Tree diversity and species identity effects on soil fungi,protists and animals are context dependent

Plant species richness and the presence of certain influential species (sampling effect) drive the stability and functionality of ecosystems as well as primary production and biomass of consumers. However, little is known about these floristic effects on richness and community composition of soil biota in forest habitats owing to methodological constraints. We developed a DNA metabarcoding approach to identify the major eukaryote groups directly from soil with roughly species-level resolution. Using this method, we examined the effects of tree diversity and individual tree species on soil microbial biomass and taxonomic richness of soil biota in two experimental study systems in Finland and Estonia and accounted for edaphic variables and spatial autocorrelation. Our analyses revealed that the effects of tree diversity and individual species on soil biota are largely context dependent. Multiple regression and structural equation modelling suggested that biomass, soil pH, nutrients and tree species directly affect richness of different taxonomic groups. The community composition of most soil organisms was strongly correlated due to similar response to environmental predictors rather than causal relationships. On a local scale, soil resources and tree species have stronger effect on diversity of soil biota than tree species richness per se.     

Species richness in boreal swamp forests of SE Norway: The role of surface microtopography

Question: What is the relative importance of environmental gradients and surface microtopography (variation in vertical level within sampling units) for fine‐scale plant species richness in Picea abies swamp forests? Location: 11 swamp forests in SE Norway. Methods: We recorded species richness (number of species of vascular plants, mosses, Sphagnum and hepatics), depth to water table, soil base status and vertical range (microtopographic relief) in 2400 microplots, (each 1/16 m²), in 150 1‐m² plots in the 11 swamp forests. Relationships between species richness and environmental predictors were modelled by GLMM. Results: Moss and hepatic species richness increased with increasing microtopographic relief, most strongly for wet acid sites, in which similar trends were also found for Sphagnum. Relief was a poor predictor of vascular plant species richness. Conclusions: Microtopographic relief is a good predictor of local species richness in Picea abies swamp forests, partly because larger vertical variability means higher within‐plot habitat diversity with respect to the wet‐dry gradient, and partly because qualitatively new microhabitats associated with steep slopes are added in drier sites. The relationship between species richness and microtopographic relief is context dependent, differing in complex ways among species groups and among sites with different environmental conditions.     

Niche partitioning in arbuscular mycorrhizal communities in temperate grasslands: a lesson from adjacent serpentine and nonserpentine habitats

Arbuscular mycorrhizal fungi (AMF) represent an important soil microbial group playing a fundamental role in many terrestrial ecosystems. We explored the effects of deterministic (soil characteristics, host plant life stage, neighbouring plant communities) and stochastic processes on AMF colonization, richness and community composition in roots of Knautia arvensis (Dipsacaceae) plants from three serpentine grasslands and adjacent nonserpentine sites. Methodically, the study was based on 454‐sequencing of the ITS region of rDNA. In total, we detected 81 molecular taxonomical operational units (MOTUs) belonging to the Glomeromycota. Serpentine character of the site negatively influenced AMF root colonization, similarly as higher Fe concentration. AMF MOTUs richness linearly increased along a pH gradient from 3.5 to 5.8. Contrary, K and Cr soil concentration had a negative influence on AMF MOTUs richness. We also detected a strong relation between neighbouring plant community composition and AMF MOTUs richness. Although spatial distance between the sampled sites (c. 0.3–3 km) contributed to structuring AMF communities in K. arvensis roots, environmental parameters were key factors in this respect. In particular, the composition of AMF communities was shaped by the complex of serpentine conditions, pH and available soil Ni concentration. The composition of AMF communities was also dependent on host plant life stage (vegetative vs. generative). Our study supports the dominance of deterministic factors in structuring AMF communities in heterogeneous environment composed of an edaphic mosaic of serpentine and nonserpentine soils.     

