Nonconsumptive effects of brook trout predators reduce secondary production of mayfly prey

The nonconsumptive effects of predators on prey include behavioral, physiological, and life-history changes that reduce the risk of predation but have associated energetic or fitness costs to prey individuals and populations. Biologists have documented such changes for a wide array of predator–prey interactions in a variety of ecosystems; however, the energetic cost of nonconsumptive effects to prey populations has rarely been measured directly. Using a reach-scale manipulation of a naturally-fishless stream, we added chemical cues produced by live Brook Trout (Salvelinus fontinalis Mitchill, 1814) to simulate the presence of trout predation risk, and we quantified the impact of nonconsumptive effects on the secondary production of mayfly prey in the stream. The addition of trout chemical cues reduced the secondary production of larval Baetis mayflies in the treatment reach by 17% compared to an upstream, unmanipulated reference reach. This reduction was driven by smaller body size and earlier emergence of mayflies from the reach with added predator cues. The nonconsumptive effects of a predator can consequently reduce the flux of energy through a dominant stream invertebrate by altering individual lifehistory and development patterns. Furthermore, quantifying the population-level impact of nonconsumptive effects enables understanding the extent to which these widespread predator effects shape food-web dynamics and ecosystem processes.