Optimal reproductive phenology under size-dependent cannibalism

Cannibalism is a size-mediated priority effect, and introduces a tradeoff between breeding at the optimal time in the season and increased predation risk from offspring born earlier. This game-theoretic situation among parents may drive adaptive reproductive phenology. However, it is not straightforward to quantify how cannibalism affects egg fitness or to distinguish emergent breeding phenology from alternative adaptive drivers. Here, we employ an age-structured game-theoretic mathematical model to find evolutionary stable breeding phenologies. We predict how size-dependent cannibalism on eggs, larvae, or both change emergent breeding phenology, and find breeding that occurs earlier than the optimal match to environmental conditions. We show that emergent breeding phenology patterns at the level of the population are sensitive to the ontogeny of cannibalism. This suggests that the nature of cannibalism among early life stages is a potential driver of the diversity of reproductive phenologies seen across taxa.