FISH COMMUNITY STRUCTURE IN DRY-SEASON STREAM POOLS

Fish assemblage patterns were examined in 40 dry-season pools in a hydrologically variable river drainage in northeast Texas, to test the hypothesis that fish assemblage structure is correlated with environmental gradients of habitat characteristics. The study focused on two questions: 1. Do discrete, identifiable fish assemblage patterns exist? 2. If so, how are they related to environmental conditions? The null hypothesis that fishes were randomly distributed among pools was rejected, indicating that assemblage patterns existed. Cluster anlayses of the relative abundance of fish species detected three fish assemblages dominated by: mosquitofish; bullhead; and sunfish-shiner-mosquitofish. Factor analysis reduced environmental variables to six factors representing pool depth, pool persistence, channel size, canopy cover, pool substrate, and pH, by which assemblages could be discriminated. These results demonstrated a relation between fish assemblages structure and environmental conditions in the pools. The discriminating variables varied along a gradient, and fish assemblages varied similarly. The study supported model predictions for gradient trends in species richness, species composition, fish size, and fish density, but not for species density.