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.植物性状(plant traits)对植食者-肉食者相互作用(herbivore-carnivore interactions)的影响，在组分群落(component communities)中已有充分研究，但在大型复杂群落(large, complex communities)层面仍未得到充分阐释。本研究依托一项为期两年的野外实验，探究8种温带林木的食物质量差异如何通过相关机制改变鸟类对广食性毛虫类群的抑制效应。不同树种的植物质量与鸟类调控效应差异显著：高质量植物上的植食者体重较低质量植物上的个体高出50%，而鸟类的调控效应范围从接近零至毛虫密度降低97%不等。本研究同时发现了两种连接寄主植物(host-plant)质量与鸟类调控效应的机制证据。通过统计控制毛虫密度后，鸟类对低质量寄主植物上的植食者具有较强的调控效应，这与慢生长-高死亡假说(slow-growth/high-mortality hypothesis)的预测一致。与此同时，毛虫密度随植物质量提升而升高，且鸟类的调控效应具有密度依赖性(density-dependent)。因此，鸟类对高质量寄主植物上的植食者的净调控效应最强，这一动态过程我们称之为高性能-高死亡假说(high-performance/high-mortality hypothesis)。由此，寄主植物质量通过两种互补但作用相反的机制，改变了高度泛化的植食者-肉食者相互作用。本研究结果凸显了植物-植食者与植食者-肉食者相互作用的关联性，进而彰显了三营养级视角(tritrophic perspective)的重要性。