Predator biomass determines the magnitude of non-consumptive effects (NCEs) in both laboratory and field environments
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Predator body size often indicates predation risk, but its significance in non-consumptive effects (NCEs) and predator risk assessment has been largely understudied. Although studies often recognize that predator body size can cause differing cascading effects, few directly examine prey foraging behavior in response to individual predator sizes or investigate how predator size is discerned. These mechanisms are important since perception of the risk imposed by predators dictates behavioral responses to predators and subsequent NCEs. Here, we evaluate the role of predator body size and biomass on risk assessment and the magnitude of NCEs by investigating mud crab foraging behavior and oyster survival in response to differing biomasses of blue crab predators using both laboratory and field methods. Cues from high predator biomass treatments including large blue crab predators and multiple small blue crab predators decreased mud crab foraging and increased oyster survival, whereas mud crab foraging in response to a single small blue crab did not differ from controls. Mud crabs also increased refuge use in the presence of large and multiple small, but not single small, blue crab predators. Thus, both predator biomass and aggregation patterns may affect the expression of NCEs. Understanding the impact of predator biomass may therefore be necessary to successfully predict the role of NCEs in shaping community dynamics. Further, the results of our laboratory experiments were consistent with observed NCEs in the field, suggesting that data from mesocosm environments can provide insight into field situations where flow and turbulence levels are moderate.
KeywordsAntipredator behavior Body size Chemical cues Trophic cascades Blue crabs
The authors would like to thank Miranda Wilson, Kristine Schaffer, and Nicholas Brantley for their assistance in the laboratory and the field and Lee Smee for loaning us ADVs to make flow comparisons. We would also like to acknowledge the Skidaway Institute of Oceanography and its staff for being wonderful hosts. We also appreciate comments from C. Peterson and two anonymous reviewers whose suggestions improved this manuscript. This work was funded by National Science Foundation (NSF) grant NSF-OCE #0424673 to MJW and the NSF Integrative Graduate Education and Research Traineeship (IGERT) Fellowship in aquatic chemical ecology.
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