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Results for “Extinction, Biological”

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PubMed2002

Bioweapons, bioterrorism and biodiversity: potential impacts of biological weapons attacks on agricultural and biological diversity.

Diseases and biological toxins have been used as weapons of war throughout recorded history, from Biblical times through to the present day. Bioweapon uses have historically been directed primarily, although not exclusively, against human populations. Specialised technicians and state-of-the-art research facilities are no longer necessary for the production or deployment of many known bioweapon agents and commercially available technologies now permit the large-scale production of bioweapon agents in small-scale facilities at relatively low cost. Failures in the detection and containment of bioweapon and emerging disease outbreaks among populations of wildlife and indigenous peoples in developing countries could result in severe erosion of genetic diversity in local and regional populations of both wild and domestic animals, the extinction of endangered species and the extirpation of indigenous peoples and their cultures. Our ability to understand and control the spread of diseases within and among human and animal populations is increasing but is still insufficient to counter the threats presented by existing bioweapon diseases and the growing number of highly pathogenic emergent infections. Interdisciplinary and international efforts to increase the monitoring, surveillance, identification and reporting of disease agents and to better understand the potential dynamics of disease transmission within human and animal populations in both industrialised and developing country settings will greatly enhance our ability to combat the effects of bioweapons and emerging diseases on biological communities and biodiversity.

Agriculture↗

PubMed2006

Dynamics of hybridization and introgression in red wolves and coyotes.

Hybridization and introgression are significant causes of endangerment in many taxa and are considered the greatest biological threats to the reintroduced population of red wolves (Canis rufus) in North Carolina (U.S.A.). Little is known, however, about these processes in red wolves and coyotes (C. latrans). We used individual-based simulations to examine the process of hybridization and introgression between these species. Under the range of circumstances we considered, red wolves in colonizing and established populations were quickly extirpated, persisted near the carrying capacity, or had intermediate outcomes. Sensitivity analyses suggested that the probabilities of quasi extinction and persistence of red wolves near the carrying capacity were most affected by the strength of two reproductive barriers: red wolf challenges and assortative mating between red wolves and coyotes. Because model parameters for these barriers may be difficult to estimate, we also sought to identify other predictors of red wolf population fate. The proportion of pure red wolves in the population was a strong predictor of the future probabilities of red wolf quasi extinction and persistence. Finally, we examined whether sterilization can be effective in minimizing introgression while allowing the reintroduced red wolfpopulation to grow. Our results suggest sterilization can be an effective short-term strategy to reduce the likelihood of extirpation in colonizing populations of red wolves. Whether red wolf numbers are increased by sterilization depends on the level of sterilization effort and the acting reproductive barriers. Our results provide an outline of the conditions likely required for successful reestablishment and long-term maintenance of populations of wild red wolves in the presence of coyotes. Our modeling approach may prove generally useful in providing insight into situations involving complex species interactions when data are few.

Animals↗

PubMed2000

Population extinction and quasi-stationary behavior in stochastic density-dependent structured models.

Density-independent and density-dependent, stochastic and deterministic, discrete-time, structured models are formulated, analysed and numerically simulated. A special case of the deterministic, density-independent, structured model is the well-known Leslie age-structured model. The stochastic, density-independent model is a multitype branching process. A review of linear, density-independent models is given first, then nonlinear, density-dependent models are discussed. In the linear, density-independent structured models, transitions between states are independent of time and state. Population extinction is determined by the dominant eigenvalue lambda of the transition matrix. If lambda < or = 1, then extinction occurs with probability one in the stochastic and deterministic models. However, if lambda > 1, then the deterministic model has exponential growth, but in the stochastic model there is a positive probability of extinction which depends on the fixed point of the system of probability generating functions. The linear, density-independent, stochastic model is generalized to a nonlinear, density-dependent one. The dependence on state is in terms of a weighted total population size. It is shown for small initial population sizes that the density-dependent, stochastic model can be approximated by the density-independent, stochastic model and thus, the extinction behavior exhibited by the linear model occurs in the nonlinear model. In the deterministic models there is a unique stable equilibrium. Given the population does not go extinct, it is shown that the stochastic model has a quasi-stationary distribution with mean close to the stable equilibrium, provided the population size is sufficiently large. For small values of the population size, complete extinction can be observed in the simulations. However, the persistence time increases rapidly with the population size.

Age Factors↗

PubMed1999

Evolutionary branching under asymmetric competition.

