Assemblage Organization in Stream Fishes: Effects of Environmental Variation and Interspecific Interactions

• Published in: Ecological monographs 1998-08, Vol.68 (3), p.395-420
• Main Authors: Grossman, Gary D., Ratajczak, Robert E., Crawford, Maurice, Freeman, Mary C.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Boulders; Cobbles; community organization; Drought; droughts; Fish; Fish populations; Fishes; Fishes, Fresh-water; floods; Fresh water ecosystems; Fundamental and applied biological sciences. Psychology; Gravel; Habitat (Ecology); Habitats; interspecific competition; microhabitat use; Microhabitats; Niche (Ecology); Pisces; Predation; Predators; resource partitioning; Rivers; spatial resources; Species; Streams; Synecology; Wildlife habitats
• ISSN: 0012-9615; 1557-7015
• DOI: 10.1890/0012-9615(1998)068[0395:AOISFE]2.0.CO;2

We assessed the relative importance of environmental variation, interspecific competition for space, and predator abundance on assemblage structure and microhabitat use in a stream fish assemblage inhabiting Coweeta Creek, North Carolina, USA. Our study encompassed a 10-yr time span (1983-1992) and included some of the highest and lowest flows in the last 58 years. We collected 16 seasonal samples which included data on: (1) habitat availability (total and microhabitat) and microhabitat diversity, (2) assemblage structure (i.e., the number and abundances of species comprising a subset of the community), and (3) microhabitat use and overlap. We classified habitat availability data on the basis of year, season, and hydrologic period. Hydrologic period (i.e., pre-drought [PR], drought [D], and post-drought [PO]) represented the temporal location of a sample with respect to a four-year drought that occurred during the study. Hydrologic period explained a greater amount of variance in habitat availability data than either season or year. Total habitat availability was significantly greater during PO than in PR or D, although microhabitat diversity did not differ among either seasons or hydrologic periods. There were significantly fewer high-flow events (i.e., ≥2.1 m3/s) during D than in either PR or PO periods. We observed a total of 16 species during our investigation, and the total number of species was significantly higher in D than in PR samples. Correlation analyses between the number of species present (total and abundant species) and environmental data yielded limited results, although the total number of species was inversely correlated with total habitat availability. A cluster analysis grouped assemblage structure samples by hydrologic period rather than season or year, supporting the contention that variation in annual flow had a strong impact on this assemblage. The drought had little effect on the numerical abundance of benthic species in this assemblage; however, a majority of water-column species increased in abundance. The increased abundances of water-column species may have been related to the decrease in high-flow events observed during the drought. Such high-flow events are known to cause mortality in stream fishes. Microhabitat use data showed that species belonged to one of three microhabitat guilds: benthic, lower water column, and mid water column. In general, species within the same guild did not exhibit statistically distinguishable pa