“Time”: the neglected dimension in cladistic biogeography?

Abstract

The value of temporal data has been widely recognised in historical biogeography. Cladistic biogeographic methods, however, have not formally incorporated “time”. A theoretical perspective suggests that area and biotic relationships will change in a complex “reticulate” manner through time. This is because the disappearance of geographic barriers (and the concomitant mixing of biotas) is likely to occur as frequently as barrier formation and vicariance. A reticulate biogeographic history will consist of a chronological series of incongruent distribution patterns. Any attempt to depict such a reticulate history using a cladistic topology will inevitably lead to interpretational error and ambiguity. Temporal data, however, may allow incongruent spatial relationships to be “teased” apart, and may, therefore, play a vital role in rigorous analytical biogeography. A simple method for integrating “time” into cladistic biogeography is proposed and tested using a data-set on dinosaur phylogeny and distribution. The results indicate that large biogeographic data-sets can contain several genuine, but incongruent, sets of area relationships that combine to obscure each other. The new method (“temporally partitioned component analysis”) is an effective means of exploring a data-set for such signals, and allows time-specific area relationships to be detected. The proposal that temporal data should play an integral role in cladistic biogeographic analysis has major implications for area cladogram interpretation, and also enhances the value of fossil evidence.