面积、温度及分布区限制对物种丰富度海拔格局的影响：以秦岭太白山为例

Effects of area,temperature and geometric constraints on elevational patterns of species richness:a case study in the Mountain Taibai,Qinling Mountains,China

物种丰富度的分布格局及其形成机制是生态学研究的热点。以往的研究主要描述丰富度的格局,而对其形成机制研究较少,且主要集中于探讨单个因子或过程的影响。物种丰富度同时受到多个因子和过程的综合作用,面积、温度及物种分布区限制被认为是控制山地物种丰富度海拔格局的主要因素,三者同时沿海拔梯度而变化,同时作用于丰富度的海拔格局。幂函数种-面积关系(SAR)、生态学代谢理论(MTE)及中域效应假说(MDE)分别基于以上3个因素,从机制上解释了物种丰富度的海拔格局。探讨这些假说的相对影响对研究物种丰富度的大尺度格局及其形成机制具有重要意义。方差分离方法有利于分解不同因素的影响,为此,该文以秦岭太白山的植物物种丰富度为例,采用方差分离和逐步回归方法,分析了SAR、MTE及MDE对物种丰富度海拔格局的影响。结果表明,太白山的植物物种丰富度沿海拔梯度呈单峰分布格局,但丰富度峰值存在类群差异;对太白山所有植物物种丰富度的垂直格局而言,SAR、MTE及MDE分别解释了其物种丰富度随海拔变化的66.4%、19.8%和37.9%,共同解释了84.6%,在消除其他因素的影响后,SAR和MTE的独立影响较高(分别为25.5%和17.7%),而MDE的独立影响不显著;分类群研究则发现,苔藓植物丰富度的海拔格局主要受MDE的影响,蕨类植物丰富度的海拔格局同时受到SAR、MTE以及MDE的影响,而种子植物物种丰富度的海拔格局主要受SAR和MTE影响。

Aims Recent studies have illustrated that area,climate and geometric constraints were the main determinants of elevational patterns of species richness;however,the relative importance of these factors is unknown because these factors co-vary with elevation.Based on these factors,the power law species-area relationship （SAR）,the metabolic theory of ecology （MTE） and the mid-domain effect hypothesis （MDE） have been proposed to explain elevational patterns of species richness.Our objective is to compare the relative performance of SAR,MTE and MDE in shaping elevational patterns of species richness,using vegetation and climatic data from Mt.Taibai,Qinling Mountains as a case study.Methods We used a database,＂Distribution of Plants in Mt.Taibai＂,composed of 2 132 plant species,to derive species richness values for different plant groups.A digital elevation model was used to calculate the area of each elevational band.Eighteen data loggers were set along south and north slopes and at different elevations to record air temperature.RangeModel software was applied to predict species richness of each elevational band,based on the MDE hypothesis.We then compared the explanatory strengths of SAR,MTE and MDE models and used variation partition and stepwise regression to assess their relative importance in shaping elevational patterns of species richness.Important findings Plant species richness followed a unimodal pattern;however,species richness of each plant group peaked at a different elevational band.As single predictors,SAR,MTE,and MDE explained 66.4%,19.8% and 37.9% of the variation in species richness,respectively.Together they explained 84.6% of the variation.When the confounding effects of all other factors were eliminated,SAR and MTE explained most （25.5% and 17.7%）,whereas MDE played a minor role.Furthermore,we found differences among taxonomic groups：the elevational pattern of lichen richness was primarily explained by MDE,that of ferns was jointly controlled by all three mechanisms and that of seed plants was mainly controlled by SAR and MTE.