Assignment and evaluation of ground beetle (Coleoptera: Carabidae) assemblages to sites on different scales in a grassland landscape

Carabid beetles and environmental parameters were investigated in 52 grassland sites with three replicate pitfall traps in each site and in the valley of the River Eider in Schleswig–Holstein (northern Germany) with 61 pitfall traps. Environmental parameters included water content of soil, sand content, organic matter content and pH. Ground beetle assemblages were derived by detrended correspondence analyses (DCA) and characterised by the specific environmental conditions as means for each assemblage. On the regional scale including all investigated sites of Schleswig–Holstein, five assemblages were differentiated. On the local scale including the investigated sites in the valley of the River Eider, three assemblages were found corresponding well with those found on the regional scale. Environmental conditions at the sites of the five assemblages were correlated with land use data, soil types, and water level stages provided by three maps of a geographic information system (GIS). The GIS maps were combined to develop smaller areas with land use, soil type and water level stage information. The characteristic environmental conditions were assigned to each area to derive the spatial distribution of the five ground beetle assemblages. Spatial prediction was correct for 65% of investigated sites. The potential area of each assemblage was estimated for the valley. The different grassland areas were evaluated as potential habitats for ground beetle species comparing total species richness with the regional species richness of each assemblage. The comparison shows that species richness in the evaluated assemblages is relatively low compared to the regional potential.     

The influence of light and nutrient availability on herb layer species richness in oak-dominated forests in central Bohemia

In this study, we examined to what extent the internal site factors (light and soil conditions) are responsible for herb layer diversity in oak-dominated forest stands growing on different substrates in central Bohemia (Czech Republic). We collected data on herb layer diversity, light and nutrient availability at nine oak stands, representing the range of environmental variability for these types of forests in the region. We found that species richness increased with light availability, but only if the site occupied predominantly by fast-colonizing species was excluded from the analysis (P < 0.05). Species richness correlated positively with soil pH and negatively with nitrogen (N) concentration in humus (P < 0.05). The highest species richness was found at sites with not only low N soil concentration, but also simultaneously with high phosphorus (P) soil concentration. Despite this finding, however, herb layer diversity is evidently threatened much more in P-rich soils than in P-poor soils. It seems that the enhancement of N in an ecosystem due to litter accumulation and N deposition generally leads to only a minor increase in N availability at P-poor sites, but a considerable increase at P-rich sites. Therefore, species richness can be exceptionally high at P-rich sites, but only under conditions of strong N limitation.     

Light heterogeneity affects understory plant species richness in temperate forests supporting the heterogeneity–diversity hypothesis

One of the most important drivers for the coexistence of plant species is the resource heterogeneity of a certain environment, and several studies in different ecosystems have supported this resource heterogeneity–diversity hypothesis. However, to date, only a few studies have measured heterogeneity of light and soil resources below forest canopies to investigate their influence on understory plant species richness. Here, we aim to determine (1) the influence of forest stand structural complexity on the heterogeneity of light and soil resources below the forest canopy and (2) whether heterogeneity of resources increases understory plant species richness. Measures of stand structural complexity were obtained through inventories and remote sensing techniques in 135 1‐ha study plots of temperate forests, established along a gradient of forest structural complexity. We measured light intensity and soil chemical properties on six 25 m² subplots on each of these 135 plots and surveyed understory vegetation. We calculated the coefficient of variation of light and soil parameters to obtain measures of resource heterogeneity and determined understory plant species richness at plot level. Spatial heterogeneity of light and of soil pH increased with higher stand structural complexity, although heterogeneity of soil pH did not increase in conditions of generally high levels of light availability. Increasing light heterogeneity was also associated with increasing understory plant species richness. However, light heterogeneity had no such effects in conditions where soil resource heterogeneity (variation in soil C:N ratios) was low. Our results support the resource heterogeneity–diversity hypothesis for temperate forest understory at the stand scale. Our results also highlight the importance of interaction effects between the heterogeneity of both light and soil resources in determining plant species richness.     

