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

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.

Western gorilla diet: a synthesis from six sites.

The objective of this paper is to collate information on western gorilla diet from six study sites throughout much of their current range, including preliminary information from two sites (Afi and Lossi), where studies of diet have begun only recently. Food lists were available from each site, derived from indirect signs of gorilla feeding (such as feces), with some observational data. Important staple, seasonal, and fallback foods have been identified, and a number of striking similarities across sites have been revealed based on a much larger data set than was previously available. It was confirmed that the western gorilla diet is always eclectic, including up to 230 items and 180 species. The greatest diversity is found among the fruit species eaten, fruit being included in western gorilla diets from all sites and throughout most or all of the year. Eight plant families provide important foods at five, or all six, sites, suggesting that it may be possible in the future to predict which habitats are the most suitable for gorillas. Gorillas exploit both rare and common forest species. Similarities and differences among sites can be explained superficially on the basis of geography and the past history of the forest. Gorilla density across sites appears to be most affected by the density of monocotyledonous bulk food plants, but its relationship to the density of important tree food species has yet to be tested.