Eco-evolutionary dynamics of sexually selected infanticide facilitate species coexistence

Understanding how biodiversity is maintained is a central question in community ecology. Modern coexistence theory predicts that stable coexistence occurs when stabilizing mechanisms are strong enough to overcome competitive ability differences. Recent studies suggest that adaptations to conspecific interactions may provide such a stabilizing mechanism when their demographic costs increase with conspecific density. We examined whether sexually selected male infanticide can promote species coexistence by generating density-dependent demographic costs. We developed a stage-structured eco-evolutionary model of two species competing for a shared resource, with infanticidal and non-infanticidal male strategies, and confirmed that the infanticidal strategy was maintained depending on the parameters related to intraspecific competition: the infanticide rate and its fecundity cost. In a competitively superior species, the infanticidal strategy, which imposed demographic costs that increase with conspecific density, was maintained at a sufficiently high frequency, thereby strengthening self-limitation and reducing the species' equilibrium density. This reduction increased the invasion growth rate of the inferior competitor and expanded the parameter region permitting stable coexistence. These results show that sexually selected infanticide favored at the individual level can generate population-level self-regulation and alter community-level coexistence.