A Taxonomic Evaluation of the Drivers of Species Invasions in the Upper Colorado River Basin

The ability to predict the establishment of non-native fishes is critical to preventing their spread and conserving native fishes.  However, the factors affecting the establishment of introduced species are relatively unclear; potentially (in part) due to the coarse scale that species invasions are commonly evaluated (e.g., species richness).  The objective of this study was to evaluate the utility of a taxonomic (i.e., family) approach to identifying the drivers of species invasions.  Fish community samples were collected from 180 wadeable stream sites in the Upper Colorado River basin from 1990 to 2010.  We calculated habitat alteration metrics using the density and severity of landscape-level threats that likely affect the ecological integrity of streams.  The probability of non-native salmonid occurrence decreased with increased native salmonid presence (P=0.002) and increased watershed habitat alteration (P=0.04).  The presence of non-native cyprinids increased with habitat alteration (P=0.003).  In contrast, the presence of non-native catostomids increased with the presence of native catostomids (P=0.002).  These results suggest that the presence of some non-native fishes may be affected by habitat alteration and native fishes, but these relationships are taxa specific.  A taxonomic approach may be an informative approach for identifying the drivers of species invasions across large geographic areas.