I investigate the evolution of a continuous trait, such as body size or arms level, which affects the outcome of competitive contests such that the contestant with the larger trait value has a higher probability of winning. I show that a polymorphism of distinctly different strategies can evolve in an initially monomorphic population even if mutations have only small phenotypic effect. In a simple Lotka-Volterra-type model of asymmetric competition, I derive the conditions under which two strategies can gradually evolve from a single ancestral strategy; the evolution of higher level polymorphisms is studied by numerical analysis and computer simulations of specific examples. High levels of polymorphism may build up during evolution. The coevolution of strategies in polymorphic populations, however, may also lead to extinction, which decreases the level of polymorphism. I discuss whether the evolution of several haploid strategies from a single initial strategy may correspond to the evolution of several sympatric species in a diploid outbreeding population.

Animals↗

PubMed1995

Screening of Bothrops snake venoms for L-amino acid oxidase activity.

Toxins, enzymes, and biologically active peptides are the main components of snake venoms from the genus Bothrops. Following the venom inoculation, the local effects are hemorrhage, edema, and myonecrosis. Nineteen different species of Brazilian Bothrops were screened for protein content and L-amino acid oxidase activity. B. cotiara, formerly found in the South of Brazil, is now threatened with extinction. Its venom contains a highly hemorrhagic fraction and, as expected from the deep yellow color of the corresponding lyophilized powder, a high L-amino acid oxidase (LAO) activity was also characterized. Flavin adenine dinucleotide (FAD) is its associate coenzyme. B. cotiara venom LAO catalyzed the oxidative deamination of several L-amino acids, and the best substrates were methionine, leucine, tryptophan, and phenylalanine, hence, its potential application for the use of biosensors for aspartame determination and for the removal of amino acids from plasma. High levels for LAO were also found in other species than B. cotiara. In addition, the technique of isoelectric focusing (IEF) was employed as a powerful tool to study the iso- or multi-enzyme distribution for LAO activity in the B. cotiara snake venom.

Amino Acid Oxidoreductases↗

PubMed2004

The relationship between species detection probability and local extinction probability.

In community-level ecological studies, generally not all species present in sampled areas are detected. Many authors have proposed the use of estimation methods that allow detection probabilities that are <1 and that are heterogeneous among species. These methods can also be used to estimate community-dynamic parameters such as species local extinction probability and turnover rates (Nichols et al. Ecol Appl 8:1213-1225; Conserv Biol 12:1390-1398). Here, we present an ad hoc approach to estimating community-level vital rates in the presence of joint heterogeneity of detection probabilities and vital rates. The method consists of partitioning the number of species into two groups using the detection frequencies and then estimating vital rates (e.g., local extinction probabilities) for each group. Estimators from each group are combined in a weighted estimator of vital rates that accounts for the effect of heterogeneity. Using data from the North American Breeding Bird Survey, we computed such estimates and tested the hypothesis that detection probabilities and local extinction probabilities were negatively related. Our analyses support the hypothesis that species detection probability covaries negatively with local probability of extinction and turnover rates. A simulation study was conducted to assess the performance of vital parameter estimators as well as other estimators relevant to questions about heterogeneity, such as coefficient of variation of detection probabilities and proportion of species in each group. Both the weighted estimator suggested in this paper and the original unweighted estimator for local extinction probability performed fairly well and provided no basis for preferring one to the other.

Animals↗

PubMed1992

Current perspectives of singlet oxygen detection in biological environments.

There is widespread acceptance that singlet oxygen is a key intermediate on one of the pathways leading to the phenomenon of photodynamic action. However, the identification of this moiety within a particular biological system and the determination of a direct link between its presence and a particular photodynamic effect is a goal which photobiologists have hitherto failed to achieve. The aim of this review is to assess the problems associated with such a goal and methods whereby they might be overcome. Initially the general photochemical and environmental factors which govern the ability of a photosensitizer to promote photodynamic action via the intermediacy of singlet oxygen are introduced and the fundamental parameters defining the formation, decay and reactivity of this species summarized. The experimental requirements for relating a particular photodynamic effect to singlet oxygen intermediacy are then analysed and the intrinsic properties of singlet oxygen which will influence this goal are discussed. Having concluded that the singlet oxygen detection method of choice for this purpose is that in which the IR emission at 1269 nm of this molecule is monitored, the advantages and disadvantages of pulsed and continuous wave photoexcitation of cellular systems are analysed. It becomes evident that, no matter what the future improvements in instrumentation are likely to be, the inherent natures of singlet oxygen and the biological system lead to a kinetic situation which will preclude a successful time-resolved solution to this problem. In contrast, experimentation with continuous wave systems holds out significant hope for the future. In particular, the use of phase modulation techniques to overcome background emission problems, the enhancement of photosensitizer optical densities as a consequence of higher extinction coefficients and/or improved photosensitizer delivery systems and the use of high power lasers and/or improved light delivery systems can, at least in principle, lead to the solution of the problem addressed herein.

