Climate change and trophic interactions in model temporary pond systems: the effects of high temperature on predation rate depend on prey size and density

1. Climatic warming has induced marked shifts in the geographical distribution and seasonal phenology of many species, although the impacts of climatic changes on the interactions between species across trophic levels are far less well known. 2. Freshwater microcosms were used to test the effect of temperature on the life history traits of a prey species, the fairy shrimp Chirocephalus diaphanus (Anostraca), the abundance of a predator, themicrocrustacean Heterocypris incongruens (Ostracoda), and on the interaction between them. 3. When reared in the absence of predators, C. diaphanus survival was low at the highest temperature (25 °C) and greatly reduced at the lowest temperature (5 °C). It was reproductively most successful at an intermediate temperature (20 °C), suggesting that it may benefit from the increase in temperature predicted under future climate change scenarios. In the absence of other species, temperature would have to increase dramatically to affect C. diaphanus adversely. 4. Heterocypris incongruens was more abundant and its predation on C. diaphanus greatest at higher temperatures, partially offsetting the positive effect of raised temperature on prey observed when the predator was absent. The net effect was that the optimal temperature for C. diaphanus when coexisting with its predator was lower than when it was in isolation. This means that currently predicted increases in temperature ultimately may be detrimental to C. diaphanus. 5. Predation rates were generally enhanced by high temperature, prey size and prey density, with significant interaction between them. Thus, the positive effects of raised temperature on predation rate were additionally dependent upon prey characteristics, being strongest when prey were large and at high density and weakest when prey were small and at low density. 6. Interactions with a natural enemy, in this case a predator, may alter how species respond to raised temperatures; prey size and density further modify the outcome of this interaction. This context dependency in the response of both predators and prey to temperature suggests that the ecological impacts of future climate change on trophic interactions may be difficult to predict.