The Impact of Cannibalism in the Prey on Predator–prey Systems

Cannibalism is ubiquitous in natural communities and has the potential to alter the functional relationship of predator–prey interactions. Although cannibalistic species are frequently subject to predation, the consequences of cannibalism in the prey for predator–prey interactions are poorly understood. Using a dragonfly larvae system, I provide the first experimental evidence that cannibalism in the prey creates behaviorand density-mediated indirect effects that result in nonlinear predator–prey interactions. As a consequence, cannibalism in the prey altered the functional relationship of the predator and its prey and reduced the impact of the predator on prey mortality by 47%. By parameterizing a mechanistic predation model, I show that the nonlethal interaction between cannibals and predators reduced cannibalism rates, which explained almost two times more of the observed mortality reduction than the consumption of cannibals. However, only a model that accounted for both behavioral interactions and the consumption of cannibals could predict ;100% of the observed mortality. Using the mechanistic model, I discuss the long-term effects of cannibalism on community dynamics and how they can differ from effects of simple density-dependent mortality. In general, these results demonstrate the importance of accounting for the trophic structure in cannibalistic populations and the resulting nonlinear interactions to predict predator–prey dynamics.