A Method of Analysis for Historical Biogeography

ments involves converting a hypothesis about the interrelationships of taxa (a cladogram indicating relative recency of common ancestry) to one concerning the interrelationships of areas (a cladogram indicating relative recency of common ancestral biotas). The generality of the area hypothesis may be tested by comparison with other groups endemic to the relevant areas. If the area hypothesis is corroborated as general, a statement of the relative recency of interconnections among areas is obtained, and evidence from historical geology may allow us to specify the nature of those interconnections and thereby the cause of those distributions that conform to the general pattern. Analysis of four-taxon statements indicates that the availability of structurally different patterns and of groups that can serve as adequate tests of the generality of those patterns increases with the addition of taxa to the hypothesis, and that neither extinction nor the failure of some groups to respond (by speciating) to given dispersal or vicariance events interferes with the analysis. [Biogeography; dispersal; vicariance.]