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Grasshopper Abundance in an Arizona Rangeland Undergoing Exurban Development

Carl E. Bock, Zach F. Jones and Jane H. Bock
Rangeland Ecology & Management
Vol. 59, No. 6 (Nov., 2006), pp. 640-647
Stable URL: http://www.jstor.org/stable/3899897
Page Count: 8
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Grasshopper Abundance in an Arizona Rangeland Undergoing Exurban Development
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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. /// El desarrollo de áreas residenciales esta substituyendo a las áreas de rancho en el sur-oeste de los Estados Unidos, con efectos ecológicos potencialmente significativos pero muy poco estudiados. Hicimos el conteo de saltamontes (orthoptera: Acrididae) y medimos la cobertura vegetal durante 2 años en un prado y sabana de enebro/roble en el sudeste de Arizona, en 48 transectos pastados por ganado, en medio de desarrollos residenciales de baja densidad, o ambos, o ninguno. La riqueza de saltamontes no estaba relacionada al pastoreo o al desarrollo, pero su abundancia fue mucho más alta en transectos exurbanos, donde los dueños de propiedades mantenían ganado, que en otras áreas. El dosel y el área basal de hierbas fueron también más altos en áreas exurbanas pastadas, probablemente porque el pastoreo, frecuentemente hecho por caballos, en áreas exurbanas estaba más parchado, y se crearon perturbaciones más conducentes al establecimiento de hierbas que en áreas de pastoreo uniforme en ranchos próximos. Los patrones de abundancia de 3 subfamilias de saltamontes fueron generalmente consistentes con sus preferencias de hábitat conocidos. Los conteos de alimentación de la subfamilia Gomphocerinae fueron relativamente altos en áreas sin pastoreo y sin quemar, y positivamente correlacionados a la cobertura vegetal. El número de hierbas y la alimentación de la subfamilia Melanoplinae estuvieron positivamente correlacionados con la cobertura de hierbas en todos los transectos y esta subfamilia dominó los conteos en las propiedades exurbanas pastadas. Los saltamontes de la subfamilia Oedipodinae prefieren áreas de vegetación escasa, y su conteo estuvo negativamente correlacionado con la altura de la vegetación y positivamente asociados con la presencia de ganado en paisajes exurbanos y no desarrollados. En general, nuestros resultados sugieren que paisajes heterogéneos en áreas exurbanas que incluyen pequeñas pasturas de ganado tuvieron mayores densidades de saltamontes que las áreas sin pastoreo o grandes ranchos ganaderos.

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