Ecosystem Functioning Research Research Articles

Proteomic characterization of Pseudogymnoascus spp. isolates from polar and temperate regions

ABSTRACT Proteomics has been used extensively in the field of mycology, mainly in trying to understand the complex network of protein-protein interactions that has been implicated in the molecular functions of fungi. It is also a useful tool to compare metabolic differences within a genus. Species of Pseudogymnoascus, a genus under the phyla Ascomycota, have been shown to play an important role in the soil environment. They have been found in both polar and temperate regions and are a known producer of many extracellular hydrolases that contribute to soil decomposition. Despite the apparent importance of Pseudogymnoascus spp. in the soil ecosystem, investigations into their molecular functions are still very limited. In the present study, proteomic characterization of six Pseudogymnoascus spp. isolated from three biogeographic regions (the Arctic, Antarctic, and temperate regions) was carried out using tandem mass spectrometry. Prior to proteomic analysis, the optimization for protein extraction was carried out. Trichloroacetic acid‑acetone‑phenol was found to be the best extraction method to be used for proteomic profiling of Pseudogymnoascus spp. The proteomic analysis identified 2003 proteins that were successfully mapped to the UniProtKB database. The identified proteins were clustered according to their biological processes and molecular functions. The shared proteins found in all Pseudogymnoascus spp. (1201 proteins) showed a significantly close relationship in their basic cellular functions, despite differences in morphological structures. Analysis of Pseudogymnoascus spp. proteome also identified proteins that were unique to each region. However, a high number of these proteins belonged to protein families of similar molecular functions, namely, transferases and hydrolases. Our proteomic data can be used as a reference for Pseudogymnoascus spp. across different global regions and a foundation for future soil ecosystem function research.

Editorial: Remote sensing advances in biodiversity and ecosystem functioning research

Editorial: Remote sensing advances in biodiversity and ecosystem functioning research

Hill-Chao numbers allow decomposing gamma multifunctionality into alpha and beta components.

Biodiversity-ecosystem functioning (BEF) research has provided strong evidence and mechanistic underpinnings to support positive effects of biodiversity on ecosystem functioning, from single to multiple functions. This research has provided knowledge gained mainly at the local alpha scale (i.e. within ecosystems), but the increasing homogenization of landscapes in the Anthropocene has raised the potential that declining biodiversity at the beta (across ecosystems) and gamma scales is likely to also impact ecosystem functioning. Drawing on biodiversity theory, we propose a new statistical framework based on Hill-Chao numbers. The framework allows decomposition of multifunctionality at gamma scales into alpha and beta components, a critical but hitherto missing tool in BEF research; it also allows weighting of individual ecosystem functions. Through the proposed decomposition, new BEF results for beta and gamma scales are discovered. Our novel approach is applicable across ecosystems and connects local- and landscape-scale BEF assessments from experiments to natural settings.

Legume integration for biological control deserves a firmer scientific base

Diversification measures are widely recognized for their potential to enhance the resilience of agri-food production systems under global change. Nitrogen-fixing legumes commonly feature in diversification schemes, where they exert positive impacts on soil structure, nutrient retention, carbon sequestration or fertilizer reduction. Though legumes are premier tools for conservation agriculture, their impacts on (invertebrate, microbial) biological control are far less clear. As legumes secrete copious amounts of energy-rich (floral, extra-floral) nectar and provide alternative host or prey items for resident natural enemies, their deployment is expected to benefit biological control. Yet, its mechanistic basis is poorly understood and scientific underpinnings weak. In this Perspective piece, we collate data from the published literature and open-access databases on the extent to which different natural enemy guilds interact with 25 legume species that are commonly used as intercrops in the (sub)tropics. Our work unveils how natural enemies regularly forage on legumes, but the portrayal of those interaction linkages –or “biostructure” data- is profoundly incomplete and their ensuing implications for biological control are under-investigated. For instance, merely 4 (out of 167) parasitoids of the globally invasive fall armyworm Spodoptera frugiperda have been recorded in association with legumes. We hope that this Perspective piece will stimulate further thought, drive a new wave of biodiversity x ecosystem function research, and ultimately result in the design and implementation (or preservation) of more resilient, resource-frugal and pest-suppressive farming systems.

