Chimpanzees employ context-specific behavioral strategies within fission-fusion societies

Abstract

Fission-fusion social systems allow individuals to make flexible choices about where, with whom, and in what contexts to spend their time in response to competing social and ecological pressures. The ability for fission-fusion societies to support individual behavioral strategies that vary across contexts has been suggested, but the potential function of such context-specific social choices remains largely understudied. We adopted the concept of social niche construction to explore possible differences in social complexity at the individual and group level across feeding contexts. Specifically, we examined patterns of co-attendance across two common ecological contexts in wild Central African chimpanzees (Pan troglodytes troglodytes) in the Goualougo Triangle, Republic of Congo. From data compiled over 6 years, we used multidimensional social network analysis to study the patterns of co-attendance generated from 436 group scans at Ficus and 4527 visits to termite mounds. These two contexts were chosen, because they are both fixed spatial features across the landscape that serve as well-defined points to compare association patterns. We identified context-specific social niche construction in a fission-fusion chimpanzee society that produce different patterns of relationships and social complexity that are consistent in their expression over many years, and offer functional benefits. While enhancing our understanding of chimpanzee behavioral strategies, culture, and conservation, our investigation also indicates that the social niche construction framework aids in elucidating the evolutionary advantages of fission-fusion sociality by accounting for intra- and interindividual variability, cognition, and choice in newfound ways.

Keywords: Agency; Behavioral ecology; Behavioral flexibility; Multidimensional social network analyses; Niche construction.

Fig. 1

Predictive factors of (a) ecologically determined models of primate sociality compared to (b) individual variation in behavioral strategies and social niche construction within fission–fusion societies as positioned within the extended evolutionary framework

Fig. 2

A framework for the study of social niche construction. Social niche construction is scaffolded from (a) patterns of repeated associations by individuals (nodes, n) across many observations (Ob_x) into aggregate weighted social relationships (edges, e) within the emergent social network (e.g., ΣOb_x) for each network (N_y) across different contexts (S_x). Visually, individual and relationship characteristics can be represented as differences in size (e.g., network centrality or importance), color (e.g., node: individual age and sex; edge: relationships strength), or position (e.g., comparable circle layouts, integrated nodes in the center, isolate nodes in the periphery). In constructing their social niches, chimpanzees make flexible social choices that change the emergent patterns of relationships and structures of context-specific networks. The emergent social networks (S_xN_y) can then be represented as (b) layers of a multidimensional social network (e.g., S_xN_1,2,3…n) that allow for individual network position, patterns of relationships, social structure, and complexity to be analyzed in biologically meaningful units. Drawn with some reference to: Barrett et al. ; Hinde

Fig. 3

Expression of context-specific behavioral strategies in patterns of relationships in (a) termite gathering and (b) Ficus feeding contexts. Node placement for each individual is held consistent across both network graphs to illustrate changes in network strength centrality (node, circle size) and patterns of relationships (edge, line thickness). Each chimpanzee’s node size is scaled to network centrality and relationship strength is scaled to line thickness. Adult male nodes are gray, adult female nodes are colored, and immature nodes are white. Node color darkens with age. The structure of these networks across contexts is significantly different