Invertebrate prey have been shown to select suboptimal resource patches in the face of predation (the food-predation risk trade-off). The foraging strategy used by a predator and the environmental context under which an interaction occurs potentially mediates prey responses to predators. Here, I determined whether season, predator presence or alternative prey availability affected prey patch use when faced with a sit-and-wait predator from streams in southern Maine. In addition, instantaneous mortality rates and predator movement behavior were assessed as possible mechanisms explaining patch use by prey in different seasons. In the absence of predators, prey did not show any preference for substrate patches based on particle size. But, depending on prey type and season, substrate position in streams had a significant effect on prey survival. Mayflies survived most in summer when pebble substrates were located upstream whereas caddisfly survival was highest when pebble substrates were located downstream in winter. Season and taxa significantly affected instantaneous mortality rates, suggesting this predator responded differently to available prey in each season. Predators changed ambush positions in the streams significantly more during winter than during summer, both with and without prey present. The presence of caddisflies in mixed-prey trials reduced consumption of mayflies in summer, but increased their mortality in winter. Increased movement behavior of predators in winter may have led to greater encounters with prey, thus increasing winter mortality. Collectively, these data reveal season can influence the outcome of predator-prey interactions. Environmental context, as well as predation mode, is critical to predicting predation effects in macroinvertebrate communities. Further studies of the seasonal changes in organism-specific behavior are needed to evaluate the importance of biotic interactions in structuring stream communities.
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