Predator-prey interactions are a fundamental feature of ecological communities. The majority of studies have focussed on the consequences of predators reducing the abundance of their prey through direct consumption (density-mediated interaction, DMIs). However, predators can also interact with prey by inducing costly behavioural and/or physiological defence strategies such as reduced foraging, anti-predator behaviour and investment in defensive structures. Evidence suggests that the cost of these phenotypic responses, termed trait-mediated interactions (TMIs), may be greater than that of DMIs. The strength of TMIs may depend on the environmental context in which prey must decide between food and safety. Because temperature can alter metabolic and foraging rates, particularly in ectotherms, this additional physiological stress may determine how prey balance this trade-off. Observations were made of the effect of predator cues and temperature on the foraging behaviour of the intertidal snail, Littorina littorea Both temperature and predation cue had independent effects on the amount of Ulva lactuca consumed, although there was no interaction between these factors. The addition of predation cue water caused L. littorea to consume 77% less Ulva compared to control treatments whereas the increased temperature resulted in 2.5 times more Ulva being consumed. The results suggest that non-consumptive effects can play an important role in shaping intertidal communities and that the effects of warming may result in intertidal consumers trading energy gain for safety when under predation risk. Understanding the direct and indirect effects of temperature and predation risk on species interactions will provide greater insights into prey dynamics and cascading trophic interactions
