Publications by authors named "Michel Loreau"

152 Publications

The hidden role of multi-trophic interactions in driving diversity-productivity relationships.

Ecol Lett 2021 Nov 30. Epub 2021 Nov 30.

EcoNetLab, German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany.

Resource-use complementarity of producer species is often invoked to explain the generally positive diversity-productivity relationships. Additionally, multi-trophic interactions that link processes across trophic levels have received increasing attention as a possible key driver. Given that both are integral to natural ecosystems, their interactive effect should be evident but has remained hidden. We address this issue by analysing diversity-productivity relationships in a simulation experiment of producer communities nested within complex food-webs, manipulating resource-use complementarity and multi-trophic animal richness. We show that these two mechanisms interactively create diverse communities of complementary producer species. This shapes diversity-productivity relationships such that their joint contribution generally exceeds their individual effects. Specifically, multi-trophic interactions in animal-rich ecosystems facilitate producer coexistence by preventing competitive exclusion despite overlaps in resource-use, which increases the realised complementarity. The interdependence of food-webs and producer complementarity in creating biodiversity-productivity relationships highlights the importance to adopt a multi-trophic perspective on biodiversity-ecosystem functioning relationships.
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http://dx.doi.org/10.1111/ele.13935DOI Listing
November 2021

Habitat percolation transition undermines sustainability in social-ecological agricultural systems.

Ecol Lett 2021 Nov 7. Epub 2021 Nov 7.

Theoretical and Experimental Ecology Station, CNRS, Moulis, France.

Steady increases in human population size and resource consumption are driving rampant agricultural expansion and intensification. Habitat loss caused by agriculture puts the integrity of ecosystems at risk and threatens the persistence of human societies that rely on ecosystem services. We develop a spatially explicit model describing the coupled dynamics of an agricultural landscape and human population size to assess the effect of different land-use management strategies, defined by agricultural clustering and intensification, on the sustainability of the social-ecological system. We show how agricultural expansion can cause natural habitats to undergo a percolation transition leading to abrupt habitat fragmentation that feedbacks on human's decision making, aggravating landscape degradation. We found that agricultural intensification to spare land from conversion is a successful strategy only in highly natural landscapes, and that clustering agricultural land is the most effective measure to preserve large connected natural fragments, prevent severe fragmentation and thus, enhance sustainability.
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http://dx.doi.org/10.1111/ele.13914DOI Listing
November 2021

Grand challenges in biodiversity-ecosystem functioning research in the era of science-policy platforms require explicit consideration of feedbacks.

Proc Biol Sci 2021 Oct 13;288(1960):20210783. Epub 2021 Oct 13.

Department of Ecology, Evolution and Behavior, University of Minnesota, St Paul, MN, USA.

Feedbacks are an essential feature of resilient socio-economic systems, yet the feedbacks between biodiversity, ecosystem services and human wellbeing are not fully accounted for in global policy efforts that consider future scenarios for human activities and their consequences for nature. Failure to integrate feedbacks in our knowledge frameworks exacerbates uncertainty in future projections and potentially prevents us from realizing the full benefits of actions we can take to enhance sustainability. We identify six scientific research challenges that, if addressed, could allow future policy, conservation and monitoring efforts to quantitatively account for ecosystem and societal consequences of biodiversity change. Placing feedbacks prominently in our frameworks would lead to (i) coordinated observation of biodiversity change, ecosystem functions and human actions, (ii) joint experiment and observation programmes, (iii) more effective use of emerging technologies in biodiversity science and policy, and (iv) a more inclusive and integrated global community of biodiversity observers. To meet these challenges, we outline a five-point action plan for collaboration and connection among scientists and policymakers that emphasizes diversity, inclusion and open access. Efforts to protect biodiversity require the best possible scientific understanding of human activities, biodiversity trends, ecosystem functions and-critically-the feedbacks among them.
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http://dx.doi.org/10.1098/rspb.2021.0783DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8511742PMC
October 2021

Universal scaling of robustness of ecosystem services to species loss.

Nat Commun 2021 08 27;12(1):5167. Epub 2021 Aug 27.

Department of Zoology, School of Natural Sciences, Trinity College Dublin, Dublin, Ireland.

