Data and code for the study: Influence of Fruit Availability on the Diet and Grouping Patterns of Spider Monkeys (Ateles spp.) in a Relatively Undisturbed and a Degraded Forest in Tropical South America

In mammals, competition for resources is known to be one of the most important determinants of grouping patterns. As a result, some animals have evolved fission-fusion strategies that allow them to balance the benefits and costs of living in large groups. In this study, we evaluated the influence of fruit availability on fruit consumption and grouping patterns in two species of spider monkeys living in ecosystems with different levels of habitat degradation: brown spider monkeys (Ateles hybridus) living in a fragmented tropical forest in the inter-Andean Rio Magdalena valley of Colombia, and white-bellied spider monkeys (Ateles belzebuth) living in a continuous tropical evergreen forest in Amazonian Ecuador. Through focal animal sampling, we recorded diet, subgroup size, and fission/fusion events involving the subgroup that contained the focal animal, and we estimated habitat-wide fruit availability every 2 weeks on phenological transects in the two habitats. We recorded behavioral and ecological data for brown spider monkeys from July 2009 to November 2012 obtaining 2270 hours of focal sampling, and for white-bellied spider monkeys from August 2006 to February 2017 obtaining 7000 hours of focal sampling. We used generalized linear mixed effects models to evaluate the relationship between fruit availability and both fruit consumption and subgroup size. In the relatively undisturbed Ecuadorian rainforest site, both fruit consumption and subgroup size of white-bellied spider monkeys were positively correlated with seasonal fruit availability. By contrast, in the fragmented Colombian tropical forest, we found no significant relationship between fruit availability and either fruit consumption or subgroup size for brown spider monkeys. Although differences between our two study groups may be due to species differences, the two species are very closely related, and spider monkeys in general show similar responses to degraded habitats. Thus, we argue that our results support the hypothesis that grouping patterns in fission-fusion species are influenced by food availability and suggests that habitat degradation might disrupt this relationship.