© 1982 by The Society for Integrative and Comparative Biology
Geographic Differentiation, Cladistics, and Vicariance Biogeography: Reconstructing the Tempo and Mode of Evolution1
Department of A natomy, University of Illinois at the Medical Center Chicago, Illinois 60680 and Research Associate, Division of Birds, Field Museum of Natural History Chicago, Illinois 60605
SYNOPSIS. Although the literature on speciation is large, surprisingly little attention has been paid to methodological considerations. If there is a general methodology within this literature, it consists of delimiting taxa and their distributions, describing patterns of phenotypic (and occasionally genotypic) variation, noting contact zones and hybridization, reviewing information on past climates and vegetations, and from these constructing a narrative scenario of the pathway of speciation. However, two kinds of knowledge, essential for reconstructing speciation, are typically lacking: a genealogical hypothesis of the relevant taxa based on cladistic analysis, and a hypothesis of the interrelationships of areas of endemism based on vicariance biogeography. Both are necessary to develop and test alternative hypotheses about the mode of taxonomic differentiation. A model of speciation analysis is constructed using taxa of Australian birds as the empirical data base. Cladistic relationships among taxa and vicariance patterns among areas of endemism reveal a specific, nonrandom historical relationship among the areas of differentiation for Australian birds and suggest that type la allopatric speciation (of Bush, 1975) is more common than type lb, that peripheral isolates are less important than previously maintained, and that parapatric speciation is rare. The model can also be used to examine the patterns of concordance between phenotypic and genotypic characteristics during geographic differentiation and to investigate their relative and absolute rates of change.