TEMPORAL VARIATION IN RANGELAND GRASSHOPPER (ORTHOPTERA: ACRIDIDAE) COMMUNITIES IN THE STEPPE REGION OF MONTANA, USA

Abstract

AbstractA study was conducted to evaluate changes in rangeland grasshopper communities over a 5-year period in the Agropyron spicatum (Pursh) Scribn. and Smith and Bouteloua gracilis (H.B.K.) Lag. provinces of the steppe region of Montana, USA. Results showed that it was possible to categorize years into outbreak, non-outbreak, and transitional based on rangeland grasshopper intensity. Nearly twice as many species were observed in outbreak versus non-outbreak years. Of the 57 total grasshopper species collected over the entire study period, 16 species were found only during outbreak years and only two were found exclusively during non-outbreak years. Of the remaining 39 species collected during outbreak and non-outbreak years, 27 species showed no significant differences in the percentage of the community that they represented and 11 species showed significant increases. The only species that made up proportionately less of the community as densities declined from outbreak to non-outbreak was Melanoplus sanguinipes (F.). Although M. sanguinipes, Ageneotettix deorum (Scudder), and Aulocara elliotti (Thomas) were the three top-ranked species in both outbreak and non-outbreak years, M. sanguinipes contributed most to overall shifts in grasshopper intensity. Results support the hypothesis that grasshopper communities overall are sensitive to temporal changes in resources, even though responses of individual species differed.