Parsimony in Vicariance Biogeography: A Quantitative Method and a Greater Antillean Example

Abstract

-The principle of the common cause and a background theory concerning the dependence-independence of the events responsible for allopatric lineage splitting are used to justify the concept of parsimony in the study of vicariance biogeography. A quantitative vicariance method is formulated, which in many respects is analogous to numerical cladistics. Syntaxon, the unit of evidence, is a composite of sister lineages which occupy two or more different areas of endemism. A new coding/weighting scheme also allows sympatric terminal taxa to be used in the analysis. Widespread terminal taxa and those missing from recognized areas of endemism are not considered relevant sources of evidence, and they are scored in a neutral manner. A Greater Antillean example illustrates the vicariance methodology. Five taxonomic sources of evidence, including boid snakes belonging to Epicrates, suggest the following biotic history: (mainland ((Cuba, Jamaica) (Hispaniola, Puerto Rico))). [Biogeography; coevolution; dispersal; Epicrates; Greater Antilles; missing taxa; phylogenetic systematics; sympatric taxa; vicariance; widespread taxa.] ... I believe that we shall not develop an analytical historical biogeography until we can codify biogeographic method in some simple phrase like interpret the distribution of homologies parsimoniously [Colin Patterson, 1981:449] My interest in historical biogeography was sparked by the publications of Gareth Nelson, Norman I. Platnick, and Donn E. Rosen (see review of their work by Humphries and Parenti, 1986). Their research, and especially that of Rosen (1976, 1978, 1985), is identified with many fundamentals. For example, vicariance explanations should be exhausted before appealing to dispersal, and taxonIarea cladograms, as provided by phylogenetic systematics, are essential. Dispersal is a universal proposition, because it can explain patterns and non-patterns alike, and some dispersal explanations are quite reasonably thought to be implausible. Still, it must be admitted that historical biogeography is without a coherent theory (Wiley, 1988), and it was Patterson's epigraph (1981; see above) that provided the impetus for me to seek a protocol corresponding in as many ways as possible to phylogenetic systematics. As I looked beyond the maxims of historical biogeography it became obvious that others had already identified some of the correspondences alluded to by Patterson (1981). The most significant of these contributions regarding parsimony and vicariance were made by Brooks (1985), Mitter and Brooks (1983), Patterson (1981), Rosen (1985), and Wiley (1987). Thus, the theory and method of vicariance biogeography that I describe below should be viewed as largely a repackaging of these authors' special insights. In addition to the synthesis that I attempt, my particular contributions may include the special treatment of sympatric, widespread, and missing terminal taxa as sources of evidence, and formulating a common cause justification for par-