Conservation implications of the link between biodiversity and ecosystem functioning

The relationship between biodiversity and individual ecosystem processes is often asymptotic, saturating at relatively low levels, with some species contributing more strongly than others. This has cast doubt on arguments for conservation based on maintenance of the functioning of ecosystems. However, we argue that the link between biodiversity and ecosystem functioning is an important additional argument for conservation for several reasons. (1) Although species differ in importance to ecosystem processes, we do not believe that this argues for preservation of just a few species for two reasons: first, it is nearly impossible to identify all species important to the numerous systems and processes on which humans depend; second, the important species themselves may depend on an unknown number of other species in their communities. (2) Arguments for conservation based on ecosystem functioning are complementary to other utilitarian, ethical and aesthetic justifications. No single reason will convince all people or protect all species, however the combination produces a strong case for conservation of biodiversity. (3) Even if the relationship between biodiversity and ecosystem functioning is asymptotic at local spatial scales and in the short term, effects of biodiversity loss are likely to be important at larger temporal and spatial scales. (4) Initial arguments for the importance of biodiversity for ecosystem functioning were largely based on a precautionary approach (points 1-3). However, we are now moving to a scientific position based on accumulating experimental evidence. The future challenge is the integration of this scientific research with policy.     

Temporal niches of shredders in lake littorals with possible implications on ecosystem functioning

Temporal growth separation of shredders is known in streams but has not been reported from lakes. In the present study, temporal niche/trait differentiations among shredders in lakes were investigated. We sampled quantitatively three lakes in SE Sweden over a period of 18 months. Dry weight and number of individuals of the collected shredders were measured monthly. Standing stock of detritus types was also monitored. The same 10 species of lentic shredders were found in each lake, one isopod and larvae of nine trichopterans. Functionally, the shredders could be categorized into two main groups; winter and summer growing species. However, also within these groups, temporal differences in growth pattern existed. The main input of detritus occurred during the autumnal leaf fall and a majority of winter shredders had the start of their lives tied to this period. A succession in loss of detritus types was evident with easily degraded matter disappearing first followed by more resistant matter. Shredder species richness, shredder biomass per m² and the ratio coarse/fine detritus all reached its annual low in late summer. We propose a temporal link between the shredder groups and the organic matter subject to decomposition; the successive palatability of coarse detritus is likely to make a temporally separated community of shredders efficient in terms of decomposition. We believe that a temporal differentiation per se is sufficient to conclude that different impact on ecosystem function exists among shredders. Additionally we discuss impacts of differences in abundance and shredding capacity among the species.     

Biodiversity and ecosystem functioning: recent theoretical advances

The relationship between biodiversity and ecosystem functioning has emerged as a major scientific issue today. As experiments progress, there is a growing need for adequate theories and models to provide robust interpretations and generalisations of experimental results, and to formulate new hypotheses. This paper provides an overview of recent theoretical advances that have been made on the two major questions in this area: (1) How does biodiversity affect the magnitude of ecosystem processes (short‐term effects of biodiversity)? (2) How does biodiversity contribute to the stability and maintenance of ecosystem processes in the face of perturbations (long‐term effects of biodiversity)?
Positive short‐term effects of species diversity on ecosystem processes, such as primary productivity and nutrient retention, have been explained by two major types of mechanisms: (1) functional niche complementarity (the complementarity effect), and (2) selection of extreme trait values (the selection effect). In both cases, biodiversity provides a range of phenotypic trait variation. In the complementarity effect, trait variation then forms the basis for a permanent association of species that enhances collective performance. In the selection effect, trait variation comes into play only as an initial condition, and a selective process then promotes dominance by species with extreme trait values. Major differences between within‐site effects of biodiversity and across‐site productivity–diversity patterns have also been clarified. The local effects of diversity on ecosystem processes are expected to be masked by the effects of varying environmental parameters in across‐site comparisons.
A major reappraisal of the paradigm that has dominated during the last decades seems necessary if we are to account for long‐term effects of biodiversity on ecosystem functioning. The classical deterministic, equilibrium approaches to stability do not explain the reduced temporal variability of aggregate ecosystem properties that has been observed in more diverse systems. On the other hand, stochastic, nonequilibrium approaches do show two types of biodiversity effects on ecosystem productivity in a fluctuating environment: (1) a buffering effect, i.e., a reduction in the temporal variance; and (2) a performance‐enhancing effect, i.e., an increase in the temporal mean. The basic mechanisms involved in these long‐term insurance effects are very similar to those that operate in short‐term biodiversity effects: temporal niche complementarity, and selection of extreme trait values. The ability of species diversity to provide an insurance against environmental fluctuations and a reservoir of variation allowing adaptation to changing conditions may be critical in a long‐term perspective.
These recent theoretical developments in the area of biodiversity and ecosystem functioning suggest that linking community and ecosystem ecology is a fruitful avenue, which paves the way for a new ecological synthesis.     

