Quantifying effects of biodiversity on ecosystem functioning across times and places

Biodiversity loss decreases ecosystem functioning at the local scales at which species interact, but it remains unclear how biodiversity loss affects ecosystem functioning at the larger scales of space and time that are most relevant to biodiversity conservation and policy. Theory predicts that additional insurance effects of biodiversity on ecosystem functioning could emerge across time and space if species respond asynchronously to environmental variation and if species become increasingly dominant when and where they are most productive. Even if only a few dominant species maintain ecosystem functioning within a particular time and place, ecosystem functioning may be enhanced by many different species across many times and places (β‐diversity). Here, we develop and apply a new approach to estimate these previously unquantified insurance effects of biodiversity on ecosystem functioning that arise due to species turnover across times and places. In a long‐term (18‐year) grassland plant diversity experiment, we find that total insurance effects are positive in sign and substantial in magnitude, amounting to 19% of the net biodiversity effect, mostly due to temporal insurance effects. Species loss can therefore reduce ecosystem functioning both locally and by eliminating species that would otherwise enhance ecosystem functioning across temporally fluctuating and spatially heterogeneous environments.     

What does biodiversity actually do? A review for managers and policy makers

Conservation managers and policy makers must often justify the need for protection of biodiversity. However, results of scientific studies testing for a positive value of biodiversity in terms of community stability and ecosystem function have been complex and inconsistent. We review recent information on the consequences of loss of biodiversity for natural systems. The relationships described vary with scale of interest – for instance, biodiversity at local scales typically has strong effects on ecosystem function, although the opposite relationship is often found at regional scales. These inconsistencies lead to some concern as to whether these relationships can be used to justify biodiversity protection. This is particularly relevant to policy, where holistic protection of biodiversity has most often been mooted and justified. For managers, who most often work to protect single species, communities or ecosystem functions, biodiversity research has failed to address questions of critical concern such as consequences of the loss of rare species or the identification of functional keystone species. For the general public, we believe that the confusion and debate surrounding biodiversity and ecosystem function relationships is in danger of eroding the positive value society places on biodiversity. We further warn that using those relationships in policy documents as justifications for biodiversity protection is fraught with difficulties. Finally, we contend that biodiversity research has largely not addressed issues of concern to conservation managers, and list a set of priorities for relevant research on the consequences of biodiversity loss.     

关键种，关键在哪儿？

 物种在生态系统功能过程中并不是同等重要的,这已经是一个普遍接受的事实,而关键种和冗余种被认为是生态系统功能过程中两类极端的生物类群。由于关键种通常被认为在生态系统功能方面中有重要作用,因此有人认为,假如我们能够甄别生态系统中的关键种及其多方面影响的作用机制,我们就有可能得到整个或大部分生态系统功能过程的信息。因此,在考虑生物多样性保护,尤其是为了有效保护它们所产生的生态系统功能过程时,生态学家和保护生物学家们引入了关键种的概念。通过对关键种的保护,更有效地保护其所在生态系统的功能过程。通过对有关关键种研究的回顾,阐述了关键种的定量测度方法,关键种在保护生物学中的意义、应用及其局限。     

生物多样性与稳定性机制研究进展

随着全球生物多样性的迅速丧失,生物多样性与生态系统稳定性的关系已成为人类面临的重要科学问题。许多研究表明生物多样性与稳定性存在正相互关系,但其内在机制尚不能被很好地理解并且存在争议。对生物多样性与稳定性的研究历史做简短的回顾,然后根据时间稳定性的计算方法将时间稳定性分为平均值、方差之和以及协方差之和3个统计组成部分,在此基础上对现在常见的生物多样性-稳定性机制进行分类和详细介绍。并对现在生物多样性和稳定研究的争论进行总结。建议未来生物多样性稳定性关系的研究应该建立更加综合的理论,增加实验时间,应用整合分析(meta-analysis)对已发表实验结果进行综合分析,此外,应多关注非生物量/多度的属性,控制物种属性而不是仅仅控制物种的数量。     

Analyzing the effects of species gain and loss on ecosystem function using the extended Price equation partition

In nature species richness and composition, as well as the functioning of individual species, all covary along environmental gradients, making it difficult to tease apart their effects on ecosystem function. Here we use a novel extension of the Price equation to partition the causes of functional variation between any two sites sharing at least one species in common. We use the extension to separate effects of species loss from those of species gain; species gain is analogous to migration in evolution. Previous theoretical and empirical studies of biodiversity and ecosystem function fail to distinguish effects of species gain from those of species loss, and so are conceptually incomplete. Application of this approach to data on total plant biomass along an experimental N enrichment gradient leads to novel empirical insights and reveals subtle effects. For instance, effects of species gain are non‐negligible even though enrichment leads to loss of many species and gain of few, and non‐random gain of high‐biomass species reduces the biomass of the persisting species. We also discuss the interpretation of this new approach, which provides a highly‐general partitioning of the factors affecting ecosystem function.     

