Historical biogeography of the South American aridlands: A molecular phylogenetic study of endemic avian taxa

This dissertation explores the historical biogeography of the South American aridlands by performing comparative systematic and biogeographic analyses of several clades of birds. The introduction provides a summary of the geologic history of South America, and introduces the methodology, region, and taxa used. In the first chapter I use distributional and taxonomic information on Neotropical birds in a Cladistic Analysis of Distributions and Endemism (CADE) to generate a testable hypothesis of area-relationships for the arid areas of endemism, particularly those of Central South America (the “Arid Diagonal”). In the resulting hypothesis, the areas of the arid diagonal form a cluster, with the Cerrado and Chaco as sister areas, and the Caatinga as basal. These areas appear to be more closely related to the forest areas than to other arid areas such as Patagonia and the Central Andes. The CADE analysis also suggested that the two passerine suborders, the suboscines (Tyranni) and the oscines (Passeri), have had different biogeographic histories across the Neotropical areas of endemism. In the following three chapters, I use morphological and molecular data to generate updated taxonomies and new phylogenies for avian groups containing aridland endemics: the family Tinamidae, with a particular focus on three lineages of aridland taxa, and oscine ( Paroaria) and subsoscine (Pseudoseisura) genera. In the final chapter I use the five resulting phylogenies to obtain a general hypothesis of area relationships and compare it to previous hypotheses of area relationships, including the null hypothesis based on raw distributions. I explore the fit of each phylogenetic tree to the general area cladogram to estimate the relative roles of extinction, dispersal, and vicariance in the diversification of these clades. I find clear evidence of both dispersal and vicariance, with dispersal playing a minor role in the speciation of these taxa. The use of a rough molecular clock allows estimation of the age of some of the vicariance events. This work also illustrates the importance of using well-resolved, updated phylogenies and phylogenetic species for biogeographic investigation.