Motile behavior and predation risk in planktonic copepods: Behavior dependent predation risk

Predation is an important source of mortality in zooplankton but factors governing predation risk in marine food webs are still not well understood. Here, we examine the role of zooplankton behavior in determining predation risk. We first quantified motility of copepods with different feeding behaviors (ambush feeding, cruising, and feeding‐current feeding).

Second, we estimated remote predator detection and escape characteristics of the studied copepods. Third, we proposed a simple behavior‐dependent encounter model to predict copepod predation risk from rheotactic predators. Finally, we compared our predictions with predation risk previously determined experimentally.

For similar sized copepods, predicted predation risks were similar 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 females depending on feeding behavior: in ambush feeders males actively search for non‐motile females and their predation risk was up to 6 times higher (range 1.2–6) than for females.

In contrast, feeding current‐ and cruising feeders showed small differences in predation risk between genders. In all cases, predicted relative predation risks between particular behaviors were confirmed by empirical data from previous predation experiments. Our results demonstrate that prey behavior of zooplankton may lead to a predictable variation in predation risk from rheotactic predators of up to an order of magnitude, and therefore that individual behavior is an important factor in structuring zooplankton communities.