We will carry out a population genetic and quantitative genetic study of the response of a natural Daphnia population to simulated changes in temperature (approx. 2050) in a large-scale mesocosm experiment (at NERI, Denmark). In the mesocosm experiment, both temperature and nutrient concentrations are varied in a factorial way. In our quantitative genetic analysis, we will not only consider temperature, but also the impact of temperature on fish predation intensity as a selective factor. The main aim of our study is to quantify evolutionary potential of Daphnia populations in relation to climate change.