Abstract: The environmental heterogeneity caused by topographical diversity is an important mechanism of the formation and maintenance of bio-geographic spatial distribution pattern at micro-scale, and also, the prerequisite for the difference in the distribution of species richness. With the help of GIS and S-Plus, the GAM model was used to study the topographic indices affecting the distribution of grasshopper on the natural grasslands in the upper reaches of Heihe River on the northern slope of Qilian Mountains from July to August 2009, and the relationship between the regional grasshopper number and terrain complexity was also studied, based on the quantitative analysis of the topographic variation characteristics. The topographical factors affecting the grasshopper density were in the order of aspect > elevation > slope > position > plane curvature > profile curvature. The distribution of grasshopper was almost balanced at different gradients of position, plane curvature, and profile curvature, and presented a quadratic parabola distribution at different gradients of aspect and slope and an “S” distribution at different gradients of evaluation. There was a higher grasshopper density in the whole region, but the grasshopper was mainly distributed in the region with an altitude of 2550-2650 m, and concentrated in the northwest and west aspect, which was consistent with the actual observation. The relationships between the grasshopper density and terrain factors and the distribution of the grasshopper indicated that the redistribution of water and heat conditions due to topographic factors caused the diversification and fragmentation of the distribution pattern of the grasshopper.

Key words: urbanization, ecosystem services, CLUE-S model, driving factor., InVEST model