On the importance of defendable resources for social evolution : Applying new techniques to a long-standing question

Abstract

Cooperative behaviour often co-occurs with the defence of key resources, typically in the form of a breeding site or territory communally exploited by a group of cooperating individuals. Nevertheless, not all animals that defend resources evolve advanced forms of cooperation and sociality—many non-cooperative species occupy resources that do not differ in obvious ways from those inhabited by cooperative species. A key question is thus whether cooperation confers more subtle benefits, for example by allowing access to higher quality resources through competitive exclusion of less social rivals. In other words, it is not clear whether defendable resources are a necessary precondition for sociality or whether they also contribute to the maintenance and enhancement of cooperative societies. Here, we highlight how advances in imaging technology, machine-learning, and environmental reconstruction enable the collection of behavioural and ecological data in unparalleled quantity and quality to address this question. These new techniques are especially suited to compare small-scale differences in resource use between cooperative and non-cooperative species that share a general habitat and have similar ecologies. The lamprologine cichlids of Lake Tanganyika are a prominent example of such a system and Michael Taborsky's pioneering work on this group has done much to promote these fishes as models of social evolution. We show that habitat features indicative of increased resource quality, namely increased stone cover, are indeed associated with the distribution of cooperative cichlids—at least where these resources are relatively scarce. We thus support a point Michael Taborsky made in 1981: the evolution of cooperative behaviour among cichlids is tied to their close association with a crucial resource, the substrate in which they hide and breed. In the future, the techniques we introduce here will allow to also investigate whether this substrate is indeed more than just the necessary precondition for cooperation among fishes; in addition, they will likely find application in a wide range of research fields interested in the interplay between biotic and abiotic environmental factors.