Manganese accumulation in rice: implications for photosynthetic functioning

In order to gain fundamental insights into the nature of the adaptation to Mn excess, the characterisation of the photosynthetic apparatus in Mn-treated rice was carried out in 21-day-old plants. We found 17- and 11-fold increases in Mn in the leaf tissues and in thylakoid, respectively, when the plants were grown hydroponically in nutrient solutions with Mn concentrations between 0.125 and 32 mg l(-1) (2.3 and 582.5 microM). Net photosynthesis and the photosynthetic capacity decreased after the 0.5 and 2 mg l(-1) (9.1 and 36.4 microM) Mn treatment, respectively. The stomatal conductance displayed a similar trend to that of photosynthetic capacity. The levels of basal chlorophyll fluorescence and the ratio between variable and maximum chlorophyll fluorescence did not vary significantly among treatments, but the photochemical quenching and the quantum yield of non-cyclic electron transport increased until the 2 mg l(-1) (36.4 microM) Mn treatment. The lipid matrix of thylakoids revealed a global increase in the proportions of phospholipids, relative to galactolipids. This pattern was coupled with diminishing levels of monogalactosyldiacylglycerol. The relative ratio between total carotenoids and total chlorophylls decreased until the last Mn treatment, yet the levels of carotenes, zeaxanthin, and violaxanthin plus antheraxanthin displayed different patterns. It was further found that the de-epoxidation state involving the components of the xanthophylls cycle increased until the 8 mg l(-1) (145.6 microM) Mn treatment. The levels of the photosynthetic electron carriers displayed different patterns, with plastocyanin and the high and low forms of cytochrome b559 remaining steady, whereas cytochromes b563 and f increased until the 8 mg l(-1) (145.6 microM) Mn treatment and the quinone pool increased until the highest Mn treatment. It was concluded that Mn-mediated inhibition of rice photosynthesis barely implicates stomatal conductance, as well as the distribution of energy within the photosystems. In this context, alterations to the relative proportions of the different acyl lipids and isoprenoids, as well as to the accumulations of the photosynthetic electron carriers, seem to play a major role.     

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?     

Effects of wind on a shallow lake ecosystem: Resuspension of particles in the Loosdrecht Lakes

Horizontal variation of seston concentration in the shallow, eutrophic Loosdrecht Lakes (A=9.8 km²; =1.9 m) was studied in relation to windspeed and effective fetch. Simple wave theory was applied in order to predict resuspension using wind data from a nearby meteorological station. Most results were consistent with the theory, but a clear limit for the occurrence of resuspension could not be established. Generally, changes in epipelon—the particles at the sediment-water interface — were not directly related to computed frequency of resuspension at the sampling station. The frequency was estimated for 37 grid points over the entire lake. Resuspension was computed to affect high percentages of the lake area in winter. In summer the frequency was much lower, but in June and July 1984 there were days with nearly 50% of the lake area subject to resuspension. The resulting input of particulate organic carbon into the water column during these days was estimated to equal 12–25 times the daytime phytoplankton carbon fixation. Most of the resuspended matter appeared to be redeposited rapidly. The computed frequency of resuspension for the 37 locations of the lake varied between 7 and 48 days in 1984.     

