Grouping dynamics of lowland woolly monkeys (Lagothrix lagotricha poeppigii) in Amazonian Ecuador




Ellis, Kelsey Morgan

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Predator avoidance, resource distribution, and reproductive strategies all play a crucial role in shaping the social structure of animal societies. The fission-fusion dynamics of some animal societies – where core social units are able to break apart or coalesce into parties of variable size and composition – can allow individuals to mediate the cost-benefit tradeoffs of varying party size according to particular environmental or social conditions. Here, I couple ecological, behavioral, and spatial data with molecular genetic methods and analytical techniques (Social Network Analysis) to examine spatiotemporal association patterns among woolly monkeys from four social groups at the Tiputini Biodiversity Station (TBS) in Amazonian Ecuador. The woolly monkeys in this populations demonstrated relatively high degrees of fission-fusion dynamics, with groups dividing frequently into subgroups and showing temporally variable cohesion among group members. I found no evidence, however, that subgroups consistently and repeatedly comprised the same sets of individuals. Spatial associations and social interactions were not limited to members of a single social group, and tolerant associations between members of some social groups occurred with relatively high frequency. Genetic analyses revealed no difference in the average relatedness of male and female same-sex dyads, although, adult males tended to have more close relatives both within and between social groups than adult females. Regardless of sex, animals were no more likely to associate with genetic relatives than with to non-relatives. This study also corroborated earlier suggestions that woolly monkeys exhibit some degree of bisexual dispersal, with some males leaving their natal group, in contrast to the pattern that characterizes closely related species of primates. Genetic data also suggest that woolly monkeys live in a dispersed network of kin, where both males and females had first order relatives in neighboring groups. Kinship ties among animals in different groups may play a role in facilitating tolerant mixed group associations, which are common in the study population. As observed in other studies, home range overlap between neighboring groups was extensive, with particular pairs of groups showing higher degrees of overlap than others. Finally, woolly monkeys demonstrated strong reproductive seasonality, with births and conceptions confined to a few months out of the year. My finding that seasonal variation in group cohesion and ranging patterns was not related to fruit availability, but did covary with a behavioral index of mating opportunities, suggest that grouping and ranging dynamics in woolly monkeys may not primarily be driven by competition over food, but rather by competition over mates.



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