Distributional Patterns of Texas Fresh-Water Fishes

Abstract

Distribution patterns of most fresh-water fishes in Texas closely resemble those of terrestrial organisms, though there are 3 exceptional groups: (1) those limited by stream divides, (2) those of marine and freshwater forms meeting in fresh waters near the coast, and (3) certain species of northeastern Texas (Austroriparian) whose ranges include outliers or extensions into other biotic provinces. It is concluded that the basic factors controlling distribution patterns of fishes are climatic and geological, these determining the properties of the water. In recent treatments on the biogeography of Texas, many distributional patterns have been delimited (Blair, 1950, and Tharp, 1939 and 1952). Although Tharp divided the state into more subdivisions than did Blair, the demarcation lines for his Vegetation Regions conform closely to those for Blair's Biotic Provinces and Districts (Fig. 1). In addition, Tharp emphasized differences associated with the coastal prairie more than Blair, who in turn separated the district known as the lower Rio Grande Valley more distinctly. Their areas approximate those of Johnson (1931) as both authors correlated the biologic distributions with geologic and climatological data. Obviously, the edaphic and climatic factors are critical to the survival of organisms in any region. Both Blair and Tharp base their conclusions chiefly on the distribution of terrestrial organisms. At least one group of aquatic organisms, the fishes, has distributional patterns that closely resemble those derived from terrestrial studies. Correlation of fresh-water fish distribution with Life Zones in Texas as given by Bailey (1905) is not very close. The life-zone boundaries of Bailey that approximate the boundaries of Blair and Tharp fit the, distribution patterns of fresh-water fishes, whereas no correlation is noted where Bailey's boundaries differ. Additional support for the general validity of these boundaries can be derived from the geographic distribution of historic Indian groups. Kroeber's (1939) maps for Indian tribal areas roughly correspond with Blair's and Tharp's regions. T. N. Campbell (personal communication, 1957) reports that the correlation at about 1500 A.D. is perhaps even better than indicated by Kroeber. He would locate the Caddo and Atakapa Indians in the Austroriparian Biotic Province with occa-