On the importance of the negative selection effect for the relationship between biodiversity and ecosystem functioning

Much of our knowledge on biodiversity and ecosystem functioning comes from studies examining the effects of biodiversity on biomass production within a trophic group. A large number of these studies have found that increasing biodiversity tends to increase biomass production, leading many ecologists to believe that there exists a general positive relationship between biodiversity and ecosystem functioning. Here we argue that such a positive relationship may not be general, particularly for ecosystem functions other than biomass. Our argument centers on the potential importance of the negative selection effect, which operates where competitively dominant species do not contribute significantly to the function of interest. We suggest that negative selection effects may be potentially common for non-biomass functions, for which species competitive ability may often be a poor indictor of its functional impact. We conclude that diverse (positive, negative, and neutral) BEF relationships are possible for non-biomass functions and that for a particular function, the exact form of the BEF relationship may depend on how species functional impacts relate to their competitive abilities in the community.     

Complex interactions among mammalian carnivores in Australia, and their implications for wildlife management

Mammalian carnivore populations are often intensively managed, either because the carnivore in question is endangered, or because it is viewed as a pest and is subjected to control measures, or both. Most management programmes treat carnivore species in isolation. However, there is a large and emerging body of evidence to demonstrate that populations of different carnivores interact with each other in a variety of complex ways. Thus, the removal or introduction of predators to or from a system can often affect other species in ways that are difficult to predict. Wildlife managers must consider such interactions when planning predator control programmes. Integrated predator control will require a greater understanding of the complex relationships between species. In many parts of the world, sympatric species of carnivores have coexisted over an evolutionary time scale so that niche differentiation has occurred, and competition is difficult to observe. Australia has experienced numerous introductions during the past 200 years, including those of the red fox (Vulpes vulpes) and the feral cat (Felis catus). These species now exist in sympatry with native mammalian predators, providing ecologists with the opportunity to study their interactions without the confounding effects of coevolution. Despite an increasing body of observational evidence for complex interactions among native and introduced predators in Australia, few studies have attempted to clarify these relationships experimentally, and the interactions remain largely unacknowledged. A greater understanding of these interactions would provide ecologists and wildlife managers world-wide with the ability to construct robust predictive models of carnivore communities, and to identify their broader effects on ecosystem functioning. We suggest that future research should focus on controlled and replicated predator removal or addition experiments. The dingo (Canis lupus dingo), as a likely keystone species, should be a particular focus of attention.     

The Importance of Microhabitat for Biodiversity Sampling

Responses to microhabitat are often neglected when ecologists sample animal indicator groups. Microhabitats may be particularly influential in non-passive biodiversity sampling methods, such as baited traps or light traps, and for certain taxonomic groups which respond to fine scale environmental variation, such as insects. Here we test the effects of microhabitat on measures of species diversity, guild structure and biomass of dung beetles, a widely used ecological indicator taxon. We demonstrate that choice of trap placement influences dung beetle functional guild structure and species diversity. We found that locally measured environmental variables were unable to fully explain trap-based differences in species diversity metrics or microhabitat specialism of functional guilds. To compare the effects of habitat degradation on biodiversity across multiple sites, sampling protocols must be standardized and scale-relevant. Our work highlights the importance of considering microhabitat scale responses of indicator taxa and designing robust sampling protocols which account for variation in microhabitats during trap placement. We suggest that this can be achieved either through standardization of microhabitat or through better efforts to record relevant environmental variables that can be incorporated into analyses to account for microhabitat effects. This is especially important when rapidly assessing the consequences of human activity on biodiversity loss and associated ecosystem function and services.     

