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Results for “Extinction, Biological”

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At least 217 records · Page 12Linked to original sources

PubMed1984

Demographic influences on mitochondrial DNA lineage survivorship in animal populations.

Probability models of branching processes and computer simulations of these models are used to examine stochastic survivorship of female lineages under a variety of demographic scenarios. A parameter II, defined as the probability of survival of two or more independent lineages over G generations, is monitored as a function of founding size of a population, population size at carrying capacity, and the frequency distributions of surviving progeny. Stochastic lineage extinction can be very rapid under certain biologically plausible demographic conditions. For stable-sized populations initiated by n females and/or regulated about carrying capacity k = n, it is highly probable that within about 4n generations all descendants will trace their ancestries to a single founder female. For a given mean family size, increased variance decreases lineage survivorship. In expanding populations, however, lineage extinction is dramatically slowed, and the final k value is a far more important determinant of II than is the size of the population at founding. The results are discussed in the context of recent empirical observations of low mitochondrial DNA (mtDNA) sequence heterogeneity in humans and expected distributions of asexually transmitted traits among sexually reproducing species.

Animals↗

PubMed1976

[Assay of carbromal and its main metabolite (2-ethyl-butyryl-urea) in biological fluids (author's transl)].

The materials mentioned above are reextracted from an ether solution by 2 N sodium hydroxide. The UV extinction of the aqueous layer at 232 nm and 30 degrees C is followed by means of a slave recorder. The original extinction is found by back-extrapolating to the time of re-extraction. It has to be corrected for the "biological matrix" by subtracting the extinction value after complete hydrolysis. Most interfering substances in the ether solution (carboxylic acids, barbiturates) may be removed previously by washing with aqueous buffers (pH 7.0 and 10.5).

Humans↗

PubMed2006

Ménage à trois on Macquarie Island: hybridization among three species of fur seal (Arctocephalus spp.) following historical population extinction.

Human-induced changes to natural systems can cause major disturbances to fundamental ecological and population processes and result in local extinctions and secondary contacts between formerly isolated species. Extensive fur seal harvesting during the nineteenth century on Macquarie Island (subantarctic) resulted in extinction of the original population. Recolonization by three species has been slow and complex, characterized by the establishment of breeding groups of Antarctic and subantarctic fur seals (Arctocephalus gazella and Arctocephalus tropicalis) and presumed nonbreeding (itinerant) male New Zealand fur seals (Arctocephalus forsteri). One thousand and seven pups from eight annual cohorts (1992-2003) were analysed using mitochondrial control region data (RFLP) and 10 microsatellite loci to estimate species composition and hybridization. Antarctic fur seals predominated, but hybridization occurred between all three species (17-30% of all pups). Involvement of New Zealand fur seals was unexpected as females are absent and males are not observed to hold territories during the breeding season. The proportion of hybrids in the population has fallen over time, apparently owing to substantial influxes of pure Antarctic and subantarctic individuals and non-random mating. Over 50% of New Zealand hybrids and 43% of Antarctic-subantarctic hybrids were not F(1), which indicates some degree of hybrid reproductive success, and this may be underestimated: simulations showed that hybrids become virtually undetectable by the third generation of backcrossing. While human impacts seem to have driven novel hybridization in this population, the present 'time slices' analysis suggests some biological resistance to complete homogenization.

Alleles↗

PubMed1982

[Mechanism of polyene antibiotic inactivation. The effect of amino sugar oxidation on polyene chain destruction].

Changes in the acid-base characteristics of levorin during its inactivation are discussed. It is shown that with a decrease in the biological activity a change in the basic characteristics of the levorin amino sugar moiety takes place. The kinetic studies with model compounds, i. e. octaenic alcohol and glucosamine showed that the processes of their oxidation were interrelated. Oxidation of the amino sugar played the role of an inducing factor in oxidation of the polyenic chromophore and in addition impaired correlation between the extinction specific coefficient of levorin and its biological activity.

Amino Sugars↗

PubMed2002

Large extinctions in an evolutionary model: the role of innovation and keystone species.

