Effects of plant diversity,community composition and environmental parameters on productivity in montane European grasslands

In the past years, a number of studies have used experimental plant communities to test if biodiversity influences ecosystem functioning such as productivity. It has been argued, however, that the results achieved in experimental studies may have little predictive value for species loss in natural ecosystems. Studies in natural ecosystems have been equivocal, mainly because in natural ecosystems differences in diversity are often confounded with differences in land use history or abiotic parameters. In this study, we investigated the effect of plant diversity on ecosystem functioning in semi-natural grasslands. In an area of 10×20 km, we selected 78 sites and tested the effects of various measures of diversity and plant community composition on productivity. We separated the effects of plant diversity on ecosystem functioning from potentially confounding effects of community composition, management or environmental parameters, using multivariate statistical analyses. In the investigated grasslands, simple measures of biodiversity were insignificant predictors of productivity. However, plant community composition explained productivity very well (R²=0.31) and was a better predictor than environmental variables (soil and site characteristics) or management regime. Thus, complex measures such as community composition and structure are important drivers for ecosystem functions in semi-natural grasslands. Furthermore, our data show that it is difficult to extrapolate results from experimental studies to semi-natural ecosystems, although there is a need to investigate natural ecosystems to fully understand the relationship of biodiversity and ecosystem functioning.     

Theme section on “Mesophotic Coral Ecosystems: Characterization, Ecology, and Management”

Mesophotic coral ecosystems (MCEs) are characterized by the presence of light-dependent corals and associated communities that are typically found at depths ranging from 30 to 40 m and extending to over 150 m in tropical and subtropical regions. The dominant communities providing structural habitat in the mesophotic zone can be comprised of coral, sponge, and algal species. Because working in this depth range is constrained by traditional SCUBA limits, less is known about corals and associated organisms there compared to shallower coral communities. Following the first-ever gathering of international scientists to review and discuss existing knowledge of MCEs, this issue focuses on the ecological characterization, geomorphology, and concept of MCEs as refugia for shallow-water populations. The review and research papers comprising this special issue reflect the current scientific understanding of these ecosystems and the underlying mechanisms that regulate them, as well as potential resource management implications. It is important to understand the value and role of mesophotic coral ecosystems in tropical and subtropical regions as these areas face increasing environmental change and human impacts     

Late-successional biological soil crusts in a biodiversity hotspot: an example of congruency in species richness

Understanding the biodiversity of functionally important communities in Earth’s ecosystems is vital in the apportionment of limited ecosystem management funds and efforts. In southern California shrublands, which lie in a global biodiversity hotspot, biological soil crusts (BSCs) confer critical ecosystem services; however, their biodiversity remains unknown. In this study, six sites (n = 4 each, 25 m²) were established along a mediterranean shrubland environmental gradient in southern California. Here, the biodiversity of all BSC-forming lichens and bryophytes was evaluated, related to environmental traits along the gradient, and compared to species richness among North American ecosystems supporting BSCs (data from previous studies). In total, 59 BSC-forming lichens and bryophytes were observed, including the very rare Sarcogyne crustacea, a rare moss, and five endemic lichen species. Over half (61%) of the species observed were found at a single site. Along the gradient, species evenness of late-successional BSC was related to dew point and elevation, and both evenness and richness were related to distance to coast. Using an ordination analysis, five distinct late-successional BSC communities were identified: Riversidian, Spike moss, Casperian, Alisian, and Lagunian. Twenty-five lichens and 19 bryophytes are newly reported for North American BSC-forming organisms, now comprising ~1/2 of the North American total. BSCs in North American hot and cold deserts were approximately 4.0 and 2.4 times less species rich than BSCs found in southern California shrublands, respectively. Given the anthropogenic impacts on quality and distribution of California mediterranean shrublands, our results show that these sites represent important refugia of BSC species in this globally important region.     

