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John R. Holsinger and David C. Culver 
Valley in Virginia were resistant to invasion, but two-species communi- 
ties often were not. In the Powell Valley, L. usdagalun successfully 
invaded a C. recurvata - C. antennatus community in Gallohan No. 2. 
On the other hand, L. usdagalun in Thompson Cedar Cave is resistant 
to invasion by L. recurvata, which is limited to a small section of stream 
near the entrance. Both of these events are in agreement with the theory. 
Salamander predators can have a large effect on species diversity. 
In McClure Cave, relative density of C. antennatus increases near G. 
porphyriticus larvae, primarily because its competitor C. recurvata is 
also preyed upon. Refugia ensure the persistence of both prey. In Sweet 
Potato Cave, G. porphyriticus eliminates C. recurvata from rimstone 
pools, but C. antennatus escapes predation by burrowing (Holsinger 
and Dickson 1977). In pools without salamander larvae, both prey spe- 
cies persist. 
Flooding has a major impact on both aquatic and terrestrial fauna. 
Caves where water slowly recedes following regular flooding often have 
a very rich terrestrial fauna as a result of the detritus left by receding 
waters. Although no quantitative data are available, caves that have 
much detritus often have a diverse fauna (Table 3). On the other hand, 
caves that flood have a depauperate aquatic fauna. In a study of caves 
of the Greenbrier Valley in West Virginia, Culver (1970) found that 
caves that flood have 0.5 amphipod and isopod species (s = 0.7, n = 13), 
while caves that do not flood have 2.3 species (s = 1.1, n = 15). 
Finally, the island-like nature of caves has two important effects 
(Culver 1976). First, the mean number of peracarid crustaceans is less 
than the predicted three due to continuing extinctions. Second, the 
regional faunal diversity is enhanced because patchiness allows coexist- 
ence of competitors. 
ZOOGEOGRAPHY 
Drainage Basins and Regional Cave Faunas 
The Appalachian Valley and Ridge in Virginia and northeastern 
Tennessee is drained by seven major river systems or drainage basins as 
indicated in Figure 2. Because each basin is well defined geographically 
and contains topographically confined karst areas with a unique 
assemblage of endemic cave species, we have chosen to treat them as 
regional cave faunal units for the purpose of analyzing and discussing 
zoogeographical relationships. Although some of the divides and inter- 
fluves that separate these basins contain carbonate rocks (limestone and 
dolomite) as indicated below, as a rule the major part of each basin is 
enclosed by clastic rocks. The faunal units, which correspond to drain- 
age basins of the same name, are: (1) Shenandoah, (2) James, (3) Roa- 
noke, (4) New, (5) Holston, (6) Clinch, and (7) Powell. A very small 
cavernous area in northern Highland County drained by the South 
