松嫩草地植物群落物种多度–分布关系及其解释

物种多度–分布关系是生物多样性科学的关键问题之一,但目前对其解释尚未有统一的观点,生态幅假说和集合种群动态理论是其中两个有代表性的假说。作者以松嫩平原羊草(Leymus chinensis)草甸的代表性群落羊草–杂类草群落斑块为研究对象,分别于2007年和2008年调查了其植物生长型组成和斑块距离,来检验上述两个假说对物种多度–分布关系的解释能力。作者提出以生长型适应指数(growth-form adaption index,GAI)作为生态幅的衡量指标,以最小斑块距离来反映植物的扩散和定居过程。结果表明:在生境尺度上,物种的多度和分布成显著正相关,且多度–分布关系在年际间相对稳定。物种的多度和分布均与植物生长型密切相关,分布广、多度高的物种以根茎型、直立型或分枝型为主,分布窄、多度低的物种以莲座型或刷状根型为主。GAI与物种的多度和分布均成显著线性正相关,少数物种的分布广,多数物种的分布窄,直接支持了生态幅假说。最近斑块距离与物种的多度和分布均成显著幂函数负相关,而群落相似性与斑块距离无显著相关性,因此本结果并未直接支持集合种群动态理论,但扩散过程可能是影响羊草草甸植物群落种多度–分布关系的重要潜在机制之一。     

喜马拉雅山东段鸟类多度-垂直分布幅关系:特有种与非特有种的对比

物种多度与分布幅之间的正相关被认为是一种普遍的规律。但近年在热带山地和岛屿的研究发现多度-分布幅关系会出现不相关或负相关的现象;该现象可能是由于当地多度高且分布幅小的特有种比例较高所导致。在喜马拉雅山东段的勒布沟沿海拔2350—4950 m开展研究：1)记录了当地鸟类多度垂直分布格局;2)验证了该区繁殖鸟总体多度-垂直分布幅关系,并对比了特有种和非特有种分组子集多度-垂直分布幅关系、平均多度和垂直分布中心的差异。研究发现勒布沟鸟类多度垂直分布格局为驼峰格局。该区繁殖鸟类与非特有种的多度-垂直分布幅关系均为正相关,但特有种的多度-垂直分布幅关系为不相关。特有种的多度及海拔分布中心位置均高于非特有种。结果表明区域的鸟类特有性对多度-垂直分布幅关系存在着重要的影响;地理隔离导致的区域物种组成差异,是造成多度-分布幅关系模式变化的重要原因之一。     

中国蛇类物种丰富度地理格局及其与生态因子的关系

物种丰富度地理格局成因是生态学和生物地理学研究重要目标之一。生态假说在解释物种丰富度地理格局的成因上受到广泛关注。该文基于100km×100km空间分辨率研究中国蛇类物种丰富度的地理分布格局,并结合生态假说探讨影响蛇类分布格局的因素。该研究采用主轴邻距法获得基于特征值的空域数据,并同生态因子进行多元回归分析,结果表明:(1)中国蛇类物种丰富度在经、纬度上呈现多峰分布格局,物种丰富度最高的地区位于东洋界亚热带、热带,丰富度较低的地区位于青藏高原、北方草原荒漠、黄淮平原、两湖平原及鄱阳湖平原等;(2)多元回归分析能解释56.5%的蛇类物种丰富度变化,分析得出蛇类物种丰富度格局的主要影响因子是归一化植被指数、最冷季降水量和年温差。(3)模型选择结果显示,在多元回归分析中,P<0.05的变量(归一化植被指数、最冷季降水量和年温差)组成的模型是解释蛇类物种丰富度格局的最优模型。这说明蛇类物种丰富度格局是由不同生态因子共同作用的结果。基于中国蛇类物种丰富度地理格局成因研究的复杂性,该文提出在进一步研究中,需重视各假说中影响因子的选择和人类活动的影响,并在不同空间尺度上对蛇类物种丰富度地理格局进行综合分析。     

