Abstract
AbstractConflicts between stable social groups (“intergroup conflicts”) can be damaging and exert a strong influence on within‐group social behaviour. The success of groups during intergroup conflict may depend on the ability of individual group members to converge upon collective defence behaviour, such as approaching or attacking. In principle, collective defence can be achieved via a united front, in which each individual responds in the same way to an intergroup threat. We tested the impact of simulated intergroup conflicts on collective defence and individual behaviour in banded mongooses (Mungos mungo), a cooperatively breeding mammal in which intergroup conflict is particularly common and costly. We presented focal groups with scent markings, call playbacks and caged live animals from rival groups and compared their responses to these stimuli with their responses to own‐group control stimuli. A greater proportion of group members approached the stimulus and acted defensively in response to rival stimuli as compared to controls, consistent with a unified collective defence response. However, counter to our expectation, groups exhibited lower behavioural homogeneity when presented with rival stimuli as compared to controls. A closer examination of the behaviours competitors used revealed that lower homogeneity was driven by a greater use, and diversity, of defensive behaviours relevant to repelling simulated rivals. Finally, group size affected responses: as group size increased, the proportion of members approaching the stimulus and behavioural homogeneity decreased. Our results lend support to the hypothesis that intergroup conflict leads to coordinated collective defence behaviour during the immediate threat of an intergroup conflict. However, collective defence need not mean that all group members execute the same behaviours.
Highlights
Intergroup conflict, in which stable social groups of two or more individuals compete over access to limited resources like territory or food, is widespread (Green et al, 2020)
Increases in collective defence have been shown in response to simulated intergroup conflict in other taxa: lions (Panthera leo) increase recruitment calling in the face of rival call playback (McComb et al, 1994); cichlid fish (Neolamprologus pulcher) are more aggressive towards simulated rivals than controls (Bruintjes et al, 2016); and green woodhoopoes (Phoeniculus purpureus) more quickly approach unfamiliar call playback as compared to familiar playback (Radford, 2005)
We examined collective defence and behavioural homogeneity in banded mongooses exposed to intergroup conflict using simulated intrusion experiments
Summary
Intergroup conflict, in which stable social groups of two or more individuals compete over access to limited resources like territory or food, is widespread (Green et al, 2020). Under the selective pressure of intergroup conflict, individual and group social behaviour might be expected to evolve in a way that maximizes the (inclusive) fitness benefits and minimizes the costs of conflict. Collective defence behaviours are thought to help groups defend resources like a territory, either through directly engaging with rivals (Grinnell et al, 1995; McComb et al, 1994) or by signalling the group's fighting ability to rivals (Christensen et al, 2016), among other possible functions
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