Speciation in Cave Faunas

Speciation in obligate cave faunas typically follows patterns reminiscent of faunas of other discontinuous habitats, such as islands, mountaintops, or desert springs (6, 95). Where cave systems are separated by frequent extrinsic barriers, as in the Appalachian Valley and Ridge province (i.e. the Appalachian Valley) of the eastern United States, many endemic species with small geographic ranges may occur ( 13, 74), but in terranes with extensive exposures of undisturbed cavernous limestones, as in the Mississippian plateaus farther west, fewer and more widely ranging cave species exist per unit area of exposed karst (4, 6). Cave speciation studies have not yet been integrated with the growing body of theory of island biogeography (92, 137), in part because progress in taxonomy of cave species has traditionally lagged behind that of most island species, but also because the degree to which various caves and cave systems are isolated from each other has not always been clear (18, 48, 49, 51, 52). Other factors to be considered in comparing caves with islands include (a) dependence of cave communities on allochthonous, epigean food sources (20); (b) dispersal of many aquatic and some small, terrestrial obligate cavernicoles widely through subterranean spaces in nonlimestone regions; and (c) separation (or not) of caves by extrinsic barriers to gene flow (and possible circularity of reasoning in determining this) (4, 6, 10, 13). The physical environment in both temperate zone and tropical caves and its implications for cave speciation have been reasonably well described (6, 20, 77). Remote from entrances, deep portions of caves are dark, with fairly