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Analysis of Simple Cave Communities: Niche Separation and Species Packing

Culver, David C.
Ecology 1970 v.51 no.6 pp. 949-958
Asellus, Gammarus, aquatic insects, immigration, leaves, microhabitats, rocks, streams, West Virginia
This paper considers various ecological relationships of three gammarid amphipods (Gammarus minus, Stygonectes emarginatus, and Stygonectes spinatus) and one asellid isopod (Asellus holsingeri) in cave streams of the Greenbrier Valley in West Virginia. Two clear—cut cases of reduction of realized niche due to the presence of other species were found: S. emarginatus is limited to small trickles of water when G. minus is present in the stream and A. holsingeri is limited to gravel—bottomed pools when G minus is present in riffles. S. spinatus prefers smaller rocks than do the larger amphipod species. All four species maintained weight equally well on rotting leaves or mud, so feeding differences appear to be minimal. Using Levins' matrix of competition coefficients as a framework, interference and exploitation competition were quantified and separated. From these data, it is indicated that the community is closed to immigration by similar species into the microhabitats occupied by the four crustacean species. Field evidence supports this. Some unused microhabitats may be available, but the aquatic insects that might potentially use them are not present.