Climate, abiotic factors, and the evolution of subterranean life

Climate, and more generally the physical conditions in caves and other subterranean habitats have a profound influence on the biota. At longer time scale (centuries), climate change can force and/or isolate species in subterranean habitats. Not only Pleistocene climate changes, but earlier ones as well, such as the Messinian salinity crisis were important in this regard. While many speleobiologists assume that caves are nearly constant environmentally and with scarce organic carbon, this is not the case, especially in non-cave subterranean habitats. Many shal- low subterranean habitats, such as epikarst, seepage springs, and talus harbor highly modified organisms, ones without eyes and pigment and with elongated appendages. Yet these habi- tats are highly variable with respect to temperature and other environmental factors, and often have high levels of organic carbon. Overall, the role of these shallow subterranean habitats in the evolution and biogeography of subterranean species may be crucial. On smaller spatial scales, environmental differences, such as differences in chemistry of epikarst water, may be im- portant in allowing large numbers of species to coexist.