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Thursday, June 7, 2007 - 9:15 AM
346
Testing a Spatial Model of Fish Assemblage Relations to Stream Network Topology
Nathaniel P. Hitt, Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, 100 Cheatham Hall, Blacksburg, VA 24061 and Paul L. Angermeier, U.S. Geological Survey, Virginia Cooperative Fish and Wildlife Research Unit, Virginia Polytechnic Institute and State University, 100 Cheatham Hall, Blacksburg, VA 24061.
Landscape context influences the organization of local biotic communities but effects vary among localities. We evaluated how the size and proximity of connecting streams (i.e., stream network topology) influences fish assemblage structure across 308 sites in the mid-Atlantic highlands, USA. We hypothesized that (a) dispersal from riverine source areas would influence local assemblage structure and (b) the relative importance of regional dispersal would be regulated by local stream size. First, we developed a spatial model to quantify stream network topology based on the rate of flow accumulation downstream from sites. Second, we used randomization procedures to explore fish assemblage relations to stream network structure at increasing spatial grain sizes. Third, we tested the prediction that the smallest sites would be least influenced by regional dispersal due to environmental filters operating at the local-scale. Mantel tests revealed significant relations between fish assemblages and stream network structure up to a distance of approximately 9 fluvial km but not beyond. These patterns were explained by spatial variation in the species richness of catostomids, cyprinids, and riverine specialists. The smallest sites contributed least to these overall patterns, consistent with the hypothesis that local factors influence the relative importance of dispersal from regional source populations.