Matt Walker BBC Nature 27 Sep 12;
Great apes, such as gorillas, chimps and bonobos, are running out of places to live, say scientists.
They have recorded a dramatic decline in the amount of habitat suitable for great apes, according to the first such survey across the African continent.
Eastern gorillas, the largest living primate, have lost more than half their habitat since the early 1990s.
Cross River gorillas, chimps and bonobos have also suffered significant losses, according to the study.
Details are published in the journal Diversity and Distributions.
"Several studies either on a site or country level indicated already that African ape populations are under enormous pressure and in decline," said Hjalmar Kuehl, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who helped organise the research.
But a wider perspective was missing; so various organisations and scientists joined to conduct the first continent-wide survey of suitable great ape habitat.
"Many of the authors have spent years to collect the data used in this study under extremely difficult conditions with a lot of personal commitment," Dr Kuehl told BBC Nature.
"Nothing comparable exists."
The scientists conducted the survey in two stages.
First, they determined the exact location of more than 15,000 sites where the various species and subspecies of African great ape have been confirmed living during the past twenty years.
"We then evaluated the environmental conditions at these locations and at all other locations across tropical Africa where great ape presence was not confirmed. This assessment included for instance percentage forest cover, human population density or climatic conditions," said Dr Kuehl.
From that the researchers could calculate the environmental conditions required for great apes to live. Then, using a statistical model, they predicted the amount of such habitat surviving across Africa, first for the 1990s, then the 2000s.
The results are grim reading for conservationists.
Gorillas have been significantly affected. Cross River gorillas have seen 59% of their habitat disappear over the past two decades. Eastern gorillas, the largest gorilla and largest surviving primate, have lost 52% of their habitat, while western gorillas have lost 31%.
The various species and subspecies of chimp have also suffered.
Bonobos, once known as pygmy chimpanzees, have lost 29% of their habitat. Of the different subspecies of common chimpanzee, those living in central Africa have lost 17% and those in western Africa 11% of their habitat respectively.
"From several site and country level studies we knew that pressure on great apes is increasing enormously. But despite these expectations it is outrageous to see how our closest living relatives and their habitats are disappearing," said Dr Kuehl.
The pressures on the great apes vary significantly depending on region.
For example, in western Africa, the loss of suitable habitat is being driven by forest clearance and hunting.
In Central Africa, huge swathes of pristine forest remain, but it is no longer suitable for great apes due to the extensive hunting that occurs within to supply the trade in bushmeat.
The scientists would like to improve their study, which provides a large scale picture of the habitat loss suffered by great apes, by including more local data.
Including socioeconomic data may help explain why apes still live in close proximity to people in some areas, while in most others they have disappeared.
"The situation is very dramatic, many of the ape populations we still find today will disappear in the near future," Dr Kuehl told BBC Nature. "In an increasingly crowding world with demand for space, wood, mineral resources and meat, apes will continue to disappear.
"Without a fundamental change in perception of how precious apes and their habitats are the current situation will not improve."
