Predicting aquatic vertebrate assemblages from environmental variables at three multistate geographic extents of the western USA

摘要

Variables for predicting assemblage differences change as the geographic extent of studies change, hindering development of useful predictive models where study data are limited, or where the chief predictive variables available are fish zones, river size, physiographic regions, ecoregions, hydrologic units, and river basins. In addition, some studies have shown that site-scale predictor metrics have accounted for more of the variation in fish assemblage response metrics than catchment-scale metrics and other studies have shown the reverse. We used cluster analysis on a 780-site database to determine 12-15 aquatic vertebrate clusters at three geographic extents (all 12 conterminous western U.S. states, all western mountain ecoregions, Pacific Northwest mountain ecoregions). Next, we determined predictor variables for those assemblage clusters through use of stepwise discriminant function analysis. Site longitude, site latitude, and catchment dam count were the most significant predictors at the three geographic extents. Site-scale variables represented most of the significant predictors for all three geographic extents, but explained only slightly more aquatic vertebrate assemblage variance than catchment or pure spatial variables. Catchment- and site-scale classification variables accounted for less than half the mean within-cluster similarity demonstrated by the aquatic vertebrate assemblage clusters. We conclude that (a) the large geographic extent of the analysis did not result in catchment-scale predictor variables being more important than site-scale predictors, (b) both catchment- and site-scale variables are important predictors, and (c) existing river basin and ecoregion classifications are useful but insufficient predictors of aquatic vertebrate assemblages. (C) 2015 Elsevier Ltd. All rights reserved.