单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,*,*,植被生态学结课汇报,姓 名：高 睿,专 业：干旱区植被与生态,学 号：,2014103059,指导老师：刘彤教授,植被生态学结课汇报姓 名：高 睿,Density-dependent mortality and the latitudinal gradient in species diversity,Journal Title,：,Nature IF,：,42.351,Janneke Hille Ris Lambers;Brian Beckage,Biology Department,Duke University,James S.Clark,Nicholas School of the Environment,and Earth Sciences,物种多样性的纬向梯度密度制约效应,植被生态学,Density-dependent mortality an,负密度制约机制,主要在,小尺度上,降低群落内,同种个体,生长率，同时提高个体死亡率，从而为其他物种的生存提供空间和资源，,促进物种共存,。目前负密度制约假说的检验研究主要侧重,密度制约、距离制约、群落补偿效应,三个方面。,植被生态学,负密度制约机制主要在小尺度上降低群落内同种个,Abstract,Ecologists have long postulated that,density-dependent mortality maintains high tree diversity in the tropics,.If species experience greater mortality when abundant,then more rare species can persist.Agents of density-dependent mortality(such as host-specific predators,and pathogens)may be more prevalent or have stronger effects in tropical forests,because they are not limited by climatic factors.,If so,decreasing density-dependent mortality with increasing latitude could partially explain the observed latitudinal gradient in tree diversity.,植被生态学,AbstractEcologists have long,This hypothesis has never been tested with latitudinal data.,Here we show that several temperate tree species experience density-dependent mortality between seed dispersal and seedling establishment.,The proportion of species affected is equivalent to that in tropical forests,failing to support the hypothesis that this mechanism is more prevalent at tropical latitudes.,We further show that density-dependent mortality is misinterpreted in previous studies.Our results and evidence from other studies suggest that density-dependent mortality is important in many forests.Thus,unless the strength of density-dependent mortality varies with latitude,this mechanism is not likely to explain the high diversity of tropical forests.,植被生态学,This hypothesis has never been,Research Background,We quantified,seed dispersal,seed bank densities,seedling emergence and seedling survival,at,100 microsites,distributed across,five temperate forest,stands,over 3 years,.,We then determined whether transition probabilities across early life-history stages were lower at high conspecific seed and seedling densities or close to conspecific trees,a phenomenon said to promote species diversity,called the“JanzenConnell”effect.,在同种的种子和幼苗密度较高或接近同种的树木的条件下，是否在早期生活史阶段的存活率更低，这种促进物种多样性现象，被称为,“简森,-,康奈尔”效应。,植被生态学,Research BackgroundWe quantif,We tested transitions from dispersed seed to seed bank(,incorporation,),seed bank to germinated seedling(,germination,),germinated seedling to established seedling(,establishment,),and first-year seedling to second-year seedling(,survival,).,（,种子散布、种子库密度、出苗率,和,幼苗存活率,）,We also determined whether effects of conspecific density(seeds,seedlings)or distance(proximity to conspecific trees)on mortality are greater than are effects of other species,a requirement if density-dependent mortality is to promote species diversity.,确定同种密度,(,种子、种苗,),或与母株距离,(,靠近同种的树,),对死亡率的影响是否大于其他物种的影响，以确定密度制约效应是否能够促进物种多样性,。,植被生态学,We tested transitions from dis,Methods,Study site and experimental design,Studies were performed in secondary temperate deciduous forests at the Coweeta Hydrologic Laboratory(western North Carolina).,We identified and mapped all trees more than 2m tall in five 80,80-m permanent vegetation plots.(,温带落叶林,),Twenty,seed traps,were located within each plot.,植被生态学,MethodsStudy site and experime,Seed traps were mesh-lined baskets(0.1764 m,2,)suspended 1m above the ground and covered with wire mesh to deter seed predation.Traps were emptied four times annually,and seeds identified and counted.Soil cores(0.0062 m,2,0.05 m deep)adjacent to each trap were removed in autumn 1996,1997 and 1998.In Duke Universitys greenhouses,soil was spread over sterile potting soil,and seedlings(each representing a viable seed)were counted and identified as they emerged.In the field,seedlings were identified and tagged in during summer 1997,1998 and 1999 in quadrats(1.0 m,2,)adjacent to each seed trap.,植被生态学,Seed traps were mesh-lined bas,Estimation and testing,For transitions from life-history stage k-1 to k for species j,we used the binomial likelihood to estimate transition probabilities(P,ijk,)and to test for density-dependent mortality in T quadrats,：,The probability of survival of species j at quadrat i,（物种的生存概率）,植被生态学,Estimation and testingFor tran,截距,参量,同种影响,异种影响,P,值,截距参量同种影响异种影响P值,Figure 1,The observed(a)and predicted(b)relationship between conspecific seed density and seed germination for Acer rubrum.a,Each circle represents a paired seed trap and seedling quadrat in 1 of 3 years.b,The best-fit relationship between germination and density of conspecific seeds(see Methods);dashed lines are 95%bootstrapped confidence intervals.,Likelihood ratio tests indicate that germination decreases at high conspecific densities.,95%,置信区间,Figure 1 The observed(a)and,Figure 2,The proportion of tree taxa experien