Chilean blind spots in soil biodiversity and ecosystem function research

AbstractSoil harbour up to a quarter of the world's biodiversity, substantially contributing to many ecosystem functions and processes. It is significantly important to identify the distribution patterns of soil organisms and their ecosystem functions, to support their conservation efforts and to build policy around them. This has been recently analysed at macroecological scales, but analyses at national or local scales are scarce. Here, we identify and analyse the blind spots in soil taxa and ecosystem functions data in continental Chile. A Web of Science search (1945–2020) was conducted focusing on ten soil taxa and four ecosystem functions (nutrient cycling, decomposition, water infiltration and soil respiration). A total of 741 sampling sites were obtained from 239 articles: in 49.25% of these sites, soil biodiversity was studied alone, while this percentage was 32.65% for ecosystem functions. In 18.10% of the sites, both soil biodiversity and ecosystem functions were jointly studied, a surprisingly high percentage compared to global‐scale studies. By far, bacteria/fungi and nutrient cycling were the most investigated taxa and function, respectively. Several soil taxa (Acari, Collembola, Nematoda, Formicoidea, Protista, Rotifera) were represented by just a few sampling sites concentrated in specific Chilean regions. Places like the central region (Metropolitan and Valparaíso administrative Regions), the Atacama Desert (north of the country) and the Valdivian temperate forests (La Araucanía, Los Ríos and Los Lagos administrative Regions) present the majority of studies on soil Fungi, Bacteria and nutrient cycling, reflecting the historical interests of well‐established research groups. Based on this research, we are identifying the causes of the data blind spots and inviting the Chilean soil ecology community to propose ideas on how to fill them, especially targeting less studied soil taxa and ecosystem functions in neglected regions of Chile.

An interdisciplinary framework to describe and evaluate the functioning of forest ecosystems

Forest ecosystems are shaped by internal dynamics and external factors like forest management. A modified physical appearance of ecosystems may affect the short- and long-term provision of ecosystem goods and services (EG&S) from forests. Ecosystem functioning research provides powerful tools for both, the mechanistic description of ecosystem dynamics and the normative assessment of the value of ecosystems. Holistic insights into the functioning of ecosystems require interdisciplinary projects. However, disciplinary differences in terminology and implicit underlying assumptions about relationships between descriptive ecosystem characteristics and their relevance for society may lead to misunderstandings hindering conceptual integration of disciplines. This highlights the need for a common language in ecosystem functioning research. Here, we provide a classification scheme of different types of ecosystem characteristics applicable across disciplines. We introduce a terminology that unambiguously differentiates between normative and descriptive uses of the terms ‘ecosystem function’, ‘ecosystem functioning’ and ‘ecosystem goods and services’. Based on this terminology, we propose a framework facilitating the explicit communication of hypotheses, underlying assumptions, analyses and conclusions belonging to three different aspects of ecosystem functioning: (1) mechanistic ecosystem functioning, (2) supplying ecosystem functioning and (3) ecosystem integrity. ‘Mechanistic ecosystem functioning’ addresses relationships and interactions between purely descriptive ecosystem characteristics and their dependence on external factors. ‘Supplying ecosystem functioning’ translates descriptive ecosystem characteristics into benefits for society in providing EG&S. ‘Ecosystem integrity’ assesses the capabilities of ecosystems to provide EG&S in the long term. We further propose the use of a mathematical interpretation of the term ‘ecosystem function’ as ‘characteristic A is the function of characteristics B, C, …, X’. This definition clearly accounts for complex relationships between ecosystem characteristics and avoids ambiguity inherent in the discrimination of ‘ecosystem-functions’ and other (‘non-functional’) ecosystem characteristics. Our approach will increase understanding across disciplines and foster joint syntheses by providing a unified framework for interdisciplinary studies.

