Species shift their geographic distributions when constraints on range boundaries are lifted and individuals colonize new areas. We expect this to occur under modern climate change if populations in a poleward or upward direction are enhanced by warming. Few studies have tested for this enhancement, however, and factors such as local adaptation or species' not filling their full climatic niche could prevent it from occurring and thus constrain range change. In addition, dispersal limitation at a historic range boundary could preclude a range shift even if enhancement were to occur. Translocation experiments have the power to reveal such processes at range boundaries. Using two species of butterfly and their host plants distributed throughout coastal, western North America, students and I performed translocation experiments to test the hypothesis of poleward population enhancement due to climate change. We also examined if populations can establish in areas outside the historic range as predicted under climate change. Results/Conclusions
Across these several species, we found local adaptation within peripheral populations, resource-dependence in peripheral population enhancement, and dispersal and colonization limitation. I briefly summarize these findings and examine their implications for range change under climate change. In several instances, these results suggest constraints on range expansion and thus a potential need for conservation strategies that overcome such constraints.