Weighting and indirect effects identify keystone species in food webs

Species extinctions are accelerating globally, yet the mechanisms that maintain local biodiversity remain poorly understood. The extinction of species that feed on or are fed on by many others (i.e. ‘hubs’) has traditionally been thought to cause the greatest threat of further biodiversity loss. Very little attention has been paid to the strength of those feeding links (i.e. link weight) and the prevalence of indirect interactions. Here, we used a dynamical model based on empirical energy budget data to assess changes in ecosystem stability after simulating the loss of species according to various extinction scenarios. Link weight and/or indirect effects had stronger effects on food‐web stability than the simple removal of ‘hubs’, demonstrating that both quantitative fluxes and species dissipating their effects across many links should be of great concern in biodiversity conservation, and the potential for ‘hubs’ to act as keystone species may have been exaggerated to date.     

Multifunctionality of biocrusts is positively predicted by network topologies consistent with interspecies facilitation

The potential of biodiversity loss to impair the delivery of ecosystem services has motived ecologists to better understand the relationship between biodiversity and ecosystem functioning. Although increasing evidence underlines the collective contribution of different biodiversity components on the simultaneous performance of multiple functions (multifunctionality), we know little about the trade‐offs between individual diversity effects and the extent to which they determine multifunctionality differentially. Here, at a subcontinental scale of 62 dryland sites, we show in phototrophic microbiota of biological soil crusts (biocrusts) that, whereas richness alone is unable to guarantee the maxima of multifunctional performance, interspecies facilitation and compositional identity are particularly stronger but often neglected predictors. The inconsistent effects of different biodiversity components imply that soil multifunctionality can be lost despite certain species remaining present. Moreover, we reveal a significant empirical association between species functional importance and its topological feature in co‐occurrence networks, indicating a functional signal of species interaction. Nevertheless, abundant species tend to isolate and merely interact within small topological structures, but rare species were tightly connected in complicated network modules. Our findings suggest that abundant and rare species of soil phototrophs exhibit distinct functional relevance. These results give a comprehensive view of how soil constructive species drive multifunctionality in biocrusts and ultimately promote a deeper understanding of the consequences of biodiversity loss in real‐world ecosystems.     

生物多样性与生态系统功能:进展与争论

生物多样性与生态系统功能的关系已成为当前人类社会面临的一个重大科学问题,生物多样性的空前丧失,促使人们开展了大量研究工作来描述物种多样性-生态系统功能关系,并试图揭示多样性与系统功能关系的内在机制,本文将多样性对生态系统功能作用机制的有关假说分为统计学与生物学两大类：前者是从统计学角度来解释观察到的多样性-系统功能模式,包括抽样效应,统计均衡效应等;而后者是基于多样性的生物学效应给出的,包括生态位互补,种间正相互作用,保险效应等,本文较为详细地介绍了该领域内有代表性的实验工作,包括“生态箱”实验,Cedar Creek草地多样性实验,微宇宙实验,欧洲草地实验,以及在这些实验结果解释上的激烈争论。     

New Insights into the Consequences of Post-Windthrow Salvage Logging Revealed by Functional Structure of Saproxylic Beetles Assemblages

Windstorms, bark beetle outbreaks and fires are important natural disturbances in coniferous forests worldwide. Wind-thrown trees promote biodiversity and restoration within production forests, but also cause large economic losses due to bark beetle infestation and accelerated fungal decomposition. Such damaged trees are often removed by salvage logging, which leads to decreased biodiversity and thus increasingly evokes discussions between economists and ecologists about appropriate strategies. To reveal the reasons behind species loss after salvage logging, we used a functional approach based on four habitat-related ecological traits and focused on saproxylic beetles. We predicted that salvage logging would decrease functional diversity (measured as effect sizes of mean pairwise distances using null models) as well as mean values of beetle body size, wood diameter niche and canopy cover niche, but would increase decay stage niche. As expected, salvage logging caused a decrease in species richness, but led to an increase in functional diversity by altering the species composition from habitat-filtered assemblages toward random assemblages. Even though salvage logging removes tree trunks, the most negative effects were found for small and heliophilous species and for species specialized on wood of small diameter. Our results suggested that salvage logging disrupts the natural assembly process on windthrown trees and that negative ecological impacts are caused more by microclimate alteration of the dead-wood objects than by loss of resource amount. These insights underline the power of functional approaches to detect ecosystem responses to anthropogenic disturbance and form a basis for management decisions in conservation. To mitigate negative effects on saproxylic beetle diversity after windthrows, we recommend preserving single windthrown trees or at least their tops with exposed branches during salvage logging. Such an extension of the green-tree retention approach to windthrown trees will preserve natural succession and associated communities of disturbed spruce forests.     