Animals↗

PubMed2006

Surprising evolutionary predictions from enhanced ecological realism.

A focus on the eco-evolutionary feedback continually operating between a population's evolution and its environment helps to appreciate the generality of ESS theory. Here we illustrate, through a sequence of four examples, how respecting such feedback in the evolutionary dynamics of quantitative traits may result in qualitatively unexpected outcomes. Reviewing existing insights and complementing these with new results, we show (1) that evolutionary matrix games are fundamentally degenerate and allow a natural unfolding, (2) that selection-driven extinction may not be rare in nature, (3) that evolutionary epidemiology should not rely on R0 maximization, and (4) why the occurrence of Hardy-Weinberg proportions generically requires an evolutionary explanation.

Biological Evolution↗

PubMed2005

Fifty millennia of catastrophic extinctions after human contact.

Debate continues to rage between enthusiasts for climate change versus humans as a cause of the catastrophic faunal extinctions that have occurred in the wake of human arrival in previously uninhabited regions of the world. A global pattern of human arrival to such landmasses, followed by faunal collapse and other ecological changes, appears without known exception. This strongly suggests to some investigators that a more interesting extinction debate lies within the realm of potential human-caused explanations and how climate might exacerbate human impacts. New observations emerging from refined dating techniques, paleoecology and modeling suggest that the megafaunal collapses of the Americas and Australia, as well as most prehistoric island biotic losses, trace to a variety of human impacts, including rapid overharvesting, biological invasions, habitat transformation and disease.

Journal Article↗

PubMed1997

The use of a mass-action model to validate the output from a stochastic simulation model of bovine viral diarrhoea virus spread in a closed dairy herd.

The spread of bovine virus diarrhoea virus (BVDV) in a closed dairy herd maintained under typical management conditions is studied using two approaches. In the first instance a stochastic computer model is used to simulate the month-to-month changes in the infection status of each animal. These results are contrasted with the results of a mass-action model which uses three differential equations. A comparison of the two approaches indicates that the results are in broad agreement. The stochastic approach has the benefit of providing an estimate of the probability of the infection becoming extinct and the herd becoming BVDV-free for different herd sizes.

Animals↗

PubMed2006

Parochial altruism in humans.

Social norms and the associated altruistic behaviours are decisive for the evolution of human cooperation and the maintenance of social order, and they affect family life, politics and economic interactions. However, as altruistic norm compliance and norm enforcement often emerge in the context of inter-group conflicts, they are likely to be shaped by parochialism--a preference for favouring the members of one's ethnic, racial or language group. We have conducted punishment experiments, which allow 'impartial' observers to punish norm violators, with indigenous groups in Papua New Guinea. Here we show that these experiments confirm the prediction of parochialism. We found that punishers protect ingroup victims--who suffer from a norm violation--much more than they do outgroup victims, regardless of the norm violator's group affiliation. Norm violators also expect that punishers will be lenient if the latter belong to their social group. As a consequence, norm violations occur more often if the punisher and the norm violator belong to the same group. Our results are puzzling for evolutionary multi-level selection theories based on selective group extinction as well as for theories of individual selection; they also indicate the need to explicitly examine the interactions between individuals stemming from different groups in evolutionary models.

Adolescent↗

PubMed2005

Climate change threats to plant diversity in Europe.

Climate change has already triggered species distribution shifts in many parts of the world. Increasing impacts are expected for the future, yet few studies have aimed for a general understanding of the regional basis for species vulnerability. We projected late 21st century distributions for 1,350 European plants species under seven climate change scenarios. Application of the International Union for Conservation of Nature and Natural Resources Red List criteria to our projections shows that many European plant species could become severely threatened. More than half of the species we studied could be vulnerable or threatened by 2080. Expected species loss and turnover per pixel proved to be highly variable across scenarios (27-42% and 45-63% respectively, averaged over Europe) and across regions (2.5-86% and 17-86%, averaged over scenarios). Modeled species loss and turnover were found to depend strongly on the degree of change in just two climate variables describing temperature and moisture conditions. Despite the coarse scale of the analysis, species from mountains could be seen to be disproportionably sensitive to climate change (approximately 60% species loss). The boreal region was projected to lose few species, although gaining many others from immigration. The greatest changes are expected in the transition between the Mediterranean and Euro-Siberian regions. We found that risks of extinction for European plants may be large, even in moderate scenarios of climate change and despite inter-model variability.

