Drought impacts on competition in Phoetaliotes nebrascensis (Orthoptera Acrididae) in a northern mixed grassland

Authors: Branson, David - Dave

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2015
Publication Date: 1/7/2016
Publication URL: http://handle.nal.usda.gov/10113/5695477
Citation: Branson, D.H. 2016. Drought impacts on competition in Phoetaliotes nebrascensis (Orthoptera Acrididae) in a northern mixed grassland. Environmental Entomology. 45(2):492-499. doi: 10.1093/ee/nvv225.

Interpretive Summary: Grasshoppers frequently reach outbreak densities that can cause economic damage to the livestock grazing industry. Weather can impact grasshopper population dynamics at scales ranging from short term to decadal time periods. In addition, extreme weather events can have large impacts on population dynamics. A manipulative cage experiment was conducted in eastern Montana to examine the impact of competition and drought on performance of an economic pest grasshopper species. Manipulating precipitation allowed an examination of weather conditions that would otherwise require multiple years of research to encounter. Despite much greater than normal late summer precipitation, grass biomass, grasshopper body size and grasshopper reproduction were all strongly affected by the drought treatment. This indicates that early summer drought could strongly negatively influence populations of this grasshopper, even when late summer precipitation is above average. The study reinforces the need to examine reproduction of adults to more clearly predict population changes due to changing climate conditions.

Technical Abstract: 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. Grassland droughts would be expected to strongly impact insect herbivores, but little field research has attempted to manipulate drought conditions with grasshoppers, the dominant grassland insect herbivore. A manipulative cage experiment was conducted in eastern Montana to examine the impact of intra and interspecific competition and drought on performance of Phoetaliotes nebrascensis, which had increased to outbreak levels at many sites in the area prior to this study. Despite the high rainfall that occurred in August, precipitation manipulation, density and the interactions between precipitation manipulation and density as well as between precipitation manipulation, density and competition all significantly affected grass biomass at the end of the experiment. Although precipitation and density treatments did not significantly affect survival, future reproduction was reduced by food limitation in high density and drought treatments. The impact of the precipitation manipulation and density treatments on grasshopper body size and reproduction were fairly similar in magnitude and much larger in magnitude than interspecific competition. The impact of precipitation manipulation and competition treatments would likely vary in a year with more typical late summer moisture. The study reinforces the need to examine reproduction of adults to more clearly predict population changes due to changing climate conditions.