Effects of invasive weeds on relative grasshopper abundance in alpine steppe in the Qilian Mountains.
The influence of weed (Stellera chamaejasme, Thermopsis lanceolata and Melica przewalskyi) invasion on the community composition, relative abundance and population of grasshoppers was studied in alpine grassland of the Qilian Mountains. The vegetation community, physical-chemical characteristics of soil, species diversity and community numbers of grasshoppers were investigated from June to September 2008-2009. Weed invasion significantly (P<3.05) reduced species richness, diversity and the evenness index of vegetation but significantly (P<0.05) increased the height and biomass. The contents of organic matter and moisture from grassland invaded by M. przewalskyi were the highest but the largest populations of grasshoppers were found in grasslands invaded by S. chamaejasme and T. lanceolata. The soil hardness in S. chamaejasme invaded grassland and total N content in natural grassland were strikingly (P<0.05) higher than in others. Weed invasion affected grasshopper community composition, reduced species diversity, and changed species relative abundance, while their effect on population size depended on the kinds of weeds: invasion by M. przewalskyi inhibited, while that of S. chamaejasme and T. lanceolata increased grasshopper populations. The mechanism of community characteristics of grasshopper response to invasive weeds, not only offers reference for studying the impact of degradation of alpine grassland caused by weed invasion on the diversity of insect and invertebrates, but gives data for managing the maintainance and conservation of biodiversity in alpine grasslands.