Document: VAN-3-56-39

Resource partitioning by natural enemies in a willow-gall community: Does size matter?

VAN HEZEWIJK, B.H* and J.ROLAND

University of Alberta, Edmonton, Alberta, Canada T6G 2E9 1

Abstract:
In this study, the size of galls formed by the midge Rabdophaga strobiloides was investigated as a potential factor influencing patterns of larval mortality due to bird predation and two parasitoid species. Over three years, all galls within a 30-hectare area were collected, the diameters measured, and the fate of each midge larva determined by dissection. In each year there was significant between-willow variation in gall diameter suggesting a plant effect on gall size. Bird predation was most severe among the smallest galls. Torymus cecidomyiae and an unidentified pteromalid escaped subsequent bird predation by preferentially parasitizing larva in medium and large galls respectively. Midge larvae in the largest galls were relatively immune to both predation and parasitism thus producing a directional selection pressure towards large gall size. These findings support the predator protection hypothesis for gall development and point to variation in gall size as a factor facilitating both coexistence of parasitoids and population stability.

Keywords: galls, parasitoids, predation, resource partitioning

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This abstract is being presented at: 3:30 PM in session:
ANIMAL ECOLOGY