Resource partitioning in a community of diurnal arboreal mammals consisting of the lion-tailed macaque Macaca silenus, bonnet macaque (BM) Macaca radiata, Nilgiri langur Semnopithecus johnii, and the Indian giant squirrel Ratufa indica of the Western Ghats, southern India, was studied. Differences in their diet, vertical stratification, food resource niche breadth, niche overlap, and behavioral interactions were examined. Resource partitioning was through differential habitat use, resource use, and vertical stratification. Of the four species, the BM was not a resident species and made frequent forays into evergreen forest from the adjacent deciduous forest during the flowering season of Cullenia exarillata and fruiting season of Ficus microcarpa. The macaques had narrower niches, and the langur and the squirrel had wider niches. Niche overlap was highest between the two macaques. Overlap among the study species was particularly pronounced during the flowering of C. exarillata. There was significant correlation between niche overlap and intolerance among the study species. Certain species pairs showed little or no mutual intolerance despite high overlap. Cooperative interactions such as alarm calls occurred more frequently among the resident species. Interaction matrices revealed an underlying pattern of interspecific dominance hierarchy, with the BM dominating over the other three species. Our study suggests that the BM do not coexist with the other three because of high overlap with its congener and low occurrence of cooperative interactions.