Abstract: The environmental heterogeneity is an important mechanism underlying the formation and maintenance of bio-geographic pattern. The spatial pattern of grasshopper species is the result of longterm adaptation in nature, reflecting the co-evolution mechanisms with which grasshoppers adapt to the habitats. Through field survey from July to August, 2009, by using the GIS and S-PLUS 8.0, we developed the GAM model for the relationship between nymph and adult adundance of Oedaleus asiaticus and topographic indices in the upper reaches of Heihe River on the northern slope of the Qilian Mountains. The topographic indices included elevation, direction, slope, position, profile and plane. The results showed that the structure and D² values of models were different for O. asiaticus nymphs and adults, so was the model stability in modeling, indicating their differences in response to the gradients of topographic indices. The gradient analysis in this model showed that the locust nymphs and adults were distributed in a wide range of environments, in different gradients of elevation, direction, slope, position, profile and plane, and in all land positions. However, it does not mean that the distribution of locust nymphs and adults is equally affected by each factor, or has a uniform distribution probability in the whole environmental range. The GAM modeling indicated that the distribution of locust nymphs and adults were mainly controlled by the elevation. With the elevation increasing, the abundance of locust nymphs and adults showed an upside-down “V” trend, but the upper limit of elevation for distribution of the locust nymphs was higher than that of adults. Adults had higher abundance in the whole regions, but they were mainly located in the region where the profile is less than 0, while the nymphs mainly concentrated in the south and southwest slopes, which was consistent with the actual observation results. The heterogeneity of O. asiaticus in selecting habitats made the spatial pattern of locust nymphs and adults in the same terrain obviously different.

Key words: Oedaleus asiaticus, nymph, adult, spatial distribution, spatial abundance, topography, GAM, Qilian Mountains