Effects of mixed-species association on resource use by Saimiri sciureus and Cebus apella.

Short-term associations between primate species offer the opportunity to measure changes in individual behavior and ecology in response to alterations in group size and composition. During a three-month study of associations between squirrel monkeys (Saimiri sciureus) and brown capuchin monkeys (Cebus apella) in Manu National Park, Peru, I measured resource use and feeding efficiency for both species when in mixed and solitary troops, as well as the context and outcome of competitive interactions. Saimiri traveled among Cebus home ranges and were periodically led by Cebus to large fruiting and flowering trees. Feeding rates in large fruit trees were altered by the presence of the other species-positively for Cebus, but negatively for Saimiri. Association increased the average diameter of the troop only for Cebus, which could control access to small, concentrated resoures found while the mixed troop moved through the forest. Results of this short-term study suggest that effects of association on resource use differ for the two species, and are related to the size of resources as well as to differences in body size and group size between the species.