阿尔泰山两河源牧区草地群落生物量及物种多样性

群落生物量和物种多样性是表征草地生态系统数量特征的重要指标。该研究以新疆阿尔泰山南麓两河源放牧区草地为研究对象,利用样方法对两河源不同放牧区的草地植被进行调查,分析研究区生物量和物种多样性变化,探讨二者与环境因子之间的关联性,为草地群落物种保护以及草地可持续利用提供理论依据。结果表明：(1) 两河源不同牧区间群落盖度、高度、植株密度、地上生物量和单位盖度生物量存在差异。(2) 两河源牧区草地群落地上生物量与群落盖度、植株密度呈显著正相关关系(P<0.05),且地上生物量主要受草地群落盖度的影响;不同牧区的物种多样性指数有一定差异,但物种分布相对均匀。(3)两河源牧区草地群落生物量及物种多样性主要受气温和降水的影响。     

Factors influencing geographic patterns in diversity of forest bird communities of eastern Connecticut,USA

At regional scales, the most important variables associated with diversity are latitudinally‐based temperature and net primary productivity, although diversity is also influenced by habitat. We examined bird species richness, community density and community evenness in forests of eastern Connecticut to determine whether: 1) spatial and seasonal patterns exist in diversity, 2) energy explains the greatest proportion of variation in diversity parameters, 3) variation in habitat explains remaining diversity variance, and 4) seasonal shifts in diversity provide clues about how environmental variables shape communities. We sought to discover if our data supported predictions of the species–energy hypothesis. We used the variable circular plot technique to estimate bird populations and quantified the location, elevation, forest type, vegetation type, canopy cover, moisture regime, understory density and primary production for the study sites. We found that 1) summer richness and population densities are roughly equal in northeastern and southeastern Connecticut, whereas in winter both concentrate toward the coast, 2) variables linked with temperature explained much of the patterns in winter diversity, but energy‐related variables showed little relationship to summer diversity, 3) the effect of habitat variables on diversity parameters predominated in summer, although their effect was weak, 4) contrary to theory, evenness increased from summer to winter, and 5) support for predictions of species–energy theory was primarily restricted to winter data. Although energy and habitat played a role in explaining community patterns, they left much of the variance in regional diversity unexplained, suggesting that a large stochastic component to diversity also may exist.     

营养盐加富和鱼类添加对浮游植物群落演替和多样性的影响

浮游植物是水体生态系统敞水区最重要的初级生产者,其组成与多样性反映了群落的结构类型和存在状态。通过围隔实验,模拟水库春季发生的营养盐加富和鱼类放养的干扰,分析在这两种干扰下的浮游植物群落演替过程中优势种和稀有种的变化,并通过以丰度与生物量为变量的香农和辛普森多样性指数的计算,分析浮游植物群落演替过程中的多样性变化特征。结果表明,营养盐加富干扰下的浮游植物群落的优势种变化和演替更为明显,营养盐加富与鱼类添加对浮游植物群落多样性变化的影响符合中度干扰理论。在优势种优势度变化较大的浮游植物群落演替过程中,多样性指数与浮游植物生物量有较高的负相关性。在浮游植物群落演替过程中,香农和辛普森多样性指数的变化趋势基本一致,采用丰度与生物量为变量的两种多样性指数的计算结果对实验系统中浮游植物群落多样性的分析结果没有明显的影响。     

Population structure of stream-dwelling darters: correspondence with habitat structure

Synopsis Patterns of ecotopic variation in the population structure of two common and relatedPercina species were examined among seven central Gulf-Coast stream sites by Kendall's concordance tests, revealing four complexes of variables with significant covariation from a total of 18 population and habitat variables. The first complex comprised three interrelated habitat variables, implying that mid-stream surface current varied inversely with both instream cover and substrate heterogeneity. The second complex of five interrelated variables revealed (1) that darter abundance was better correlated with the area of instream cover than with total area, and (2) that site density [number m^-2] varied inversely with site area. Along with three other variables, cover density (number per square meter of instream cover) formed a third complex, demonstrating resource complementarity between instream cover and macroinvertebrate abundance. Variables within the fourth complex all increased concomitantly with the key variable of mean darter size, including body-size diversity, biomass, relative abundance of the two darter species and mid-stream depth. Within the study region, local ecological factors largely regulate distributions, abundances and size-structures ofPercina populations, apparently even outweighing the effects of stochastic and historical factors     