A transcontinental comparison of the diversity and composition of tropical forest understory herb assemblages

Although tropical forests are renowned for their high plant diversity, to date there has been no global quantitative evaluation of the local species richness of terrestrial forest herbs in tropical forests. In this paper, richness and composition of terrestrial herb assemblages is compared in tropical forests of America, Africa and South East Asia. We established 86 non-continuous transects of 445 m each. Herb species richness was analysed and compared to six environmental parameters using minimal adequate regression models and simultaneous autoregressive models. At the global scale, we found a close relationship between herb species richness and temperature parameters, with no differences between continents. The subdivision into three main taxonomic groups (ferns, monocots, dicots) showed that each group has distinct relations to environmental factors and differences in richness between continents. Most of the 72 families found have pantropical distributions but 12, 11, and 16 families were significantly over-represented in America, Africa, and Asia, respectively. Although total species richness was closely related to climatic factors, ferns, monocots and dicots were represented by distinct sets of families with varying species richness on each continent. Which species are found at a given site may thus reflect group-specific evolutionary and historical factors.     

Diversity of plant assemblages in isolated depressional wetlands from Central-Western Europe

A closed depression is defined as a geomorphologic element where a sediment depository is encircled by hillslopes. Despite the fact that closed depressions are often the only stagnant water points in many European landscapes, few ecological researches on their plant assemblages have been done. The main goal of this study was to give first results of the environmental factors responsible for the vegetation composition, richness and rarity in the closed depressions of the Lorraine biogeographical district (Belgium, France and grand-duché de Luxembourg). We surveyed for plant presence 85 forest and 77 grassland closed depressions. For each site, wetland area, local environmental factors and regional connectivities registered. For each species, the Ellenberg values were compiled. To investigate the main source of variation in species composition and in species richness (including richness in rare species), Non-metric Multidimensional Scaling analyses and Generalized Linear Models were respectively used. Species pools in forest (forest and preforest species) and in grassland (bog plants, pioneers, helophytes) were quite different. In both landscapes, a gradient from plants typical of basic high-productive soils to plants typical of acid low-productive soils reflects a shared successional gradient. The accumulation of organic matter allowed the establishment of Sphagnum spp., which slowly acidified the soil and thus acted as ecosystem engineers for the arrival of bog plants. Moreover, the species composition was additionally driven by the plant light tolerance in forests and by the plant water requirements in grasslands. Mechanisms of species accumulation (increase in species richness) were different in forests and in grasslands: respectively related to the plant light tolerance and to the wetland area. At the regional level, the averaged soil productivity was negatively related to the richness in rare species. Indeed, perennial highly-competitive plants such as Glyceria spp., Iris pseudacorus or Urtica dioica impeded the establishment of smaller and rarer species. At the habitat level, isolated closed depressions (due to either low connectivity or low grazing pressure) have more habitat rare species, giving evidences of dispersal limitation in plant assemblages of closed depressions.     

Species richness of vascular plants, bryophytes and lichens in dry grasslands: The effects of environment, landscape structure and competition

We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m² plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric.     

Biodiversity of galling insects: historical, community and habitat effects in four neotropical savannas

Five hypotheses were tested to explain the pattern of galling insect species richness in four neotropical savanna physiognomies, 'canga ', 'campo sujo', 'cerrado' s. st., and 'cerradão', that occur in Minas Gerais, southeastern Brazil. We found 125 species of galling insects on 80 host plant species. The increase of plant species richness explained 35% of the variation in galling insect richness, corroborating the plant species richness hypothesis. Most of the galling species occurred on trees, followed by shrubs, and herbs. However, the difference in mean number of galls was only statistically significant between herbs and trees, corroborating partially the plant structural complexity hypothesis. A significant relationship was observed between galling species richness and density of herbs, and shrubs, corroborating partially the resource concentration hypothesis. Galling insect richness showed a negative correlation with magnesium, potassium, and zinc on soil, corroborating the soil fertility hypothesis. The content of magnesium, potassium, iron and CTC (T) explained 72% of the variation in galling insect richness. Plant family size positively influenced galling insect richness, corroborating the plant family size hypothesis. Overall, the results corroborate the hypothesis that predicts that habitat stress is the main factor generating the patterns of galling insect richness in Brazilian savannas.     

Ecological correlates of invasion by <Emphasis Type="Italic">Arundo donax</Emphasis> in three southern California riparian habitats

Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature, incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies also suggests that a high degree of environmental tolerance contributes to invasion success.     

