Planning successful restoration and conservation strategies in a rapidly warming world is a critical challenge in ecology and evolution that cuts across scales, from individual variation in temperature tolerance to whole-ecosystem consequences. One efficient way to predict and plan for ecosystem responses to climate change may be to integrate across these levels by focusing on key species with particularly large effects. In many ecosystems, a single or few dominant species provide a large proportion of ecosystem services or functions such as habitat formation, food provision, and nutrient cycling. Whether these species maintain their ecological contributions in the future will be determined by their ability to acclimate and/or adapt to changing conditions without disrupting their community interactions. This depends critically on (1) whether intraspecific variation within key species is determined by genetic variation, environmental responses (phenotypic plasticity), or interactions between genetics and the environment, and (2) how this intraspecific variation impacts associated communities and ecosystems. In this context, enhancing conservation success depends on answering the following questions: should restoration and conservation efforts focus on individuals of these key species that are locally adapted to warmer climates, or individuals that are able to acclimate to variable climactic conditions? What are the ecological consequences of each scenario? In this session, we bring together ecologists working to answer these questions for keystone, foundation, or dominant species in freshwater, riparian, and marine systems already responding to climate change. Speakers will compare sources of intraspecific variation and demonstrate consequences of this variation for associated communities (from microbes to invertebrates) and ecosystem processes (from productivity to nutrient cycling). Drawing from a diversity of systems and approaches, this session will illustrate the ecological and evolutionary dimensions of predicting the future functioning of key species and the systems they shape.