The causes of major and rapid transitions observed in biological macroevolution as well as in the evolution of social systems are a subject of much debate. Here we identify the proximate causes of crashes and recoveries that arise dynamically in a model system in which populations of (molecular) species coevolve with their network of chemical interactions. Crashes are events that involve the rapid extinction of many species, and recoveries the assimilation of new ones. These are analyzed and classified in terms of the structural properties of the network. We find that in the absence of large external perturbation, "innovation" is a major cause of large extinctions and the prime cause of recoveries. Another major cause of crashes is the extinction of a "keystone species." Different classes of causes produce crashes of different characteristic sizes.

Biological Evolution↗

PubMed2026

De-extinction technology and its application to conservation.

De-extinction, once the realm of science fiction, has evolved into a tangible scientific endeavor thanks to breakthroughs in genome sequencing, engineering, advanced assisted reproductive technologies, and stem cell biology. Alongside this work are innovations in reintroduction science and artificial intelligence, which are refining strategies for species translocations, rewilding, and long-term ecosystem monitoring of de-extinct species and populations. While the primary motivation for de-extinction is restoring lost ecological functions to eroded ecosystems, each of these technologies can also be applied to conservation biology for de-endangerment, offering new solutions for biodiversity preservation. This review synthesizes the technological advancements emerging from de-extinction science and explores their broad applications in conservation, demonstrating how de-extinction is both about resurrecting lost species and about expanding the conservation toolkit to sustain and rebuild biodiversity in the face of accelerating environmental change.

Conservation of Natural Resources↗

PubMed2000

Faces call for attention: evidence from patients with visual extinction.

Three patients with left spatial neglect and visual extinction from right brain damage were studied to determine whether faces are privileged in summoning attention. In a first experiment, either a face, a name, or a meaningless shape were briefly presented in the right, left or both visual hemifields. On bilateral trials, all patients extinguished a left-side face much less often than a left-side name or a left-side shape. Conversely, they extinguished a left-side shape more often when it was accompanied by a right-side face rather than a right-side name. In a second experiment, either a face or a scrambled face could appear in the right, left or both hemifields. Again, on bilateral trials, a left-side face was less likely to be missed than a scrambled one. These results suggest an advantage of faces in capturing attention and overcoming extinction, which may be related to their special biological and social value, or to the very efficient and automatic operation of specific perceptual processses that extract facial organization in extrastriate visual areas. These findings also demonstrate that the distribution of spatial attention and extinction can be modulated by the relevance of visual stimuli. This implies that substantial analysis and categorization may take place in the visual system before information from the contralesional field is selected for, or excluded from, attentive vision.

Aged↗

PubMed2007

DNA barcoding in animal species: progress, potential and pitfalls.

Despite 250 years of work in systematics, the majority of species remains to be identified. Rising extinction rates and the need for increased biological monitoring lend urgency to this task. DNA sequencing, with key sequences serving as a "barcode", has therefore been proposed as a technology that might expedite species identification. In particular, the mitochondrial cytochrome c oxidase subunit 1 gene has been employed as a possible DNA marker for species and a number of studies in a variety of taxa have accordingly been carried out to examine its efficacy. In general, these studies demonstrate that DNA barcoding resolves most species, although some taxa have proved intractable. In some studies, barcoding provided a means of highlighting potential cryptic, synonymous or extinct species as well as matching adults with immature specimens. Higher taxa, however, have not been resolved as accurately as species. Nonetheless, DNA barcoding appears to offer a means of identifying species and may become a standard tool.

Animals↗

PubMed2003

Ecological risk assessment of pollutant chemicals: extinction risk based on population-level effects.

The extinction probability is one of the most useful endpoints that are utilized in conservation biology. A parallel approach is advocated for the ecological risk assessment of chemical pollutants. The presented framework estimates extinction probability induced by pollutant chemicals in order to evaluate ecological hazards of pollution, and is applicable to any biological community (aquatic or terrestrial). The analytical framework, which is based on stochastic population dynamics theory, is briefly explained. The extinction risk estimation is feasible if ecotoxicological data concerning pollutant effects on population growth rate of organisms (the intrinsic rate of natural increase), and if environmental exposure concentration is provided. Tentative risk estimation was made for some agrochemicals and surfactants on zooplankton populations (Daphnia) as target organisms.

