Investigation on multi-level society in primates : intra-specific variation of proboscis monkeys

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I focused on environmental factors and clarified what "environmental conditions" were important in formation of multi-level society in proboscis monkeys. Environmental condition in this study means the vegetation patterns : mangrove and riverine forest. In this study, I clarified the ecology and social structureof proboscis monkeys inhabiting mangrove forest, and then evaluated the effects of environmental condition on their social structure in mangrove forest by comparing ecology and social structure of proboscis monkeys inhabiting riverine forest in my former study. The activity budget of proboscis monkeys in the mangrove forest was different from that in the riverine forest : proboscis monkeys in the mangrove forest spent more time for feeding and more time for fruit-eating compared to those in the riverine forest. In addition, the dietary diversity of proboscis monkeys in the mangrove forest was extremely lower than that in the riverine forest. Base on the data of the locations of proboscis monkey groups along the river, we clarified the significant effects of the environmental factors, especially food availability and predation pressure, on the degree of the cohesiveness among the groups in the riverine forests. However, the degree of the cohesiveness among the groups in the mangrove forest seemed to be influenced by strongly food availability.