Background/Question/Methods Climate change is impacting the performance and phenotypic expression of many species, as well as the strength of species interactions. By focusing on foundation species with large effects on multiple types of associated communities, we may be able to disentangle the direct and indirect links between changing climate, organismal phenotypes, and ecosystem functioning. To do this, we used a set of three common gardens along a steep climate gradient, planted with the same populations and genotypes of an important riparian tree species of the Southwest (Fremont cottonwood). Within these gardens, we used a simulated herbivory experiment to test the combined effects of changing abiotic and biotic stress on trait expression across these genetically divergent populations. We then examined the effects of genetic and plastic trait variation on community assembly in foliar arthropods, microbes, and aquatic detritivores colonizing leaf litter.
Results/Conclusions We found interactive effects of tree population and growing conditions on many tree traits. This complicates the prediction of community responses to climate change, even if we know the genetic identity of the foundation species and forecasted future climates. Importantly, translating trait variation into community effects varied strongly across different types of communities. For aquatic invertebrate communities consuming leaf litter, the growing environment of the litter had a stronger effect than tree identity, partly because hot and dry conditions homogenized trait diversity across populations. For foliar arthropods, both abundance and diversity decreased on trees that were responding to experimental herbivory by inducing defenses, regardless of growing environment. However, total leaf herbivory was higher on local tree populations than foreign populations. In contrast, some endophytes reached higher abundance in foreign populations than local populations. Taken together, these results show the importance of understanding both genetic and environmental effects on a wide range of leaf and tree traits, as well as the relative importance of trait means and trait diversity for the assembly of different types of associated communities. With continued synthesis of these results, we aim to assist managers in forecasting higher level ecological consequences of key restoration decisions.