The direct and indirect effects of temperature on a predator-prey relationship

Abiotic factors may directly influence community structure by influencing b iotic interactions. In aquatic systems, where gape-limited predators are co mmon, abiotic factors that influence organisms' growth rates potentially me diate predator-prey interactions indirectly through effects on prey size. W e tested the hypothesis that temperature influences interactions between aq uatic size-limited insect predators (Notonecta kirbyi) and their larval anu ran prey (Hyla regilla) beyond its indirect effect on prey size. Notonecta kirbyi and H. regilla were raised and tested in predator-prey trials at one of three experimentally maintained temperatures, 9.9, 20.7, or 25.7 degree sC. Temperature strongly influenced anuran growth and predator success; mea n tadpole mass over time was positively related to temperature, while the n umber of prey caught was negatively related. At higher temperatures tadpole s attained greater mass more quickly, allowing them to avoid capture by not onectids. However, the probability of capture is a function of both mass an d temperature; temperature was a significant explanatory variable in a logi stic regression equation predicting prey capture. For a given prey mass, ta dpoles raised in warmer water experienced a higher probability of capture b y notonectids. Thus, rather than being static, prey size refugia are influe nced directly by abiotic factors, in this case temperature. This suggests t hat temperature exerts differential effects on notonectid and larval anuran s, leading to differences in the probability of prey capture for a given pr ey mass. Therefore, temperature can influence predator-prey interactions vi a indirect effects on prey size and direct effects on prey.