Perspective: Phylogeography is not enough: The need for multiple lines of evidence

Abstract

perspectives ISSN 1948-6596 Phylogeography is not enough: The need for multiple lines of evidence A. Townsend Peterson Biodiversity Research Center, The University of Kansas, Lawrence, Kan- sas 66045 USA e-mail: town@ku.edu; http://specify5.specifysoftware.org/Informatics/ bios/biostownpeterson/ Figure 1. Temperature and precipitation fluctuations over the past 135,000 yr: shown are annual mean temperature profiles (all on the same scale) for the present day, Last Glacial Maximum (21,000 yr ago; CCSM scenario), and Last Interglacial (135,000 yr ago; Otto-Bliesner et al. 2006). The 10 shading classes cover equal intervals between -50° and +31.5°C. Last Glacial Maximum Present day date translated into detailed analyses of key events structuring biogeographic patterns in many phylogeographic analyses. In particular, the Pleistocene was character- ized by a complex series of warm periods (similar to present-day climates) and cold periods (“ice ages”), with impressively short transitions in be- tween (Figure 2; Dansgaard et al. 1993). Although considerable attention has focused on the last of the glacial maxima (~21,000 yr before present), in reality, all of these alternating periods of warm and cold climates probably had some influence on present patterns of diversity and distribution of biodiversity (Svenning and Skov 2004). The pur- pose of this commentary is to reflect on likely ef- fects of such repeated and dramatic global climate fluctuations in shaping patterns of distribution of species, and to emphasize the need for broader Last Interglacial The concepts of equilibrium and stability in bio- geography are perhaps much more fleeting than has generally been appreciated, and disequilib- rium may actually rule the situation in most cases (Manning et al. 2009). That is, although research- ers may discuss current distributional patterns as fixed, those patterns may have been in place only for a relatively short period of time (~10 4 yr), per- haps since the last major global cool period at the end of the Pleistocene (Figure 1). Although Pleis- tocene climatic fluctuations have been considered a major force in biogeography, and some have argued that they may have produced much of cur- rent species diversity (Mengel 1970, Haffer 1997), the validity of the Pleistocene speciation paradigm has been debated hotly recently—see, e.g., Klicka and Zink (1997) versus Weir and Schluter (2004). “The Pleistocene” is often cited as a bio- geographic force, but too often uncritically and without full consideration of the complexity of world climates over the past million years. That is, molecular systematists frequently use molecular “clocks” that date splitting events imprecisely, usually with confidence intervals so broad as to inspire concern (Peterson 2007); these studies often refer to Pleistocene climatic fluctuations, but with no specifics, although the ability to date splitting events may improve with broader use of population-genetic approaches to the challenge (Arbogast et al. 2002). This general appreciation of the role of Pleistocene climatic fluctuations as im- portant biogeographically nonetheless has not to frontiers of biogeography 1.1, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society