Motile behavior and predation risk in planktonic copepods

Abstract

Predation is an important source of mortality in zooplankton but factors governing predation risk inmarine food webs are still not well understood. Here, we examine the role of zooplankton behavior in deter-mining predation risk. We first quantified motility of copepods with different feeding behaviors (ambushfeeding, cruising, and feeding-current feeding). Second, we estimated remote predator detection and escapecharacteristics of the studied copepods. Third, we proposed a simple behavior-dependent encounter model topredict copepod predation risk from rheotactic predators. Finally, we compared our predictions with preda-tion risk previously determined experimentally. For similar sized copepods, predicted predation risks weresimilar between feeding-current feeders and cruising feeders, whereas predation was up to 8.5 times lower(range: 1.5–8.5) for ambush feeders. Predicted predation risks further differed between males and femalesdepending on feeding behavior: in ambush feeders males actively search for non-motile females and theirpredation risk was up to 6 times higher (range 1.2–6) than for females. In contrast, feeding current- andcruising feeders showed small differences in predation risk between genders. In all cases, predicted relativepredation risks between particular behaviors were confirmed by empirical data from previous predationexperiments. Our results demonstrate that prey behavior of zooplankton may lead to a predictable variationin predation risk from rheotactic predators of up to an order of magnitude, and therefore that individualbehavior is an important factor in structuring zooplankton communities