Doctoral Dissertations

Date of Award

5-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Benjamin M. Fitzpatrick

Committee Members

Brian Omeara, Benjamin P. Keck, Augustus Engman

Abstract

Anthropogenic impacts such as overlogging and the introduction of nonnative species threaten native species' habitats. These forms of habitat degradation fragment populations across their historical ranges, reducing connectivity and creating isolated populations. Species reintroductions are a common conservation tool for restoring native species to their historical habitats after local extirpation caused by human activity. However, because many of these populations are isolated, fragmented, and often small in density, reintroductions require multiple source populations for initial stocking. In the Great Smoky Mountains National Park (GRSM), native Brook Trout (Salvelinus fontinalis) have lost 75% of their historical habitat due to extreme overlogging and the introduction of Rainbow Trout (Oncorhynchus mykiss). Contemporary populations persist in isolated headwater streams with little connectivity. Park management implemented a reintroduction program using wild, native fish (rather than hatchery-reared fish) to restore Brook Trout to their historical distribution. However, using multiple source populations raises key concerns. Our research addresses three critical questions related to population mixing in reintroductions: (1) How well and evenly will source populations mix genetically? (2) How do physical barriers impact the mixture of sources? (3) How long have source populations been isolated, and does this exceed general guidelines for outbreeding concerns? In the first chapter, we reanalyze a 20-year-old dataset from one of the earliest reintroductions, which initially suggested assortative mating among three source populations in the restored site. We found that these conclusions were premature. After 23 years, the restored population showed no signs of assortative mating, with all three ancestral sources evenly represented. In the second chapter, we examine a reintroduction that inadvertently created a one-way migration scenario, leading to genetic swamping by one of the source populations. We use this case to highlight the importance of considering post-reintroduction dispersal. Lastly, we estimate isolation times between populations and compare our findings to the 500-year threshold, a general guideline for the maximum isolation period before mixing populations. Together, our findings emphasize the importance of careful source population selection, post-restoration genetic monitoring, and long-term planning to ensure the resilience of restored populations. These insights provide valuable guidance for future native species reintroductions

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