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Extinction Dynamics (extinction + dynamics)
Selected AbstractsThe fate of the homoctenids (Tentaculitoidea) during the Frasnian,Famennian mass extinction (Late Devonian)GEOBIOLOGY, Issue 3 2006DAVID BONDArticle first published online: 18 AUG 200 ABSTRACT The homoctenids (Tentaculitoidea) are small, conical-shelled marine animals that are among the most abundant and widespread of all Late Devonian fossils. They were a principal casualty of the Frasnian,Famennian (F-F, Late Devonian) mass extinction, and thus provide an insight into the extinction dynamics. Despite their abundance during the Late Devonian, they have been largely neglected by extinction studies. A number of Frasnian,Famennian boundary sections have been studied, in Poland, Germany, France, and the USA. These sections have yielded homoctenids, which allow precise recognition of the timing of the mass extinction. It is clear that the homoctenids almost disappear from the fossil record during the latest Frasnian ,Upper Kellwasser Event'. The coincident extinction of this pelagic group, and the widespread development of intense marine anoxia within the water column, provides a causal link between anoxia and the F-F extinction. Most notable is the sudden demise of a group, which had been present in rock-forming densities, during this anoxic event. One new species, belonging to Homoctenus is described, but is not formally named here. [source] The concept of the taxon cycle in biogeographyGLOBAL ECOLOGY, Issue 5 2002Robert E. Ricklefs Abstract Taxon cycles are sequential phases of expansion and contraction of the ranges of species, associated generally with shifts in ecological distribution. The important contribution of the taxon cycle to biogeographical analysis is its emphasis on evolutionary and ecological interactions among colonizing and resident species, which influence their extinction dynamics and establish patterns of geographical distribution. Taxon cycles were inferred originally from the distribution of species across island archipelagos, where a correlation was noted between gaps in island occupancy and the degree of phenotypic differentiation. This pattern implied that phases of colonization were followed by range contraction, while endemic Antillean species that were undifferentiated between islands suggested secondary expansion and the beginning of a new cycle. This interpretation was met with scepticism, but reconstruction of phylogenetic relationships from gene sequences has now permitted us to characterize taxon cycles in Lesser Antillean birds. The relative timing of phases of the cycle can be deduced from genetic divergence between island populations. We have found that taxon cycles have periods in the order of 106 years and that cycles in different lineages occur independently of each other and independently of Pleistocene climate cycles. Individual island populations may persist for several millions of years on the larger islands of the Lesser Antilles; occasional expansion phases lead to the replacement of island populations that have disappeared, thus reducing the archipelago-wide rate of extinction to nil. What drives taxon cycles is unknown, but we speculate that they may be caused by co-evolution with enemy populations, and a probable mechanism would involve infrequent mutations influencing parasite virulence and avian host disease resistance. Taxon cycles undoubtedly occur on continents, but the geographical configuration of island archipelagos reveals more clearly their presence and invites their study. [source] Large-scale dynamics in colonization and extinction for breeding birds in BritainJOURNAL OF ANIMAL ECOLOGY, Issue 3 2002Kevin J. Gaston Summary 1A number of generalizations have been made as to the effects of the area of occupancy, population size, dispersal ability and body size of species on their relative rates of local colonization and extinction. 2Here, data on the breeding bird assemblage of Britain are used to test these generalizations. The complete geographical ranges of British birds have been censused twice, in the periods 1968,72 and 1988,91, allowing rates of colonization and extinction between these periods to be estimated. 3The local colonization dynamics of species are influenced independently by their range sizes and the dispersal abilities of adult birds: species with smaller range sizes and larger dispersal distances were more likely to have colonized new areas between the two census periods. 4The local extinction dynamics of species are influenced independently by their population sizes and body masses: species with smaller population sizes and body sizes were more likely to have gone extinct from areas inhabited in the first census period. 5These results remain when controlling for the effects of phylogenetic relatedness. 6These analyses uphold many commonly held generalizations about the correlates of local colonization and extinction, and suggest that the long-term evolutionary history of these bird species has influenced their potential to respond to current ecological conditions. [source] Temporal and spatial genetic variation in a metapopulation of the annual Erysimum cheiranthoides on stony river banksJOURNAL OF ECOLOGY, Issue 1 2009Olivier Honnay Summary 1Metapopulation dynamics , the recurrent extinction and colonization in spatially discrete habitats , is expected to strongly affect within and between population genetic diversity. So far, however, accounts of true plant metapopulations are extremely scarce. 2We monitored the colonization and extinction dynamics of an assemblage of populations of the annual Erysimum cheiranthoides on stony river banks during three consecutive years. Each year, winter flooding drives some populations to extinction, while vacant banks may become colonized. We describe the dynamics of these ephemeral populations using amplified fragment length polymorphism (AFLP) markers to quantify changes in the metapopulation genetic structure over time, and assessing the direction and relative amount of migration and colonization events. 3Average extinction and colonization rates were high (0.39 and 0.34, respectively). While population genetic differentiation (FST) tripled from 0.06 in 2005 to 0.17 in 2007, total metapopulation genetic diversity remained fairly constant through the years. Genetic assignment analyses allowed assigning more than 50% of the genotyped individuals to populations extant the year before. Colonizing individuals originated from different source populations (, << 1) and there was considerable evidence of upstream seed dispersal. 4The degree and pattern of spatial genetic structure varied between years and was related to variation in the flooding intensity of the Meuse River through the years. Possibly, activation of the soil seed bank also played a role in structuring the genetic make-up of the populations. 5Because migration and colonization events were qualitatively equal, and colonizing individuals originated from different sources, the increase in FST was in agreement with previous theoretical work. Very high migration and colonization rates, and the short monitoring period, may explain why there was no loss of genetic diversity from the metapopulation through recurrent extinction and colonization events. 6Synthesis. This study gives one of the first accounts of the dynamics of a true plant metapopulation. Temporal monitoring of genetic variation gave evidence of extensive and bidirectional seed dispersal, highly variable and increasing genetic differentiation, and rather constant within population genetic diversity. An important suggestion from this research is to include a dormant seed stage in further theoretical work on (meta) population genetics. 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