广东古兜山自然保护区蕨类植物多样性对植被不同演替阶段的生态响应

蕨类植物是最早登陆的维管植物,至今仍然是生态系统初级生产力的重要组成部分。它们一方面可以通过改造生态环境影响森林群落发生和发展的过程,另一方面由于它们对生态因子变化的敏感性,其组成的多样性及其对环境的适应组合也随着森林群落发生和发展而不断变化。为了解蕨类植物在群落演替的各个阶段的种类组成、物种多样性格局演变规律及其适应方式的选择,本文选择广东古兜山自然保护区中的草丛、灌丛、次生常绿阔叶林和地带性南亚热带季风常绿阔叶林(以下相对简称“原生林”)等4个处于不同演替阶段的植被类型中的蕨类植物群落进行研究。每一植被类型中选取4个5m×5m代表性小样方进行取样调查,对其主要数量特征、群落的α多样性、β多样性、不同群落间的相似性系数和蕨类植物的种类性质进行了分析。结果表明:随着群落演替的进展,草丛、灌丛、次生林和原生林各阶段植被中:(1)群落之间的β多样性指数逐渐增大,而相似性指数依次降低;(2)蕨类植物的物种丰富度依次增大,而群落的多样性指数、生态优势度和均匀度并不伴随着群落的丰富度呈明显的规律性变化;(3)具革质叶的蕨类、阳生蕨类和进行无性繁殖的蕨类植物在各阶段所占的比例和重要值比重逐渐减少,而具草质叶的蕨类、阴生蕨类和进行有性繁殖的蕨类植物则     

古田山不同干扰程度森林的群落恢复动态

森林采伐后次生林的恢复过程对于生物多样性的保护和生态系统功能的重建具有重要意义。作者以古田山不同干扰程度的12个1 ha 森林样地为研究对象, 运用群落多元统计方法, 探讨了自然恢复过程中森林群落组成及物种多样性的动态变化及趋势。结果表明: 不同恢复阶段森林样地的群落组成存在显著性差异, 而同一恢复阶段的样地具有高度的相似性。物种丰富度随恢复进程有增加的趋势, 但各阶段差异并不显著; 物种均匀度除人工林较低以外, 其他恢复阶段之间无显著性差异。不同恢复阶段研究样地的群落组成及物种多样性的差异主要存在于林冠层。灌木及更新层具有各自的指示种, 人工林的指示种为落叶灌木或阳性乔木, 幼龄次生林的指示种为常绿灌木或小乔木, 老次生林的指示种为亚乔木层常绿树种, 老龄林的指示种为林冠层树种。上述结果表明古田山不同人为干扰程度森林群落的物种多样性具有较强的自我恢复能力。尽管物种组成难以预测, 但处于同一恢复阶段的森林, 其幼树的生活型组成呈现出一致的变化趋势。     

濒危植物永瓣藤所在群落物种多样性初步研究

永瓣藤(Monimopetalum chinense)是卫矛科(Celastraceae)的一个中国特有单型属植物,被列为国家二级稀有濒危保护物种。以11个样地调查资料为基础,从物种丰富度指数、物种多样性指数和均匀度指数等方面对濒危植物永瓣藤所在群落物种多样性进行了分析。结果表明:永瓣藤所在群落物种多样性较高,植物群落结构复杂,物种丰富;从平均值来看,物种丰富度指数和物种多样性指数灌木层>草本层>乔木层,物种均匀度指数草本层>灌木层>乔木层;乔木层物种贫乏,物种多样性较低,优势树种突出;永瓣藤受人类活动干扰较大,森林的乱砍滥伐和旅游的不合理开发给该物种带来严重的威胁。     

