112 
David C. Culver and Timothy J. Ehlinger 
genetic differences (Dickson et al. 1979), suggests environmental deter- 
mination of size. On the other hand, the extensive genetic differentiation 
of the amphipod Gammams minus in narrow anticlinal valleys similar to 
those in our study area (Gooch and Golladay, in press) suggests that dif- 
ferences in body size on a small geographic scale may be genetically 
determined. 
Even if C. cannulus is genetically larger than C. holsingeri, it is not 
clear that this is the result of past competition. The two species may have 
descended from a common surface ancestor, and the larger size of C. can- 
nulus may be the result of past competition. However, the two species 
may have descended from separate ancestors that differed in body size. 
There is no way to determine which of the two scenarios is the correct 
one. 
Finally, elimination of some of the data would result in the conclu- 
sion that character displacement is important. In particular, if data for 
Harman Cave and Glady Cave are eliminated, character displacement 
would be indicated. Individuals in allotopic populations of C. holsingeri 
are large (Linwood Cave) and individuals of C. cannulus in such popula- 
tions are small (Cave Hollow Cave). In fact, we originally studied these 
two species because they appeared to show character displacement (see 
Holsinger et al. 1976). This supports the critique of character displace- 
ment by Strong et al. (1979) and shows that sampling should not be 
ended merely because the “correct” results have been obtained. 
ACKNOWLEDGMENTS. John R. Holsinger and Mr. 
William K. Jones assisted in the field. Dr. Thomas Bowman loaned 
specimens from Mill Run Cave and provided measurements of the type 
series of C. cannulus from Cave Hollow Cave. Mr. Julian Lewis helped 
with identifications. Dr. John R. Holsinger provided information on his 
collections in the area. TJE was supported by funds from the Orlando 
Park Fund of Northwestern University. 
LITERATURE CITED 
Culver, David C. 1970. Analysis of simple cave communities. 1. Caves as islands. 
Evolution 2^:463-474. 
1971. Analysis of simple cave communities. III. Control of abun- 
dance. Am. Midi. Nat. (55:173-187. 
1973. Competition in spatially heterogeneous systems: an analysis 
of simple cave communities. Ecology 54:102-110. 
1976. The evolution of aquatic cave communities. Am. Nat. 
y/t}:945-957. 
and T.J. Ehlinger. In preparation. Determinants of body size of 
two subterranean ho^od?,~Caecidotea cannulus and Caecidotea holsingeri 
(Isopoda: Asellidae). 
Davies, William M. 1965. Caverns of West Virginia, with supplement. W. Va. 
Geol. Survey, Morgantown. 401 pp. 
