More species,but all do the same: contrasting effects of flood disturbance on ground beetle functional and species diversity

The role of habitat disturbance on biodiversity is central as it promotes changes in ecological systems. That said, still little is known about the functional consequences of such changes. Functional diversity can be used to revealing more mechanistically the disturbance effects on communities by considering the richness and the distribution of traits among the species. Here we analyzed the response of functional and species diversity of ground beetles to flood disturbance to better understand the functioning of alluvial invertebrate communities. Ground beetles were sampled in periodically flooded grasslands along the Elbe River in Germany. We used generalized linear mixed effects models to unveil the relationships between flood disturbance, species and functional diversity, respectively. We measured different components of functional diversity (functional richness, evenness, dispersion, and divergence) and analyzed species diversity by means of rarefied species richness, abundances, evenness and Simpson's diversity. We found contrasting relationships in that most species diversity measures peaked at highest disturbance levels, while most functional diversity measures decreased with increasing disturbance intensities. Inversed relationships between species and functional diversity are rarely observed, as most studies report on positive correlations. We explain increasing species diversity with a higher amount of resources available in highly disturbed sites. Decreasing functional diversity is best explained through the convergence of species traits by flood disturbance and uneven resource exploitation in highly disturbed plots (low functional evenness), suggesting strong impacts from functionally different generalist species in floodchannels. We show that the amount of resources available, and how these resources are exploited, play major roles in the functioning of floodplain ground beetle communities.     

Scaling Disturbance Instead of Richness to Better Understand Anthropogenic Impacts on Biodiversity

A primary impediment to understanding how species diversity and anthropogenic disturbance are related is that both diversity and disturbance can depend on the scales at which they are sampled. While the scale dependence of diversity estimation has received substantial attention, the scale dependence of disturbance estimation has been essentially overlooked. Here, we break from conventional examination of the diversity-disturbance relationship by holding the area over which species richness is estimated constant and instead manipulating the area over which human disturbance is measured. In the boreal forest ecoregion of Alberta, Canada, we test the dependence of species richness on disturbance scale, the scale-dependence of the intermediate disturbance hypothesis, and the consistency of these patterns in native versus exotic species and among human disturbance types. We related field observed species richness in 1 ha surveys of 372 boreal vascular plant communities to remotely sensed measures of human disturbance extent at two survey scales: local (1 ha) and landscape (18 km²). Supporting the intermediate disturbance hypothesis, species richness-disturbance relationships were quadratic at both local and landscape scales of disturbance measurement. This suggests the shape of richness-disturbance relationships is independent of the scale at which disturbance is assessed, despite that local diversity is influenced by disturbance at different scales by different mechanisms, such as direct removal of individuals (local) or indirect alteration of propagule supply (landscape). By contrast, predictions of species richness did depend on scale of disturbance measurement: with high local disturbance richness was double that under high landscape disturbance.     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.     

Does disturbance regime change community assembly of angiosperm plant communities in the boreal forest?

Aims To examine if and how species and phylogenetic diversity change in relation to disturbance, we conducted a review of ecological literature by testing the consistency of the relationship between phylogenetic diversity and disturbance and compared taxonomic groups, type of disturbance and ecosystem/habitat context. We provide a case study of the phylogenetic diversity–disturbance relationship in angiosperm plant communities of a boreal forest region, compared with types of natural and anthropogenic disturbances and plant growth forms.Methods Using a large-scale sampling plot network along a complete (0–100%) anthropogenic disturbance gradient in the boreal biome, we compared the changes of angiosperm plant community structure and composition across plots. We estimated natural disturbance with historical records of major fires. We then calculated phylogenetic diversity indexes and determined species richness in order to compare linear and polynomial trends along disturbance gradients. We also compared the changes of community structure for different types of anthropogenic disturbances and examined how the relationships between species and phylogenetic diversity and disturbance regimes vary among three different life forms (i.e. forbs, graminoids and woody plants).Important findings Phylogenetic diversity was inconsistently related to disturbance in previous studies, regardless of taxon, disturbance type or ecosystem context. In the understudied boreal ecosystem, angiosperm plant communities varied greatly in species richness and phylogenetic diversity along anthropogenic disturbance gradients and among different disturbance types. In general, a quadratic curve described the relationship between species richness and anthropogenic disturbance, with the highest richness at intermediate anthropogenic disturbance levels. However, phylogenetic diversity was not related to disturbance in any consistent manner and species richness was not correlated with phylogenetic diversity. Phylogenetic relatedness was also inconsistent across plant growth forms and different anthropogenic disturbance types. Unlike the inconsistent patterns observed for anthropogenic disturbance, community assembly among localities varying in time since natural disturbance exhibited a distinct signature of phylogenetic relatedness, although those trends varied among plant growth forms.     