Towards a multidimensional view of biodiversity and ecosystem functioning in a changing world

Towards a multidimensional view of biodiversity and ecosystem functioning in a changing world

A cross‐scale assessment of productivity–diversity relationships

AbstractAimBiodiversity and ecosystem productivity vary across the globe, and considerable effort has been made to describe their relationships. Biodiversity and ecosystem functioning research has traditionally focused on how experimentally controlled species richness affects net primary productivity (S → NPP) at small spatial grains. In contrast, the influence of productivity on richness (NPP → S) has been explored at many grains in naturally assembled communities. Mismatches in spatial scale between approaches have fuelled debate about the strength and direction of biodiversity–productivity relationships. Here, we examine the direction and strength of the influence of productivity on diversity (NPP → S) and the influence of diversity on productivity (S → NPP) and how these vary across spatial grains.LocationContiguous USA.Time period1999–2015.Major taxa studiedWoody species (angiosperms and gymnosperms).MethodsUsing data from North American forests at grains from local (672 m2) to coarse spatial units (median area = 35,677 km2), we assess relationships between diversity and productivity using structural equation and random forest models, while accounting for variation in climate, environmental heterogeneity, management and forest age.ResultsWe show that relationships betweenSand NPP strengthen with spatial grain. Within each grain,S → NPP and NPP → Shave similar magnitudes, meaning that processes underlyingS → NPP and NPP → Seither operate simultaneously or that one of them is real and the other is an artefact. At all spatial grains,Swas one of the weakest predictors of forest productivity, which was largely driven by biomass, temperature and forest management and age.Main conclusionsWe conclude that spatial grain mediates relationships between biodiversity and productivity in real‐world ecosystems and that results supporting predictions from each approach (NPP → SandS → NPP) serve as an impetus for future studies testing underlying mechanisms. Productivity–diversity relationships emerge at multiple spatial grains, which should widen the focus of national and global policy and research to larger spatial grains.

Blind spots in global soil biodiversity and ecosystem function research

Soils harbor a substantial fraction of the world’s biodiversity, contributing to many crucial ecosystem functions. It is thus essential to identify general macroecological patterns related to the distribution and functioning of soil organisms to support their conservation and consideration by governance. These macroecological analyses need to represent the diversity of environmental conditions that can be found worldwide. Here we identify and characterize existing environmental gaps in soil taxa and ecosystem functioning data across soil macroecological studies and 17,186 sampling sites across the globe. These data gaps include important spatial, environmental, taxonomic, and functional gaps, and an almost complete absence of temporally explicit data. We also identify the limitations of soil macroecological studies to explore general patterns in soil biodiversity-ecosystem functioning relationships, with only 0.3% of all sampling sites having both information about biodiversity and function, although with different taxonomic groups and functions at each site. Based on this information, we provide clear priorities to support and expand soil macroecological research.

An Extended Ecosystem Model for Understanding EE2 Indirect Effects on a Freshwater Food Web and its Ecosystem Function Resilience

Freshwater species are highly impacted by human activities and the consequences on ecosystem functioning are still not well understood. In the literature, a multitrophic perspective appears to be key to advance future biodiversity and ecosystem functioning (BEF) research. This paper aims at studying indirect effects of the synthetic hormone 17α-ethinylestradiol (EE2) on a freshwater food web by creating BEF links, through the interpretation of seasonal cycles and multitrophic interactions. An ecosystem model previously developed using experimental data from a unique whole-ecosystem study on EE2 was extended with the addition of Chaoborus, an omnivorous insect. During the experimental study, a collapse of fathead minnow was measured after one year of exposure. The simulation results showed that EE2 indirect effects on other fishes (horizontal diversity) and lower trophic levels (vertical diversity) were connected to multitrophic interactions with a top-down cascade effect. The results also demonstrated that adding an omnivorous, mid-trophic level group such as Chaoborus enhances resilience. Conversely, missing such a species means that the actual resilience of an ecosystem and its functioning cannot be properly simulated. Thus, the extended ecosystem model offers a tool that can help better understand what is happening after environmental perturbations, such as with EE2.