Forest biodiversity,ecosystem functioning and the provision of ecosystem services

Forests are critical habitats for biodiversity and they are also essential for the provision of a wide range of ecosystem services that are important to human well-being. There is increasing evidence that biodiversity contributes to forest ecosystem functioning and the provision of ecosystem services. Here we provide a review of forest ecosystem services including biomass production, habitat provisioning services, pollination, seed dispersal, resistance to wind storms, fire regulation and mitigation, pest regulation of native and invading insects, carbon sequestration, and cultural ecosystem services, in relation to forest type, structure and diversity. We also consider relationships between forest biodiversity and multifunctionality, and trade-offs among ecosystem services. We compare the concepts of ecosystem processes, functions and services to clarify their definitions. Our review of published studies indicates a lack of empirical studies that establish quantitative and causal relationships between forest biodiversity and many important ecosystem services. The literature is highly skewed; studies on provisioning of nutrition and energy, and on cultural services, delivered by mixed-species forests are under-represented. Planted forests offer ample opportunity for optimising their composition and diversity because replanting after harvesting is a recurring process. Planting mixed-species forests should be given more consideration as they are likely to provide a wider range of ecosystem services within the forest and for adjacent land uses. This review also serves as the introduction to this special issue of Biodiversity and Conservation on various aspects of forest biodiversity and ecosystem services.     

Linking biodiversity to ecosystem function: implications for conservation ecology

We evaluate the empirical and theoretical support for the hypothesis that a large proportion of native species richness is required to maximize ecosystem stability and sustain function. This assessment is important for conservation strategies because sustenance of ecosystem functions has been used as an argument for the conservation of species. If ecosystem functions are sustained at relatively low species richness, then arguing for the conservation of ecosystem function, no matter how important in its own right, does not strongly argue for the conservation of species. Additionally, for this to be a strong conservation argument the link between species diversity and ecosystem functions of value to the human community must be clear. We review the empirical literature to quantify the support for two hypotheses: (1) species richness is positively correlated with ecosystem function, and (2) ecosystem functions do not saturate at low species richness relative to the observed or experimental diversity. Few empirical studies demonstrate improved function at high levels of species richness. Second, we analyze recent theoretical models in order to estimate the level of species richness required to maintain ecosystem function. Again we find that, within a single trophic level, most mathematical models predict saturation of ecosystem function at a low proportion of local species richness. We also analyze a theoretical model linking species number to ecosystem stability. This model predicts that species richness beyond the first few species does not typically increase ecosystem stability. One reason that high species richness may not contribute significantly to function or stability is that most communities are characterized by strong dominance such that a few species provide the vast majority of the community biomass. Rapid turnover of species may rescue the concept that diversity leads to maximum function and stability. The role of turnover in ecosystem function and stability has not been investigated. Despite the recent rush to embrace the linkage between biodiversity and ecosystem function, we find little support for the hypothesis that there is a strong dependence of ecosystem function on the full complement of diversity within sites. Given this observation, the conservation community should take a cautious view of endorsing this linkage as a model to promote conservation goals. Received: 2 September 1999 / Accepted: 26 October 1999     

Context dependence of marine ecosystem engineer invasion impacts on benthic ecosystem functioning

