An intense concentration of biodiversity, combined with complex yet well-understood geologic and climatic histories, make the Philippines an ideal system for phylogeographic studies. This research will evaluate the relative effects of Pleistocene climate changes, geological history, and complex topography on the process of diversification in a suite of island bird species. The project integrates diverse sources of data, including mitochondrial and nuclear DNA sequences, earth history data, spatial modeling, ongoing field research, and study of museum collections. The results of this study will broadly apply to questions of how periodic climate-associated sea level changes influenced diversification and the geographic distributions of organisms in island systems.
The Philippines is considered a "megadiverse country" and a "global conservation hotspot", yet traditional recognition of bird species has greatly underestimated diversity and obscured biogeographic patterns. Gene flow estimates from this study will provide an interesting new perspective on species limits across an island archipelago, and will likely elucidate novel evolutionary patterns and highlight under-appreciated centers of avian endemism in the Philippines. The project will also provide opportunities for undergraduates at the University of Kansas to gain experience in biodiversity research techniques, including DNA sequencing and analysis, and to develop research skills such as scientific writing and public presentation.
A long-held view in avian biogeography states that birds do not diversify within oceanic islands, because islands do not posses suitable geographic features to isolate populations--- the first stage of the speciation process. Furthermore, during Pleistocene low sea level stands, islands separated by shallow seas became connected, forming larger conglomerate islands. Hence, these "Pleistocene aggregate island complexes" are thought to show similar biogeographic patterns to single islands. However, these ideas of how birds diversify on island archipelagos are relatively untested with genetic data. To investigate the relative roles of different classes of geographical barriers (permanent marine barriers, intermittent marine barriers, and environmental barriers) in the isolation and subsequent diversification of insular birds, we inferred the evolutionary relationships of 20 avian groups from the Philippine archipelago with DNA sequence data. We determined that marine barriers alone explain only a portion of the diversification events in Philippine birds, and that current-day environmental barriers, paleo-environmental barriers, and complex topography acted in concert to produce the avian diversity of the Philippines. Specifically, we identified a group of sunbirds that diversified in montane sky-islands within the single island of Mindanao, and that environmentally unsuitable habitats during Pleistocene low sea levels isolated birds long-term across a putative Pleistocene land bridge. Congruence between molecular markers and plumage characters support that avian taxonomy in the Philippines is extremely conservative, and most Philippines species would be more appropriately treated as sets of allopatric evolutionary lineages, rather than widespread polytypic species. Using molecular markers and plumage characters as criteria, our results suggest that Philippine forest bird species numbers may be underestimated by 75%. Such underestimation of diversify can confound evolutionary and macroecological studies, and has strong conservation implications. Many species once thought to be widespread are actually sets of range-restricted endemic species, likely of conservation concern. Additionally, Several additional areas of avian endemism should be recognized for practical conservation and management purposes: the Eastern Visayas, Bohol, and the Zamboanga Peninsula. In addition to the scientific findings, this project provided undergradutate training in DNA sequencing techniques, phylogenetic analysis, and preparation of scientific manuscripts.