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Many genetic patterns observed within and between species are often attributed to processes that affect interpopulation genetic exchange. These patterns are often taken as evidence of the genetic processes without explicit tests of the population genetic dynamics operating within species. The first chapter of this thesis uses a population genetic approach to test Wallace's riverine barrier hypothesis, a 150-year-old theory that has largely been based on interpretation of broad scale patterns rather than focused studies of the process. This work helps clarify the definitions of many riverine hypotheses and uses a Bayesian model comparison approach to test these hypotheses in Pseudacris feriarum, the upland chorus frog, along the Apalachicola-Chattahoochee River using eleven microsatellite loci. A flood model of gene migration best explains riverine effects in this species. This model is proposed as an alternative way to think about riverine effects on gene flow that should be tested more broadly. The second chapter of this thesis builds on previous observations of reproductive character displacement and its effects on speciation. A Bayesian model testing approach is used to determine if predictions based on female choice experiments lead to population differentiation. Eleven microsatellite loci are used to model gene migration across a region of reproductive character displacement. This approach provides evidence for the genetic consequences expected under a speciation cascade model of taxon diversification.