The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


Predicting subgroup size in a lemur with high fission-fusion dynamics

SHEILA M. HOLMES1, ADAM D. GORDON2, EDWARD E. LOUIS3 and STEIG E. JOHNSON1.

1Anthropology, University of Calgary, 2Anthropology, University at Albany, 3Grewcock Center for Conservation and Research, Henry Doorly Zoo

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A growing number of primate species have been noted to live in social groups with low cohesion (i.e., high fission-fusion dynamics), yet the proximate causes for subgrouping dynamics remain obscure. The most frequently cited explanations for group fissions are ecological; species that feed on high-quality patchily distributed resources form small foraging parties to avoid intragroup competition. Here we investigate potential environmental influences on subgroup size in two social groups of black-and-white ruffed lemurs (Varecia variegata) at Kianjavato-Vatovavy, Madagascar. Focal individuals (N=17) were followed for 2-hour periods (N=192) during Jun-Aug 2012. Group membership, focal individual behavior, tree diameter, and phenology were recorded using instantaneous sampling at the start of each follow, and whenever group size changed. Climatic variables were collected on a daily basis. We conducted a multiple regression model to determine which independent variables best predicted subgroup size in this species. The model that explained the greatest percent of the variance in subgroup size (R-squared=0.0947, p=0.006) included tree diameter, behavior, maximum daily temperature, daily precipitation, phenology, and site variables. Tree diameter and behavior were the only variables accounting for a significant proportion of the variation in subgroup size (p<0.05). These results suggest that ecological factors, including food availability and climate, may influence fission-fusion dynamics in this species. Additionally, behaviors (e.g. social interactions) vary in tandem with subgroup size. Further research should address how seasonal changes in climate and food availability influence subgroup size in this species.

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