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Sci Adv. 2018 Apr 25;4(4):eaar2964. doi: 10.1126/sciadv.aar2964. eCollection 2018 Apr.

Guns, germs, and trees determine density and distribution of gorillas and chimpanzees in Western Equatorial Africa.

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Wildlife Conservation Society, Global Conservation Program, 2300 Southern Boulevard, Bronx, New York, NY 10460, USA.
Faculty of Natural Sciences, University of Stirling, Stirling FK9 4LA, Scotland, UK.
Department of Biology, Saint Louis University, Macelwane Hall, St. Louis, MO 63108, USA.
Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
Conservation International, 2011 Crystal Drive, Suite 500, Arlington, VA 22202, USA.
Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)-Monitoring the Illegal Killing of Elephants (MIKE), MIKE Subregional Office, Yaoundé, BP 5506, Cameroon.
World Wildlife Fund International, Regional Office for Africa, BP 6776 Yaoundé, Cameroon.
Instituto Nacional de Desarrollo Forestal y Gestión del Sistema Nacional de Áreas Protegidas, Bata, Equatorial Guinea.
Robert Bosch Junior Professor, German Centre for Integrative Biodiversity Research (iDiv), Halle-Leipzig-Jena, Leipzig, Germany.
The Jane Goodall Institute, 1595 Spring Hill Road, Suite 550, Vienna, VA 22182, USA.
Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, 2001 North Clark Street, Chicago, IL 60614, USA.
Department of Anthropology, Washington University, 1 Brookings Drive, St. Louis, MO 63130, USA.


We present a range-wide assessment of sympatric western lowland gorillas Gorilla gorilla gorilla and central chimpanzees Pan troglodytes troglodytes using the largest survey data set ever assembled for these taxa: 59 sites in five countries surveyed between 2003 and 2013, totaling 61,000 person-days of fieldwork. We used spatial modeling to investigate major drivers of great ape distribution and population trends. We predicted density across each taxon's geographic range, allowing us to estimate overall abundance: 361,900 gorillas and 128,700 chimpanzees in Western Equatorial Africa-substantially higher than previous estimates. These two subspecies represent close to 99% of all gorillas and one-third of all chimpanzees. Annual population decline of gorillas was estimated at 2.7%, maintaining them as Critically Endangered on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List. We quantified the threats to each taxon, of which the three greatest were poaching, disease, and habitat degradation. Gorillas and chimpanzees are found at higher densities where forest is intact, wildlife laws are enforced, human influence is low, and disease impacts have been low. Strategic use of the results of these analyses could conserve the majority of gorillas and chimpanzees. With around 80% of both subspecies occurring outside protected areas, their conservation requires reinforcement of anti-poaching efforts both inside and outside protected areas (particularly where habitat quality is high and human impact is low), diligent disease control measures (including training, advocacy, and research into Ebola virus disease), and the preservation of high-quality habitat through integrated land-use planning and implementation of best practices by the extractive and agricultural industries.

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