Agriculture↗

PubMed2002

Earth's biggest 'whodunnit': unravelling the clues in the case of the end-Permian mass extinction.

The mass extinction that occurred at the end of the Permian period, 250 million years ago, was the most devastating loss of life that Earth has ever experienced. It is estimated that ca. 96% of marine species were wiped out and land plants, reptiles, amphibians and insects also suffered. The causes of this catastrophic event are currently a topic of intense debate. The geological record points to significant environmental disturbances, for example, global warming and stagnation of ocean water. A key issue is whether the Earth's feedback mechanisms can become unstable on their own, or whether some forcing is required to precipitate a catastrophe of this magnitude. A prime suspect for pushing Earth's systems into a critical condition is massive end-Permian Siberian volcanism, which would have pumped large quantities of carbon dioxide and toxic gases into the atmosphere. Recently, it has been postulated that Earth was also the victim of a bolide impact at this time. If further research substantiates this claim, it raises some intriguing questions. The Cretaceous-Tertiary mass extinction, 65 million years ago, was contemporaneous with both an impact and massive volcanism. Are both types of calamity necessary to drive Earth to the brink of faunal cataclysm? We do not presently have enough pieces of the jigsaw to solve the mystery of the end-Permian extinction, but the forensic work continues.

Animals↗

PubMed2000

Predicting extinction risks for plants: environmental stochasticity can save declining populations.

An emerging generalization from theoretical and empirical studies on conservation biology is that high levels of environmental stochasticity increase the likelihood of population extinction. However, coexistence theory has illustrated that there are circumstances under which environmental stochasticity can increase the chance of population persistence. These theoretical studies have shown that the sign of the effect of environmental stochasticity on population persistence is determined by interactions between life history and environmental stochasticity. These interactions mean that the stochastic and deterministic rates of population growth might differ fundamentally. Although difficult to demonstrate in real systems, observed life histories and variance in the vital rates of populations suggest that this phenomenon is likely to be common, and is therefore of much relevance to conservation biologists.

Journal Article↗

PubMed2006

Latent extinction risk and the future battlegrounds of mammal conservation.

Global conservation prioritization usually emphasizes areas with highest species richness or where many species are thought to be at imminent risk of extinction. However, these strategies may overlook areas where many species have biological traits that make them particularly sensitive to future human impact but are not yet threatened because such impact is currently low. In this article, we identify such areas for the world's mammals using latent extinction risk, the discrepancy between a species' current extinction risk and that predicted from models on the basis of biological traits. Species with positive latent risk are currently less threatened than their biology would suggest, usually because they inhabit regions or habitats still comparatively unmodified by human activity. Using large new geographic, biological, and phylogenetic databases for nearly 4,000 mammal species, we map the global geographic distribution of latent risk to reveal areas where the mammal fauna is still relatively unthreatened but has high inherent sensitivity to disturbance. These hotspots include large areas such as the Nearctic boreal forests and tundra that are unrepresented in most current prioritization schemes, as well as high-biodiversity areas such as the island arc from Indonesia to the south Pacific. Incorporating latent extinction risk patterns into conservation planning could help guard against future biodiversity loss by anticipating and preventing species declines before they begin.

Animals↗

PubMed1979

Cure and care of neurosis. I. Cure.

Behavioural psychotherapy has long historical roots. Recently it has led to effective treatment for selected neuroses, including phobic, obsessive-compulsive and sexual disorders. Potent therapy has become a tool of experimental psychopathology which advances theory and practice. A pervasive principle is exposure of the patient to those stimuli which evoke his discomfort until this subsides. Level of arousal during exposure does not affect outcome. Theoretical issues are reviewed which decide when exposure will be sensitizing or habituating. Both psychoanalytical and conditioning models of neurosis are out of date, and models derived more directly from clinical experiment are becoming possible. The aetiology of phobias and rituals can be seen as failed extinction rather than enhanced acquisition. Relevant phylogenetic and biological factors are discussed. At the other extreme, well-documented faith-healing indicates huge gaps in our knowledge of psychotherapy.

Antidepressive Agents, Tricyclic↗

PubMed1980

The extinction of slowly evolving dynamical systems.

