 Fig. 1. Dr. Bloodworth sampling for grassland bugs written by: Allison Huysman, Leo Kerner and Ben Burgunder It is a dry day in the Montana rangelands, a vast landscape of sagebrush, prairie junegrass, and purple prairie clover. Dr. Kathryn Bloodworth is vacuuming the plants. She wields a modified leaf blower designed to suck up the insects that call this wide-open space home (Fig. 1). Her goal: to understand the links between insects, grassland plant communities, and drought. Before European colonization of North America, more than 2 million acres of the continental United States consisted of these types of rangelands (Bloodworth 2024, Doherty et al. 2022). Today, around 38% of the original acreage remains. Despite this reduction, grasslands still cover 30% of the US landmass (Bloodworth 2024). The loss of rangeland was, and remains, driven by conversion into cropland and expanding urbanization. The remaining rangeland is threatened by environmental stressors facilitated by climate change (Holechek et al. 2020). Climate change can heat and dry rangelands. This can cause changes to plant functional traits such as the nutritional content, growth, and leaf thickness (Augustine et al. 2018), which can impact animals higher up the food chain, including insects (Holechek et al. 2020). As a Ph.D. student at the University of North Carolina, Greensboro (UNCG), Dr. Bloodworth first investigated the effects of drought on plant communities and their traits before exploring the effects of drought and cattle grazing on grassland insects. She conducted the first part of her study at two Great Plains sites in Montana and Wyoming (Fig. 2). While the effect of drought on plant communities is well documented, the effect on plant functional traits is barely explored. Dr. Bloodworth argues that understanding how drought affects these traits is important if we are to predict how different grassland plant species will respond to drought.  Fig. 2. Sample sites. Figure produced by Dr. Bloodworth At both her sites, Dr. Bloodworth created five experimental drought treatments, using shelters to reduce rain. In each treatment, she measured plant species richness, abundance, and functional traits like height, leaf thickness, and leaf dry matter content (LDMC). During her three year study, there was a 1-year natural drought during different years in each state, which allowed her to also measure the effects of a natural drought on the plant communities. Dr. Bloodworth hypothesized that with her treatments, the plant community would exhibit functional traits that facilitated resistance to drought through two mechanisms: tolerance (traits that sustain growth during drought) and avoidance (traits that conserve resources). Overall, her results showed that plants at her study sites demonstrated both drought resistant mechanisms. The dominant species in Montana, a fast-growing invasive, was able to avoid drought by growing rapidly when water was available. In contrast, slower-growing native grasses in Wyoming tolerated drought by storing resources in their leaves. This adds to our understanding of how different plant communities respond to changing precipitation through different species-level responses.  Fig. 3. Diversity of grassland insects. Figure produced by Dr. Bloodworth. Next, Dr. Bloodworth delved into how the community composition of grassland insects shifts with drought and cattle grazing intensity. Grasslands harbor abundant and rich insect communities (Fig. 3). Grasshoppers, caterpillars, true bugs, and beetles all abound. These insects depend on the grassland plants for food and shelter. By vacuuming up all the insects in standardized square plots set up at her study sites. Dr. Bloodworth quantified the insect diversity and biomass at each site (Fig. 1). She found the arthropod community changes in response to an interaction between cattle grazing intensity and precipitation. Arthropod communities are resistant to grazing intensity in years with average precipitation when there is plenty of plant food for all to eat. However, in drought years, arthropod abundance decreases and diversity increases in response to increased grazing intensity. This means that as droughts become more frequent, grazing intensity is likely to have a stronger effect on arthropod communities. While there is still so much to explore in this field, especially as patterns of drought fluctuate across the contiguous United States’ grasslands, Dr. Bloodworth has made a remarkable contribution to advancing our understanding of the complex relationships that are constantly shifting out of sight.
References Augustine, D.J., Blumenthal, D.M., Springer, T.L., LeCain, D.R., Gunter, S.A. and Derner, J.D. (2018), Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie. Ecol Appl, 28: 721-735. https://doi.org/10.1002/eap.1680 Bloodworth, K. (2024). Precipitation drives arthropod and plant community shifts in mixed-grass prairie [PowerPoint slides]. University of Maryland. Doherty, K., Theobald, D.M., Bradford, J.B., Wiechman, L.A., Bedrosian, G., Boyd, C.S., Cahill, M., Coates, P.S., Creutzburg, M.K., Crist, M.R., Finn, S.P., Kumar, A.V., Littlefield, C.E., Maestas, J.D., Prentice, K.L., Prochazka, B.G., Remington, T.E., Sparklin, W.D., Tull, J.C., Wurtzebach, Z., and Zeller, K.A., 2022, A sagebrush conservation design to proactively restore America’s sagebrush biome: U.S. Geological Survey Open-File Report 2022–1081, 38 p., https://doi.org/10.3133/ofr20221081. Gely, C., Laurance, S.G.W. and Stork, N.E. (2020), How do herbivorous insects respond to drought stress in trees?. Biol Rev, 95: 434-448. https://doi.org/10.1111/brv.12571 Holechek, Jerry & Geli, Hatim & Cibils, Andres & Sawalhah, Mohammed. (2020). Climate Change, Rangelands, and Sustainability of Ranching in the Western United States. Sustainability. 12. 4942. 10.3390/su12124942. Authors: Allison Huysman is a Ph.D. student in the Gruner lab. She researches cavity nesting birds and how they can contribute to pest control in working landscapes. Leo Kerner is a master’s student in the Hooks Lab. His focus is on developing ecologically and economically sustainable solutions in agriculture using living mulches. Currently he is looking into the effects of using a red clover living mulch on suppressing insect pests, improving beneficial arthropod numbers, and reducing weed invasion. Ben Burgunder is a master’s student in the Fritz Lab. He is interested in whether mosquito vector community composition and West Nile virus prevalence can help explain patterns of human West Nile virus cases in Chicago. Comments are closed.
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