Ensuring reliable supply of services from nature is key to the sustainable development and well-being of human societies. Varied and frequently complex relationships between biodiversity and ecosystem services have, however, frustrated our capacity to quantify and predict the vulnerability of those services to species extinctions. Here, we use a qualitative Boolean modelling framework to identify universal drivers of the robustness of ecosystem service supply to species loss. These drivers comprise simple features of the networks that link species to the functions they perform that, in turn, underpin a service. Together, they define what we call network fragility. Using data from >250 real ecological networks representing services such as pollination and seed-dispersal, we demonstrate that network fragility predicts remarkably well the robustness of empirical ecosystem services. We then show how to quantify contributions of individual species to ecosystem service robustness, enabling quantification of how vulnerability scales from species to services. Our findings provide general insights into the way species, functional traits, and the links between them together determine the vulnerability of ecosystem service supply to biodiversity loss.
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http://dx.doi.org/10.1038/s41467-021-25507-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8397752PMC
August 2021

Metapopulation capacity determines food chain length in fragmented landscapes.

Proc Natl Acad Sci U S A 2021 08;118(34)

Theoretical and Experimental Ecology Station, CNRS, Moulis 09200, France.

Metapopulation capacity provides an analytic tool to quantify the impact of landscape configuration on metapopulation persistence, which has proven powerful in biological conservation. Yet surprisingly few efforts have been made to apply this approach to multispecies systems. Here, we extend metapopulation capacity theory to predict the persistence of trophically interacting species. Our results demonstrate that metapopulation capacity could be used to predict the persistence of trophic systems such as prey-predator pairs and food chains in fragmented landscapes. In particular, we derive explicit predictions for food chain length as a function of metapopulation capacity, top-down control, and population dynamical parameters. Under certain assumptions, we show that the fraction of empty patches for the basal species provides a useful indicator to predict the length of food chains that a fragmented landscape can support and confirm this prediction for a host-parasitoid interaction. We further show that the impact of habitat changes on biodiversity can be predicted from changes in metapopulation capacity or approximately by changes in the fraction of empty patches. Our study provides an important step toward a spatially explicit theory of trophic metacommunities and a useful tool for predicting their responses to habitat changes.
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http://dx.doi.org/10.1073/pnas.2102733118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8403957PMC
August 2021

Predator avoidance and foraging for food shape synchrony and response to perturbations in trophic metacommunities.

J Theor Biol 2021 11 13;528:110836. Epub 2021 Jul 13.

Theoretical and Experimental Ecology Station, UPR 2001, CNRS, 09200 Moulis, France.

The response of species to perturbations strongly depends on spatial aspects in populations connected by dispersal. Asynchronous fluctuations in biomass among populations lower the risk of simultaneous local extinctions and thus reduce the regional extinction risk. However, dispersal is often seen as passive diffusion that balances species abundance between distant patches, whereas ecological constraints, such as predator avoidance or foraging for food, trigger the movement of individuals. Here, we propose a model in which dispersal rates depend on the abundance of the species interacting with the dispersing species (e.g., prey or predators) to determine how density-dependent dispersal shapes spatial synchrony in trophic metacommunities in response to stochastic perturbations. Thus, unlike those with passive dispersal, this model with density-dependent dispersal bypasses the classic vertical transmission of perturbations due to trophic interactions and deeply alters synchrony patterns. We show that the species with the highest coefficient of variation of biomass governs the dispersal rate of the dispersing species and determines the synchrony of its populations. In addition, we show that this mechanism can be modulated by the relative impact of each species on the growth rate of the dispersing species. Species affected by several constraints disperse to mitigate the strongest constraints (e.g., predation), which does not necessarily experience the highest variations due to perturbations. Our approach can disentangle the joint effects of several factors implied in dispersal and provides a more accurate description of dispersal and its consequences on metacommunity dynamics.
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http://dx.doi.org/10.1016/j.jtbi.2021.110836DOI Listing
November 2021

Consistent functional clusters explain the effects of biodiversity on ecosystem productivity in a long-term experiment.

Ecology 2021 09 30;102(9):e03441. Epub 2021 Jul 30.

CEFE, University of Montpellier-CNRS-EPHE-IRD-University Paul-Valéry Montpellier, 1919 route de Mende, Montpellier, 34293, France.

Biomass production in ecosystems is a complex process regulated by several facets of biodiversity and species identity, but also species interactions such as competition or complementarity between species. For studying these different facets separately, ecosystem biomass is generally partitioned in two biodiversity effects. The composition effect is a simple, linear effect, and the interaction effect is a more subtle, nonlinear effect. Here we used a clustering approach (1) to separately and comprehensively capture all linear and nonlinear effects induced by both biodiversity effects on ecosystem functioning, and (2) to determine the functional composition at the origin of each biodiversity effect. We used data from the long-term Cedar Creek BioDIV experiment carried out over 22 yr, and we partitioned multiplicatively the biomass in composition and interaction effects. Both biodiversity effects were weakly correlated. Our clustering approach accurately explains and predicts each diversity effect over time: each one is modeled by a different functional composition. Even if environmental conditions and the strength of interaction effect strongly varied over time, the functional clusters of species that govern the interaction effect do not change over the 22 yr of the experiment. The functional composition governing the interaction effect is therefore very robust. In contrast, the functional clusters of species that govern the composition effect are less robust and change with environmental conditions. Understanding ecosystem functioning therefore requires that ecological properties are first partitioned by type, then each type of property is analyzed and modeled separately. Approaches without a priori groupings of species, such as functional clustering, appear particularly efficient and robust to unravel the web of species interactions, and identify the role played by species on biodiversity effects.
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http://dx.doi.org/10.1002/ecy.3441DOI Listing
September 2021

Biodiversity as insurance: from concept to measurement and application.