Non‐additive effects of invasive tree litter shift seasonal N release: a potential invasion feedback

Many invasive plant species strongly alter ecosystem processes by producing leaf litter that decomposes faster and releases N more quickly than that of native species. However, while most studies of invasive species litter impacts have only considered the decomposition of species in monoculture, forest litter layers typically contain litter from many species. Many litter mixtures decompose in a non‐additive manner, in which the mixture decomposes more quickly (synergistic effect) or more slowly (antagonistic effect) than would be expected based on decomposition of the component species’ litters in isolation. We investigated the potential for non‐additive effects of invasive species’ litter by conducting a one‐year litter bag experiment in which we mixed the litters of four native tree species with each of four invasive species. Litter mixtures frequently lost mass at non‐additive rates, although not at every loading ratio, and the presence, sign, and strength of effects depended on species composition. Non‐additive effects on N loss occurred in more litter combinations, and were almost always antagonistic at 90 days and synergistic at 365 days. Invasive species litter with lower C:N led to more strongly synergistic N loss with time. During the growing season, non‐additive patterns of N loss almost always resulted in increased N release – up to six times greater than would be expected based on single‐species decomposition. Consequently, we suggest that invasive species may further synchronize N release from the litter layer with plant N demand, enhancing any positive litter feedback to invasion. These results highlight the need to consider non‐additive effects of litter mixing in invaded forest communities, and suggest that estimates of invasive species’ impacts on ecosystem processes would be improved by considering these effects.     

Assessing the ecology in ecotoxicology: a review and synthesis in freshwater systems

The field of ecotoxicology is experiencing a surge in attention among ecologists as we gain a deeper appreciation for how contaminants can impact natural ecosystems. This interest is particularly strong in aquatic systems where many non-target organisms experience pesticides. In this article, we assess how pesticides affect freshwater systems by applying the conceptual framework of density- and trait-mediated indirect effects from the field of basic ecology. We demonstrate the utility of this framework for understanding the conditions under which pesticides affect species interactions, communities and ecosystems. Through the integration of laboratory toxicity tests and this ecological framework, ecotoxicologists should be better able to identify the mechanisms through which pesticides affect communities and ecosystems. We also identify several areas of research that are in critical need of empirical attention including synergistic effects between pesticides and natural stressors, the importance of pesticides on community assembly via habitat preferences and oviposition effects, the timing and frequency of pesticide applications, pesticide effects on population dynamics, the evolution of pesticide resistance in non-target organisms and ecosystem recovery. With this knowledge, one can improve upon management decisions and help protect non-target species that are of conservation concern.     

Quantifying the evidence for biodiversity effects on ecosystem functioning and services

Concern is growing about the consequences of biodiversity loss for ecosystem functioning, for the provision of ecosystem services, and for human well being. Experimental evidence for a relationship between biodiversity and ecosystem process rates is compelling, but the issue remains contentious. Here, we present the first rigorous quantitative assessment of this relationship through meta-analysis of experimental work spanning 50 years to June 2004. We analysed 446 measures of biodiversity effects (252 in grasslands), 319 of which involved primary producer manipulations or measurements. Our analyses show that: biodiversity effects are weaker if biodiversity manipulations are less well controlled; effects of biodiversity change on processes are weaker at the ecosystem compared with the community level and are negative at the population level; productivity-related effects decline with increasing number of trophic links between those elements manipulated and those measured; biodiversity effects on stability measures ('insurance' effects) are not stronger than biodiversity effects on performance measures. For those ecosystem services which could be assessed here, there is clear evidence that biodiversity has positive effects on most. Whilst such patterns should be further confirmed, a precautionary approach to biodiversity management would seem prudent in the meantime.     

Stochastic formulation of ecological models and their applications

The increasing use of computer simulation by theoretical ecologists started a move away from models formulated at the population level towards individual-based models. However, many of the models studied at the individual level are not analysed mathematically and remain defined in terms of a computer algorithm. This is not surprising, given that they are intrinsically stochastic and require tools and techniques for their study that may be unfamiliar to ecologists. Here, we argue that the construction of ecological models at the individual level and their subsequent analysis is, in many cases, straightforward and leads to important insights. We discuss recent work that highlights the importance of stochastic effects for parameter ranges and systems where it was previously thought that such effects would be negligible.     

