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Results for “Extinction, Biological”

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At least 199 records · Page 11Linked to original sources
PubMed2006

Can neutral theory predict the responses of Amazonian tree communities to forest fragmentation?

We use Hubbell's neutral theory to predict the impact of habitat fragmentation on Amazonian tree communities. For forest fragments isolated for about two decades, we generate neutral predictions for local species extinction, changes in species composition within fragments, and increases in the probability that any two trees within a fragment are conspecific. We tested these predictions using fragment and intact forest data from the Biological Dynamics of Forest Fragments Project in central Amazonia. To simulate complete demographic isolation, we excluded immigrants--species absent from a fragment or intact forest plot in the initial census but present in its last census--from our tests. The neutral theory correctly predicted the rate of species extinction from different plots as a function of the diversity and mortality rate of trees in each plot. However, the rate of change in species composition was much faster than predicted in fragments, indicating that different tree species respond differently to environmental changes. This violates the key assumption of neutral theory. When immigrants were included in our calculations, they increased the disparity between predicted and observed changes in fragments. Overall, neutral theory accurately predicted the pace of local extinctions in fragments but consistently underestimated changes in species composition.

Conservation of Natural Resources↗
PubMed2001

Mathematical conservation ecology: a one-predator-two-prey system as case study.

A method is presented to analyse the long-term stochastic dynamics of a biological population that is at risk of extinction. From the full ecosystem the method extracts the minimal information to describe the long-term dynamics of that population by a stochastic logistic system. The method is applied to a one-predator-two-prey model. The choice of this example is motivated by a study on the near-extinction of a porcupine population by mountain lions whose presence is facilitated by mule deer taking advantage of a change in land use. The risk of extinction is quantified by the expected time of extinction of the population.

Animals↗
PubMed2004

Large perturbations of the carbon cycle during recovery from the end-permian extinction.

High-resolution carbon isotope measurements of multiple stratigraphic sections in south China demonstrate that the pronounced carbon isotopic excursion at the Permian-Triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the Early Triassic before ending abruptly early in the Middle Triassic. The unusual behavior of the carbon cycle coincides with the delayed recovery from end-Permian extinction recorded by fossils, suggesting a direct relationship between Earth system function and biological rediversification in the aftermath of Earth's most devastating mass extinction.

Animals↗
PubMed1976

Interactions of nucleic acid bases with catechol: UV studies.

UV absorption studies on weak interactions of adenine, cytosine, thymine, and uracil with cathechol in aqueous solutions containing 0.1 N HCl gave evidence for the formation of charge transfer complexes. The absorptions of these complexes were found in the UV region at longer wavelengths than those of the pure components. It was possible to calculate various thermodynamic parameters and molar extinction coefficients at different wavelengths. The biological significance of the results is discussed.

Adenine↗
PubMed2004

Simulation of rat behavior by a reinforcement learning algorithm in consideration of appearance probabilities of reinforcement signals.

Brown and Wanger [Brown, R.T., Wanger, A.R., 1964. Resistance to punishment and extinction following training with shock or nonreinforcement. J. Exp. Psychol. 68, 503-507] investigated rat behaviors with the following features: (1) rats were exposed to reward and punishment at the same time, (2) environment changed and rats relearned, and (3) rats were stochastically exposed to reward and punishment. The results are that exposure to nonreinforcement produces resistance to the decremental effects of behavior after stochastic reward schedule and that exposure to both punishment and reinforcement produces resistance to the decremental effects of behavior after stochastic punishment schedule. This paper aims to simulate the rat behaviors by a reinforcement learning algorithm in consideration of appearance probabilities of reinforcement signals. The former algorithms of reinforcement learning were unable to simulate the behavior of the feature (3). We improve the former reinforcement learning algorithms by controlling learning parameters in consideration of the acquisition probabilities of reinforcement signals. The proposed algorithm qualitatively simulates the result of the animal experiment of Brown and Wanger.

Algorithms↗
PubMed2003

Abundance not linked to survival across the end-Cretaceous mass extinction: patterns in North American bivalves.

Ecological studies suggest that rare taxa are more likely to go extinct than abundant ones, but the influence of abundance on survivorship in the fossil record has received little attention. An analysis of Late Maastrichtian bivalve subgenera from the North American Coastal Plain found no evidence that survivorship is tied to abundance across the end-Cretaceous mass extinction (65 million years ago), regardless of abundance metric or spatial scale examined. The fact that abundance does not promote survivorship in end-Cretaceous bivalves suggests that the factors influencing survivorship during mass extinctions in the fossil record may differ from those operating during intervals of background extinction.

Animals↗
PubMed2002

Hotspots and the conservation of evolutionary history.

