The Meta-analysis Of Exotic Plant Invasion Mechanism: Comparison Between Native Range And Introduced Range

Biological invasion is one of the most important part of globalization,it cannot only threaten ecosystem biodiversity,alter the structure and function of ecosystems,but also cause huge economic losses.Study from the biogeography perspective can help us get more information.Although a number of studies have been published in recent years on the differences of alien species between their invasive and native ranges,the results are often controversial.It is necessary to perform a systematic comparison of exotic species between native and introduced ranges,to determine 1)what kind of trait differences exist between introduced range and native range,and 2)The relative contribution of different mechanisms to the invasion,and the influence of research method,the biological properties of species and other factors.Following the protocol of meta-analysis,this study retrieved and collected more than 3000 original research papers published between 1990 to 2016 in the Web of Science database using the combination of certain key words.In total,120 qualified references(involving 40 species)were selected to establish a unified research database.The database includes growth and reproduction related traits(height,density,biomass,reproductive performance and seed germination rate),natural enemy pressure related trait(percentage of biomass removed by natural enemies),and genetic variation related trait(genetic diversity)as well as scientific name,life form,life history,native range of the invasive species,study area and research method.The growth and reproduction performance of invasive plants were generally better in their invasive range than in native range(the total effect size was between 0.11 and 1.85),while the natural enemy pressure and genetic diversity were lower than that in native range.Among them,the density of invasive plants in invasive range was significantly greater than in native range(g=0.8,P<0.01),sexual reproduction output and seed germination rate were significantly increased in the introduced range(g=0.83,P<0.05;g=1.85,P<0.05),and the percentage of biomass removed by natural enemies decreased significantly in the introduced range(g=-1.10,P<0.05).The Egger test was carried out on the indicators that significant differed from zero,which showed that there was significant publication bias of the effect size of sexual reproduction output(df= 12,t = 2.97,P< 0.01).Specially for small sample studies,those with positive effect size were much easier to be published.The experimental method influenced the changes of sexual reproduction output and percentage of biomass removed by natural enemies of invasive plants.In common garden experiments,the sexual reproduction output of invasive populations was significantly higher than native populations(g=1.2,P<0.01),while the effect size of sexual reproduction output of invasive plants in common garden experiment was higher than that in field investigation,and the difference was marginally significant(Q=3.1,df=1,P=0.08).In field investigation,percentage biomass removed by natural enemies in introduced range was significantly lower than that in native range(g=-2.07,P<0.01).The percentage of biomass removed by natural enemies was significantly higher in common garden experiments than that in field investigation(Q=12.49,df=1,P<0.01).The life history influenced the effect size of sexual reproduction output between the invasive and the native range.After invasion,the sexual reproduction output of annual plants in invasive range was significantly higher than that in native range(g=1.51,P<0.05),but not plants(g=0.5,P=0.16).The original climate region also affected the effect size of natural enemy.The percentage of biomass removed by natural enemies of temperate invasive plants in invasive range is significantly higher than that in native range(g=-1.15,P<0.01),and the effect size was significantly greater than that of the tropical invasive plants(Q=3.99,df=1,P<0.05).To sum up,there are various differences between exotic plants in their invasive range and in native range.The differences also varied depending on other factors,such as research methods,life form,life history,and the origin of exotic plants.The growth and reproduction performance of invasive plants is generally improved in their introduced range.But due to the complexity of growth indices,there are many mechanisms affecting their performance.The natural enemy release hypothesis is one of the main interpretation of plant invasion,but it does not mean that the invasion of plants is completely driven by natural enemies.In this research,we improved our understanding of invasion mechanism,provided suggestions to the future of plant invasion research,and offered help for the prevention,control and management of plant invasion.