Understory Plant Community Composition Is Associated with Fine-Scale Above- and Below-Ground Resource Heterogeneity in Mature Lodgepole Pine (Pinus contorta) Forests

Understory plant communities play critical ecological roles in forest ecosystems. Both above- and below-ground ecosystem properties and processes influence these communities but relatively little is known about such effects at fine (i.e., one to several meters within-stand) scales, particularly for forests in which the canopy is dominated by a single species. An improved understanding of these effects is critical for understanding how understory biodiversity is regulated in such forests and for anticipating impacts of changing disturbance regimes. Our primary objective was to examine the patterns of fine-scale variation in understory plant communities and their relationships to above- and below-ground resource and environmental heterogeneity within mature lodgepole pine forests. We assessed composition and diversity of understory vegetation in relation to heterogeneity of both the above-ground (canopy tree density, canopy and tall shrub basal area and cover, downed wood biomass, litter cover) and below-ground (soil nutrient availability, decomposition, forest floor thickness, pH, and phospholipid fatty acids (PLFAs) and multiple carbon-source substrate-induced respiration (MSIR) of the forest floor microbial community) environment. There was notable variation in fine-scale plant community composition; cluster and indicator species analyses of the 24 most commonly occurring understory species distinguished four assemblages, one for which a pioneer forb species had the highest cover levels, and three others that were characterized by different bryophyte species having the highest cover. Constrained ordination (distance-based redundancy analysis) showed that two above-ground (mean tree diameter, litter cover) and eight below-ground (forest floor pH, plant available boron, microbial community composition and function as indicated by MSIR and PLFAs) properties were associated with variation in understory plant community composition. These results provide novel insights into the important ecological associations between understory plant community composition and heterogeneity in ecosystem properties and processes within forests dominated by a single canopy species.     

Phorophyte specificity and environmental parameters versus stochasticity as determinants for species composition of corticolous crustose lichen communities in the Atlantic rain forest of northeastern Brazil

A transect of 47 mature trees was studied within an Atlantic rain-forest plot in northeastern Brazil to determinate effects of phorophyte specificity and environmental parameters vs. stochasticity on the structure of corticolous, crustose microlichen communities. A total of 150 lichen species was found, most being rare to extremely rare. Multivariate analysis of sample plots indicated subtle phorophyte preferences among certain lichen species, corresponding to differences in bark pH, degree of bark shedding, density and size of bark lenticels, and presence of milk sap. Individual and multiple regressions revealed correlations between lichen species richness; respectively, area cover and bark pH (negative); density and size of bark lenticels (negative); degree of bark shedding (negative); presence of milk sap (positive); and diffuse site factor (positive). No strongly delimited lichen communities were detected, but cluster analysis revealed three main groups and six subgroups with slightly different lichen species composition, each one with characteristic indicator species but with highly variable overall species composition. Beta diversity was high among samples and lacked spatial structure. However, beta diversity was significantly lower among samples belonging to the same tree species, independent of their spatial arrangement. It was concluded that community formation in tropical rain-forest understory lichens subtly correlates with two main environmental factor complexes—phorophyte bark characteristics and microclimate—but is to a large extent determined by the stochastic effects of species dispersal, especially of rare species.     

