Between Biodiversity And Ecosystem Functioning Relationships Research Articles

Revisiting Biodiversity and Ecosystem Functioning through the Lens of Complex Adaptive Systems

Understanding the relationship between biodiversity and ecosystem functioning (BEF) is essential to comprehend the impacts of biodiversity changes on ecosystem functioning. This knowledge helps to detect and anticipate significant trends in global biodiversity loss and the homogenization of biota worldwide to prevent them. Species act together with climate, resource availability, and disturbance regimes to modulate ecological processes defining ecosystems’ complexity and their dynamic adaptation to variability. In this article, we revisit the BEF paradigm by addressing current knowledge of how biodiversity connects to ecosystem functioning across scales in the context of complex adaptive systems (CAS). We focus on ecosystem processes that lead to the emergence of the BEF relationship, considering ecosystem functioning as a macroscopic emergent property. Specifically, this work integrates the knowledge of the processes that connect biodiversity to ecosystem functioning. It addresses how biodiversity supports ecosystem multifunctionality across scales, resulting in the persistence of CAS in a rapidly changing world. We present a framework for ecological management considering the BEF relationship within the scope of CAS. The CAS standpoint brings new insights into the BEF field and its relevance for future ecological conservation of the Earth’s life support.

Effects of Tree Diversity, Functional Composition, and Large Trees on the Aboveground Biomass of an Old-Growth Subtropical Forest in Southern China

Forest aboveground biomass (AGB) plays an important role in regulating the global carbon cycle and is thus an essential component of ecosystem functioning. In the relationships between biodiversity and ecosystem functioning (BEF), studies have shown that many biotic factors (e.g., species, functional traits, and large trees) and abiotic factors have significant impacts on AGB. However, the relative strength of these affecting factors remains unclear. In this study, we analyzed woody plants (diameter at breast height [DBH] ≥ 1 cm) within a 1.6 ha plot in an old-growth subtropical natural forest in southern China. We used structural equation models to test the effects of tree diversity (species, phylogenetic, functional, and size inequality), functional composition, large trees, and environmental factors (topography, soil nutrients, and understory light) on AGB. Our results indicated that size inequality, the community-weighted mean of maximum DBH (CWM_MDBH), and large trees had significant, positive effects on AGB (p < 0.001), while lower soil phosphorus content was found to promote an increase in AGB. Furthermore, large trees, which were mostly composed of dominant tree species, were the main driver of AGB, and the effect of functional composition (e.g., CWM_MDBH) on AGB was substantially reduced by large trees. We argue that the selection effect plays a key role in regulating BEF relationships in subtropical natural forests and conclude that retaining large-diameter trees and dominant species, along with sustaining a complex stand structure, are key measures for improving productivity.

Evenness, biodiversity, and ecosystem function of intertidal communities along the Italian coasts: Experimental short-term response to ambient and extreme air temperatures

Biodiversity can promote ecosystem functioning in both terrestrial and marine environments, emphasizing the necessity of biodiversity conservation in order to preserve critical ecosystem functions and associated services. However, the role of biodiversity in buffering ecosystem functioning under extreme events caused by climate change remains a major scientific issue, especially for intertidal systems experiencing stressors from both terrestrial and marine drivers. We performed a regional-scale field experiment along the Italian coast to investigate the response of unmanipulated intertidal communities (by using a natural biodiversity gradient) to low tide aerial exposure to both ambient and short-term extreme temperatures. We specifically investigated the relationship between Biodiversity and Ecosystem Functioning (BEF) using different biodiversity indexes (species richness, functional diversity and evenness) and the response of the intertidal communities' ecosystem functioning (community respiration rates). Furthermore, we investigated which other environmental variables could influence the BEF relationship. We show that evenness explained a greater variation in intertidal community ecosystem functioning under both temperature conditions. Species richness (the most often used diversity metric in BEF research) was unrelated to ecosystem functioning, while functional diversity was significantly related to respiration under ambient but not extreme temperatures. We highlight the importance of the short-term thermal history of the communities (measured as body temperature) in the BEF relationship as it was consistently identified as the best predictor or response under both temperature conditions. However, Chlorophyll a in seawater and variation in sea surface temperature also contributed to the BEF relationship under ambient but not under extreme conditions, showing that short-duration climate-driven events can overcome local physiological adaptations. Our findings support the importance of the BEF relationship in intertidal communities, implying that systems with more diverse and homogeneous communities may be able to mitigate the effects of extreme temperatures.