Introduced ecosystem engineers can severely modify the functioning on invaded systems. Species-level effects on ecosystem functioning (EF) are context dependent, but the effects of introduced ecosystem engineers are frequently assessed through single-location studies. The present work aimed to identify sources of context-dependence that can regulate the impacts of invasive ecosystem engineers on ecosystem functioning. As model systems, four locations where the bivalve Ruditapes philippinarum (Adams and Reeve) has been introduced were investigated, providing variability in habitat characteristics and community composition. As a measure of ecosystem engineering, the relative contribution of this species to community bioturbation potential was quantified at each site. The relevance of bioturbation to the local establishment of the mixing depth of marine sediments (used as a proxy for EF) was quantified in order to determine the potential for impact of the introduced species at each site. We found that R. philippinarum is one of the most important bioturbators within analysed communities, but the relative importance of this contribution at the community level depended on local species composition. The net contribution of bioturbation to the establishment of sediment mixing depths varied across sites depending on the presence of structuring vegetation, sediment granulometry and compaction. The effects of vegetation on sediment mixing were previously unreported. These findings indicate that the species composition of invaded communities, and the habitat characteristics of invaded systems, are important modulators of the impacts of introduced species on ecosystem functioning. A framework that encompasses these aspects for the prediction of the functional impacts of invasive ecosystem engineers is suggested, supporting a multi-site approach to invasive ecology studies concerned with ecosystem functioning.     

Biodiversity effects on ecosystem functioning: insights from aquatic systems

Unprecedented rates of species extinctions have prompted extensive research into the consequences of biodiversity losses on ecosystem functioning. While aquatic species are most threatened, research with freshwater and marine model systems has lagged behind progress made in terrestrial environments. This editorial to a special feature summarizes the main outcomes of a conference aimed at setting the stage for exploring the potential of aquatic systems to assess the role of biodiversity in ecosystem functioning. This series of papers proposes fresh approaches to the study of biodiversity effects on ecosystem functioning, outlines a new way of analyzing experimental data, presents a model that considers scale as an important factor determining outcomes, explores the effects of multiple stressors on species richness and ecosystem processes, and develops a food-web perspective that relates ecosystem properties to biodiversity. An insightful synthesis of lessons learned from aquatic systems is premature at present, but the papers clearly demonstrate the role that marine and freshwater systems can play in resolving open questions. The implications go well beyond the biodiversity in, and functioning of, ecosystems shaped by free-flowing or standing water.     

Biodiversity and ecosystem functioning: the mystery of the deep sea

Experiments performed in various ecosystems have shown a near-universal, saturating relationship between biodiversity and ecosystem processes. Analyses of deep-sea ecosystems challenge this generalisation and suggest that positive species interactions might be more widespread than previously believed.     

Impacts of marine-derived nutrients on stream ecosystem functioning

Energy and nutrient subsidies transported across ecosystem boundaries are increasingly appreciated as key drivers of consumer-resource dynamics. As purveyors of pulsed marine-derived nutrients (MDN), spawning salmon are one such cross-ecosystem subsidy to freshwaters connected to the north Pacific. We examined how salmon carcasses influenced detrital processing in an oligotrophic stream. Experimental manipulations of MDN inputs revealed that salmon carcasses indirectly reduced detrital processing in streams through temporarily decoupling the detrital resource-consumer relationship, in which detrital consumers shifted their diet to the high-nutrient resource, i.e. salmon carcasses. The average decomposition rate of alder leaves with salmon carcass addition was significantly lower than that without the carcass, which was associated with lower abundance and biomass of detritivorous Trichoptera on the carcass-treated leaves. There were generally larger in size Trichopteran detritivores on the carcasses than on leaves. These results imply that cross-boundary MDN subsidies indirectly retard the ecosystem processing of leaf litter within the short term, but may enhance those food-limited detritivorous consumers. Because unproductive freshwaters in the Pacific northwest are highly dependent upon the organic matter inputs from surrounding forests, this novel finding has implications for determining conservation and management strategies of salmon-related aquatic ecosystems, in terms of salmon habitat protection and fisheries exploitation.     

