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Fear reduces energy flow in a rocky intertidal food chain

Predators have the potential to shape entire landscapes via their effects on prey and cascading effects on other species, including the prey’s resources.  For instance, when wolves disappeared from Yellowstone, populations of browsing ungulates (elk, deer) were released from predation and decimated vegetation in the park, resulting in vast changes in the ecology and landscape of the area.  Ecologists now realized that these far reaching impacts occur not only when predators eat prey, but also when predators scare prey.  In her recent publication, MSC postdoctoral researcher Catherine Matassa of the Trussell Lab delves into this “ecology of fear”, investigating how prey hunger level might change their response to predation risk, with consequences for how energy moves up food chains. 

In this study, appearing in Proceedings of the Royal Society B, Matassa used a rocky intertidal food chain to examine how starved and fed prey respond to different temporal patterns of predation risk. Results indicate that chemical cues signaling predation risk from an invasive predatory crab cause a reduction the feeding rates and energetic efficiency of prey dogwhelks, resulting in a cost of reduced growth. Predators come and go, but when present for long periods of time, starved prey cannot pay this cost, weakening the effects of fear. On the other hand, risk effects are amplified when prey can burn energy reserves instead of foraging, producing what Matassa calls “trophic heat.” The relative amount of energy lost as ‘trophic heat’ increases with the duration of risky periods and depends on the ability of prey to build up reserves during safe periods, which should be easier in more productive systems.  Since predation risk is variable in nature, these results help to explain why some systems have relatively short food chains despite abundant basal resources, bettering our understanding of how predator-prey interactions shape ecological communities.

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