As human population size increases and cities become denser, several urban-related selection pressures increasingly affect species composition in both terrestrial and aquatic habitats. Yet, it is not well known whether and how urbanization influences other facets of biodiversity, such as the functional and evolutionary composition of communities, and at what spatial scale urbanization acts. Here we used a hierarchical sampling design in which urbanization levels were quantified at seven spatial scales (ranging from 50 to 3200 m radii). We found that urbanization gradients are associated with a strong shift in cladoceran zooplankton species traits, which in turn affected phylogenetic composition of the entire metacommunity, but only when considering urbanization at the smallest spatial scale (50 m radius). Specifically, small cladoceran species dominated in more urbanized ponds whereas large-bodied, strong competitors prevailed in less urbanized systems. We also show that trait and phylogenetic metrics strongly increase the amount of variation in b-diversity that can be explained by degree of urbanization, environmental and spatial factors. This suggests that the mechanisms shaping b-diversity in our study system are mediated by traits and phylogenetic relatedness rather than species identities. Our study indicates that accounting for traits and phylogeny in metacommunity analyses helps to explain seemingly idiosyncratic patterns of variation in zooplankton species composition along urbanization gradients. The fact that urbanization acts only at the smallest spatial scale suggests that correctly managing environmental conditions locally has the power to counteract the effects of urbanization on biodiversity patterns. The multidimensional approach we applied here can be applied to other systems and organism groups and seems to be key in understanding how overall biodiversity changes in response to anthropogenic pressures and how this scales up to affect ecosystem functioning.

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. Climate change is profoundly affecting biota on a global scale, impacting ecosystems and their functioning worldwide (IPCC 2014). The impact of climate change is manifested at all biological levels, ranging from genetic changes, changes in physiology, morphology, behavior, and life-history traits of populations, to alterations in populations dynamics, changes in community structure and biodiversity, and changes in