9419645 Ricklefs This research will test the hypothesis that ecological relationships of populations evolve in consistent directions with increasing age, and these changes ultimately result in increased probability of extinction through restricted habitat breadth and reduced population size. To address this hypothesis, the investigators will use an historical and evolutionary approach. The research will focus on land bird populations of the West Indies. Previous work has suggested that older populations exhibit restricted habitat breadth and reduced population size, and have higher risk of extinction, than do younger populations. In this study, evolutionary age of an island population will be estimated by the genetic divergence between it and the most closely related sister population on a neighboring island or on the continent. Each population provides a time-slice through evolutionary trends of long duration. The chronological sequence of populations will allow reconstruction of historical trends in habitat breadth, population density, and genetic diversity that apply generally to small land birds, and to examine their consistency across taxa. This research will allow us to gain a better understanding of ecological and evolutionary processes associated with species extinction. A better understanding of extinction processes of birds on islands can provide the framework for conservation of declining populations of species in an increasingly fragmented landscape through the US and the world.