莽山浪畔湖国家重要湿地植物多样性及环境解释

研究莽山高山湖泊湿地植物多样性对环境因子的响应分析,不仅有助于深入了解湿地植物对环境变化下的适应策略,同时对保护当地湿地珍稀濒危物种具有重要价值。采用系统聚类分析、典范对应分析(CCA)和Pearson相关性分析等方法,对研究区30个植物群落样方进行分析,研究植物多样性与环境因子(土壤、水)之间的相互关系。研究结果表明:浪畔湖国家重要湿地植物群落可分为蕨状苔草+宽叶泽苔草群丛、雪白睡莲+莼菜群丛、水毛花+宽叶泽苔草群丛、莼菜+宽叶泽苔草群丛等4类。雪白睡莲+莼菜群丛Patrick丰富度指数和Pielou均匀度指数最低,Simpson多样性指数最高,水毛花+宽叶泽苔草群丛与之相反。浪畔湖国家重要湿地植物多样性与土壤速效钾和水深呈极显著相关性,与水质氨氮呈显著相关性,水深和土壤速效钾是影响湿地植物群落分布格局的主要因子。群落物种多样性指数与环境因子之间存在显著相关性,群落物种丰富度指数随水深增加呈先增后降的趋势,群落物种均匀度指数与水质氨氮浓度之间呈负相关关系。本研究旨在揭示浪畔湖国家重要湿地植物多样性与环境因子之间的生态关系,为保护湿地珍稀物种及维持湿地生态系统稳定提供理论依据。     

The influence of Prosopis canopies on understorey vegetation: Effects of landscape position

Abstract. The influence of canopy trees and shrubs on under‐storey plants is complex and context‐dependent. Canopy plants can exert positive, negative or neutral effects on production, composition and diversity of understorey plant communities, depending on local environmental conditions and position in the landscape. We studied the influence of Prosopis velutina (mesquite) on soil moisture and nitrogen availability, and understorey vegetation along a topographic gradient in the Sonoran Desert. We found significant increases in both soil moisture and N along the gradient from desert to riparian zone. In addition, P. velutina canopies had positive effects, relative to open areas, on soil moisture in the desert, and soil N in both desert and intermediate terrace. Biomass of understorey vegetation was highest and species richness was lowest in the riparian zone. Canopies had a positive effect on biomass in both desert and terrace, and a negative effect on species richness in the terrace. The effect of the canopy depended on landscape position, with desert canopies more strongly influencing soil moisture and biomass and terrace canopies more strongly influencing soil N and species richness. Individual species distributions suggested interspecific variation in response to water‐ vs. N‐availability; they strongly influence species composition at both patch and landscape position levels.     

Bryophyte biomass and species richness on the Park Grass Experiment,Rothamsted, UK

The relationships between bryophyte biomass and species richness and soil pH, nutrient applications and vascular plant biomass and species richness were analyzed for the Park Grass Experiment (Rothamsted, UK). The study examined the abundance of bryophytes in relation to long-term fertilizer and lime application and to fertilizer treatments recently being ceased on some plots. The probability of bryophytes being present on a plot increased with increasing soil pH, and on plots at soil pH 3.3–4.5, the lowest values in this experiment, there were virtually no mosses present. Total bryophyte biomass decreased with increasing vascular plant biomass and vascular plant richness. Both bryophyte biomass and species richness showed a curvilinear response to soil pH. Bryophyte biomass was markedly increased on plots where nitrogen (N) fertilization had recently been ceased. The abundance of the common bryophyte species showed individualistic responses to treatments. N had a negative effect on the abundance of Brachythecium rutabulum. Increasing soil pH, and the application of phosphorus (P) and potassium (K) fertilizer together, had a positive effect on Eurhynchium praelongum. This species was also negatively affected by N, but tolerated larger amounts of it (100–150 kg ha^–1 N) than B. rutabulum. An ephemeral moss, Bryum subapiculatum, had a unimodal response to soil pH but showed no response to N, P, K or other explanatory variables.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

Plant species richness and diversity along an altitudinal gradient in the Sierra Nevada, Mexico

