Tuesday, May 27, 2008
253

Coupling changes in physical habitat and fish community structure between two interannual extremes in stream discharge

Charles E. Stanley, Jason Taylor, and Ryan King. Department of Biology, Center for Reservoir and Aquatic Systems Research, Baylor University, One Bear Place #97266, Waco, TX 76798-7266

Hydrological variability plays a predominant role in governing fish communities in lotic ecosystems. Hydrologic extremes of drought (2006) and flood (2007) events were the backdrop for fish assemblage and physical habitat data collected during summer in 29 central Texas streams. We evaluated the correspondence between the magnitude of physical habitat and fish community assemblage change in stream reaches sampled in these two contrasting years. Principle Components Analysis (PCA) and Non-metric Multi-dimensional Scaling (NMS) techniques were used to ordinate streams in 3-dimensional space according to physical habitat measures and fish species abundance data, respectively. Successional vectors illustrated the direction and magnitude of change of streams in 3-d PCA and NMS ordination space between years and the correspondence between vector lengths was estimated using linear regression.  The magnitude of interannual change in physical habitat and fish communities were only weakly correlated when considering all 29 streams.  However, excluding from the analysis streams that had no measurable discharge in 2006 showed a relatively strong coupling between the amount of change in habitat and fish species composition between years.  Streams that were reduced to non-flowing pools in 2006 had wildly variable community composition in both years, suggesting strong biotic interactions and decoupling from habitat.


Web Page: Principle Components Analysis, Non-metric Multi-dimensional Scaling, Successional Vectors