The Consequences of Changing Biodiversity - Solutions and Scenarios

Editors: Daniel Bunker, Andy Hector, Michel Loreau, Charles Perrings, and Shahid Naeem

1 Introductory material

1.1. Preface by the editors

1.2. Consequences of biodiversity loss in experimental ecosystems

Bernhard Schmid*, Patricia Balvanera, Andrea B. Pfisterer, David Raffaelli and Bradley Cardinale, Jasmin Godbold, Martin Solan, Diane Srivastava

Over the past 15 years a number of studies have manipulated species richness of particular groups of organisms in experimental ecosystems and measured a variety of response variables such as primary productivity, resource uptake, secondary productivity and diversity of un-manipulated groups of organisms. The heterogeneity of manipulations and response variables measured makes it difficult to assess general patterns in biodiversity relationships across studies. Here we combine approaches and data used in two recent meta-analyses to obtain deeper insight into these relationships and confront the pattern with predictions expected under the operation of different generating mechanisms. We will compare terrestrial with aquatic systems, manipulations of plant with manipulations of microbial diversity and responses of mass with responses of diversity variables. We expect that depending on the setting the number, difference or identity components of biodiversity predominantly determine the generating mechanisms.

2 Ecosystem Consequences of Biodiversity Loss

2.1. Measuring functional diversity and functional redundancy.

Owen Petchey, Dan Flynn*, Martin Solan, Justin Wright, Eoin O'Gorman

Spatial and temporal patterns in functional diversity can inform about the processes that structure species assemblages and the functional consequences of extinctions. Small functional consequences of extinctions indicate a certain extent of functional diversity. The important of these questions councils for care when measuring functional diversity. As an example pitfall, functional group richness is a measure of functional diversity that cannot be used to reliably inform about levels of redundancy. Here we show how different measures of functional diversity, some which incorporate species abundances and some which do not, alter our perception of functional diversity and redundancy. We also show how different types of functional traits used to calculate functional diversity affect perceived redundancy. In particular, we compare patterns of redundancy between effect and response functional traits. Finally, we discuss one remaining challenge for measuring functional diversity, how to include intraspecific variation in functional traits, and its likely impact on perceived redundancy.

2.2. Forecasting biodiversity change and loss of ecosystem function

Kate E. Jones*, Emmett Duffy, Jennie McLaren, Daniel E. Bunker, John Griffin, Eoin O'Gorman

In the face of our current extinction crisis, we need to move beyond recording past extinctions and the pattern of currently threatened or declining species to examine the processes driving these patterns. Only through an understanding of these processes can we build predictive models to forecast and prevent future extinction and loss of ecosystem services. It is likely that factors currently affecting and threatening biodiversity are some combination of anthropogenic threats, species biology and environmental stresses. However, how these specifically interact to influence biodiversity and concomitant ecosystem functioning is less certain. Here we review current progress in modelling and forecasting extinction in a number of different plant and animal groups on local and global scales, using both species-based and area-based approaches. We also investigate how changes in communities through the extinction of species with extinction prone traits (e.g., large body sizes, small geographic or home ranges) could cause ecosystem processes to alter and change the services ecosystems provide to humans.

2.3. Diversity and Stability

John Griffin*, Claire Jouseau, Amy Symstad, Loreau, Eoin O'Gorman

The effect of diversity on stability at population and community levels has emerged as a key issue in ecology. Whilst of fundamental importance to basic ecology, research in this area has taken on a renewed urgency in light of the current anthropogenic erosion of biodiversity. It is paramount that the diversity-stability debate is fully resolved if we are to understand whether, and to what extent, we are compromising the ability of communities to buffer, resist and recover from specific perturbations and background environmental variability. After a brief synopsis of the long-running debate and definitions of the various facets of stability, we comprehensively review recent theoretical advancements and empirical findings. Our focus is on assessing the relative importance of mechanisms linking diversity to various aspects of stability. The broad scope of this review incorporates diversity-stability in multi-trophic systems and the important lessons emerging from food-web analysis on the structural properties and mechanisms leading to stability in diverse systems. Finally, we provide a road-map to future advancements in this field, particularly emphasising areas where empirical verification of theory is lacking.

