Data from: Tritrophic interactions at a community level: effects of host-plant species quality on bird predation of caterpillars

Effects of plant traits on herbivore-carnivore interactions are well documented in component communities, but are not well understood at the level of large, complex communities. We report on a two-year field experiment testing mechanisms by which variation in food quality among eight temperate forest tree species alters avian suppression of an assemblage of dietary generalist caterpillars. Plant quality and bird effects varied dramatically among tree species; high quality plants yielded herbivores of 50% greater mass than those on low quality plants, and bird effects ranged from near zero to 97% reductions in caterpillar density. We also find evidence for two mechanisms linking host-plant quality to bird effects. Statistically controlling for caterpillar density, birds had relatively strong effects on the herbivores of low quality plants, as predicted by the slow-growth/high-mortality hypothesis. At the same time, caterpillar density increased with plant quality, and bird effects were density-dependent. Consequently, the net effect of birds was strongest on the herbivores of high quality plants, a dynamic we call the high-performance/high-mortality hypothesis. Host-plant quality thus changes highly generalized herbivore-carnivore interactions by two complementary but opposing mechanisms. These results highlight the inter-relatedness of plant-herbivore and herbivore-carnivore interactions, and thus the importance of a tritrophic perspective