Abstract
Next to plants, insects make up a smaller, but regular part of the diet of sympatric western lowland gorillas (G. g. gorilla) and chimpanzees (P. t. troglodytes). This study, in recently exploited rainforest in south-east Cameroon, is the first one that investigates simultaneously the consumption of insects by both ape species, and the abundance and temporal activity of the preys (especially ants and termites) in the study area. The aim is to find whether both great apes show different strategies (niche differentiation) in their insectivorous behaviour. We expect that the temporal variations in the frequency of insect-eating by gorillas and chimpanzees are not mutually correlated, and are explained by other factors in both species. In order to test this hypothesis the following parameters must be considered: 1) the composition of the insect and plant (fruit and foliage) diet of chimpanzees and gorillas during a period of one year, and 2) the spatio-temporal distribution of these resources. First, the insect composition of the diet will be compared between both apes. Secondly, the relation will be investigated between the temporal variation in the frequency of insectivory and 1) the spatio-temporal availability of insects in the forest, and 2) the seasonal variation of plant food in the diet. The composition and the monthly distribution of the insect and plant proportion in their diet will be determined by analysing faecal samples and feeding traces. All feeding remains will be identified and quantified. Data collection on the distribution of plant food in the different vegetation types and identification of the plant feeding remains will be done by botanists present in the project. I will estimate the relative densities of the ant and termite prey in these vegetation types by using a belt-transect method and I will follow up the temporal activity of the preys by regular visits to their nests and by using a pitfall-method. If the results confirm the hypothesis noted earlier, differences in feeding on insects by gorillas and chimpanzees can be interpreted in terms of niche differentiation.
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