No Evidence of Coordination Between Different Subgroups in the Fission-Fusion Society of Spider Monkeys (Ateles geoffroyi)

Flexibility in spatial cohesion allows species with high fission-fusion dynamics to exploit variable habitats and decrease the costs of feeding competition. However, coordination among highly dispersed group members becomes problematic. In spider monkeys (Ateles spp.), individuals can spread over wide areas, forming several subgroups that appear to travel independently from each other. To explore their relative travel patterns, we compare the distance between different subgroups with the distance predicted by a null model of independent travel. Observations of distance between subgroups come from simultaneous follows of ≥2 subgroups in 2 different groups of spider monkeys in Punta Laguna, Mexico. We estimated space use using the kernel method, which produces areas with a given probability of presence of the subgroups, based on the frequency with which they were observed in each location. The null model consisted of the frequency distribution of distances between randomly chosen pairs of points within the home range, choosing each point independently with a probability proportional to the corresponding observed probability of presence. In all cases, the observed distances between subgroups were very close to those predicted by the null model, which suggests that subgroups do not coordinate their relative travel patterns. Also, the distance separating 2 individuals when in different subgroups was not affected by their sex or association index. These findings underscore the low cohesiveness between group members in species with high fission-fusion dynamics and challenge us to find the mechanisms by which groups maintain their social structure.