Biotic Interactions as Mediators of Context-Dependent Biodiversity-Ecosystem Functioning Relationships

Biodiversity drives the maintenance and stability of ecosystem functioning as well as many of nature’s benefits to people, yet people cause substantial biodiversity change. Despite broad consensus about a positive relationship between biodiversity and ecosystem functioning (BEF), the underlying mechanisms and their context-dependencies are not well understood. This proposal, submitted to the European Research Council (ERC), aims at filling this knowledge gap by providing a novel conceptual framework for integrating biotic interactions across guilds of organisms, i.e. plants and mycorrhizal fungi, to explain the ecosystem consequences of biodiversity change. The overarching hypothesis is that EF increases when more tree species associate with functionally dissimilar mycorrhizal fungi. Taking a whole-ecosystem perspective, we propose to explore the role of tree-mycorrhiza interactions in driving BEF across environmental contexts and how this relates to nutrient dynamics. Given the significant role that mycorrhizae play in soil nutrient and water uptake, BEF relationships will be investigated under normal and drought conditions. Resulting ecosystem consequences will be explored by studying main energy channels and ecosystem multifunctionality using food web energy fluxes and by assessing carbon storage. Synthesising drivers of biotic interactions will allow us to understand context-dependent BEF relationships. This interdisciplinary and integrative project spans the whole gradient from local-scale process assessments to global relationships by building on unique experimental infrastructures like the MyDiv Experiment, iDiv Ecotron and the global network TreeDivNet, to link ecological mechanisms to reforestation initiatives. This innovative combination of basic scientific research with real-world interventions links trait-based community ecology, global change research and ecosystem ecology, pioneering a new generation of BEF research and represents a significant step towards implementing BEF theory for human needs.

Functional redundancy changes along a drought stress gradient for the shift of selection effect to complementarity effect in experimental plant communities

ABSTRACT Species interactions alter with environmental change, which influences the relationship between biodiversity and ecosystem functioning (BEF). How BEF relationships change with environments requires knowledge of the changes of functional attributes in individual species in response to environmental change. Here, we assembled experimental plant communities with different species richness (1, 2, 4, 8, and 16) and exposed them to a drought stress gradient (control, moderate and intensive drought stress). Functional redundancy decreased with increasing drought stress for a shift from selection effect to complementarity effect. In response to drought stress, species interactions shifted from competition to facilitation and the role of light-asymmetric competition in the competitive ability of species gradually decreased. Many species that are redundant under control conditions make essential contributions to biomass production under moderate and intensive drought stress conditions. Consequently, biodiversity effects should be evaluated from a predicted climate change model and redundant species should be carefully defined.

Functional trait complementarity and dominance both determine benthic secondary production in temperate seagrass beds

AbstractDefining relationships between biodiversity and ecosystem functioning (BEF) is key to understanding the consequences of biodiversity loss. Although species functional traits are strongly linked to ecosystem processes, their integration into BEF models has been focused mainly on terrestrial ecosystems. Application is limited because functional trait‐based BEF models typically have small‐sample sizes and highly correlated predictors, making it difficult for model selection and identifying underlying drivers. We examine the BEF relationship between secondary production and benthic invertebrate taxonomic and functional diversity for seagrass beds located across a range of environmental conditions. Specifically, we evaluate the role of complementarity (i.e., dissimilarity in species or traits) and dominance (disproportional importance of traits) in determining secondary production at 20 sites using 34 metrics of taxonomic diversity, functional diversity, and functional traits. Here, diversity metrics represent complementarity and functional traits represent dominance. We used elastic‐net regression and commonality analysis to evaluate the BEF model, because its properties (i.e., few observations and many potential, and highly correlated, predictors) precluded more standard approaches and it is well suited to this situation. Functional richness and five functional traits (crawling, surface deposit feeding [SurDF], location on sediment surface, lifespan 1–3 yr, and semi‐continuous breeding) were identified as important determinants of secondary production, explaining 74% of the variance. SurDF was the most important predictor that acted in isolation to influence secondary production, while all other predictors acted together. All six selected variables in three different combinations explained 68% of the total variance in the BEF model. These results indicate that both dominance and complementarity mechanisms were important for the BEF relationship. Our study highlights elastic‐net regression and commonality analysis as a powerful approach to model functional trait‐based BEF relationships. We further show that inclusion of the functional landscape into BEF models is highly valuable, allowing the implications of species loss for ecosystem functioning to be mechanistically understood.

