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15 January 2003 Exclusive from New Scientist Print Edition
The well-known "Red List" that details which species are
threatened with extinction is inaccurate, according to a new assessment.
It concludes the list fails to reflect the true threat to species,
by not taking full account of the threat posed by people.
The Red List, which is compiled by the World Conservation Union (IUCN),
gauges a species' risk of extinction mainly on the basis of its population
size, rate of decline and geographic range.
But Alexander Harcourt and Sean Parks at the University of California,
Davis, argue that this is not enough. They compare an endangered
species to a house that has been left unlocked. The house is vulnerable
to burglary, but it only becomes threatened when there is a burglar
nearby.
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)
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