Submitted to: Ecological Society of America Bulletin
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 2002
Publication Date: May 30, 2002
Citation: BRANSON, D.H., HAFERKAMP, M.R. GRASSHOPPER AND SHEEP HERBIVORY IMPACTS ON GRASSHOPPER POPULATION DYNAMICS, VEGETATION AND NITROGEN AVAILABILITY: RESULTS FROM A TWO YEAR EXPERIMENT. ECOLOGICAL SOCIETY OF AMERICA BULLETIN. V.83, P. 324. 2002. Technical Abstract: Little experimental work has taken place on the ecological interactions between livestock grazing and grasshopper population dynamics and their impact on grassland vegetation. Livestock grazing can impact grasshopper population dynamics by changing factors such as host plant quantity or quality and microhabitat conditions. I conducted an experiment during 2000 and 2001 in eastern Montana to determine how the presence, timing and intensity of sheep grazing affected grasshopper population dynamics and vegetation characteristics; and, to examine if the relationships between sheep herbivory and grasshopper population dynamics changed with grasshopper stocking density. In 2000, 10m2 screen cages were stocked at 33% and 100% of the field density of 120 grasshoppers per square meter. Both grasshopper stocking density and sheep grazing significantly reduced both vegetation biomass and grasshoppers surviving to the end of the experiment. However, there were few treatment differences between the timing and intensity of sheep grazing on grasshopper survival or vegetation characteristics in 2000. Grasshoppers were smaller in both grazed and field density stocked cages. In 2001, fewer grasshoppers hatched in field density treatment cages than in reduced density treatment cages. Although grazing had small effects on hatching density in 2001, grazed cages had higher nitrate bioavailability and higher vegetation nitrogen content. To understand the effects of grasshopper densities and grazing on grasshopper population dynamics and vegetation, multiyear studies are required.