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Open Access Publications from the University of California

Why Do Females Live in Groups? : : Dominance, Grooming, and Experimental Testing of the Effects of Food Distribution on the Behavior of Commensal Bonnet Macaque (Macaca radiata) Females

  • Author(s): Chacko, Sandra Rose
  • et al.

According to the socioecological model of female sociality, females living in environments with clumped resources should exhibit strong, linear dominance hierarchies and females in the upper part of these hierarchies should receive less aggression, gain better access to food and receive more grooming than their lower ranked counterparts. This dissertation investigates the predictions of this model using females in a group of bonnet macaques (Macaca radiata). It also investigates the effects of three food distributions (0.25 m², 1 m², and 4 m²) on female aggression. This group had a moderately linear dominance hierarchy (0.63 Modified Landau Index). Although aggressive behavior increased during the feeding experiments, the overall strength of the dominance hierarchy was not significantly affected by an increase in food clumping. Higher ranked females did not receive more grooming than lower ranked females. Females engaged in both reciprocal (12.6%) and non-reciprocal bouts (87.4 %) of grooming and reciprocal grooming was time matched. Although most grooming was not immediately reciprocated, females did not appear to be trading grooming for another commodity, except, potentially, for coalitionary support. Grooming was more reciprocal across bouts than within bouts showing increased grooming reciprocity between partners over time. This long-term reciprocity suggests that bonnet macaque females reciprocate grooming over long spans of time effectively increasing the proportion of reciprocal grooming and decreasing the amount traded in a biological market. Females showed different types of competition as the experimental food distribution was decreased. High ranking females consumed more than low ranking females in each distribution. The greatest rank asymmetry in feeding was found in the highly clumped condition due to the ability of dominant individuals to monopolize the feeding platform. However, the number of aggressive acts among females was significantly lower in both clumped distributions than in the dispersed condition. Usurpation, as measured by agonistic acts, was higher in the dispersed condition, but competition through monopolization was greatest in the highly clumped condition as expected by the socioecological model. Competition in the highly clumped condition could not be measured by quantity of agonistic behavior illustrating the importance of distinguishing between monopolizability and usurpability when analyzing levels of competition

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