Shifting community composition determines the biodiversity–productivity relationship under increasing precipitation and N deposition

AbstractQuestionsThe relationships between biodiversity and ecosystem functioning (BEF) vary largely across natural ecosystems, with a unimodal, monotonous linear or no relationship. However, it remains unclear how BEF relationships vary under global change. Given future predicted changes in precipitation and nitrogen (N) deposition, it is crucial to determine how precipitation change and N deposition affect grassland biodiversity and productivity, and regulate their relationships.LocationA Dry Mixed‐Grass Prairie of western Canada.MethodsWe established a manipulative field experiment of increased precipitation (water addition with approximately 15% and 30% more monthly precipitation) and N addition (10 g/m2) using a randomized complete block design, including six treatments, each replicated five times (30 plots). We conducted vegetation sampling with a 1 m × 1 m quadrat in each plot from 2016 to 2017, to examine the individual and interactive effects of water and N addition on plant diversity, functional group composition, above‐ and below‐ground productivity, and the diversity–productivity relationships.ResultsWe found a positive linear diversity–above‐ground biomass (AGB) relationship under increased precipitation, which was attributed to the water‐induced increase in the abundance of forbs in the plant community, further promoting the positive effect of plant diversity on AGB. However, N addition caused a negative linear diversity–AGB relationship by increasing AGB and reducing plant diversity. The effects of N on diversity and productivity can be further strengthened under increased precipitation, which was due to the increase of C3rhizomatous grasses with high above‐ and below‐ground biomass and the decrease of forbs with high richness.ConclusionsOur results suggest that changes in functional group composition determine the plant species’ diversity, productivity, and their relationships under increasing precipitation and N deposition, which has significant implications for understanding and modelling ecosystem productivity in the context of global change.

Biodiversity increases ecosystem functions despite multiple stressors on coral reefs

Positive relationships between biodiversity and ecosystem functioning (BEF) highlight the importance of conserving biodiversity to maintain key ecosystem functions and associated services. Although natural systems are rapidly losing biodiversity due to numerous human-caused stressors, our understanding of how multiple stressors influence BEF relationships comes largely from small, experimental studies. Here, using remote assemblages of coral reef fishes, we demonstrate strong, non-saturating relationships of biodiversity with two ecosystem functions: biomass and productivity. These positive relationships were robust both to an extreme heatwave that triggered coral bleaching and to invasive rats which disrupt nutrient subsidies from native seabirds. Despite having only minor effects on BEF relationships, both stressors still decreased ecosystem functioning via other pathways. The extreme heatwave reduced biodiversity, which, due to the strong BEF relationships, ultimately diminished both ecosystem functions. Conversely, the loss of cross-system nutrient subsidies directly decreased biomass. These results demonstrate multiple ways by which human-caused stressors can reduce ecosystem functioning, despite robust BEF relationships, in natural high-diversity assemblages.

Climatic humidity mediates the strength of the species richness–biomass relationship on the Mongolian Plateau steppe

The relationships between biodiversity and ecosystem functioning (BEF) have been extensively studied over past decades. However, the environmental factors affecting their relationships, and how their relationships vary under the influence of environmental factors, remain controversial. Studying the BEF relationships in natural/wild environments is of great significance for devising strategies in biodiversity conservation and ecosystem functioning. Using the data from 75 sites on the Mongolian Plateau steppe, we analyzed the relationship between species richness and biomass with general linear models (GLMs) and linear mixed models (LMMs), and analyzed the variation in the species richness–biomass relationships under environmental conditions by the partial least square path modeling (PLSPM). The results showed that de Martonne aridity index affected both species richness and community biomass in parallel, and that hydrothermal coupling conditions were more important direct impact factors for aboveground biomass. However, the significant species richness–biomass relationships became weaker when the effects of environmental factors (i.e. climate and soil properties) were present. Climate humidity was the most important factor in mediating the relationship between species richness and community biomass. Our research suggested that species richness–biomass relationships are weak in the natural grasslands of the Mongolian Plateau, and that this may be due to the differences in the regional-scale environment and changes in species interactions. We recommend that a more comprehensive understanding of the relationship between diversity and biomass requires further research within broader environmental gradients.

Land use alters relationships of grassland productivity with plant and arthropod diversity in Inner Mongolian grassland.

