Trait-mediated indirect effects driven by predator behavior.
Prasad, Renee1, Snyder, William, 1 Washington State University, Pullman, WA
ABSTRACT- Trait-mediated indirect effects become more prevalent as species richness in food webs increases. Most examples of trait-mediated indirect effects are due to changes in prey behavior. However, in recent studies of two predator-two prey food webs we have observed indirect effects driven by predator behavior. Our focal predator and prey, for these studies, were a guild of small, <1 cm in length, ground beetles and eggs of herbivorous flies. In two sets of field and greenhouse experiments we measured the impact of an additional prey, aphids, and an additional predator, either a larger ground beetle or ladybirds, on egg predation. In the first experiment our additional predator was the ground beetle, Pterostichus melanarius, an intraguild predator of the small beetles. Egg predation by small beetles was reduced in treatments with either aphids or intraguild predator. However, in the treatment combining aphids and intraguild predator, egg predation was similar to the control treatment with neither disruptive force present. Subsequent experiments demonstrated increased activity and incidental predation of fly eggs by P. melanarius in the presence of aphids. In this case the increase in egg predation, in the combined treatment, was driven by changes in P. melanarius behavior. In the second experiment our additional predator was an assemblage of three ladybirds, which forage in the foliage and do not eat fly eggs. We found the lowest rates of egg predation in the combined aphid and ladybird treatment. Two follow-up experiments demonstrated that, first, aphids are more likely to leave foliage if ladybirds are present and, second, small beetles eat fewer fly eggs when both aphids and ladybirds present. The reduction in egg predation, in the second experiment, was driven by aphid anti-predator behavior and prey switching by small beetles.
Key words: indirect effects, trait-mediated, Pterostichus melanarius>
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