Effects of predation risk on the grouping patterns of white-bellied spider monkeys (Ateles belzebuth belzebuth) in Western Amazonia.

Predation is proposed to be one of the most important factors influencing the evolution of mammalian societies. Although predation risk is thought to influence both the behavior and grouping patterns of most diurnal primates, evidence supporting this hypothesis is still limited. The spatial and temporal patterns of mineral lick use by one group of white-bellied spider monkeys (Ateles belzebuth) were evaluated, based on the growing evidence that mineral licks are perceived as areas of relative high predation risk by Neotropical primates. The area immediately surrounding the mineral lick was the most intensively used area within the home range of the study group, particularly by large subgroups of monkeys, and there were differences in mean subgroup size on days of mineral lick visitation versus days without lick visits. Additionally, on days of mineral lick visitation, subgroup size reached its maximum specifically during the period of lick visitation. Finally, on visit days subgroups showed a greater increase in size and higher fusion rates in the 2 hr before arriving at the lick in comparison with matched time windows on non-visit days. Together, these results provide an example of how primates employ behavioral strategies that might reduce the effects of predation. This study also demonstrates how taxa characterized by a high degree of fission-fusion dynamics can allow us to test hypotheses regarding the effects of socioecological variables on primate grouping patterns.