三江平原农田地表和地下土壤螨类丰富度与环境因子的空间关联性

地表和地下土壤动物群落空间格局及其与环境因子的空间作用关系,是揭示地表-地下生态系统格局与过程及生物多样性维持机制的重要基础。于2011年在三江平原农田生态系统,在50m×50m的空间尺度内,基于地统计空间分析方法,揭示地表和地下土壤螨群落及不同螨类物种丰富度的空间格局,并分析这种空间格局与土壤含水量、土壤p H值及大豆株高空间格局的空间关联性。半方差函数和普通克里格插值表明,8月份地表、地下和10月份地下螨群落及这些群落内大部分螨类物种在特定空间尺度内形成集群,表现为空间异质性特征,且这种空间分异多由结构性因素或结构性因素和随机性因素共同调控。交叉方差函数表明,土壤螨群落和不同螨类物种的空间格局与环境因子的空间格局在多种尺度上表现出复杂的空间关联性(正的或负的)。但简单Mantel检验仅发现8月份地表中气门亚目未定种1(Mesostigmata unidentified sp.1)和大豆株高存在明显的正的空间关联性。研究结果表明地下螨群落和生长季节的地表螨群落具有明显的空间异质性结构,地表和地下螨群落及大多数螨类物种丰富度与土壤含水量、土壤p H值及大豆株高的空间关联性并不显著。促进地表-地下生态系统土壤动物群落空间格局研究,为地表-地下格局与过程研究奠定基础。     

A synthesis of species interactions,metacommunities, and the conservation of avian diversity in hemiboreal and boreal forests

The rate at which climate is changing in northern latitudes presents a significant threat to bird populations that rely on boreal forests. Alterations in the distributions of trees and other plants as a result of warming will alter the habitat suitability of vast regions of boreal and hemiboreal forests. Climate change associated habitat alterations along with range expansions of bird species are likely to have substantial consequences on avian communities and biodiversity. Identifying factors that contribute to species coexistence and community assembly processes at local and regional scales will facilitate predictions about the impact of climate change on avian communities in these forest ecosystems. This paper provides a comprehensive review of historic and current theories of community ecology dynamics providing a theoretical synthesis that links the evolution of species traits at the individual level, the dynamics of species interactions, and the overall maintenance of biodiversity. Integration of these perspectives is necessary to provide the scientific means to face growing environmental challenges in boreal ecosystems.     

热带雨林退化生态系统生物多样性消失与修复探讨

热带雨林退化生态系统的主要类型有：（１）人工生态系统;（２）次生森林生态系统和（３）片断森林生态系统等。在退化生态系统中,物种多样性的损失与人类干扰程度、频率和持续时间密切相关;而在片断的热带雨林中则随着环境变化强度的加大和持续时间的延长而增加。退化生态系统的修复主要在于减少人类的干扰、改善地区性的环境和在保护与发展相结合的原则下,采取多种有效的综合措施。尊重当地民族生物多样性传统管理经验,实行封     

Climate change and alpine stream biology: progress,challenges, and opportunities for the future

In alpine regions worldwide, climate change is dramatically altering ecosystems and affecting biodiversity in many ways. For streams, receding alpine glaciers and snowfields, paired with altered precipitation regimes, are driving shifts in hydrology, species distributions, basal resources, and threatening the very existence of some habitats and biota. Alpine streams harbour substantial species and genetic diversity due to significant habitat insularity and environmental heterogeneity. Climate change is expected to affect alpine stream biodiversity across many levels of biological resolution from micro‐ to macroscopic organisms and genes to communities. Herein, we describe the current state of alpine stream biology from an organism‐focused perspective. We begin by reviewing seven standard and emerging approaches that combine to form the current state of the discipline. We follow with a call for increased synthesis across existing approaches to improve understanding of how these imperiled ecosystems are responding to rapid environmental change. We then take a forward‐looking viewpoint on how alpine stream biologists can make better use of existing data sets through temporal comparisons, integrate remote sensing and geographic information system (GIS) technologies, and apply genomic tools to refine knowledge of underlying evolutionary processes. We conclude with comments about the future of biodiversity conservation in alpine streams to confront the daunting challenge of mitigating the effects of rapid environmental change in these sentinel ecosystems.     

Nutrient enrichment weakens the stabilizing effect of species richness

With global freshwater biodiversity declining at an even faster rate than in the most disturbed terrestrial ecosystems, understanding the effects of changing environmental conditions on relationships between biodiversity and the variability of community and population processes in aquatic ecosystems is of significant interest. Evidence is accumulating that biodiversity loss results in more variable communities; however, the mechanisms underlying this effect have been the subject of considerable debate. We manipulated species richness and nutrients in outdoor aquatic microcosms composed of naturally occurring assemblages of zooplankton and benthic invertebrates to determine how the relationship between species richness and variability might change under different nutrient conditions. Temporal variability of populations and communities decreased with increasing species richness in low nutrient microcosms. In contrast, we found no relationship between species richness and either population or community variability in nutrient enriched microcosms. Of the different mechanisms we investigated (e.g. overyielding, statistical averaging, insurance effects, and the stabilizing effect of species richness on populations) the only one that was consistent with our results was that increases in species richness led to more stable community abundances through the stabilizing effect of species richness on the component populations. While we cannot conclusively determine the mechanism(s) by which species richness stabilized populations, our results suggest that more complete resource-use in the more species-rich low nutrient communities may have dampened population fluctuations.     

