Biogeography and paleobiology

Abstract

In the past decade paleobiologists have applied the techniques of both ecological and historical biogeography, although vicariance/cladistic approaches have as yet had minimal impact. The traditional focus of paleobiogeographic study has been the province, a statistical entity defined by clusters of range endpoints of individual taxa. The study of such provinces has been useful in inferring past continental positions (although ambiguities remain that must be resolved using independent geological criteria) and in understanding the role of past global geographies in regulating biotic diversity through changes in the numbers and extent of provinces. This approach can be complemented by the treatment of geographic ranges of taxa as irreducible or emergent traits with far-reaching evolutionary effects upward and downward within a genealogical hierarchy. Temperature tolerances in benthic marine organisms appear to be by-products of selection for enzyme structures imparting favorable activity levels within the normal temperature range rather than direct products of selection for resistance to temperature extremes. Thus geographic range endpoints, which are also influenced by dispersal capability and the resulting scale of gene flow among disjunct populations, are not direct products of selection. However, the magnitudes of geographic ranges of species and clades behave as emergent properties and significantly influence taxonomic survivorship during background and mass extinctions in ways that are not extrapolations of effects at lower hierarchical levels. Biogeography shapes macroevolutionary patterns of origination and extinction during times of normal, background extinction and mass extinction. Preferential extinction among regions or among endemic rather than widespread clades can result in strong biases in the nature of the survivors of mass extinctions, with taxa being lost not because of selection against attributes of individual organisms but because of higher-order patterns of geographic selectivity.