新疆开都河流域水生植物多样性及其影响因素

河流是一个连续的、流动的、独特而完整的系统,研究河流生态系统中水生植物的多样性分布格局及其影响因素对河流生态学研究具有重要意义。本文通过野外调查,研究了新疆开都河流域水生植物多样性、主要水生植物群落特征及与环境因子之间的关系,并利用水分-能量动态假说和栖息地异质性假说对该流域水生植物物种多样性的地理格局进行解释。结果表明: 开都河流域共有水生植物71种,隶属于24科39属;聚类分析可将开都河流域水生植物群落划分为10个主要群落类型,其中芦苇群落物种丰富度最高,狭叶香蒲群落和金鱼藻群落物种丰富度最低;流域水生植物群落Shannon指数与pH呈显著负相关,Simpson指数与pH、经度呈显著负相关,与海拔呈显著正相关;流域水生植物群落类型主要受海拔、水深及水温的影响;流域水生植物物种多样性随经纬度无明显变化规律。水分-能量动态假说和栖息地异质性假说共解释开都河流域水生植物多样性格局变量的31.4%,表明这两个假说对于该流域水生植物多样性格局的解释力并不高。     

Global patterns of species richness of the holarctic alpine herb Saxifraga: the role of temperature and habitat heterogeneity

北半球高山和极地虎耳草属物种丰富度的地理格局：温度和生境异质性的作用 现代气候、生境异质性和长期气候变化对森林生态系统中分布的木本植物的物种丰富度格局的影响在以往研究中受到广泛关注,但对高寒-极地生态系统中的草本植物物种丰富度格局及其影响因素的研究仍较少。本研究旨在检验以往研究中基于物种丰富度和环境因子关系提出的假说是否能够解释高寒-极地地区典型草本植物-虎耳草属(Saxifraga)的物种丰富度格局。本研究利用全球437种虎耳草属物种分布数据,探讨了全部物种、广域和狭域物种丰富度格局的影响因素。采用广义线性模型和空间自回归模型,评估了现代气候、生境异质性和历史气候对虎耳草属物种丰富度格局的影响。采用偏回归分析了不同变量对物种丰富度的独立解释率和共同解释率,并检验了4种广泛使用的物种丰富度与环境关系模型对物种丰富度格局的解释能力。研究结果表明,温度与虎耳草属所有物种和广域物种的物种丰富度格局呈显著负相关关系,是影响物种丰富度格局最重要的环境因子,这可能反映了虎耳草属对其祖先温带生态位的保守性。生境异质性和末次冰期以来的气候变化是虎耳草属狭域物种丰富度空间变异的最佳预测因子。总体而言,包含5个预测变量的组合模型可以解释大约40%–50%的虎耳草属物种丰富度的空间变异。此外,进化和生物地理过程在虎耳草属物种丰富度格局形成方面可能发挥了重要作用,这有待进一步研究。     

中国黑戈壁地区植物物种丰富度格局的水热解释

我国黑戈壁地区自然环境恶劣,植物多样性格局受到极端干旱气候的影响而形成了特殊的分布格局。为了揭示黑戈壁地区极端气候对物种丰富度格局的影响,通过对5000 km样线内174个样方中的植物进行调查,结合气候数据,研究影响中国黑戈壁地区植物物种丰富度格局的气候因素以及不同生活型植物物种丰富度格局与气候关系的差异。结果表明,水热动态假说对物种丰富度格局的解释率为62.3%,未解释部分为37.7%,说明其能够很好的解释黑戈壁地区的植物群落物种丰富度格局;能量对物种丰富格局的单独解释率仅为3.5%,水分的单独解释率为16.4%,两者共同解释率为42.4%,水分和能量共同决定的水资源可利用性主导着物种丰富度格局;不同生活型植物对气候因子的响应存在显著差异,水热综合作用对草本植物丰富度格局的解释率为65.4%,但对灌木仅有37.9%,表明水热动态假说不适用于解释灌木植物的物种丰富度格局,植物对气候的适应特性及种间相互作用对物种丰富度格局有着重要的影响。     

