Extinction Risk for Many Species Vastly Underestimated, Study Suggests

The study appears in the journal Biological Conservation.

The maps describing species’ geographic ranges, which are used by the International Union for Conservation of Nature (IUCN) to determine threat status, appear to systematically overestimate the size of the habitat in which species can thrive, said Don Melnick, senior investigator on the study and the Thomas Hunt Morgan Professor of Conservation Biology in the Department of Ecology, Evolution and Environmental Biology (E3B).

“Concerned about this issue, we aimed to determine how far off those maps were. In doing so, we found there is an enormous amount of freely available data on many species around the world that can be employed to get a better picture of exactly how many species are truly under extreme threat. This picture, grim as it may be, is necessary if we are going to accurately plan the steps needed to stem those threats, locally and globally.”

Currently, IUCN makes use of species sightings reported by experts to draw boundaries reflecting the geographic range of a given species. From these maps, the IUCN develops its Red List, which assigns a threat status to wild species: Vulnerable, Endangered, or Critically Endangered. Though the accuracy of threat risk assigned to a species relies heavily on these maps, Melnick and his colleagues believe they almost always overestimate the actual distribution of a species by incorporating areas of unsuitable habitat. This overestimation of range size, in turn, leads to a significant overestimation of population size and therefore an underestimation of extinction risk.

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Image: Nilgiri flycatcher (Eumyias albicaudatus). The researchers found that the estimated range for this particular species is actually 65 percent smaller than IUCN determined and thus suggest uplisting the threat level from "Near Threatened" to "Vulnerable." Photo by Adesh Shivkar