Geographic Variation in Migratory Grasshopper Recruitment under Projected Climate Change

John M Humphreys,David H Branson,Robert B Srygley

doi:10.3390/geographies2010003

John M Humphreys, David H Branson + Show 1 more

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https://doi.org/10.3390/geographies2010003

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Abstract

Climate change is expected to alter prevailing temperature, precipitation, cloud cover, and humidity this century, thereby modifying insect demographic processes and possibly increasing the frequency and intensity of rangeland and crop impacts by pest insects. We leveraged ten years of migratory grasshopper (Melanoplus sanguinipes) field surveys to assess the response of nymph recruitment to projected climate conditions through the year 2040. Melanoplus sanguinipes is the foremost pest of grain, oilseed, pulse, and rangeland forage crops in the western United States. To assess nymph recruitment, we developed a multi-level, joint modeling framework that individually assessed nymph and adult life stages while concurrently incorporating density-dependence and accounting for observation bias connected to preferential sampling. Our results indicated that nymph recruitment rates will exhibit strong geographic variation under projected climate change, with population sizes at many locations being comparable to those historically observed, but other locations experiencing increased insect abundances. Our findings suggest that alterations to prevailing temperature and precipitation regimes as instigated by climate change will amplify recruitment, thereby enlarging population sizes and potentially intensifying agricultural pest impacts by 2040.

Highlights

Climate is the dominant force driving biogeographic patterns at large spatial scales [1,2]and exerts an overriding influence on insect distributions, abundances, and demographic processes [3,4,5,6,7]
Component loadings for the top five contributing climate variables indicated that temperature was most important in describing M. sanguinipes (Msang) occurrence, with mean temperature of the warmest quarter contributing 33.7% to the synthetic covariate followed by temperature diurnal range (16.3%), temperature seasonality (13.3%), day-to-night temperatures oscillations, and average temperature during the coldest quarter of the year (7.9%)
Moderate Resolution Imaging Spectroradiometer (MODIS) derived remote sensing data suggested that pixel diversity calculated using the Simpson (61.6%) and Shannon (26.0%) indices accounted for the vast majority of variation in the synthetic vegetation covariate, with image texture metrics contributing slightly more

Summary

Introduction

Climate is the dominant force driving biogeographic patterns at large spatial scales [1,2]and exerts an overriding influence on insect distributions, abundances, and demographic processes [3,4,5,6,7]. Through a combination of anthropogenic forcing and natural variability, climate change is expected to alter prevailing temperature and precipitation patterns this century, propelling departure from historic conditions and potentially increasing the regularity and severity of extreme weather events in the western United States (US) [8,9,10,11]. Vital to nutrient processing and ecosystem function [23], grasshopper population densities often show dramatic increases that beget substantial economic harm to cultivated crops and rangeland forage [22,24]. Despite their potential as focal species for climate change research, enormous uncertainty exists in foreseeing how climate change may affect grasshopper populations. As an initial step in understanding how climate change may affect grasshopper populations in the US, process models were developed to forecast future reproductive rates for the migratory grasshopper (Melanoplus sanguinipes)

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