Local variances in group size and density of A. palliata on Barro Colorado Island are reported, and their relationship to local variance in the density of food and non-food species is investigated via nonparametric statistical techniques. Group size is significantly and positively related to the density of 2 major food species but not to the density of minor food species or non-food species. The density of Ficus spp., which supply over half the diet by weight and which have complex, asynchronous, phenological cycles, is highly correlated with group size over 9 study plots. Differential reproductive success and lower levels of intragroup competition for food in areas of high Ficus density are discussed.