Unifying the relationships of species richness to productivity and disturbance

Although species richness has been hypothesized to be highest at 'intermediate' levels of disturbance, empirical studies have demonstrated that the disturbance-diversity relationship can be either negative or positive depending on productivity On the other hand, hypothesized productivity diversity relationships can be positive, negative or unimodal, as confirmed by empirical studies. However, it has remained unclear under what conditions each pattern is realized, and there is little agreement about the mechanisms that generate these diverse patterns. In this study, I present a model that synthesizes these separately developed hypotheses and shows that the interactive effects of disturbance and productivity on the competitive outcome of multispecies dynamics can result in these diverse relationships of species richness to disturbance and productivity The predicted productivity diversity relationship is unimodal but the productivity level that maximizes species richness increases with increasing disturbance. Similarly, the predicted disturbance diversity relationship is unimodal but the peak moves to higher disturbance levels with increasing productivity Further, these patterns are well explained by the opposite effects of productivity and disturbance on competitive outcome that are suggested by the change in community composition along these two environmental gradients: higher productivity favours superior competitors while higher disturbance levels favour inferior competitors.     

Comparing Neutral and Trade-off Community Models in Shaping the Community Biomass-Diversity Relationship Under Different Disturbance Levels

Among numerous mechanisms shaping the unimodal relationship between diversity and community biomass, the trade-off model of “CRS” theory is the most famous one. However, recent researches indicate that this relationship may also emerge under the neutral model where all species are identical with each other. By using an individual-based spatially-explicit model, we evaluated the underlying mechanisms shaping this curve for both models under different disturbance levels. We found unimodal relationships emerged for both models at low and medium disturbance levels; the richness for the trade-off community was lower than the neutral community for most of the environment severity levels, especially at the benign environment due to the strong competitive exclusions among species. Whereas under high disturbance level, the positive relationships emerged for both models; both communities had similar richness with their curves nearly overlapped with each other, that is, because the high disturbance intensity strongly decreased the competitive exclusions within the trade-off community. Our results indicate that although the underlying mechanisms are totally different, both models will produce the similar relationship between diversity and community biomass under different disturbance levels.     

Different responses of plants and herbivore insects to a gradient of vegetation height: an indicator of the vertebrate grazing intensity and successional age

Empirical studies have suggested that species richness of grassland insects usually decreases under grazing management. By contrast, grazing has been shown to increase the species density and richness of vascular plants, especially on productive soils. In order to test the suggested differences in response to management between plants and insects, we simultaneously studied species richness of vascular plants and their insect herbivores, butterflies and moths, in 68 semi-natural grasslands with varying grazing intensity and frequency in SW Finland. Species richness of plants and insects was for the first time related to a quantitative measure of disturbance intensity and successional age, mean vegetation height, by using generalized additive models (GAM). The effects of soil nutrients on vegetation height were accounted for by using phosphorus concentration as a productivity surrogate.
The results showed that species richness of butterflies and moths peaked in taller vegetation compared with vascular plants, corresponding to a lower disturbance intensity and increasing time since abandonment. These patterns are discussed in the light of two hypotheses, the "structural diversity hypothesis" and "dynamic equilibrium model" of Huston, both suggesting a weaker disturbance tolerance of insects compared with plants. Butterflies and moths which are specialists in their larval host-plant use (monophagous and oligophagous species) preferred lower vegetation (higher disturbances) compared with generalists (polyphagous species), as predicted by Huston's model. This difference indicates a stronger relationship with plant species richness for specialist than for generalist butterflies and moths. Our results support the application of regionally and temporally varying grazing intensities in grassland conservation management.     

