Niche écologique et diversité spécifique des espèces sympatriques dans le genre Cercopithecus

Abstract

It is difficult to separate the ecological niches of three sympatric species of Cercopithecus living in North-East Gabon on the basis of the niche parameters usually studied by prima-tologists : their habitats are very similar, their activity rhythms are the same and the vegetation layers they frequent overlap broadly. The three species have a very similar diet at the times of the year when food is readily available. The inter-specific differences in diet only become apparent during the “lean season”. At that critical period of the yearly cycle, the two species (C. nictitans and C. pogonias) whose habitat is the most similar, are also those whose diet is the most different. Food preferences between C. nictitans and C. cephus on one side, C. pogonias and C. cephus on the other side are not so marked, but C. cephus tends to forage in the lowest layers of the forest vegetation and in the areas where foliage density is the highest. The three sympatric Cercopithecus species appear to feed upon the same kinds of fruits. They differ however in their preferred animal prey. The three Cercopithecus species concerned also frequently live in “mixed groups” in the same area. Such an inter-specific association does not appear to reduce the niche breadth of the participating species, and no competition was observed. The formation of mixed groups of sympatric forest monkeys might then be considered as an adaptative strategy to optimize the utilization of available forest resources, three closely related but complementary species being more efficient resource-users than a single “generalist” one.