Effects of deforestation on fish community structure in Ecuadorian Amazon streams

SUMMARY 1. There is little information on the impacts of deforestation on the fish fauna in neotropical streams, and on parameters influencing species diversity and community structure of fish. We analysed these aspects in 12 stream sites in the Ecuadorian Amazon. The stream sites represented a large gradient in canopy cover and were located in an area of fragmented forest. While some streams had been deforested, they had not suffered gross degradation of the habitat.
2. The species richness of stream fish was not related to deforestation. Local fish diversity (Fisher's Alpha) was positively related to the surface area of stream pools (m²). Beta diversity was higher among forested than deforested sites, indicating greater heterogeneity in species composition among forested than deforested sites. The percentage of rare species was positively correlated with canopy cover.
3. Total fish density increased with deforestation, and the fish community changed from dominance by omnivorous and insectivorous Characiformes at forested sites to dominance of periphyton-feeding loricariids at deforested sites.
4. Multidimensional statistical analysis of fish community structure showed that six environmental variables (the area of stream bottom covered by leaves, relative pool area, particulate organic matter, mean depth, conductivity and suspended solids) were related to the ordination axes. The presence of leaves, which was strongly correlated to canopy cover, was the variable most closely related to fish community structure, while relative pool area was the second strongest variable. Thus, fish community structure was strongly affected by deforestation.     

Species richness, environmental fluctuations, and temporal change in total community biomass

Theory and empirical results suggest that high biodiversity should often cause lower temporal variability in aggregate community properties such as total community biomass. We assembled microbial communities containing 2 to 8 species of competitors in aquatic microcosms and found that the temporal change in total community biomass was positively but insignificantly associated with diversity in a constant temperature environment. There was no evidence of any trend in variable temperature environments. Three non-exclusive mechanisms might explain the lack of a net stabilising effect of species richness on temporal change. (1) A direct destabilising effect of diversity on population level variances caused some populations to vary more when embedded in more diverse communities. (2) Similar responses of the different species to environmental variability might have limited any insurance effect of increased species richness. (3) Large differences in the population level variability of different species (i.e., unevenness) could weaken the relation between species richness and community level stability. These three mechanisms may outweigh the stabilising effects of increases in total community biomass with diversity, statistical averaging, and slightly more negative covariance in more diverse communities. Our experiment and analyses advocate for further experimental investigations of diversity-variability relations.     

Do biotic interactions shape both sides of the humped‐back model of species richness in plant communities?

A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity-diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity.     

A functional trait-based approach to understand community assembly and diversity–productivity relationships over 7 years in experimental grasslands

Several multi-year biodiversity experiments have shown positive species richness–productivity relationships which strengthen over time, but the mechanisms which control productivity are not well understood. We used experimental grasslands (Jena Experiment) with mixtures containing different numbers of species (4, 8, 16 and 60) and plant functional groups (1–4; grasses, legumes, small herbs, tall herbs) to explore patterns of variation in functional trait composition as well as climatic variables as predictors for community biomass production across several years (from 2003 to 2009). Over this time span, high community mean trait values shifted from the dominance of trait values associated with fast growth to trait values suggesting a conservation of growth-related resources and successful reproduction. Increasing between-community convergence in means of several productivity-related traits indicated that environmental filtering and exclusion of competitively weaker species played a role during community assembly. A general trend for increasing functional trait diversity within and convergence among communities suggested niche differentiation through limiting similarity in the longer term and that similar mechanisms operated in communities sown with different diversity. Community biomass production was primarily explained by a few key mean traits (tall growth, large seed mass and leaf nitrogen concentration) and to a smaller extent by functional diversity in nitrogen acquisition strategies, functional richness in multiple traits and functional evenness in light-acquisition traits. Increasing species richness, presence of an exceptionally productive legume species (Onobrychis viciifolia) and climatic variables explained an additional proportion of variation in community biomass. In general, community biomass production decreased through time, but communities with higher functional richness in multiple traits had high productivities over several years. Our results suggest that assembly processes within communities with an artificially maintained species composition maximize functional diversity through niche differentiation and exclusion of weaker competitors, thereby maintaining their potential for high productivity.     

