Results/Conclusions Our results show that for some ecosystem responses the effects of evolution and coevolution were actually larger than the effects of species invasion (i.e., alteration of species assemblage). Guppies originating from a source that experiences intense predation increased algal biomass and accrual rates relative to guppies from a site with less risk of predation. These effects on primary producers appear to be associated with divergence in rates of nutrient excretion and algae consumption. Rivulus-guppy coevolution significantly influenced the biomass of aquatic invertebrates. Specifically, locally coevolved populations reduced invertebrate biomass relative to non-coevolved populations. In combination, these findings challenge the general assumption that population diversity is a less critical determinant of ecosystem function than is interspecific diversity. Moreover, given existing evidence for contemporary evolution in these fishes along similar ecological gradients, our findings suggest considerable potential for eco-evolutionary feedbacks to operate as populations adapt to natural or anthropogenic perturbations.