From inter-group conflict to inter-group cooperation: insights from social insects

Abstract

The conflict between social groups is widespread, often imposing significant costs across multiple groups. The social insects make an ideal system for investigating inter-group relationships, because their interaction types span the full harming–helping continuum, from aggressive conflict, to mutual tolerance, to cooperation between spatially separate groups. Here we review inter-group conflict in the social insects and the various means by which they reduce the costs of conflict, including individual or colony-level avoidance, ritualistic behaviours and even group fusion. At the opposite extreme of the harming–helping continuum, social insect groups may peacefully exchange resources and thus cooperate between groups in a manner rare outside human societies. We discuss the role of population viscosity in favouring inter-group cooperation. We present a model encompassing intra- and inter-group interactions, and local and long-distance dispersal. We show that in this multi-level population structure, the increased likelihood of cooperative partners being kin is balanced by increased kin competition, such that neither cooperation (helping) nor conflict (harming) is favoured. This model provides a baseline context in which other intra- and inter-group processes act, tipping the balance toward or away from conflict. We discuss future directions for research into the ecological factors shaping the evolution of inter-group interactions. This article is part of the theme issue ‘Intergroup conflict across taxa’.

Intergroup conflict: origins, dynamics and consequences across taxa

“…Individuals may be averse to such negative impacts and have prosocial concerns for out-group conspecifics (∂p i /∂α O < 0). This should reduce conflict participation and afford cooperative intergroup interactions as seen in, for instance, ant species [33], bonobos [18,100] and humans [101][102][103]. However, in the case of antisocial preferences for out-groups, individuals may initiate and escalate conflict out of 'spite' [104][105][106].…”

“…They also provide a mathematical model of multi-level population structures wherein the increased likelihood of cooperative partners being kin is balanced by increased kin competition, such that neither cooperation nor conflict is favoured. The model by Rodrigues et al [33] provides a useful baseline context in which other intra-and intergroup processes act, tipping the balance towards or away from conflict. One such factor may be changes in the groups' ecology, as suggested by various contributions to the current theme.…”

“…Rodrigues et al [ 33 ] make an important advance in this respect by modelling how social insects reduce the costs of conflict through individual or colony level avoidance, ritualistic behaviours and even group fusion. They also provide a mathematical model of multi-level population structures wherein the increased likelihood of cooperative partners being kin is balanced by increased kin competition, such that neither cooperation nor conflict is favoured.…”

“…It provides, for the first time, to our knowledge, a side-by-side treatment of intergroup conflict across taxa, detailing the origins and consequences of intergroup conflict. Each in their own way, the contributions provide insight on intergroup conflict for social insects [32,33], social fishes [40], group-living birds [26,27], non-primate mammals such as banded mongoose [24], lions and wolves [17], several monkey species [41][42][43], chimpanzees [18,44] and humans [45][46][47].…”

“…Intergroup conflict has also been observed in spider monkeys ( Ateles paniscus ) [ 19 ], hyaenas ( Crocuta crocuta ) [ 20 ], wolves ( Canis lupus ) [ 21 ], meerkats ( Suricata suricatta ) [ 22 ], banded mongooses ( Mungos mungo ) [ 23 , 24 ], in various group-living birds [ 25 – 27 ] and social fishes [ 28 ]. Social insects raid neighbouring colonies and kill enemy conspecifics [ 29 – 33 ].…”