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83 Biogeography is the scientific discipline that seeks to understand the distribution of animal and plant life on earth. As a fundamentally integrative, multidisciplinary field, biogeography has both historical and predictive powers. Such varied fields as climatology , ecology, geology, phylogenetics, and physiology contribute to our understanding of why species naturally occur where they do, providing the most complete picture obtainable of how and where biodiversity is generated as well as how and where it is lost. In recent decades it has become evident that if we are to understand the patterns of natural distributions of organisms on earth, we need to begin to elucidate the processes driving these patterns. Islands have played and continue to play key roles in revealing the mechanisms that influence species diversity and distributions. The biotas of the thirty thousand islands of the Pacific (Spiess 2007), more islands than are found in the Indian and Atlantic Oceans combined, have been central to biogeography since the eighteenth century when Captain Cook and his ships’ companies began the exploration of the Pacific, returning to Europe with specimens of strange and previously unknown organisms. A century later, the inferences made independently by Charles Darwin and Alfred Russell Wallace greatly heightened scientific interest in the unique flora and fauna of islands. Ultimately these insights sparked the birth of island biogeography, an important field that focuses on the natural history, biodiversity, and conservation of life on islands. Today Pacific Island biogeography continues to contribute in major ways to our understanding of biodiversity. The birds of New Guinea served as model organisms for Mayr’s (1942) groundbreaking definition of allopatric speciation. The ants of Melanesia were key players in Wilson’s Taxon Cycle (1961) and MacArthur and Wilson’s Theory of Island Biogeography (1967). The finches of the Galápagos (Grant 1986) and the Hawaiian honeycreepers (Freed, Conant, and Fleisher 1987), spiders (Gillespie 2004), moths (Rubinoff 2008), and silverswords (Baldwin and Sanderson 1998) provide classic examples of adaptive radiations. Pacific Island tree snails are important to ongoing biodiversity research and to conceptsofspeciationwithoutadaptiveradiationandinsularendemism (Gulick 1890; Clarke and Murray 1969; Holland and Hadfield 2002, 2004; Lee et al. 2007; Cowie and Holland 2008). In addition to dozens of studies focusing on Pacific Island biogeography published in recent years, important compilations of studies and reviews include the seminal book Hawaiian Biogeography: Evolution on a Hot Spot Archipelago (Wagner and Funk 1995) and more recently a special issue of the Philosophical Transactions of the Royal Society (Trewick and Cowie 2008), commemorating the 150th anniversary of Darwin ’s publication of On the Origin of Species and the bicentennial of his birth. These works showcase recent molecular approaches to biogeographic studies of terrestrial Pacific Island radiations. Although we are still addressing some of the same questions the pioneers in the field of Pacific Island biogeography posed starting in the late eighteenth century, thanks to new sets of powerful molecular tools the field has been reinvigorated and a number of these fundamental questions are beginning to yield answers: How do animals and plants arrive on islands? Why are island species so different from their continental ancestors? How do a few colonizing species diversify into dozens over time? What is the pace of speciation on islands versus continental environments? In this chapter, trends in island distribution patterns and some of the mechanisms that explain these observations are discussed and distinguished, to highlight differences in pattern and process among insular island biotas and those of the continents, both terrestrial and marine. Recent commentaries (e.g., Cowie and Holland 2006; Trewick, Paterson, and Campbell 2007) have highlighted the need for a shift toward more integrated studies if hypotheses about the evolution of island biotas are to be adequately addressed. The application of molecular approaches to biogeography has enhanced our ability to understand patterns in biodiversity and diversification. With increasing confidence and precision, biologists can explore topics such as relative roles of vicariance and dispersal in island species diversification, and geographic sources, pathways, and timing of island colonization events. A molecular approach enables researchers to delineate precisely and quantitatively the spatial extent of endemic species distributions, species boundaries, and hierarchical systematic relationships among lineages from proximate islands, distant islands, and continents and islands. Importantly, molecular phylogenetics has enabled testing of evolutionary hypotheses including those that were first stimulated by observations of the island faunas. We conclude the chapter with a brief discussion of human impacts and conservation considerations. The tremendous number of recent studies employing a DNA approach to island 7 Biogeography Brenden...

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