![]() 2000 Cardillo and Bromham 2001 Cardillo 2003 Fisher et al. A number of recent studies have linked variation in extinction risk or decline among species to biological traits ( Gaston and Blackburn 1995 Bennett and Owens 1997 Owens and Bennett 2000 Purvis et al. Biological traits that confer ecological flexibility and allow populations to recover rapidly from depletion may offer a degree of protection from external threats. 2001 McKinney 2001 Ceballos and Ehrlich 2002 Harcourt and Parks 2002 Parks and Harcourt 2002).Īlthough exposure to threatening processes is the ultimate cause of extinction, a species' biology determines how well it is able to withstand the threats to which it is exposed. Threatening processes such as these vary in intensity across the surface of the Earth, and species that inhabit more heavily impacted regions are expected to have a higher risk of extinction ( Forester and Machlis 1996 Woodroffe 2000 Brashares et al. The underlying cause of virtually all recent and ongoing declines of mammal species is the growth of human populations and associated impacts such as habitat loss, hunting, and the spread of invasive species. Understanding the ecological processes that cause some species to decline, while others remain relatively safe, may help to predict future declines and focus conservation efforts on species in urgent need. Mammals have been severely affected by the current extinction crisis: around a quarter of extant species are considered to be threatened with extinction ( Hilton-Taylor 2000). ![]() We suggest that a preemptive approach to species conservation is needed to identify and protect species that may not be threatened at present but may become so in the near future. African viverrid species are particularly likely to become threatened, even though most are currently considered relatively safe. We demonstrate how a model predicting extinction risk from biology can be combined with projected human population density to identify species likely to move most rapidly towards extinction by the year 2030. The results suggest that biology will become a more critical determinant of risk as human populations expand. However, biology interacts with human population density to determine extinction risk: biological traits explain 80% of variation in risk for carnivore species with high levels of exposure to human populations, compared to 45% for carnivores generally. Using phylogenetic comparative methods, we show that extinction risk in the mammal order Carnivora is predicted more strongly by biology than exposure to high-density human populations. However, little is known about the relative and interacting effects of intrinsic and external variables on extinction risk. ![]() Recent studies have shown that a species' extinction risk may be determined by two types of factors: intrinsic biological traits and exposure to external anthropogenic threats. Understanding why some species are at high risk of extinction, while others remain relatively safe, is central to the development of a predictive conservation science.
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