Chimpanzee grouping patterns and food availability in Mahale Mountains National Park,Tanzania |
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Authors: | Noriko Itoh Toshisada Nishida |
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Institution: | (1) Cultural, Regional and Historic Studies on the Environment (Cultural Anthropology), Department of Studies in Human Coexistence, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan;(2) Japan Monkey Centre, Inuyama, Japan |
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Abstract: | The aim of this study was to test for a correlation between party size and food (fruit) availability among the M group chimpanzees
(Pan troglodytes) in the Mahale Mountains, Tanzania. Chimpanzee unit groups (or communities) show fission–fusion grouping patterns and form
temporal parties. Fruit availability is assumed to be one of the important limiting factors in relation to the size of these
parties. Different methods have been proposed to measure party size, but they all appear to focus mainly on two aspects of
grouping phenomena. In “face-to-face parties”, party size is measured by scan sampling, whereas in “nomadic parties”, all
members observed during a specific time period are counted. The mean monthly group size resulting from these two measures
was compared with fruit availability, i.e. fruiting plant density and mean potential patch size. Nomadic party size was correlated
with both values. Thus, party formation at this level was considered to be sensitive to overall fruit availability in the
habitat. On the other hand, face-to-face party size remained stable and showed weak or no correlations with density and potential
patch size. Although large patches are available during the peak fruiting season, Mahale chimpanzees depend on the liana species
Saba comorensis, which, when fruiting, encourages individuals to spread out to eat. Thus, the lack of correlation between face-to-face-party
size and fruit availability was attributed to the influence of physical limitations countervailing the fluctuation in fruit
availability. Maximum face-to-face party size relative to unit-group size, regarded as the cohesiveness of a unit group, was
compared among sites. The values differed largely: Mahale groups M and K, Bossou, and, in some years, Budongo, showed high
cohesiveness, while others remained low. Thus, the distribution of the most important food during the fruiting season in each
study site may be a crucial factor in the grouping phenomena of chimpanzees. |
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Keywords: | Chimpanzee Party Fruit availability Physical limitation Unit-group cohesiveness |
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