Causes and Consequences of Species Range Edge Shifts in a Warming Ocean

ABSTRACT

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 US 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 US, I reported that cold range edges shifted further and were more closely related to temperature than warm edges. When I extended this analysis to several US regions with different warming histories and quantified edges using a spatiotemporal model, I found notable regional differences: cold range edges did not always track temperature better than warm edges. Few species shifted as far as predicted by temperature alone, despite expectations that marine ectotherms will track temperature closely during periods of pronounced warming. 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, clarified the conditions under which marine species are expected to track climate change, and provided tools for managing range-shifting species.

BIO

Alexa Fredston-Hermann is a quantitative ecologist using data science, modeling, and synthetic approaches to tackle interdisciplinary environmental problems. Her focus is biogeography and climate change; she also researches coastal marine ecology and sustainable fisheries. Alexa previously worked at the Environmental Defense Fund, where she collaborated with stakeholders and managers to improve the economic viability of the West Coast groundfish fishery. She graduated summa cum laude from Princeton University with a BA in Ecology and Evolutionary Biology and a certificate in Environmental Studies.