Predicting the effects of extreme drought on insect herbivore control of grassland ecosystem function

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Extreme droughts in North America have occurred with surprising frequency for the last 2,000 years. Recent droughts of the 1930s and 2012 highlighted the vulnerability of grasslands to severe rainfall shortages. These droughts resulted in an estimated $30 billion in damages and caused significant changes to animal habitat availability, soils, and nutrient cycling. The role of insects in US grasslands and their responses to extreme drought is poorly understood. This is an important omission, because insects regulate grassland nutrient cycling, suppress primary production, and often achieve outbreak densities during severe droughts (e.g. the Dust Bowl). This award will quantify insect regulation of primary production and nutrient cycling in US grasslands spanning the Midwest, from the Rocky Mountains to the Mississippi River. The award will address drought impacts on grassland insects and how drought may cause harmful pest outbreaks that could further exacerbate drought conditions. In addition, this award will train two graduate studies and provide hands-on experience for multiple undergraduate students from traditionally underrepresented groups. Finally, this research will produce a comprehensive and modern guide to grasshopper identification in Midwestern grasslands that will be of use to managers, researchers, and educators.This project consists of two separate components. A manipulative field study will impose severe drought at three grasslands across a xeric to mesic precipitation gradient. Drought treatments will be combined with insect exclosures. Over three years, researchers will measure aboveground net primary production, nutrient cycling, plant physiology, plant traits, and insect herbivore densities. These data will be analyzed to identify the mechanism by which insects regulate production and nutrient cycling under ambient and drought conditions. A laboratory experiment will identify how both plant and insect physiology change under drought conditions. Physiological measurements will be incorporated into mathematical models to predict nutrient cycling under ambient and drought conditions in grasslands of the central US.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.