Experimental Study of Avian Predation on Coexisting Grasshopper Populations (Orthoptera: Acrididae) in a Sandhills Grassland

Abstract

An experiment was performed to examine the impact of avian predation on populations and assemblages of insect herbivores in a grassland system. Here, I examine the effect of avian predators on grasshopper populations in regard to overall density, densities of individual species, species diversity, and overall taxonomic composition. Predation pressure was examined by comparing each of these attributes of grasshopper populations in 10 m .times. 10 m exclosures where birds were excluded with equally sized plots where birds were allowed to forage normally. In general, avian predation significantly affected grasshopper populations in a sandhills grassland. Overall densities were reduced 27.4% in the predation treatment, most species occurred in lower numbers (though some exceptions were observed), and fewer species coexisted. Specific differences in overall taxonomic composition between the treatments were not detecting using MANOVA. The relevance of these results to understanding community organization of herbivorous insects is discussed; the compensatory mortality hypothesis is not supported although other plausible hypotheses cannot be further evaluated with the present data.