长白山北坡不同海拔及干扰程度下访花食蚜蝇群落的差异

本研究采用垂直面取样法,对中国长白山北坡不同海拔及干扰程度下访花食蚜蝇群落的物种组成、多度、丰富度及多样性进行了调查研究。我们选择了不同垂直带的两个样地,分别位于800~1 100 m和1 750 ~2 150 m;每个样地选取3种生境类型,每一生境类型采样面积为20 m×20 m。252组调查数据表明,共采到访花食蚜蝇42种2 540个体。不同海拔生境访花食蚜蝇的组成、多度、丰富度及多样性的差异分析结果表明: 低海拔样地内不同生境访花食蚜蝇的群落相似性高于高海拔样地;低海拔样地访花食蚜蝇的多度高于高海拔样地,而物种丰富度低于高海拔样地;不同生境类型访花食蚜蝇多样性指数存在差异,但高海拔样地与低海拔样地多样性差异不显著;过渡林生境（岳桦林带）与次生林生境（针阔混交林带Ⅱ）中访花食蚜蝇的多样性较高。保护珍稀植物物种的人工植物花园访花食蚜蝇多样性仅次于过渡林生境（岳桦林带）与次生林生境（针阔混交林带Ⅱ）,保护作用显著。     

千岛湖岛屿小型兽类群落的多样性

2007 年秋季和2008 年春季,选取千岛湖地区14 个岛屿和2 个半岛作为样地,采用夹夜法进行小型兽类群落组成调查。两季度共布夹20 400 个,捕获小型兽类1 141 只,隶属2 目3 科9 属13 种,啮齿目(Rodentia)鼠科(Muridae)10 种和仓鼠科(Cricetidae)1 种,食虫目(Insectivora)鼩鼱科(Soricidae)2 种。利用以上结果分析其群落多样性,结果显示:14 个岛屿小型兽类群落春、秋两季的多样性指数、均匀度指数和优势度指数均呈现极显著差异且优势种发生变化;对可能影响岛屿小型兽类群落多样性的岛屿面积、距最近陆地距离、距最近大岛距离和植物丰富度等因素进行逐步回归分析,发现只有植物丰富度对小型兽类群落的物种丰富度有显著影响;对16 个样地按照物种组成比进行聚类,许源半岛样地与14 个岛屿聚为一类,姚家半岛样地单独归为一类,相似性指数比较结果亦显示姚家半岛样地与其它样地的相似性指数偏低。结论:景观破碎化导致千岛湖岛屿小型兽类群落的稳定性下降,物种多样性季节变化强烈;随岛屿面积的增加,小型兽类物种丰富度并非总是增加的,而是出现反复,呈现明显的小岛效应;14 个岛屿的物种与许源半岛样地物种构成比接近,推断在水库未形成前属同一生境。     

云南苍山火烧迹地不同恢复期地表蜘蛛群落多样性

为了解云南苍山针阔混交林火烧迹地恢复过程地表蜘蛛群落多样性变化,于2009年1月份-2009年12月份,运用陷阱法,以“空间序列代替时间序列”,调查了苍山森林火干扰后不同恢复期样地(火干扰后2、10、18、23、33a和对照样地)地表蜘蛛多样性.研究结果表明,(1)物种组成及相对多度:不同恢复期随着恢复时间的增加优势类群更替趋势明显;(2)多样性:恢复1Oa样地地表蜘蛛群落多度显著大于其他恢复期(P＜0.05),而不同恢复期地表蜘蛛物种多样性却没有显著差异;(3)群落相似性:PCoA相似性分析将地表蜘蛛群落发展过程划分为火烧后2a、火烧后10a和火烧后18-33a 3个阶段;(4)指示物种:西菱头蛛Sibianor sp.1等是阶段1的指示物种,格氏狼蛛Lycosa grahami等是阶段2的指示物种,花蟹蛛Xysticus sp.2等是阶段3的指示物种,弱蛛Leptoneta sp.1等是对照的指示物种.火干扰改变了苍山针阔混交林原有的地表蜘蛛群落多样性;指示物种对生境的选择能够反映出不同恢复阶段地表环境变化;5个不同恢复时期火烧迹地中恢复最久的火烧迹地地表蜘蛛群落仍没有完成恢复,说明云南苍山火迹地地表蜘蛛的恢复需要30a以上.     

