PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Extinction, Biological”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1996

Biological Diversity Conservation: A Public Policy Perspective

/ While extinctions of individual species are part of a normal cycle, the current rate of extinctions should be a concern to us all. The maintenance of biological diversity is important for utilitarian reasons, quality of life considerations, and because biodiversity is important to sustainable regional economies. Single-species approaches are too limited to protect biodiversity at the landscape, habitat, and watershed levels. New approaches are necessary to deal with the complexity of biological diversity. The administration is using provisions in the Endangered Species Act to bring about broader multispecies habitat protection. The ecosystem approach provides a framework for ensuring that ecological considerations are taken into account, along with economic and social factors, and that all interested parties are able to participate in the decision-making process.KEY WORDS: Biodiversity; Ecosystem management; Endangered Species Act; Public policy; Stewardship; Regional economies; Habitat protection

Journal Article↗
PubMed2004

How species respond to multiple extinction threats.

It is well established that different species vary in their vulnerability to extinction risk and that species biology can underpin much of this variation. By contrast, very little is known about how the same species responds to different threat processes. The purpose of this paper is therefore twofold: to examine the extent to which a species' vulnerability to different types of threat might covary and to explore the biological traits that are associated with threat-specific responses. We use an objective and quantitative measure of local extinction risk to show that vulnerability to local population decline in primates varies substantially among species and between threat types. Our results show that a species' response to one threat type does not predict its response to others. Multivariate analyses also suggest that different mechanisms of decline are associated with each type of threat, since different biological traits are correlated with each threat-specific response. Primate species at risk from forestry tend to exhibit low ecological flexibility, while those species vulnerable to agriculture tend to live in the canopy and eat low-fruit diets; in further contrast, primates at risk from hunting tend to exhibit large body size. Our analyses therefore indicate that a species' vulnerability to local extinction can be highly variable and is likely to depend on both threat type and biology.

Agriculture↗
PubMed2006

Muller's ratchet in random graphs and scale-free networks.

Muller's ratchet is an evolutionary process that has been implicated in the extinction of asexual species, the evolution of mitochondria, the degeneration of the Y chromosome, the evolution of sex and recombination and the evolution of microbes. Here we study the speed of Muller's ratchet in a population subdivided into many small subpopulations connected by migration, and distributed on a network. We compare the speed of the ratchet in two distinct types of topologies: scale free networks and random graphs. The difference between the topologies is noticeable when the average connectivity of the network and the migration rate is large. In this situation we observe that the ratchet clicks faster in scale free networks than in random graphs. So contrary to intuition, scale free networks are more prone to loss of genetic information than random graphs. On the other hand, we show that scale free networks are more robust to the random extinction than random graphs. Since these complex networks have been shown to describe well real-life systems, our results open a framework for studying the evolution of microbes and disease epidemics.

Algorithms↗
PubMed2006

Polyploids with different origins and ancestors form a single sexual polyploid species.

Polyploidization is one of the few mechanisms that can produce instantaneous speciation. Multiple origins of tetraploid lineages from the same two diploid progenitors are common, but here we report the first known instance of a single tetraploid species that originated repeatedly from at least three diploid ancestors. Parallel evolution of advertisement calls in tetraploid lineages of gray tree frogs has allowed these lineages to interbreed, resulting in a single sexually interacting polyploid species despite the separate origins of polyploids from different diploids. Speciation by polyploidization in these frogs has been the source of considerable debate, but the various published hypotheses have assumed that polyploids arose through either autopolyploidy or allopolyploidy of extant diploid species. We utilized molecular markers and advertisement calls to infer the origins of tetraploid gray tree frogs. Previous hypotheses did not sufficiently account for the observed data. Instead, we found that tetraploids originated multiple times from extant diploid gray tree frogs and two other, apparently extinct, lineages of tree frogs. Tetraploid lineages then merged through interbreeding to result in a single species. Thus, polyploid species may have complex origins, especially in systems in which isolating mechanisms (such as advertisement calls) are affected directly through hybridization and polyploidy.

