Patterns of Invertebrate Community Composition and Functional Structure Across a Dune Succession Gradient

Abstract

The world’s most extensive freshwater sand dunes lie along the eastern shore of Lake Michigan, USA. These dunes follow a succession gradient from open canopy, grass-covered dunes to forested dunes further inland with wetlands interspersed in the dune landscape. We asked if macroinvertebrate assemblages in interdunal wetlands showed predictable change along the dune succession gradient. In April through October 2017, we collected physical–chemical data, characterized wetland habitat, and macroinvertebrate assemblages at 11 interdunal wetlands distributed along an open-forested dune gradient. We evaluated patterns of taxonomic diversity and abundance and functional richness, community composition, and community dissimilarity along the gradient. The dune gradient represented changes in water chemistry variables associated with terrestrial and aquatic vegetation. Overall, interdunal wetlands in open dune habitat showed lower taxonomic diversity and were dominated by communities with functional traits tailored to variable habitats (active dispersal, bi/multi-voltine). Variation in assemblage composition along the gradient is correlated with differences in water temperature, pH, dissolved oxygen, and amount of surrounding terrestrial vegetation. Community dissimilarity is driven primarily by terrestrial vegetation surrounding wetlands and secondarily by spatial location. This is the first study to document aquatic diversity across a dune succession gradient illustrating that terrestrial dune vegetation has a large impact on patterns of aquatic community and functional structure. To maintain high species diversity in Great Lakes sand dunes ecosystems we promote protection for both forest and dune habitat to safeguard unique species and biological traits that use interdunal wetlands.