A Vicariance Model of Caribbean Biogeography

Caribbean biogeography is reviewed to illustrate within a particular geographic framework how evidence of plant and animal distribution may be interpreted without commitment to special assumptions other than allopatric speciation (vicariance). The distributional data are examined with respect to whether or not they form recognizable patterns within the Caribbean region. Four main patterns and one lesser pattern are identified. The patterns or generalized distributional tracks are regions or geographical features (e.g., islands, coastlines, oceanic and continental regions) in which the distributions of monophyletic groups of diverse organisms are coincident. The generalized tracks are compared with geophysical theories of Caribbean history. The one geophysical theory which is strongly consistent with the distributional evidence (generalized tracks) specifies that Antillean land was originally or had its origin as part of an early lower Central American archipelago that was later replaced by the tectonically and topographically similar, presentday, lower Central American land. The postulated events associated with this replacement involve continental drift, the main effect of which would have been to intrude a portion of the eastern Pacific sea floor into the tropical western Atlantic, carrying the early lower Central American archipelago with it. The hypothesized intruded sea floor, now forming the Caribbean Sea, is bounded on the north and east by a transposed, original archipelago, the Antilles, and on the west by a new archipelago, now represented by the continuous land of present-day lower Central America. The separate parts of each generalized track are interpreted as the remnants of an ancestral biota that underwent geographical fragmentation followed by allopatric speciation (vicariance). This vicariance model of Caribbean biogeography specifies where dispersal, rather than vicariance, is the most parsimonious interpretation of a particular individual distribution, and contrasts strongly with other biogeographic interpretations in which dispersal is assumed aprioristically to be the sole, or single most important, feature of Caribbean biotic history. The vicariance model is also shown to predict, and therefore to be tested by, phylogenies (cladograms) of geographically included taxa. Biogeography; Caribbean; vicariance; continental drift; plate tectonics.