Avian diversification across space

Two main processes drive the evolution of birds across space: dispersal and vicariance (the appearing and disappearing of landscape elements that separate or join populations). These two have often been viewed as contrasting viewpoint, but I find they often act in concert to shape diversification. In the first two chapters, I investigate the geographic spread of lineages of two North American bird species; one northern species that shows unusually high genetic diversity in its northern range because of the mixing of a number of populations that were separated during the last Ice Age, and one widely occurring species known for extensive movements, that apparently erase genetic diversity at the fringes of its range through gene flow. Then, I investigate the correlation between the diversification of a group of poorly known open-country birds and major geological events affecting open landscapes. Most speciation in the group is associated with long-distance dispersal, while in continuous blocks of grassland habitat, little genetic structure exists, likely through gene flow. Finally, I focus on the diversification of all songbirds across elevations in the world’s mountains using a novel R package. I find that elevation per se does not cause differences in the speed of the buildup of diversity, but high diversity at lower and elevations can be explained through these elevations offering a stable stage for a large part of the evolutionary history of songbirds. Speciation events from high mountains to low elevations and vice versa are rare.