Predator foraging strategy influences prey population dynamics: arthropods predating a gregarious leaf beetle PETER DALIN * , OSKAR KINDVALL † & CHRISTER BJO ¨ RKMAN * *Department of Entomology and ySwedish Species Information Centre, Swedish University of Agricultural Sciences (Received 19 October 2005; initial acceptance 8 December 2005; final acceptance 14 February 2006; published online 22 September 2006; MS. number: 8709) 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 en- emies 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 lab- oratory, 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 sto- chastic 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 be- come 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 pop- ulation establishment. Ó 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The importance of behaviour in predatoreprey dynamics has been emphasized for decades (Holling 1961; Van Drie- sche & Bellows 1996; Venzon et al. 2000). Prey is often patchily distributed in space, implying that many preda- tors need to search actively to find food. Accordingly, high search efficiency is considered to be an important be- havioural attribute of predators to control prey popula- tions (Van Driesche & Bellows 1996). The predator’s ability to stay and consume prey in dense prey patches might also be important, especially in systems where the prey occurs in dense aggregations (Kareiva & Odell 1987). The foraging behaviour of a predator, such as its search intensity, is often related to the type of food eaten (Huey & Pianka 1981). For example, broad diet predators (generalists) are considered to search less frequently for a given prey type than specialists because generalists can feed on a wide range of other food items that are encoun- tered (Westoby 1978; Coll & Guershon 2002). Besides en- counter frequencies, foraging behaviour is also influenced by factors such as predation risk, prey behaviour and nutritional requirements (Sih 1993; Biesinger & Haefner 2005). This often results in a large variation in foraging strategies within predator complexes where species or age classes of predators differ in, for example, the area of search and how they respond to dense patches (Wiskerke & Vet 1994; McCauley et al. 1996; Cisneros & Rosenheim 1998). Few researchers, however, have investigated whether such behavioural variations within enemy com- plexes influence the population dynamics of the prey. Primary consumers, such as herbivorous insects, are often attacked by a diverse complex of natural enemies (Polis 1991). The insect order Heteroptera (true bugs) con- tains a large number of generalist predator species with Correspondence and present address: P. Dalin, Marine Science Institute, University of California at Santa Barbara, CA 93106-6150, U.S.A. (email: dalin@msi.ucsb.edu). O. Kindvall is at the Swedish Species In- formation Centre, Swedish University of Agricultural Sciences, P.O. Box 7007, SE-750 07 Uppsala, Sweden. C. Bjo ¨rkman is at the Department of Entomology, Swedish University of Agricultural Sciences, P.O. Box 7044, SE-750 07 Uppsala, Sweden. 1025 0003e 3472/06/$30.00/0 Ó 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2006, 72, 1025e1034 doi:10.1016/j.anbehav.2006.02.017