2.4. Biodiversity and ecosystem functioning: Advances in the analysis of relationships and mechanisms

Andy Hector*, Tom Bell, Jeremy Fox, Michel Loreau, Bernhard Schmid, Jasmin Godbold, Philippe Saner, and Jennie McLaren

The logistical constraint of performing a full-factorial analysis of the functional effects of all species in diverse communities has made the analysis and interpretation of biodiversity experiments extremely complex. There have been few recent major advances in the analysis of biodiversity patterns. A notable exception is the development of an experimental design which limits the potential for sampling effects and generates orthogonality between aspects of the richness and compositional components of biodiversity. The primary development in methodologies aimed at testing mechanisms has been an extension of the additive partitioning method. The complementarity effect from the original additive partition assumes that effects are spread equally over all species. This results in any inequality in the complementarity effect being confounded with the selection effect. The new tripartite extension of the additive partitioning method separates a new 'trait-dependent complementarity' out from the selection effect. Depending on the sign of the trait-dependent complementarity effect previous studies may have under- or over-estimated its effects. The few analyses done to date suggest that conclusions drawn with the two versions of the method are broadly consistent. However, a wider assessment is required. We discuss whether the two aspects of the complementarity effect are best interpreted separately or whether they could be combined into a new 'total complementarity effect'.

2.6. Ecosystem Consequences of Biodiversity Loss: Integrating complexity within and among trophic levels

Brad Cardinale*, Emmett Duffy, Claire Jouseau, Mahesh Sankaran, Diane Srivastava, Matthew Thomas

Ecologists have long sought to understand how the number of species in a food web can influence biological processes that are fundamental to the functioning of ecosystems. Even so, it wasn't until the 1990's that a large body of theory and empirical work begin to formalize this area of research. During this period, an increasing number of studies began to detail the functional role of biodiversity, with most of these studies using primary producers in grassland ecosystems as a model system. As the field of diversity-function research expanded from its origin to include a wider variety of organisms comprising multiple trophic levels, the focus generally remained on single trophic groups in isolation. There is now a growing sentiment among ecologists that if we are to truly understand the functional consequence of biodiversity loss, we must move beyond inferences from monotrophic groups of organisms, towards an understanding of the functional role of biodiversity within whole food webs. Here we summarize data from recent studies that have begun to integrate the complexity of diversity effects within and among trophic levels. We take advantage of datasets recently used for meta-analyses to address four broad questions: (i) does species diversity have a greater impact on resource consumption and the production of biomass at higher vs. lower trophic levels, (ii) can a higher (lower) trophic level t qualitatively alter the effect of species richness on resource consumption and biomass production at a lower (higher) level, (iii) do the impacts of extinction in any single trophic level cascade through a food web, and (iv) is the 'top-down' effect of biodiversity on resource consumption and production of biomass reinforcing or antagonistic to the 'bottom-up' effects of diversity in a food web? We conclude by outlining what we believe to be the unanswered questions and key extensions needed to move diversity-function research into a truly multi-trophic perspective.

2.7. Microbial diversity and functioning in the laboratory and in the wild

Thomas Bell*, Mark Gessner, Rob Griffiths, Jennie McLaren, Peter Morin, Shahid Naeem, Marcel van der Heijden, Wim van der Putten

The primary production and decomposition provided by microbial communities often underpins the functioning of terrestrial and aquatic ecosystems. Microbial communities also provide economically important services, for example by breaking down pollutants and sewage. We review the recent experiments that have constructed communities of microbes in the laboratory, and discuss why these experiments have occasionally produced conflicting results. In addition to the laboratory experiments, environmental microbiologists have now produced many in situ studies of the functioning of natural microbial communities. Natural microbial communities are notoriously complex, and there is ongoing debate both on how to measure microbial diversity and on how differences in microbial communities affect functioning. We suggest that there is a disconnect between the laboratory experiments and field studies. To try to remedy this, we contrast the results of the laboratory experiments with those of observational and experimental studies of natural microbial communities, and suggest explanations for some of the inconsistencies that exist between these lines of research.

3 Applied Consequences of Biodiversity Loss

3.1. Diversity and carbon storage

Daniel Bunker*, John Griffin; Andy Hector, Chris Phillipson; Philippe Saner, and Mahesh Sankaran

Carbon storage is emerging as a critical ecosystem service. We review the relationship between biodiversity and carbon storage, examining both the effects of functional diversity on C storage and the compatibility of biodiversity conservation and C storage as management goals. At the local scale, where neighborhood interactions determine the effects of functional diversity on carbon storage, available data suggest that while functional diversity may increase carbon storage, species composition is likely to play an important role as well. Specifically, species that promote a high C:N ratio within plant litter may slow decomposition and increase C storage. More broadly, we find that intact ecosystems are rich in both carbon and species diversity, whereas restoration often fails to recover fully either carbon or diversity. Efforts to extend the Kyoto protocol to include credit for forest conservation, in contrast to reforestation, will likely increase terrestrial carbon pools and increase biological diversity.

