Effects Of Grazing By Large Herbivores On The Performance And Abundance Of Grasshopper (Acrididae:Euchorthippus)in Songnen Grassland

Grasshoppers are important invertebrates and primary consumers in grasslands, and contribute significantly affect ecosystem services and functioning. Grazing is one of the most important management of grasslands and large herbivores may influence habitat quality for grasshoppers by altering food availability and microclimate. Therefore, for a better understanding of the relationship between large herbivores and small insect herbivores, the effects of large herbivores grazing on the abundance and performance of grasshoppers will be examined. The knowledge takes important implications for effectively controlling the outbreak of grasshoppers, and determining reasonable and effective grazing management in grasslands.In this study, a manipulated field experiment with different grazing intensities (no grazing, moderate grazing, and heavy grazing) was conducted to examine the effects of large herbivores on the abundance and performance of a grasshopper (Euchorthippus cheui) in meadow steppe. The main results are as follows:(1) Grasshopper abundance significantly differed among different grazing intensities (total abundance, P<0.01; abundance of female grasshopper, P<0.01), and increased with increasing grazing intensities.(2) Survival rate and median survival time of grasshoppers significantly differed among the three grazing intensities (no grazing, moderate grazing, and heavy grazing), but grasshopper oviposition was not affected by large herbivores. Median survival time and survival rate of grasshoppers (total and female) were significantly higher in heavy grazing intensities treatments when plant community was dominated by Grass, but were higher in moderate grazing treatments and were lower in heavy grazing intensities treatments when plant community was dominated by mixed grass-forb.(3) Vegetation characteristics had different responses to grazing intensities in grass-dominated and grass-forb mixed plant communities. Plant height, coverage and aboveground biomass in grass-dominated plant community were increased in moderate grazing treatments, but the coverage and N content of plant community were decreased in heavy grazing treatments. Plant height, coverage and aboveground biomass in grass-forb mixed plant community were decreased in heavy grazing treatments. There were significant differences for light intensities on5cm in aboveground, but the surface temperature and relative humidity were not significantly affected. (4) The main factors affecting grasshopper survival rates were different between grass-dominated and grass-forb mixed plant communities in different grazing intensities. Survival rate was mainly driven by forb biomass, and plant biomass in grass-dominated plant community. Light intensities is most important factor for grasshopper survival rate in forb-grass mixed plant community. Additionally, plant coverage, aboveground biomass and Grass height also significantly affected survival rate of grasshoppers in forb-grass mixed plant community.In conclusion, large herbivores had a significant impact on population and individual of grasshoppers among different grazing intensities. Grasshopper abundance was higher in heavy grazing intensities treatments. The responses of grasshopper individual to grazing intensities depended on plant community types. In grass-dominated plant community, large herbivores affected survival rate of grasshoppers by altering forb biomass, and influenced it through changing light intensities and plant coverage in grass-forb mixed plant community. Our results showed that grasshopper performance (survival rate) was closely related to abundance of grasshopper in grazed grassland ecosystems. In addition, it suggested that the response of individual grasshopper to grazing was differed at heterogeneous habitats. Therefore, vegetation heterogeneity should be considered in grasslands when large herbivore grazed:...