Species identity and negative density dependence lead to convergence in designed plant mixtures of twelve species

Competition effects on community development are difficult to quantify in species-rich plant communities due to the complexity of possible interactions. We used multispecies mixtures to investigate how species identity and competitive interactions influence the development of plant communities. Given the same set of species with differing initial abundance in various communities, we tested whether communities would become more similar (converge) or dissimilar (diverge) over time depending on the relative importance of species identity and competition. Twenty-four experimental communities were established by planting seedlings of twelve wetland species at different relative abundances and absolute densities. The development of the communities was monitored over three years, and yearly changes in biomass were modelled as a linear function of the species biomass at the start of each period. After three years, a clear dominance structure had developed, with four species making up 80% of the aboveground biomass. In all three years, community dynamics was driven by differences in relative growth rates among the species (i.e. an effect of species identity). However, in the second and third years negative density dependence was also important, with changes in the relative abundance of the most abundant species being negatively related to their biomass at the start of the period. Multiple species interactions – though generally weaker than effects of species identity and intraspecific competition – became increasingly important and also contributed to the dominance pattern. It is concluded that species identity and negative density dependence of the dominant species were the most important factors causing the experimental plant communities to converge. We suggest that model systems composed of several species offer a useful method for investigating the influence of functional traits upon community dynamics.     

三江源地区不同建植期人工草地植被特征及其与土壤特征的关系

研究了三江源地区不同建植期人工草地群落生物量、物种组成、多样性指数和土壤理化特征,并用多元逐步回归分析法探讨了土壤理化特征对群落生物量、多样性变化的响应.结果表明:研究区不同建植期人工草地植物群落的种类组成、植物功能群组成和群落数量特征存在显著差异;土壤含水量随着物种多样性指数的增加而增加,土壤容重随着物种多样性的增加而减小;土壤微生物生物量碳与土壤含水量、土壤有机质呈极显著正相关,与土壤容重呈极显著负相关;土壤有机碳含量明显呈"V"字型变化,且与土壤含水量的变化趋势相一致,随土壤容重的增加而减少;群落生物量与土壤养分和土壤含水量之间呈显著正相关,群落地上、地下生物量的增加有利于提高土壤养分含量.     

优势种去除对崇明东滩盐沼湿地生态系统的影响

盐沼生态系统环境梯度明显,物种组成较简单,是研究生物多样性与生态系统功能关系的理想对象。本研究以崇明东滩盐沼湿地为研究区域,研究优势种去除对植物群落结构以及底栖动物群落的影响。结果表明:(1)去除处理仅对植物群落分株密度有极显著效应(P0.01)。去除组和对照组物种组成差异随时间增加而减小,处理效应逐渐减弱。(2)去除组底栖动物密度均低于对照组,但差异不显著。(3)盐沼植物群落特征与底栖动物群落有密切关系,植物密度、冠层高度与底栖动物密度相关性极显著。去除优势种后,植物群落分株密度升高,群落内剩余物种占比有所上升,次优势种对群落的补偿效应具有较大贡献;而底栖动物群落密度下降,其生物量和多样性指数的变化趋势与密度并不一致。上述结果表明生物多样性变化影响了盐沼湿地生态系统植物群落和底栖动物群落结构,进而可能影响物质循环和能量流动过程。     

Density may alter diversity–productivity relationships in experimental plant communities

Contemporary biodiversity experiments, in which plant species richness is manipulated and aboveground productivity of the system measured, generally demonstrate that lowering plant species richness reduces productivity. However, we propose that community density may in part compensate for this reduction of productivity at low diversity. We conducted a factorial experiment in which plant functional group richness was held constant at three, while plant species richness increased from three to six to 12 species and community density from 440 to 1050 to 2525 seedlings m⁻². Response variables included density, evenness and above- and belowground biomass at harvest. The density gradient converged slightly during the course of the experiment due to about 10% mortality at the highest sowing density. Evenness measured in terms of aboveground biomass at harvest significantly declined with density, but the effect was weak. Overall, aboveground, belowground and total biomass increased significantly with species richness and community density. However, a significant interaction between species richness and community density occurred for both total and aboveground biomass, indicating that the diversity–productivity relationship was flatter at higher than at lower density. Thus, high species richness enabled low-density communities to reach productivity levels otherwise seen only at high density. The relative contributions of the three functional groups C₃, C₄ and nitrogen-fixers to aboveground biomass were less influenced by community density at high than at low species richness. We interpret the interaction effects between community density and species richness on community biomass by expanding findings about constant yield and size variation from monocultures to plant mixtures.     

