Should I stay or should I go?: The role of dispersal and cannibalism in exploitation strategies of a predatory mite

In nature species can persist despite local extinctions, because of dispersal among local patches. In predator-prey interactions, early dispersal of some predators after some reproduction decreases the predation rate and as a consequence the offspring of the dispersed predator will have more food available, resulting in a longer interaction period between the predators and their prey in the local patch. Conversely, late predator dispersal drives the local prey population to extinction faster, resulting in a shorter interaction period between the predator and its prey. The early and late dispersal strategy, known as “Milker” and “Killer” respectively, are the extremes of a continuum of exploitation strategies. When the local prey population is depleted, an alternative way for the predators to temporarily obtain food is through cannibalism. Such intraspecific predation is common in a wide range of animal taxa and may significantly affect population dynamics. Even though cannibalism and dispersal are important phenomena for the persistence of populations, can be driven by overexploitation, and likely affect each other, they hardly ever have been studied together. In this thesis, therefore, the central question is how exploitation strategies of predators are shaped by both timing of dispersal and cannibalistic tendency. Using an acarine predator-prey system, I show that it is possible to select for Milkers and Killers that prolonged culturing can affect cannibalism of predatory mites, and I experimentally link cannibalism and dispersal to investigate how these phenomena affect each other. Finally, I discuss the use of Milkers and Killers as biological control agents