Dissertation Research: Socioecology of Spider Monkeys (Ateles geoffroyi panamensis) in Wet Forest

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Investigating the range of behavioral and ecological variability within species is crucial for understanding broader patterns of social adaptation while minimizing confounding effects of phylogeny. Variability may be seen by studying the social system of one species in several different habitats. Differences in social systems within the same species may be explained by differences in food availability and distribution across different habitats. This project will investigate social system variation of spider monkeys (Ateles spp.) by studying them in productive, wet forest, a habitat where they have never before been studied. Spider monkeys are one of only several mammalian species that has a fission-fusion social system, in which the entire group rarely coalesces but instead is split into subgroups with fluid, variable membership. These monkeys specialize on eating ripe fruit, and their social system has been suggested to be an adaptation for reducing feeding competition within the group. How spider monkeys respond to fluctuations in their environment, and how their responses vary across a wide range of habitats, is informative for the broad scope of socioecology. The fluid nature of spider monkeys' fission-fusion social system allows sensitive detection of how such variables as diet, food availability and distribution, and subgroup size and composition interact. No long-term studies exist of spider monkeys living in a large, continuous tract of productive, diverse, lowland wet forest where they also live with a complete suite of potential predators. Living in this productive forest may result in relatively decreased feeding competition for this population of spider monkeys, so their social system may differ from populations living in drier habitats. The objectives of this project are the following: (1) to test hypotheses relating diet and foraging ecology to the social structure and organization of spider monkeys living in a diverse, wet forest with a decreased dry season, (2) to gain a clearer view of this primate's variation in behavior and ecology by comparing the results of this study with those of published studies of spider monkeys from other sites, and (3) to provide the first investigation of the relationships between subgroup changes and social and ecological variables in a large group of spider monkeys. This project has intellectual merit that spans several academic disciplines. This project will be of interest to physical anthropologists because chimpanzees and bonobos (Pan spp.), our closest living relatives, are the only other primates to consistently display a fission-fusion social system like that of spider monkeys; comparative studies of Pan and Ateles provide a relatively phylogenetically-independent approach for understanding the environmental determinants of the fission-fusion social system. This project will be of interest to biologists, especially behaviorists and ecologists, due to its focus on the relationships between spider monkeys' demography, social behavior, and ecology.