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 behavior- and 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.