The threats of land-use intensification to biodiversity have motivated considerable research directed toward understanding the relationship between biodiversity and ecosystem functioning (BEF). Functional diversity is deemed a better indicator than species diversity to clarify the BEF relationships. However, most tests of the BEF relationship have been conducted in highly controlled plant communities, with terrestrial animal communities largely unexplored. Additionally, most BEF studies examined the effects of biodiversity on ecosystem functions, with the effects of ecosystem functioning strength on biodiversity hardly considered. Based on a 6-yr grassland experiment in the typical steppe region of Inner Mongolia, we examined the variation of taxonomic diversity (TD) and functional diversity (FD) of both plant and arthropod communities, and their relations with grassland productivity, across three land management types (moderate grazing, mowing, and enclosure). We aimed to clarify the interrelations among plant FD, arthropod FD, grassland productivity, and soil factors. We found the following: (1) Grassland under mowing performed best in terms of sustaining a high TD and FD of plants and arthropods compared to that under grazing and enclosure. (2) The relationships between plant and arthropod diversity and productivity varied with management types. Plant TD and FD were negatively related, whereas arthropod FD was positively related with productivity under enclosure; plant FD, but not arthropod FD, was positively related with productivity under grazing; arthropod FD, but not plant FD, was negatively related with productivity under mowing. (3) Grassland productivity was positively interrelated with plant FD, but not plant TD; and was negatively interrelated with arthropod TD, but not arthropod FD across different management types. The respective positive vs. negative bidirectional relationships of productivity with plant diversity vs. arthropod diversity, were majorly a consequence of divergent grazing/mowing effects on plant vs. arthropod diversity. The results indicate that grazing increases plant diversity, but decreases arthropod diversity, whereas fall mowing provides a management strategy for conservation of both trophic levels. These results also provide new insights into the effects of land-use changes on biodiversity and ecosystem processes, and indicate the importance of incorporating the functional interrelations among different trophic groups in sustainable grassland management.

Biodiversity-ecosystem functioning relationships in fish communities: biomass is related to evenness and the environment, not to species richness.

The relationship between biodiversity and ecosystem functioning (BEF) is a topic of considerable interest to scientists and managers because a better understanding of its underlying mechanisms may help us mitigate the consequences of biodiversity loss on ecosystems. Our current knowledge of BEF relies heavily on theoretical and experimental studies, typically conducted on a narrow range of spatio-temporal scales, environmental conditions, and trophic levels. Hence, whether a relationship holds in the natural environment is poorly understood, especially in exploited marine ecosystems. Using large-scale observations of marine fish communities, we applied a structural equation modelling framework to investigate the existence and significance of BEF relationships across northwestern European seas. We find that ecosystem functioning, here represented by spatial patterns in total fish biomass, is unrelated to species richness-the most commonly used diversity metric in BEF studies. Instead, community evenness, differences in species composition, and abiotic variables are significant drivers. In particular, we find that high fish biomass is associated with fish assemblages dominated by a few generalist species of a high trophic level, who are able to exploit both the benthic and pelagic energy pathway. Our study provides a better understanding of the mechanisms behind marine ecosystem functioning and allows for the integration of biodiversity into management considerations.

Biodiversity-ecosystem functioning relationships of overstorey versus understorey trees in an old-growth temperate forest

