SPECIES DENSITY/Krrr * 10' 
Invertebrate Cave Fauna 
121 
CAVE DENSITY/Km 2 » 10' 2 
Fig. 37. Relationship of species density to cave density in the seven drainage 
basins of the study area. Regression line calculated by least squares method. 
Drainage basins: S = Shenandoah; J = James; R = Roanoke; N = New; H = 
Holston; C = Clinch; P = Powell. 
The geological structure of an area, then, appears to play a signifi- 
cant role in determining the diversity of cave species. There are appar- 
ently several complex, interrelated reasons for this. First, large areas of 
continuously exposed, cavernous limestone would increase the oppor- 
tunities for invasion of subterranean habitats by surface ancestors of 
cavernicoles; expand the potential for dispersal by hypogean species fol- 
lowing cave colonization; increase potential habitat space in the form of 
cave passages and solution channels, thus allowing additional coloniza- 
tions and, subsequently, the development of complex communities as 
the number of species increased; and increase the accessibility of caves 
to trogloxenes and troglophiles, which periodically introduce food 
underground. Second, well-developed karst terranes, characterized in 
the Appalachians by numerous sinkholes, blind valleys, sinking streams, 
bare limestone outcrops, and springs, would provide accessible avenues 
for the invasion of subterranean habitats by surface ancestors, greatly 
facilitate the movement of organic nutrients into subterranean channels, 
and increase the hydrological complexity of subterranean groundwater 
systems. 
Regional terrains and the potential for cave and karst development 
in the seven drainage basins have already been characterized briefly, and 
