Coevolution and Coexistece Mechanism of African Great Apes

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This study aims to clarify the coexistence mechanism of gorillas and chimpanzees inhabiting tropical montane and lowland (coast and inland) forests sympatrically, by analyzing data on dietary composition, foraging patterns, group formation and interspecies relationships. Coevolution process of such apes with other fauna and flora of tropical forests is also analyzed and considered. This year field research was conducted in Gabon. Data on the fruit phenology were collected in the coastal forest of Petit Loango Reserve by the transect census. We found the positive correlation between chimpanzee ranging patterns and the fruit availability in the coastal forest. The different seasonality in fruit scarcity between the coastal and inland forests may influence movements and grouping patterns of chimpanzees. The lack of terrestrial herbaceous vegetation also stimulate chimpanzees to disperse in wide range. BASABOSE, K.was invited to Japan, and we analyzed data collected in the Kahuzi-Biega National Park, D.R.Congo with him.The results show a positive correlation between fruit availability and the length of day range for gorillas, while it was negative for chimpanzees. The distribution of nests also shows chimpanzee's avoidance to nest in the same food trees as gorillas. These tendencies suggest that the shortage of high quality foods may promote niche separation between gorillas and chimpanzees. We are still analysing data on differences in socioccological features between sympatric gorillas and chimpanzees and will present new perspectives on their speciation and coevolution in the near future.