Introduction
Presence of predators often causes prey to modify traits, including
behavior, physiology, morphology, and life history, in order to reduce
predation risk (Lima and Dill 1990, Lima 1998a, Agrawal 2001). Such
risk-induced trait responses and their ensuing consequences, termed risk
effects (also nonlethal effects and fear effects; terminology reviewed
in Peacor et al. 2020), have received much attention. Whereas
risk-induced trait response in prey generally benefit prey by reducing
predation risk, they also may have associated costs to fitness
components in the prey. These consequences of the trait response on prey
are termed non-consumptive effects (NCEs), and include reduced growth or
condition, reduced fecundity, or increased mortality from other
predators, and consequent effects on prey population growth rate and
prey abundance (Abrams 1984, Brown 1988, Lima 1998b, Peckarsky et al.
2008, Ohgushi et al. 2012, Sheriff et al. 2020, Peacor et al. 2022). The
risk-induced trait-responses of the prey can also have indirect effects
(termed trait-mediated indirect effects, TMIEs; Peacor et al. 2020),
with other species including their resources, competitors, or other
predators (Sih et al. 1998, Werner and Peacor 2003). NCEs and TMIEs have
received much attention given their potential to profoundly influence
ecological communities and management of natural resources (reviewed in
Werner and Peacor 2003, Schmitz et al. 2004, Creel and Christianson
2008, Heithaus et al. 2008, Peckarsky et al. 2008, Ohgushi et al. 2012,
Say-Sallaz 2019).
Indeed, it is often claimed that risk effects are as important to the
net effect of predators on prey abundance as their direct consumptive
effects (Sheriff et al. 2020). However, that conclusion has been based
largely on experiments done in relatively simple systems with only a few
interacting species and little temporal or spatial environmental
heterogeneity (Nelson 2007, Sheriff et al. 2020), even when performed in
natural settings (Sheriff et al. 2020, Peacor et al. 2022). Thus, if we
are to incorporate risk effects into management plans, it is important
to know that the effects demonstrated in simplified systems are
generalizable to more complex systems incorporating many interacting
species and spatial and temporal heterogeneity.
Here we investigate risk effects of fish on the abundance of different
zooplankton prey species in complex experimental communities. Here we
investigate risk effects of fish on the abundance of different
zooplankton prey species in complex experimental communities. The
novelty of our approach is that we look at these effects across multiple
experiments, each with a very similar experimental conditions,
objectives, measurables and implementation. Thus, any observed
variability in the effect of predation risk across experiments arises
from differences in the experiments that are purely incidental (i.e.,
differences that were not of consequence to the study design or
implementation). These incidental differences in environmental
conditions are much smaller than the environmental variation that would
be expected in natural settings. Our approach thereby represents a
conservative examination of contingency in natural settings, which
allows us to ask whether risk effects on prey abundance are robust and
generalizable.