Biotic interactions, community assembly, and eco-evolutionary dynamics as drivers of long-term biodiversity–ecosystem functioning relationships

The functioning and service provisioning of ecosystems in the face of anthropogenic environmental and biodiversity change is a cornerstone of ecological research. The last three decades of biodiversity–ecosystem functioning (BEF) research have provided compelling evidence for the significant positive role of biodiversity in the functioning of many ecosystems. Despite broad consensus of this relationship, the underlying ecological and evolutionary mechanisms have not been well understood. This complicates the transition from a description of patterns to a predictive science. The proposed Research Unit aims at filling this gap of knowledge by applying novel experimental and analytical approaches in one of the longest-running biodiversity experiments in the world: the Jena Experiment. The central aim of the Research Unit is to uncover the mechanisms that determine BEF relationships in the short- and in the long-term. Increasing BEF relationships with time in long-term experiments do not only call for a paradigm shift in the appreciation of the relevance of biodiversity change, they likely are key to understanding the mechanisms of BEF relationships in general. The subprojects of the proposed Research Unit fall into two tightly linked main categories with two research areas each that aim at exploring variation in community assembly processes and resulting differences in biotic interactions as determinants of the long-term BEF relationship. Subprojects under “Microbial community assembly” and “Assembly and functions of animal communities” mostly focus on plant diversity effects on the assembly of communities and their feedback effects on biotic interactions and ecosystem functions. Subprojects under “Mediators of plant-biotic interactions” and “Intraspecific diversity and micro-evolutionary changes” mostly focus on plant diversity effects on plant trait expression and micro-evolutionary adaptation, and subsequent feedback effects on biotic interactions and ecosystem functions. This unification of evolutionary and ecosystem processes requires collaboration across the proposed subprojects in targeted plant and soil history experiments using cutting-edge technology and will produce significant synergies and novel mechanistic insights into BEF relationships. The Research Unit of the Jena Experiment is uniquely positioned in this context by taking an interdisciplinary and integrative approach to capture whole-ecosystem responses to changes in biodiversity and to advance a vibrant research field.

Intraspecific niche partitioning in macrodetritivores enhances mixed leaf litter decomposition

Abstract In biodiversity and ecosystem functioning research, the consideration of intraspecific trait variation and multiple trophic levels – both largely overlooked so far – has been proposed as a promising step towards a consensus about causal relationships and mechanisms. Soil invertebrates contribute crucially to leaf litter decomposition and thus to the functioning of one of the most diverse ecosystem components on Earth. On the one hand, a positive effect of leaf litter diversity on decomposition was shown by several studies. On the other hand, at the interspecific level, differences in body size and feeding traits of consumers influence this process by interacting with leaf litter traits that define decomposability, such as nutrient content and physical properties. It is also known that the feeding niche of consumers can vary during their ontogeny as it depends on individual body size, metabolism and physiology. However, whether and how intraspecific trait variation of macrodetritivores contributes through niche partitioning to the positive effect of litter combinations on decomposition was never investigated. Here, we tested experimentally the effect of intraspecific body size differences in the common terrestrial isopod species Oniscus asellus on the decomposition of the two co‐occurring litter species Acer platanoides and Betula pendula. We hypothesized complementary resource use by two distinct isopod body size classes, leading to decreased competition and higher overall litter decomposition. In a full factorial design with all possible combinations of litter species and isopod body size classes, litter mixtures enhanced decomposition beyond the additive effect of each single species, especially in isopod mixed‐body size treatments. Our results suggest an interaction between litter and consumer diversity driving intraspecific feeding niche partitioning. Although the focus on a single detritivore species does not allow for generalizations, our results should stimulate the investigation of the mechanisms of biotic interactions among individual organisms. A free Plain Language Summary can be found within the Supporting Information of this article.

