Effects of Temperature on Functional Relationships Among Michigan's Fluvial Fish Assemblages: Identifying Management Opportunities in the Face of Environmental Changes

Biodiversity is declining precipitously in fluvial ecosystems due to factors like habitat alteration from landscape-level anthropogenic disturbances.  Besides impacts experienced directly by organisms from such habitat changes, interactions among species, including competition and predation, will change with additions or loss of organisms responding to altered habitat.  In Michigan streams, landscape-level disturbances like urbanization and agriculture affect various characteristics of habitat including stream thermal regimes which are important in controlling distributions and abundances of stream fishes, and thermal characteristics are considered one of the most important habitat factors structuring fish assemblages in this region.  To allow for better management opportunities to current landscape-level disturbances and to plan for potential changes that may result with changes in climate, the goal of this study is to consider ways that stream thermal regimes structure fluvial fish assemblages.  Objectives include: 1) evaluating thermal regimes to understand spatial variability in characteristics important to fish across Michigan, 2) quantifying taxonomic verses functional response of fish assemblages to thermal regimes, and 3) quantifying the extent to which fish assemblages respond to thermal characteristics while controlling for other factors like catchment area, local and catchment land cover, and local groundwater inputs known to influence both stream fish assemblages and temperature in the Michigan.  Multivariate techniques (canonical correspondence analysis, redundancy analysis) were used to evaluate relationships among 1) various metrics characterizing stream thermal regimes, 2) landscape factors and 3) fish assemblages summarized by taxonomic and functional metrics. Results showed regional patterns in landscape-level controls on stream thermal regimes and indirectly on stream fishes.  Further, response of fish varied regionally as represented by both taxonomic and functional metrics.  Additional work using covariance structure analysis (CSA) indicated regional differences in interactions among groups of fishes as mediated by landscape factors including urbanization and agriculture working through select thermal metrics.  Top predators in northern Michigan, for example, decreased with increasing summer temperature while generalists increased, potentially due to altered habitat as well as altered biological interactions.  Together, our results provide new insights on regional differences in controls on stream fish assemblages and offer opportunities for improved conservation and restoration of stream systems due to current and future threats.