Biol Rev Camb Philos Soc 2021 10 2;96(5):2333-2354. Epub 2021 Jun 2.

Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, 1900 Pleasant St., Boulder, CO, 80303, U.S.A.

Biological insurance theory predicts that, in a variable environment, aggregate ecosystem properties will vary less in more diverse communities because declines in the performance or abundance of some species or phenotypes will be offset, at least partly, by smoother declines or increases in others. During the past two decades, ecology has accumulated strong evidence for the stabilising effect of biodiversity on ecosystem functioning. As biological insurance is reaching the stage of a mature theory, it is critical to revisit and clarify its conceptual foundations to guide future developments, applications and measurements. In this review, we first clarify the connections between the insurance and portfolio concepts that have been used in ecology and the economic concepts that inspired them. Doing so points to gaps and mismatches between ecology and economics that could be filled profitably by new theoretical developments and new management applications. Second, we discuss some fundamental issues in biological insurance theory that have remained unnoticed so far and that emerge from some of its recent applications. In particular, we draw a clear distinction between the two effects embedded in biological insurance theory, i.e. the effects of biodiversity on the mean and variability of ecosystem properties. This distinction allows explicit consideration of trade-offs between the mean and stability of ecosystem processes and services. We also review applications of biological insurance theory in ecosystem management. Finally, we provide a synthetic conceptual framework that unifies the various approaches across disciplines, and we suggest new ways in which biological insurance theory could be extended to address new issues in ecology and ecosystem management. Exciting future challenges include linking the effects of biodiversity on ecosystem functioning and stability, incorporating multiple functions and feedbacks, developing new approaches to partition biodiversity effects across scales, extending biological insurance theory to complex interaction networks, and developing new applications to biodiversity and ecosystem management.
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http://dx.doi.org/10.1111/brv.12756DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8519139PMC
October 2021

Global data on earthworm abundance, biomass, diversity and corresponding environmental properties.

Sci Data 2021 05 21;8(1):136. Epub 2021 May 21.

Forest Sciences and Forest Ecology, University of Göttingen, Büsgenweg 1, Göttingen, Germany.

Earthworms are an important soil taxon as ecosystem engineers, providing a variety of crucial ecosystem functions and services. Little is known about their diversity and distribution at large spatial scales, despite the availability of considerable amounts of local-scale data. Earthworm diversity data, obtained from the primary literature or provided directly by authors, were collated with information on site locations, including coordinates, habitat cover, and soil properties. Datasets were required, at a minimum, to include abundance or biomass of earthworms at a site. Where possible, site-level species lists were included, as well as the abundance and biomass of individual species and ecological groups. This global dataset contains 10,840 sites, with 184 species, from 60 countries and all continents except Antarctica. The data were obtained from 182 published articles, published between 1973 and 2017, and 17 unpublished datasets. Amalgamating data into a single global database will assist researchers in investigating and answering a wide variety of pressing questions, for example, jointly assessing aboveground and belowground biodiversity distributions and drivers of biodiversity change.
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http://dx.doi.org/10.1038/s41597-021-00912-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8140120PMC
May 2021

Consistently positive effect of species diversity on ecosystem, but not population, temporal stability.

Ecol Lett 2021 Oct 17;24(10):2256-2266. Epub 2021 May 17.

School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA.

Despite much recent progress, our understanding of diversity-stability relationships across different study systems remains incomplete. In particular, recent theory clarified that within-species population stability and among-species asynchronous population dynamics combine to determine ecosystem temporal stability, but their relative importance in modulating diversity-ecosystem temporal stability relationships in different ecosystems remains unclear. We addressed this issue with a meta-analysis of empirical studies of ecosystem and population temporal stability in relation to species diversity across a range of taxa and ecosystems. We show that ecosystem temporal stability tended to increase with species diversity, regardless of study systems. Increasing diversity promoted asynchrony, which, in turn, contributed to increased ecosystem stability. The positive diversity-ecosystem stability relationship persisted even after accounting for the influences of environmental covariates (e.g., precipitation and nutrient input). By contrast, species diversity tended to reduce population temporal stability in terrestrial systems but increase population temporal stability in aquatic systems, suggesting that asynchronous dynamics among species are essential for stabilizing diverse terrestrial ecosystems. We conclude that there is compelling empirical evidence for a general positive relationship between species diversity and ecosystem-level temporal stability, but the contrasting diversity-population temporal stability relationships between terrestrial and aquatic systems call for more investigations into their underlying mechanisms.
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http://dx.doi.org/10.1111/ele.13777DOI Listing
October 2021

Synchrony and Perturbation Transmission in Trophic Metacommunities.

