Dissertation Research: Splitting and Joining Decisions, and Adaptations to Temporal Resource Variation in Long-Haired Spider Monkeys (Ateles Belzebuth Belzebuth)

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This project will investigate the fission-fusion behavior of long-haired spider monkeys (Ateles belzebuth belzebuth) in the Yasuni National Park, Ecuador, and its relationship to ecological and social factors. Spider monkeys live in social groups in which all of the members of a community are rarely in the same place at the same time. Instead, subsets (subgroups) of the community associate temporarily and change associations frequently. Few studies have addressed what causes individuals to split from or join these subgroups. This project will estimate how the expectation of the amount of fruit in feeding trees affects subgroup splitting decisions, the competitive or cooperative nature of subgroup fusions, and to what extent subgroup changes are influenced by non-food-related causes, such as social factors. To interpret these issues, this project will provide evidence of the level at which spider monkeys understand where to find feeding trees, and when those trees can be profitably visited. To accomplish these goals, adult females will be followed for two-week periods from dawn to dusk to collect data on subgroup changes and resource use. Additionally, data on the fruiting patterns of important feeding trees will be collected to measure fine-scale changes in fruit abundance. This project will clarify our knowledge of why subgroups form and split, providing a clearer understanding of the factors causing the evolution of a fission-fusion society, and thereby provide important comparative information for the understanding of the evolution of primate social systems. Additionally, it will provide evidence bearing upon the possession of mental maps by primates, and will provide some of the first data on primate understanding of temporal variation in fruit availability.