长白山牛皮杜鹃群落物种多样性的海拔梯度变化及相似性

采用样地调查法,研究了牛皮杜鹃群落物种组成、群落结构特征、物种多样性及其沿海拔梯度的变化规律,对不同海拔牛皮杜鹃群落进行相似性分析。结果表明:(1)牛皮杜鹃群落相同海拔高度,草本层的物种多样性普遍高于灌木层的物种多样性。自海拔1926—1986m,灌木层α多样性指数先降低后升高,1986m后再次降低,到达海拔2010m处达到最低点,适应高山苔原带特殊生境条件的物种逐渐增多,多样性指数开始回升。海拔2250m,生物多样性指数的变化趋于平缓,物种组成相对较为稳定。海拔2528m以上,生物多样性再次呈降低趋势。草本层的α多样性指数中,物种多样性指数SW、丰富度指数D和均匀度指数R沿海拔梯度的变化趋势大致相同。海拔1986m处时出现最小值,海拔2350m时达最大值。牛皮杜鹃群落α多样性指数间呈P0.01水平极显著正相关性,物种丰富度指数对群落的物种多样性贡献率最大,表现为丰富度指数(D1、D2)种间机遇指数(H)生态优势度指数(SN)群落均匀度指数(R)。(2)牛皮杜鹃群落β多样性沿海拔梯度基本呈波形变化,草本层β多样性指数普遍高于灌木层β多样性指数。在牛皮杜鹃群落物种沿海拔梯度的替换速率上,草本植物高于灌木物种。Routledge指数的变化趋势不显著。海拔1986m处和海拔2250m处,草本层Cody指数出现两处极值,海拔2250m以上群落灌木层之间差异和变化较小,Whittaker多样性指数和Cody指数逐渐趋于平稳。(3)海拔梯度间生境及群落结构差异性越大,生物多样性变化越明显。海拔高度接近的群落间相似性系数较高,海拔是影响牛皮杜鹃群落差异的主要因素。     

古田山中亚热带常绿阔叶林群落物种多样性的空间变异特征

古田山常绿阔叶林的群落组成、结构及其维持机制已有许多研究, 但该地区亚热带常绿阔叶林生物多样性空间变异特征还缺乏认识。本文以古田山24 ha大样地(划分为24个1 ha小样地)为基础, 具体分析了α多样性和β多样性在1 ha尺度上的空间变异特征。结果表明: (1)群落第一、二优势物种在各小样地之间变化不大, 但第三优势种变化较大; (2) α多样性变化中, 样地间木本植物个体数量变异最大, 物种丰富度其次, Pielou均匀度指数变异性最小; (3)物种丰富度与植株个体数量、Pielou均匀度指数没有显著的相关性, 与Shannon-Wiener指数呈显著正相关; Shannon-Wiener指数与Pielou均匀度指数呈显著正相关; (4)相邻样地间物种替代速率空间变异较大, 与物种丰富度的空间变化格局有明显差异。这些结果说明尺度对认识群落结构、探讨群落维持机制有重要作用; 由于森林群落是多尺度生态过程作用的结果, 大尺度样地可能有利于更好地揭示森林群落维持机制。     