Animals↗
PubMed2001

Microsporogenesis in the endangered species Cupressus dupreziana A. Camus: evidence for meiotic defects yielding unreduced and abortive pollen.

To understand the reproductive biology of Cupressus dupreziana A. Camus (Cupressaceae), a highly endangered Mediterranean conifer, the processes of microsporogenesis and pollen differentiation were investigated cytologically. Pre-meiotic development proved to be similar to the coniferous pattern: the microsporangia differentiated sporogenous tissue in which microsporocytes separated and underwent meiosis. As the meiotic steps proceeded, unexpected irregularities were observed concerning chromosomal and nuclear behaviour. This mainly included: abnormal chromosome segregation and cytokinesis, and nuclear fusion of the meiotic products. The result was the formation, in the same microsporangium, of heterogeneous microspore populations arranged in monads, dyads, triads, tetrads, and polyads, and cytoplasts giving rise to pollen grains of different sizes. This indicates that in C. dupreziana both abortive and unreduced pollen grains are generated. The significance of the finding is discussed in relation to reproductive biology and vulnerability to extinction.

Cell Differentiation↗
PubMed1983

Isolation and characterization of 15-hydroxylated metabolites of leukotriene C4.

A polar metabolite of leukotriene C4 was formed by sequential conversions with soybean lipoxygenase I and liver peroxidase. The structure of this product was found to be 5(S), 15(S)-dihydroxy-6(R)-S-glutathionyl-7,9,13-trans-11-cis-eicosatetraenoic acid (15-hydroxy-delta 13-trans-leukotriene C3. The HPLC behaviour, the molar extinction coefficient and the biological activity of the metabolite are reported. Preliminary evidence suggests that this product is formed by mammalian tissues.

Animals↗
PubMed2003

The importance of hippocampus-dependent non-spatial tasks in analyses of homology and homoplasy.

The hippocampus or a homologous region plays a role in spatial tasks in a large number of vertebrate species. This result, in combination with recent findings of adaptive specializations of the hippocampus for spatial demands, has led to the conclusion that the prominent selective force behind hippocampal evolution was a need for spatial abilities. However, a review of non-spatial hippocampus-dependent tasks shows that many vertebrate species also share non-spatial functions of the hippocampus. Placed in the appropriate phylogenetic context, it becomes clear that non-spatial facets of hippocampal function were just as likely to be present in our vertebrate ancestors as spatial ones. In addition, the absence of spatial strategy use in three lineages suggests divergence of this feature. Divergence in this character and other characteristics of hippocampal function are meaningful indicators of lineage specific functions. Studies of the evolution of the hippocampus must include examination of spatial and non-spatial functions of the hippocampus and consider both conserved, as well as derived, features.

Animals↗
PubMed2001

[Biological crisis at the end of the Cretaceous and the extinction of the dinosaurs. Validity of the cosmic hypothesis].

The history of life, which appeared more than 500 million years ago, has been characterized by a constant faunal and floral turnover. On five occasions, the background extinctions has become a mass extinction (ME), i.e. a major biotic crisis collapsing the upward curve of the biodiversity. The mass extinction of the end of the Permian is the most murderous but the end-Cretaceous one, which experiences dinosaur's death, is the most well-known. In fact, these land-dwelling reptiles with upright limbs, as well as the pterosaurs, the mosasaurs and numerous invertebrates die as far as the last. There exists a lot of hypotheses tending to explain their death but they are often extravagant and/or impossible to be verified. The last one, referring to a collapse between the earth and a heavenly large bolide has given rise, since more than 20 years, to heated debates between catastrophists and gradualists, even if the reality of the impact seems no more doubtful (discovery of Chicxulub impact crater, iridium anomaly, tektite glass, shocked quartz, spinels with high nickel concentrations). It is now the extent of the deleterious effects (regional or worldwide repercussion) which is debating. By referring to the obtained data in oceanic environment and, if necessary, in terrestrial environment where fossil record is too often incomplete, it can be noticed an important fact corresponding to a selective character of extinctions, the event of the C/T boundary killing off some taxa while others are preserved. This remark does not really correspond to the hypothesis of a sudden planetary catastrophe of large magnitude. Consequently, it seems to be reasonable to make arise intrinsic factors associated to the dynamics of the globe (volcanic eruptions, marine regression, fall of temperature) over a long period. The collapse with the Chicxulub asteroid should then come up, especially in Western North-America, as a "coup de grâce" in a weakened ecosystem.

