Ecological succession, patch age, and the evolution of social behaviour and terminal investment.

16 July 2018

Rodrigues, Antonio

Recent years have witnessed a growing interest in understanding the evolution of social behaviour in heterogeneous spatially structured populations. These studies, however, have neglected the impact of extinction-colonisation dynamics and ecological succession on the dynamical expression of social behaviour over time. Here, we present a kin-selection model in which patches are structured into age-classes. We show that ecological succession and patch age lead to highly plastic social phenotypes that vary dramatically as societies age since their initial establishment until their ultimate collapse. We find that the mode of colonisation following dispersal strongly influences the patch age-dependent trajectories of social phenotypes. When patches are colonised by a random collection of immigrants, aggression is favoured during the build-up of a society, but it slowly subsides until it eventually gives place to cooperation throughout the later stages of a society’s lifespan. When newly established societies are formed by collectives of close relatives, cooperation is favoured during the build-up of the society as well as when the society nears its eventual collapse. At intermediate societal ages, the genetic structure of the society is sufficiently resilient to the influx of immigrants such that cooperation remains relatively high. Moreover, we report a novel form of social terminal investment, whereby cooperative effort rises when patches approach their collapse. When dispersal is allowed to co-evolve with cooperation, we observe a sudden rise in dispersal phenotypes before a patch’s collapse, and the surprising result that clonal colonisation does not yield significantly higher levels of cooperation than the individual mode of colonisation. More generally, our results show that ecological succession strongly determines the dynamics of kin selection after colonisation, and therefore we expect that these findings will be valuable for understanding behavioural syndromes during range expansion or biological invasions.