Integrating pattern with process at biogeographic boundaries: the legacy of Wallace

Biogeography is a vital discipline today because of its extraordinarily integrative nature, drawing from and informing biological and Earth sciences in order to explain the history and future of life on our planet. Yet, even as we continue to build more sophisticated syntheses using molecular genetics, GIS-based distribution modelling, and ever-better analytical and visualizing approaches, we should recall that exploring causal connections between biological and Earth history is not a particularly new endeavor. For example, the biogeographic principles advocated in the late 1800s by Alfred Russel Wallace (see Box 2.1 in Lomolino et al. 2006) were infused with ideas associating distributional and diversification histories of organisms with geology and climate. But even a century before Wallace, in 1761 Compte de Buffon had recognized the differences between mammals in the New World and Old World tropics and proposed a rudimentary evolutionary causation for their divergence and distribution based on separation of formerly united continents. Certainly, de Buffon and Wallace were not alone during their times in describing the non-random distributions of animals and plants, exploring causal explanations (see contributions reproduced in the ‘‘Early Classics’’ section of Lomolino et al. 2004), and recognizing regions of rapid transition between geographically distinct biotas. Wallace stood out, however, in the magnitude and synthetic nature of his focus on a single biogeographic boundary. After spending eight years exploring the mosaic of islands that lay between southeast Asia and New Guinea/Australia, Wallace concluded that ‘‘ . . .we may consider it established that the Strait of Lombock (only 15 miles wide) marks the limits and abruptly separates two of the great zoological regions of the world’’ (Wallace 1860, pp. 173 174). He called this region the Malay Archipelago and it includes the most famous biogeographic transition of all, named Wallace’s Line by T. H. Huxley in 1868. The four papers in this Special Feature were first presented in January 2009 in the ‘‘Patterns and Processes at Biogeographic Boundaries’’ symposium convened at the 4th Biennial Meeting of the International Biogeography Society in Mérida, México. Here, we develop a background to these papers (Cody et al. 2010, Daza et al. 2010, Morrone 2010, Smith and Klicka 2010) by summarizing several highlights in the historical focus of biogeographers on boundaries.