OUR closest relatives, the great apes, could soon become a zoological curiosity confined to wildlife parks, zoos and animal sanctuaries. Population surveys have revealed that the effects of the bushmeat trade and Ebola virus are combining to decimate gorilla and chimpanzee populations in western equatorial Africa, their last major refuge.
Commercial hunters are slaughtering gorillas and chimpanzees near urban centres and logging camps. And the often fatal haemorrhagic fever Ebola, which affects humans and non-human primates, is wiping out large gorilla groups living in remote forests. This double whammy could push the apes to the brink of extinction in just a decade, warns Peter Walsh of Princeton University in a study published by Nature this week.
Gabon and the Democratic Republic of Congo are home to most of the world’s remaining gorillas and common chimps. Satellite photos of Gabon show only modest deforestation, which was thought to be the worst threat. But Walsh found a thicket of problems under the canopy.
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While selective logging preserves tree cover by thinning rather than clearing forests, the roads built to remove timber give hunters easy access to the apes, helping to boost the bushmeat market. Meanwhile, gorillas that are protected within reserves or that are living in prime habitat that is out of the reach of hunters are being wiped out by Ebola.
The last survey of gorilla and chimp sleeping nests, from 1981 to 1983, showed large ape populations across Gabon. But surveys conducted by a 23-person team between 1998 and 2002, revealed that large groups remained only in the north-east and south-west. The average population density of great apes across the area dropped by 56 per cent, or 4.7 per cent a year.
Losses were alarmingly heavy in areas where populations had been largest. Up to 99 per cent of apes have vanished in the Minkebe forest area in north-east Gabon. And some of the losses came suddenly. In just three months, a group of 143 gorillas being studied in the Lossi area of Congo was reduced to seven as Ebola swept through the region.
The average annual population decline is now severe enough for gorillas and chimps to be moved from the World Conservation Union’s “endangered” list to its “critically endangered” list, Walsh says. Species must have a projected loss of 80 per cent of the population within three generations to be on this list.
“If we don’t do something about hunting in 10 to 20 years, there will just be isolated pockets of gorillas left,” Walsh says, urging “radical intervention” to stop it.
Hunting would be easier to stop than Ebola, since no one knows what causes outbreaks of the virus. Many suspect that ecological change has increased human contact with an as yet unidentified animal that harbours the virus. Walsh suspects Ebola may be an epidemic disease that emerges when gorillas exceed a certain population density. Finding out which theory is correct is critical.
If these apes are wiped out, says Sandy Harcourt of the University of California at Davis, “we’ve lost a very, very direct connection to the rest of the animal world”. But though he agrees the problem is grave, he believes recovery is possible if the animals can be protected. Mountain gorillas have survived several wars, he points out. “The situation is way worse than we ever thought, but very far from hopeless.”