Abstract
To evaluate the importance of non‐consumptive effects of predators on prey life histories under natural conditions, an index of predator abundance was developed for naturally occurring populations of a common prey fish, the yellow perch Perca flavescens , and compared to life‐history variables and rates of prey energy acquisition and allocation as estimated from mass balance models. The predation index was positively related to maximum size and size at maturity in both male and female P. flavescens , but not with life span or reproductive investment. The predation index was positively related to size‐adjusted specific growth rates and growth efficiencies but negatively related to model estimates of size‐adjusted specific consumption and activity rates in both vulnerable (small) and invulnerable (large) size classes of P. flavescens . These observations suggest a trade‐off between growth and activity rates, mediated by reduced activity in response to increasing predator densities. Lower growth rates and growth efficiencies in populations with fewer predators, despite increased consumption suggests either 1) a reduction in prey resources at lower predator densities or 2) an intrinsic cost of rapid prey growth that makes it unfavourable unless offset by a perceived threat of predation. This study provides evidence of trade‐offs between growth and activity rates induced by predation risk in natural prey fish populations and illustrates how behavioural modification induced through predation can shape the life histories of prey fish species.