Reproduction and survival in Melanoplus sanguinipes (Orthoptera: Acrididae) in response to resource availability and population density: the role of exploitative competition

Abstract

AbstractThe relative importance of exploitative competition for resources on grasshopper reproductive allocation has not been fully examined. Given the large fluctuations in grasshopper densities that periodically occur in western North America, an increased understanding of how grasshopper survival and reproduction vary in response to intraspecific densities and per capita resource availability is important. I examined if exploitative resource competition could explain variation in reproductive allocation in Melanoplus sanguinipes (Fabricius) in response to resource availability and grasshopper population density. I also examined whether individual differences in competitive ability resulted in increased variance in egg production with low per capita resource availability. As expected with exploitative resource competition, per capita resource availability explained a significant amount of the variation in all reproductive characteristics examined. There was no effect of per capita resource availability on survival. Residuals of the regressions of egg production and vitellogenesis versus per capita resource availability did not differ for resource or density treatments, indicating that exploitative competition for resources played a more important role than interference competition in determining reproductive allocation in M. sanguinipes. Individual differences were evident, as variation around the mean of egg production increased with resource limitation. Exploitative competition for resources was important in determining both individual and population-level reproductive responses of grasshoppers to resource availability.