The central objective of this project is to evaluate to what extent biomarkers can be used to predict pollutant effects at the community level, with special attention for the interaction with predator stress and competition. Focus will be on studying the pesticide endosulfan, worldwide one of the most commonly used insecticides. Model organisms will be three aquatic insect groups: midge larvae (Chironomidae), water boatmen (Corixidae) and damselflies (Coenagrionidae). We will use a hierarchical approach to study taxon-specific effects of individual and joint exposure to pollutant and biotic stress. The species-specific sensitivity to the stressors will be determined using: (1) biomarkers (functional traits, gene expression) and (2) organismal traits (growth rate, survival, reproductive success) in exposure experiments in the laboratory; growth and abundance patterns of individual species in mesocosm experiments with (3) populations of single species and (4) simple communities in which interspecific interactions between the different model taxa are allowed. (5) Finally, we will combine all information obtained to evaluate to what extent biomarkers (functional traits) covary among each other (horizontal covariation), and to what extent the patterns obtained for the biomarkers covary with the patterns for traits measured at higher levels of biological organization (vertical covariation).