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Why should we have concern for desert springs and biotas? Some simply say" because they are there"(Rolston 1991). Because surface water is quite uncommon in desert lands, springs often attract attention mostly as anomalies. These isolated oases harboring aquatic organisms in the midst of seas of arid land are also often described as" aquatic archipelagos," similar to oceanic islands that allow dry-land plants and animals to live surrounded by seawater. Most islands are, however, populated by organisms dispersing from elsewhere, such as an adjacent mainland. Conversely, biotas of desert springs often are remnants, left behind as surface water disappears with the expansion of deserts (Hubbs and Miller 1948; Hubbs et al. 1974; Dumont 1982; Por et al. 1986; Leveque 1990). Thus, spring biotas are often relicts of wetter times, providing clues to conditions in the distant past (Scates 1968; Por 1984; Roth 1987; Hershler et al. 1999). In many cases, individual species are restricted to one or only a few springs. Because dry land is a greater barrier to obligate aquatic organisms than water is to creatures that fly, swim, or float, their purity of isolation presents unmatched opportunities for evolutionists to study processes of speciation (eg, Miller 1948, 1950; JH Brown 1971; Nxomani et al. 1994; Duvernell and Turner 1999). Field research on other important questions, such as thermal or physicochemical preferences or tolerances of species, can be undertaken in the unique up-to downstream gradients of spring-runs (Brues 1928, 1932; Mason 1939; Brain and Koste 1991). A spring is difficult to define more precisely than a place where water rises at …