Interdunal wetlands are a globally rare habitat that hosts a wealth of aquatic diversity. The freshwater sand dune ecosystem of the Great Lakes stretches across 4 degrees of latitude and up to 5 km wide creating strong environmental and vegetation succession gradients. We focused on identifying biodiversity patterns at local and regional scales, while examining the influence of and change across environmental gradients in taxonomic, functional, and genetic diversity.
At a local scale, we characterized macroinvertebrate assemblages at 11 interdunal wetlands distributed along an open to forested dune succession gradient and assessed patterns of taxonomic and functional diversity along the gradient. On a regional scale, we sampled macroinvertebrates and assessed spatiotemporal patterns of beta diversity in 38 interdunal wetlands along the latitudinal gradient of the eastern coastline of Lake Michigan. In addition, we used COI and RADseq data to investigate how dispersal ability of Anax junius, Notonecta undulata, and Caenis amica and biogeographic gradients correspond with population genetic structuring of these insects in interdunal wetlands.
We found unique macroinvertebrate communities both along the coastline and vegetation succession gradient structured by species replacement and environmental differences in pH, temperature and surrounding vegetation. Wetlands in the open dune field with little surrounding terrestrial vegetation hosted invertebrates with life-history traits conferring resilience to a fluctuating habitat. Species richness increased with decreasing latitude, underlaid by temperature and precipitation variation. We found both A. junius and N. undulata populations separated into two genetic clusters along the coastline, and genetic diversity increased with increasing latitude. COI data uncovered a near complete delineation of species of Caenis between northern (C. amica) and southern (C. diminuta) sites that geographically matches a floristic tension zone across the Great Lakes.
Conservation of and connectivity within and among the freshwater sand dune ecosystem is advocated to preserve unique aquatic communities.