PS 50-55
Local adaptation across multiple trophic levels shapes eco-evolutionary dynamics
Local adaptation, defined as when individuals evolve towards an optimal phenotype within a given environment, has been shown to be an important component of niche specialization and speciation. There is growing evidence that the phenotypic variation that corresponds from adaptation can also have consequences for the assembly of communities and ecosystem functioning. Yet, multiple co-occurring species can exhibit locally adapted phenotypes and range in their trophic position, from producers to predators. It remains unclear what ecological consequences result from intraspecific trait variation at interacting trophic levels. In this study, we merged a common garden consisting of different genotypes of riparian trees (Populus trichocarpa) growing adjacent to aquatic mesocosms (1200 L cattle tanks) containing benthic or limnetic forms of three-spine stickleback (Gasterosteus aculeatus), with a fishless control. This work occurred in the overlapping native range of both organisms in British Columbia, where each displays considerable phenotypic variation that has been well-studied and attributed to adaptation to climate (trees) or lake habitats (fish).
Results/Conclusions
We found that tree genotypes varied in the amount and quality of leaf litter inputs to aquatic mesocosms, which had cascading effects on phytoplankton, zooplankton, and benthic invertebrates, as well as nutrient dynamics within mesocosms. The presence of fish had strong, top-down effects on zooplankton and invertebrates and tended to dampen the genotype effects of tree litter. Moreover, there were significant interactions between the different tree and fish genotypes on invertebrate assemblages. Taken together, our results reinforce the importance of top predators in aquatic food webs, but also suggest that ecosystems are shaped by genetic differences that occurs from both the bottom-up and the top-down. Consequently, a complete understanding of eco-evolutionary dynamics will require the adoption of a multi-trophic perspective.