Evidence that niche specialization explains species-energy relationships in lake fish communities

1. Interspecific niche differences have long been identified as a major explanation for the occurrence of species-rich communities. However, much fieldwork studying variation in local species richness has focused upon physical habitat attributes or regional factors, such as the size of the regional species pool. 2. We applied indices of functional diversity and niche overlap to data on the species niche to examine the importance of interspecific niche differentiation for species richness in French lake fish communities. We combined this information with environmental data to test generalizations of the physiological tolerance and niche specialization hypotheses for species-energy relationships. 3. We found evidence for a largely non-saturating relationship (relative to random expectation) between species richness and functional evenness (evenness of spacing between species in niche space), while functional richness (volume of niche space occupied) peaked at moderate levels of species richness and niche overlap showed an initial decrease followed by saturation. This suggests that increased niche specialization may have allowed species to coexist in the most species-rich communities. 4. We tested for evidence that increased temperature, local habitat area, local habitat diversity and immigration affected species richness via increased niche specialization. Temperature explained by far the largest amount of variation in species richness, functional diversity and niche overlap. These results, combined with the largely non-saturating species richness-functional evenness relationship, suggest that increased temperature may have permitted increased species richness by allowing increased niche specialization. 5. These results emphasize the importance of niche differences for species coexistence in species-rich communities, and indicate that the conservation of functional diversity may be vital for the maintenance of species diversity in biological communities. Our approach may be applied readily to many types of community, and at any scale, thus providing a flexible means of testing niche-based hypotheses for species richness gradients.     

Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality.     

Plant diversity changes and succession along resource availability and disturbance gradients in Kamchatka

Changes in plant species richness across environmental and temporal gradients have often been explained by the intermediate disturbance hypothesis and a unimodal diversity–productivity relationship. We tested these predictions using two sets of mountain plant communities assembled along postglacial successional and snow depth (disturbance and stress) gradients in maritime Kamchatka. In each community, we counted the number of species in plots of increasing sizes (0.0025–100 m²) and analyzed them using species–area curves fitted by the Arrhenius power function and the Gleason logarithmic function. A comparison of successional communities along a 270-year-old moraine chronosequence behind the receding Koryto Glacier—representing gradients of increasing productivity and resource competition—confirmed the unimodal species richness pattern. The plant diversity peaked in a 60–80-year-old Salix–Alnus stand where light availability was sufficient to sustain a rich understory combining pioneer and late successional herbs. The closed Alnus canopy on older moraines caused a pronounced decrease in species richness for all plot sizes (interactive stage 80–120 years since deglaciation). A slight increase in species richness in the oldest assortative stages (120–270 years), when Alnus stands are mature, was found only at the smaller spatial scales. This reflects (i) the consolidation of clonal understory dominants and (ii) the absence of other woody species such as Betula ermanii whose invasion would eliminate Alnus and increase diversity at larger spatial scales. A comparative study of major mountain plant communities distributed above the Koryto Glacier foreland did not confirm the highest species richness at intermediate levels of disturbance and stress. Contrary to our expectation, the species richness was highest in alpine tundra and snowbed communities, which are subjected to severe winter frost and a short summer season, while less disturbed communities of subalpine meadows, heaths, and Betula ermanii woods were less species-rich. We attribute this pattern to differences in habitat area and species pool size.     

The relationship between species richness and biomass changes from boreal to subtropical forests in China

Diversity‐manipulation experiments suggest a positive effect of biodiversity on ecosystem properties (EPs), but variable relationships between species richness and EPs have been reported in natural communities. An explanation for this discrepancy is that observed richness–EPs relationships in natural communities change with environment and species functional identities. But how the relationships change along broad‐scale climatic gradients has rarely been examined. In this paper, we sampled 848 plots of 20 × 30 m² from boreal to tropical forests across China. We examined plot biomass with respect to environmental factors, tree species richness and functional group identity (FGI, i.e. evergreen vs deciduous, and coniferous vs broadleaf). Variation partitioning was used to evaluate the relative effects of the three classes of factors. We found that, most of the ‘effects’ (percentage of variation explained) of richness and FGI on forest biomass were shared with environmental factors, but species richness and FGI still revealed significant effects in addition to environment for plots across China. Richness and FGI explained biomass mainly through their shared effects instead of independent effects, suggesting that the positive biodiversity effect is closely associated with a sampling effect. The relative effects of richness, FGI and environment varied latitudinally: the independent effects of environment and richness decreased from boreal to subtropical forests, whereas the total effect of FGI increased. We also found that the slope of richness–biomass relationship decreased monotonically from boreal to subtropical forests, possibly because of decreasing complementarity and increasing competition with increasing productivity. Our results suggest that while species richness does have significant effects on forest biomass it is less important than environmental gradients and other biotic factors in shaping large‐scale biomass patterns. We suggest that understanding how and why the diversity–EPs relationships change along climatic gradient would be helpful for a better understanding of real biodiversity effects in natural communities.     

