Socioecological Studies on Coexistence and Coevolution of the Great Apes and Humans

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Our project aims to clarify the coexistence and coevolution of the African great apes (gorillas and chimpanzees) and humans (hunter-gatherers), through comparison of their socioecological features under the same environmental conditions of tropical forests. Since 2000 we have monitored seasonal changes in temperature and rainfall in two study sites (Moukalaba National Park, Gabon and Kahuzi-Biega National Park, DRC), both of which are regarded as refuge forests during the past glacial periods. Phonological data on fruits eaten by gorillas and chimpanzees have been collected twice per month, and groups of gorillas and chimpanzees have been habituated to, collect behavioral data. Data on subsistence and movement patterns of Babongo hunter-gatherers were also collected by direct observation and interviews. This year we have analyzed the data collected until now, and have gotten important results showing distinct differences in food choice, foraging behavior and social interactions with foods among the great apes and humans. Especially, during the period of fruit scarcity, niche differentiation becomes significant: Gorillas tend to decrease day journey length and shift their diet from fruit to vegetative food ; and chimpanzees tend to increase day range seeking fruit persistently. Social features of both apes support their foraging strategies. More dispersal foraging with food sharing and fluid social system of hunter-gatherers ma have developed to avoid competition with the sympatric apes in the past. Future analysis and more elaborate researches on diet and subsistence ecology of apes and humans may clarify their coevolution in the same habitat of tropical forests.