This article presents an analysis of plant species richness and diversity and its association with climatic and soil variables along a 1300‐m elevation gradient on the Cerro Tláloc Mountain in the northern Sierra Nevada in Mexico. Two 1000‐m² tree sampling plots were created at each of 21 selected sampling sites, as well as two 250‐m² plots for shrubs and six 9‐m² plots for herbaceous plants. Species richness and diversity were estimated for each plant life form, and beta diversity between sites was estimated along the gradient. The relationship between species richness and diversity and environmental variables was modelled using simple linear correlation and regression trees. Species richness and diversity showed a unimodal pattern with a bias towards high values in the lower half of the elevation gradient under study. This response was consistent for all three life forms. Beta diversity increased steadily along the elevation gradient, being lower between contiguous sites at intermediate elevations and high – the species replacement rate was nearly 100%– between sites at the extremes of the gradient. Few species were adapted to the full spectrum of environmental variation along the elevation gradient studied. The regression tree suggests that differences in species richness are mainly influenced by elevation (temperature and humidity) and soil variables, namely A₂ permanent wilting point, organic matter and horizon field capacity and A₁ horizon Mg²⁺.     

Relationship between soil nutrient availability and plant species richness in a tropical semi‐arid environment

Question: What is the relationship between soil fertility and plant species richness in the ‘fertile islands’ occurring beneath two species of legume (Cercidium praecox and Prosopis laevigata)? Location: Tehuacán‐Cuicatlán region, central Mexico. Methods: Plant richness was measured in three micro‐environments (below canopies of C. praecox, below canopies of P. laevigata and in areas without canopies). The concentration of soil nutrients (C, N and P), C and N in the microbiota, and processes of ecosystem functioning (net C mineralization rate and N mineralization) were measured. The relationship between soil variables and plant richness were assessed with ANCOVAs. Results: Soil nutrients and species richness increases markedly under fertility islands. There were higher concentrations of C and N in the soil, faster rates of C mineralization, and higher species richness under P. laevigata canopies. The relationship between soil fertility and species richness was always positive except for total N, ammonium and net C mineralization rate under C. praecox, and for available P under P. laevigata. Conclusions: The sign of the relationship between soil fertility and species richness varies according to the nutrient and the micro‐environment. Positive relationships could result from between species complementarity and facilitation. Negative relationships could be explained by a specific limitation threshold for some soil resources (P and N for plants and C for the soil microbiota) which eliminate the possibilities of between species complementarity and facilitation above that threshold. As in all observational studies, these relationships should be considered only correlational.     

河西走廊天然固沙植被区地表甲虫多样性及其对沙漠化的指示作用

干旱、半干旱区沙漠化强烈影响动植物分布及多样性,地表甲虫是荒漠中主要的动物类群,它们对沙漠化引起的植被和土壤环境变化响应十分敏感。鉴于此,以河西走廊中部张掖绿洲外围的天然固沙植被区作为研究区,依据沙漠化发育程度选择流动沙丘（ASD）、丘间低地（IL）、半固定（SFSD）和固定沙丘（FSD）4种生境,调查了地表甲虫群落组成及影响甲虫分布的植被和土壤环境。研究发现,4种生境地表甲虫群落组成明显不同并存在季节变异,5月ASD与IL、SFSD和FSD生境地表甲虫群落的相异性大于8月。5月和8月SFSD生境地表甲虫活动密度均显著高于其他生境,8月FSD生境地表甲虫多样性指数显著高于其他生境。不同大小甲虫对沙漠化的响应模式不同,大中型甲虫对沙漠化的响应较小型甲虫敏感,这在5月表现尤为明显。地表甲虫与环境因子的RDA分析结果表明,12个植被和土壤环境因子解释了49.8%的地表甲虫群落变异,其中植被环境解释了甲虫群落变异的16.3%,土壤环境解释了甲虫群落变异的4.2%,植被和土壤环境相互作用解释了甲虫群落变异的29.3%。pRDA分析结果表明,草本物种丰富度、灌木盖度、土壤有机碳含量和粗砂含量是影响地表甲虫分布的主要环境因子,它们解释了43.7%的地表甲虫群落变异。Pearson相关分析表明,草本物种丰富度与地表甲虫活动密度呈显著正相关,而与地表甲虫均匀度呈显著负相关;灌木盖度与地表甲虫多样性呈显著正相关;地表甲虫物种丰富度与灌木盖度和草本物种丰富度均呈显著正相关。此外,研究还发现戈壁琵甲、克氏扁漠甲、中华砚甲和甘肃齿足象可以用于指示FSD生境,东鳖甲属昆虫可以用于指数SFSD生境,谢氏宽漠王可以用于指示IL及ASD生境。     

