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John R. Holsinger and David C. Culver 
unrecognized sibling species. In any case, they complicate interpretation 
of the results. The third reason for limiting the analysis is that aquatic 
troglobites frequently inhabit caves and interstitial or non-cave karstic 
waters simultaneously. 
The lists of basin endemic terrestrial species are given in Tables 5 
through 11, and various area measurements for the drainage basins are 
given in Table 15. The primary basis for choosing between regression 
models is whether the residuals after regression show any systematic 
pattern (see Sugihara 1981). However, the residuals of neither equation 
(1) nor equation (2) show any systematic bias, which is not surprising 
given the small number of points. A secondary criterion, how much of 
the variance in the dependent variable is explained by the independent 
variable, can be used to tentatively decide between alternatives (see 
Connor and McCoy 1979). 
The results are given in Table 16, and given the small number of 
data points, the results are remarkably consistent. For both the log and 
linear models, number of caves (or log of the number of caves) 
explained more of the variance than either drainage area or limestone 
area. The log model consistently gave a better fit than the linear model. 
Finally, the best fit was provided by the log model using number of 
caves as the independent variable, with C = 0.007 and z = 1.20. The large 
z-value indicates extinctions have been occurring since the Pleistocene, 
but that the basic island analogy holds. The lack of significant correlation 
between the log of species and a measure of limestone fragmentation, 
namely percent of area covered by limestone, indicates that speciation 
resulting from underground movement is unimportant. Finally, we must 
stress the tentative nature of our conclusions, especially because 
correlations among independent variables have not been thoroughly 
explored. 
Origin, Evolution, and Dispersal 
Because there are fundamental differences between aquatic and 
terrestrial cave species with respect to modes of origin, habitats, and 
dispersal, we will discuss them under separate headings. 
Aquatic Species . — Basically two different patterns have been noted 
for aquatic troglobites in the study area with regard to their origin. It 
should be noted that these patterns are perceived as general trends only 
and are not intended to be rigid categories. The first pattern is 
exemplified by species that appear to have evolved directly from 
preadapted epigean ancestors. Morphological and physiological changes 
have developed concurrently with colonization of subterranean waters. 
These species belong to genera that are simultaneously represented by 
eyed, pigmented surface species, some of which are not far removed 
taxonomically (or genetically?) from subterranean forms. Taxa fitting 
this pattern are hydrobiid snails ( Fontigens ), some crangonyctid 
amphipods ( Crangonyx ), and asellid isopods ( Caecidotea and Lirceus). 
