The joint effect of phenotypic variation and temperature on predator-prey interactions

Understanding the factors underpinning to food web structure and stability is a long-standing issue in ecology. This is particularly important in a context of global climate change, where rising environmental temperatures may impact the way species interact, potentially leading to changes in food web structure and to secondary extinctions resulting from cascading effects. In order to understand and predict these changes, we need to hone our comprehension on the way predators and their prey interact. Recent studies suggest that, in order to do so, we need to focus on the traits controlling those interactions, such as body size. Mean body size and its intraspecific variation can in turn be affected by temperature, a pattern known as the temperature-size rule. To understand how warming may affect predator-prey interactions and through them, food web structure and dynamics, we thus first need to understand how traits, their within species variation, and temperature, may jointly affect these interactions. Here, I address these unknowns using both empirical and theoretical tools. I have shown that variation in the traits controlling predator-prey interactions may determine the strengths of these interactions, and through them, their stability and overall dynamics. I have also shown this to be truth for species living as metapopulations, where variation in the traits controlling migration plays an important role in determining their chance of persisting. Moreover, I showed empirically that many of these findings hold in a freshwater predator-prey system, and based on empirical results on how temperature affects body size and its variation, I made predictions as to how warming may affect interaction strengths in this system. I thus found evidence of temperature determining the way predators and their prey interact, leading to important changes in the body size structure of entire food webs across aquatic ecosystems. My results highlight how intraspecific variation has important yet largely overlooked ecological effects, and how these effects can be mediated by environmental temperature