Responses Of Insect Diversity To Grazing By Large Herbivores And Altered Precipitation In Songnen Grassland

Grassland ecosystems,one of the most widely distributed in terrestrial ecosystems,are affected by multiple factors,such as climate change and human disturbance.Precipitation change(climate change)and grazing by large herbivores(human disturbance)usually exist simultaneously in grassland ecosystems,but their effects on grassland ecosystems are uncertain.As one of the richest and largest number of animal groups in grassland ecosystems,insects belong to both consumers and decomposers.A close relationship between insects and other trophic level is often found,and insects also plays an important role on ecosystem functioning of grasslands.However,the effects of precipitation and grazing on insect diversity is still not clear.Therefore,this study aimed to investigate the impact of changes in precipitation,grazing,and the interactions between precipitation and grazing on insect diversity.It is likely to reveal the variation of insect diversity under climate change and grazing disturbance,and provide important scientific value and guidance for developing a reasonable grassland management.In this study,4-year grazing treatments(no grazing,moderate grazing and heavy grazing)and 3-year precipitation treatments(ambient precipitation and increased precipitation)has been carried out in the experimental sites.By analyzing the impact of grazing intensity and precipitation on insect species richness,diversity and quantity,and the relationship between the insect diversity index and vegetation characteristics,micro-climate,and main conclusions were as follows.(1)The interactions between different grazing intensity and precipitation on insect diversity(including species richness and diversity index)and abundance were not significant.However,insect abundance increased with the increasing grazing intensity,while the total insect Shannon-Wiener index and evenness index decreased;the total number of insect abundance declined under increased precipitation.(2)The effects of grazing intensity and precipitation on insect diversity and abundance are order-specific.Grazing had a significant impact on diversity index of Coleoptera,Hemiptera and Homoptera,but such impacts were different from each order.The abundance of each order insect in moderate grazing and heavy grazing plots were higher than that of control plots.Increased precipitation significantly increased the abundance of Orthoptera,but decreased abundance of Coleoptera and Homoptera.The interactions between grazing and precipitation significantly affected Orthoptera abundance,Shannon-Wiener index,evenness index,and Homoptera Shannon-Wiener and evenness index,but significant effect on Coleoptera and Hemiptera were not detected.(3)The effects of grazing intensity and precipitation on insect abundance were speciesspecific.The abundance of Euchorthippus cheui,Coccinula quatuordec-impustulata,Adonia variegate,Cicadellidae sp.2,Trigonotylus ruficornis and Nabis stenoferus in grazing plots were higher than that of control plots.The abundance of Cicadellidae sp.1 in moderate grazing plots is higher,and was lower in heavy grazing plots.The abundance of Monolepta hieroglyphica decreased after grazing.Increased precipitation increased the abundance of Euchorthippus cheui and decreased the abundance of Monolepta hieroglyphica,Cicadellidae sp.1 and Nabis stenoferus.There was significant interaction between grazing intensity and precipitation on Euchorthippus cheui,Adonia variegate,Cicadellidae sp.1,Cicadellidae sp.2,Trigonotylus ruficornis and Nabis stenoferus.(4)Grazing intensity and precipitation changes had significant effects on the vegetation characteristics and environment microclimate,and consequently this effects affected insect diversity and abundance.Changed plant community induced by grazing intensity and altered precipitation did not provide a reasonable explanation for the alternations in diversity and abundance of some insects,but micro-climate have a significant effect on insect abundance.Increase temperature and light intensity enhanced the abundance of total insects,Orthoptera,Coleoptera,and Hemiptera.Part of the dominant insect species had close relationship with vegetation characteristics and microclimate,and the changes of dominant species abundance might also be affected by the interaction between vegetation and microclimate.In summary,the large herbivore grazing and altered precipitation strongly affected the diversity and abundance of grassland insects,and these effects were order-specific and speciesspecific.Under different precipitation treatments,grazing intensity had different effects on the diversity and abundance of insects.Grazing intensity and changed precipitation influenced insect diversity and abundance by partly mediating the changes of plant community characteristics and micro-climate of habitat environment.The results of this study suggests that grassland management should take a different approach to protect insect diversity in grassland ecosystems under the background of climate change,and it is necessary to consider the response of different groups of insect diversity.