Effects Of Grazing On Insect Community Composition And Structure In Inner Mongolia Grasslands

Insects are important components in regulating the structure and function of ecosystems and have an irreplaceable role in maintaining the diversity and stability of grassland.Livestock grazing is the most common management tool in grassland.Large herbivores have strong effects on productivity,vegetation structure,plant diversity,and composition through foraging,trampling,and excretion in grasslands,and then influencing the composition and structure of grassland insect communities.However,the effect of grazing on insects varied due to large herbivores,or habitat complexity.In order to better understand the interactions between large herbivores and insects,we examined the response of insects to large herbivores grazing in grasslands in northern China,which will take profound implications to formulate a scientific and sustainable plan of grassland production and managements.In this study,a field experiment with manipulating grazing(no grazing,cattle grazing,sheep grazing,and mixed herds grazing)was conducted to examine the effects of grazing by large herbivores on insect composition and structure in 3 grasslands(meadow steppe,typical steppe,and desert steppe).Variables of insect and plant communities were analyzed,including insect species richness,abundance,Shannon-Wiener index,plant height,aboveground biomass,height variation,species richness,Shannon-Wiener index.The main results are as follows:(1)Grazing has a significant impact on plant height,height variation and aboveground biomass,and the response of plant community to grazing depends on the grassland type.In meadow steppe,mixed grazing significantly reduced plant height,while sheep grazing and mixed grazing significantly increased plant height variation;In typical steppe,grazing significantly reduced plant height and aboveground biomass,but increased plant height variation;In desert steppe,grazing significantly reduced aboveground biomass,while cattle grazing and mixed grazing have significantly increased the plant height variation.(2)The effect of grazing on insect abundance depends on grassland type.In meadow steppe,only cattle grazing significantly reduced insect abundance;grazing significantly decreased insect abundance in typical steppe,Different taxa of insect abundance also responded varied among grassland types: In meadow steppe,cattle grazing and mixed grazing significantly reduced abundance of Hemiptera,while cattle grazing also significantly decreased Coleoptera abundance;In typical steppe,grazing significantly reduced abundance of Hemiptera,Coleoptera,Hymenoptera,and Diptera.(3)The responses of insect diversity to grazing depend on the type of grassland.In meadow steppe,sheep grazing significantly reduced the diversity of Hemiptera,while cattle grazing significantly increased the diversity of Coleoptera,and mixed grazing significantly reduced the diversity of Coleoptera;In typical steppe,mixed grazing significantly decreased the diversity of Hemiptera and Coleoptera and grazing significantly reduced the diversity of Hymenoptera and Diptera.(4)Grazing affects the community composition and structure of insects mainly through changing plant community characteristics and microclimate.In meadow steppe,insect abundance was affected by plant height,aboveground biomass and sun light;Hemiptera abundance was reduced with the decrease of plant height.Coleoptera abundance positively correlated with plant biomass and negatively correlated with the light intensity.In typical steppe,Coleoptera abundance was mostly affected by plant height,which was positively correlated between each other.The variation of insect diversity was also dependent on the grassland type.In meadow steppe,the diversity of Hemiptera negatively correlated with light intensity and the temperature.The diversity of Coleoptera decreased with the reduction of plant height,but was increased under the condition of cattle grazing.In typical steppe,the diversity of Hymenoptera positively correlated with the aboveground biomass,and negatively correlated with the temperature.The diversity of Diptera decreased with decreasing of biomass and increasing of light intensity.In conclusion,large herbivores can affect the abundance and diversity of insects,and the role of grazing depends on the type of grassland.Grazing affects insects mainly by regulating plant community characteristics(plant height,aboveground biomass)and microclimate(light,temperature).This study explored the responses of insects to grazing,which is helpful to understand the variation of insect diversity under grazing disturbance,and formulate reasonable grassland management,which are of great importance to grassland ecosystem diversity and services.