Drought Impacts on Competition in Phoetaliotes nebrascensis (Orthoptera Acrididae) in a Northern Mixed Grassland

Global climate change is predicted to significantly modify patterns of precipitation, making it critical to develop a better understanding of how this will modify biotic interactions. Short-term to decadal-scale weather patterns can impact grasshopper population dynamics, but drought impacts on grasshoppers have rarely been studied in manipulative experiments. A cage experiment was conducted in eastern Montana to examine the impact of intra- and interspecific competition and precipitation manipulation treatments on performance of a common melanopline grasshopper Phoetaliotes nebrascensis (Thomas). High-density and drought treatments had similarly strong negative impacts on food availability. Proportional grasshopper survival did not differ significantly by treatment, but density dependence was evident in both body size and reproductive traits. The impact of precipitation and density treatments on grasshopper body size and reproduction were typically similar in magnitude and much larger than interspecific competition, with the exception of male femur length. Even with high late summer precipitation, drought had strong effects on individual body size and future reproduction. This study provides valuable information on population dynamics of an abundant grasshopper, with moderate precipitation reductions negatively affecting reproduction and body size. No positive impacts of drought as predicted by the plant stress hypothesis were observed. The study reinforces the need to examine drought manipulations to better predict grasshopper population changes due to changing climate conditions.