The Relationship Between Woody Plant Diversity And Leaf Insect Herbivory In Zhoushan Islands

Herbivorous insects are known as the most diverse group of primary consumers.The feeding intensity of herbivory insects on plant leaves is not only influenced by plant species richness but also regulated by environmental factors.In past,most of the studies mainly focus on the influence of single feeding type insect herbivory on plant leaves,and there is a lack of in-depth investigation of whether the influence of different types of insect herbivory(such as chewing,sucking,etc)on leaves are the same at the community level,and it is impossible to effectively explain the changes in different insect food types along the environmental gradient.At present,this relationship between area or isolation and plant species diversity has been widely studied in island ecosystems,but the patterns of insect feeding intensity of island plants are lacking and direct/indirect effects of island area and isolation on plant leaf insect herbivory intensity are still unclear.In this study,we have established 36 permanent plots across 30 islands in Zhoushan Islands,Zhejiang Province.Relevant data have been collected in 2019 and2021.We have examined the feeding intensity of four insect guilds(chewers,suckers,leaf-miners,and rollers)on the common plant species.Using multiple linear analysis and variance partitioning we studied the patterns of different types of insect feeding intensity on plant species richness,island area,and isolation,along with climate and soil characteristics across the gradient.Finally,the structural equation modeling(SEM)approach was used to identify how island area and isolation directly/indirectly influence leaf damage intensity with the change in plant species richness.The main findings of the current study are as follows:(1)At the community level,the leaf damage intensity of the four insect guilds varies significantly.In 2019,the average total feeding intensity recorded was 11%,with,chewing insects having the largest contribution(5.9%),which is twice that of mining(3.0%)and more than three times that of sucking(1.8%).However,the total intensity dropped slightly to 5%in 2021,where,the intensity of chewing and mining insects has been decreased to 3.0%and 1.6%,respectively,while the intensity of sucking insects increased to 2.6%.(2)Leaf insect feeding intensity increases with plant species richness.In 2019,the total insect feeding intensity increased significantly with an increase in plant species richness(R~2=0.38,P<0.05).In terms of an individual type,the sucking insect’s feeding intensity plays a dominant role and explained 64%of the variance(R~2=0.64,P<0.05);the mining insects feeding intensity changed faster than that of chewing insects explaining 15%of the variance(R~2=0.15,P<0.05).However,the feeding intensity of chewing insects was not related to tree species diversity(P>0.05),although the feeding intensity of chewing insects was the highest.In 2021,the feeding intensity of insect explained 20%of the total variance(R~2=0.20,P<0.05).Across individual types,there was no significant relationship between the feeding intensity of sucking insects and plant species richness(P>0.05).The degree of variation explained by the feeding intensity of mining was reduced by 3%i.e.,12%(R~2=0.12,P<0.05),and the feeding intensity of chewing was positively related to plant species richness(R~2=0.10,P<0.05).Plant species richness,tree height,and soil nutrition(total carbon,total nitrogen,and total phosphorus)collectively explain60%of the variation(R~2=0.60,P<0.05)in 2019.The tree height explains 16%of the variation,followed by soil nutrient content(soil carbon,nitrogen,and phosphorus),and tree species richness explains 11%of the variation.The interaction between tree height and tree species richness accounted for the largest proportion explaining 37%of the total variance.For mining insects feeding intensity,plant species richness,soil nitrogen and C:N,and soil carbon,phosphorus,C:P collectively explain 32%of the total variation(R~2=0.32,P<0.05)in 2019.Plant species richness explains 29%of the variance,soil nitrogen,and C:N explain 26%of the variance,and soil carbon,phosphorus,and C:P explain 25%of the variance,the interaction of those three factors could explain 13%of the variance.(3)In 2019,the feeding intensity of mining insects increased significantly with island area(R~2=0.28,P<0.05)and decreased with isolation(R~2=0.14,P<0.05).However,the feeding intensity of other types of insects was not significantly related to island area and isolation.In 2021,the total feeding intensity(R~2=0.21,P<0.01),mining insects(R~2=0.13,P<0.01)and chewing insects(R~2=0.17,P<0.01)were significantly related to island area,while feeding intensity of mining insect was not significantly related to island area(P>0.05).There was also no significant relationship between types of herbivory insects and isolation(P>0.05).(4)Using the structural equation model,we considered the direct and indirect effects of island area and isolation on leaf damage.It was found that in 2019,plant species richness,island area,and isolation collectively explain 42%of total insect feeding intensity variance,67%of sucking insects,19%of mining insects,and 3%variance of chewing insects feeding intensity.Meanwhile,we found significant indirect effects of island area and isolation occurred on sucking and mining insects,as well as on the total feeding intensity.However,in 2021,the variance of the island area,isolation,and plant species richness on total feeding intensity,sucking insects,and mining insects dropped to 26%,3%,and 10%,while increased to 21%in chewing insects feeding intensity.In conclusion,through a 2-year repeated survey of leaf insect food intensity of woody plant communities on islands with different areas and isolation degrees in Zhoushan Islands,it was found that the insect feeding intensity of leaves was mainly regulated by plant diversity.The island area and isolation can either directly or indirectly regulates leaf insect feeding intensity by changing plant species richness,and this regulation has not only significant interannual fluctuations but also depends on different leaf insect feeding types.These findings deepen our understanding of the island biogeography of plant leaf insect feeding intensity and provide a research basis for deepening the interaction between plants and insects in island ecosystems.