Cheng, BrianBrodie, RenaeStaudinger, MichelleBradley, BethanyBarley, Jordanna M2024-04-262025-02-012024-022024-0210.7275/36515418https://hdl.handle.net/20.500.14394/19426Climate change is causing large changes to our species and ecosystems on physiological, evolutionary, and ecological levels. In addition, there is considerable spatial variability in global temperature changes, meaning that species, and populations of the same species, are experiencing vastly different rates of warming. Therefore, it is important to include population-level perspectives when researching the effects of climate change so that we can more precisely predict how species are going to respond in the future. In chapter 1, I use meta-analytic techniques to quantify the difference in thermal tolerance plasticity across populations of the same species. I provide evidence that populations with higher average thermal tolerances have limited thermal tolerance plasticity, likely because maintaining a high thermal tolerance comes with trade-offs. My results show that one trade-off is likely that populations lose their ability to change their viii thermal tolerance through plasticity. In chapter 2, I use a current range expansion of a salt marsh crab species into the Gulf of Maine to examine the possibility of spatial sorting as a mechanism for range expansion in marine systems. I provide possible evidence for the first observation of spatial sorting in marine systems. In addition, these results suggest that spatial sorting could be an important factor in marine range expansions in many coastal systems. In chapter 3, I examine why a similar crab species in the same system has not expanded its range at the same rate as other species in the Gulf of Maine. My results suggest that both temperature and spatial sorting are unlikely to be important in this species range edge dynamics. Instead, results on the larval behavior in this species provide a possible avenue for future research to determine this species’ range limit mechanisms. Together, these studies show that population level perspectives in research determining the effects of climate change are imperative to predicting how and if species are going to be able to respond and add to a growing body of research investigating the mechanisms that underlie these responses.Attribution-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nd/4.0/climate changepelagic larval durationspatial sortingrange expansionthermal tolerance plasticitylocal adaptationEcology and Evolutionary BiologyMarine BiologyDissertation (Open Access)https://orcid.org/0000-0002-2936-0670