vol. 155, no. 4 the american naturalist april 2000 Detecting the Geographical Pattern of Speciation from Species-Level Phylogenies Timothy G. Barraclough 1,* and Alfried P. Vogler 1,2,† 1. Department of Biology and Natural Environment Research Council Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berkshire SL5 7PY, United Kingdom; 2. Department of Entomology, Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom Submitted September 9, 1998; Accepted October 24, 1999 abstract: We introduce a general approach for investigating the role of geography in speciation, based on analyzing the geography of sister clades across all nodes in a species-level phylogeny. We examine the predictions of allopatric, sympatric, and peripatric mod- els of speciation in several animal groups, using patterns of range overlap and range size symmetry between sister clades. A simple model of cladogenesis incorporating random movements of species’ ranges is used to illustrate the effects of range changes on expected patterns. We find evidence for a predominantly allopatric mode of speciation in our study groups, with sympatry arising through post- speciational range changes. In addition, we find that relatively recent speciation events are characterized by greater asymmetry in range size between sister clades than expected under our null models, pro- viding potential support for the peripatric model of speciation. We discuss the possible confounding effects of postspeciational range changes on our conclusions. Keywords: speciation, diversity, null models, biogeography, modes. The molecular revolution in phylogenetics has provided new sources of information for the study of evolution and macroecology, answering questions that were difficult to address until recently (Lutzoni and Pagel 1997; Omland 1997; Bleiweiss 1998; Farrell 1998; Losos et al. 1998). One area gaining new vitality from this information is the study of speciation. Phylogenies represent the pattern of clad- ogenetic splits leading to present-day species and may pro- vide a trace of processes involved in the origin of those * E-mail: t.barraclough@ic.ac.uk. † E-mail: a.vogler@nhm.ac.uk. Am. Nat. 2000. Vol. 155, pp. 419–434.  2000 by The University of Chicago. 0003-0147/2000/15504-0001$03.00. All rights reserved. species (Nee et al. 1996; Purvis 1996; Sanderson and Don- oghue 1996; Barraclough et al. 1998, 1999a). Hence, pub- lication of large numbers of species-level phylogenies will provide the opportunity for a comparative biology of spe- ciation across a range of groups. However, this approach involves reconstructing past events, and so it is important to consider how changes occurring since speciation events influence our ability to infer the pattern of speciation (Mayr 1963). In this article, we investigate one particular issue, namely the use of species-level phylogenies for in- vestigating the role of geography in speciation. Geography is widely recognized as the key factor in the study of speciation. The primary classification of specia- tion, into so-called geographic modes, is based on the pattern of geographic ranges seen among daughter species (Mayr 1963; Bush 1975; Templeton 1981). However, the theoretical and empirical basis for different modes remains controversial, with particular emphasis on two issues. First, there is the question of whether geographical isolation is necessary for the formation of new species, resulting in debate over the relative frequencies of allopatric and sym- patric speciation (Mayr 1963; Maynard Smith 1966; Ro- senzweig 1978; Bush 1994; Doebeli 1996; Duffy 1996; Johnson et al. 1996; Shoemaker and Ross 1996). If allo- patric speciation is the predominant mode, then we need to explain the subsequent origin of sympatry within clades. Second, within the context of allopatric speciation, many authors advocate the importance of small, founder pop- ulations in the process of speciation (Mayr 1963; Carson and Templeton 1984). This view is manifest in the pre- diction of the peripatric theory of speciation that new species tend to form as small range fragments around a widely distributed ancestral species. An alternative view is that speciation is caused by geographic features that split a species’ range and that these may arise at any point within the ancestral species’ range. Active debate over these two alternatives persists to the present day (Barton and Charlesworth 1984; Rice and Hostert 1993; Coyne 1994; Moya et al. 1995; Slatkin 1996, 1997; Templeton 1996; Charlesworth 1997). The original evidence for these discussions was based