Functional dependence underlies a positive plant-grasshopper richness relationship

A central focus of ecology is identifying the factors that shape spatial patterns of species diversity and this is particularly relevant in an era of global change. Positive relationships between plant and consumer diversity are common, but could be driven by direct responses of each trophic level to underlying environmental gradients, or indirectly where changes in environmental conditions propagate through food webs. Here we use structural equation modeling to examine the relative importance of soil resource availability and disturbance (fire) in mediating relationships between plant and grasshopper richness in insular grasslands. We found a positive relationship between plant and consumer richness that became stronger after accounting for disturbance, despite unique responses of plants and consumers to the two environmental gradients. Plant richness responded to an underlying gradient in soil resource availability. Time since the last fire had a direct positive effect on grasshopper richness but had no effect on plant richness. This work supports that plant and consumer richness are functionally linked, rather than having similar responses to environmental gradients. By disentangling the direct and indirect processes underlying a positive relationship between plant and consumer diversity in a natural system that spans multiple environmental gradients, we demonstrate the importance of investigating biodiversity through explicit multivariate models.     

Does plant phylogenetic diversity increase invertebrate herbivory in managed grasslands?

Plant diversity and land-use intensity have been shown to affect invertebrate herbivory. Several hypotheses predict positive (e.g. associational susceptibility) or negative (e.g. associational resistance) relationships of herbivory with plant species richness. Also, the strength and direction of reported relationships vary greatly between studies leading to the conclusion that relationships either depend on the specific system studied or that other unconsidered factors are more important. Here, we hypothesized that plant phylogenetic diversity is a stronger predictor of invertebrate herbivory than plant species richness because it integrates additional information about the phenotypical and functional composition of communities. We assessed the community-wide invertebrate herbivory, plant species richness and phylogenetic diversity across a range of land-use intensities including a total of 145 managed grasslands in three regions in Germany. Increasing land-use intensity decreased plant species richness and phylogenetic diversity. Plant species richness did not predict invertebrate herbivory. By contrast herbivory moderately increased with increasing plant phylogenetic diversity even after accounting for the effects of region and land use. The strength of direct effects of land-use intensity and indirect effects via altered phylogenetic diversity on herbivory, however, varied among regions. Our results suggest that increasing phylogenetic diversity of plant communities increases invertebrate herbivory probably by providing higher resource diversity. Differences between regions underline the need to account for regional peculiarities when attempting to generalize land-use effects on invertebrate herbivory.     

The response of benthic rhizopods to sediment disturbance does not support the intermediate disturbance hypothesis

Disturbance is one of the mechanisms which counteract competitive exclusion of populations in resource-limited communities, thereby facilitating coexistence and maintaining community species diversity. The intermediate disturbance hypothesis predicts maximum diversity at intermediate disturbance intensities and frequencies. This paper reports results of an experimental test of this hypothesis using a coastal benthic community of rhizopods (Protozoa: Rhizopoda), and experimental sediment resuspension as a simulated natural disturbance. We carried out two experiments of 5 d duration which focussed on the effects of resuspension intensity and frequency, respectively, on the abundance, species richness and on the Shannon-Weaver diversity index of rhizopod communities in surface sediments of natural sediment cores from the coastal southern Baltic. Care was taken to adjust the experimental treatments to the natural disturbance regime in this area.
Twenty-four and 28 rhizopod species were present during the intensity and frequency experiment, respectively. Small bacterivorous rhizopods of the Vannellidae, Cochliopodidae, Paramoebidae and Rhizopoda incertae sedis dominated the communities during both experiments. Rhizopod abundance, species richness and diversity increased towards the end of the intensity experiment, but they did not show effects of disturbance intensity. Similarly, no effects of disturbance frequency were found during the frequency experiment. Our results indicate that coexistence and community diversity maintenance in benthic rhizopod communities, and probably in benthic heterotrophic protistan communities in general, may rely on different mechanisms than intermediate disturbance, such as trophic niche separation and high rates of dispersal and colonisation.     

