1Department of Evolutionary Anthropology, Duke University, 2School of Human Evolution and Social Change, Arizona State University
April 12, 2014 2:45, Hyatt Stephen AB
In 1972, the main chimpanzee study group at Gombe split into two separate communities, Kasekela and Kahama. Over four years, the Kasekela community killed the adult males and one female of the Kahama community. Here we use social network analysis to explore this unique community fission by examining social associations measured by arrival together at the provisioning site. First, we test the hypothesis that the pre-split community was actually two communities brought together by provisioning. Using the Girvan-Newman algorithm, we found no evidence of subgrouping until November 1971, suggesting that the two communities split from one original cohesive community. Next, we explored proximate causes of the fission. Candidate catalysts were changes in the 1) provisioning regimen, 2) male dominance hierarchy, 3) demography. The timing of the fission most closely coincided with a dominance struggle between three high-ranking males that occurred in late 1971-2. Finally, we found that post-split community membership significantly predicted pre-split association patterns in each year from 1968-1972 (MR-QAP Linear Reg: all p <0.03). Thus, initial analysis suggests that the community abruptly split during the course of a dominance struggle, and that individuals remained with others with whom they had preferentially associated in the previous four years. We will use a generalized Louvain community detection code to precisely determine the date of subgroup formation, and the CONCOR algorithm to identify the relationship between pre-fission social roles and post-fission community membership. This project provides vital clues to the importance of individuals in maintaining group cohesion in chimpanzee populations.
Data collection was supported by the Jane Goodall Institute; construction of the long-term database was supported by grants from the NSF (DBS-9021946, SBR-9319909, BCS-0452315, IOS-LTREB-1052693).