The effects of livestock grazing and climate variation on vegetation and grasshopper communities in the northern Chihuahuan Desert

David C. Lightfoot

doi:10.3897/jor.27.19945

Abstract

Grasshoppers are important herbivores of North American semi-arid grasslands and shrublands, and vegetation and climate are key factors controlling their species compositions and population dynamics. Domestic livestock grazing is a historic and a current landscape-scale ecological perturbation that has caused reductions of perennial grasses and increases in woody shrubs and weedy annual herbs in desert grassland communities. Climate variation also affects vegetation and grasshopper production, and the combined effects of livestock grazing and climate variation on vegetation and grasshoppers have not been adequately studied in the American Southwest. I measured vegetation and grasshoppers for five years at a series of five semi-arid sites in the northern Chihuahuan Desert to evaluate the interactive effects of short-term livestock grazing and climate variation on plant and grasshopper community structure and species abundances. The study sites ranged from shrub dominated to grass dominated landscapes, with livestock fence lines separating land that was grazed at 30% annual forage utilization, and lands on the other sides of the fences excluded from grazing for at least 20 years. I assigned grasshopper species to life-form guilds based on their ecomorphologies and their microhabitat substrate uses that I observed. A wet spring/dry summer El Niño event occurred at the beginning of the study, and a dry spring/wet summer La Niña event occurred at the end of the study. Livestock grazing changed plant and grasshopper species compositions and abundances significantly during those wet years, further favoring annual forbs, annual grasses and non-graminicole grasshoppers on grazed lands during wet years, while favoring perennial grasses and graminicoles on non-grazed lands also during wet years. The biotic communities at all sites probably supported more perennial grasses and more graminicoles prior to European settlement and livestock grazing that began over a century before this study.

Highlights

IntroductionGrasshoppers are important primary consumers in semi-arid regions throughout the world (Uvarov 1977), and grasshopper species compositions are determined largely by geographic proximity to evolutionary source regions (Key 1959, Otte 1976) and by species adaptations to local soils and vegetation composition and structure (e.g. Anderson 1964, Mulkern 1967, 1982, Otte and Joern 1977, Joern 1979, 1982, Kang et al 1989, Fielding and Brusven 1995a, Torrusio et al 2002, Cigliano et al 2010, Savitsky 2010)
I measured vegetation and grasshoppers for five years at a series of five semi-arid sites in the northern Chihuahuan Desert to evaluate the interactive effects of short-term livestock grazing and climate variation on plant and grasshopper community structure and species abundances
How grasshopper communities and populations respond to environmental disturbance such as domestic livestock grazing and climate change depends to what extent soil, vegetation and weather conditions change in magnitude, space and time, and to what extent different grasshopper species with variable environmental tolerances are affected by the changes

Summary

Introduction

Grasshoppers are important primary consumers in semi-arid regions throughout the world (Uvarov 1977), and grasshopper species compositions are determined largely by geographic proximity to evolutionary source regions (Key 1959, Otte 1976) and by species adaptations to local soils and vegetation composition and structure (e.g. Anderson 1964, Mulkern 1967, 1982, Otte and Joern 1977, Joern 1979, 1982, Kang et al 1989, Fielding and Brusven 1995a, Torrusio et al 2002, Cigliano et al 2010, Savitsky 2010). Population densities of many grasshopper species fluctuate widely over time, apparently largely due to bottom-up changes in food plant availability and quality, caused by variation in precipitation, and by physiological responses to variation in temperature and moisture conditions (Rodell 1977, Capinera 1987, Fielding and Brusven 1990, Joern and Gaines 1990, Belovsky and Joern 1995). How grasshopper communities and populations respond to environmental disturbance such as domestic livestock grazing and climate change depends to what extent soil, vegetation and weather conditions change in magnitude, space and time, and to what extent different grasshopper species with variable environmental tolerances are affected by the changes. Some species are likely to respond in certain ways, while other species may show different responses (Fielding and Brusven 1996). The grasshopper community guild concept has been used to describe grasshopper community structure for specific assemblages and locations in North America (e.g. Joern and Journal of Orthoptera Research 2018, 27(1)

Methods

Results

Conclusion