GEOGRAPHIC ORIGIN OF SPECIES: THE TEMPERATE-TROPICAL INTERCHANGE

The tropics are often evoked as a center for species origination. Foraminifera are one of the few groups of organisms with a sufficient fossil record to establish the geographic origin of species. The modern foraminiferal biota on the Atlantic continental margin of North America contains 259 species with a fossil record. The world-wide geographic origin of these species was documented using museum collections. Only 14% of these species originated in the subpolar regions whereas nearly equal proportions originated in the temperate regions (46%) and tropical regions (40%). Moreover, the majority (76%) of species originating in the temperate regions now also occur in the modern tropical biota. These data suggest that the biota of temperate and tropical latitudes act in concert with a substantial species interchange between them.