Abstract

Determining how organisms respond, at a population-level, to novel environmental conditions is an important area of research in the rapidly changing Anthropocene. Many factors have been theorized to affect population-level responses, including the nature of the habitat change, the genetic characteristics of exposed populations, and the levels of plasticity populations exhibit across environments. Using a combination of meta-analytical techniques and empirical experimentation, my thesis examined the relative influence of genetic and environmental factors on population-level responses to novel environments. For Chapter 1, I conduct a meta-analysis using reciprocal transplants and common garden experiments in novel environments with known census population sizes (Nc) to test the effect of Nc on survival in novel environments. I found that large populations exhibited stronger local adaptation, but that this comes with potential trade-offs in novel environments. For Chapter 2, I conducted translocations of brook trout (Salvelinus fontinalis) to novel pond environments to test the relative importance of habitat and genetic factors (genomic diversity (Ho) and effective number of breeders (Nb)) on fitness correlates. I found that habitat overwhelmingly predicted performance, with little influence of genetic factors on performance in novel environments. For Chapter 3, I tested if phenotypic plasticity in body morphology was released in the Chapter 2 transplants and evaluated if released plasticity was correlated with Ho. I found limited evidence that phenotypic plasticity was released, and no evidence that Ho affected phenotypic diversity in novel environments. In Chapter 4 I evaluated whether Nb can be used to effectively monitor Nc in salmonids and found that, overall, it could not. Collectively, my research demonstrates that habitat is the primary predictor of fitness correlates in novel environments, with Nc, Nb, and Ho explaining little variation in performance or plasticity across studies. Our results provide evidence that small, low-diversity populations may often be capable of persistence and potentially adaptation, and further highlight the importance of conserving habitat. Furthermore, my research demonstrates that there is no “free lunch” – Nb cannot be used to “cost-effectively” monitor Nc in populations of conservation concern, which require actual census operations to monitor changes in Nc.