Productivity-diversity relationships in lake plankton communities

One of the most intriguing environmental gradients connected with variation in diversity is ecosystem productivity. The role of diversity in ecosystems is pivotal, because species richness can be both a cause and a consequence of primary production. However, the mechanisms behind the varying productivity-diversity relationships (PDR) remain poorly understood. Moreover, large-scale studies on PDR across taxa are urgently needed. Here, we examined the relationships between resource supply and phyto-, bacterio-, and zooplankton richness in 100 small boreal lakes. We studied the PDR locally within the drainage systems and regionally across the systems. Second, we studied the relationships between resource availability, species richness, biomass and resource ratio (N:P) in phytoplankton communities using Structural Equation Modeling (SEM) for testing the multivariate hypothesis of PDR. At the local scale, the PDR showed variable patterns ranging from positive linear and unimodal to negative linear relationships for all planktonic groups. At the regional scale, PDRs were significantly linear and positive for phyto- and zooplankton. Phytoplankton richness and the amount of chlorophyll a showed a positive linear relationship indicating that communities consisting of higher number of species were able to produce higher levels of biomass. According to the SEM, phytoplankton biomass was largely related to resource availability, yet there was a pathway via community richness. Finally, we found that species richness at all trophic levels was correlated with several environmental factors, and was also related to richness at the other trophic levels. This study showed that the PDRs in freshwaters show scale-dependency. We also documented that the PDR complies with the multivariate model showing that plant biomass is not mirroring merely the resource availability, but is also influenced by richness. This highlights the need for conserving diversity in order to maintain ecosystem processes in freshwaters.     

Resource availability dominates and alters the relationship between species diversity and ecosystem productivity in experimental plant communities

Experimental evidence that plant species diversity has positive effects on biomass production appears to conflict with correlations of species diversity and standing biomass in natural communities. This may be due to the confounding effects of a third variable, resource availability, which has strong control over both diversity and productivity in natural systems and may conceal any positive effects of diversity on productivity. To test this hypothesis, I independently manipulated resource availability (soil fertility) and sown species diversity in a field experiment and measured their individual and interactive effects on productivity. Although fertility was a far stronger predictor of productivity than diversity, the effect of diversity on productivity significantly increased with fertility. Relative yield analyses indicated that plant mixtures of high fertility treatments significantly "overyielded," or were more productive than expected based on monoculture yields of component species. In contrast, plant mixtures of low fertility treatments had significantly lower-than-expected yields. The effect of diversity on productivity was also driven by sampling effects, where more species-rich mixtures were more likely to include particularly productive species. Unexpectedly, the strength of sampling effects was largely insensitive to fertility, although the particular species most responsible for sampling effects did change with fertility. These results suggest that positive effects of species diversity on ecosystem productivity in natural systems are likely to be masked by variation in environmental factors among habitats.     

