Rates and causes of extinction

Craig Loehle and Willis Eschenbach are the authors of “Historical bird and terrestrial mammal extinction rates and causes” (Diversity and Distributions 18(1):84-91). They developed estimates of extinction rates for islands and continents over the past 500 years using IUCN’s Red List (www.iucnredlist.org) and records compiled and maintained by the Committee on Recently Extinct Organisms at the American Museum of Natural History (http://creo.amnh.org). Extinction rates for the past 500 years were compared with published estimates of longer-term background extinction rates derived from analyses of fossil records.

Six continental birds and three continental mammals have become extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Per unit of land area, extinction rates for the past 500 years are more than 100 times higher on islands than on continents for both birds and mammals. Relative to background, island extinction rates for the past 500 years are higher by a factor on the order of 80 to 800. In contrast, continental extinction rates for the past 500 years differ from background by a factor on the order of 1 to 10. This finding conflicts with some published modeling studies that have reported recent extinction rates for continents more than 100 times higher than background.

Loehle and Eschenbach review several lines of evidence indicating that high extinction rates on islands are attributable to effects of uncontrolled hunting by humans and predation by introduced animal species. They also
discuss reasons why models of extinction risk based on rates and causes of extinction on islands have limited applicability in conservation strategies for birds and mammals on continents. Their article is available at http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4642.2011.00856.x/pdf 

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