Environmental metabarcoding reveals heterogeneous drivers of microbial eukaryote diversity in contrasting estuarine ecosystems

Assessing how natural environmental drivers affect biodiversity underpins our understanding of the relationships between complex biotic and ecological factors in natural ecosystems. Of all ecosystems, anthropogenically important estuaries represent a ‘melting pot'' of environmental stressors, typified by extreme salinity variations and associated biological complexity. Although existing models attempt to predict macroorganismal diversity over estuarine salinity gradients, attempts to model microbial biodiversity are limited for eukaryotes. Although diatoms commonly feature as bioindicator species, additional microbial eukaryotes represent a huge resource for assessing ecosystem health. Of these, meiofaunal communities may represent the optimal compromise between functional diversity that can be assessed using morphology and phenotype–environment interactions as compared with smaller life fractions. Here, using 454 Roche sequencing of the 18S nSSU barcode we investigate which of the local natural drivers are most strongly associated with microbial metazoan and sampled protist diversity across the full salinity gradient of the estuarine ecosystem. In order to investigate potential variation at the ecosystem scale, we compare two geographically proximate estuaries (Thames and Mersey, UK) with contrasting histories of anthropogenic stress. The data show that although community turnover is likely to be predictable, taxa are likely to respond to different environmental drivers and, in particular, hydrodynamics, salinity range and granulometry, according to varied life-history characteristics. At the ecosystem level, communities exhibited patterns of estuary-specific similarity within different salinity range habitats, highlighting the environmental sequencing biomonitoring potential of meiofauna, dispersal effects or both.     

Longitudinal river zonation in the tropics: examples of fish and caddisflies from the endorheic Awash River,Ethiopia

Specific concepts of fluvial ecology are well studied in riverine ecosystems of the temperate zone but poorly investigated in the Afrotropical region. Hence, we examined the longitudinal zonation of fish and adult caddisfly (Trichoptera) assemblages in the endorheic Awash River (1,250 km in length), Ethiopia. We expected that species assemblages are structured along environmental gradients, reflecting the pattern of large-scale freshwater ecoregions. We applied multivariate statistical methods to test for differences in spatial species assemblage structure and identified characteristic taxa of the observed biocoenoses by indicator species analyses. Fish and caddisfly assemblages were clustered into highland and lowland communities, following the freshwater ecoregions, but separated by an ecotone with highest biodiversity. Moreover, the caddisfly results suggest separating the heterogeneous highlands into a forested and a deforested zone. Surprisingly, the Awash drainage is rather species-poor: only 11 fish (1 endemic, 2 introduced) and 28 caddisfly species (8 new records for Ethiopia) were recorded from the mainstem and its major tributaries. Nevertheless, specialized species characterize the highland forests, whereas the lowlands primarily host geographically widely distributed species. This study showed that a combined approach of fish and caddisflies is a suitable method for assessing regional characteristics of fluvial ecosystems in the tropics.

     

Trait structure and redundancy determine sensitivity to disturbance in marine fish communities

Trait diversity is believed to influence ecosystem dynamics through links between organismal traits and ecosystem processes. Theory predicts that key traits and high trait redundancy—large species richness and abundance supporting the same traits—can buffer communities against environmental disturbances. While experiments and data from simple ecological systems lend support, large‐scale evidence from diverse, natural systems under major disturbance is lacking. Here, using long‐term data from both temperate (English Channel) and tropical (Seychelles Islands) fishes, we show that sensitivity to disturbance depends on communities’ initial trait structure and initial trait redundancy. In both ecosystems, we found that increasing dominance by climatically vulnerable traits (e.g., small, fast‐growing pelagics/corallivores) rendered fish communities more sensitive to environmental change, while communities with higher trait redundancy were more resistant. To our knowledge, this is the first study demonstrating the influence of trait structure and redundancy on community sensitivity over large temporal and spatial scales in natural systems. Our results exemplify a consistent link between biological structure and community sensitivity that may be transferable across ecosystems and taxa and could help anticipate future disturbance impacts on biodiversity and ecosystem functioning.     

