Fish distributions in the St. Croix River Basin: The importance of ecoregions versus local ecological conditions
Aquatic ecoregions, based on regional landscape features, have been proposed as a model for aquatic resource management. The model assumes the existence of a typical biota associated with a given ecoregion, and serves as the basis for biological assessment, reference site designation, and determinat...
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| Format: | Dissertation |
| Language: | English |
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ProQuest Dissertations & Theses
01-01-1996
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| Online Access: | Get full text |
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| Summary: | Aquatic ecoregions, based on regional landscape features, have been proposed as a model for aquatic resource management. The model assumes the existence of a typical biota associated with a given ecoregion, and serves as the basis for biological assessment, reference site designation, and determination of stream potential, based on this biotic assemblage. In this study of fish distributions in the St. Croix River basin, I demonstrate the inadequacy of ecoregions, and provide evidence of the importance of local site conditions in the delineation of aquatic species assemblages. A classification of over one hundred sites in the mainstream of the St. Croix River using species assemblages delineated three site groups. The major environmental conditions associated with these groups were drainage area, bed substrate, and riparian tree cover. Further analyses expanded the classification to include tributary sites where the combined total of over four hundred sites were investigated. For this analysis drainage area and geological conditions were most associated with site groupings. Ecoregion location very poorly predicted the distribution of the species-based groups. Chi-square tests of independence found no significant relationships between ecoregions and species-based site groups, and a discriminant function analysis correctly predicted less than twenty-five per cent of site group allocations using ecoregions. In contrast, the chi-square tests indicated significant dependence between drainage area classes and species-based classification (p-value $<$ 0.000), and the discriminant function analysis correctly predicted nearly seventy-nine per cent of site allocations to site groups using drainage area classes. These results show that drainage area, which is a proxy of local watershed hydrologic, geomorphic, and geologic conditions is a much better predictor of environmental factors controlling fish ecology than are broad scale ecoregions. The results indicate that an ecoregional model is unlikely to benefit management and assessment of aquatic ecosystems, whereas drainage area and other local site conditions may provide real management benefit. Without searching for and incorporating variability within an ecoregion, local aquatic communities may be overlooked. |
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| ISBN: | 9798684657672 |