Animals↗
PubMed2005

Seasonal distribution of physico- chemical parameters in effluent discharge area of Uppanar estuary, Cuddalore, south-east coast of India.

Seasonal distribution of physico-chemical characteristics such as rainfall, pH, salinity, temperature, light extinction coefficient, dissolved oxygen, biological oxygen demand and nutrients like total phosphorus, inorganic phosphate, nitrite, nitrate and reactive silicate has been studied at two stations of Uppanar estuary in relation to effluent discharges from SIPCOT industries. There are 44 industries discharges their effluents into Uppanar estuary, which may influence the biota. Nutrient concentrations were higher during monsoon season and low during summer season. The mean concentrations of nutrients were high at station 1 than station 2 due to discharges from industries, coconut husk retting grounds near the station 1. In the present study, the physico-chemical characteristic of Uppanar estuary carried out and variations are discussed.

Agriculture↗
PubMed2006

Human evolution: humanistic selection and looking to the future.

Cultural evolution has predominated over biological evolution in modern man (Homo sapiens sapiens). Cultural evolution differs from biological evolution not only by inheritance of acquired characteristics but also, as is proposed in the present essay, by another kind of selection mechanism. Whereas selection in biological evolution is executed according to a criterion of reproductive success (the natural selection), selection in cultural evolution appears to be carried out according to human and humanistic criteria (success or fitness in meeting human needs, interests and humanistic values--"humanistic selection"). Many humanistic needs or values do not seem to be prerequisite for reproductive success, yet some of them (e.g. a need for freedom) seem to be inborn. Innateness, humanistic selection (decisive at a community level) and hierarchy of some human needs, interests and values appear to give cultural evolution a generally upward trend although long periods of stagnation or even regression may occur. Modern humans appear to be still at the early stage of their cultural evolution. A further cultural evolution of man appears to be, in contrast to biological evolution, predictable (with an optimistic outlook) and testable. The problem is that the hopeful result of this test will probably be known only in the fairly remote future provided that this species will not become extinct before that.

Biological Evolution↗
PubMed2004

Modeling and analysis of stoichiometric two-patch consumer-resource systems.

Ecological stoichiometry studies the balance of energy and multiple chemical elements in ecological interactions to establish how the laws of thermodynamics affect food-web dynamics and nutrient cycling in ecosystems. In this paper, we incorporate stoichiometric principles in a model with habitat heterogeneity and dispersal in order to better understand population growth dynamics. This model describes a situation where a resource is separated into two patches by a barrier. Growth of the resource in each patch is limited by soil fertility and self-crowding. The consumer disperses between the two patches and is not affected by the barrier. The consumer's growth is potentially limited by the phosphorus content of the acquired resource. Mathematical analysis of this model and simulations are performed. Several biological implications, including an observed "stoichiometric extinction effect," are demonstrated with simulation where the stoichiometric mechanism appears to promote extinction in a patchy environment. This is in sharp contrast to the notion that stoichiometry mechanism promotes diversity in spatially homogeneous settings. Another important result is the rediscovery of a simple and plausible biological mechanism that generates local and global extinction. In this setting, which can be considered a spatially mediated form of apparent competition, the dispersal of the consumer from the rich patch can des the growth of the resource in the poor patch and in some situations can lead to the extinction of the resource in the poor patch.

Animals↗
PubMed2004

Role of evolution by natural selection in population dynamics.