Zooplankton community structure along a pollution gradient at fine geographical scales in river ecosystems: The importance of species sorting over dispersal

The release of anthropogenic pollution into freshwater ecosystems has largely transformed biodiversity and its geographical distribution patterns globally. However, for many communities including ecologically crucial ones such as zooplankton, it is largely unknown how different communities respond to environmental pollution. Collectively, dispersal and species sorting are two competing processes in determining the structure and geographical distribution of zooplankton communities in running water ecosystems such as rivers. At fine geographical scales, dispersal is usually considered as the dominant factor; however, the relative role of species sorting has not been evaluated well, mainly because significant environmental gradients rarely exist along continuously flowing rivers. The Chaobai River in northern China represents a rare system, where a significant environmental gradient exists at fine scales. Here, we employed high‐throughput sequencing to characterize complex zooplankton communities collected from the Chaobai River, and tested the relative roles of dispersal and species sorting in determining zooplankton community structure along the pollution gradient. Our results showed distinct patterns of zooplankton communities along the environmental gradient, and chemical pollutant‐related factors such as total phosphorus and chlorophyll‐a were identified as the major drivers for the observed patterns. Further partial redundancy analyses showed that species sorting overrode the effect of dispersal to shape local zooplankton community structure. Thus, our results reject the dispersal hypothesis and support the concept that species sorting caused by local pollution can largely determine the zooplankton community structure when significant environmental gradients exist at fine geographical scales in highly polluted running water ecosystems.     

滇西北高山微水体与溪流生境底栖动物多样性和环境特征

高山微水体由于面积微小且通过地表径流形成串联结构常常被认为与高山溪流具有类似的生境, 然而由于这两类生境中环境因子与底栖动物多样性存在差异, 它们在生态系统中的作用可能完全不同。滇西北地区是全球生物多样性热点区域之一, 境内高山微水体和高山溪流分布密集, 在区域底栖生物多样性维持方面具有重要的功能, 然而目前对这两类高山淡水生态系统的研究较少。为了比较这两类生境环境因子的异同及其对底栖动物多样性的维持作用, 2015年6月, 作者在云南省怒江州贡山县的高山峡谷内, 对27个高山微水体和同区域分布的1条高山溪流(海拔高差500 m范围)的底栖动物多样性和水环境因子进行了实地调查。结果表明: (1)高山微水体和高山溪流底栖动物群落中优势分类单元种群数量均比较庞大, 而稀有分类单元数量较多且种群较小; (2)两种生境在环境因子、物种多样性、功能多样性和群落结构方面的差异明显, 高山溪流有较高的物种丰富度、物种多样性和功能多样性; (3)高山微水体底栖动物多样性的分布与水环境因子无关, 而高山溪流底栖动物多样性与群落结构的形成受到与流速关联的水环境因子和海拔的影响。因此, 高山微水体与高山溪流不能简单地视为类似的生境类型, 它们对区域底栖动物多样性和生态功能维持可能具有不同的作用。     

Regional zooplankton biodiversity provides limited buffering of pond ecosystems against climate change

1. Climate change and other human-driven environmental perturbations are causing reductions in biodiversity and impacting the functioning of ecosystems on a global scale. Metacommunity theory suggests that ecosystem connectivity may reduce the magnitude of these impacts if the regional species pool contains functionally redundant species that differ in their environmental tolerances. Dispersal may increase the resistance of local ecosystems to environmental stress by providing regional species with traits adapted to novel conditions. 2. We tested this theory by subjecting freshwater zooplankton communities in mesocosms that were either connected to or isolated from the larger regional species pool to a factorial manipulation of experimental warming and increased salinity. 3. Compensation by regional taxa depended on the source of stress. Warming tolerant regional taxa partially compensated for reductions in heat sensitive local taxa but similar compensation did not occur under increased salinity. 4. Dispersal-mediated species invasions dampened the effects of warming on summer net ecosystem productivity. However, this buffering effect did not occur in the fall or for periphyton growth, the only other ecosystem function affected by the stress treatments. 5. The results indicate that regional biodiversity can provide insurance in a dynamic environment but that the buffering capacity is limited to some ecosystem processes and sources of stress. Maintaining regional biodiversity and habitat connectivity may therefore provide some limited insurance for local ecosystems in changing environments, but is unable to impart resistance against all sources of environmental stress.     

