Effects of hydromorphological impacts on river ecosystem functioning: a review and suggestions for assessing ecological impacts

Because of the serious effects of pollution on water supply much closer attention has been paid to water quality than to other aspects of river integrity. However, channel form and water flow are relevant components of river health, and recent evidences show that their impairment threatens the services derived from them. In this article, we review the literature on the effects of common hydromorphological impacts (channel modification and flow modification) on the functioning of river ecosystems. There are evidences that even light hydromorphological impacts can have deep effects on ecosystem functioning, and that different functional variables differ in their responses. Three criteria (relevance, scale and sensitivity) in the selection of functional variables are suggested as a guide for the river scientists and managers to assess the ecological impacts of hydromorphological modifications.     

Recent advances in exploring physiology and biodiversity of ectomycorrhizas highlight the functioning of these symbioses in ecosystems

Ectomycorrhizas, the dominating mycorrhizal symbiosis in boreal, temperate and some tropical forests, are formed by 5000-6000 species of the asco- and basidiomycetes. This high diversity of fungal partners allows optimal foraging and mobilisation of various nitrogen and phosphorus forms from organic soil layers. In this review, two approaches to study the functioning of this multitude of symbiotic associations are presented. On selected culture models, physiological and molecular investigations have shown that the supply of hexoses has a key function in controlling the plant-fungus interaction via partner-specific regulation of gene expression. Environmental factors which affect fungal carbon supply, such as increased nitrogen availability, also affect mycorrhiza formation. Based on such laboratory results, the adaptative capability of ectomycorrhizas to changing field conditions is discussed. The second approach consists of analysing the distribution of mycorrhizas in ecosystem compartments and to relate distribution patterns to variations of ecological factors. Recent advances in identification of fungal partners in ectomycorrhizas by analysing the internal transcribed spacer of ribosomal DNA are presented, which can help to resolve sampling problems in field studies. The limits of the laboratory and the field approaches are discussed. Despite some problems, this combined approach is the most promising. Direct investigation of gene expression, which has been introduced for soil bacteria, will be difficult in the case of mycorrhizal fungi which constitute organisms with functionally varying structures.     

生物多样性和生态系统功能研究综述

生物多样性和生态系统功能之间关系 ,是生态学和环境科学的热门话题。围绕这一主题 ,文章系统回顾了近 2 0年来的研究历史及学术界的不同观点 ,全面展示了目前在理论和实验领域的主要工作结果和研究进展 ,并对今后的发展趋势和面临的挑战作了展望。理论和实验研究都表明 ,生物多样性趋于与生态系统功能 (稳定性 )呈正相关性 ,但是多样性并非是这种关系的直接驱动力。生态系统功能 (稳定性 )潜在地依赖于物种之间相互作用的强度 ,物种的功能反应特性以及生态系统的类型和尺度等。在生物多样性和生态系统功能的研究中 ,重要的不只是结论 ,还应包括其中所隐含的机制。     

Origins of mangrove ecosystems and the mangrove biodiversity anomaly

1. Mangrove species richness declines dramatically from a maximum in the Indo-West Pacific (IWP) to a minimum in the Caribbean and Western Atlantic. Explaining this ‘anomalous’ biogeographic pattern has been a focus of discussion for most of this century. 2. Two hypotheses have been put forward to explain the mangrove biodiversity anomaly. The ‘centre-of-origin hypothesis’ asserts that all mangrove taxa originated in the IWP and subsequently dispersed to other parts of the world. The ‘vicariance hypothesis’ asserts that mangrove taxa evolved around the Tethys Sea during the Late Cretaceous, and regional species diversity resulted from in situ diversification after continental drift. 3. Five lines of evidence are used to test between these two hypotheses. First, we review the mangrove fossil record. Second, we compare modern and fossil distributions of mangroves and eight genera of gastropods that show high fidelity to the mangrove environment. Third, we describe species-area relationships of mangroves and associated gastropods with respect to area of available habitat. Fourth, we analyse patterns of nestedness of individual plant and gastropod communities in mangrove forests. Fifth, we analyse patterns of nestedness of individual plant and gastropod species. 4. All five lines of evidence support the vicariance hypothesis. The first occurrences in the fossil record of most mangrove genera and many genera of gastropods associated with mangrove forests appear around the Tethys Sea from the Late Cretaceous through the Early Tertiary. Globally, species richness in any given mangrove forest is tightly correlated with available area. Patterns of nestedness at the community and species-level both point towards three independent regions of diversification of mangrove ecosystems: South-east Asia, the Caribbean and Eastern Pacific, and the Indian Ocean region.     

