Analysing the effects of group size and food competition on Japanese macaque social relationships

Bonaventura Majolo, Raffaella Ventura, Nicola F. Koyama, Scott M. Hardie, Bethan M. Jones, Leslie A. Knapp, Gabriele Schino

Research output: Contribution to journalArticlepeer-review

25 Citations (Scopus)


Socio-ecological models predict group size to be one major factor affecting the level of food competition. The aims of this study were to analyse how grooming distribution and reconciliation were affected by differences in group size and food competition in a habitat where predation risk is absent. Data were collected on two groups of different size of wild Japanese macaques (Macaca fuscata yakui), living on Yakushima Island, Japan. The large group faced a greater level of intra-group scramble and a lower level of inter-group food competition. However, intra-group food competition appeared to be greater in the small group as evidenced by the stronger rank-related effects on diet composition in the small group. Grooming and reconciliation were more matrilineally kin-biased and more directed toward close-ranking monkeys in the small group than in the large group. Reconciliation was more frequent in the small group, but monkeys in the large group spent more time grooming and had a greater number of grooming partners. These results indicate that social relationships within the two groups were the result of the combination of group size differences and of the balance between the benefits and costs of a lower/greater level of inter- and intra-group food competition.
Original languageEnglish
Pages (from-to)113-137
Number of pages25
Issue number1
Publication statusPublished - Jan 2009


  • Aggression
  • Grooming
  • Kinship
  • Rank
  • Reconciliation


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