The Amazon basin has high biodiversity and is an ideal region in which to examine geographic influences on species diversification. Large Amazonian rivers are known to act as barriers that separate genetically distinct populations of related birds (species pairs or different subspecies). Rivers, however, cease to act as barriers in their headwaters, where many pairs of otherwise divided populations of birds come into contact. The aim of this study is to explore both the role of rivers as barriers to gene flow (phylogeographic breaks) and the rivers' headwaters as meeting points (contact zones) using 90 pairs of species or subspecies of birds. This research will pioneer a comparative multi-species approach to study bird distributions and species interactions in remote regions of the Amazon, focusing on plumage characters and molecular data. This study will address long-standing questions in evolutionary biology, including the role of physical and ecological barriers in the geographic location of contact zones, the role of rivers as historical and contemporary barriers to bird species (the "Riverine Barrier" hypothesis), and the relationship between genetic distinctness and the likelihood that two populations will interbreed when in contact.
This project relies on close cooperation between American, Brazilian, and Venezuelan institutions. Fieldwork in Amazonia included Brazilian students and assistants, who were introduced to museum-based studies of biodiversity. This project is likely to lead to long-term collaborations with South American scientists. Understanding how physical barriers prevent gene flow will help understand the consequences of large-scale human-created fragmentation on natural populations.