气候假说对内蒙古草原群落物种多样性格局的解释

物种丰富度的地理格局是宏观生态学和生物地理学的中心议题之一。本文基于内蒙古草原192个野外样地的调查数据, 结合各样地年平均气温、年降水量等9个气候因子, 探讨内蒙古草原物种丰富度格局及其主导因素, 以确定气候假说在该区的适用性。结果表明: (1)内蒙古草原物种丰富度经度格局显著, 呈现沿经度升高而增加的趋势, 同时由于经纬度的共线性, 也呈现出沿纬度升高而增加的趋势。(2)方差分解显示, 能量单独解释率为2.7%, 水分单独解释率为11.4%, 水分和能量共同解释率为46.3%, 未解释部分为39.6%, 可见能量与水分的共同作用在物种丰富度格局形成中占主导地位, 支持水热动态假说。这说明水热动态假说适用于解释内蒙古草原物种丰富度 格局。     

山西霍山油松林的物种多度分布格局

物种多度格局分析对理解群落结构具有重要的意义。该文首次选用描述种-多度关系的生态位模型(生态位优先模型NPM、分割线段模型BSM、生态位重叠模型ONM)、生物统计模型(对数级数分布模型LSD、对数正态分布模型LN)以及中性理论模型NT, 对山西霍山油松(Pinus tabulaeformis)林的物种数量关系进行了拟合研究, 并采用卡方(χ²)检验、Likelihood-ratios (L-R)检验、Kolmogorov-Smirnov (K-S)检验和赤池信息量准则(AIC)选择最适合模型, 结果表明: (1)描述乔木层物种多度格局的最优生态位模型为NPM (3种检验方法均接受该模型, p > 0.05, 且该模型具有最小的 AIC值), ONM的拟合效果次之, 不服从BSM; 三种生态位模型均可较好地拟合灌木层物种多度格局; ONM是草本层最佳生态位模型, BSM、NPM拟合效果较差; LSD可以描述油松林各层物种多度结构; LN可以很好地解释灌草层物种数量关系; NT不能解释油松林任何层次的物种多度结构。(2)霍山油松林乔木层和灌木层的物种丰富度和物种多样性均明显小于草本层; 该群落物种富集种少而稀疏种多, 且群落的均匀度相对较小。(3)从该区油松林种-多度分布来看, 同一个模型可以拟合不同的物种多度数据, 相同的数据可以由不同的模型来解释。因此, 研究森林群落物种分布时, 应采用多个模型进行拟合, 同时选用多种方法筛选最优模型。     

科尔沁沙地植物物种丰富度格局及其与环境的关系

能量、水分和生境异质性是物种丰富度分布格局的重要因素。本文以特殊环境科尔沁沙地为对象,通过植物区域物种丰富度数据和对应气候数据统计,结合生境异质性分析,对科尔沁沙地物种丰富度格局及其主导因素进行研究。结果显示:(1)科尔沁沙地植物共计有115科1030种,呈现显著的空间异质分布,随着经度的增加物种丰富度呈先下降后上升的趋势,而受纬度影响较小。(2)水热动态假说最适合用于解释科尔沁沙地植物物种丰富度格局。说明水资源可利用性是科尔沁沙地植物物种丰富度的主要影响因素。     

季风常绿阔叶林不同恢复阶段乔木优势种群生态位和种间联结

生态位和种间联结是群落动态研究的重要内容之一,物种间相互作用影响着群落的恢复和演替。本文在对云南普洱地区不同恢复阶段(恢复15年、恢复30年和原始林群落)季风常绿阔叶林群落的野外调查基础上,采用生态位宽度、生态位重叠、方差比率(VR)和基于2×2联列表的χ2检验、联结系数(AC)等方法,分析了不同恢复阶段各种群的变化趋势。结果表明:3种群落类型中物种的重要值与相对应的生态位宽度之间存在着显著的正相关,恢复15年群落有78.22%的种对之间的生态位重叠值在0.4～0.8,说明其群落优势物种存在较强的资源利用性竞争,而恢复30年和原始林群落结构则具有一定的稳定性,多数生态位宽度较大的物种之间的生态位重叠要大于生态位较小的物种,反映出优势物种具有较强的竞争能力;恢复15年和恢复30年群落物种间总体呈不显著正联结,原始林群落则呈不显著负联结;3种群落231种对中,绝大多数种对联结系数未达显著水平,种对间的独立性相对较强,群落中物种间正负联结对数占总种的比例随恢复进程而出现下降趋势。不同恢复阶段群落中联结系数与生态位重叠值之间存在显著正相关,生态位重叠值越大,其联结系数也越大。     

Positive relationship between regional distribution and local abundance in stream insects: a consequence of niche breadth or niche position?

