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Results for “Extinction, Biological”

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PubMed1994

Locus coeruleus-evoked responses in behaving rats: a clue to the role of noradrenaline in memory.

Neuromodulatory properties of noradrenaline (NA) suggest that the coreruleo-cortical NA projection should play an important role in attention and memory processes. Our research is aimed at providing some behavioral evidence. Single units of the locus coeruleus (LC) are recorded during controlled behavioral situations, in order to relate LC activation to specific behavioral contexts. LC cells respond in burst to imposed novel sensory stimuli or to novel objects encountered during free exploration. When there is no predictive value of the stimulus or no behavioral response required, there is rapid habituation of the LC response. When a stimulus is then associated with reinforcement, there is a renewed response, which is transient. During extinction, LC neuronal responses reappear. Thus, LC cells respond to novelty or change in incoming information, but do not have a sustained response to stimuli, even when they have a high level of biological significance. The gating and tuning action of NA released in target sensory systems would promote selective attention to relevant stimuli at the critical moment of change. The adaptive behavioral outcome would result from the integration of retrieved memory with the sensory information selected from the environment.

Animals↗

PubMed2005

Keystone species and vulnerable species in ecological communities: strong or weak interactors?

The loss of a species from an ecological community can trigger a cascade of secondary extinctions. The probability of secondary extinction to take place and the number of secondary extinctions are likely to depend on the characteristics of the species that is lost--the strength of its interactions with other species--as well as on the distribution of interaction strengths in the whole community. Analysing the effects of species loss in model communities we found that removal of the following species categories triggered, on average, the largest number of secondary extinctions: (a) rare species interacting strongly with many consumers, (b) abundant basal species interacting weakly with their consumers and (c) abundant intermediate species interacting strongly with many resources. We also found that the keystone status of a species with given characteristics was context dependent, that is, dependent on the structure of the community where it was embedded. Species vulnerable to secondary extinctions were mainly species interacting weakly with their resources and species interacting strongly with their consumers.

Animals↗

PubMed2004

Dispersal and the evolution of specialisation in a two-habitat type metapopulation.

Metapopulation theory for the evolution of specialisation is virtually absent. In this article, therefore, we study a metapopulation model for consumers with a fitness trade-off between two habitats. We focus on effects of habitat abundance, dispersal rate and trade-off strength on the evolution of specialisation under two types of trade-off. Adaptation affects either the intrinsic growth rates r or the carrying capacities K. Depending on dispersal rate and trade-off strength, evolution can result in one generalist, one specialist or two specialist types. Higher dispersal rate and a weaker trade-off favour the evolution of a generalist, for both trade-off structures. However, we also find differences between the two trade-off structures. Our results are qualitatively similar to analyses of two-patch models, suggesting that insights from such simpler models can be extrapolated to metapopulation models. Additional effects, however, occur because in classical metapopulations patch lifetime depends on extinction rate. Counterintuitively, this favours the evolution of specialisation when the trade-off affects r.

Adaptation, Physiological↗

PubMed2001

Multiple attractors and boundary crises in a tri-trophic food chain.

The asymptotic behaviour of a model of a tri-trophic food chain in the chemostat is analysed in detail. The Monod growth model is used for all trophic levels, yielding a non-linear dynamical system of four ordinary differential equations. Mass conservation makes it possible to reduce the dimension by 1 for the study of the asymptotic dynamic behaviour. The intersections of the orbits with a Poincaré plane, after the transient has died out, yield a two-dimensional Poincaré next-return map. When chaotic behaviour occurs, all image points of this next-return map appear to lie close to a single curve in the intersection plane. This motivated the study of a one-dimensional bi-modal, non-invertible map of which the graph resembles this curve. We will show that the bifurcation structure of the food chain model can be understood in terms of the local and global bifurcations of this one-dimensional map. Homoclinic and heteroclinic connecting orbits and their global bifurcations are discussed also by relating them to their counterparts for a two-dimensional map which is invertible like the next-return map. In the global bifurcations two homoclinic or two heteroclinic orbits collide and disappear. In the food chain model two attractors coexist; a stable limit cycle where the top-predator is absent and an interior attractor. In addition there is a saddle cycle. The stable manifold of this limit cycle forms the basin boundary of the interior attractor. We will show that this boundary has a complicated structure when there are heteroclinic orbits from a saddle equilibrium to this saddle limit cycle. A homoclinic bifurcation to a saddle limit cycle will be associated with a boundary crisis where the chaotic attractor disappears suddenly when a bifurcation parameter is varied. Thus, similar to a tangent local bifurcation for equilibria or limit cycles, this homoclinic global bifurcation marks a region in the parameter space where the top-predator goes extinct. The 'Paradox of Enrichment' says that increasing the concentration of nutrient input can cause destabilization of the otherwise stable interior equilibrium of a bi-trophic food chain. For a tri-trophic food chain enrichment of the environment can even lead to extinction of the highest trophic level.

