African great apes are susceptible to infections with several species of Plasmodium, including the predecessor of Plasmodium falciparum. Little is known about the ecology of these pathogens in gorillas. A total of 131 gorilla fecal samples were collected from Dzanga-Sangha Protected Areas to study the diversity and prevalence of Plasmodium species. The effects of sex and age as factors influencing levels of infection with Plasmodium in habituated gorilla groups were assessed. Ninety-five human blood samples from the same locality were also analysed to test for cross-transmission between humans and gorillas. According to a cytB PCR assay 32% of gorilla's fecal samples and 43·1% human individuals were infected with Plasmodium spp. All Laverania species, Plasmodium vivax, and for the first time Plasmodium ovale were identified from gorilla samples. Plasmodium praefalciparum was present only from habituated individuals and P. falciparum was detected from human samples. Although few P. vivax and P. ovale sequences were obtained from gorillas, the evidence for cross-species transmission between humans and gorillas requires more in depth analysis. No association was found between malaria infection and sex, however, younger individuals aged ≤6 years were more susceptible. Switching between two different Plasmodium spp. was observed in three individuals. Prolonged monitoring of Plasmodium infection during various seasons and recording behavioural data is necessary to draw a precise picture about the infection dynamics.

The frails of Cola lizae, an endemic tree with a limited geographical distribution, have been a major food source for lowland gorillas in the Lopé Reserve during part of each year over a six-year period. Faecal analysis indicated that 11,000-18,000 Cola seeds km-2 were deposited by gorillas during the 4-month season in 1989. Gorillas are the only important dispersers of this species: other primates consume the succulent mesocarp, but do not swallow the large seed; elephants do not eat Cola fruits. Observations of Cola seeds in gorilla faeces showed a very high germination rate and, despite initial high mortality, 18% of seedlings still survived six months after deposition. Survival of seedlings was significantly better in faeces left at nest-sites than in other areas of the forest: 40% of seedlings were viable at nest-sites six months after deposition. This suggests that the open areas of forest, preferred by gorillas as nest-sites, are advantageous to the propagation of this species.

The population density and nesting behaviour of gorillas (Gorilla gorilla gorilla) was studied in the Ngotto forest, Central African Republic. We carried out a nest count along 94 km of transects. Also, the herbaceous vegetation of the understory was quantified and we attempted to assess the decay rate of nest sites. A total of 145 gorilla nests in 27 nest sites was found. We found 82.1% of gorilla nests > 2 m above ground. There was a significant correlation between the height of nests and the diameter of trees with nests. The density was estimated at 0.34–0.40 weaned gorillas per km2 depending on the value of nest site decay rate used. The herbaceous vegetation was scarce in the study site (42 out of 50 quadrats had no herbaceous stems). Compared with the gorilla population of the nearby Dzanga-Sangha forest, the population density of gorillas at Ngotto was lower but the proportion of nests found above ground was much higher. These differences are discussed and we suggest that they were the result of the scarcity of herbaceous vegetation in the Ngotto forest.