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In the same way, a small population of animals susceptible to extinction only becomes actively

threatened when it is being poached or its habitat is destroyed. Harcourt and Parks advocate modifying the Red List criteria to include local human population density.

Although a large number of people nearby may not in itself be a threat, they argue that hunting, pollution and habitat destruction, for example, are all likely to increase as people encroach on wildlife. What is more, data on human density is readily available. "We have the numbers, why not use them?" says Harcourt.

Low to high

To illustrate their point, the researchers reassessed 200 primate species from the 1996 Red List. They found that 17 species designated as being at relatively low risk by the Red List should now be reassigned as high priority. Two such species are Wied's tufted-ear marmoset (Callithrix kuhlii) and the golden lion tamarin (Leontopithecus rosalia) from South America.

Contrary to the expectations of many, the researchers also found that two high-profile species, the gorilla and the pygmy chimpanzee, or bonobo, should be downgraded to a lower level of threat.

But Craig Hilton-Taylor, Red List Programme Officer based in Cambridge, England, says that the IUCN has already introduced a specific classification system for threats such as human density. The system runs in parallel to the main Red List classification.

Besides, part of the Red List's value is that you can make comparisons with past assessments, he says, and tweaking the criteria would make this impossible. "We've been asked by everyone, please don't change the system again," says Hilton-Taylor.

Harcourt maintains that making explicit threats part of the criteria is not only more accurate, it may also help highlight future problems. Matt Walpole, a conservation researcher at the University of Kent at Canterbury, England, agrees: "Where [population] data is lacking, it might be a useful way of flagging up potentially threatened species."

Journal reference: Biological Conservation (vol 109, p 137)

source: http://www.newscientist.com/news