UC Santa Barbara

Climate change is causing species to shift their geographical distributions, with profound consequences for nature and people around the world. These climate-related species range shifts have created opportunities for some species to thrive, threatened others with extinction, and led to cascading effects through communities and ecosystems. While historical range shifts are often correlated with climate change, this relationship alone cannot always predict range shifts, forcing natural resource managers and conservation practitioners to act amidst high uncertainty about the future. I explored this uncertainty from management and ecological perspectives. First, I synthesized guidelines and evidence from global change, biogeography, and conservation planning literature to collate concrete recommendations for marine protected area design for range-shifting species. Next, I conducted some of the first analyses of species range edge dynamics over time, using long-term annual biodiversity monitoring efforts in U.S. oceans, which allowed for detection of fine-scale changes in range edge positions. I tested several biogeographical hypotheses about whether and how much cold and warm range edges will shift in response to changing temperatures. In the Northeast U.S., I reported that cold range edges shifted further and were more closely related to temperature than warm edges. I extended this analysis to several U.S. regions with different warming histories, where I quantified edges using a spatiotemporal model and then tested for thermal niche conservatism at range edges. I found notable regional differences, but thermal niche tracking was detected even in regions that did not warm during the study period. Species varied markedly in the degree to which they tracked temperature, even among related taxa in the same region. However, thermal niche conservatism occurred more frequently at cold range edges than at warm range edges. These patterns would not have emerged from methods using fewer time points, underscoring the need to use long time-series. This work tested biogeographical theories about the fundamental drivers of range edge dynamics, identified range edges of marine species that are expected to track climate change, and provided tools for managing range-shifting species.