Synergistic Interaction Between Temperature and Algal Abundance on a Size-Structured Daphnia Population
Reductions in body size has been suggested as a universal response to global warming for many species. Here, I investigate the population level consequence of changes in body size and size-dependent life history characteristics using size-structured matrix projection models. Analyzing experimental data from 412 isolated Daphnia magna individuals raised under varying temperature and food levels, I show that temperature and food availability interact in a complex fashion in shaping Daphnia population size structure and the asymptotic population growth rate. I find food abundance determines the direction of population growth and temperature affects the magnitude of demographic variability, mediated through simultaneous limitation on size-dependent growth, survival and reproduction. Given the evidence for the synergistic interaction between temperature and food abundance on Daphnia individual fitness and population demography, I argue that accounting for the variation in food availability is crucial in understanding how populations might respond to rapid climate change.