LAUSR

Many studies document genetic and phenotypic trait changes of species in response to climate change, or document how evolution of individual species can impact population abundances and community composition. An integration of population and community‐level responses requires, however, a multiple species approach. Here we quantify among‐ and within‐species differences in thermal tolerance and life‐history traits in three co‐occurring Daphnia species upon exposure to a naturally occurring heat wave. Populations of randomly isolated clones of Daphnia magna, Daphnia pulicaria, and Daphnia galeata from the same pond were exposed to a natural heat wave in outdoor mesocosms. We subsequently conducted a common garden experiment in the laboratory using clonal lineages isolated at the end of the mesocosm selection experiment, at two rearing temperatures, measuring thermal tolerance and life‐history traits. We find pronounced plasticity responses to higher rearing thermal regime in each study species. We observe only few significant microevolutionary responses involving evolution of plasticity in D. pulicaria. Yet in terms of effect size, evolutionary trait change within species contributes more than 25% to total trait change in response to the heat wave for a majority of the trait × species combinations. The relative importance of intraspecific to interspecific variation varies widely among traits. Our results show that the relative importance of interspecific variation, phenotypic plasticity, and evolutionary trait change differs strongly depending on the set of species and traits studied. Taking into account this variation at different levels of biological organization is important to predict community‐wide responses to global change.