Species diversity is unevenly distributed across the globe, with terrestrial diversity concentrated in a few restricted biodiversity hotspots. These areas are associated with high losses of primary vegetation and increased human population density, resulting in growing numbers of threatened species. We show that conservation of these hotspots is critical because they harbor even greater amounts of evolutionary history than expected by species numbers alone. We used supertrees for carnivores and primates to estimate that nearly 70% of the total amount of evolutionary history represented in these groups is found in 25 biodiversity hotspots.

Animals↗
PubMed2002

Whole-tree methods for detecting differential diversification rates.

Prolific cladogenesis, adaptive radiation, species selection, key innovations, and mass extinctions are a few examples of biological phenomena that lead to differential diversification among lineages. Central to the study of differential diversification rates is the ability to distinguish chance variation from that which requires deterministic explanation. To detect diversification rate variation among lineages, we propose a number of methods that incorporate information on the topological distribution of species diversity from all internal nodes of a phylogenetic tree. These whole-tree methods (M(Pi), M(Sigma), and M(R)) are explicitly connected to a null model of random diversification--the equal-rates Markov (ERM) random branching model--and an alternative model of differential diversification: M(Pi) is based on the product of individual nodal ERM probabilities; M(Sigma) is based on the sum of individual nodal ERM probabilities, and M(R) is based on a transformation of ERM probabilities that corresponds to a formalized system that orders trees by their relative symmetry. These methods have been implemented in a freely available computer program, SYMMETREE, to detect clades with variable diversification rates, thereby allowing the study of biological processes correlated with and possibly causal to shifts in diversification rate. Application of these methods to several published phylogenies demonstrates their ability to contend with relatively large, incompletely resolved trees. These topology-based methods do not require estimates of relative branch lengths, which should facilitate the analysis of phylogenies, such as supertrees, for which such data are unreliable or unavailable.

Animals↗
PubMed1996

Geographic structure of insect populations: gene flow, phylogeography, and their uses.

Geographic structure of populations is a fundamental component of ecology and evolution that combines both demographic and genetic processes, such as gene flow and migration, genetic drift, selection, and population extinction. Recent advances in both molecular biology and theory have revolutionized the field and have not only expanded the availability of data but also facilitated the accessibility and interpretation of current data. These new techniques allow analysis of genetic similarity among populations to be coupled with phylogeography and the distribution of genotypes within and among populations relative to the history of those genotypes. The numerous case studies described herein illustrate the growing impact of geographic structure on insect science, as well as the importance of insect model systems for understanding general concepts in ecology and evolution.

Journal Article↗
PubMed1995

Conservation genetics.

Inbreeding depression, accumulation and loss of deleterious mutations, loss of genetic variation in small populations, genetic adaptation to captivity and its effect on reintroduction success, and outbreeding depression are reviewed. The impact of genetic factors in endangerment and extinction has been underestimated in some recent publications. Inbreeding depression in wildlife and in the field has been clearly established, while its impact has been greatly underestimated. The size of populations where genetic factors become important is higher than previously recognized, as Ne/N ratios average 0.11. Purging effects have been overestimated as a mechanism for eliminating deleterious alleles in small populations. The impact of loss of genetic variation in increasing the susceptibility of populations to environmental stochasticity and catastrophes has generally been ignored. Consequently, extinctions are often attributed to "nongenetic" factors when these may have interacted with genetic factors to cause extinction.

Adaptation, Biological↗
PubMed2003

Methodologies for the care, maintenance, and breeding of tropical poison frogs.

The Biodiversity Laboratories at Saint Joseph's University house more than 100 exotic and endangered animal species-including insects, fish, amphibians, and reptiles. Research in the laboratories is devoted, primarily, to understanding the genetic and ecological bases of animal behavior. In addition, a common theme of the work is the development of techniques for the successful care of exotic animals within a laboratory setting. Such techniques may be critical to studies aimed at understanding the life histories of endangered species and saving them from extinction. Current projects to study the biology of tropical poison frogs have methodologies to improve captive care, maintenance, and breeding. In this article, I present these methodologies and their impact on the welfare of captive poison frogs.

Animal Welfare↗
PubMed2003

Genetics and conservation biology.

Conservation genetics encompasses genetic management of small populations, resolution of taxonomic uncertainties and management units, and the use of molecular genetic analyses in forensics and to understanding species' biology. The role of genetic factors in extinctions of wild populations has been controversial, but evidence now shows that they make important contributions to extinction risk. Inbreeding has been shown to cause extinctions of wild populations, computer projections indicate that inbreeding depression has important effects on extinction risk, and most threatened species show signs of genetic deterioration. Inappropriate management is likely to result if genetic factors are ignored in threatened species management.

Animals↗