Animals↗

PubMed1999

On the quasi-stationary distribution of the stochastic logistic epidemic.

An approximation is derived for the quasi-stationary distribution of the stochastic logistic epidemic in the intricate case where the transmission factor R0 lies in the transition region near the deterministic threshold value 1. An approximation for the expected time to extinction from quasi-stationarity in the same parameter region is also given.

Endemic Diseases↗

PubMed2003

Metapopulation theory for fragmented landscapes.

We review recent developments in spatially realistic metapopulation theory, which leads to quantitative models of the dynamics of species inhabiting highly fragmented landscapes. Our emphasis is in stochastic patch occupancy models, which describe the presence or absence of the focal species in habitat patches. We discuss a number of ecologically important quantities that can be derived from the full stochastic models and their deterministic approximations, with a particular aim of characterizing the respective roles of the structure of the landscape and the properties of the species. These quantities include the threshold condition for persistence, the contributions that individual habitat patches make to metapopulation dynamics and persistence, the time to metapopulation extinction, and the effective size of a metapopulation living in a heterogeneous patch network.

Animals↗

PubMed2003

Fingerprints of global warming on wild animals and plants.

Over the past 100 years, the global average temperature has increased by approximately 0.6 degrees C and is projected to continue to rise at a rapid rate. Although species have responded to climatic changes throughout their evolutionary history, a primary concern for wild species and their ecosystems is this rapid rate of change. We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or 'fingerprint', in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations. The synergism of rapid temperature rise and other stresses, in particular habitat destruction, could easily disrupt the connectedness among species and lead to a reformulation of species communities, reflecting differential changes in species, and to numerous extirpations and possibly extinctions.

Animals↗

PubMed1970

Chemical properties of guinea-pig immunoglobulins gamma-1 G, gamma-2 G and gamma M.

The isolation of guinea-pig immunoglobulins gamma(1)G, gamma(2)G and gammaM are described and methods for separating the polypeptide chains of each examined. The molecular weights, extinction coefficients and carbohydrate and amino acid compositions of the immunoglobulins and their constituent chains have been analysed. The findings provide a basis for further studies attempting to relate structural differences to distinct biological properties of guinea-pig immunoglobulins.

Amino Acids↗

PubMed2001

Centrifuge polarizing microscope. II. Sample biological applications.

The rationale, design and general performance of the CPM (centrifuge polarizing microscope) were described in Part I of this study (Inoué et al. J. Microsc. 201 (2001) 341-356. In this second part, we describe observations on several biological samples that we have explored over the past two years using the CPM. As described in the first part of the study, although the CPM was basically designed as a high-extinction centrifuge polarizing microscope, it also allows observations of the specimen exposed to high centrifugal fields up to 10 500 x g (earth's gravitational acceleration) in fluorescence (532-nm excitation) and in DIC (differential interference or Nomarski contrast).

Anemia, Sickle Cell↗

PubMed2006

Space and stochasticity in population dynamics.

Organisms interact with each other mostly over local scales, so the local density experienced by an individual is of greater importance than the mean density in a population. This simple observation poses a tremendous challenge to theoretical ecology, and because nonlinear stochastic and spatial models cannot be solved exactly, much effort has been spent in seeking effective approximations. Several authors have observed that spatial population systems behave like deterministic nonspatial systems if dispersal averages the dynamics over a sufficiently large scale. We exploit this fact to develop an exact series expansion, which allows one to derive approximations of stochastic individual-based models without resorting to heuristic assumptions. Our approach makes it possible to calculate the corrections to mean-field models in the limit where the interaction range is large, and it provides insight into the performance of moment closure methods. With this approach, we demonstrate how the buildup of spatiotemporal correlations slows down the spread of an invasion, prolongs time lags associated with extinction debt, and leads to locally oscillating but globally stable coexistence of a host and a parasite.

