Large-scale heterogeneity gradient drives the structure and biodiversity of branchiopod (Anostraca, Cladocera) egg-banks in the Nebraska Sandhills wetlands, USA

Branchiopods use resting eggs to maintain permanent populations in temporally dynamic environments as well as for dispersing to neighboring habitat patches. We used a large-scale longitudinal salinity gradient that overlays the Nebraska Sandhills, USA to determine how changes in metacommunity environmental heterogeneity influences species composition and biodiversity of branchiopod egg banks from freshwater and saline temporary wetlands. We sampled the egg banks of 54 wetlands from three metacommunities across the Nebraska Sandhills (eastern, central, and western) in which the relative abundance and salinity of saline wetlands increased westwards. Salinity had a strong effect on structuring the egg-bank metacommunities with a clear shift in species composition and species richness from the eastern to western metacommunities. Egg-bank alpha richness of the freshwater wetlands and metacommunity gamma richness declined westwards as the abundance of freshwater wetlands decreased relative to the saline wetlands. The low-salinity wetlands represented an intermediate stage between the freshwater and high-salinity wetlands, overlapping in species composition with both habitat types and supporting similar numbers of species as freshwater wetlands. High-salinity wetlands had the lowest alpha richness with only halotolerant and halophilic species.