Grasshopper Abundance in an Arizona Rangeland Undergoing Exurban Development

Abstract

Housing developments are replacing ranches in the southwestern United States, with potentially significant but little-studied ecological effects. We counted grasshoppers (Orthoptera: Acrididae) and measured vegetative cover for 2 years in a grassland and mesquite/oak savanna in southeastern Arizona, on 48 transects that were grazed by livestock, embedded in low-density housing developments, or both, or neither. Grasshopper species richness was unrelated to grazing or development, but grasshopper abundance was much higher on exurban transects where homeowners kept livestock than in the other areas. Forb canopy and basal area also were highest in grazed exurban areas, perhaps because exurban grazing was relatively patchy, frequently involved horses, and created disturbances more conducive to forb establishment than did relatively uniform grazing on nearby ranches. Abundance patterns of 3 grasshopper subfamilies were generally consistent with their known habitat preferences. Counts of grass-feeding Gomphocerinae were relatively high in ungrazed and unburned areas, and positively correlated with grass cover. Numbers of forb- and mixed-feeding Melanoplinae were positively correlated with forb cover across all transects, and melanoplines dominated counts on grazed exurban properties. Band-winged grasshoppers (Oedipodinae) prefer areas of sparse vegetation, and their numbers were negatively correlated with height of ground vegetation and positively associated with the presence of livestock, in both exurban and undeveloped landscapes. Overall, our results suggest that heterogeneous landscapes in exurban areas that included small livestock pastures had higher grasshopper densities than either ungrazed areas or large cattle ranches.