Predator foraging capabilities and prey antipredator behaviours: Pre- versus postcapture constraints on size-dependent predator-prey interactions

In order to understand patterns of predator diets and foraging efficiency relative to predator and prey size, it is essential to determine which particular suite of constraints determines the outcome of predator prey interactions. Feeding experiments were carried out with differently-sized piscivorous Eurasian perch (13-24 cm total length) and prey fish, roach (3.4-11.6 cm total length), at two different spatial scales, tanks and wading pools. The tank experiments Focused on morphological constraints in the predation process, as the: spatial scale of the tanks (0.4 m(3)) restricted antipredator behaviour. The pool experiments focused on prey anti-predator behaviour. such as schooling capacity. evasive behaviours, predator and prey swimming capacities. and predator reaction times, as the spatial scale of tanks (2.5 m(3)) allowed prey to express antipredator behaviours. In the tanks, for a given predator size, the number of attacks and the manipulation time after prey had been caught increased with prey size. The maximum size of prey caught appeared to be related mainly to predator gape limitation. In the pools the maximum size at which prey were captured by predators generally was smaller than in the tanks, indicating that prey evasive behaviour was important in determining predator success. The scaling of prey schooling, positioning in the water column and evading by jumping out of the water with prey size did not indicate that these behaviours were determining the maximum size of prey consumed in pools. Rather, the relation between predator and prey mobility seemed to be the most important factor determining the maximum size of prey consumed in the pools. This suggests that foraging models using handling time as currency may be poor predictors of active predator-active prey foraging patterns.