A positive relationship between regional distribution and local abundance of species is almost ubiquitous macroecological pattern, yet the mechanisms behind this pattern remain poorly understood. I tested for the relationship between regional distribution and local abundance of stream insect species in a boreal drainage system, with a specific aim to examine if this relationship follows the mechanistic basis of either the niche-based (niche breadth and niche position) or metapopulation models. There was a positive relationship between regional distribution and local abundance of stream insects, and there also were significant relationships between distribution/abundance and niche breadth or niche position. These results thus suggest that widely distributed species tend to be, on average, locally more abundant, have wider niches and lower marginality of niche position with regard to environmental factors than species that have more restricted distributions. However, although significant, there was much unexplained variability around these relationships, suggesting that other mechanisms (e.g. metapopulation dynamics) besides differences in species' niches are likely to affect the distribution and abundance of stream insects, at least within a drainage system. The results thus showed that 1) although niche position was more consistently related to the positive distribution-abundance relationship, ecologists should not abandon niche breadth as a potential mechanism behind this relationship, and 2) that several mechanisms are likely to act in concert in determining the relationship between distribution and abundance of species.     

The relationships between abundance, range size and niche breadth in Central European tree species

Aim  Range size and niche breadth have been found to be positively related to abundance in many plant and animal groups. We tested these two relationships for the tree species flora of Central Europe; that is, for all 25 species that have their distribution centre in this region.
Location  Eurasia, with a focus on Central Europe.
Methods  We devised an abundance and niche variable classification system to transform the existing literature data into a semi-quantitative assessment of abundance and niche breadth (in terms of soil chemical and physical variables, and temperature) for each of the 25 tree species. Regression analyses between abundance, range size and niche breadth were conducted for the entire species sample and for subsets of species defined by their ecology or phylogeny.
Results  The relationship between abundance in the distribution centre and range size was weak for the Central European tree species. However, significant abundance–range size relationships were found for phylogenetically or ecologically more homogenous species groups (for example for trees of the order Rosales and for mid-successional tree species). Realized niche breadth was positively related to range size in the case of temperature, but not for soil-related variables. No relationship existed between niche breadth and abundance in the distribution centre.
Main conclusions  We hypothesize that the weak relationship between abundance and range size is primarily a consequence of substantial ecological and phylogenetic heterogeneity within this rather species-poor assemblage. The positive relationship between realized temperature niche breadth and range size emphasizes the strong influence of climatic variables on plant distribution patterns over continental or global scales.     

The role of niche breadth, resource availability and range position on the life history of butterflies

We analysed the relationship between three life history characteristics (mobility, length of flight period and body size) and niche breadth (larval host plant specificity and adult habitat breadth), resource availability (distribution and abundance of host plants) and range position (distance between the northernmost distribution record and southernmost point of Finland) of the butterfly fauna of Finland. The data is based on literature and questionnaires. Often in across species studies phylogeny may create spurious relationships between life-history and ecological variables. We took the phylogenetic relatedness of butterfly species into account by analysing the data with phylogenetically independent contrasts (CAIC method). Butterfly mobility was positively related to the niche breadth, resource availability and range position. The length of the flight period was negatively related to the range position, indicating that the species at the northern edge of their distribution range have shorter flight period than species which are further way from the range edge. After controlling for the phylogenetic relatedness we found no significant correlations between body size and niche breadth, resource availability or range position. We suggest that the relationship between the length of the flight period and range position may arise as a consequence of lower hatching asynchrony in edge species as a result of lower environmental variance in larval growth conditions. Our results on the mobility suggest that there is selection pressure towards lower migration rate in species that have restricted niche breadth, low resource availability and in species that are on the northern edge of their geographical distribution range. In such species, selection against mobile individuals is likely to result from the decreased probability of finding another habitat patch suitable for egg laying.     

