Grasshoppers exhibit asynchrony and spatial non-stationarity in response to the El Niño/Southern and Pacific Decadal Oscillations

Authors: Humphreys Jr, John; Srygley, Robert; LAWTON, DOUGLAS - North Carolina State University; HUDSON, AMY - US Department Of Agriculture (USDA); Branson, David - Dave

Submitted to: Ecological Modeling
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2022
Publication Date: 6/22/2022
Citation: Humphreys Jr., J.M., Srygley, R.B., Lawton, D., Hudson, A.R., Branson, D.H. 2022. Grasshoppers exhibit asynchrony and spatial non-stationarity in response to the El Niño/Southern and Pacific Decadal Oscillations. Ecological Modeling. 471. Article 110043. https://doi.org/10.1016/j.ecolmodel.2022.110043.
DOI: https://doi.org/10.1016/j.ecolmodel.2022.110043

Interpretive Summary: This research was conducted as part of the USDA ARS research project, "Forecasting, Outbreak Prevention, and Ecology of Grasshoppers and Other Rangeland and Crop Insects in the Great Plains." Grasshoppers are perhaps the most significant rangeland pests in the United States (US). However, despite the important ecosystem functions they provide, grasshopper populations often obtain densities that cause significant economic harm to grazing operations and other agricultural industries. This study assessed the influence of temperature, precipitation, and climate-oceanographic variability on a 42-year record of grasshopper density in the Western US. Our results show that changes in grasshopper abundance were correlated with long-term El Nino/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) variability. This study represents an important first step towards anticipating how grasshopper populations may respond to future climate change.

Technical Abstract: Grasshoppers are preeminent herbivores, essential to grassland function, and perhaps the most significant rangeland pests in the United States (US). However, despite the important ecosystem functions they provide, grasshopper populations often obtain densities that cause significant economic harm to grazing operations and other agricultural industries. Although numerous local studies, conducted at the level of individual field sites, have examined potential mechanisms contributing to grasshopper population "boom and bust" cycles, there has yet to be a large, landscape scale study quantifying grasshopper variation across the Western US as a whole. While taking steps to account for data collection biases, we assessed the influence of temperature, precipitation, and climate-oceanographic variability on a 42-year record of grasshopper density in the Western US. Central to our analysis was employing spatially varying coefficients to model location-specific variation in grasshopper response to climate. Our results quantitatively demonstrated inter-annual changes in grasshopper abundance to be correlated with long-term El Nino/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) variability and to exhibit spatial non-stationarity and asynchrony such that the relative influence of climate on grasshopper abundance varied both through time and across geographic space. Our results suggest that the Western US can effectively be divided into seven geographic regions of approximately homogeneous character with respect to how grasshoppers respond to climate. Our study is the first to incorporate climate-oceanographic indices as spatially varying coefficients for assessment of a terrestrial species and represents a critical step towards anticipating how grasshopper populations may respond to future climate change.