VICARIANCE AND DISPERSAL IN CARIBBEAN BIOGEOGRAPHY

The species diversity and phylogenetic relationships of West Indian vertebrates are incompletely known, but several lines of evidence support a dispersal origin for most of the fauna. Crother and Guyer have contested much of that evidence, claiming a far greater role for vicariance. However, it is shown here that none of their criticisms can be substantiated and their paper is dominated by inconsistencies. They have used the irrelevant evidence from intra-Caribbean vi- cariance events to address the origin of the fauna, failed to discriminate between old and new geologic syntheses by the same authors, chosen molecular estimates of divergence time randomly rather than with respect to phylogeny, attempted to diminish the consequences of a catastrophic event in Earth history (the K-T bolide impact), and have claimed to have discovered a congruent pattern of area relationships when in fact their proposed phylogenetic pattern is present in only a THE West Indies harbors a rich biota that has intrigued biogeographers for over a century. The numerous islands, some of which are of great age, and the complex geologic history of the region are factors that have influenced the evolutionary his- tories of these organisms to varying de- grees. In the two decades since Rosen (1975) proposed a vicariance model for Caribbean biogeography, attention has fo- cussed on determining the relative roles of vicariance and dispersal in the origin of the West Indian biota. The vicariance model proposes that the present biota rep- resents the fragmented remnants of an an- cient proto-Antillean biota that was con- tinuous with those of North and South America in the late Cretaceous. The al- ternative explanation is that over-water dispersal has been responsible for the or- igin of the West Indian biota (e.g., Pregill, 1981; Simpson, 1956). Hedges et al. (1992) tested these two hypotheses using estimates of amino acid sequence divergence in the protein serum albumin across a broad array of West In- dian terrestrial vertebrates: bufonid, hylid, eleutherodactyline, and leptodactyline frogs; anoline, iguanine, sphaerodactyline, tropidurine, teiid, and anguid lizards; am- phisbaenians; and alsophine and tropido- phiid snakes (inter-island divergences also