A. B.; Jones, J.; Richards, M.

2016-12-01

Paleoclimate reconstructions are usually limited by the availability of climate proxies to compare with GCM results. This is especially true regarding terrestrial environments where pollen records are scarce or potentially biased. The analysis of stable isotopes from animal bones has recently opened new possibilities of objectively establishing past environmental shifts. The potential of this method and its implications for human evolution is demonstrated in northern Iberia during the MIS3, a period that witnessed rapid and acute changes as evidenced in ice cores, whose effects on European ecological conditions might be behind the extinction of Neanderthals and their sudden replacement by Anatomically Modern Humans. The lack of a continuous, fine-grained, and well-dated terrestrial palaeoclimatic sequence has precluded verification of this hypothesis in a region that comprises a relevant archaeological record of both human species during Late Pleistocene. Hence, a long and well-dated chronology of N15, C13 and O18 variation in combination with a human dietary study, as a recollection of human resilience to ecological change, is used to assess if ecosystems were pushed beyond tipping points towards catastrophic scenarios.

Mapping of the stochastic Lotka-Volterra model to models of population genetics and game theory

NASA Astrophysics Data System (ADS)

Constable, George W. A.; McKane, Alan J.

2017-08-01

The relationship between the M -species stochastic Lotka-Volterra competition (SLVC) model and the M -allele Moran model of population genetics is explored via timescale separation arguments. When selection for species is weak and the population size is large but finite, precise conditions are determined for the stochastic dynamics of the SLVC model to be mappable to the neutral Moran model, the Moran model with frequency-independent selection, and the Moran model with frequency-dependent selection (equivalently a game-theoretic formulation of the Moran model). We demonstrate how these mappings can be used to calculate extinction probabilities and the times until a species' extinction in the SLVC model.

Martian Chronology: Goals for Investigations from a Recent Multidisciplinary Workshop

NASA Technical Reports Server (NTRS)

Nyquist, L.; Doran, P. T.; Cerling, T. E.; Clifford, S. M.; Forman, S. L.; Papanastassiou, D. A.; Stewart, B. W.; Sturchio, N. C.; Swindle, T. D.

2000-01-01

The absolute chronology of Martian rocks and events is based mainly on crater statistics and remains highly uncertain. Martian chronology will be critical to building a time scale comparable to Earth's to address questions about the early evolution of the planets and their ecosystems. In order to address issues and strategies specific to Martian chronology, a workshop was held, 4-7 June 2000, with invited participants from the planetary, geochronology, geochemistry, and astrobiology communities. The workshop focused on identifying: a) key scientific questions of Martian chronology; b) chronological techniques applicable to Mars; c) unique processes on Mars that could be exploited to obtain rates, fluxes, ages; and d) sampling issues for these techniques. This is an overview of the workshop findings and recommendations.

The effect of chronic phenytoin administration on single prolonged stress induced extinction retention deficits and glucocorticoid upregulation in the rat medial prefrontal cortex.

PubMed

George, Sophie A; Rodriguez-Santiago, Mariana; Riley, John; Rodriguez, Elizabeth; Liberzon, Israel

2015-01-01

Post-traumatic stress disorder (PTSD) is a chronic, debilitating disorder. Only two pharmacological agents are approved for PTSD treatment, and they often do not address the full range of symptoms nor are they equally effective in all cases. Animal models of PTSD are critical for understanding the neurobiology involved and for identification of novel therapeutic targets. Using the rodent PTSD model, single prolonged stress (SPS), we have implicated aberrant excitatory neural transmission and glucocorticoid receptor (GR) upregulation in the medial prefrontal cortex (mPFC) and hippocampus (HPC) in fear memory abnormalities associated with PTSD. The objective of this study is to examine the potential protective effect of antiepileptic phenytoin (PHE) administration on SPS-induced extinction retention deficits and GR expression. Forty-eight SPS-treated male Sprague Dawley rats or controls were administered PHE (40, 20 mg/kg, vehicle) for 7 days following SPS stressors; then, fear conditioning, extinction, and extinction retention were tested. Fear conditioning and extinction were unaffected by SPS or PHE, but SPS impaired extinction retention, and both doses of PHE rescued this impairment. Similarly, SPS increased GR expression in the mPFC and dorsal HPC, and PHE prevented SPS-induced GR upregulation in the mPFC. These data demonstrate that PHE administration can prevent the development of extinction retention deficits and upregulation of GR. PHE exerts inhibitory effects on voltage-gated sodium channels and decreases excitatory neural transmission via glutamate antagonism. If glutamate hyperactivity in the days following SPS contributes to SPS-induced deficits, then these data may suggest that the glutamatergic system constitutes a target for secondary prevention.

Ketamine facilitates extinction of avoidance behavior and enhances synaptic plasticity in a rat model of anxiety vulnerability: Implications for the pathophysiology and treatment of anxiety disorders.