Safeguarding marine life: conservation of biodiversity and ecosystems

Reviews in Fish Biology and Fisheries - Marine ecosystems and their associated biodiversity sustain life on Earth and hold intrinsic value. Critical marine ecosystem services include maintenance of...     

Multiple states in river and lake ecosystems

Nonlinear models of ecosystem dynamics that incorporate positive feedbacks and multiple, internally reinforced states have considerable explanatory power. However, linear models may be adequate, particularly if ecosystem behaviour is primarily controlled by external processes. In lake ecosystems, internal (mainly biotic) processes are thought to have major impacts on system behaviour, whereas in rivers, external (mainly physical) factors have traditionally been emphasized. We consider the hypothesis that models that exhibit multiple states are useful for understanding the behaviour of lake ecosystems, but not as useful for understanding stream ecosystems. Some of the best-known examples of multiple states come from lake ecosystems. We review some of these examples, and we also describe examples of multiple states in rivers. We conclude that the hypothesis is an oversimplification; the importance of physical forcing in rivers does not eliminate the possibility of internal feedbacks that create multiple states, although in rivers these feedbacks are likely to include physical as well as biotic processes. Nonlinear behaviour in aquatic ecosystems may be more common than current theory indicates.     

Two-zone model for stream and river ecosystems

A mechanistic two-zone model is developed to represent the food web dynamics of stream and river ecosystems by considering the benthic and nonbenthic (or water-column) zones as two separate, but interacting biotopes. Flow processes, solar radiation, and temperature are the dynamic external environmental drivers. State variables are defined to represent the hierarchical levels of detritus, limiting nutrient, vegetation, and invertebrates. The fish trophic level is included as a constant input parameter. Model parameters, constants, and boundary conditions are defined based on watershed as well as channel hydrology, stream geomorphology, and biological activities. Recent advances in ecological science and engineering are used in representing important biogeochemical processes. In particular, the turbulent diffusion, as well as sloughing or detachment, processes are defined based on these recent advancements. The two-zone model was evaluated for a gravel bed prealpine Swiss stream named River Necker with data for the study period of January 1992 through December 1994. The model was able to capture the general trends and magnitudes of the food web state variables. A comprehensive relative sensitivity analysis with five moment-based measures found that approximately 5% of the model parameters were important in predicting benthic vegetation. Results of sensitivity analysis guided the model calibration. Simulated benthic vegetation with the calibrated model, which was obtained by adjusting only four parameters, corresponded with observed data. Hydrology-dependent sloughing and detachment were dominant in determining the response of benthic vegetation and invertebrates. The proposed two-zone food web model is a potentially useful research tool for stream and river ecosystems.     

Consequences of plant-herbivore coevolution on the dynamics and functioning of ecosystems

The potential consequences of plant-herbivore coevolution for ecosystem functioning are investigated using a simple nutrient-limited ecosystem model in which plant and herbivore traits are subject to adaptive dynamics. Although the ecological model is very simple and always reaches a stable equilibrium in the absence of evolution, coevolution can generate a great diversity of dynamical behaviors. The evolutionary dynamics can lead to a stable equilibrium. If the evolution of plants is fast enough, certain values of the trade-off parameters lead to complex evolutionary cycles bounded by physiological constraints. The dynamical behavior of the model is very different when the dynamics of inorganic nutrient is ignored and plant competition is modeled by a logistic growth function. This emphasizes the importance of including explicit nutrient dynamics in studies of plant-herbivore coevolution.     

Post-fire functioning of Eastern Cisbaikalian forest ecosystems

The post-fire dynamics of Eastern Cisbaikalian forest ecosystems is analyzed. Forest productivity is shown to be reduced by litter and humus ground fires. The study characterizes understory and soil changes after fires of various severities and remoteness.     

European grassland ecosystems: threatened hotspots of biodiversity

Biodiversity is not homogenously distributed over the globe, and ecosystems differ strongly in the number of species they provide. With this special issue we highlight the ecology and endangerment of one of the most diverse ecosystem of Europe: the European grassland ecosystems. The selected 16 contributions describe interactions from below-ground to the atmosphere and focus on (1) effects of abiotic and biotic on species diversity, (2) the impact of various factors along spatial and temporal gradients, (3) the relevance of falling abandoned and eutrophication—including countervailing management strategies like encroachment; and (4) intraspecific effects based on physiology, genetics and intraspecific plasticity. The contributions cover fungi, plants, and invertebrates and highlight effects taking place at the level of ecosystem, species community, species, populations, and also within individuals (physiology and genetics).     

