VARIABLE IMPACT OF AVIAN PREDATION ON GRASSHOPPER ASSEMBLIES IN SANDHILLS GRASSLAND

Spatial and temporal variability in the impact of avian predation on total grasshopper density and species diversity in a sandhills grassland was evaluated with field experiments. Experiments were run for 3 years at two locations along a topographic gradient created by a large sand dune system which supports a mixed-grass prairie. Overall average grasshopper densities at the site were approximately 3-4 individuals/m2, considered low to moderate densities in the long-term record, and densities were about the same for all years within sites. I eliminated avian predation from plots at each site through the use of large, wide-mesh exclosures set up in early July each year. I sampled 5-6 weeks later and compared grasshopper densities and number of species from the enclosure cages with control plots. When significant differences were observed, grasshopper densities were depressed about 25% and the number of species usually decreased by two. Variability in the impact of avian predators was observed among years and among sites for both total grasshopper density and number of grasshopper species. Assessment of the impact of avian predation on population or community dynamics of grasshoppers must include spatial and temporal variability.