PubMed

Fortress, Ashley M; Smith, Ian M; Pang, Kevin C H

2018-05-08

Anxiety disorders and posttraumatic stress disorder (PTSD) share a common feature of pathological avoidance behavior. The Wistar Kyoto (WKY) rat has been used as a model of anxiety vulnerability, expressing a behaviorally inhibited temperament, acquiring avoidance behavior more rapidly and displaying extinction-resistant avoidance compared to Sprague Dawley (SD) rats. Subanesthetic levels of ketamine have gained attention as a rapid antidepressant in treatment-resistant depression. While traditional antidepressants are commonly used to treat anxiety disorders and PTSD, the therapeutic utility of ketamine for these disorders is much less understood. The hippocampus is critical for the actions of antidepressants, is a structure of implicated in anxiety disorders and PTSD, and is necessary for extinction of avoidance in SD rats. WKY rats have impaired hippocampal long-term potentiation (LTP), suggesting that persistent avoidance in WKY rats may be due to deficient hippocampal synaptic plasticity. In the present study, we hypothesized that ketamine would facilitate extinction of avoidance learning in WKY rats, and do so by enhancing hippocampal synaptic plasticity. As predicted, ketamine facilitated extinction of avoidance behavior in a subset of WKY rats (responders), with effects lasting at least three weeks. Additionally, LTP in these rats was enhanced by ketamine. Ketamine was not effective in facilitating avoidance extinction or in modifying LTP in WKY non-responders. The results suggest that subanesthetic levels of ketamine may be useful for treating anxiety disorders by reducing avoidance behaviors when combined with extinction conditions. Moreover, ketamine may have its long-lasting behavioral effects through enhancing hippocampal synaptic plasticity. Copyright © 2018. Published by Elsevier Ltd.

Assessment of light extinction at a European polluted urban area during wintertime: Impact of PM1 composition and sources.

PubMed

Vecchi, R; Bernardoni, V; Valentini, S; Piazzalunga, A; Fermo, P; Valli, G

2018-02-01

In this paper, results from receptor modelling performed on a well-characterised PM 1 dataset were combined to chemical light extinction data (b ext ) with the aim of assessing the impact of different PM 1 components and sources on light extinction and visibility at a European polluted urban area. It is noteworthy that, at the state of the art, there are still very few papers estimating the impact of different emission sources on light extinction as we present here, although being among the major environmental challenges at many polluted areas. Following the concept of the well-known IMPROVE algorithm, here a tailored site-specific approach (recently developed by our group) was applied to assess chemical light extinction due to PM 1 components and major sources. PM 1 samples collected separately during daytime and nighttime at the urban area of Milan (Italy) were chemically characterised for elements, major ions, elemental and organic carbon, and levoglucosan. Chemical light extinction was estimated and results showed that at the investigated urban site it is heavily impacted by ammonium nitrate and organic matter. Receptor modelling (i.e. Positive Matrix Factorization, EPA-PMF 5.0) was effective to obtain source apportionment; the most reliable solution was found with 7 factors which were tentatively assigned to nitrates, sulphates, wood burning, traffic, industry, fine dust, and a Pb-rich source. The apportionment of aerosol light extinction (b ext,aer ) according to resolved sources showed that considering all samples together nitrate contributed at most (on average 41.6%), followed by sulphate, traffic, and wood burning accounting for 18.3%, 17.8% and 12.4%, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mechanisms to medicines: elucidating neural and molecular substrates of fear extinction to identify novel treatments for anxiety disorders

PubMed Central

Bukalo, Olena; Pinard, Courtney R; Holmes, Andrew

2014-01-01

The burden of anxiety disorders is growing, but the efficacy of available anxiolytic treatments remains inadequate. Cognitive behavioural therapy for anxiety disorders focuses on identifying and modifying maladaptive patterns of thinking and behaving, and has a testable analogue in rodents in the form of fear extinction. A large preclinical literature has amassed in recent years describing the neural and molecular basis of fear extinction in rodents. In this review, we discuss how this work is being harnessed to foster translational research on anxiety disorders and facilitate the search for new anxiolytic treatments. We begin by summarizing the anatomical and functional connectivity of a medial prefrontal cortex (mPFC)–amygdala circuit that subserves fear extinction, including new insights from optogenetics. We then cover some of the approaches that have been taken to model impaired fear extinction and associated impairments with mPFC–amygdala dysfunction. The principal goal of the review is to evaluate evidence that various neurotransmitter and neuromodulator systems mediate fear extinction by modulating the mPFC–amygdala circuitry. To that end, we describe studies that have tested how fear extinction is impaired or facilitated by pharmacological manipulations of dopamine, noradrenaline, 5-HT, GABA, glutamate, neuropeptides, endocannabinoids and various other systems, which either directly target the mPFC–amygdala circuit, or produce behavioural effects that are coincident with functional changes in the circuit. We conclude that there are good grounds to be optimistic that the progress in defining the molecular substrates of mPFC–amygdala circuit function can be effectively leveraged to identify plausible candidates for extinction-promoting therapies for anxiety disorders. Linked Articles This article is part of a themed section on Animal Models in Psychiatry Research. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-20 PMID:24835117

DEVELOPMENT OF AQUATIC MODELS FOR TESTING THE RELATIONSHIP BETWEEN GENETIC DIVERSITY AND POPULATION EXTINCTION RISK

EPA Science Inventory

The relationship between population adaptive potential and extinction risk in a changing environment is not well understood. Although the expectation is that genetic diversity is directly related to the capacity of populations to adapt, the statistical and predictive aspects of ...

