We quantified trophic and reproductive functional diversity (SES FDis) of freshwater fish communities and related these measurements to environmental indicators to inform conservation planning actions as part of the South Atlantic Landscape Conservation Cooperative (SALCC). We estimated functional diversity at two different spatial scales (regional and local) using datasets of different sampling intensity and time duration. Our regional-scale analysis measures functional diversity across the SALCC at the sub-basin, or HUC8-scale, using occurrence data obtained from the MARIS and NAS databases. Our local-scale analysis is based on a systematic sampling program conducted by the South Carolina Department of Natural Resources (SCDNR).
Key results include:
1. Regionally (SALCC level), trophic and reproductive SES FDis were highly correlated, and decreased from higher elevations to coastal regions. Locally (South Carolina level), trophic and reproductive SES FDis were not correlated, and trophic SES FDis decreased from the highlands to the coast while reproductive SES FDis increased. Overall, we found these trends informative in reflecting elevational differences in land cover, land use, habitat, and endemism across the SALCC and South Carolina.
2. Regionally, the indicators available from the SALCC and evaluated (percent of natural cover, urbanization, agriculture, and open water) were not significantly associated with SES FDis. At the local scale, a different set of indicators including buffer-scale forest cover, elevation, conductivity, and ecoregion were the most important indicators of SES FDis. At the regional-scale, additional indicators should be identified and compiled by the SALCC, and then used in an analysis of SES FDis before the final determination of the utility of this approach. At the local-scale, because a larger suite of indicators was available our inference on the relationship between indicators and SES FDis likely is more insightful to resource managers than the regional analyses.
3. At both scales, we did not identify strong relationships between the numbers of threatened and invasive species and SES FDis. Therefore, functional diversity provides additional information regarding the integrity of freshwater ecosystems in the south Atlantic region and should not be used as a surrogate measure for either of these variables, but rather complementarily.
4. Data limitations must be considered when interpreting our results. Our regional fish sampling data merges data from multiple databases containing sampling efforts of different intent, while our local fish sampling data comes from one systematic sampling effort. For this reason, we feel that the local data from South Carolina are likely a better representation of the extant fish community. Nonetheless, our regional analysis does provide informative patterns of functional diversity, and leads us to believe that assessing functional diversity using this type of approach is not misguided.
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