Spatial aggregation of fruits explains food selection in a neotropical primate (Alouatta pigra)

The availability and spatial distribution of food resources affect animal behavior and survival. Black howler monkeys (Alouatta pigra) have a foraging strategy to balance their nutrient intake that involves mixing their consumption of leaves and fruits. The spatial aggregation of food items should impact this strategy, but how it does so is largely unknown. We quantified how leaf and fruit intake combined (here termed food set selection) was spatially aggregated in patches and how food aggregation varied across seasons. Using variograms we estimated patch diameter and with Generalized Least Square models determined the effect of food spatial aggregation on food selection. Only fruits were structured in patches in the season of highest availability (dry-season). The patches of food set selection had a diameter between 6.9 and 14 m and were explained by those of mature fruit availability which were between 18 and 19 m in diameter. Our results suggest that the spatial pattern of food selection is influenced by patches of large fruit-bearing trees, not by particular species. Fruit also occur along spatial gradients, but these do not explain food selection, suggesting that howlers maximize food intake in response to local aggregation of fruit that are limiting during certain seasons. We demonstrate how the independent spatial modelling of resources and behavior enables the definition of patches and testing their spatial relationship.