Context, Learning, and Extinction

ERIC Educational Resources Information Center

Gershman, Samuel J.; Blei, David M.; Niv, Yael

2010-01-01

A. Redish et al. (2007) proposed a reinforcement learning model of context-dependent learning and extinction in conditioning experiments, using the idea of "state classification" to categorize new observations into states. In the current article, the authors propose an interpretation of this idea in terms of normative statistical inference. They…

Pavlovian disgust conditioning as a model for contamination-based OCD: Evidence from an analogue study

PubMed Central

Armstrong, Thomas; Olatunji, Bunmi O.

2017-01-01

Pavlovian fear conditioning provides a model for anxiety-related disorders, including obsessive-compulsive disorder (OCD). However, disgust is the predominant emotional response to contamination, which is a common theme in OCD. The present study sought to identify disgust conditioning abnormalities that may underlie excessive contamination concerns relevant to OCD. Individuals high and low in contamination concern (HCC, n = 32; LCC, n = 30) completed an associative learning task in which one neutral face (conditioned stimulus; CS+) was followed by a disgusting image (unconditioned stimulus; US) and another neutral face (CS−) was unreinforced. Following this acquisition procedure, there was an extinction procedure in which both CSs were presented unreinforced. The groups did not show significant differences in discriminant responding to the CSs following acquisition. However, following extinction, the HCC group reported less reduction in their expectancy of the US following the CS+, and also reported greater disgust to the CS+, compared to the LCC group. Increased disgust to the CS+ following both acquisition and extinction was correlated with increased symptoms of contamination-based OCD and increased disgust sensitivity. Additionally, disgust sensitivity mediated group differences in disgust responding to the CS+ at acquisition and extinction. Also, failure to adjust US expectancy in response to extinction partially mediated group differences in disgust to the CS+ following extinction. Together, these findings suggest that excessive contamination concerns observed in OCD may be related to difficulty inhibiting acquired disgust, possibly due to elevated disgust sensitivity that characterizes the disorder. PMID:28391115

Comparisons of Airborne HSRL and Modeled Aerosol Profiles

NASA Astrophysics Data System (ADS)

Ferrare, R. A.; Burton, S. P.; Hostetler, C. A.; Hair, J. W.; Ismail, S.; Rogers, R. R.; Notari, A.; Berkoff, T.; Butler, C. F.; Collins, J. E., Jr.; Fenn, M. A.; Scarino, A. J.; Clayton, M.; Mueller, D.; Chemyakin, E.; Fast, J. D.; Berg, L. K.; Randles, C. A.; Colarco, P. R.; daSilva, A.

2014-12-01

Aerosol profiles derived from a regional and a global model are compared with aerosol profiles acquired by NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidars (HSRLs) during recent field missions. We compare simulated aerosol profiles obtained from the WRF-Chem regional model with those measured by the airborne HSRL-2 instrument over the Atlantic Ocean east of Cape Cod in July 2012 during the Department of Energy Two-Column Aerosol Project (TCAP). While deployed on the LaRC King Air during TCAP, HSRL-2 acquired profiles of aerosol extinction at 355 and 532 nm, as well as aerosol backscatter and depolarization at 355, 532, and 1064 nm. Additional HSRL-2 data products include profiles of aerosol type, mixed layer depth, and aerosol microphysical parameters (e.g. effective radius, concentration). The HSRL-2 and WRF-Chem aerosol profiles are compared along the aircraft flight tracks. HSRL-2 profiles acquired during the NASA Deriving Information on Surface Conditions from COlumn and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) mission over Houston during September 2013 are compared with the NASA Goddard Earth Observing System global model, version 5 (GEOS-5) profiles. In addition to comparing backscatter and extinction profiles, the fraction of aerosol extinction and optical thickness from various aerosol species from GEOS-5 are compared with aerosol extinction and optical thickness contributed by aerosol types derived from HSRL-2 data. We also compare aerosol profiles modeled by GEOS-5 with those measured by the airborne LaRC DIAL/HSRL instrument during August and September 2013 when it was deployed on the NASA DC-8 for the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) mission. DIAL/HSRL measured extinction (532 nm), backscatter (532 and 1064 nm), and depolarization profiles (532 and 1064 nm) in both nadir and zenith directions during long transects over the continental United States. DIAL/HSRL measurements acquired during SEAC4RS allow comparisons with GEOS-5 simulations of forest fire smoke over the western U.S. The fraction of aerosol extinction attributed to dust derived from the DIAL/HSRL depolarization measurements are compared with the corresponding GEOS-5 dust simulations.