The results of this study, based on a large dataset with mapped tree locations, suggest that the relationship between biodiversity and ecosystem functioning (BEF) is different between the over- and understorey in the investigated forest community. Neither the functional nor the phylogenetic diversity showed a significant advantage in predicting aboveground biomass and biomass production (aboveground biomass increment) when compared with species richness. Consistent conclusions have still not been reached regarding the relative importance of the different diversity indices in predicting biomass production. Furthermore, the effects of certain forest strata on the BEF relationship remain unclear. The woody plant species in the study area were classified as two vertical strata and were referred to as the “overstorey” (trees with dbh > 10 cm) and “understorey” (trees with dbh ≤ 10 cm). The relationships between different metrics of tree diversity and biomass production were quantified using linear models. The set of the best predictors for tree biomass and productions were determined using a multi-model selection approach. The differences in diversity-ecosystem functioning relationships between the two forest vertical strata, and the effects of canopy trees on the understorey trees, were investigated using structural equation models. The relative importance of the species diversity, phylogenetic diversity, and functional diversity in predicting the aboveground biomass production (ABP) was examined to compare the potential of phylogenetic and functional diversity indices and species richness in predicting biomass productivity and compare the influence of niche complementarity, selection effects, or mass-ratio effects on aboveground biomass variables and to assess possible differences in the BEF relationships between the overstorey and understorey layers in the studied ecosystems. Also, this study investigated possible differences in the BEF relationships between the overstorey and understorey layers in the studied ecosystems. The results confirmed a positive diversity-productivity relationship in the natural coniferous and broadleaved mixed forest. However, the relationship in the overstorey stratum was statistically stronger than that in the understorey layer. The combination of diversity indices and functional traits could explain more of the variations in the biomass and productivity than when examined separately. The correlation between the richness of the overstorey and understorey species was found to be positive. However, the aboveground woody biomass of the overstorey layer had negative effects on the understorey biomass. In summary, this study found a stronger positive correlation between the woody plant diversity and productivity in the overstorey than in the understorey stratum. These findings indicate that the BEF relationships are hierarchically dependent, and supported by niche complementarity. Also, a much weaker relationship was observed between the functional diversity and biomass production than between the species diversity and biomass production due to a selection effect. The aboveground woody biomass was found to be enhanced in communities dominated by functional traits correlated to smaller leaf areas, greater maximum tree heights, and higher leaf carbon content. These findings suggest that the BEF relationships were driven by a mass-ratio hypothesis.

Functional diversity promotes phytoplankton resource use efficiency

Abstract Understanding the relationship between biodiversity and ecosystem functioning (BEF) is a central topic in ecology. Multi‐trait–based functional diversity has been proposed to improve mechanistic understanding of the BEF relationship; however, how trait‐based functional diversity affects ecosystem functioning and processes has rarely been addressed in aquatic ecosystems. Here, we examined the causal relationships between three phytoplankton functional diversity indices (FAD2, functional diversity based on dendrograms [FDc], FRic) and Shannon diversity index versus resource use efficiency for nitrogen (RUEN), phosphorus (RUEP) and silicate (RUESi), with monthly long‐term datasets from the marine (Western English Channel, 2000–2014) and freshwater (Lake Kasumigaura, 1984–2012) ecosystems. We employed Convergent Cross Mapping (CCM), a novel method developed for identifying causality for nonlinear dynamical systems; this is in contrast to linear approaches that cannot distinguish causality from correlation. CCM found that FDc is the most robust functional diversity index among the selected functional diversity indices (FAD2, FDc, FRic) in predicting phytoplankton resource use efficiency and exhibited a much stronger causal effect than the Shannon index. Furthermore, scenario exploration analysis indicates that most causal effects from phytoplankton diversity indices on resource use efficiency (RUEN, RUEP and RUESi) are on average positive, and FDc exhibited the most consistent positive causal effects on phytoplankton resource efficiency in both marine and freshwater ecosystems. Thus, increasing FDc can enhance phytoplankton resource use efficiency in aquatic ecosystems. Synthesis. Our results show significant causal effects of functional diversity on phytoplankton resource use efficiency in both marine and freshwater ecosystems. Among all selected functional diversity indices, functional diversity based on dendrogram is the most robust functional diversity index in promoting phytoplankton resource efficiency. Our study provides empirical evidences in natural aquatic systems that trait‐based functional diversity represents better species niche partitioning than the Shannon index and thereafter enhances resource use efficiency. This finding can improve our understanding on trophic transfer and nutrient cycling in aquatic ecosystems.

Establishing causal links between aquatic biodiversity and ecosystem functioning: Status and research needs

Understanding how changes in biodiversity affects ecosystem functioning is imperative in allowing Ecosystem-Based Management (EBM), especially when addressing global change and environmental degradation. Research into the link between biodiversity and ecosystem functioning (BEF) has indeed increased considerably over the past decades. BEF research has focussed on terrestrial ecosystems and aquatic ecosystems have received considerably less attention. Due to differences in phylogenetic diversity, ecological processes and reported BEF relationships, however, it may at least be questionable whether BEF relationships are exchangeable between these ecosystems (i.e. terrestrial and aquatic). The aim of the present paper was therefore to pinpoint key areas and bottlenecks in establishing BEF relationships for aquatic ecosystems (freshwater, transitional, and marine). To this end, the available literature with special emphasis on the last 10 years was assessed to evaluate: i) reported mechanisms and shapes of aquatic BEF relationships; ii) to what extent BEF relations are interchangeable or ecosystem-specific; and iii) contemporary gaps and needs in aquatic BEF research. Based on our analysis, it may be concluded that despite considerable progress in BEF research over the past decades, several bottlenecks still need to be tackled, namely incorporating the multitude of functions supported by ecosystems, functional distinctiveness of rare species, multitrophic interactions and spatial-temporal scales, before BEF relationships can be used in ecosystem-based management.

