A non-trophic interaction chain links predators in different spatial niches
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Non-trophic interactions, driven by one species changing the behavior but not density of another species, appear to be as pervasive as those involving consumption. However, ecologists have only begun to explore non-trophic interactions in species-rich communities. We investigated interactions within a community including two predator–prey linkages separated in space: ground-active predatory beetles and their fly egg prey on the ground, and lady beetles and their aphid prey in plant foliage. In field and greenhouse experiments we found that ground-active predators preyed heavily on fly eggs except when both aphids and lady beetles were present. The aphids drop from the foliage to escape foraging lady beetles, and once on the ground apparently triggered ground-active predators to switch from attacking fly eggs to attacking aphids. This suggests that the first non-trophic interaction in the foliage, mediated by aphid antipredator behavior, in turn initiated and accentuated a second non-trophic interaction on the ground, mediated by prey-switching behavior by ground predators. Our results demonstrate that successive non-trophic interactions can be propagated along chains of more than three species, and can serve to link species that are otherwise spatially isolated.
KeywordsPredator–prey interactions Antipredator behavior Herbivores Biodiversity Biological control
This work was supported by grants from the Organic Farming Research Foundation, the United States Department of Agriculture’s Western Sustainable Agriculture Research and Education program, and the Natural Resources Conservation Endowment at Washington State University. D. Finke, S. Steffan, G. Snyder, C. Straub and D. Gillespie provided valuable comments on preliminary drafts of the manuscript. This study complies with the current laws in the country in which it was performed.
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