Intraspecific variation alters ecosystem and next-generation performance as much as temperature

Functional differences among populations can affect community structure and ecosystem functioning. However, there is considerable uncertainty about the relative importance of these effects compared to key environmental factors such as temperature. Moreover, it is unclear whether these effects are persistent enough to affect the performance of individuals from subsequent generations. Here, we quantified the effects of intraspecific variation on community and ecosystem properties and on next-generation performance, and we compared these effects to those induced by a 2°C warming. We performed an experiment simultaneously varying the genotypes and phenotypes of a freshwater fish species (the European minnow, Phoxinus phoxinus) and temperature. We demonstrated that the effects of intraspecific variation were as strong as those induced by a 2°C temperature increase, and that these effects were mostly temperature-independent. Differences in fish body mass and activity had the strongest effects. For instance, a 2-fold difference in body mass among populations strongly affected prey abundance and algae stock, which ultimately affected fitness traits of the next fish generation. Temperature significantly modulated some ecosystem functions, such as litter decomposition, which was also associated to effects on the next generation. Our findings demonstrate that intraspecific variation has a key role for ecological and evolutionary dynamics.