Variation In Extinction Rates Research Articles

Macroevolutionary Origins of Comparative Development

Abstract Advances in evolutionary theories (the Extended Synthesis) demonstrate that organisms systematically modify environments in ways that influence their own and other species’ evolution. This paper utilises these theories to examine the economic consequences of human dispersal from Africa. Evidence shows that early humans’ dispersal affected the adaptability of animal species to human environments and, through this, the extinction of large mammals during Homo sapiens’ out-of-Africa migration. Empirical analyses explore the variation in extinction rates as a source of exogenous pressure for cooperation and innovation among hunter-gatherers and examine the impact of extinction on long-run development. The results indicate that extinction affects economic performance by driving continental differences in biogeography, disease environments and institutions. Eurasia’s location along the out-of-Africa migratory path provided human and animal populations with co-evolutionary foundations for domestication and agriculture, which gave Eurasians technological and institutional advantages in comparative development.

Influence of climate drivers on colonization and extinction dynamics of wetland‐dependent species

AbstractFreshwater wetlands are particularly vulnerable to climate change. Specifically, changes in temperature, precipitation, and evapotranspiration (i.e., climate drivers) are likely to alter flooding regimes of wetlands and affect the vital rates, abundance, and distributions of wetland‐dependent species. Amphibians may be among the most climate‐sensitive wetland‐dependent groups, as many species rely on shallow or intermittently flooded wetland habitats for breeding. Here, we integrated multiple years of high‐resolution gridded climate and amphibian monitoring data from Grand Teton and Yellowstone National Parks to explicitly model how variations in climate drivers and habitat conditions affect the occurrence and breeding dynamics (i.e., annual extinction and colonization rates) of amphibians. Our results showed that models incorporating climate drivers outperformed models of amphibian breeding dynamics that were exclusively habitat based. Moreover, climate‐driven variation in extinction rates, but not colonization rates, disproportionately influenced amphibian occupancy in monitored wetlands. Long‐term monitoring from national parks coupled with high‐resolution climate data sets will be crucial to describing population dynamics and characterizing the sensitivity of amphibians and other wetland‐dependent species to climate change. Further, long‐term monitoring of wetlands in national parks will help reduce uncertainty surrounding wetland resources and strengthen opportunities to make informed, science‐based decisions that have far‐reaching benefits.

Two sides of the same coin: extinctions and originations across the Atlantic/Indian Ocean boundary as consequences of the same climate oscillation

Global climate change is correlated not only with variation in extinction rates, but also with speciation rates. However, few mechanisms have been proposed to explain how climate change may have driven the emergence of new evolutionary lineages that eventually became distinct species. Here, we discuss a model of range extension followed by divergence, in which the same climate oscillations that resulted in the extinction of coastal species across the Atlantic/Indian Ocean boundary in southwestern Africa also sowed the seeds of new biodiversity. We present evidence for range extensions and evolutionary divergence from both fossil and genetic data, but also point out the many challenges to the model that need to be addressed before its validity can be accepted.

Plant extinction dynamics in an insular metacommunity

Changes in the composition of local communities through time (i.e. species turnover) is a common phenomenon in insular biology. However, the mechanisms promoting variation in species turnover, both among islands and among species, are poorly understood. In an effort to better understand the causes of variation in species turnover, we evaluated the colonization and extinction dynamics of plant populations on 18 small islands off the west coast of Canada. In 1997, we quantified total population sizes of 10 woody angiosperm species. A decade later, we resampled islands to test whether: 1) species turnover occurred, 2) colonization events were offset by extinction events, 2) variation in extinction rates among islands was associated with population sizes, average plant heights, island area, island isolation or each island's exposure to ocean‐born disturbances, and 3) variation in extinction rates among species was associated with plant life history traits. Results showed that extinction events outnumbered colonization events, suggesting that the metacommunity is in ‘disequilibrium’. Variation in extinction rates among islands was unrelated to island area and isolation. However, extinction rates increased with exposure to ocean‐born disturbances and decreased with both initial population sizes and average plant heights. Species with thicker, tougher leaves (i.e. high leaf mass per area) were less prone to extinction than species with thinner, more papery leaves. Overall results indicate that species turnover is common and that it is generated primarily by extinction. Variation in extinction rates appears to result from an interaction between among‐island effects (exposure, population size and plant stature) and among‐species effects (leaf toughness), suggesting that ocean‐born disturbances play a key role in determining metacommunity structure.

Human demography and reserve size predict wildlife extinction in West Africa.

Species-area models have become the primary tool used to predict baseline extinction rates for species in isolated habitats, and have influenced conservation and land-use planning worldwide. In particular, these models have been used to predict extinction rates following the loss or fragmentation of natural habitats in the absence of direct human influence on species persistence. Thus, where direct human influences, such as hunting, put added pressure on species in remnant habitat patches, we should expect to observe extinction rates higher than those predicted by simple species-area models. Here, we show that extinction rates for 41 species of large mammals in six nature reserves in West Africa are 14-307 times higher than those predicted by models based on reserve size alone. Human population and reserve size accounted for 98% of the observed variation in extinction rates between reserves. Extinction occurred at higher rates than predicted by species-area models for carnivores, primates and ungulates, and at the highest rates overall near reserve borders. Our results indicate that, where the harvest of wildlife is common, conservation plans should focus on increasing the size of reserves and reducing the rate of hunting.