老秃顶子石河冰缘地貌森林群落物种多样性及其影响因素

基于对24个样地的调查数据,采用物种丰富度指数、Shannon-Wiener指数以及Jaccard相似性指数,对辽东山地老秃顶子石河冰缘地貌森林群落物种多样性及其影响因子进行了研究。结果显示:(1)石河冰缘地貌森林群落中落叶阔叶林、针阔混交林和暗针叶林的物种丰富度指数平均值分别为41±10、34±5和31±7。森林群落物种丰富度变异系数均为中等变异性。(2)石河冰缘地貌森林群落中落叶阔叶林、针阔混交林和暗针叶林的Shannon-Wiener指数平均值分别为1.67±0.32、1.50±0.18和1.29±0.25。(3)石河冰缘地貌森林群落间Jaccard相似性指数为0.037~0.530,且集中在极不相似和中等不相似区间。(4)相关性分析结果显示,石河冰缘地貌海拔高度与森林群落乔木层物种丰富度指数、Shannon-Wiener指数呈极显著负相关(P0.01),与灌木层物种丰富度指数呈显著负相关(P0.05);土壤电导率和含盐量均与森林群落物种多样性指数呈显著正相关(P0.05);土壤pH值与灌木层物种丰富度指数、Shannon-Wiener指数呈极显著正相关(P0.01);土壤CaO含量分别与乔木层和灌木层的物种丰富度指数、乔木层Shannon-Wiener指数呈显著正相关(P0.05)。这表明海拔高度、土壤电导率、盐含量、pH值和CaO含量是影响石河冰缘地貌森林群落物种多样性变化的重要因素。     

缙云山森林林隙与非林隙物种多样性比较研究

运用Gleason物种丰富度指数、Shannon-Wiener指数、Pielou均匀度指数、Simpson指数、生态优势度指数、均优多指数和群落优势度指数对缙云山森林群落林隙与非缃隙物种多样性进行了研究,对群落稳定性进行了探讨。结果表明,林隙以个体数为基础的物种丰富度为12.14,Shannon-Wiener指数为4.62,均匀度为0.70,Simpson指数为13.32,灌木层所起作用较大;非林隙林分各项物种多样性指数明显低于林隙,依次为6.32、3.74、0.66、8.16。林隙植物群落物种多样性指数显著高于非林隙,而生态优势度和群落优势度又明显低于非林隙,表明作为自然干扰和人为干扰的产物,林隙的存在增加了群落物种多样性,但同时也降低了群落的稳定性。     

西双版纳热带山地常绿阔叶林蕨类植物的组成及生态特征

根据4个50m×50m样地(400个5m×5m小样方,共计1hm2取样面积)的详细调查及对各样地外蕨类植物区系的采集调查,研究了西双版纳热带山地常绿阔叶林蕨类组成特点及其数量特征等。结果表明:在所调查的5hm2滇南热带山地常绿阔叶林里记录有蕨类植物64种;在生活型组成上,以地面芽和地下芽为主;在叶特征上,以革质和纸质叶居多,叶形以一回羽状和二回羽状叶占优势;在森林群落中蕨类植物有明显的季相变化;在重要值上,狗脊、疏叶蹄盖蕨、苏铁蕨、光叶鳞盖蕨、清秀复叶耳蕨和假稀羽鳞毛蕨的重要值之和占重要值总和的84.02%,其中,狗脊的重要值占重要值总和的1/3以上,它们是该森林群落中占优势的蕨类种类,在生态分布上为该森林群落的"适宜种";研究还发现,勐腊凤尾蕨为该森林群落的确限种。     

西双版纳勐腊南贡山季风常绿阔叶林蕨类植物初步研究

勐腊南贡山季风常绿阔叶林(山坡类型)1 hm2面积样地上有蕨类31种,在该森林群落草本层中占有 极其显著的地位。这些蕨类植物的地理成分分析表明它们属于亚洲热带的印度——马来西亚植物区系的一 部分,表现为东南亚热带北缘植物区系的性质,并有热带山地向亚热带山地过渡的特点。在生态表现上,它们 的生活型组成是高位芽蕨类(地生蕨种)占6．45％;地上芽蕨类12．90％;地面芽蕨类32．26％;地下芽蕨类 32．26％;附生蕨类16．13％。由于该地区的季节性干旱气候,高位芽蕨类较少和几种附生蕨类的附生高度也 相对较低,蕨类植物种群的数量与林下空气湿度及土壤表层的湿度一般成正相关。     

Does the Existence of Bird's Nest Ferns Enhance the Diversity of Oribatid (Acari: Oribatida) Communities in a Subtropical Forest?