Ecological correlates of geographical range occupancy in North American birds

Aim  The degree to which a species is predictably encountered within its range varies tremendously across species. Understanding why some species occur less frequently within their range than others has important consequences for conservation and for analyses of ecological patterns based on range maps. We examined whether patterns in geographical range occupancy can be explained by species-level traits.
Location  North America.
Methods  We used survey data from 1993 to 2002 from the North American Breeding Bird Survey along with digital range maps produced by NatureServe to calculate range occupancy for 298 species of terrestrial birds. We tested whether species traits explained variation in range occupancy values using linear regression techniques.
Results  We found three species traits that together explained more than half of the variation in range occupancy. Population density and niche breadth were positively correlated with occupancy, while niche position was negatively correlated with occupancy.
Main conclusions  Our results suggest that high range occupancy will occur in species that are common at sites on which they occur, that tolerate a relatively wide range of ecological conditions and that tend to have ranges centred on areas with common environmental conditions. Furthermore, it appears that niche-based characteristics may explain patterns of distribution and abundance from local habitats up to the scale of geographical ranges.     

Mechanisms underpinning community stability along a latitudinal gradient: Insights from a niche-based approach

At large scales, the mechanisms underpinning stability in natural communities may vary in importance due to changes in species composition, mean abundance, and species richness. Here we link species characteristics (niche positions) and community characteristics (richness and abundance) to evaluate the importance of stability mechanisms in 156 butterfly communities monitored across three European countries and spanning five bioclimatic regions. We construct niche-based hierarchical structural Bayesian models to explain first differences in abundance, population stability, and species richness between the countries, and then explore how these factors impact community stability both directly and indirectly (via synchrony and population stability). Species richness was partially explained by the position of a site relative to the niches of the species pool, and species near the centre of their niche had higher average population stability. The differences in mean abundance, population stability, and species richness then influenced how much variation in community stability they explained across the countries. We found, using variance partitioning, that community stability in Finnish communities was most influenced by community abundance, whereas this aspect was unimportant in Spain with species synchrony explaining most variation; the UK was somewhat intermediate with both factors explaining variation. Across all countries, the diversity–stability relationship was indirect with species richness reducing synchrony which increased community stability, with no direct effects of species richness. Our results suggest that in natural communities, biogeographical variation observed in key drivers of stability, such as population abundance and species richness, leads to community stability being limited by different factors and that this can partially be explained due to the niche characteristics of the European butterfly assemblage.     

Distribution, abundance and niche breadth of birds: scale matters

We used local habitat niche breadth, local abundance and body size of non-passerine afrotropical birds in Tsavo East National Park (Kenya) to predict species distributional ranges in Kenya and across Africa. Univariate analysis revealed a significant positive correlation between local abundance and distribution only on the scale of Kenya. Performing a multiple regression analysis, local abundance, local habitat niche breadth and body size explained a significant part of the variance in bird distribution, again only on the Kenyan scale. From these results, we speculate that on continental scales distributions may be more influenced by macroclimatic conditions and historical factors, whereas distributions on regional scales are predominantly influenced by ecological factors.     

Variation in niche parameters along the diversity gradient of unicellular eukaryote assemblages

We examined the relationship between average niche parameters and species richness of benthic diatom assemblages of boreal streams. We hypothesized that diverse assemblages should be typified by small average niche breadth of species, whereas low-diversity assemblages should be typified by broad average niche breadth. We also hypothesized that low-diversity sites should be dominated by either non-marginal species only or marginal species only, depending on the degree to which these sites could be categorized to range from environmentally typical sites to atypical sites. Niche breadth and niche position for each species were determined via Outlying Mean Index analysis. As hypothesized, we found that median niche parameters were significantly related to species richness. Median niche breadth showed both significant linear (R(2)=0.328, p<0.001) and unimodal (R(2)=0.354, p<0.001) relationship to species richness. The relationship between median niche position and species richness was best approximated by a unimodal model (R(2)=0.214, p=0.005). The underlying gradient in species richness was best accounted for by a regression model including moss cover, iron, and nitrogen, and explained 32% of variability in species richness. Our results showed that sites with high-diversity assemblages are likely to be occupied by specialists with a narrow niche breadth, whereas low diversity assemblages are dominated by generalists. Furthermore, the unimodal relationship between niche position and species richness suggested that species-poor sites may be typified by either non-marginal or marginal species.     