Reptile Extinctions on Land‐Bridge Islands: Life‐History Attributes and Vulnerability to Extinction

One of the central questions of conservation biology is what life-history traits render a species prone to extinction. We addressed this problem by calculating extinction rates for 35 species of turtles and squamates (lizards and snakes) occurring on 87 land-bridge islands in the Mediterranean Sea. We calculated extinction rates in two ways: first, by incorporating the known sequence of historical island separations and second by ignoring history and assuming that the islands became isolated simultaneously. The second procedure is simpler and more frequently used in the literature and produces estimates of extinction rates that are similar to the first, more complex procedure. We then determined the relationship between extinction rates (calculated using both methods) and body mass, longevity, habitat specialization, and population abundance using two methods: first, by accounting for the phylogenetic relationships among species and, second, by ignoring them. Only population abundance and habitat specialization explained a significant amount of the observed variation in species extinction rates. Body mass itself did not explain variation in extinction rates, although it was strongly correlated with abundance. These conclusions were obtained using both procedures for calculating extinction rates and both procedures for correlating extinction rates with life-history traits.

Reptile Extinctions on Land-Bridge Islands: Life-History Attributes and Vulnerability to Extinction

One of the central questions of conservation biology is what life‐history traits render a species prone to extinction. We addressed this problem by calculating extinction rates for 35 species of turtles and squamates (lizards and snakes) occurring on 87 land‐bridge islands in the Mediterranean Sea. We calculated extinction rates in two ways: first, by incorporating the known sequence of historical island separations and second by ignoring history and assuming that the islands became isolated simultaneously. The second procedure is simpler and more frequently used in the literature and produces estimates of extinction rates that are similar to the first, more complex procedure. We then determined the relationship between extinction rates (calculated using both methods) and body mass, longevity, habitat specialization, and population abundance using two methods: first, by accounting for the phylogenetic relationships among species and, second, by ignoring them. Only population abundance and habitat specialization explained a significant amount of the observed variation in species extinction rates. Body mass itself did not explain variation in extinction rates, although it was strongly correlated with abundance. These conclusions were obtained using both procedures for calculating extinction rates and both procedures for correlating extinction rates with life‐history traits.

An evolutionary framework for the polar regions

Abstract: Our knowledge of the nature, generation and maintenance of largescale biodiversity patterns is still far from complete. This is particularly so in the Southern Hemisphere and in the marine realm, where recent taxonomic investigations of Mollusca and other invertebrate groups has cast doubt upon the existence of a simple cline in species richness between the tropics and the pole. Comparatively high regional diversity values for the shelled gastropods and other epifaunal taxa implies a considerable evolutionary legacy; this is supported, at least in part, by available evidence from the fossil record. Certain families within the living gastropod fauna maintain their prominence when traced back 40 m.y., and perhaps even longer; in addition, several Southern Ocean gastropod and bivalve genera can now be traced back to at least the late Eocene. Use of a variety of refugia may have enabled many taxa to survive repeated glacial advances.As we begin to revise our concept of the nature of latitudinal diversity gradients, so we also need to examine regional variations in evolutionary rates. Clearly this is a complex issue. but recourse to a pilot study based on the molluscan fossil record suggests that there may be no significant difference between the rates of radiation of tropical and cold‐temperatdpolar taxa. The most diverse clades, which are all tropical, are simply the oldest. What data are available from the fossil record indicate that there is no appreciable latitudinal variation in rates of extinction either. Time, but not necessarily environmental stability, would appear to be crucial to the development of pockets of high taxonomic diversity.Recent improvement in our understanding of the biology of many polar marine invertebrates suggests that life in cold water is not an insuperable evolutionary problem. Of qual importance to any intrinsic properties of organisms which may have governed the differentiation of large‐scale biodiversity patterns is the role of extrinsic processes. Foremost among these has almost certainly been repeated range shifts in response to Cenozoic climatic cycles.

Sources of variation in extinction rates, turnover, and diversity of marine invertebrate families during the Paleozoic

We have recently shown how capture-recapture models can be used in conjunction with stratigraphic range data to estimate taxonomic extinction rates and taxonomic diversity. Here we present a new method that can be used to estimate taxonomic turnover (defined here as the proportion of taxa extant at time i, that originated in the interval i – 1 to i). We used these methods in conjunction with stratigraphic range data for families in five phyla of Paleozoic marine invertebrates. We estimated fossil encounter probabilities, extinction rates, diversity, and turnover and used these estimates to test hypotheses about variation among phyla and geologic series. Encounter probabilities varied among taxa and showed evidence of a decrease over time for the geologic series examined. The number of families varied substantially among the five phyla and showed some evidence of an increase over the series examined. There was no evidence of variation in extinction probabilities among the phyla. Although there was evidence of temporal variation in extinction probabilities within phyla, there was no evidence of a linear decrease in extinction probabilities over time, as has been reported by others. We did find evidence of high extinction probabilities for the two intervals that had been identified by others as periods of mass extinction. We found no evidence of variation in turnover among the five phyla. There was evidence of temporal variation in turnover, with greater turnover occurring in the older series.

Testing for variation in taxonomic extinction probabilities: a suggested methodology and some results

Several important questions in evolutionary biology and paleobiology involve sources of variation in extinction rates. In all cases of which we are aware, extinction rates have been estimated from data in which the probability that an observation (e.g., a fossil taxon) will occur is related both to extinction rates and to what we term encounter probabilities. Any statistical method for analyzing fossil data should at a minimum permit separate inferences on these two components. We develop a method for estimating taxonomic extinction rates from stratigraphic range data and for testing hypotheses about variability in these rates. We use this method to estimate extinction rates and to test the hypothesis of constant extinction rates for several sets of stratigraphic range data. The results of our tests support the hypothesis that extinction rates varied over the geologic time periods examined. We also present a test that can be used to identify periods of high or low extinction probabilities and provide an example using Phanerozoic invertebrate data. Extinction rates should be analyzed using stochastic models, in which it is recognized that stratigraphic samples are random variates and that sampling is imperfect.