Biological Evolution↗

PubMed2006

Metapopulation dynamics and biological invasions: a spatially explicit model applied to a freshwater snail.

The spatial spread of invading organisms is a major contemporary concern. We focus here on invasions in inherently fragmented habitats, such as freshwater systems, and explore the usefulness of metapopulation models in this context. Maximum-likelihood methods allow the estimation of colonization and extinction rates, as functions of habitat patch sizes and positions, from time series of presence/absence data. This framework also provides confidence intervals of these estimates and hypotheses tests. We analyze a previously unpublished 12-year survey of the spread of the introduced snail Tarebia granifera in 47 Martinican rivers. Simple metapopulation models reproduce with reasonable accuracy several quantitative aspects of the invasion, including regional abundance, spatiotemporal structure, and site-by-site colonization dates. Sensitivity analysis reveals that the invasion sequence depended strongly on metapopulation size (number of sites) and spatial structure (distances among sites). The invasion history has also been accelerated by stochastic events, as illustrated by a large, central river that happened to be colonized very early and served as an invasion pool. Finally, we discuss the benefits of this approach for the understanding of invasions in fragmented landscapes.

Animals↗

PubMed2001

Selective extinction and rapid loss of evolutionary history in the bird fauna.

The extinction of species results in a permanent loss of evolutionary history. Recent theoretical studies show that this loss may be proportionally much smaller than the loss of species, but under some conditions can exceed it. Such conditions occur when the phylogenetic tree that describes the evolutionary relationships among species is highly imbalanced due to differences between lineages in past speciation and/or extinction rates. I used the taxonomy by C. G. Sibley and B. L. Monroe Jr to estimate the global loss of bird evolutionary history from historical and predicted extinctions, and to quantify the ensuing changes in balance of the bird phylogenetic tree. In the global bird fauna, evolutionary history is being lost at a high rate, similar to the rate of species extinction. The bird phylogenetic tree is highly imbalanced, and the imbalance is increased significantly by anthropogenic extinction. Historically, the elevated loss of bird evolutionary history has been fuelled mostly by phylogenetic non-randomness in the extinction of species, but the direct effect of tree imbalance is substantial and could dominate in the future.

Animals↗

PubMed2006

Spatial components of bird diversity in the Andes of Colombia: implications for designing a regional reserve system.

Beta diversity, or the turnover in species composition among sampling sites in a region, is an important criterion for obtaining adequate representation of regional biodiversity in systems of protected areas. Recently, the additive model for partitioning regional (gamma) diversity (in opposition to the multiplicative model) has been proposed because it allows a direct measure of the contribution of beta diversity to gamma diversity. We determined avian beta diversity along latitudinal (among neighboring river drainages) and elevational axes in a 1347-km2 region on the western slope of the Central Cordillera of the Colombian Andes, where a regional system of protected areas is being designed. We then compared avian beta diversity between sites based on rapid versus long-term (>1 year) inventories and between fragmented sites versus continuous forest. Overall, beta diversity represented 63.1% of gamma diversity among 16 sites. Elevational differences in species composition accounted for 43.3% of regional diversity, whereas differences among drainages accounted for 19.8%. A complementary cluster analysis showed that sites grouped by elevational zones. Rapid inventories overestimated beta diversity because of sampling effects, but the effect was biologically small. Estimators of species richness derived from species accumulation curves provided a useful alternative to compensate for undersampling in short-term surveys. Forest fragmentation increased beta diversity because of differential local extinction of populations. Nevertheless, in our region, forest fragments contributed to gamma diversity because they contained complementary sets of species. More importantly, they contained populations of special-interest species. Although the region is relatively small, our analyses indicate that spatial differentiation of the biota is an important factor for deciding number and location of protected areas in the Andean region.

Animals↗

PubMed2004

Does sex age you?

The evolution of aging and longevity has typically been considered to be a resolution of the conflicting demands on an organism to grow, reproduce, and survive. When social or environmental factors change the opportunities for reproduction in a way that affects differently aged individuals, there will be an evolutionary response in the schedule of senescence. This means that social dynamics can have an important effect on aging. A recent study by Berec and Boukal has shown that the dynamics of mating and divorce can also affect observed life spans through their effect on population dynamics. If females cannot find and maintain mating pairs for long enough to replace themselves, the population will become extinct. This puts a lower limit on the levels of longevity that will be observed in nature.