Growth–trait relationships in subtropical forest are stronger at higher diversity

Abstract Understanding how species diversity affects plant performance is a central question in biodiversity–ecosystem functioning (BEF) research. At the community level, functional trait means and trait dissimilarities have been used to explain biodiversity effects, but with mixed success. To disentangle how functional traits explain community growth and underpin biodiversity–ecosystem functioning relationships, we should elucidate how plant traits affect individual growth across species richness levels, because the role of functional traits on growth depends on the ecological context of the individual. We addressed this topic by using detailed data of twelve functional traits and annual growth for 529 individual trees of 31 species at five species‐richness levels in a large forest biodiversity experiment in south‐east China from 4 to 9 years after planting. Our analyses show first that individual trait values can change with species richness, indicating that trait values can change due to the biotic context. Secondly, we show that early tree growth is more strongly affected by traits than by species richness. Finally, our data show that growth–trait relationships can change with species richness and with forest age. Trait effects on growth are more pronounced at higher richness levels, indicating that measuring traits on individual trees across richness levels can improve growth predictions and inference of BEF relationships that are shaped by functional traits. Synthesis. This study shows that functional trait values and their effect on individual tree growth depend on species richness. Our data support the notion that to elucidate how functional traits shape biodiversity–ecosystem functioning relationships, an important step is to consider the biotic context of individual trees within a community. We have made an initial step by analysing how functional traits affect individual‐tree growth in a diversity‐dependent manner and future research should continue by elucidating the role of traits on tree–tree interactions across diversity levels.

Integrating trait and evolutionary differences untangles how biodiversity affects ecosystem functioning.

Biodiversity and ecosystem functioning (BEF) research advocates that biodiversity loss has a drastic alteration on ecosystem functioning. However, studies have barely investigated how the evolutionary dependence of species traits affects EF. Here, we developed an integrated approach combining functional (FD) and phylogenetic diversity (PD) into a single space to disentangle the effects of diversity on leaf decomposition. We conducted an experiment manipulating plant leaves into litterbags containing four species (from a pool of 27) combined in four different treatments represented by low or high FD and PD; these treatments present different scenarios of trait evolution and, therefore, a treatment with high FD and low PD, for instance, mimics a community assembled by divergent trait evolution of close relatives. We found that leaf decomposition was 30% slower in pools with high FD and PD. We show species pool with higher FD and PD have non-additive effects on decomposition, which means there is a negative effect of mixtures combining species with great functional and evolutionary differences. In addition, interactive effects of PD and FD were more important to leaf decomposition than their isolated effects. Our results suggest that PD and FD have interactive effects on decomposition and represent different axes of ecosystem variation, indicating we should avoid using phylogenies as a proxy for functional diversity. We argue that future BEF experiments may alter their design by considering a multifaceted scenario investigating community effects on ecosystem functioning, and idiosyncratic effects of key traits which may determine community assembly and ecosystem processes.

Ecosystem function in predator-prey food webs-confronting dynamic models with empirical data.

