Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

Abstract

<em>Abstract</em>.—Stream fish assemblages are influenced indirectly by natural and anthropogenic landscape features acting through intermediate factors like flow and temperature regimes, water quality, and physical habitat. These relationships affect distributions and abundances of individual species and also frame potential interactions among different types of fishes. This hierarchical influence of environmental factors, also known as the landscape perspective, is a widely accepted view of fluvial systems. However, few studies have attempted to quantify the complex mechanistic relationships among landscape variables, intermediate factors, and fish, a gap due partially to limitations of traditional analytical techniques for devolving such relationships. Using covariance structure analysis (CSA), we attempt to quantify the influence of natural and anthropogenic land uses on stream fish assemblages through indirect effects on fluvial physical habitat, including descriptors of habitat complexity, flow stability, and channel size, for 46 streams of southeastern Michigan. CSA was selected for this investigation because of its ability to quantify indirect effects of variables through intermediate factors and to account for intercorrelations among related measures. For analysis, fish assemblages were summarized by their richness and diversity and also according to functional groups that included trophic guilds and preferences for stream size, substrate, and geomorphological units, such as riffles and pools. Our analysis showed that, when acting through habitat factors, assemblages were more strongly influenced by natural landscape features, including catchment area and geology, than by anthropogenic land uses of our study region. Further, the analyses revealed that different aspects of fish assemblages varied with different habitat variables. While diversity and richness increased with habitat complexity and channel size, numbers of carnivores decreased with flow stability, possibly due to the link between flow and stream temperature regimes of our study region. Diversity and richness, however, were not affected by human land uses. Numbers of invertivores, fish preferring fine substrate, and fish preferring pool/ run habitat all increased with agriculture while numbers of detritivores increased with both agriculture and urban land use. These results emphasize complex effects of landscape features on stream fishes through intermediate factors and underscore the importance of understanding the varied response of different aspects of fish assemblages to environmental influences for improved conservation and restoration opportunities.