Passive uplift of montane biotas: recent advances

Passive tectonic uplift of populations is being discussed in a growing number of studies from many regions around the world, usually for areas that have undergone dramatic uplift in fold mountains (orogens). It is also proposed in belts of uplift along the margins ("shoulders") of rifts, as in south-eastern Brazil, West Africa and the rift mountains of Central and East Africa. Many groups show signs of having been left stranded inland with the retreat of inland epicontinental seas in the Cretaceous, consistent with the long-term persistence and passive uplift of populations in situ. Passive uplift provides a mechanism in which groups are elevated and also a mode of speciation that can help explain the anomalous, high diversity of areas such as the Andes ("Humboldt's enigma"). We suggest that one focus of future research could be on the location of elevational anomalies in species distributions. Studying these will require good information on the three-dimensional distribution of species, and this is still lacking for most groups. If these data were available, it would be possible to use niche models to identify populations at anomalous elevations.