Non‐Consumptive Effects of Predators on Prey That Outgrow the Predation Window

ABSTRACT In many aquatic predator–prey relationships, prey species can outgrow the ‘predation window’ and reach a size refuge. After the prey outgrow the predation window, predators can no longer affect prey density and phenotypes through consumption (i.e., consumptive effects). In contrast, whether predators have non‐consumptive effects on prey during this period is unclear because the cues triggering risk‐induced trait responses in prey may exist during the entire persistence period of predators. The movement of interacting members of predator populations among patches of habitat creates variation in the timing and duration of predator and prey co‐occurrence. The period even after the prey outgrow the predation window can also matter in explaining magnitudes of risk‐induced trait responses in prey. To explore the possibility of non‐consumptive effects of predators on prey after they have outgrown the predation window, we conducted a laboratory experiment using adult Notonecta triguttata (backswimmers) and their prey, Zhangixalus arboreus (forest green tree frog) tadpoles. We assessed the effect of backswimmer presence/absence (1) during the period in which tadpoles are within the predation window and (2) after the tadpoles outgrow the predation window on tadpole life‐history traits. Backswimmer presence during the predation window and following the predation window independently resulted in a slightly extended tadpole period. These results suggest the importance of considering the entire period of predator and prey co‐occurrence to understand all of the non‐consumptive effects that predators have on prey. Several aquatic predators that consume a fixed range of prey sizes and are also capable of movement across land, such as backswimmers and newts, can move among ponds. Predator mobility can contribute to creating variation in key early life‐history traits of prey by varying predation intensity while prey are within the predation window, but also when prey have outgrown it, eventually affecting prey population dynamics.