Land-use intensification reduces functional redundancy and response diversity in plant communities

Ecosystem resilience depends on functional redundancy (the number of species contributing similarly to an ecosystem function) and response diversity (how functionally similar species respond differently to disturbance). Here, we explore how land-use change impacts these attributes in plant communities, using data from 18 land-use intensity gradients that represent five biomes and > 2800 species. We identify functional groups using multivariate analysis of plant traits which influence ecosystem processes. Functional redundancy is calculated as the species richness within each group, and response diversity as the multivariate within-group dispersion in response trait space, using traits that influence responses to disturbances. Meta-analysis across all datasets showed that land-use intensification significantly reduced both functional redundancy and response diversity, although specific relationships varied considerably among the different land-use gradients. These results indicate that intensified management of ecosystems for resource extraction can increase their vulnerability to future disturbances.
Ecology Letters (2010) 13: 76–86     

Effects of disturbance frequency,intensity, and area on assemblages of stream macroinvertebrates

Disturbance frequency, intensity, and areal extent may influence the effects of disturbance on biological communities. Furthermore, these three factors may have interacting effects on biological diversity. We manipulated the frequency, intensity, and area of disturbance in a full-factorial design on artificial substrates and measured responses of benthic macroinvertebrates in a northern Vermont stream. Macroinvertebrate abundance was lower in all disturbance treatments than in the undisturbed control. As in most other studies in streams, species density (number of species/sample) was lower in disturbed treatments than in undisturbed controls. However, species density is very sensitive to total abundance of a sample, which is usually reduced by disturbance. We used a rarefaction method to compare species richness based on an equivalent number of individuals. In rarefied samples, species richness was higher in all eight disturbed treatments than in the undisturbed control, with significant increases in species richness for larger areas and greater intensities of disturbance. Increases in species richness in response to disturbance were consistent within patches, among patches with similar disturbance histories, and among patches with differing disturbance histories. These results provide some support for Huston’s dynamic-equilibrium model but do not support the intermediate-disturbance hypothesis. Our analyses demonstrate that species richness and species density can generate opposite patterns of community response to disturbance. The interplay of abundance, species richness, and species density has been neglected in previous tests of disturbance models. Received: 20 July 1999 / Accepted: 26 January 2000     

Parallel responses of species and genetic diversity to El Niño Southern Oscillation-induced environmental destruction

Species diversity within communities and genetic diversity within species are two fundamental levels of biodiversity. Positive relationships between species richness and within-species genetic diversity have recently been documented across natural and semi-natural habitat islands, leading Vellend to suggest a novel macro-ecological pattern termed the species-genetic diversity correlation. We tested whether this prediction holds for areas affected by recent habitat disturbance using butterfly communities in east Kalimantan, Indonesia. Here, we show that both strong spatial and temporal correlations exist between species and allelic richness across rainforest habitats affected by El Niño Southern Oscillation-induced disturbance. Coupled with evidence that changes in species richness are a direct result of local extirpation and lower recruitment, these data suggest that forces governing variation at the two levels operate over parallel and short timescales, with implications for biodiversity recovery following disturbance. Remnant communities may be doubly affected, with reductions in species richness being associated with reductions in genetic diversity within remnant species.     

