The timing and causes of a unique chimpanzee community fission preceding Gombe's "Four‐Year War". Issue 3 (22nd March 2018)

• Record Type: Journal Article
• Authors: Feldblum, Joseph T.; Manfredi, Sofia; Gilby, Ian C.; Pusey, Anne E.
• Other Names: Tagg Nikki guestEditor.; Stewart Fiona A. guestEditor.
• Is Part Of: American journal of physical anthropology. Volume 166:Issue 3(2018)
• Page Start: 730
• Page End: 744
• Publication Date: 2018-03-22
• Subjects: community detection -- modularity -- social network analysis -- sociality -- territoriality; Physical anthropology -- Periodicals; Anthropology -- Periodicals; Anthropologie physique -- Périodiques; 599.9
• DOI: 10.1002/ajpa.23462
• Languages: English
• ISSNs: 0002-9483

Abstract

Abstract: Objectives: While permanent group fissions are documented in humans and other primate species, they are relatively rare in male philopatric primates. One of the few apparent cases occurred in 1973 in Gombe National Park, Tanzania, when a community of chimpanzees split into two separate groups, preceding the famous "Four‐Year War." We tested the hypothesis that the original group was a single cohesive community that experienced permanent fission, and investigated several potential catalysts. Materials and Methods: We calculated association, grooming, and ranging metrics from historical data and used community detection algorithms and matrix permutation tests to determine the timing, dynamics, and causes of changes in social network subgrouping structure. Results: We found that the two communities indeed split from one cohesive community, albeit one with incipient subgrouping. The degree of subgrouping in grooming and association networks increased sharply in 1971 and 1972, a period characterized by a dominance struggle between three high‐ranking males and unusually high male:female sex ratios. Finally, we found a relationship between post‐split community membership and previous association, grooming and ranging patterns in most periods of analysis, one that became more pronounced as the fission approached. Discussion: Our analysis suggests that the community began to split during a time of an unusually male‐biased sex ratio and a protracted dominance struggle, and that adult males remained with those with whom they had preferentially associated prior to the split. We discuss the costs and benefits of group membership in chimpanzees and contrast these results with group fissions in humans and other taxa.