Association Networks and Life History of Female Spider Monkeys

Abstract

The social system of spider monkeys is characterized by female dispersal and fission–fusion social organization. After emigration from a natal group, a female spider monkey is expected to experience variation in their reproductive status, which may in turn be expected to alter association patterns within the new group. Until now, analyses on association patterns in spider monkeys have most often been studied on an annual basis, but such time-constrained analyses may bury long-term patterns of association and potential variation across multiple reproductive cycles. In this study, I examine the variation of female association in relation with her reproductive status through social network analysis in three relatively short-term periods of 2–3 months each across several years. Network analysis showed clear clusters for each sex, but there was variation among periods. Lactating females were always central, and cycling females were always drawn outside of their core network. Pregnant and possibly cycling females, and a lone immigrant female, were typically peripheral in other females’ cluster. Two metrics – both eigenvector centrality and network strength – were affected by females’ reproductive status, which were highest in lactating females and lowest in cycling females. Although initially peripheral in the network, a young immigrant female subsequently became the center of a female cluster upon giving birth to a baby, one and a half years after immigrating. Short-term network analysis was useful to explain the variation of roles an individual plays in fission–fusion social organization.