Conditions for kin selection to bring cooperation and improve population growth: A response to Iritani

Abstract

To clarify how intraspecific competition over fertilization affects population growth rates and community dynamics in plants, Kobayashi (Journal of Ecology, 2019) proposed analytical and simulation models based on the game theory. Within this framework, it is suggested that the negative density-dependent effect arising from sexual selection is an important force for sustaining biodiversity. Relaxing certain assumptions made in the analytical model, Iritani (Journal of Ecology, 2019) successfully incorporated the effect of kin selection in the model. This change makes a significant contribution towards improving the generality of the model. Here, I clarify the contribution of Iritani (Journal of Ecology, 2019) and explain the condition under which kin selection promotes the evolution of cooperation (facilitativeness). Kin selection has the potential to promote the evolution of cooperation under certain conditions. However, it is difficult to maintain cooperative traits in high-density environments where individuals must interact with many other conspecifics. Thus, even after the model was extended by Iritani, it cannot be used to state that the negative density-dependent effect arising from intraspecific competition over fertilization does not exist, but it has successfully revealed that the situation is more complex in nature. Synthesis. Kin selection exists wherever intraspecific interactions between individuals occur, but does not necessarily lead to the evolution of cooperation. More detailed theoretical and empirical studies are needed to determine whether sexual selection generally produces negative density dependence, even when kin selection is taken into account.