3.3. Restoration of Biodiversity and Ecosystem Function

James M. Bullock*, Amy Symstad, Justin Wright, Katia Engelhardt

Restoration of species and communities is the major approach to reversing biodiversity loss worldwide. Curiously, while there is much research into methods for restoration, this subject does not have a good theoretical basis. This lack has led to much debate about the utility of restoration, which is often based on philosophical positions rather than hard facts. In particular, there is a long-standing argument that while restoration may create communities which resemble their natural targets, these re-created systems are "facsimiles'' which lack critical functions. There is little evidence to support this suggestion. In fact, there is accumulating evidence that the restoration of diverse communities targeted to the local environment can enhance ecosystem functions. This can help with maintaining restored communities in the long-term, and even facilitate colonisation by desirable species, e.g. through creating pollinator networks or improving soil microbial processes. Critically, much restoration is on farmland, for example through agri-environment schemes. While farmers tend to regard restoration as leading to lower production and thus a cost, recent work is showing that restoration of biodiversity in low input farming systems can enhance certain ecosystem services. Those important to the farmer include increased quantity and quality of hay and other products, soil conservation and water retention. For society as a whole such restored communities, especially on former croplands, can provide benefits such as carbon sequestration as well as hotspots of biodiversity. In this chapter we provide a novel synthesis of biodiversity and ecosystem function in order to set up a rigorous theoretical basis to the new science of ecological restoration.

3.4. Biodiversity and Ecosystem Functions in Managed Ecosystems

Louise Jackson*, Amy Symstad, Matthew Thomas, and Justin Wright

Biodiversity is rapidly being lost in the landscapes that are dominated by managed ecosystems, largely as a result of intensified management and expansion into wildland areas. Agricultural, pastoral and forestry management occurs on nearly half of the terrestrial land area. This chapter will explore how sustainable production relies on the ability to utilize and conserve biodiversity for its ecosystem functions and services. There are three main themes in this chapter: 1) As intensification increases, managed ecosystems become increasingly depauperate in biodiversity compared to traditional management systems, also affecting wildland counterparts. 2) Basic ecological information on life history traits, phenology, and trophic interactions between species is needed to explain ecosystem processes for pest and pathogen control, nutrient cycling and ecosystem restoration, and thus to predict the effect of species richness on ecosystem services. 3) Integration of biophysical and socioeconomic research approaches strengthens the potential for utilizing and conserving biodiversity in human-dominated landscapes. From a fundamental perspective, the chapter will give examples of the complexity of species relationships that occur even in these apparently simplified types of ecosystems. From a more applied perspective, it will give examples of how the manipulation of biodiversity at different trophic levels can reduce the reliance on agricultural chemicals that have non-target effects on other biota including humans, as well as restore degraded ecosystems to increase their productivity and stability.

3.5. Consequences of biodiversity loss for pollination services

Alexandra-Maria Klein*, Christine Müller, Patrick Höhn

Flower-visiting insect diversity has been shown to improve pollination services to maintain reproduction of many wild plants and production of the majority of crop plants. Most studies, however, are correlative and cannot contrast effects of species richness and those of abundance for successful pollination, but a few exceptions show that species richness per se is more important for pollination success than abundance of flower-visiting insects.

The factors leading to declining pollinator diversity have been studied on both, the habitat and the landscape scale and studies on plant - pollinator webs show that the links between plants and pollinators are highly nested. Therefore, indirect community effects can become prevalent and nestedness may be a mechanism to infer stability against species loss. Some recent studies on pollinator webs inform about the role of species diversity and the importance of diversity for the community structure of plant-pollinator assemblages.
It has been suggested that complementary effects are responsible for the importance of diversity for pollination and it could be shown recently that pollinator morphology, foraging behaviour and inter-specific interactions leads to complementarity's among pollinating species.

We review the relevant studies and the currently known mechanisms that contribute to our understanding of the relationship between biodiversity and pollination success. We will point to future research needs that will be crucial in filling the gaps of current knowledge of the pollination function and its link to biodiversity. We will also summarize the ecological consequences of pollinator losses for natural communities in general and human well-being in particular.

