Understanding how genetic and demographic factors affect establishment, adaptation, and persistence of small populations in changing environments is a critical question in fundamental and applied ecological and evolutionary research. My dissertation addresses this question using observational data, experiments, and modeling in three separate studies of plant populations. Chapter 1 investigates divergence of two ecotypes of prairie sunflower in the face of gene flow. This study is relevant for understanding persistence as populations differentially adapt in response to changing and novel habitats. To understand how divergence is maintained, and if each ecotype is expected to persist, I analyze genomic sequence data in combination with demographic data from a reciprocal transplant experiment. I found that i) divergent adaptation is maintained via habitat and life stage specific-selection. And ii) different life history strategies in neighbouring ecotypes appear to have evolved by optimization of different fitness components, which in turn contribute to the persistence of each ecotype in its respective habitat. Chapter 2 investigates the effects of increased genetic variation on population performance across a range of environments. I quantify these effects by using experiments that compare the performance of high versus low genetic diversity lineages of prairie sunflower in plots that vary in biotic and abiotic environmental conditions. My results show that high diversity lineages have either improved average performance, lower sensitivity to environmental variation, or both. Chapter 3 focuses on the development of an analysis method to improve demographic modeling of threatened species when datasets have gaps through time. I validate and apply this method to investigate the dynamics of a rare, endemic plant species; Brandegee's buckwheat. By modeling vital rates, from data with missing years, and their dependence on annual climate, and building an integral projection model, I found that i) this approach can successfully assess current and predict future population viability from data with multi-year gaps. And ii) the focal population of this species is at risk of extirpation, but population dynamics vary considerably across small spatial scales within the population. Together these three projects provide empirical examples of how genetics and environment contribute to population establishment, adaptation, and persistence.</p