We examined the effects of the presence of bird's nest ferns on the species diversity of oribatid mites in the whole forest in terms of the three categories of species diversity (α-, β-, and γ-diversity) in a subtropical forest in south-western Japan. The species diversity (1 − D) of oribatid communities in the ferns was significantly lower than those in bark of trees and the forest-floor litter and soil, and was similar to that in the branches. The oribatid faunas in the litter in and the roots of the fern were more similar to those in both the forest-floor litter and soil than to the faunas in the other arboreal habitats. However, the ferns can be colonized by endemic oribatid species specialized to such environments. The number of oribatid species estimated for a hypothetical stand with no ferns was about 180 species from 80 samples; this value did not differ significantly from that in another hypothetical stand with ferns (ca. 190 species). Thus, the species richness of oribatid communities estimated for the whole forest (the γ-diversity) was not affected by the presence or absence of bird's nest ferns. The α- and β-diversities of oribatid communities on bird's nest ferns were lower than those in other habitats, and they might not dramatically raise the overall γ-diversity of invertebrate communities in the whole forest. The bird's nest ferns, however, can generate a unique habitat for specialized species, and this would help to maintain species diversities of invertebrates at the whole-forest scale in subtropical forests.     

Species diversity in spatial and temporal dimensions of fruit-feeding butterflies from two Ecuadorian rainforests

To test the hypotheses that butterflies in an intact lowland rainforest are randomly distributed in space and time, a guild of nymphalid butterflies was sampled at monthly intervals for one year by trapping 883 individuals of 91 species in the canopy and understory of four contiguous, intact forest plots and one naturally occurring lake edge. The overall species abundance distribution was well described by a log-normal distribution. Total species diversity (γ-diversity) was partitioned into additive components within and among community subdivisions (α-diversity and β-diversity) in vertical, horizontal and temporal dimensions. Although community subdivisions showed high similarity (l-β-diversity/γ-diversity), significant β-diversity existed in each dimension. Individual abundance and observed species richness were lower in the canopy man in the understory, but rarefaction analysis suggested that the underlying species richness was similar in both canopy and understory. Observed species richness varied among four contiguous forest plots, and was lowest in the lake edge plot. Rarefaction and species accumulation curves showed that one forest plot and the lake edge had significantly lower species richness than other forest plots. Within any given month, only a small fraction of total sample species richness was represented by a single plot and height (canopy or understory). Comparison of this study to a similar one done in disturbed forest showed diat butterfly diversity at a naturally occurring lake edge differed strongly from a pasture-forest edge. Further comparison showed that species abundance distributions from intact and disturbed forest areas had variances that differed significandy, suggesting mat in addition to extrapolation, rarefaction and species accumulation techniques, the shapes of species abundance distributions are fundamental to assessing diversity among sites. This study shows the necessity for long-term sampling of diverse communities in space and time to assess tropical insect diversity among different areas, and the need of such studies is discussed in relation to tropical ecology and quick surveys in conservation biology.     

Computing β-diversity with Rao's quadratic entropy: a change of perspective

Ecologists have traditionally viewed β-diversity as the ratio between γ-diversity and average α-diversity. More recently, an alternative way of partitioning diversity has been proposed for which β-diversity is obtained as the difference between γ-diversity and average α-diversity. Although this additive model of diversity decomposition is generally considered superior to its multiplicative counterpart, in both models β-diversity is a formally derived quantity without any self-contained ecological meaning; it simply quantifies the diversity excess of γ-diversity with respect to average α-diversity. Taking this excess as an index of β-diversity is a questionable operation. In this paper, we show that a particular family of α-diversity measures, the most celebrated of which is Rao's quadratic entropy, can be adequately used for summarizing β-diversity. Our proposal naturally leads to a new additive model of diversity for which, given two or more sets of plots, overall plot-to-plot species variability can be additively partitioned into two non-negative components: average variability in species composition within each set of plots and the species variability between the set of plots. For conservation purposes, the suggested change of perspective in the summarization of β-diversity allows for a flexible analysis of spatial heterogeneity in ecological diversity so that different hierarchical levels of biotic relevance (i.e. from the genetic to the landscape level) can be expressed in a significant and consistent way.     

