Abstract:  The n-alkanes in plant cuticular wax have been used as markers to estimate the diet composition and intake of grazing herbivores, but limited information is available about diet pattern of grasshoppers in natural grasslands based on the n-alkane technique. The objective of this research was to estimate the diet composition and trophic niche of Oedaleus asiaticus, a dominant grasshopper species, using the n-alkane technique in combination with quadrats. Experiments were conducted in three typical plant communities (i.e., Stipa klemenzii, Leymus chinensis, and Stipa grandis communities) along precipitation gradients in the Inner Mongolian steppe from July to August of 2003. Twenty quadrats were selected randomly and clipped to ground level in each community to measure plant species diversity and aboveground biomass. Main plant species in each community and the feces of O. asiaticus were analyzed for concentration patterns of n-alkanes. Our results indicate that the diet composition of O. asiaticus in natural grasslands can be accurately estimated using the n-alkane technique, and it is significantly different under different grazing pressures and in different plant communities. The grasshopper shifted its diet pattern from a specialist (graminivorous) in L. chinensis and S. grandis communities to a generalist (mixed graminivorous) in S. klemenzii community. The overlapping indexes of trophic niche between O. asiaticus and sheep were 0.0619, 0.0172 and 0.1815 in L. chinensis, S. grandis and S. klemenzii community, respectively. The community structures of the vegetation (plant species diversity, biomass proportion, and frequency distribution) had significant influences on the diet composition of O. asiaticus. Grazing altered the plant community and indirectly affected the grasshoppers’ food selection. The results suggest that certain competition may exist for food resources between grasshoppers and livestock.

Key words: Oedaleus asiaticus, plant community, grazing pressure, diet pattern, trophic niche, sheep, n-alkane technique, Inner Mongolian steppe