Nonconsumptive predator effects

Through fear, predators can induce prey to change their behavior, morphology, or life history in ways which cascade to affect entire communities.  These defenses mimic prey consumption; but, unlike consumptive effects, prey responses to fear can be influenced by changes in the cues which inform prey about their risk, by characteristics of the predators that make them more dangerous or of the prey which make them more vulnerable, and by the environment in which the interaction takes place.  These factors make nonconsumptive effects more complicated to understand and predict.

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Oysters make heavier, stronger shells in response to crab predators.   Studying this morphological defense in oysters, I have investigated a diverse array of factors which can alter nonconsumptive predator effects.  For example, oysters react more strongly to chemical cues from predators, as opposed to cues from other injured bivalves.  They respond more strongly when crabs consume fresh oysters, rather than to starved or scavenging crabs.  And they produce greater increases in shell strength when they are smaller and more vulnerable to predation.  Researching how these factors influence prey responses is important to understand how healthy communities function and how anthropogenic disturbances may alter these communities. 

Prey produce plastic, rather than fixed, defenses because defending is costly, requiring prey to reallocate energy away from growth and reproduction.  Defense costs are important to understand the consequences of nonconsumptive predator effects.  But defense mechanisms and costs are characterized for only a small number of species.  Previously, oysters were assumed to increase small amounts of energy-expensive organic shell material to maximize shell strength.  But my research demonstrates oysters exposed to crab predators have lower proportions of organic shell material.  This suggests oysters increase calcium carbonate material shell, which is cheap to produce and may minimize the costs of defending.  I have ongoing research to understand the consequences of this defense mechanism on oyster reproduction.