Un primate granivore : le Colobe noir dans la forêt du Gabon ; potentialité d’évolution du comportement alimentaire

Abstract

This paper presents preliminary data on the feeding strategy of the Black colobus, Colobus satanas, in central Gabon. The study was conducted in the Réserve de la Lopé, using frequency method and systematic monthly samples to quantify the diet on one focal group of monkeys. The Black colobus feeds predominantly on immature seeds, unlike most of its folivorous relatives, while the consumption of young leaves is second in importance. Despite considerable variation in resource availability, seeds always dominate in the monthly diet. An increase in young leaf consumption was associated with an abundance of flush leaves, but also a reduction in seed availability ; a subsequent seasonal peak of flush leaves showed rm increase in their contribution to the diet, as seeds were also commonly available. Mature leaves were rarely eaten, and their occurence in the diet could explain some aspects of concomitant geophagy. Seasonal variation in diet and resources is compared with that of other primates of North-East Gabon : availability of foliage also partly influences consumption, but the dependence largely on fruit pulp and lack of seeds in the diet contrasts sharply with Black colobus. A similar biomass of Cercopithecidae is found in North-East Gabon where colobus are absent, and Lopé where one might have expected a larger biomass if the Black colobus had been a true folivore. Folivorous and frugivorous dietary strategies are contrasted on the basis of energetically economical vs expensive feeding. The Colobinae tend towards economical feeding strategies with their specialized digestive apparatus, but C. satanas represents a contrast, favoring an expensive seed-eating strategy. A hypothetical mechanism for the behavioural regulation of these strategies is discussed, based on conditioning principles. With such behavioural flexibility, we suggest that seed-eating by Black colobus may be a positive choice rather than a result of selective pressures against folivory.