Apr. 7, 2003 The population of apes in Western Equatorial Africa has declined severely over the last 20 years and, without aggressive intervention, may soon reach the "brink of extinction," a study has found.
In a process that went largely unnoticed, years of illegal hunting and an epidemic of Ebola virus have slashed the population of wild chimpanzees and gorillas by more than 50 percent in the last part of the world to have widespread ape habitats, according to the study, which was published in an online edition of Nature April 6. The findings contradict estimates, from as recently as 1995, that the number of wild apes has been relatively stable.
"The species that are most similar to humans are just disappearing before our eyes," said Peter Walsh, a Princeton University scientist who led an international group of 23 researchers from the Wildlife Conservation Society and other institutions.
The study authors called for immediate improvements in anti-hunting law enforcement and in Ebola research and intervention. "The stark truth is that if we do not act decisively our children may live in a world without wild apes," the researchers concluded.
Previous estimates were deeply flawed, said Walsh, because they assumed that the best indicator of ape populations is the amount of intact forestland, which is relatively abundant in Western Equatorial Africa. They did not account for the possibility that hunting and disease could deplete the population even in densely forested areas, he said.
The new study is based on several surveys conducted between 1998 and 2002 in which teams of trained observers traveled through 4,800 kilometers of dense jungle and counted ape nests. In their paper, the researchers compared their results with those of the last comprehensive ape survey, which was done between 1981 and 1983, as well as with results from smaller surveys completed in the intervening years.
"Those who work in the field have had an idea of what's happening, both the hunting and the Ebola, for a while now, but it's been under the public radar," said Walsh. "Ours is a rigorous, quantitative estimate that I hope people will pay attention to. If you ask anybody, even in the international conservation community, they'll tell you that there are lots of apes. The fact is there are not. They've really been hammered, and it's actually accelerating."
The researchers predicted that, given the current trend, the ape population will decline by another 80 percent within 30 years, but probably much sooner if the loss continues to accelerate. That rate of decline, which spans just one or two generations of the animals, qualifies apes for "critically endangered" status under the World Conservation Union, according to the study. Gorillas and chimpanzees currently are listed as "endangered."
"They won't be extinct," said Walsh, "but we'll have gone from widespread, large populations to scattered pockets in 20 years." Small, isolated populations are often not sustainable, he said.
Walsh emphasized that the researchers did not attempt to estimate the actual number of apes that exist in the study region, which was mainly in the country of Gabon. Observing and counting even a single group of apes is difficult because they are very reclusive, he said. Instead, he used widely accepted statistical techniques to compare the spatial distribution of nests found in the new surveys to the spatial distribution of nests reported in the earlier studies.
As an example of the decline, Walsh cited a small study from 1991 in which researchers cutting a straight line through 20 kilometers of forest found 67 ape nest groups. In 1997 and 1998, researchers in the same area covered 2,700 kilometers -- more than 100 times the distance -- and found 91 nest groups.
The researchers found that the density of nests varied according to how far the site was from one of Gabon's four major cities and how far it was from a documented outbreak of human Ebola virus, which transfers from apes to humans.
Illegal hunting of apes, a problem for many years, has worsened with an increase in mechanized logging, Walsh said. Many people in the region eat ape meat, although it is taboo in some ethnic groups. Logging companies have created isolated towns of several thousand workers deep in the jungle where employees, with regular salaries, buy large quantities of "bushmeat." In addition, logging roads have opened forests to organized groups of hunters who have "transformed hunting from a subsistence activity to a commercial enterprise," the researchers wrote.
"In the few areas where it's been seriously addressed, strong law enforcement has cut down on poaching," Walsh said. "It takes political will and it takes money, both of which have been lacking in the past."
The Ebola problem also demands immediate financial support for rigorous studies of the forces driving the epidemic, Walsh said. He recommended that Congress make a $10-million emergency supplement to the U.S. Fish and Wildlife Service Great Ape Conservation Fund earmarked specifically for Ebola field research and intervention.
Walsh said the ape problem progressed as far as it has in part because of a lack funding for large-scale studies that are not tied to small, individual projects. He attributed the success of the study to the dedication of Lee White and other researchers with the Wildlife Conservation Society, for which Walsh worked before coming to Princeton in 1999. Researchers with the society, the World Wildlife Fund, and the Gabonese Water and Forests Ministry gathered important data as part of a successful project to create 13 national parks in Gabon.
"People in the field knew that commercial hunting was taking a huge toll but it took 10 extra years to piece together the data to make it a compelling story. Let's not make the same mistake with Ebola."
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