Climate and intraspecific diversity in a consumer species drive ecosystem multifunctionality.

Climate change is altering the multifunctionality of ecosystems worldwide, and is often associated to changes in biodiversity that can modulate the impacts of climate change on ecosystems through interactive effects. Genetic and phenotypic variation within species are particularly influenced by climatic conditions, and can mediate several ecosystem processes. Here, we tested whether climate change can interact with intraspecific diversity to drive ecosystem multifunctionality. We used a mesocosm experiment to test the consequences of intraspecific variation (population identity and trait variation) of a consumer fish species (European minnow, Phoxinus phoxinus) and climate on ecosystem multifunctionality, as well as on the biomass of a subsequent fish generation (long-term effects). We found that individuals from different populations affect ecosystem multifunctionality independently of climate, and that multifunctionality differed between cold and warm mesocosms. Moreover, when investigating sub-components of multifunctionality, we found a positive relationship between individual metabolic rate and multifunctional primary production in warm mesocosms, whereas this relationship was reversed in cold mesocosms. We similarly found evidence that the long-term effect of intraspecific trait variation on the biomass of the next fish generation was climate-dependent. These findings demonstrate that intraspecific diversity can have strong consequences on ecosystem multifunctionality, and that intraspecific diversity must be considered in addition to other components of global change to predict the impacts of global change on ecosystem multifunctionality.