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Ecosystems & Groundwater
Eurycea sosorum – the Barton Springs salamander.
Photo from Mahler (2004); taken by Lisa O’Donnell.
Cave Organisms
Organisms within caves may occur on the ground, within debris, on the roof and walls, or on any cave formation. Cave organisms are typically divided into troglobites, troglophiles, and trogloxenes (Gunn, 2004).

Tadarida brasiliensis mexicanus ? Mexican free-tailed bat.  Photo from Pollak (2004).
Tadarida brasiliensis mexicanus ? Mexican free-tailed bat. Photo from Pollak (2004).
Troglobites live permanently and exclusively in caves. Troglobites generally show morphological and physiological adaptations for life in caves. Such adaptations include the reduction (or loss) of eyes, pigmentation, egg volume, body size, swim bladder, circadian rhythms, scales, and aggression; some troglobites also exhibit increased lifespan (Gunn, 2004). There are nearly 1000 described species of troglobites within the 48 contiguous states of the US, and most of these species are known only from a single county (Culver et al., 2000). The caves in the region of the Edwards Aquifer in central Texas contain 108 species of troglobites (Culver et al., 2003).

Troglophiles are species that can live completely underground, but also occur in surface ecosystems. These species typically do not have the modifications seen in troglobites.

Trogloxenes are animals that use caves occasionally, but belong to surface ecosystems. This includes bats that sleep and hibernate in caves and carnivores that den in caves.

Eurycea sosorum ? the Barton Springs salamander.  Photo from Mahler (2004); taken by Lisa O?Donnell.
Eurycea sosorum ? the Barton Springs salamander. Photo from Mahler (2004); taken by Lisa O?Donnell.
Aquatic Organisms
Animal species that live exclusively in subterranean waters are called stygobites. Only about 8% of named species of aquatic animals are known to live within groundwater. This number is so limited because of the limited accessibility of habitats, the homogeneity of the environment, and low amounts of food resources (Sket, 1999). The Edwards Aquifer of central Texas contains a total of 55 stygobite species (Culver et al., 2003)







REFERENCES
Culver, D. C., L. L. Master, M. C. Christman, and H. H. Hobbs. 2000. Obligate cave fauna of the 48 contiguous United States. Conservation Biology 14:386-401.
Culver, D. C., M. C. Christman, W. R. Elliott, H. H. Hobbs, III, and J. R. Redell. 2003. The North American obligate cave fauna: regional patterns. Biodiversity and Conservation 12:441-468.
Gunn, J. 2004. Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, New York, 902 pp.
Mahler, B. 2004. What?s in the water? The history and future of Barton Springs. UT Outreach Lecture Series 31.
Pollak, G. D. 2004. Seeing the world through their ears: the exotic world of bats. UT Outreach Lecture Series 32.
Sket, B. 1999. The nature of biodiversity in hypogean waters and how it is endangered. Biodiversity and Conservation 8:1319-1338.