Cultural differences in ant-dipping tool length between neighbouring chimpanzee communities at Kalinzu, Uganda

Kathelijne Koops, Caspar Schöning, Mina Isaji, Chie Hashimoto
2015
Cultural variation has been identified in a growing number of animal species ranging from primates to cetaceans. The principal method used to establish the presence of culture in wild populations is the method of exclusion. This method is problematic, since it cannot rule out the influence of genetics and ecology in geographically distant populations. A new approach to the study of culture compares neighbouring groups belonging to the same population. We applied this new approach by comparing
more » ... oach by comparing ant-dipping tool length between two neighbouring communities of chimpanzees (Pan troglodytes schweinfurthii) in the Kalinzu Forest, Uganda. Ant-dipping tool length varies across chimpanzee study sites in relation to army ant species (Dorylus spp.) and dipping location (nest vs. trail). We compared the availability of army ant species and dipping tool length between the two communities. M-group tools were significantly longer than S-group tools, despite identical army ant target species availabilities. Moreover, tool length in S-group was shorter than at all other sites where chimpanzees prey on epigaeic ants at nests. Considering the lack of ecological differences between the two communities, the tool length difference appears to be cultural. Our findings highlight how cultural knowledge can generate small-scale cultural diversification in neighbouring chimpanzee communities. Cultural variation has been identified in a growing number of animal species ranging from primates to cetaceans. The principal method used to establish the presence of culture in wild populations is the method of exclusion. This method is problematic, since it cannot rule out the influence of genetics and ecology in geographically distant populations. A new approach to the study of culture compares neighbouring groups belonging to the same population. We applied this new approach by comparing ant-dipping tool length between two neighbouring communities of chimpanzees (Pan troglodytes schweinfurthii) in the Kalinzu Forest, Uganda. Ant-dipping tool length varies across chimpanzee study sites in relation to army ant species (Dorylus spp.) and dipping location (nest vs. trail). We compared the availability of army ant species and dipping tool length between the two communities. M-group tools were significantly longer than S-group tools, despite identical army ant target species availabilities. Moreover, tool length in S-group was shorter than at all other sites where chimpanzees prey on epigaeic ants at nests. Considering the lack of ecological differences between the two communities, the tool length difference appears to be cultural. Our findings highlight how cultural knowledge can generate small-scale cultural diversification in neighbouring chimpanzee communities. Cultural phenomena have been identified in a growing number of animal species, ranging from primates to cetaceans 1-3 . The principal method used to establish culture in wild animal populations is the method of exclusion 1 . This method identifies geographically variable behaviour patterns across study sites and seeks to exclude those variants that can be attributed to genetic or ecological differences across sites. Problematically, this method cannot conclusively exclude the influence of genetic and environmental factors 4-6 , especially since comparisons generally involve geographically distant populations. Moreover, cultural processes interact with genetics 7 and ecology 8 , in terms of innate predispositions and ecological opportunities for tool use. Therefore, a novel approach to the study of animal material culture was developed aimed at minimizing the influence of genetics and ecology: comparing neighbouring groups belonging to the same population 9 . Studying genetically similar groups living under very similar environmental conditions allows for investigation of fine scale cultural differences, whilst keeping genetics constant. However, (subtle) ecological differences between neighbouring communities still need to be excluded. The argument for cultural differences between neighbouring groups is especially convincing when immigrating individuals can be observed to change their behaviour according to the customs of their new group 10 .
doi:10.5167/uzh-120266 fatcat:m332fv2ctfa65cmffecek52gq4