Most ecosystem functions and related services involve species interactions across trophic levels, for example, pollination and biological pest control. Despite this, our understanding of ecosystem function in multitrophic communities is poor, and research has been limited to either manipulation in small communities or statistical descriptions in larger ones. Recent advances in food web ecology may allow us to overcome the trade-off between mechanistic insight and ecological realism. Molecular tools now simplify the detection of feeding interactions, and trait-based approaches allow the application of dynamic food web models to real ecosystems. We performed the first test of an allometric food web model's ability to replicate temporally nonaggregated abundance data from the field and to provide mechanistic insight into the function of predation. We aimed to reproduce and explore the drivers of the population dynamics of the aphid herbivore Rhopalosiphum padi observed in ten Swedish barley fields. We used a dynamic food web model, taking observed interactions and abundances of predators and alternative prey as input data, allowing us to examine the role of predation in aphid population control. The inverse problem methods were used for simultaneous model fit optimization and model parameterization. The model captured >70% of the variation in aphid abundance in five of ten fields, supporting the model-embodied hypothesis that body size can be an important determinant of predation in the arthropod community. We further demonstrate how in-depth model analysis can disentangle the likely drivers of function, such as the community's abundance and trait composition. Analysing the variability in model performance revealed knowledge gaps, such as the source of episodic aphid mortality, and general method development needs that, if addressed, would further increase model success and enable stronger inference about ecosystem function. The results demonstrate that confronting dynamic food web models with abundance data from the field is a viable approach to evaluate ecological theory and to aid our understanding of function in real ecosystems. However, to realize the full potential of food web models, in ecosystem function research and beyond, trait-based parameterization must be refined and extended to include more traits than body size.

Integrating trait-based empirical and modeling research to improve ecological restoration.

A global ecological restoration agenda has led to ambitious programs in environmental policy to mitigate declines in biodiversity and ecosystem services. Current restoration programs can incompletely return desired ecosystem service levels, while resilience of restored ecosystems to future threats is unknown. It is therefore essential to advance understanding and better utilize knowledge from ecological literature in restoration approaches. We identified an incomplete linkage between global change ecology, ecosystem function research, and restoration ecology. This gap impedes a full understanding of the interactive effects of changing environmental factors on the long‐term provision of ecosystem functions and a quantification of trade‐offs and synergies among multiple services. Approaches that account for the effects of multiple changing factors on the composition of plant traits and their direct and indirect impact on the provision of ecosystem functions and services can close this gap. However, studies on this multilayered relationship are currently missing. We therefore propose an integrated restoration agenda complementing trait‐based empirical studies with simulation modeling. We introduce an ongoing case study to demonstrate how this framework could allow systematic assessment of the impacts of interacting environmental factors on long‐term service provisioning. Our proposed agenda will benefit restoration programs by suggesting plant species compositions with specific traits that maximize the supply of multiple ecosystem services in the long term. Once the suggested compositions have been implemented in actual restoration projects, these assemblages should be monitored to assess whether they are resilient as well as to improve model parameterization. Additionally, the integration of empirical and simulation modeling research can improve global outcomes by raising the awareness of which restoration goals can be achieved, due to the quantification of trade‐offs and synergies among ecosystem services under a wide range of environmental conditions.

Leaf litter diversity and structure of microbial decomposer communities modulate litter decomposition in aquatic systems

Abstract Leaf litter decomposition is a major ecosystem process that can link aquatic to terrestrial ecosystems by flows of nutrients. Biodiversity and ecosystem functioning research hypothesizes that the global loss of species leads to impaired decomposition rates and thus to slower recycling of nutrients. Especially in aquatic systems, an understanding of diversity effects on litter decomposition is still incomplete. Here we conducted an experiment to test two main factors associated with global species loss that might influence leaf litter decomposition. First, we tested whether mixing different leaf species alters litter decomposition rates compared to decomposition of these species in monoculture. Second, we tested the effect of the size structure of a lotic decomposer community on decomposition rates. Overall, leaf litter identity strongly affected decomposition rates, and the observed decomposition rates matched measures of metabolic activity and microbial abundances. While we found some evidence of a positive leaf litter diversity effect on decomposition, this effect was not coherent across all litter combinations and the effect was generally additive and not synergistic. Microbial communities, with a reduced functional and trophic complexity, showed a small but significant overall reduction in decomposition rates compared to communities with the naturally complete functional and trophic complexity, highlighting the importance of a complete microbial community on ecosystem functioning. Our results suggest that top‐down diversity effects of the decomposer community on litter decomposition in aquatic systems are of comparable importance as bottom‐up diversity effects of primary producers. A plain language summary is available for this article.

