Non-native species pose one of the greatest threats to native biodiversity. The literature provides plentiful empirical and anecdotal evidence of this phenomenon; however, such evidence is limited to local or regional scales. Employing geospatial analyses, we investigate the potential threat of non-native species to threatened and endangered aquatic animal taxa inhabiting unprotected areas across the continental US.
We compiled distribution information from existing publicly available databases at the watershed scale (12-digit hydrologic unit code). We mapped non-native aquatic plant and animal species richness, and an index of cumulative invasion pressure, which weights non-native richness by the time since invasion of each species. These distributions were compared to the distributions of native aquatic taxa (fish, amphibians, mollusks, and decapods) from the International Union for the Conservation of Nature (IUCN) database. We mapped the proportion of species listed by IUCN as threatened and endangered, and a species rarity index per watershed. An overlay analysis identified watersheds experiencing high pressure from non-native species and also containing high proportions of threatened and endangered species or exhibiting high species rarity. Conservation priorities were identified by generating priority indices from these overlays and mapping them relative to the distribution of protected areas across the US.
Results/Conclusions
Spatial overlays of these datasets indicate that non-native species likely pose a significant potential threat to native aquatic diversity in multiple regions, particularly in the southeastern US. This region harbors the highest richness of native aquatic species, especially along the Mississippi River, while most protected areas are concentrated in the western US. The watersheds in the southeast also harbor the native species assemblages with the greatest rarity, as well as hotspots of non-native species richness. Thus, we found the most incongruence between vulnerable native species assemblages and protected areas is in the Southeast, where the threat of exotic species invasions is also high. Our findings suggest that many regions of high native aquatic species endemism are compromised by high invasion pressure, and also may be poorly safeguarded by existing conservation mechanisms.
This abstract has been reviewed and approved by the U.S. Environmental Protection Agency. Its contents do not necessarily reflect the views and policies of the Agency.