环境因子和干扰强度对高寒草甸植物多样性空间分异的影响

采用样带与样地结合的方法在三江源自然保护区的核心区沿海拔梯度在阴坡、阳坡分别进行草本植被调查,通过因子分析和偏相关分析研究丰富度指数、多样性指数与环境梯度（包括海拔梯度、裸斑面积、坡度、土壤总碳、总氮含量、土壤pH值、土壤总可溶性盐含量）和干扰强度（鼠类干扰强度、放牧强度）之间的关系。研究结果表明：杂类草丰富度指数（DMa杂）与总物种丰富度指数（DMa总）极显著相关（P<0.01）;阳坡DMa杂和DMa总均呈现“中海拔膨胀”现象,阴坡DMa杂和DMa总与海拔梯度呈正相关,莎草科和禾本科的丰富度指数（DMa莎和DMa禾）随海拔升高并无明显规律;通过主成分分析,及偏相关分析,第一主成分（裸斑面积、鼠类干扰和放牧强度）与除莎草科Margalef丰富度指数、禾本科Simpson指数和禾本科Pielou均匀度指数外的其他草地多样性指数均显著相关,是影响阳坡草地植物多样性的主要因子,土壤总碳、总氮含量对阳坡禾本科类群的多样性指数和均匀度指数有极显著影响,土壤pH值、TDS含量和坡度对阳坡莎草科类群的丰富度有显著影响;海拔梯度、土壤总碳、总氮以及pH值对阴坡草本植物群落的多样性影响较大。研究结论认为,植物群落生物多样性的空间分异特征是地理环境、土壤环境以及干扰强度等因素综合作用的结果。无干扰或干扰较弱时,物种多样性主要受土壤环境状况所影响;而在强干扰存在条件下,干扰强度对物种丰富度和多样性的影响比环境因子更显著;遏制高寒草甸植物多样性降低应首先控制放牧及鼠类等强干扰活动。     

Latitudinal gradients in the phenetic diversity of New World bat communities

Although the examination of latitudinal gradients of species richness is common, little attention has been devoted to other components of biodiversity such as phenetic diversity. Because the phenotype reflects aspects of an organism's environment, ecological relationships and evolutionary history, measures of phenetic diversity likely provide complimentary information to that of species richness, and may provide unique insights for understanding the mechanistic basis to patterns of biodiversity. Herein, we evaluate latitudinal gradients in the phenetic diversity of 32 New World bat communities. Seven morphological characters were used to estimate phenotypic variation among bat species within local communities. Principal components analysis decomposed this variation into axes of size and shape. Three measures of phenetic diversity were calculated separately for size and for shape axes. The range of species scores on a particular axis described the amount of phenetic variation encompassed by species in a community. The standard deviation of minimum spanning‐tree segment lengths described uniformity of species. Average nearest‐neighbor distances described local packing. We separately regressed these six measures on local species richness and latitude separately. Variation in species richness accounted for a significant amount of variation in each measure of phenetic diversity. Latitude also accounted for significant variation in phenetic diversity except for the standard deviation of minimum‐spanning tree segment lengths and the average nearest‐neighbor distance on the shape axis. More importantly, gradients in phenetic diversity were significantly different than would be expected as a consequence of latitudinal gradients in species richness. Nonetheless, when variation among communities regarding the richness and composition of their regional faunas was taken into consideration, differences between empirical and simulated gradients were nonsignificant. Thus, factors that determine the composition of regional faunas have a great impact on the phenetic diversity of communities and ultimately the latitudinal gradient in biodiversity.     

不同干扰强度下江西武夷山河岸带阔叶林群落的结构与数量特征

为揭示中亚热带典型河岸带阔叶林群落的结构特征、数量特征和干扰强度的耦合关系,根据干扰强度的不同,在江西武夷山保护区内选取3条主要水系进行阔叶林群落调查,共统计到河岸带维管束植物93科174属304种,分别占保护区维管束植物总数的41.5%、18.0%、11.9%。物种组成以壳斗科（6属22种）、山茶科（7属22种）、樟科（6属16种）、蔷薇科（8属16种）为主。不同干扰强度下的河岸带植被群落相似性Jaccard系数均在0.2-0.3之间,各群落优势种完全不同,且存在特有分布的物种,但群落乔木层优势种优势度（重要值）差异不显著（P〉0.05）。不同干扰强度下,物种数量、群落Jaccard系数、丰富度指数、多样性指数、均匀度指数总体上为：轻微干扰〉中等干扰〉无干扰;而乔木的平均高度和平均胸径却为：无干扰〉中等干扰〉轻微干扰。研究结果表明,江西武夷山河岸带阔叶林以常绿阔叶树种为主,但不同干扰梯度下群落的结构和数量特征差异性较大。