不同红树植物群落中大型底栖动物群落的比较

2005—2006年对广东湛江红树林国家级自然保护区湿地三种红树植物群落(白骨壤 桐化树群落、桐花树群落、木榄 桐花树群落)的大型底栖动物群落特征进行了分析研究。白骨壤 桐化树群落大型底栖动物群落的物种数、栖息密度、生物量、丰富度指数和多样性指数均最高,优势度指数居中,均匀度指数略低于桐花树群落;桐花树群落大型底栖动物物种数急剧减少,尤其是底内型、底上附着型和穴居型种类减少明显,生物量和栖息密度下降到最低,由于个体数种间分配较为均匀而导致优势度指数下降而均匀度指数增高,虽丰富度指数略低于白骨壤 桐化树群落,但多样性指数接近于白骨壤 桐化群落;木榄 桐花树群落,大型底栖动物群落的物种数,尤其是穴居型和底内型种数继续减少,但生物量和栖息密度有所上升,个体数种间分配不均匀而使优势度指数增高而均匀度下降,加上丰富度指数最低,故多样性指数最小。白骨壤 桐化树群落优势种的生活型是底内型和穴居型;桐花树和木榄 桐花树群落优势种的生活型均是穴居型。三种红树植物群落中的大型底栖动物群落的GS/GSB分别为0.48、0.63、0.80。相同红树植物群落大型底栖动物群落结构都较为相似,木榄 桐花树群落的相似性最高,而不同红树植物群落大型底栖动物群落特征的差异明显,反映了不同红树群落对底栖动物群落作用的差别,同时也展示了各种大型底栖动物对不同红树群落生境的适应情况。     

Heterogeneity of xerophytic vegetation of limestone outcrops in a tropical deciduous forest region in southern México

The heterogeneity of xerophytic vegetation developing on limestone outcrops immersed in a tropical deciduous forest matrix was studied in Nizanda (S México). The study units comprised three clearly distinct communities based on their physiognomy and substrate, representing a gradient of edaphic aridity: (1) xerophytic scrub (XS); (2) tropical deciduous forest on rock (TDFr); and (3) tropical deciduous forest on deeper soil (TDFs). Structural and floristic variables were gathered in nine 100 m² plots by community. In the 0.27 ha sampled 211 plant species were recorded. Total floristic richness by community decreased with increasing edaphic aridity: 159 species in TDFs, 107 in TDFr, and 36 in XS. Although significant differences were observed between the three communities for only four structural variables (total and upper stratum species densities, and relative monocotyledon density and cover), other variables confirmed the differences between the two forest communities and the XS (total and upper stratum cover, density, and basal area). TDFr and XS also differed from TDFs with respect to lower stratum species density, and absolute monocotyledon density and cover. The results showed the importance of monocotyledons and the prevalence of clonality in TDFr and XS. A comparison between limestone outcrop and inselberg vegetation indicated a virtual absence of therophytes, graminoid herbs, cryptogamic crusts, and desiccation-tolerant and carnivorous plants in the former, whereas the prevalence of monocotyledon mats, and xerophytic and succulent plants is the most striking similarity between these rocky environments. Xerophytic vegetation of limestone outcrops in Nizanda may be seen as analogous of relictual communities that existed during a northbound migration of Neotropical flora, towards the arid zones of North America.     

土壤肥力和物种属性决定亚高寒草甸实验群落的生产力

生物多样性与生态系统功能之间的关系及其形成的内在机制还存在很多争议。为了揭示植物群落生产力形成的生态学机制, 采用盆栽方法探讨了物种多样性、物种属性以及施肥水平与植物群落生产力之间的关系。研究结果显示: 在不施肥和每盆施5.0 g磷酸二铵的条件下, 随着物种多样性的增加, 地上生物量增加不显著; 在每盆施10.0 g磷酸二铵的条件下, 随着物种多样性的增加, 地上生物量显著增加。相对于中华羊茅(Festuca sinensis)而言, 垂穗披碱草(Elymus nutans)和垂穗鹅观草(Roegneria nutans)对群落生产力的贡献较大, 但在不同施肥水平和播种密度下, 其影响不完全相同。这表明物种多样性对群落生产力的影响随着土壤肥力的变化而变化; 并且植物群落生产力受组成群落的物种属性影响较大, 而物种属性又与特定时间和特定生境下资源的利用方式相联系。在高肥力水平下, 物种多样性之所以对群落生产力具有正效应, 可能是因为高肥力水平增加了可利用的生态位空间, 最终仍体现在物种组合上。因此, 植物群落的生产力与物种多样性之间没有必然的联系, 而与土壤肥力和土壤肥力决定的物种属性有关。