With the worms: Soil biodiversity and ecosystem functioning

The role of soil as a carbon sink, nutrient recycler and pollutant remover is becoming increasingly apparent. But it is the animals and microbes that live in the soil that enable all these activities. Do we know enough about these systems to prevent permanent damage?     

Insect natural history,multi-species interactions and biodiversity in ecosystems

The composition and dynamics of ecosystems are influenced by insects serving as providers, eliminators and facilitators across multiple trophic levels. The role of insects in ecosystems may be documented by manipulative field studies involving exclusion techniques applied to species that are decomposers, herbivores or predators. The presence or absence of insects is important to the distribution, abundance and diversity of plants and vertebrates, which typically are the premier species in conservation efforts. Thus, policy-making in environmental management programmes should consider the role of insects in ecosystems when establishing objectives and procedures for species conservation and biodiversity.     

Linking biodiversity and ecosystems: towards a unifying ecological theory

Community ecology and ecosystem ecology provide two perspectives on complex ecological systems that have largely complementary strengths and weaknesses. Merging the two perspectives is necessary both to ensure continued scientific progress and to provide society with the scientific means to face growing environmental challenges. Recent research on biodiversity and ecosystem functioning has contributed to this goal in several ways. By addressing a new question of high relevance for both science and society, by challenging existing paradigms, by tightly linking theory and experiments, by building scientific consensus beyond differences in opinion, by integrating fragmented disciplines and research fields, by connecting itself to other disciplines and management issues, it has helped transform ecology not only in content, but also in form. Creating a genuine evolutionary ecosystem ecology that links the evolution of species traits at the individual level, the dynamics of species interactions, and the overall functioning of ecosystems would give new impetus to this much-needed process of unification across ecological disciplines. Recent community evolution models are a promising step in that direction.     

Assessing the functional implications of soil biodiversity in ecosystems

Soil communities are among the most species-rich components of terrestrial ecosystems. A major challenge for soil ecologists is to formulate feasible research strategies that will preserve and capitalize on the biodiversity resources of the soil. This article considers the role of soil organism diversity by concentrating on: (i) the relationship between soil biodiversity and ecosystem function; (ii) what issues need to be explored; (iii) studies carried out in the Ecotron controlled environment facility; and (iv) how stable isotope techniques can improve our understanding of the relationship between soil biodiversity and ecosystem function. It is advocated that: (i) the objective of any soil biodiversity study should always be the generation of general concepts, rather than local, system-specific observations; and (ii) any empirical study can be properly interpreted only within a quantitative ecological framework.     

Estimation of river ecosystem biodiversity based on the Chao estimator

The research was focused on identification of plant diversity assessment approach which would be suitable for flowing waters. Moreover, the study attempted to estimate the extent of the survey (sampling effort) needed for detection of full plant diversity in river ecosystems. The analysed data were collected in a botanical survey carried out on the lowland sandy bottom Wel river, which is a very common river type in Europe. The Chao method of estimation of total species richness of macrophytes and Hill numbers were used to estimate the diversity based on very common plants (inverse Simpson index) as well as frequent species (Shannon index) and also including rare species (species richness). The analysis showed that using standard macrophyte survey approach for rivers, it is relatively easy to record abundant plants, but it is not possible to detect all species, because many aquatic macrophytes occur with low frequency and abundance requiring enormous sampling effort to detect all of them. It exceeds capabilities of most scientific projects. To improve the accuracy of diversity estimation, the rarefaction and extrapolation method was recommended. This method can reduce the bias in diversity estimates based on limited observational data, and thus limit inaccurate conclusions and subsequent wrong decisions in the conservation frameworks related to freshwater protection.     

Density compensation can cause no effect of biodiversity on ecosystem functioning

The role of density compensation (the decline of species density with increasing diversity), in the context of biodiversity and ecosystem functioning, has not been explicitly explored. I used aquatic microbial communities containing bacterivorous consumers (protozoans and rotifers) to investigate whether competition can lead to density compensation and whether density compensation can contribute to the relationship between biodiversity and ecosystem functioning. The experiment employed a nested design in which the consumer diversity gradient (0, 1, 2 or 4 species) was constructed by drawing all possible species or species combinations at each diversity level from a five-species pool. All consumer species coexisted but there was little evidence for overyielding or species dominance, suggesting weak complementarity and sampling effects. Rather, increasing number of consumer species resulted in community-wide density compensation, such that aggregate consumer biomass was unaffected by consumer diversity. Whereas culturable bacterial density declined as consumer diversity increased, total bacterial density showed no discernible response to changes in consumer diversity, a result probably due in part to heterogeneity in bacterial edibility. This study demonstrates the potential for density compensation to shape the relationship between biodiversity and ecosystem functioning.