种间互作网络的结构、生态系统功能及稳定性机制研究

生态群落中不同物种间发生多样化的相互作用, 形成了复杂的种间互作网络。复杂生态网络的结构如何影响群落的生态系统功能及稳定性是群落生态学的核心问题之一。种间互作直接影响到物质和能量在生态系统不同组分之间的流动和循环以及群落构建过程, 使得网络结构与生态系统功能和群落稳定性密切相关。在群落及生态系统水平上开展种间互作网络研究将为群落的构建机制、生物多样性维持、生态系统稳定性、物种协同进化和性状分化等领域提供新的视野。当前生物多样性及生态系统功能受到全球变化的极大影响, 研究种间互作网络的拓扑结构、构建机制、稳定性和生态功能也可为生物多样性的保护和管理提供依据。该文从网络结构、构建机制、网络结构和稳定性关系、种间互作对生态系统功能的影响等4个方面综述当前种间网络研究进展, 并提出在今后的研究中利用机器学习和多层网络等来探究环境变化对种间互作网络结构和功能的影响, 并实现理论和实证研究的有效整合。     

Functional complementarity in the arbuscular mycorrhizal symbiosis

The causes and consequences of biodiversity are central themes in ecology. Perhaps one reason for much of the current interest in biodiversity is the belief that the loss of species (by extinction) or their gain (by invasion) will significantly influence ecosystem function. Arbuscular mycorrhizal (AM) fungi are components of most terrestrial ecosystems and, while many research programs have shown that variability among species or isolates of AM fungi does occur (Giovannetti & Gianinazzi-Pearson, 1994), the basis for this variability and its consequences to the function of communities and ecosystems remains largely unexplored. Smith et al . (pp. 357–366 in this issue) now show clearly that ecologically significant functional diversity exists among AM fungal species in the regions of the soil from which they absorb phosphate, and their results suggest that such diversity may have significant ecological consequences.     

Do experiments exploring plant diversity–ecosystem functioning relationships inform how biodiversity loss impacts natural ecosystems?

An enormous recent research effort focused on how plant biodiversity (notably species richness) influences ecosystem functioning, usually through experiments in which diversity is varied through random draws of species from a species pool. Such experiments are increasingly used to predict how species losses influence ecosystem functioning in ‘real’ ecosystems. However, this assumes that comparisons of experimental communities with low vs high species richness are analogous to comparisons of natural communities from which species either have or have not been lost. I explore the validity of this assumption, and highlight difficulties in using such experiments to draw conclusions about the ecosystem consequences of biodiversity loss in natural systems. Notably, these experiments do not mimic what happens in real ecosystems either when local extinctions occur or when species losses are offset by gains of new species. Despite limitations, this single experimental approach for studying how biodiversity loss affects ecosystems has often been advocated and implemented at the expense of other approaches; this limits understanding of how natural ecosystems respond to biodiversity loss. I conclude that a broader spectrum of approaches, and more explicit consideration of how species losses and gains operate in concert to influence ecosystems, will help progress this field.     

Antarctic microbial diversity: the basis of polar ecosystem processes

Microorganisms are fundamental to the functioning of Antarctic ecosystems. Although microbial biomass can be immense in Southern Ocean blooms and freshwater cyanobacterial mats, species richness is generally more restricted than it is in temperate regions. However, there are representatives of a broad variety of taxa providing a diverse gene pool. Species diversity may be low while metabolic flexibility is high so that a few strains can provide most necessary functions. In this context, biodiversity is the sum of biological potential. This Special Issue highlights aspects of microbial ecology that can be studied only in Antarctica or which are defined most clearly in Antarctic habitats. Relatively simple microbial communities, or conspicuous species within them, can be used as indicators of microbial processes and responses to environmental change. These include the palaeological record of benthic diatoms and response of soil cyanobacterial communities to regional warming and UV-B stress. The climatic conditions and relict babitats of the Antarctic dry valleys are a valuable analogue for detecting microbial life and diversity on Mars. The global microbial biodiversity initiative Diversitas and international Antarctic networks such as BIOTAS (Biological Investigations of Terrestrial Antarctic Systems) harness taxonomic and ecophysiological expertize to understand better these unique polar ecosystems.     

Predicting ecosystem stability from community composition and biodiversity

As biodiversity is declining at an unprecedented rate, an important current scientific challenge is to understand and predict the consequences of biodiversity loss. Here, we develop a theory that predicts the temporal variability of community biomass from the properties of individual component species in monoculture. Our theory shows that biodiversity stabilises ecosystems through three main mechanisms: (1) asynchrony in species’ responses to environmental fluctuations, (2) reduced demographic stochasticity due to overyielding in species mixtures and (3) reduced observation error (including spatial and sampling variability). Parameterised with empirical data from four long‐term grassland biodiversity experiments, our prediction explained 22–75% of the observed variability, and captured much of the effect of species richness. Richness stabilised communities mainly by increasing community biomass and reducing the strength of demographic stochasticity. Our approach calls for a re‐evaluation of the mechanisms explaining the effects of biodiversity on ecosystem stability.