Evolution can occur on ecologically relevant timescales, creating the potential for a bidirectional link between evolution and ecology. For example, migrating species provide important pulses of resources to recipient ecosystems, but are increasingly subject to intense selection due to ongoing global change. If heritable variation underlies migration, then contemporary evolution may increase non-migratory life histories, thereby increasing population persistence, but at the expense of important ecological processes. I examine contemporary evolution and its consequences of migration in an economically and ecologically important species, the resident and migratory ecotypes of the species Oncorhynchus mykiss. In Chapter 2, I show that a stream barrier has driven the evolutionary loss of the migratory ecotype in only ∼25 generations. I estimated the genetic contribution to variation in traits underlying the expression of migration and show that in the above-barrier population there has been a 30% decrease in expression of the migratory ecotype relative to the below-barrier population of origin. In Chapter 3, I examine the ecological consequences of this contemporary evolution. I show that the density decreases associated with loss of anadromy consistently had a greater effect on mesocosm ecosystems than the per-capita effects of the ecotypes. In Chapter 4, I use an analytical model to explore whether a population of O. mykiss would evolve toward greater residency in response to increased costs of migration. I find that evolution can rescue isolated populations; populations that persist are those that evolve in response to the changing selection regime on timescales that prevent population extinction. However, when conditions are restored to the pre-disturbance state, the rate of recovery of the migratory ecotype was unpredictable and generally slower than its loss. Finally, in Chapter 5 I review pathways for restoring the migratory ecotype, and how restoration of a life history may differ from restoring a species. Effective restoration of this life history will entail understanding the ecological and genetic mechanisms underpinning the expression of migratory behavior. Together, these chapters highlight that migratory barriers can drive contemporary evolution of the non-migratory ecotype that increases population persistence, but decreases their ecological impacts. More generally, this research highlights the importance of incorporating evolutionary perspectives in manage- ment, conservation, and restoration.
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Thesis advisor: Moore, Jonathan
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