Data from: Dietary specialization is conditionally associated with increased ant predation risk in a temperate forest caterpillar community

The enemy-free space hypothesis (EFSH) contends that generalist predators
select for dietary specialization in insect herbivores. At a community
level, the EFSH predicts that dietary specialization reduces predation
risk, and this pattern has been found in several studies addressing the
impact of individual predator taxa or guilds. However, predation at a
community level is also subject to combinatorial effects of multiple
predator types, raising the question of how so-called multiple predator
effects relate to dietary specialization in insect herbivores. Here we
test the EFSH with a field experiment quantifying ant predation risk to
insect herbivores (caterpillars) with and without the combined predation
effects of birds. Assessing a community of 20 caterpillar species, we use
model selection in a phylogenetic comparative framework to identify the
caterpillar traits that best predict the risk of ant predation. A
caterpillar species’ abundance, dietary specialization, and behavioral
defenses were important predictors of its ant predation risk. Abundant
caterpillar species had increased its risk of ant predation irrespective
of bird predation. Caterpillar species with broad diet breadth and
behavioral responsiveness to attack had reduced ant predation risk, but
these ant effects only occurred when birds also had access to the
caterpillar community. These findings suggest that ant predation of
caterpillar species is density- or frequency-dependent, that ants and
birds may impose countervailing selection on dietary specialization within
the same herbivore community, and that contingent effects of multiple
predators may generate behaviorally mediated life history trade-offs
associated with herbivore diet breadth.