Recurrent landslides affect the functional beta diversity of a megadiverse tropical forest

Background: Natural disturbance is an important factor that contributes to structuring plant communities. In tropical mountain areas, landslides are frequent and could enhance the diversity in mountain forests. However, the spatial scale in which landslide affect diversity is not known.

Aims: To investigate whether landslides affect taxonomic and functional diversity at different spatial scales. We tested if: (1) taxonomic and functional α-diversity were lower in areas with landslide history; (2) the taxonomic β-diversity was high while the functional β-diversity was low in landslide-affected areas; and (3) plants in areas with landslide history would have, on average, smaller and thicker leaves, with greater pubescence, lower specific leaf area and higher dry matter content.

Methods: At five sites in the Atlantic Forest, we sampled five 5 m × 5 m plots in areas with recent landslide history (from 2 to 39 years) and in adjacent control areas. We identified all juvenile trees (30–100 cm in height) and measured their leaf traits.

Results: Taxonomic α-diversity and functional β-diversity and the occurrence of leaves with trichomes were greater in areas affected by landslide.

Conclusion: The habitat heterogeneity in areas subject to recurrent landslides influenced the functional dispersion and the structuring of plant communities.     

西双版纳热带山地雨林的植物多样性研究

 根据6块样地的调查资料,分析了西双版纳热带山地雨林植物多样性特征。结果表明：在2 500 m2的样地上,西双版纳热带山地雨林群落共有植物物种99～181种。其中乔木层的物种丰富度（S）为54～113,Shannon-Wiener指数（H′）为1.648 7～4.049 1,Simpson指数（λ）为0.503 5～0.969 5,Pielou 均匀度指数（Jsw）为0.413 3～0.854 9。灌木层的S为35～89,H′为2.413 2～3.716 2,λ为0.762 7～0.958 2,Jsw为0.678 8～0.859 3。草本层的各指数值：S为31～65,H′ 为2.792 1～3.499 2,λ为0.902 0～0.938 2,Jsw为0.729 3～0.838 2。低海拔带上的山地雨林（Ⅰ号、Ⅱ号样地）的各指数值（H′、λ、Jsw）在群落不同层次中均表现为草本层 > 灌木层 > 乔木层,而物种丰富度在不同层次中无一定变化规律;高海拔带上山地雨林（Ⅲ号、Ⅳ号、Ⅴ号、Ⅵ号样地）的物种丰富度和多样性指数（H′、λ）表现为乔木层 > 灌木层 > 草本层,而均匀度指数（Jsw）在不同层次中则无一定变化趋势。高海拔带上的山地雨林乔木层和灌木层的物种丰富度、多样性和均匀度指数均明显高于低海拔带上的山地雨林,这是由于前者所处生境较为优越。沿着海拔梯度,群落乔木层的物种丰富度、多样性和均匀度指数均在中等海拔高度地带（约1 200～1 220 m）达到最高值,这是由于中等海拔高度的山地雨林位于生境条件最为优越的沟谷地带,而且与低地季节雨林毗邻,热带雨林植物成分丰富。     

