Revenge of the host: Cannibalism, ontogenetic niche shifts, and the evolution of life-history strategies in host-parasitoid systems

Question: How does cannibalism in the host alter the evolution of a parasitoid’s oviposition strategy? Can differences in cannibalism risk between parasitized vs. healthy hosts alter the stage foraging of parasitoids? Can host specific differences in cannibalistic behaviour explain why parasitoids vary in what host stages they attack?
Mathematical Methods: We analyzed evolutionary dynamics of a stage-structured host- parasitoid model with two complementary approaches: i) individual based numerical simulations of evolutionary dynamics, and ii) the theory of adaptive dynamics focusing on evolutionary stable strategies (ESS).
Assumptions: Cannibalism in the host is assumed to be stage structured, with larger stages consuming smaller stages. Consumption of parasitized hosts also results in killing of the parasitoid offspring. Vulnerability to cannibalism of parasitized vs. healthy hosts was allowed to. Parasitoids preference for attacking early vs. late host stages was the trait under selection and allowed to evolve.
Results: When cannibalism rates increased relative to the parasitoid' attack rates, the evolutionary stable strategy of the parasitoids shifts from attacking only early host stages to attacking only late host stages. This shift occurs at lower cannibalism rates when parasitized hosts are more susceptible to cannibalism than healthy hosts. Under equilibrium conditions, a small boundary area exists between these two regions where attacking only early or only late host stages are alternative stable ESSs. The threshold and alternative stage ESSs are the result of cannibalism which creates a positive feedback between the parasitoid’s oviposition rate and its 
own mortality. Intermediate strategies, where parasitoids evolve to attack both stages occurred only when host populations exhibit large population oscillations or when generalist parasitoids parasitoids that attack both stages had a foraging advantage.