Invasive grass causes biotic homogenization in wetland birds in a Lake Erie coastal marsh

Plant invasions often lead to homogenization of plant communities, but the potential for homogenization of other trophic levels is understudied in many systems. Biotic communities in coastal wetlands are closely tied to daily and yearly water-level fluctuations. We compared the bird community in invasive Phragmites australis (European common reed) habitat and remnant, uninvaded marsh in a year with average water depths and a year with above-average water depths in Long Point (Ontario, Canada), a World Biosphere Reserve. Our results demonstrate the spatial and temporal homogenization of the wetland bird community following P. australis invasion. The bird community present in P. australis was a nested subset of the species present in remnant marsh, and total beta diversity in P. australis habitat decreased when water depths were above average. In contrast, total beta diversity was high in remnant marsh vegetation. The distinctively structured vegetation zones in remnant marsh yield structural complexity and habitat heterogeneity that support greater taxonomic turnover in the bird community. These results provide evidence that invasion by a plant has resulted in the biological homogenization of the wetland bird community and illustrate that habitat use will change with prevailing environmental conditions, such as high- and low-water levels.