白龙江干旱河谷不同坡向主要灌丛群落随海拔梯度变化的物种多样性研究

采用样方调查法,研究了白龙江干旱河谷不同坡向主要灌丛群落沿着海拔梯度的结构特征、物种多样性的变化规律,旨在了解白龙江干旱河谷不同海拔梯度植被特征和物种多样性变化,为白龙江干旱河谷区域不同海拔植被恢复提供理论依据。研究结果表明：（1）不同海拔梯度同一坡向物种数不同,同一海拔不同坡向物种数也不同,随着海拔的升高不同坡向物种数表现为先增加后减少的趋势,同一海拔梯度内不同坡向主要植被类型也不同。（2）主要灌木群落α多样性在不同坡向随着海拔梯度的升高,表现出先升高后减小的趋势。不同坡向草本群落α多样性随着海拔的升高,也表现出先升高后减小的趋势。对主要灌丛α多样性指数进行相关性分析得物种丰富度指数对物种多样性贡献率最大,表现为丰富度指数（D₁、D₂）> 生态优势度指数（SN）> 种间机遇指数（H）> 群落均匀度指数（R）。（3）不同坡向主要灌丛群落β多样性Whittaker指数沿着不同海拔梯度变化不大,最大值出现在海拔1250~1650m;Routledge和Codyβ多样性指数在海拔1450~1650m出现最大值,但是大体呈现出波形变化。草本β多样性随着海拔的升高变化较大,阳坡植物的β多样性指数在海拔1050~1250m达到最大,阴坡和半阴半阳坡在海拔区间1250~1450m达到最大,半阴半阳坡的β多样性指数均大于阳坡。白龙江干旱河谷不同坡向、不同海拔梯度物种α多样性和β多样性都不同,且不同坡向随着海拔梯度的变化物种α多样性和β多样性呈一定的相关性,说明海拔和坡向是影响生物多样性主要因子之一。     

Response of reed community to the environment gradient water depth in the Yellow River Delta, China

We investigated and monitored a reed community in the fields.Data on the bio-ecologieal characteristics and β-diversity of reed communities in different environmental gradients (mainly based on water depth) of the Yellow River Delta were collected through multianalysis,extremum analysis and β-diversity index analysis.In accordance with the square sum of deviations (Ward)cluster analysis,10 sampling plots were divided into six types with the dominant plants in different plots varying according to the change in environmental gradients.The dominant plants in these plots varied from aquatic plants to xerophytes and salt tolerant plants as water depth decreased.The average height and diameter of the reeds at breast level were significantly correlated with the average water depth.The fitness curves of average density and coverage with average water depth were nonlinear.When the average water depth was 0.3 m,the average density and coverage of reeds reached the apex value,while the height and diameter of the reeds at breast level increased with the water depth.There were obvious changes to the environmental gradient in the Yellow River Delta.The transitional communities were also found to exist in the Yellow River Delta by β-diversity analysis.Vicarious species appeared with the change in water depth.The occurrence of substitute species is determined by the function of common species between adjacent belts.The different functions of common species led to differences in community structure and function and differences in dominant plants.The result reflects the variations of species present in different habitats and directly reflects environmental heterogeneity.The values of//-diversity indices of adjacent plots were higher than those of nonadjacent plots.There are transition zones between the xerophytes and aquatic plants in the Yellow River Delta.In an aquatic environment,the similarity of reed community is higher than that of xeromorphic plants.The β-diversity index can reflect plant succession trends caused by the change in environmental gradients in the Yellow River Delta.The β-diversity index reveals plant responses to changes in environmental gradient and is helpful in observing changes in patterns of species diversity in relation to environmental gradient change and evolving trends in the future,which in turn plays a prominent role when environmental water requirements of wetland are discussed.     

A simulation approach to determine statistical significance of species turnover peaks in a species-rich tropical cloud forest

Use of β-diversity indices in the study of spatial distribution of species diversity is hampered by the difficulty of applying significance tests. To overcome this problem we used a simulation approach in a study of species turnover of ferns, aroids, bromeliads, and melastomes along an elevational gradient from 1700 m to 3400 m in a species-rich tropical cloud forest of Bolivia. Three parameters of species turnover (number of upper/lower elevational species limits per elevational step, Wilson–Shmida similarity index between adjacent steps) were analysed. Significant species turnover limits were detected at 2000 (± 50) m and 3050 m, which roughly coincided with the elevational limits of the main vegetation types recognized in the study area. The taxon specificity of elevational distributions implies that no single plant group can be used as a reliable surrogate for overall plant diversity and that the response to future climate change will be taxon-specific, potentially leading to the formation of plant communities lacking modern analogues. Mean elevational range size of plant species was 490 m (± 369). Elevational range sizes of terrestrial species were shorter than those of epiphytes. We conclude that our simulation approach provides an alternative approach for assessing the statistical significance of levels of species turnover along ecological gradient without the limitations imposed by traditional statistical approaches.