Reconstructing the Past and Predicting the Future of Stonefly Assemblages in the Midwest
Stoneflies (Insecta: Plecoptera) are the most environmentally sensitive of aquatic insects and are imperiled in many areas of world. Over 20% of all species that have ever been known to exist in Illinois can no longer be found. Could this loss be widespread in the Midwest? In an effort to set the baseline distribution for stoneflies in the Illinois, Indiana, Michigan, Ohio, and Wisconsin new samples and museum specimens from 22 regional institutions were examined, identified, and their data captured. These specimen data, over 100 environmental variables, and Maximum Entropy (Maxent) distribution modeling were used to predict “pre-European settlement” distributions for species and species richness at the USGS HUC12 (>8700 of them in the region) drainage scale across the region. Species distribution models largely correspond to taxonomist’s professional judgment and often correlated well with a validation data set. Predicted species richness hotspots and coldspots are concentrated in unglaciated sections of southern Illinois, Indiana, and Ohio and in more northern areas where the landscape is forested, little disturbed, and topographically diverse. These patterns correspond well with observed richness values. Preliminary analysis of climate related changes in distribution and richness using climate variables only (the worst case scenario) predicts significant range loss in many species and greatest reduction of species richness in areas that are currently the richest in the region. The future for stonefly assemblages in the Midwest looks bleak and saving them may require a big investment in creating and maintaining migration corridors and even “artificial migration” northward.