Next-Generation Individual-Based Models Integrate Biodiversity and Ecosystems: Yes We Can, and Yes We Must

Ecosystem and community ecology have evolved along different pathways, with little overlap. However, to meet societal demands for predicting changes in ecosystem services, the functional and structural view dominating these two branches of ecology, respectively, must be integrated. Biodiversity–ecosystem function research has addressed this integration for two decades, but full integration that makes predictions relevant to practical problems is still lacking. We argue that full integration requires going, in both branches, deeper by taking into account individual organisms and the evolutionary and physico-chemical principles that drive their behavior. Individual-based models are a major tool for this integration. They have matured by using individual-level mechanism to replace the demographic thinking which dominates classical theoretical ecology. Existing individual-based ecosystem models already have proven useful both for theory and application. Still, next-generation individual-based models will increasingly use standardized and re-usable submodels to represent behaviors and mechanisms such as growth, uptake of nutrients, foraging, and home range behavior. The strategy of pattern-oriented modeling then helps make such ecosystem models structurally realistic by developing theory for individual behaviors just detailed enough to reproduce and explain patterns observed at the system level. Next-generation ecosystem scientists should include the individual-based approach in their toolkit and focus on addressing real systems because theory development and solving applied problems go hand-in-hand in individual-based ecology.

Pseudomonas spp. diversity is negatively associated with suppression of the wheat take-all pathogen.

Biodiversity and ecosystem functioning research typically shows positive diversity- productivity relationships. However, local increases in species richness can increase competition within trophic levels, reducing the efficacy of intertrophic level population control. Pseudomonas spp. are a dominant group of soil bacteria that play key roles in plant growth promotion and control of crop fungal pathogens. Here we show that Pseudomonas spp. richness is positively correlated with take-all disease in wheat and with yield losses of ~3 t/ha in the field. We modeled the interactions between Pseudomonas and the take-all pathogen in abstract experimental microcosms, and show that increased bacterial genotypic richness escalates bacterial antagonism and decreases the ability of the bacterial community to inhibit growth of the take-all pathogen. Future work is required to determine the generality of these negative biodiversity effects on different media and directly at infection zones on root surfaces. However, the increase in competition between bacteria at high genotypic richness and the potential loss of fungal biocontrol activity highlights an important mechanism to explain the negative Pseudomonas diversity-wheat yield relationship we observed in the field. Together our results suggest that the effect of biodiversity on ecosystem functioning can depend on both the function and trophic level of interest.

A persistence enhancing propensity account of ecological function to explain ecosystem evolution

We argue that ecology in general and biodiversity and ecosystem function (BEF) research in particular need an understanding of functions which is both ahistorical and evolutionarily grounded. A natural candidate in this context is Bigelow and Pargetter’s (1987) evolutionary forward-looking account which, like the causal role account, assigns functions to parts of integrated systems regardless of their past history, but supplements this with an evolutionary dimension that relates functions to their bearers’ ability to thrive and perpetuate themselves. While Bigelow and Pargetter’s account focused on functional organization at the level of organisms, we argue that such an account can be extended to functional organization at the community and ecosystem levels in a way that broadens the scope of the reconciliation between ecosystem ecology and evolutionary biology envisioned by many BEF researchers (e.g. Holt 1995; Loreau 2010a). By linking an evolutionary forward-looking account of functions to the persistence-based understanding of evolution defended by Bouchard (2008, 2011) and others (e.g. Bourrat 2014; Doolittle 2014), and to the theoretical research on complex adaptive systems (Levin 1999, 2005; Norberg 2004), we argue that ecosystems, by forming more or less resilient assemblages, can evolve even while they do not reproduce and form lineages. We thus propose a Persistence Enhancing Propensity (PEP) account of role functions in ecology to account for this overlap of evolutionary and ecological processes.