Effects of altered seasonality of precipitation on grass production and grasshopper performance in a northern mixed prairie

Authors: Branson, David - Dave

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2017
Publication Date: 5/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5700686
Citation: Branson, D.H. 2017. Effects of altered seasonality of precipitation on grass production and grasshopper performance in a northern mixed prairie. Environmental Entomology. 46(3):589-59. doi:10.1093/ee/nvx053.

Interpretive Summary: At drought timing could be more important than drought intensity in how it affects both rangeland production and grasshopper populations, there is a need to understand how rangeland responds to seasonal variation in precipitation. Grasshopper outbreaks frequently lead to expensive large scale chemical control efforts, but manager’s abilities to proactively rather than reactively manage grasshopper problems are constrained by an inability to predict population responses to weather variation. We modified seasonal patterns of precipitation and grasshopper density in a manipulative experiment, to examine if seasonality of drought combined with herbivory affected plant biomass, nitrogen content and grasshopper performance. The results confirm that the season of drought is critical for understanding grasshopper outbreaks, with early summer drought positively affecting grasshopper survival, while season long and late season drought did not. Extreme early summer drought conditions combined with high grasshopper densities are likely required to strongly affect M. sanguinipes population dynamics in this system.

Technical Abstract: Climatic changes are leading to differing patterns and timing of precipitation in grassland ecosystems, with the seasonal timing of precipitation affecting plant biomass and plant composition. No previous studies have examined how drought seasonality affects grasshopper performance and the impact of herbivory on vegetation. We modified seasonal patterns of precipitation and grasshopper density in a manipulative experiment to examine if seasonality of drought combined with herbivory affected plant biomass, nitrogen content and grasshopper performance. Grass biomass was significantly affected by both precipitation and grasshopper density treatments, while nitrogen content of grass was higher with early season drought. Proportional survival was negatively affected by initial density, indicative of density dependent mortality, while survival in the early drought treatment was higher than in the full season drought treatment. The results of this experiment confirm that the season of drought is critical, with early summer drought affecting grass nitrogen content and grasshopper survival, while season long and late season drought did not. The support arguments that our knowledge of plant responses to seasonal short term variation in climate is limited and point to the need to conduct additional experiments manipulating the seasonality of precipitation to better predict grasshopper outbreak dynamics.