The Effects Of Large Herbivores Grazing On Insect Community In Typical Steppe Of Inner Mongolia

Large herbivores and arthropods,important components of grassland ecosystem and biodiversity,play significant roles in the maintenance of ecosystem stability.How does the large herbivores disturbance affect insect community structure is an important question for the grassland scientific management.Therefore,in order to clarify the effect of grazing gradients on insect community dynamic and adaptability in typical steppe of Inner Mongolia,and to offer insights to livestock management and provide the basis for maintaining species diversity and ecosystem health,we investigated the insect diversity and their physiological responses to a series of 0,4,8,12,16 sheep 1.33 ha^-1 intensive grazing from 2014 to 2016 by conducting enclosed experiments and transcriptome analyses.We found that,continuous intensive grazing significantly decrease plant coverage,height,density,above-biomass,plant litter and grass biomass?P<0.05?,but no effect on forbs biomass.Grazing affects insect diversity,species richness,abundance,and trophic structure.Continuous grazing firstly changed insects abundance,followed by changes in species richness,which eventually led to changes in insect diversity;light grazing increased insect diversity index,species richness and abundance.Continuous grazing has a significant cumulative effect on insects.The insect population dynamics differed in temporal.In 2014,insect abundance increased significantly after livestock grazing30 days in light grazing plots,with a significant downward trend in insect abundance under continued grazing.In 2015 and 2016,insect abundance reached the peak after 10 days grazing.In 2015,insect abundance declined significantly in heavy grazing and over grazing plots?P<0.05?.In 2016,compared with the non-grazing plots,insect abundance also had significant decline in grazing disturbance?P<0.05?.Thus,insect community well conformed with the intermediate disturbance theory,with moderate grazing highly increased the diversity of insect.Grazing significantly influenced the abundance of trophic levels as well with a decrease in phytophagous insects after a first increase.While natural enemy insects significantly decreased,indicating higher trophic level is more susceptible to grazing.Insect groups showed different responses to grazing intensities and duration.The survey indicated that three-years continuous grazing does not affect the abundance of Formicidae.The abundance of Acrididae first increased and then decreased in 2016.The abundance of Cicadellidae showed a significant linear decrease in 2014,while showed a quadratic relation with gazing intensity in 2015 and2016?P<0.0001?.Insect communities,plant community,and grazing intensity were analyzed by redundancy analysis.We found that the vegetation community in heavy grazing plots is conducive to the Formicidae,vegetation community in moderate grazing is conducive to Acrididae and Cicadellidae,and vegetation community in light grazing is conducive to carnivorous insects.Chorthippus albonemus had lower population density in the early period of grazing disturbance,their abundance reached maximum in middle period of moderate grazing disturbance,then significantly decreased with the increase of grazing intensity in the late of grazing disturbance.Transcriptomics analysis of Chorthippus albonemus revealed the grasshoppers'adaptive response to different grazing intensities.Compared to non-grazing,the FPKM of phlorizin hydrolase and heat shock proteins et al were significantly up-regulated under grazing pressure.