The importance of meiofauna to lotic ecosystem functioning

• 1 Although meiofauna occur in large numbers in many streams, almost nothing is known about their functional role.
• 2 In other systems, meiofauna influence microbial and organic matter dynamics through consumption and bioturbation. Given that these are important processes in streams, meiofauna have the potential to influence lotic function by changing the quality and availability of organic matter as well as the number and biotic activity of benthic microbes. Selective feeding by meiofauna has the potential to alter the availability of nutrients and organic carbon.
• 3 Meiofauna generally contribute only a small amount to metazoan production and biomass in streams, although exceptions occur. Within a stream, the relative importance of meiofauna may reflect whether the temporary or permanent meiofauna dominate the meiobenthos as well as the season when samples are collected.
• 4 We suggest stream conditions (small sediment grain size, restricted interstitial flow) under which meiofauna have the greatest likelihood of influencing stream ecosystem function.
• 5 Important areas for future research include addressing whether meiofauna feed selectively, whether meiofauna are links or sinks for carbon in streams, and whether bioturbation by meiofauna influences stream ecosystem processes in a predictable manner.

     

Genetic mosaics of ecosystem functioning across aspen-dominated landscapes

Genetic diversity is the foundation of all biodiversity, and the genetic variation within species is increasingly recognized as being important to ecosystem level processes. Recent research demonstrates that plant genotype influences above- and belowground communities as well as basic ecosystem functions. However, the extent to which plant genotypes create spatial mosaics of genetically mediated ecosystem processes in natural forests is uncertain. We use Populus tremuloides as a model system to demonstrate the importance of plant genotype on carbon and nitrogen cycling in natural systems. We identified 24 distinct P. tremuloides clones with multiple ramets across 25 km² in southern Wisconsin, United States, using microsatellite makers. We then sampled clone leaf chemistry and belowground nutrient content and microbial extracellular enzyme activity. Aspen-induced variation in belowground carbon and nitrogen content, and microbial activity, varied widely among clones. Variation in green leaf chemistry and belowground microbial activity were correlated with genetic distance among clones, such that more genetically distant clones created more divergent patches of ecosystem processes. These data suggest that aspen genotypes create spatial mosaics of genetically mediated ecosystem functioning across natural landscapes and can therefore have evolutionary consequences for co-occurring species.     

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。     

Modeling transmembrane transport through cell membrane wounds created by acoustic cavitation

Cells exposed to acoustic cavitation and other mechanical stresses can be transiently permeabilized to permit intracellular uptake of molecules, including drugs, proteins, and genes. Microscopic imaging and other studies suggest that intracellular loading occurs through plasma membrane wounds of submicrometer radius that reseal over time through the aggregation and fusion of lipid vesicles trafficked to the wound site. The goal of this study was to 1), determine the size of membrane wounds as a function of time after in vitro sonication of DU145 prostate cancer cells under conditions that caused extensive acoustic cavitation; and 2), theoretically model transport processes leading to intracellular loading. Our overall hypothesis was that intracellular loading is governed by passive diffusion through porous membrane wounds of up to 300-nm radius containing pores that permit entry of molecules up to at least 28-nm radius over a timescale of minutes. Experimental measurements showed intracellular loading of molecules with radii from 0.6 to 28 nm, where most loading occurred after sonication over a timescale up to minutes and where smaller molecules were taken up to a greater extent and over a longer timescale than larger molecules. Theoretical modeling predicted that membrane wounds would have a 300-nm radius initially and then would shrink, with a half life of 20 to 50 s. Uptake was shown to occur predominantly by diffusion and the increasing levels of uptake with decreasing molecular size was explained primarily by differences in molecular diffusivity and, for the largest molecule, geometrical hindrance within the wound. Mathematical modeling was simplified, because transport through porous wounds of possibly complex internal nanostructure was governed largely by transport at the edge of the wound, and depended only weakly on the size, number, and distribution of nanopores within the wound under the conditions relevant to this study. Overall, this study developed a theoretical framework for analysis of transmembrane transport through cell membrane wounds and thereby provided quantitative estimates of their size and lifetime.