The Edwards Aquifer ecosystem is blessed with more than 60 species of plants and animals that live here and nowhere else in the world. Blind salamanders, catfish, crustaceans, and other "cave critters" have evolved in isolated habitat "islands" within the aquifer, in the dry caves above the water table, and at the Great Springs. The Barton Springs and Austin Blind salamanders live only at Barton Springs, Texas Wild Rice and the San Marcos gambusia live only in the San Marcos River, and the Texas Blind salamander is known only from a few caves that reach into the Southern Edwards Aquifer.
The Edwards Aquifer Ecosystem has such a diversity of wildlife that it is on a global list of biodiversity "hot spots" deserving the immediate attention of conservationists. New species are still being discovered, right here in the backyard of major research institutions like the University of Texas, Texas A&M, and Texas State University.
Distinct Hill Country plant communities are characterized by mixed oak and ashe juniper woodlands, oak savannah and shinnery, wildflowers, native grasses and riparian woodlands. Several centuries of farming and ranching have altered the landscape, but the ruggedness of the Hill Country has assured that many of the native plants and animals have survived. For example, mature oak and ashe juniper woodlands provide nesting habitat for the endangered Golden-cheeked Warbler, a small migratory songbird that is the only bird species (out of 590 that come through Texas) entirely native to Texas.
Many of the plants and animals unique to the Hill Country are listed as "threatened" or "endangered" by the U.S Fish & Wildlife Service because they have extremely limited ranges which are being destroyed by rapid urbanization, urban runoff pollution, and/or excessive water withdrawals. The threat of extinction to sensitive fish, salamanders and other species that live in the Edwards Aquifer and its Great Springs is particularly acute.
Conservation measures that will sustain these endangered species will assure that the Aquifer and Springs are sustained for human use and enjoyment as well.
Through a process known as "parallel evolution," the salamander species from different spring outlets are distinct species, but resemble not just each other but also salamanders found in karst limestone aquifers in other parts of the world. All of these Edwards Aquifer aquatic salamander species are known as "neotenic," meaning they reproduce in the aquatic form and do not metamorphose into a terrestrial adult form (a trait most amphibians are known for). If their springs become polluted or pumped dry, they cannot walk on land to find another place to live.
A number of fish species have evolved both within the aquifer and in the spring outflows. These species include the Texas Blind catfish, which only lives deep within the San Antonio segment of the aquifer; the Fountain Darter and San Marcos gambusia from the San Marcos River, and the recently discovered San Felipe gambusia.
Troglobites (Cave Dwellers)
The largest group of species unique to the Edwards Aquifer Ecosystem consists of cave-dwelling invertebrates. These include insects, crustaceans, spiders, bugs, and other small "cave critters." Many are terrestrial, living in limestone caves above the water table, and are known from one to only a few caves. The isolated cave networks that dot the Edwards and associated limestones--like the large springs--are isolated from each other and thus have provided laboratories for the evolution of unique life forms.
A number of interesting and at-risk plant species also live in the Hill Country. Perhaps best known (and at greatest risk of extinction) is the Texas wild rice, which lives in the upper reaches of the San Marcos River and no where else in the world. The Bracted twistflower and the Canyon mock orange are also plant species threatened with extinction.