Predation and kin-structured populations: an empirical perspective on the evolution of cooperation

In animal societies, kin selection is a critical evolutionary process, with cooperation evolving principally among relatives living in kin-structured populations. Theoretical and empirical studies have largely focused on population viscosity--the timing or distance of dispersal--as the key factor generating kin structure. This is despite extensive theoretical broadening of the factors and processes influencing effective population size, variance in reproduction, and relatedness. Here, we explore predation mortality as a specific driver of population-level reproductive skew and variance in fecundity to show how a common and perhaps underappreciated event in organism life history can give rise to patterns of relatedness. We develop our case study around an empirically derived model where elevated relatedness arises from predation that alters the timing and nature of offspring mortality, essentially driving variance in fecundity. This leads to dramatic changes in the emergent kin structure of the surviving breeding population. Our in-silico experiments recover the theoretical predictions that when predation acts on clusters of individuals and effectively removes whole family groups (i.e., broods), rather than individuals, from the pool of potential recruits, there is a greater kin structure in the emergent adult population. We conclude that empirical attempts to understand the factors promoting kin-structured populations and the evolution of sociality should now match theoretical efforts to be more inclusive of ecological process generating life history and demographic variability. Copyright 2011, Oxford University Press.