Aging↗

PubMed1998

Biotic transitions in global marine diversity.

Long-term transitions in the composition of Earth's marine biota during the Phanerozoic have historically been explained in two different ways. One view is that they were mediated through biotic interactions among organisms played out over geologic time. The other is that mass extinctions transcended any such interactions and governed diversity over the long term by resetting the relative diversities of higher taxa. However, a growing body of evidence suggests that macroevolutionary processes effecting biotic transitions during background times were not fundamentally different from those operating during mass extinctions. Physical perturbations at many geographic scales combined to produce the long-term trajectory of Phanerozoic diversity.

Animals↗

PubMed1997

[Identification of latent forms of Chlamydia trachomatis in the conjunctiva signifying "new interpretation of ocular chlamydia infections"].

Chlamydia trachomatis (CT) sérovar D through K was demonstrated with electron microscopy and biology in 114 patients with bilateral dry eyes. Long time ago latent CT was recognised in conjunctival epithelium of vernal kerato conjunctivitis patients. CT was found in conjunctival section of patients with an extinct trachoma. Aberrants forms of chlamydia bear the responsibility of this long lasting infection. Reticuled body does not product elementary bodies. It becomes an aberrant body which could remain latent during years. DIF and others classical investigations are negatives because abberrant chlamydiae have lost most part of their MOMP albeit keeping immunopathogenicity.

Antibodies, Bacterial↗

PubMed2004

Anticipatory cues differentially provoke in vivo peptidergic and monoaminergic release at the medial prefrontal cortex.

Like primary reinforcers, the anticipation of reward ought to affect neurochemical release in brain regions, such as the medial prefrontal cortex (mPFC), which are associated with appraisal processes. To assess the neurochemical changes associated with anticipation, rats were exposed to the pairing of auditory (60-dB white noise), visual, and olfactory cues with the daily presentation of a palatable snack (Cue Relevant group). Rats of a second group were similarly trained, but for a 2-week period, the snack was no longer provided following cue presentation (Extinction group). In the third condition, the presentation of the snack and cues was uncorrelated (Cue Irrelevant group). Analyses of dialysates collected in vivo from the mPFC revealed that release of corticotropin-releasing hormone (CRH), gastrin-releasing peptide (GRP), and the 5-HT catabolite, 5-hydroxyindole acetic acid (5-HIAA), had increased bilaterally in response to the anticipatory cues, whereas DA release increased only within the right mPFC. In the case of CRH and GRP, these increases were also apparent in the extinction condition, despite the fact that behavioral arousal to the anticipatory cues (increased exploration, rearing, grooming, and vigilance) was only evident in the Cue Relevant condition. In contrast, the elevated DA and 5-HIAA were apparent exclusively in the Cue Relevant condition. Thus, CRH and GRP systems may serve to allocate salience and/or incentive reward value to biologically significant stimuli or reflect the emotional response to the anticipatory stimulus. The activity of DA and 5-HT neurons, in contrast, is more closely aligned with the cognitive appraisal of predictor stimuli.

Animals↗

PubMed2003

Extrinsic versus intrinsic factors in the decline and extinction of Australian marsupials.

Recent attempts to explain the susceptibility of vertebrates to declines worldwide have largely focused on intrinsic factors such as body size, reproductive potential, ecological specialization, geographical range and phylogenetic longevity. Here, we use a database of 145 Australian marsupial species to test the effects of both intrinsic and extrinsic factors in a multivariate comparative approach. We model five intrinsic (body size, habitat specialization, diet, reproductive rate and range size) and four extrinsic (climate and range overlap with introduced foxes, sheep and rabbits) factors. We use quantitative measures of geographical range contraction as indices of decline. We also develop a new modelling approach of phylogenetically independent contrasts combined with imputation of missing values to deal simultaneously with phylogenetic structuring and missing data. One extrinsic variable-geographical range overlap with sheep-was the only consistent predictor of declines. Habitat specialization was independently but less consistently associated with declines. This suggests that extrinsic factors largely determine interspecific variation in extinction risk among Australian marsupials, and that the intrinsic factors that are consistently associated with extinction risk in other vertebrates are less important in this group. We conclude that recent anthropogenic changes have been profound enough to affect species on a continent-wide scale, regardless of their intrinsic biology.

Animals↗