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DYNAMICS AND STRUCTURE OF GRASSHOPPER ASSEMBLAGES IN SHORTGRASS PRAIRIE

Published online by Cambridge University Press:  31 May 2012

John L. Capinera
Affiliation:
Department of Entomology, Colorado State University, Fort Collins, Colorado, USA80523
David C. Thompson
Affiliation:
Department of Entomology, Colorado State University, Fort Collins, Colorado, USA80523

Abstract

Grasshopper assemblages inhabiting eight pastures of shortgrass prairie rangeland in northeast Colorado were studied for 4–6 years during a general increase and decrease in grasshopper abundance. Average densities increased 10-fold during a 3- to 4-year increase phase, with individual species and populations in separate pastures exhibiting greater or lesser changes. Asynchrony in grasshopper population characteristics was noted. The co-dominant species, Opeia obscura (Thomas) and Melanoplus gladstoni Scudder, exhibited similar trends in density, but M. gladstoni dominance, expressed as its proportion of the population, declined steadily relative to O. obscura. Subdominant species similarly were asynchronous. Species richness did not change during this cycle. Grasshopper densities and assemblage structure were not affected by rangeland management practices of fertilizer (nitrogen) and herbicide (atrazine) application.

Résumé

On a étudié les communautés de criquets de huit pâturages en prairie à herbages courts du nord-est du Colorado pendant 4–6 ans au cours d’un cycle de croissance–décroissance d’abondance. Les densités moyennes ont augmenté de 10 fois durant la phase croissante d’une durée de 3–4 ans, les espèces et populations des différents pâturages montrant des fluctuations plus ou moins importantes. On a noté une asynchronie des caractéristiques démographiques des populations de criquets. La densité des espèces co-dominantes Opeia obscura (Thomas) et Melanoplus gladstoni Scudder montrait des tendances similaires, mais la dominance de M. gladstoni, exprimée en tant que proportion de la population qu’elle représentait, a diminué constamment relativement à O. obscura. Les espèces sous-dominantes étaient également asynchrones. La richesse en espèces n’a pas changé durant ce cycle. Les densités de criquets et la composition de leurs communautés n’ont pas été affectées par les pratiques d’application de fertilisants (azote) et d’herbicides (atrazine) du programme de régie des terres.

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Type
Articles
Copyright
Copyright © Entomological Society of Canada 1987

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