Using a Monte Carlo approach we study the role of inheritance and natural selection in the dynamics of populations. We show that a population subject to inheritance has a much better chance of survival in a given condition than a population where new generations do not inherit genomes of their parents. The dependence of the survival chance on such factors as selection pressure, fecundity, or carrying capacity of the system is much stronger when selection and inheritance are present. We demonstrate, in accordance with biological observations, that in certain conditions evolution can save a population which would perish without it.

Animals↗
PubMed2002

Time-dependent extinction rate and species abundance in a tangled-nature model of biological evolution.

We present a model of evolutionary ecology consisting of a web of interacting individuals, a tangle-nature model. The reproduction rate of individuals characterized by their genome depends on the composition of the population in genotype space. Ecological features such as the taxonomy and the macroevolutionary mode of the dynamics are emergent properties. The macrodynamics exhibit intermittent two-mode switching with a gradually decreasing extinction rate. The generated ecologies become gradually better adapted as well as more complex in a collective sense. The form of the species abundance curve compares well with observed functional forms. The model's error threshold can be understood in terms of the characteristics of the two dynamical modes of the system.

Biological Evolution↗
PubMed1988

Patterns of generic extinction in the fossil record.

Analysis of the stratigraphic records of 19,897 fossil genera indicates that most classes and orders show largely congruent rises and falls in extinction intensity throughout the Phanerozoic. Even an ecologically homogeneous sample of reef genera shows the same basic extinction profile. The most likely explanation for the congruence is that extinction is physically rather than biologically driven and that it is dominated by the effects of geographically widespread environmental perturbations influencing most habitats. Significant departures from the congruence are uncommon but important because they indicate physiological or habitat selectivity. The similarity of the extinction records of reef organisms and the marine biota as a whole confirms that reefs and other faunas are responding to the same history of environmental stress.

Animals↗
PubMed2005

Simultaneous Quaternary radiations of three damselfly clades across the Holarctic.

If climate change during the Quaternary shaped the macroevolutionary dynamics of a taxon, we expect to see three features in its history: elevated speciation or extinction rates should date to this time, more northerly distributed clades should show greater discontinuities in these rates, and similar signatures of those effects should be evident in the phylogenetic and phylodemographic histories of multiple clades. In accordance with the role of glacial cycles, speciation rates increased in the Holarctic Enallagma damselflies during the Quaternary, with a 4.25x greater increase in a more northerly distributed clade as compared with a more southern clade. Finer-scale phylogenetic analyses of three radiating clades within the northern clade show similar, complex recent histories over the past 250,000 years to produce 17 Nearctic and four Palearctic extant species. All three are marked by nearly synchronous deep splits that date to approximately 250,000 years ago, resulting in speciation in two. This was soon followed by significant demographic expansions in at least two of the three clades. In two, these expansions seem to have preceded the radiations that have given rise to most of the current biodiversity. Each also produced species at the periphery of the clade's range. In spite of clear genetic support for reproductive isolation among almost all species, mtDNA signals of past asymmetric hybridization between species in different clades also suggest a role for the evolution of mate choice in generating reproductive isolation as species recolonized the landscape following deglaciation. These analyses suggest that recent climate fluctuations resulted in radiations driven by similar combinations of speciation processes acting in different lineages.

Adaptation, Biological↗
PubMed1989

[Morphologic changes in the heart atrium in frogs after extinction of current due to suction electrode induced damage].

In biological model experiments in frog heart morphological substrate was observed in current extinction due to damage under suction electrode. After short-term suction discharge monophase recording disappeared without demonstrable myocyte ultrastructure changes by means of reparation ad integrum. Monophase recording spontaneously disappeared in distinct changes of monocyte structure with enlarged spaces in between myofibrils, with breakdown of cristae in mitochondria and with dilatation of tubules and cisternae of the endoplasmic reticulum. This tissue disintegration leads to demarcation and forming of new cellular surfaces on the border with the healthy tissue so that the damaged area turns into a mere electric conductor.

Animals↗