From Individuals to Populations: Prey Fish Risk-Taking Mediates Mortality in Whole-System Experiments

Abstract

Recent research suggests that the behavior of individuals under risk of predation could be a key link between individual behavior and population and community dynamics. Yet existing theory remains largely untested at large spatial and temporal scales. We manipulated food available to age‐0 rainbow trout while at risk of cannibalism, in a replicated factorial whole‐lake experiment, to test whether the trade‐off between growth and mortality rates is mediated by foraging activity by young fish under predation risk. We found that this trade‐off exists for young fish at the whole‐system scale, and that food‐dependent behavioral variation has large mortality consequences. In high‐food lakes, age‐0 trout spent less time moving, fewer individuals swam continuously, and those swimming continuously swam at slower speeds relative to those in low‐food lakes. Age‐0 trout also used deep, risky habitats less when food was abundant. This lower activity, combined with avoidance of risky habitats, coincided with 68% higher survival in high‐food lakes. If general, this trade‐off may be a key mechanism linking individual behavior to population‐level processes in size‐structured populations.

Predators select against high growth rates and risk–taking behaviour in domestic trout populations

“…While this is a valid approach, it also has problems. For instance, augmenting food abundance for prey fish in small lakes by fertilization can affect water clarity (reducing predator-prey encounter rates) and also increase food for predators that share food resources with prey fish (Biro et al 2003a). These spin-off effects can confound, at least in part, the lower predation mortality observed at low food abundance and thus overestimate the contribution of risk-taking behaviour to mortality (Biro et al 2003a).…”

“…Characteristics of the lakes used (K1, K2, B2, B3 and CP1) are described in detail in Biro et al (2003a). The lakes contain no natural fish populations and are closed to fishing.…”

“…We conducted only a single netting trial for habitat use to minimize killing fishes that had survived, because vulnerability to gillnets (and therefore mortality) increases with body size (Biro et al 2003a). Rainbow trout of the size used in this experiment primarily eat zooplankton, which is most abundant in the open-water, or pelagic, habitat (Post et al 1999).…”

“…We estimated autumn population size and mean mass from 22 to 27 September by lethal gillnet sampling in all habitats for five consecutive nights with a standardized effort (Post et al 1999;Biro et al 2003a). One week before autumn netting, we stocked two sizeclasses each of domestic and wild trout into all lakes to estimate the proportion of each group recaptured over the five nights of netting, and size dependence in recapture probability (maxillary and ventral fin clips were used).…”

Ontogeny of energy allocation reveals selective pressure promoting risk-taking behaviour in young fish cohorts

“…Ludwig & Rowe 1990;Rowe & Ludwig 1991;Houston et al 1993;Werner & Anholt 1993;Clark 1994) and laboratory experiments ( Johansson & Rowe 1999;Anholt et al 2000;Johansson et al 2001) show that prey take greater risks as the window of time to reach a particular state becomes smaller. Understanding the selective pressures promoting risk-taking behaviour is important given that variation in risk-taking within and among prey populations is widespread (Lima 1998) and has large population-level mortality consequences (Biro et al 2003a(Biro et al ,c, 2004a.…”