Wildlife and Conservation Biology
Preisser, Evan, L
Non-consumptive effect (NCE), predator-prey interactions, refuge, Physa acuta
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While it is well known that predators eat their prey, prey that avoid predation risk can also incur substantial fitness costs through risk-induced changes in survival and reproduction, growth, and morphology. Changes in prey that occur without the predator physically consuming the prey are referred to as ‘non-consumptive effects’. One way to reduce the risk of predation is to use a refuge. While refuge use may reduce predation risk, however, it may also be costly to the prey. These costs may include within-refuge competition for resources, which can alter prey population dynamics, coexistence, and metapopulation dynamics. While these costs may be significant for the affected prey, no one has ever measured how much refuge-mediated avoidance of predation ‘costs’ in terms of prey growth.
This experiment uses freshwater snails (Physa acuta) and crayfish (Cambarus bartonii bartonii) as the prey and predator, respectively. Previous research on this predator-prey pair found that the addition of either crayfish cues or crushed snails to snail-containing tanks changed the patterns of snail refuge use and growth, and that the snail responded differently to cues from different predator species. These studies and other demonstrate how complex non-consumptive effects can be, and illustrate the need for further research on how refuges factor into the model.
To accomplish this goal, twenty-four ten-gallon tanks are set up to hold fifteen snails each. We cross two factors, predator present/absent with refuge present/absent, for a total of four treatments: predator present/refuge present, predator present/refuge absent, predator absent/refuge present, and predator absent/refuge absent. Each treatment is replicated six times (i.e., six tanks per treatment). The ‘predator present’ treatments have crayfish water and dead conspecifics added to the tanks weekly as a predation risk cue for the snails. Prior to the snails being placed in the tanks, each snail is measured for shell length, diameter, and thickness; the data is averaged on a per-tank basis for analysis. The experiment continues for three weeks. Whether the snails are present in a refuge or outside of the refuge is recorded twice a day. After three weeks, the snails are removed and the same size measurements as were previously taken are recorded.
Through this experimental design this study aims to determine whether the presence or absence of a refuge affects how snails respond to cues from a crayfish predator and crushed conspecifics. This tests whether refuges impact the non-consumptive effects of the crayfish on snail growth and behavior, and increases our understanding of how prey use refuges, and how costly it is to use them.