The time evolution of slowly evolving discrete dynamical systems xi + 1 = T(ri, xi), defined on an interval [0, L], where a parameter ri changes slowly with respect to i is considered. For certain transformations T, once ri reaches a critical value the system faces a non-zero probability of extinction because some xj psi [0, L]. Recent ergodic theory results of Ruelle, Pianigiani, and Lasota and Yorke are used to derive a simple expression for the probability of survival of these systems. The extinction process is illustrated with two examples. One is the quadratic map, T (r, x) = rx (1 - x), and the second is a simple model for the growth of a cellular population. The survival statistics for chronic myelogenous leukemia patients are discussed in light of these extinction processes. Two other dynamical processes of biological importance, to which our results are applicable, are mentioned.

Biological Evolution↗

PubMedDate not supplied

Improvements in the selective perception and training of rats using an original analog of the C-terminal fragment of vasopressin.

This report presents studies on the effects of intranasal administration of five doses (0.001, 0.01, 0.1, 1, and 10 microg/kg) of a new analog of arginine-vasopressin fragment AVP(6-9), i.e., D-MPRG, on the learning ability of rats with positive and negative reinforcement. All doses of the peptide improved learning. The most effective dose was 0.01 microg/kg, at which the peptide accelerated the acquisition of a conditioned active avoidance reflex both when given 1 h before and when given immediately after training sessions. The peptide had greater effects when animals were trained with negative reinforcement. Analysis of the results suggests that the action of D-MPRG is mainly on perception processes, i.e., extraction of the conditioned stimulus from the environmental surroundings and evaluation and enhancement of its biological significance. In addition, this peptide prevented extinction of the acquired habit and improved the processes of consolidation, though this effect was weaker than its effect on perception.

Administration, Intranasal↗

PubMed1991

Retinoic acid in mono- or combined differentiation therapy of myelodysplasia and acute promyelocytic leukemia.

Myelodysplastic preleukemic syndromes (MDPS) and acute promyelocytic leukemia (APL) share a surprising in vivo sensitivity to the hormonally acting 13 cis or all trans retinoic acids (transRA). Here we show that transRA as a monotherapeutic agent induced a stable remission in APL at the third relapse. In MDPS, treatment with prednisone and 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25D3) 13 cis RA induced a long-lasting hematological remission. Initially both patients had an impaired BM microenvironment which regenerated on retinoid therapy as judged by reappearance of the Hematon fraction in the BM aspirates. Our preclinical experiments using long-term liquid BM cultures (LTBMC) indicated that several individual patterns of growth and differentiation responses can be induced by combinations of transRA, 1 alpha,25D3 and hemopoietic growth factors (HGFs). The biological responses may vary from complete clonal extinction to a significant growth stimulation of the leukemic blast cell populations. These results further support the importance of preclinical studies in selecting "good" responders for, and excluding "poor" responders from protocols using differentiation therapy.

Bone Marrow↗

PubMed1998

Persistence, chaos and synchrony in ecology and epidemiology.

The decline of species in natural habitats concerns ecologists, who view extinction as a danger and conservation of biological diversity as a goal. In contrast, the proliferation of 'undesirable' species is the principal concern of epidemiologists, who view persistence as a problem and eradication as an achievement. While ecologists and epidemiologists have essentially opposite goals, the mathematical structure of the population dynamics that they study is very similar. We briefly review the similarities and differences between these two fields, emphasizing recent work in both areas on the effects of spatial synchrony and dynamical chaos. We hope to stimulate further cross-fertilization of ideas between the disciplines.

Animals↗

PubMed1999

Evolutionary patterns from mass originations and mass extinctions.

The Fossil Record 2 database gives a stratigraphic range of most known animal and plant families. We have used it to plot the number of families extant through time and argue for an exponential fit, rather than a logistic one, on the basis of power spectra of the residuals from the exponential. The times of origins and extinctions, when plotted for all families of marine and terrestrial organisms over the last 600 Myr, reveal different origination and extinction peaks. This suggests that patterns of biological evolution are driven by its own internal dynamics as well as responding to upsets from external causes. Spectral analysis shows that the residuals from the exponential model of the marine system are more consistent with 1/f noise suggesting that self-organized criticality phenomena may be involved.

Animals↗