Predator foraging strategy influences prey population dynamics: arthropods predating a gregarious leaf beetle

We examined whether behavioural variation within an enemy complex attacking the willow leaf beetle, Phratora vulgatissima, influences the population dynamics of this gregarious prey. The most common enemies are three species of heteropteran arthropods: the two mirids Orthotylus marginalis and Closterotomus fulvomaculatus and the anthocorid Anthocoris nemorum. When attacking egg clusters on plants in the laboratory, the two mirids consumed a greater proportion of eggs within egg clusters than the anthocorid. The anthocorid visited and ate eggs from more egg clusters than both the mirids. The two foraging strategies have been characterized as ‘find and stay’ for the mirids and ‘run and eat’ for the anthocorid. By using a stochastic exponential growth model we showed that model prey experienced different temporal dynamics when exposed to predators that differ in the probabilities of finding prey aggregations and of consuming prey within aggregations. Model prey exposed to the find and stay type of predator was less likely to become established and to increase in abundance than model prey exposed to the run and eat type. In a field study, we found a correspondence between high abundance of find and stay mirids and low densities of leaf beetles. The results suggest that, even when average predation rate is constant, the foraging strategy of the predator can have population level consequences for the prey. The consumption of prey in dense patches seems to be important in the control of gregarious prey, especially in the early phase of prey population establishment.