The influence of temporally variable predation risk on indirect interactions in an aquatic food chain |
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Authors: | Jeremy M Wojdak D Coleman Trexler |
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Institution: | (1) Department of Biology, Radford University, Radford, VA 24142, USA |
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Abstract: | We know little about how temporally variable predation risk influences prey behavior. The risk allocation hypothesis predicts
that prey facing more frequent risk should show weak anti-predator responses, and should be particularly active foragers during
rare periods of safety, compared to prey facing infrequent risk. Several studies offer support for the risk allocation hypothesis,
but how these responses might propagate through the larger ecological community remains largely unknown. We experimentally
investigated the relative strength of trait- and density-mediated indirect effects of a predator on its prey’s resource across
predation treatments that varied the lethality (caged or free-swimming predators) and temporal variability (always, often,
or sometimes present) of predation. We performed this experiment in pond mesocosms using a giant water bug predator (Belostoma lutarium), an herbivorous pond snail (Physa gyrina), and algae as the basal resource. Snails greatly reduced the abundance of their algal resource when in the absence of predation.
Lethal predation at low and medium intensities had significant positive indirect effects on the abundance of algae, mostly
by reducing snail density. Snails responded behaviorally to high levels of deadly predation by foraging more and hiding less
than in other situations, as predicted by the risk allocation hypothesis, and thus ameliorated the density-mediated indirect
effects of predators on algae. Behavioral responses to caged predators, and the subsequent trait-mediated indirect effects,
were negligible regardless of predation intensity. Our previous work has demonstrated that trait-mediated indirect effects
are weak when resources are abundant, as they were in this experiment. This work demonstrates that temporal variation in predation
intensity plays a key role in determining the relative strength of TMIIs and DMIIs in an aquatic food chain. |
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