Consequences of Lemur Loss for Above-Ground Carbon Stocks in a Malagasy Rainforest

Anthropogenic disturbances have resulted in declines of seed-dispersing primate frugivores in tropical forests. Previous work has suggested that loss of seed dispersal by large frugivores may have a negative impact on ecosystem carbon storage by reducing tree biomass. However, we know little about the potential impacts of losing frugivores in Madagascar’s diverse rainforest ecosystem. Understanding the effects of frugivore extinction on carbon loss is relevant in Madagascar, where threatened lemur taxa are the only dispersers of many large-seeded plant species. Using a dataset of tree species composition and traits from the southeastern rainforests of Ranomafana National Park, we examined whether seed size and lemur-dependent dispersal are positively associated with above-ground tree biomass. We then simulated different scenarios of population declines of large-seeded trees (>10 mm seed length) dependent on lemur-mediated seed dispersal, to examine potential directional changes in carbon storage capacity of Malagasy forests under lemur loss. Lemur-dispersed tree species, which have large seeds, had higher above-ground biomass than other species. Our simulations showed that the loss of large frugivorous primates in Madagascar may decrease the forest’s potential to store carbon. These results demonstrate the importance of primate conservation for maintaining functioning ecosystems and forest carbon stocks in one of the world’s hottest hotspots of biodiversity.     

Anthropogenic impacts on tropical forest biodiversity: a network structure and ecosystem functioning perspective

Huge areas of diverse tropical forest are lost or degraded every year with dramatic consequences for biodiversity. Deforestation and fragmentation, over-exploitation, invasive species and climate change are the main drivers of tropical forest biodiversity loss. Most studies investigating these threats have focused on changes in species richness or species diversity. However, if we are to understand the absolute and long-term effects of anthropogenic impacts on tropical forests, we should also consider the interactions between species, how those species are organized in networks, and the function that those species perform. I discuss our current knowledge of network structure and ecosystem functioning, highlighting empirical examples of their response to anthropogenic impacts. I consider the future prospects for tropical forest biodiversity, focusing on biodiversity and ecosystem functioning in secondary forest. Finally, I propose directions for future research to help us better understand the effects of anthropogenic impacts on tropical forest biodiversity.     

The growing difference between limnology and aquatic ecology

Research objectives of ecology and limnology differ: in the first emphasis is on the species approach and in the second on the ecosystem approach. It is stressed that the formation of compartments in ecosystem studies leads to a loss of information essential to the understanding of ecosystem functioning. The disciplines differ in yet another respect, namely the predominance of biotic factors in ecological research and of abiotic factors in limnological research. The research of aquatic ecologists is mostly species oriented thus compares better with ecology than with limnology. The raised points of discussion are illustrated with examples from studies of the author and his co-workers into diel vertical migration of zooplankton. As a final conclusion, it is suggested that feedback information flows regulate quantities of compartments and material flows. A picture in which material flows between compartments is combined with immaterial flows of information is presented. Last but not least, the increasing attention of limnologists, especially in The Netherlands, to applied research is considered a danger for the development of limnology as a science and for the education of students. Thus a plea is made to concentrate on fundamental research at least by those at universities and research institutes originally established with the aim to do pure science.     

Abrupt declines in marine phytoplankton production driven by warming and biodiversity loss in a microcosm experiment

Rising sea surface temperatures are expected to lead to the loss of phytoplankton biodiversity. However, we currently understand very little about the interactions between warming, loss of phytoplankton diversity and its impact on the oceans' primary production. We experimentally manipulated the species richness of marine phytoplankton communities under a range of warming scenarios, and found that ecosystem production declined more abruptly with species loss in communities exposed to higher temperatures. Species contributing positively to ecosystem production in the warmed treatments were those that had the highest optimal temperatures for photosynthesis, implying that the synergistic impacts of warming and biodiversity loss on ecosystem functioning were mediated by thermal trait variability. As species were lost from the communities, the probability of taxa remaining that could tolerate warming diminished, resulting in abrupt declines in ecosystem production. Our results highlight the potential for synergistic effects of warming and biodiversity loss on marine primary production.