Data from: Resource levels and prey state influence antipredator behavior and the strength of nonconsumptive predator effects

The risk of predation can drive trophic cascades by causing prey to engage
in antipredator behavior (e.g. reduced feeding), but these behaviors can
be energetically costly for prey. The effects of predation risk on prey
(nonconsumptive effects, NCEs) and emergent indirect effects on basal
resources should therefore depend on the ecological context (e.g. resource
abundance, prey state) in which prey manage growth/predation risk
tradeoffs. Despite an abundance of behavioral research and theory
examining state-dependent responses to risk, there is a lack of empirical
data on state-dependent NCEs and their impact on community-level
processes. We used a rocky intertidal food chain to test model predictions
for how resources levels and prey state (age/size) shape the magnitude of
NCEs. Risk cues from predatory crabs (Carcinus maenas) caused juvenile and
sub-adult snails (Nucella lapillus) to increase their use of refuge
habitats and decrease their growth and per capita foraging rates on
barnacles (Semibalanus balanoides). Increasing resource levels (high
barnacle density) and prey state (sub-adults) enhanced the strength of
NCEs. Our results support predictions that NCEs will be stronger in
resource-rich systems that enhance prey state and suggest that the
demographic composition of prey populations will influence the role of
NCEs in trophic cascades. Contrary to theory, however, we found that
resources and prey state had little to no effect on snails in the presence
of predation risk. Rather, increases in NCE strength arose because of the
strong positive effects of resources and prey state on prey foraging rates
in the absence of risk. Hence, a common approach to estimating NCE
strength – integrating measurements of prey traits with and without
predation risk into a single metric – may mask the underlying mechanisms
driving variation in the strength and relative importance of NCEs in
ecological communities.