The strength of the biodiversity-ecosystem function relationship depends on spatial scale.

Our understanding of the relationship between biodiversity and ecosystem functioning (BEF) applies mainly to fine spatial scales. New research is required if we are to extend this knowledge to broader spatial scales that are relevant for conservation decisions. Here, we use simulations to examine conditions that generate scale dependence of the BEF relationship. We study scale by assessing how the BEF relationship (slope and R2) changes when habitat patches are spatially aggregated. We find three ways for the BEF relationship to be scale-dependent: (i) variation among local patches in local (α) diversity, (ii) spatial variation in the local BEF relationship and (iii) incomplete compositional turnover in species composition among patches. The first two cause the slope of the BEF relationship to increase moderately with spatial scale, reflecting nonlinear averaging of spatial variation in diversity or the BEF relationship. The third mechanism results in much stronger scale dependence, with the BEF relationship increasing in the rising portion of the species area relationship, but then decreasing as it saturates. An analysis of data from the Cedar Creek grassland BEF experiment revealed a positive but saturating slope of the relationship with scale. Overall, our findings suggest that the BEF relationship is likely to be scale dependent.

How does habitat fragmentation affect the biodiversity and ecosystem functioning relationship?

The relationship between biodiversity and ecosystem functioning (BEF) has been a central topic in ecology for more than 20 years. While experimental and theoretical studies have produced much knowledge of how biodiversity affects ecosystem functioning, it remains poorly understood how habitat fragmentation affects the BEF relationship. To develop a framework that connects habitat fragmentation to the BEF relationship from a landscape perspective. We reviewed the literature on habitat fragmentation, BEF, and related fields, and developed a framework to analyze how habitat fragmentation affects the BEF relationship through altering biodiversity, environmental conditions, and both, based on the pattern-process-scale perspective in landscape ecology. Our synthesis of the literature suggests that habitat fragmentation can alter BEF relationship through several processes. First, habitat fragmentation causes the non-random loss of species that make major contributions to ecosystem functioning (decreasing sampling effect), and reduces mutualistic interactions (decreasing complementarity effects) regardless of the changes in species richness. Second, environmental conditions within patches and ecological flows among patches vary significantly with the degree of fragmentation, which potentially contributes to and modulates the BEF relationship. Habitat fragmentation can affect the BEF relationship directly by altering community composition, as well as indirectly by changing environmental conditions within and among habitat patches on both local and landscape levels. The BEF relationship obtained from small plots and over short time periods may not fully represent that in real landscapes that are fragmented, dynamic, and continuously influenced by myriad human activities on different scales in time and space.

Biodiversity ecosystem functioning research in freshwater phytoplankton: A comprehensive review of trait-based studies

In an effort to reach a clearer mechanistic understanding of the influence of biological diversity on ecosystem functioning, research in the field is increasingly applying a trait-based approach. In this comprehensive review, I searched for and analyzed studies that focused on the relationship between biodiversity and ecosystem functioning (BEF) using a trait-based approach in freshwater phytoplankton from lentic systems (lakes, ponds, reservoirs). I found that this type of studies is very rare and included a plethora of traits, diversity metrics, statistical analyses and study locations that contributed to the high variability in the results they obtained. Overall, trait-based diversity is not a very good predictor of ecosystem functioning in freshwater lentic ecosystems. Null relationships between trait-based diversity and ecosystem functioning in freshwater lentic systems were the more frequent outcome. When significant, the amount of variation in ecosystem functioning explained by trait-based diversity was small. Still, trait-based research remains a promising approach to increase the mechanistic understanding of BEF relationships. For this purpose, studies directly testing the underlying mechanistic rationale, exploring diversity effects on the temporal stability of ecosystem functions, including multiple functions at a time, focusing more in cell size and shape and confirming the relative importance of individual trait variation for ecosystem functioning are needed.