Biodiversity↗

PubMed1992

Behavioral effects of atrial and brain natriuretic peptides in rats.

The effects of intracerebroventricular administration of rat atrial natriuretic peptide (rANP-1-28) and porcine brain natriuretic peptide-32 (pBNP-32) on passive and active avoidance behavior and on electroconvulsive shock-induced amnesia were studied in rats. The dose range for both peptides was selected to lie between 0.016 and 0.32 nmol. The two peptides were found to facilitate consolidation of the passive avoidance response, to delay extinction of the active avoidance response, and to prevent electroconvulsive shock-induced amnesia in a similar way. It is suggested that some modulatory functions in the central nervous system of the rat, so far attributed to ANP, may in fact involve a dual control by both ANP and BNP, and there is no difference in the biological activity of the two peptides as far as fear-motivated learning behavior is concerned.

Amnesia↗

PubMed2002

Dynamics of extinction and the selection of nature reserves.

Familiar quantitative reserve-selection techniques are tailored to simple decision problems, where the representation of species is sought at minimum cost. However, conservationists have begun to ask whether representing species in reserve networks is sufficient to avoid local extinctions within selected areas. An attractive, but previously untested idea is to model current species' probabilities of occurrence as an estimate of local persistence in the near future. Using distribution data for passerine birds in Great Britain, we show that (i) species' probabilities of occurrence are negatively related to local probabilities of extinction, at least when a particular 20-year period is considered, and (ii) local extinctions can be reduced if areas are selected to maximize current species' probabilities of occurrence We suggest that more extinctions could be avoided if even a simple treatment of persistence were to be incorporated within reserve selection methods.

Animals↗

PubMed2004

Sexual selection and the risk of extinction in mammals.

Sexual selection is commonly envisaged as a force working in opposition to natural selection, because extravagant or exaggerated traits could apparently have never evolved via natural selection alone. There is good evidence that a selection load imposed by sexual selection may be eased experimentally by restricting the opportunity for it to operate. Sexual selection could therefore potentially play an important role in influencing the risk of extinction that a population faces, thereby contributing to the apparent selectivity of extinctions. Conversely, recent theory predicts that the likelihood of extinction may decrease when sexual selection is operating because it could accelerate the rate of adaptation in concert with natural selection. So far, comparative evidence (coming mostly from birds) has generally indicated support for the former scenario, but the question remains open. The aim of this study was therefore to examine whether the level of sexual selection (measured as residual testes mass and sexual size dimorphism) was related to the risk of extinction that mammals are currently experiencing. We found no evidence for a relationship between these factors, although our analyses may have been confounded by the possible dominating effect of contemporary anthropogenic factors.

Animals↗

PubMed1994

The reconstructed evolutionary process.

Phylogenies reconstructed from contemporary taxa do not contain information about lineages that have gone extinct. We derive probability models for such phylogenies, allowing real data to be compared with specified null models of evolution, and lineage birth and death rates to be estimated.

Animals↗

PubMedDate not supplied

Androgens in human evolution. A new explanation of human evolution.

Human evolution consists of chronological changes in gene regulation of a continuous and relatively stable genome, activated by hormones, the production of which is intermittently affected by endogenous and exogenous forces. Periodic variations in the gonadal androgen, testosterone, and the adrenal androgen, dehydroepiandrosterone (DHEA), significantly participated in all hominid transformations. The hominid characteristics of early Australopithecines are primarily a result of increased testosterone. The first significant cold of the early Pleistocene resulted in an increase in DHEA that simultaneously produced Homo and the robust Australopithecines. Subsequent Pleistocene climatic changes and differential reproduction produced changes in DHEA and testosterone ratios that caused extinction of the robust Australopithecines and further changes and continuation of Homo. Changes in testosterone and DHEA produce allometric and behavioral changes that are identifiable and vigorous in modern populations.

Adolescent↗

PubMedDate not supplied

[Analysis of seasonal fluctuations in the Lotka-Volterra model].

A modification of the Lotka-Volterra model was proposed. The modification takes into account the factor of seasonal fluctuations in a "predator-prey" model. In this modification, interactions between species in summer are described by the Lotka-Volterra equations; in winter, individuals of both species extinct. This generalization makes the classic model unrough, which substantially extends the field of its application. The results of numerical simulation illustrate the statement formulated above.

Animals↗