LTREB Renewal: Ecosystem Structure and Function in Palouse Grasslands

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Grasshopper abundance in the western United States varies dramatically across years and locations. Grasshoppers can have high numbers at one site and low numbers at a nearby site in the same year, while in the next year the numbers at the sites may be reversed. This can create economic hardship for livestock producers that depend on reliable forecasts of both weather and pests. Possible reasons for the large variation in grasshoppers include weather patterns, plant quantity and nutritional quality, and predation. Understanding grasshopper dynamics cannot be advanced by studies of only one possible reason or at a just one site over a few years, but requires long-term studies across a number of sites. This project will involve a number of graduate students and provide outreach to Federal, State and Tribal agencies, non-governmental organizations and civic groups. The project will also be woven into an established summer field ecology program run by the University of Notre Dame. This program provides 10-week field research experiences to undergraduates and specifically recruits Native American and non-Native students in order to help to promote cultural exchange. The program has been successful in that all of the participating Native American students have completed undergraduate degrees and a number are now working for Tribal natural resource agencies.While weather cannot be experimentally altered, results from different years and sites will be compared to help disentangle the effects of food and predation on grasshopper populations over a range of weather conditions. Grasshoppers will also be experimentally studied by keeping some populations in large field cages at different sites where plant quality and quantity and predation are manipulated relative to natural levels in any given year. Grasshopper populations can reduce plant production directly through consumption and indirectly through their effects on the cycling of nutrients needed by plants. Results of long term studies thus far indicate that populations at some sites are more frequently controlled by one or the other mechanism, but populations across all sites are not controlled by the same mechanism in any year. This project will add to that long term record in order to answer why one mechanism operates only in some years at certain sites, and also to reveal long-term trends due to climate changes. And while the numbers of larger plant-eating animals, such as bison, elk, deer, or rabbits, may not vary as much as grasshoppers do, they also may be controlled by availability of food at some times and places, or by predation at others. Therefore, the grasshopper system is a model useful for addressing this question more generally.