DOI: 10.5061/dryad.15535rh1
title: Data from: Tritrophic interactions at a community level: effects of host-plant species quality on bird predation of caterpillars

description: 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.
description: Focal herbivore final
 mass 04-08This excel file contains
 data on the final mass of 7 focal lepidopteran species reared on the 8
 focal tree species of this study. These data were collected over 5 years
 (2004-2008) from field-sampled caterpillars that were subsequently reared
 in the laboratory on wild-harvested leaves from the same tree species from
 which they were sampled. These data were analyzed to quantify variation in
 host-plant quality among the 8 tree species.Bird exclusion on gen
 caterpillars 08-09This Excel file contains
 the data from a field experiment evaluating the effect of bird exclusion
 on the density of generalist caterpillar species. The experiment was
 conducted over a 3-week caterpillar sampling period period in each of 2
 years (2008, 2009). 2008 included 2 additional weeks of sampling (1 and 5)
 and these were used to obtain an independent estimate of caterpillar
 density per tree species. The spatial design included 6 complete blocks of
 8 tree species at each of 3 field sites in each year. Note that the block
 identity number at each site was not necessarily consistent from year,
 thus a unique block2 column is given to designate block identity. Density
 of generalist caterpillars was calculated for each branch or sapling,
 designated as bagged or unbagged to indicate the bird exclusion treatment.
 Density is calculated as the number of generalist caterpillars divided by
 the estimated total leaf area of the branch or sapling. Total leaf area
 was originally calculated in square cm, based on the the number of leaves
 multiplied by the average leaf area from a sample of approximately 10
 leaves from each branch.