Spatial clustering of rangeland grasshoppers (Orthoptera : Acrididae) in the Qinghai Lake region of northwestern China

摘要

Geostatistical analyses were used to examine the pattern of spatial distribution of rangeland grasshoppers in the basin of Qinghai Lake in northwestern China. Two sampling expeditions were undertaken to collect relevant data. In the first case, data were collected across an area of 1295 km(2) to the west of the lake in August 1999. Moran's I was used to analyze spatial clustering of grasshoppers across this study region. Local G-statistics were used to analyze the pattern of grasshopper population density using two units of distance (100 m and 1 km). The analyses revealed spatial clustering at both 300-1300 m and 13-16 km. In the second expedition, in July 2000, grasshoppers were sampled at a fine scale (100, 30 m x 30 m plots) in a smaller area (Tiebujia) embedded within the previous region. The correlograms of Moran's I showed a strong, positive spatial correlation among the densities of both: all grasshoppers and the dominant species (Mymeleotettix palpalis Zub.), with clustering at a separation distance of 120 m. Analysis of the local G-statistic value in the regularly sampled area indicated that clustering occurred mainly between 120 and 150 m. These analyses showed that the rangeland grasshoppers in the study area had an obvious spatial clustering which varied with the spatial scale. At a large scale, clustering occurs at 13-16 km and at a local-scale at 120-150 and 300-1300 m.