Authors: Gilby, Ian¹; Wrangham, Richard²

Source: Behavioral Ecology and Sociobiology, Volume 62, Number 11, September 2008 , pp. 1831-1842(12)

Publisher: Springer

Abstract:

Theory predicts that frequent dyadic association should promote cooperation through kin selection or social tolerance. Here we test the hypothesis that sex differences in the strength and stability of association preferences among free-ranging chimpanzees conform to sex differences in cooperative behavior. Using long-term data from the Kanyawara chimpanzee (Pan troglodytes schweinfurthii) community (Kibale National Park, Uganda), we calculated indices of intra-sexual dyadic association over a 10-year period. We found that (1) male-male dyads had significantly stronger association indices than female-female dyads, (2) the pattern of association preferences in both sexes changed little over the entire study period, and (3) when comparing periods with different alpha males, changes in association strength were more frequent among males. These results demonstrate that both the strength and stability of association patterns are important components of social relationships. Male chimpanzees, which are characterized by frequent cooperation, had association preferences that were both strong and stable, suggesting that forming long-term bonds is an important dominance strategy. However, the fact that male association patterns were sensitive to upheaval in the male dominance hierarchy suggests that males also take advantage of a changing social climate when choosing association partners. By contrast, the overall strength of female associations was relatively weak. Female association preferences were equally stable as males'; however, this reflected a dyad's tendency to be found in the same party rather than to associate closely within that party. Therefore, in this community, female association patterns appear to be more a consequence of individual ranging behavior rather than a correlate of cooperation.

Keywords: Association patterns; Social bonds; Cooperation; Sex differences; Alliance; Chimpanzee

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s00265-008-0612-6

Affiliations: 1: Department of Anthropology, Harvard University, Cambridge, MA, USA, Email: gilby@fas.harvard.edu 2: Department of Anthropology, Harvard University, Cambridge, MA, USA

Publication date: 2008-09-01

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