Non-consumptive effects of predators have been shown to reduce the fitness of their prey across a wide range of aquatic and terrestrial taxa.  However, how other factors such as abiotic conditions can influence non-consumptive effects is less understood, which likely limits our ability to quantify the net effect of predators on prey in nature.  Herein, we evaluate how non-consumptive effects incurred by prey in aquatic ecosystems are modulated by turbidity (water clarity), an attribute of water that exhibits large and rapid changes in many systems.  We hypothesized that increased turbidity would lessen the magnitude of non-consumptive effects by reducing perceived predation risk.  To test this hypothesis, we conducted two laboratory experiments that evaluated changes in foraging rates of larval and juvenile yellow perch (Perca flavescens) on zooplankton under contrasting turbidity (turbid vs. non-turbid) and predation-risk (predator vs. no predator) treatments wherein predation risk was mimicked, using visual and chemical cues.  In addition, we quantified foraging success of similar-sized yellow perch collected from Lake Erie across a wide turbidity range. 

Results/Conclusions

Our experimental results supported our hypothesis, as foraging success in the absence of turbidity was significantly lower in the presence of a predator than without a predator, whereas no differences in foraging were observed between predation-risk treatments under turbid conditions.  Variability in consumption rates among individual yellow perch also was greater in turbid than in non-turbid conditions, suggesting that individual variation in the non-consumptive effect incurred is magnified in less risky environments.  Field observations support our experimental findings in that the relationship between turbidity and Lake Erie yellow perch consumption was humped-shaped, peaking at turbidity level at which risk was likely low but the individual’s own foraging ability was not substantially compromised.  Our findings demonstrate the variable nature of non-consumptive effects in dynamic environments, and also help to explain why recruitment success to juvenile stages is disproportionately higher for larvae that forage in turbid versus non-turbid open-lake river plumes in Lake Erie.