Exploring the Relationship between Macrofaunal Biodiversity and Ecosystem Functioning in the Deep Sea

The global scale of the biodiversity crisis has stimulated research into the relationship between biodiversity and ecosystem functioning (BEF). Even though the deep sea is the largest biome on Earth, BEF studies in deep-sea benthic ecosystems are scant. Moreover, the small number of recent studies, which mostly focus on meiobenthic nematodes, report conflicting results that range from a very clear positive relationship to none at all. In this BEF study, the deep-sea macrofauna were used as a model to investigate the structural and functional diversity of macrofauna assemblages at three depths (1200, 1900, and 3000 m) in seven open-slope systems from the North-Eastern Atlantic Ocean to the Central-Eastern Mediterranean Sea. The presence and nature of BEF relationships were studied considering two spatial scales, the large and the basin scale, in different environmental settings. Total benthic biomass and macrofaunal predator biomass were used as proxies to assess ecosystem functioning. Ecosystem efficiency was expressed as macrofaunal biomass to biopolymeric carbon content ratio, macrofaunal biomass to prokaryotic biomass ratio, macrofaunal biomass to meiofaunal biomass ratio, and meiofaunal biomass to prokaryotic biomass ratio. On both large and basin spatial scales, some significant relationships between macrofaunal diversity and ecosystem functioning and efficiency were reported. When significant, the nature of BEF relations was positive and exponential or linear supporting the general idea that a higher diversity can enhance ecosystem functioning. Other BEF relationships were explained by the effect of environmental variables. More data from different deep-sea systems are needed, to better elucidate the consequences of biodiversity loss on the ocean floor.

Seafloor heterogeneity influences the biodiversity-ecosystem functioning relationships in the deep sea.

Theoretical ecology predicts that heterogeneous habitats allow more species to co-exist in a given area. In the deep sea, biodiversity is positively linked with ecosystem functioning, suggesting that deep-seabed heterogeneity could influence ecosystem functions and the relationships between biodiversity and ecosystem functioning (BEF). To shed light on the BEF relationships in a heterogeneous deep seabed, we investigated variations in meiofaunal biodiversity, biomass and ecosystem efficiency within and among different seabed morphologies (e.g., furrows, erosional troughs, sediment waves and other depositional structures, landslide scars and deposits) in a narrow geo-morphologically articulated sector of the Adriatic Sea. We show that distinct seafloor morphologies are characterized by highly diverse nematode assemblages, whereas areas sharing similar seabed morphologies host similar nematode assemblages. BEF relationships are consistently positive across the entire region, but different seabed morphologies are characterised by different slope coefficients of the relationship. Our results suggest that seafloor heterogeneity, allowing diversified assemblages across different habitats, increases diversity and influence ecosystem processes at the regional scale, and BEF relationships at smaller spatial scales. We conclude that high-resolution seabed mapping and a detailed analysis of the species distribution at the habitat scale are crucial for improving management of goods and services delivered by deep-sea ecosystems.

Biodiversity and ecosystem functioning in dynamic landscapes.

The relationship between biodiversity and ecosystem functioning (BEF) and its consequence for ecosystem services has predominantly been studied by controlled, short-term and small-scale experiments under standardized environmental conditions and constant community compositions. However, changes in biodiversity occur in real-world ecosystems with varying environments and a dynamic community composition. In this theme issue, we present novel research on BEF in such dynamic communities. The contributions are organized in three sections on BEF relationships in (i) multi-trophic diversity, (ii) non-equilibrium biodiversity under disturbance and varying environmental conditions, and (iii) large spatial and long temporal scales. The first section shows that multi-trophic BEF relationships often appear idiosyncratic, while accounting for species traits enables a predictive understanding. Future BEF research on complex communities needs to include ecological theory that is based on first principles of species-averaged body masses, stoichiometry and effects of environmental conditions such as temperature. The second section illustrates that disturbance and varying environments have direct as well as indirect (via changes in species richness, community composition and species' traits) effects on BEF relationships. Fluctuations in biodiversity (species richness, community composition and also trait dominance within species) can severely modify BEF relationships. The third section demonstrates that BEF at larger spatial scales is driven by different variables. While species richness per se and community biomass are most important, species identity effects and community composition are less important than at small scales. Across long temporal scales, mass extinctions represent severe changes in biodiversity with mixed effects on ecosystem functions. Together, the contributions of this theme issue identify new research frontiers and answer some open questions on BEF relationships in dynamic communities of real-world landscapes.