Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references (leaves 55-62).Issued also on microfiche from Lange Micrographics.Relationships between environmental variability and natural communities have been extensively studied. However the relative strengths of abiotic and biotic factors in structuring stream communities continues to be debated. Although North American crayfish are taxonomically diverse, occur across a variety of habitats, and are important components of stream ecosystems, when compared to other invertebrates or fish, factors influencing their distribution are poorly studied. Crayfishes may respond differently to disturbance and predators or competitors. In intermittent streams of East Texas, fishes that may influence the distribution of crayfish are rare or absent, so crayfish assemblages may differ between hydrologically variable and stable streams. In order to understand abiotic and biotic factors structuring native crayfish assemblages, environmental variables and densities of fishes and crayfishes were quantified simultaneously in 16 East Texas streams during June and October 1999, and February and April 2000. Three crayfish species, Procambarus clarkii, Orconectes palmeri, and Procambarus kensleyi, and several fishes were collected. Although fish and crayfish assemblages were similar in all streams during June before drought occurred, relative densities varied across intermittent and perennial streams following drought. After flow resumed in intermittent streams, densities of juvenile P. kensleyi were higher, but predatory fishes and adult O. palmeri were reduced, whereas in perennial streams, the opposite pattern occurred. These results suggest that P. kensleyi could tolerate abiotic stress, exploit resources, and maintain higher densities in intermittent streams where predators were reduced, but its smaller size may have facilitated higher predation by fish in perennial streams. Assemblages in perennial streams suggested interactions among crayfishes and fishes favored O. palmeri and P. clarkii, which appeared to be superior competitors and resistant to predators. Procambarus clarkii was not strongly correlated with either abiotic or biotic factors measured in this study, including stressful conditions associated with drought. These results are consistent with life history trade-offs among stress tolerance, resistance to disturbance and predation, and competitive ability. The occurrence of both perennial and intermittent streams within a drainage provides a range of habitats that maintains more crayfish species from among those in the regional species pool than would either habitat alone
