On a global scale, taxonomic and phenotypic diversity result from diversification and extinction operating across all levels of biological organization, from populations to species, communities, and biomes. At each of these levels, extrinsic mechanisms like climate are interacting with organismal traits like dispersal ability to shape global patterns of species diversity and to drive phenotypic evolution. This dissertation focuses on how global climate shifts and isolation on oceanic islands drive evolutionary processes and patterns of community assembly and how organismal differences in habitat use and breeding biology influence species responses to these shared global events. Reed frogs (Hyperoliidae) are an ideal group for asking questions about broad-scale patterns of diversification because there are over 200 species broadly distributed throughout sub-saharan Africa in rainforest, bushland and savannah habitats and there are at least two cases of overseas dispersal to oceanic islands. They also exhibit a number of unusual traits including sexual dichromatism, a form of sexual dimorphism where males and females are different colors, a diverse assortment of reproductive modes, and physiological adaptations for living in arid environments, which provides a rich framework for investigating the mechanisms that shape this phenotypic diversification as well as how these phenotypes mediate species' responses to environmental change. Chapter 1 describes the prevalence of sexual dichromatism in frogs (including Hyperoliidae) and outlines future lines of research for understanding the evolution and function of this unusual trait. Chapter 2 investigates potential dispersal routes for reed frogs that colonized the oceanic islands of São Tomé and Príncipe in the Gulf of Guinea. Chapter 3 uses population genomic approaches to characterize inter-island dispersal and in situ speciation in reed frogs endemic to the Gulf of Guinea islands. Finally, Chapter 4 employs a comparative phylogeographic study across three species of reed frogs that inhabit a spectrum of habitats to investigate mechanisms shaping diversification in the Guineo-Congolian forest of Central Africa and the land-bridge island Bioko.