Doctor of Philosophy (PhD)


Renewable Natural Resources

Document Type



Characterizing population structure and genetic differentiation can inform the management of imperiled species and the relative influences of ecological and evolutionary factors on species evolution. One trait that is expected to influence the amount of population structure a species exhibits is vagility, or the ability to move across the landscape. Species with higher vagility may be more likely to disperse, potentially facilitating gene flow among populations and limiting population structure. My dissertation focuses on characterizing population structure in 2 imperiled sparrows that are both largely nonmigratory with broad distributions in eastern North America: Seaside Sparrow (Ammospiza maritima) and Bachman’s Sparrow (Peucaea aestivalis). Seaside Sparrow is restricted to tidal saltmarsh habitat that is temporally and spatially more stable than the fire-mediated pine savannas that Bachman’s Sparrow is closely associated with. As a result of these habitat differences these sparrows likely have differing vagility and exhibit different patterns of population structure. First, I describe the population structure of Seaside Sparrow and identify potential distinct population segments to inform future management of the species. Through comprehensive sampling of several thousand single nucleotide polymorphisms (SNPs) in 272 individuals from 24 sites across the species distribution, I identify 5 to 7 possible distinct population segments (Chapter 2). In the remainder of my dissertation, I focus on Bachman’s Sparrow and the population genetics and conservation implications of recent changes to its distribution. Through systematic review of several thousand occurrence records from historical field observations, natural history collections, and eBird I confirm that Bachman’s Sparrow experienced a rapid range expansion and subsequent retraction since the mid-1800s (Chapter 4). Finally, I infer population structure before, during, and immediately following the range expansion and modern time using approximately 1,000 SNPs sampled from 144 museum samples and 285 modern samples to determine if panmixia arose in Bachman’s Sparrow during the range shifts. I show that high gene flow is characteristic of Bachman’s Sparrow and not the result of recent range shift, but that recent anthropogenic landscape change results in barriers to dispersal that promote differentiation even in this highly vagile bird.



Committee Chair

Taylor, Sabrina S.

Available for download on Thursday, August 29, 2024