Effects of prey‐size and predator‐instar on the predation of Daphnia by Notonecta

. 1. Attack rates and handling times are measured by a series of separate functional response experiments for each instar of Notonecta glauca attacking four size classes of Daphnia magna as prey. The resulting attack rate and handling time surfaces are complex, with maximum attack rates for small predators attacking small prey, and large predators attacking large prey. Adult Notonecta have lower attack rates than the two previous juvenile instars (4 and 5). 2. The literature on attack rates and handling times in other predator—prey interactions that involve a series of different predator and prey size or age classes is reviewed in the context of the Notonecta‐Daphnia results. The data suggest that small predator instars will usually compete with large instars for food, unless there is spatial or temporal separation between them. 3. Complex attack rate and handling time surfaces are to be expected wherever a wide range of prey and predator sizes is involved. 4. Size related changes in attack rates and handling times can introduce very complex dynamics into predator‐prey interactions.