The Comparative Ecology of Two Populations of the Troglobitic Isopod Crustacean Lirceus Usdagalun (Asellidae)

Aquatic communities of two caves in Lee Co., Virginia, were compared, and an examination was made of the life history phenomena of the troglobitic isopod Lirceus usdagalun. Measurements of physical and biological parameters were made in Thompson Cedar Cave and Gallohan Cave No. l. A contagious distribution was exhibited by populations of L. usdagalun in both caves and also by the population of another troglobitic isopod, Caecidotea recurvata, in Gallohan Cave No. 1. This distribution was attributed to aggregations of individuals which were considered to occur in areas of preference or optimal habitat patches. Lirceus usdagalun exhibited a greater density in fast moving water and C. recurvata generally exhibited a greater density in slow moving water. The virtual absence of C. recurvata from Thompson Cedar Cave was presumably the result of higher stream flows than in Gallohan Cave No. 1, where it maintains a population due to a seasonal increase in density during a period of low stream flow in the summer. Other factors such as silt, detritus and fused gravel appeared to have an adverse effect on the population densities of both isopods. Crangonyx antennatus, a troglobitic amphipod, had small populations in both caves. Variations in body length, sex ratio and seasonal densities of L. usdagalun appear to be the result of varying degrees and types (lnterspecific or intraspeclfic) of competition, as well as differences in the physical environment.