title: Herbivore diet breadth mediates the cascading effects of carnivores in food webs.
abstract: Predicting the impact of carnivores on plants has challenged community and food web ecologists for decades. At the same time, the role of predators in the evolution of herbivore dietary specialization has been an unresolved issue in evolutionary ecology. Here, we integrate these perspectives by testing the role of herbivore diet breadth as a predictor of top-down effects of avian predators on herbivores and plants in a forest food web. Using experimental bird exclosures to study a complex community of trees, caterpillars, and birds, we found a robust positive association between caterpillar diet breadth (phylodiversity of host plants used) and the strength of bird predation across 41 caterpillar and eight tree species. Dietary specialization was associated with increased enemy-free space for both camouflaged (n = 33) and warningly signaled (n = 8) caterpillar species. Furthermore, dietary specialization was associated with increased crypsis (camouflaged species only) and more stereotyped resting poses (camouflaged and warningly signaled species), but was unrelated to caterpillar body size. These dynamics in turn cascaded down to plants: a metaanalysis (n = 15 tree species) showed the beneficial effect of birds on trees (i.e., reduced leaf damage) decreased with the proportion of dietary specialist taxa composing a tree species' herbivore fauna. We conclude that herbivore diet breadth is a key functional trait underlying the trophic effects of carnivores on both herbivores and plants.
authors: Department of Biology, Wesleyan University, Middletown, CT 06459; msinger@wesleyan.edu.
authors: Michael S
authors: MS
authors: Singer
authors: Department of Biology, Wesleyan University, Middletown, CT 06459;
authors: Isaac H
authors: IH
authors: Lichter-Marck
authors: Department of Biology, Wesleyan University, Middletown, CT 06459;Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom;
authors: Timothy E
authors: TE
authors: Farkas
authors: Department of Computer Science, Vassar College, Poughkeepsie, NY 12604;
authors: Eric
authors: E
authors: Aaron
authors: Department of Biology, University of New Mexico, Albuquerque, NM 87131; and.
authors: Kenneth D
authors: KD
authors: Whitney
authors: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697.
authors: Kailen A
authors: KA
authors: Mooney
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001717:Birds / Q000502:physiology*; D060435:Carnivory / Q000502:physiology*; D003237:Connecticut; D004032:Diet; D020387:Food Chain; D060434:Herbivory / Q000502:physiology*; D006801:Humans; D007814:Larva / Q000502:physiology; D008954:Models, Biological; D009036:Moths / Q000502:physiology*; D010802:Phylogeny; D013997:Time Factors; D014197:Trees / Q000235:genetics
keywords: ecological specialization; host specificity; plant–herbivore interactions; tritrophic interactions; trophic cascade