3.6. Interactions between Biodiversity Loss and Infectious Disease

Richard S. Ostfeld, Felicia Keesing, and Matthew Thomas*

Infectious diseases of plants, wildlife, and humans can be influenced by species diversity, genetic diversity within species, and landscape-level diversity (e.g., number and types of land-cover types). In this chapter we provide an updated review of studies that assess the effects of biodiversity loss on disease dynamics. For pathogens that infect only one species of host (host specialists), the predominant mechanism by which diversity loss affects pathogen transmission is through impacts on the abundance and behavior of the host. Typically, host abundance is expected to be regulated more strongly in more diverse than in less diverse communities. Effects of diversity on behaviors that influence transmission are poorly studied. For pathogens that infect >1 species of host (host generalists), diversity loss additionally can influence: (1) interspecific transmission events; (2) the distribution of pathogens among various host species; and (3) virulence of the pathogen. The predominant effect of biodiversity loss is to increase risk, incidence, or rates of disease spread in host populations and communities, although some exceptions have been noted. We argue that the reduction of disease risk, incidence, or spread should be considered an ecosystem function provided by biodiversity.
In addition to effects of biodiversity loss on the dynamics of pathogens and their hosts, pathogens can affect biodiversity via their impacts on host populations. Increasingly, pathogens are used as agents for intentionally controlling exotic species and pests. Some of these pests (e.g., Anopheles mosquitoes) themselves are involved in transmitting pathogens. Therefore, biodiversity loss can affect pathogens, pathogens can affect biodiversity, and these reciprocal interactions can occur simultaneously. We provide examples of this feedback loop between biodiversity and pathogens.

3.7. The economics of biodiversity loss and ecosystem services

Charles Perrings*, Claire Jouseau, Anne Hélène Prieur-Richard, Matthew Thomas

Forthcoming

3.8. The influence of invasive species on the relationship between biodiversity change and ecosystem functioning - A critical evaluation of the negative, positive, and neutral impacts of invasive species.

Katia Engelhardt*, Amy Symstad, Thomas, Helene Prieur-Richard

Ecosystems around the world are witnessing one of the largest natural experiments in human history - the introduction of species into new areas either through natural range expansion, the breakdown of dispersal barriers, or the human transport of viable populations. Society and natural resource managers generally consider the introduction of non-natives to be detrimental to biodiversity and ecosystem functioning. As a consequence, millions of dollars are spent each year in the United States alone to eradicate or control invasive species populations. The impacts of some species are real and documented by rigorous science, such as the brown tree snake in Guam and salt cedar in the southwestern U.S. However, society's tendency is to generalize from the relatively few high-profile case studies that report a negative impact, thereby fueling the popular sentiment that non-native species are detrimental to ecosystems (Hager and McCoy 1998, Slobodkin 2001). Our proposed chapter intends to place invasive species into a general context that (1) critically evaluates the relative effects of invasive species on biodiversity; these impacts may be negative or positive, weak or strong. Once we better understand the impacts of invasive species on biodiversity, we can start developing linkages between biodiversity and ecosystem functioning with invasive species enhancing or dampening the effects of biodiversity loss (or gain) on ecosystem functioning. Specifically, we plan to (2) review common traits of invaders that allow them to respond to environmental change (response traits) and affect ecosystem functioning (effect traits). We also plan to broadly (3) review the patterns and processes of the impact of plant and animal invasions on biodiversity and ecosystem functioning. Finally, we plan to (4) develop a process-oriented framework for evaluating why, or why not, invasive species trigger changes in ecosystem functioning through affecting biodiversity.

4 Future directions

4.1. Biodiversity-ecosystem function research and biodiversity futures: Early bird catches the worm or a day late and a dollar short?

Martin Solan*, Jasmin Godbold, et al…

Following over a decade of intensive research it is now clear that changes in biodiversity affect key ecosystem properties and that biodiversity loss has compromised service delivery in a broad range of systems. These findings have raised concern over the consequences of ecosystem change for human well-being and have prompted international calls for a sound scientific basis to support future management decisions and policy. Articulating the appropriate interpretation of biodiversity and ecosystem functioning research is of fundamental importance, however achieving this goal is proving difficult. Discussion surrounding fundamental differences in opinion over experimental methodology and the interpretation of results give the impression that the BEF community is divided and that advice is contradictory, discrediting scientific findings to the wider ecological community. Recent quantitative analyses have reinforced this viewpoint by revealing that the conclusions of empirical studies are not always consistent with theoretical predictions, thereby increasing the potential for extending debate. Yet, current projections of biodiversity loss and global change warrant a rapid response from the scientific community if we are to provide a tenable solution to the biodiversity crisis. The gradual dissemination of results and ideology through the literature is inefficient and likely to frustrate timely application of any practical solutions. It is clear that a fundamental shift in current practice is urgently required, otherwise the BEF community runs the risk of being an independent, primarily academic field that does not contribute to environmental policy or impending global scale problems.

4.2. Can we predict the effects of global change and the concomitant loss of species on ecosystem function?

Editors