Social network changes during space restriction in zoo chimpanzees

Abstract

Several studies across anthropoid species have demonstrated how primates respond to the increased risk of conflict during space restriction with various behavioral strategies. Three strategies have been proposed relating to tension regulation, conflict avoidance, and inhibition. Prior research supporting these strategies has focused on individual- and dyadic-level analyses, yet group-living animals live within a web of inter-individual connections. Here, for the first time, we used a network approach to investigate how social structure and individuals' connectedness change during space restriction. We collected grooming and aggression data during a 6-week control period and a 5-week period of space restriction in a large group of zoo chimpanzees. We compared network density and individual centrality measures (degree, eigenvector, and betweenness centrality) between these two periods using permutation tests. The density of the unidirectional grooming network was significantly lower during space restriction, indicating fewer grooming partners and a less cohesive network. This was mainly due to a reduction in females' grooming partners (degree) and an increase in females' betweenness centrality. We found no differences in the mutual grooming or aggression networks. Our findings are consistent with a conflict avoidance strategy and complement previous findings from the same dataset based on individual behavioral rates that supported a selective inhibition strategy. The results highlight the dynamic nature of social structure and its inherent flexibility to respond effectively to short-term changes in the environment.

Social Network Analysis of a Chimpanzee (Pan troglodytes) Group in Captivity Following the Integration of a New Adult Member

“…Interestingly, male agonistic behavior significantly increased during the third period of the study. Although space restriction due to bad weather was more common during the last period of the study, this is unlikely to be a determining factor in the increase of male agonistic behavior, as studies found no differences in mutual grooming and agonistic behavior in the same group during periods of space restriction (Koyama and Aureli 2019). Instead, this increase in male agonistic behavior is likely to indicate intensification of the conflict between the dominant male and the two young males that were beginning to challenge his dominance.…”

“…We also calculated betweenness centrality (the number of times the focal is in the shortest path connecting two other nodes) to determine which individuals are important in keeping the group connected (Rose and Croft 2015). Degree is useful to measure which individuals have strong direct connections in the network, while betweenness allows the identification of individuals that play an important role in connecting isolated members of the group (Kanngiesser et al 2011;Koyama and Aureli 2019). Both measures work well with weighted data in both directed and undirected networks (Borgatti et al 2013).…”

“…Group size has been found to relate to differences in personalities (Murray 1998), with those living in larger groups displaying higher levels of traits associated with positive characteristics-including sociability, gentleness, and intelligence-in contrast to those housed in pairs or trios. Captive groups of chimpanzees are flexible and show stable structures during changes of environment (Koyama and Aureli 2019) and partial stability during changes in dominance (Koyama et al 2017). The effects of rearing history in adult socialization are well studied in chimpanzees.…”

Early life experience and alterations of group composition shape the social grooming networks of former pet and entertainment chimpanzees (Pan troglodytes)

“…Most studies on chimpanzees define the social networks by scoring dyadic grooming interactions [44,76,90], or by recording information of dyadic spatial association [43]. Due to the database available for this study and based on the fact that grooming is an important social behaviour in chimpanzees [52] we created matrices of directed dyadic grooming interactions obtained for each time period and group composition.…”

Editorial: Social networks analyses in primates, a multilevel perspective

“…Papers in this issue include Xia et al's (2019) relationships affect male immigration and vice versa in Japanese macaques (Macaca fuscata). Finally, social network analysis is also a useful tool for applied ethology, as it can be used to assess how captive conditions and unnatural group compositions might influence the social relationships of group members, as reported by Koyama and Aureli (2018), and by Rodrigues and Boeving (2018) in chimpanzees and bonobos (Pan paniscus). Network studies are not just a matter of topologies or dynamics but also of influence.…”