A massive decade-long study of Western Equatorial Africa’s gorillas and chimpanzees,named “Guns, germs and trees determine density and distribution of gorillas and chimpanzees in Western Equatorial Africa” that appears in the latest edition of the journal Science Advances has uncovered both good news and bad about our nearest relatives.
The good news: there are one third more western lowland gorillas and one tenth more central chimpanzees than previously thought.
The bad news: the vast majority of these great apes (80 percent) exist outside of protected areas, and gorilla populations are declining by 2.7 percent annually.
The newly published paper was written by 54 co-authors from several organizations and government agencies, including WCS (Wildlife Conservation Society), WWF (World Wide Fund for Nature), Max Planck Institute for Evolutionary Anthropology, Jane Goodall Institute, Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) — Monitoring the Illegal Killing of Elephants (MIKE), Lincoln Park Zoo, and the Universities of Stirling and Washington, and involved the protected area authorities of five countries.
Researchers collected field data during foot surveys carried out over a 10-year period across the range of both western lowland gorillas (Gorilla gorilla gorilla) and central chimpanzees (Pan troglodytes troglodytes) — surveying an area of 192,000 square kilometers (72,000 square miles — equivalent to the size of the state of Washington) and including some of the most remote forests on the African continent.
The authors of the study report an estimated abundance of over 360,000 gorillas and nearly 130,000 chimpanzees across the combined ranges of both subspecies, both of which were higher than previously believed.
The gorilla estimate is approximately one-third higher and the chimpanzee estimate is about one-tenth higher.
These revised numbers come largely from refinements to the survey methodology, new data from areas not previously included in range-wide estimates, as well as predictions of numbers in the areas between survey sites.
The study suggests that protecting large and intact forested areas, with protected areas at their core, is critical to conserving gorillas and chimpanzees in this region.
The data analysis also revealed a 2.7 percent annual decline in gorilla numbers, a finding that supports the continued status of the species as “Critically Endangered” on the IUCN Red List of Threatened Species. Chimpanzees are listed as “Endangered.”
The main factors responsible for the decline of gorillas and chimpanzees are illegal hunting, habitat degradation, and disease.
David Greer of WWF said: “All great apes, whether in Africa or Asia, are threatened by poaching, especially for the bushmeat trade. Our study found that apes could live in safety, and thus in higher numbers, at guarded sites than if there was no protection.”
An additional threat to great apes — as well as human health — is the Ebola virus disease.
Of all the 14 living great ape taxa, western lowland gorillas and central chimpanzees have the largest remaining populations.
Liz Williamson from the University of Stirling and the IUCN Red List Authority Coordinator for great apes said: “Our study has revealed that it is not too late to secure a future for gorillas and chimpanzees.”