The Combined Effects Of Livestock Grazing And Seasonal Precipitation Increasing On Development And Survival Of Grasshoppers In Inner Mongolia

Precipitation and grazing are important factors to drive grasshopper out breaks in grassland ecosystem,but there are still controversies about how the factors to play roles in forecasting grasshopper population dynamic.In this paper,we studied the coupling effect of sheep grazing and increasing precipitation seasonally on variation of C%and N%elemental content and available C%,N%nutrient content in food plant,to reveal the physiological and ecological mechanism of grazing and precipitation in driving grasshopper disasters.We constructed grazed and seasonally increasing precipitation treatments in field manipulated experiments,which was conducted in typical steppe of Inner Mongolia,and used three dominant grasshopper species(early-season species:Dasyhippus barbipes,midlle-season species:Oedaleus asiaticus,and late-season species:Chorthippus dubius),which possessed different phenology and varied preference to Leymus chinensis and Stipa krylovii,to investigate the fitness responses of grasshoppers to seasonal precipitation change and sheep grazing and their coupled effects.The results indicated that:1.Grazing significantly decreased the content of soluble sugar C%and available C%in leaves of L.chinensis in spring,but did not affect the content of starch C%and total C%.Grazing also significantly increased the content of the amino acid N%,the available N%,the total N%,and decrease the available C%:N%ratio.However,it did not affect on protein N%.The effects of seasonal precipitation increasing on nutrient content were varied between grazing treatments.There was a trend that increasing precipitation might drop the content of soluble sugar C%and amino acids N%,but no significant difference existed among precipitation treatments.Moreover,grazing significantly decreased the mortality,shorten the development duration,increased the growth rate,and increased the adult body weight when D.barbipes developed from fifth instar nymph to adult in laboratory rearing experiment,and increased survival and developmental rate in field cage experiment.Nevertheless,the increasing precipitation did not have significant effect on any biological parameters of the grasshopper.2.Grazing significantly decreased the content of available C%and starch C%in leaves of S.krylovii in summer,and significantly increased the content of total C%.Grazing also significantly increased the content of the amino acid N%,the total N%.However,it did not have significant effect on protein N%,but significantly decreased the total C%:N%ratio.The effects of seasonal precipitation increasing on nutrient content were valried between grazing treatments,but no significant difference existed among precipitation treatments.Moreover,grazing significantly increased the adult body weight,decreased the mortality,shorten the development duration,increased the growth rate when O.asiaticus developed from fifth instar nymph to adult in laboratory rearing experiment.Nevertheless,the precipitation increasing significant increased developmental rate in field cage experiment.3.Grazing significantly decreased the content of soluble sugar C%,in leaves of L.chinensis in autumn,but did not affect the content of starch C%and total C%.Grazing also significantly decreased the content of the total N%.However,it did not have significant effect on the amino acid N%,the available N%,protein N%.Grazing significantly increased the available C%:N%ratio.The effects of seasonal precipitation increasing significantly decreased the content of the total N%L.chinensis in autumn and significantly increased the total C%:N%ratio.Moreover,grazing significantly decreased the mortality,shorten the development duration,increased the growth rate,and increased the adult body weight when C.dubius developed from fifth instar nymph to adult in laboratory rearing experiment.Nevertheless,the increasing precipitation did not have significant effect on any biological parameters of the grasshopper.