Ecoregional, catchment, and reach-scale environmental factors shape functional-trait structure of stream fish assemblages

Patterns of association between functional traits and environmental gradients can improve understanding of species assemblage structure from local to regional scales, and therefore may be useful for natural resource management. We measured functional traits related to trophic ecology, habitat use, and life-history strategies of fishes and examined their associations with environmental factors in the Brazos and Trinity River basins in Central Texas. We also examined the relationship between functional diversity of fish assemblages and indices of biotic integrity and habitat quality. Environmental characteristics at the local reach and catchment scales, including the extent of forested area in the watershed, amount of land developed for urban and agricultural uses, stream size, substrate characteristics, and availability of riffle and pool habitats, were significantly associated with functional trait composition of fish assemblages. Broad physiographic differences between ecoregions also had a large influence on taxonomic and functional assemblage structure. In general, the volume of functional trait space occupied by fish assemblages was greatest in streams with high habitat quality scores located within landscapes having less alteration from agriculture and urban development. Distributions of functional traits in fish assemblages might provide an additional basis for assessment of stream condition in relation to environmental impacts.