Estimating the normal background rate of species extinction.

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2015-04

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Abstract

A key measure of humanity's global impact is by how much it has increased species extinction rates. Familiar statements are that these are 100-1000 times pre-human or background extinction levels. Estimating recent rates is straightforward, but establishing a background rate for comparison is not. Previous researchers chose an approximate benchmark of 1 extinction per million species per year (E/MSY). We explored disparate lines of evidence that suggest a substantially lower estimate. Fossil data yield direct estimates of extinction rates, but they are temporally coarse, mostly limited to marine hard-bodied taxa, and generally involve genera not species. Based on these data, typical background loss is 0.01 genera per million genera per year. Molecular phylogenies are available for more taxa and ecosystems, but it is debated whether they can be used to estimate separately speciation and extinction rates. We selected data to address known concerns and used them to determine median extinction estimates from statistical distributions of probable values for terrestrial plants and animals. We then created simulations to explore effects of violating model assumptions. Finally, we compiled estimates of diversification-the difference between speciation and extinction rates for different taxa. Median estimates of extinction rates ranged from 0.023 to 0.135 E/MSY. Simulation results suggested over- and under-estimation of extinction from individual phylogenies partially canceled each other out when large sets of phylogenies were analyzed. There was no evidence for recent and widespread pre-human overall declines in diversity. This implies that average extinction rates are less than average diversification rates. Median diversification rates were 0.05-0.2 new species per million species per year. On the basis of these results, we concluded that typical rates of background extinction may be closer to 0.1 E/MSY. Thus, current extinction rates are 1,000 times higher than natural background rates of extinction and future rates are likely to be 10,000 times higher.

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10.1111/cobi.12380

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De Vos, Jurriaan M, Lucas N Joppa, John L Gittleman, Patrick R Stephens and Stuart L Pimm (2015). Estimating the normal background rate of species extinction. Conservation biology : the journal of the Society for Conservation Biology, 29(2). pp. 452–462. 10.1111/cobi.12380 Retrieved from https://hdl.handle.net/10161/23550.

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Pimm

Stuart L. Pimm

Doris Duke Distinguished Professor of Conservation Ecology in the Nicholas School of the Environment and Earth Sciences

Stuart Pimm is a world leader in the study of present-day extinctions and what can be done to prevent them. His research covers the reasons why species become extinct, how fast they do so, the global patterns of habitat loss and species extinction and, importantly, the management consequences of this research. Pimm received his BSc degree from Oxford University in 1971 and his Ph.D. from New Mexico State University in 1974. Pimm is the author of over 350 scientific papers and five books. He is one of the most highly cited environmental scientists. Pimm wrote the highly acclaimed assessment of the human impact to the planet: The World According to Pimm: a Scientist Audits the Earth in 2001. His commitment to the interface between science and policy has led to his testimony to both House and Senate Committees on the re-authorization of the Endangered Species Act. He was worked and taught in Africa for nearly 30 years on elephants, most recently lions — through National Geographic’s Big Cats Initiative — but always on topics that relate to the conservation of wildlife and the ecosystems on which they depend. Other research areas include the Everglades of Florida and tropical forests in South America, especially the Atlantic Coast forest of Brazil and the northern Andes — two of the world's "hotspots" for threatened species. His international honours include the Tyler Prize for Environmental Achievement (2010), the Dr. A.H. Heineken Prize for Environmental Sciences from the Royal Netherlands Academy of Arts and Sciences (2006), the Society for Conservation Biology’s Edward T. LaRoe III Memorial Award (2006), and the Marsh Award for Conservation Biology, from the Marsh Christian Trust (awarded by the Zoological Society of London in 2004). Sigma Xi, The Scientific Research Society, awarded him the William Proctor Prize for Scientific Achievement in 2007. In 2019, he won the International Cosmos Prize, which recognised his founding and directing Saving Nature, www.savingnature.org, a non-profit that uses donations for carbon emissions offsets to fund local conservation groups in areas of exceptional tropical biodiversity to restore their degraded lands. 


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