Untangling the relationships among regional occupancy,species traits,and niche characteristics in stream invertebrates

The regional occupancy and local abundance of species are affected by various species traits, but their relative effects are poorly understood. We studied the relationships between species traits and occupancy (i.e., proportion of sites occupied) or abundance (i.e., mean local abundance at occupied sites) of stream invertebrates using small‐grained data (i.e., local stream sites) across a large spatial extent (i.e., three drainage basins). We found a significant, yet rather weak, linear relationship between occupancy and abundance. However, occupancy was strongly related to niche position (NP), but it showed a weaker relationship with niche breadth (NB). Abundance was at best weakly related to these explanatory niche‐based variables. Biological traits, including feeding modes, habit traits, dispersal modes and body size classes, were generally less important in accounting for variation in occupancy and abundance. Our findings showed that the regional occupancy of stream invertebrate species is mostly related to niche characteristics, in particular, NP. However, the effects of NB on occupancy were affected by the measure itself. We conclude that niche characteristics determine the regional occupancy of species at relatively large spatial extents, suggesting that species distributions are determined by environmental variation among sites.     

Variations on a theme: sources of heterogeneity in the form of the interspecific relationship between abundance and distribution

1. A positive interspecific relationship between abundance and distribution is widely considered to be one of the most general patterns in ecology. However, the relationship appears to vary considerably across assemblages, from significant positive to significant negative correlations and all shades in between. 2. This variation has led to the suggestion that the abundance-distribution relationship has multiple forms, with the corollary that different patterns may inform about, or have different, causes. However, this variation has never been formally quantified, nor has it been determined whether the observed variation is indicative of sampling error in estimating a single effect or of real heterogeneity in such relationships. Here, we use the meta-analytical approach to assess variation in abundance-distribution relationships, and to test different hypotheses for it. 3. Analysis of 279 relationships found a mean effect size of 0.655, which was both highly significantly different from zero and indicative of a strong positive association between abundance and distribution. However, effect sizes were highly heterogeneous, supporting the contention that this relationship does indeed have multiple forms. 4. Most notably, relationships vary significantly in strength across realms, with the strongest in the marine and intertidal, intermediate relationships for terrestrial and parasitic assemblages, and the weakest relationships in freshwater systems. Effect sizes in all of the aquatic realms are homogeneous, suggesting that realm is an important source of the heterogeneity observed across all studies. We posit that this may be because the different spatial structure of the environment in each realm affects the opportunity for the dispersal of individuals between sites. 5. Some of the remaining heterogeneity in effect sizes for terrestrial assemblages could be explained by partitioning assemblages by habitat, scale, biogeographical region and taxon, but considerable heterogeneity in effect sizes for terrestrial and parasitic assemblages remained unexplained.     

Determinants of local abundance and range size in forest vascular plants

Aim For a large set of forest herbs we tested: (1) whether there is a positive relationship between local abundance and geographical range size; (2) whether abundance or range size are affected by the niche breadths of species or niche availability; and (3) whether these are affected by the species life‐history traits. Location Northwestern Germany. Methods We measured abundance as mean density in 22 base‐rich deciduous forests and recorded range size as area of occupancy on four different spatial scales (local to national). Niche breadth was expressed in terms of habitat specificity (specialists, generalists) and of the ability to grow across a broad range of soil pH. The species’ pH niche position was used as a measure of the importance of habitat availability. As life‐history traits we used diaspore mass and number, plant height, seed longevity, lifespan/clonality, pollination mode, dispersal capability and flowering time. Results There were mainly no positive relationships between the abundance of species and their range size, as tested across species and across phylogenetically independent contrasts. Forest specialists were generally distributed less widely than generalists, but habitat specificity was not related to local abundance. Species with a broader pH niche breadth were more common, but the positive relationships between niche breadth and abundance or range size disappeared when accounting for sample size effects. Clonal species with few and heavy diaspores were most abundant, as well as early‐flowering species and those lacking dispersal structures. Local and regional range size were determined largely by habitat availability, while national range was positively affected by plant height and diaspore mass. Main conclusions Different processes determine the local density of species and their range size. Abundance within habitat patches appears to be related mainly to the species life histories, especially to their capacity for extensive clonal reproduction, whereas range size appears to be determined strongly by the availability of suitable habitat.