Dietary overlap of sympatric apes is complex and understudied, but its examination is essential to further our understanding of species distribution, abundance, and community ecology. Over 3 yr we studied food availability and dietary composition of central chimpanzees (Pan troglodytes troglodytes) and western gorillas (Gorilla gorilla gorilla) in Loango National Park, Gabon. We predicted that living in a habitat dominated by mature forest with sparse terrestrial herbaceous vegetation would lead to an increase in frugivory by gorillas, resulting in increased dietary overlap between the 2 ape species vs. other sites, but that chimpanzees would remain more frugivorous than gorillas. Through fecal analysis we measured overlap in fruit consumption between the 2 species on a bimonthly basis using the Renkonens method. Mean overlap was 27.5% but varied greatly seasonally, ranging between 0.3% and 69%, indicating that when examined on a finer scale, the degree of overlap appears much lower than at other study sites. In contrast to studies elsewhere, there was not a positive correlation between rainfall and fruit availability in Loango, and the long dry season was a period of high fruit production. As observed elsewhere, we found a positive correlation between fruit consumption and fruit availability for both chimpanzees and gorillas and we found that chimpanzees were more frugivorous than gorillas. A very low availability of herbs did not lead to increased frugivory by gorillas nor increased overlap between Int J Primatol (2011) 32:755-775 the 2 ape species vs. other field sites. We conclude that forest composition, fruit availability, and dietary variability of sympatric species can vary greatly between locations, and that chimpanzees and gorillas can adapt to primary forest with little undergrowth, where they concentrate their diet on fruit and leaves.

Wildlife managers are urgently searching for improved sociodemographic population assessment methods to evaluate the effectiveness of implemented conservation activities. These need to be inexpensive, appropriate for a wide spectrum of species and straightforward to apply by local staff members with minimal training. Furthermore, conservation management would benefit from single approaches which cover many aspects of population assessment beyond only density estimates, to include for instance social and demographic structure, movement patterns, or species interactions. Remote camera traps have traditionally been used to measure species richness. Currently, there is a rapid move toward using remote camera trapping in density estimation, community ecology, and conservation management. Here, we demonstrate such comprehensive population assessment by linking remote video trapping, spatially explicit capture–recapture (SECR) techniques, and other methods. We apply it to three species: chimpanzees Pan troglodytes troglodytes, gorillas Gorilla gorilla gorilla, and forest elephants Loxodonta cyclotis in Loango National Park, Gabon. All three species exhibited considerable heterogeneity in capture probability at the sex or group level and density was estimated at 1.72, 1.2, and 1.37 individuals per km2 and male to female sex ratios were 1:2.1, 1:3.2, and 1:2 for chimpanzees, gorillas, and elephants, respectively. Association patterns revealed four, eight, and 18 independent social groups of chimpanzees, gorillas, and elephants, respectively: key information for both conservation management and studies on the species' ecology. Additionally, there was evidence of resident and nonresident elephants within the study area and intersexual variation in home range size among elephants but not chimpanzees. Our study highlights the potential of combining camera trapping and SECR methods in conducting detailed population assessments that go far beyond documenting species diversity patterns or estimating single species population size. Our study design is widely applicable to other species and spatial scales, and moderately trained staff members can collect and process the required data. Furthermore, assessments using the same method can be extended to include several other ecological, behavioral, and demographic aspects: fission and fusion dynamics and intergroup transfers, birth and mortality rates, species interactions, and ranging patterns.

Abstract:Species commonly exist in sympatry, yet ecological studies are often based on a single species approach while ignoring the impact of sympatric competitors. Over 13 mo we used 24 remote video-camera traps to monitor habitat use of sympatric chimpanzee, gorilla and elephant in four different habitat types in Loango National Park, Gabon. Habitat use by each species was predicted to vary according to seasonal changes in food availability and precipitation. Increased interspecific competition between the three species was expected at times of reduced resource availability, leading to exclusion of the inferior competitor. Supporting the predictions, species abundance per habitat showed seasonal variation: all three species responded positively to increased fruit availability in all habitats, but the response was only significant for gorilla in mature forest and elephant in coastal forest. Responses to rainfall varied, with the chimpanzee responding negatively to rainfall in swamp forest, the gorilla responding positively to rainfall in coastal and secondary forest, and the elephant responding positively to rainfall in mature forest. Elephant presence resulted in competitive exclusion of the apes under certain conditions: the chimpanzee was excluded by the elephant where fruit availability was low, whereas the gorilla was excluded by the elephant in areas of low herb density despite high fruit availability. Our results emphasize the value of applying a multi-species, longer-term approach to studying variation in habitat use among sympatric species and highlight the impact competitors can exert on one another's distribution.

Afrotropical forests host many of the world’s remaining megafauna, but even here they are confined to areas where direct human influences are low. We use a rare long-term dataset of tree reproduction and a photographic database of forest elephants to assess food availability and body condition of an emblematic megafauna species at Lopé National Park, Gabon. We show an 81% decline in fruiting over a 32-year period (1986-2018) and an 11% decline in body condition of fruit-dependent forest elephants from 2008-2018. Fruit famine in one of the last strongholds for African forest elephants should raise concern for the ability of this species and other fruit-dependent megafauna to persist in the long-term, with consequences for broader ecosystem and biosphere functioning.

Background The humid tropical forests of Central Africa influence weather worldwide and play a major role in the global carbon cycle. However, they are also an ecological anomaly, with evergreen forests dominating the western equatorial region despite less than 2,000 mm total annual rainfall. Meteorological data for Central Africa are notoriously sparse and incomplete and there are substantial issues with satellite-derived data because of persistent cloudiness and inability to ground-truth estimates. Long-term climate observations are urgently needed to verify regional climate and vegetation models, shed light on the mechanisms that drive climatic variability and assess the viability of evergreen forests under future climate scenarios. Methods We have the rare opportunity to analyse a 34 year dataset of rainfall and temperature (and shorter periods of absolute humidity, wind speed, solar radiation and aerosol optical depth) from Lopé National Park, a long-term ecological research site in Gabon, western equatorial Africa. We used (generalized) linear mixed models and spectral analyses to assess seasonal and inter-annual variation, long-term trends and oceanic influences on local weather patterns. Results Lopé’s weather is characterised by a cool, light-deficient, long dry season. Long-term climatic means have changed significantly over the last 34 years, with warming occurring at a rate of +0.25 °C per decade (minimum daily temperature) and drying at a rate of −75 mm per decade (total annual rainfall). Inter-annual climatic variability at Lopé is highly influenced by global weather patterns. Sea surface temperatures of the Pacific and Atlantic oceans have strong coherence with Lopé temperature and rainfall on multi-annual scales. Conclusions The Lopé long-term weather record has not previously been made public and is of high value in such a data poor region. Our results support regional analyses of climatic seasonality, long-term warming and the influences of the oceans on temperature and rainfall variability. However, warming has occurred more rapidly than the regional products suggest and while there remains much uncertainty in the wider region, rainfall has declined over the last three decades at Lopé. The association between rainfall and the Atlantic cold tongue at Lopé lends some support for the ‘dry’ models of climate change for the region. In the context of a rapidly warming and drying climate, urgent research is needed into the sensitivity of dry season clouds to ocean temperatures and the viability of humid evergreen forests in this dry region should the clouds disappear.