Persistence and Structure of the Fish Assemblage in a Small California Stream

TitlePersistence and Structure of the Fish Assemblage in a Small California Stream
Publication TypeJournal Article
Year of Publication1985
AuthorsMoyle, P. B., & Vondracek B.
Date Published02/1985
AbstractThe persistence and structure of a small but morphologically diverse fish assemblage of a California stream was examined to see if it had the characteristics of a deterministically regulated or stochastically regulated community. We evaluated persistence by monitoring the fish populations for 5 yr and examined resource use by measuring summer microhabitats and diets of each species. We also compared the microhabitats and diets of the juveniles and adults of each species to investigate the hypothesis that in stream fish assemblages at low diversity, juvenile fishes essentially function ecologically as separate species. Species composition in each of four stream sections was persistent over the 5-yr period, which included extreme flood conditions. Differences in species composition among sections reflected differences in their physical characteristics. The most abundant species were segregated by habitat, microhabitat, and/or diet. In addition, in all but one species, young-of-year were ecologically segregated from the adults; this increased the functional complexity of the assemblage. The observed fish assemblage thus appears to have the characteristics of a highly structured community, as expected under Connell's "niche diversification hypothesis." The structure observed is probably characteristic of fish assemblages in cold-water streams throughout North America that contain the same or similar species.