海南尖峰岭不同热带雨林类型与物种多样性变化关联的环境因子

环境因子是影响物种分布并导致物种多样性形成的重要因素,采伐后恢复的热带森林次生林和原始林的环境因子是否一致是一个很重要的问题.对于该问题的回答对长期监测热带森林次生林的变化具有重要意义.该文基于在海南尖峰岭地区设置的164个625 m2植被公里网格样地数据,记录了每个样地的采伐历史并测定了其他的17个环境变量指标,分析了17个环境因子之间的相关关系;将164个样地划分成3种不同采伐历史的森林,通过典范对应分析(CCA)探讨3种森林类型中影响物种分布的环境因子组成;比较两种多元回归模型的优劣,来揭示3种森林类型中影响物种丰富度形成的环境因子组成的差异.结果表明:驱动海南尖峰岭地区物种分布并导致物种多样性差异的环境因子在森林采伐前后并不是一成不变的,而是与森林采伐历史有关联的.除了人为森林采伐干扰外,海拔梯度是形成海南尖峰岭热带天然林物种多样性的最重要因素.CCA分析显示:原始林中,物种分布与海拔、土壤交换性钙和交换性镁含量3个环境因子有较密切的关系,也与4个土壤物理性质环境因子(土壤密度、土壤最大持水能力、毛细管持水量和毛管孔隙度)关系密切;森林采伐后的恢复森林中,土壤全磷和速效磷含量对物种分布的影响增强,但皆伐后土壤交换性钙和交换性镁含量对物种分布的影响减弱.多元回归分析显示:原始林的物种丰富度与海拔和土壤交换性钙含量显著相关,径级择伐后恢复热带天然林的物种丰富度和海拔、土壤全磷含量和速效钾含量显著相关,皆伐后恢复热带天然林的物种丰富度仅和海拔显著相关.研究结果还显示,如果数据中存在空间自相关,建立多元回归模型时应该考虑数据中的空间自相关属性,虽然它并不总是存在的.     

Variation in freshwater fish assemblages along a regional elevation gradient in the northern Andes,Colombia

Studies on elevation diversity gradients have covered a large number of taxa and regions throughout the world; however, studies of freshwater fish are scarce and restricted to examining their changes along a specific gradient. These studies have reported a monotonic decrease in species richness with increasing elevation, but ignore the high taxonomic differentiation of each headwater assemblage that may generate high β‐diversity among them. Here, we analyzed how fish assemblages vary with elevation among regional elevation bands, and how these changes are related to four environmental clines and to changes in the distribution, habitat use, and the morphology of fish species. Using a standardized field sampling technique, we assessed three different diversity and two structural assemblage measures across six regional elevation bands located in the northern Andes (Colombia). Each species was assigned to a functional group based on its body shape, habitat use, morphological, and/or behavioral adaptations. Additionally, at each sampling site, we measured four environmental variables. Our analyses showed: (1) After a monotonic decrease in species richness, we detected an increase in richness in the upper part of the gradient; (2) diversity patterns vary depending on the diversity measure used; (3) diversity patterns can be attributed to changes in species distribution and in the richness and proportions of functional groups along the regional elevation gradient; and (4) diversity patterns and changes in functional groups are highly correlated with variations in environmental variables, which also vary with elevation. These results suggest a novel pattern of variation in species richness with elevation: Species richness increases at the headwaters of the northern Andes owing to the cumulative number of endemic species there. This highlights the need for large‐scale studies and has important implications for the aquatic conservation of the region.