Am Nat 2021 06 19;197(6):E188-E203. Epub 2021 Apr 19.

AbstractIn a world where natural habitats are ever more fragmented, the dynamics of metacommunities are essential to properly understand species responses to perturbations. If species' populations fluctuate asynchronously, the risk of their simultaneous extinction is low, thus reducing the species' regional extinction risk. However, identifying synchronizing or desynchronizing mechanisms in systems containing several species and when perturbations affect multiple species is challenging. We propose a metacommunity model consisting of two food chains connected by dispersal to study the transmission of small perturbations affecting populations in the vicinity of an equilibrium. In spite of the complex responses produced by such a system, two elements enable us to understand the key processes that rule the synchrony between populations: (1) knowing which species have the strongest response to perturbations and (2) the relative importance of dispersal processes compared with local dynamics for each species. We show that perturbing a species in one patch can lead to asynchrony between patches if the perturbed species is not the most affected by dispersal. The synchrony patterns of rare species are the most sensitive to the relative strength of dispersal to demographic processes, thus making biomass distribution critical to understanding the response of trophic metacommunities to perturbations. We further partition the effect of each perturbation on species synchrony when perturbations affect multiple trophic levels. Our approach allows disentangling and predicting the responses of simple trophic metacommunities to perturbations, thus providing a theoretical foundation for future studies considering more complex spatial ecological systems.
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http://dx.doi.org/10.1086/714131DOI Listing
June 2021

General statistical scaling laws for stability in ecological systems.

Ecol Lett 2021 Jul 4;24(7):1474-1486. Epub 2021 May 4.

Department of Physiological Diversity, Helmholtz Centre for Environmental Research (UFZ), Leipzig, Germany.

Ecological stability refers to a family of concepts used to describe how systems of interacting species vary through time and respond to disturbances. Because observed ecological stability depends on sampling scales and environmental context, it is notoriously difficult to compare measurements across sites and systems. Here, we apply stochastic dynamical systems theory to derive general statistical scaling relationships across time, space, and ecological level of organisation for three fundamental stability aspects: resilience, resistance, and invariance. These relationships can be calibrated using random or representative samples measured at individual scales, and projected to predict average stability at other scales across a wide range of contexts. Moreover deviations between observed vs. extrapolated scaling relationships can reveal information about unobserved heterogeneity across time, space, or species. We anticipate that these methods will be useful for cross-study synthesis of stability data, extrapolating measurements to unobserved scales, and identifying underlying causes and consequences of heterogeneity.
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http://dx.doi.org/10.1111/ele.13760DOI Listing
July 2021

A graphical causal model for resolving species identity effects and biodiversity-ecosystem function correlations: comment.

Ecology 2021 May 3:e03378. Epub 2021 May 3.

Department of Geography, Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, Zurich, 8057, Switzerland.

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http://dx.doi.org/10.1002/ecy.3378DOI Listing
May 2021

Divergent above- and below-ground biodiversity pathways mediate disturbance impacts on temperate forest multifunctionality.

Glob Chang Biol 2021 Jun 30;27(12):2883-2894. Epub 2021 Mar 30.

Aix Marseille Univ, CNRS, Avignon Université, IRD, IMBE, Technopôle Arbois-Méditerranée Bât. Villemin - BP 80, Aix-en-Provence cedex 04, France.

Biodiversity plays a fundamental role in provisioning and regulating forest ecosystem functions and services. Above-ground (plants) and below-ground (soil microbes) biodiversity could have asynchronous change paces to human-driven land-use impacts. Yet, we know very little how they affect the provision of multiple forest functions related to carbon accumulation, water retention capacity and nutrient cycling simultaneously (i.e. ecosystem multifunctionality; EMF). We used a dataset of 22,000 temperate forest trees from 260 plots within 11 permanent forest sites in Northeastern China, which are recovering from three post-logging disturbances. We assessed the direct and mediating effects of multiple attributes of plant biodiversity (taxonomic, phylogenetic, functional and stand structure) and soil biodiversity (bacteria and fungi) on EMF under the three disturbance levels. We found the highest EMF in highly disturbed rather than undisturbed mature forests. Plant taxonomic, phylogenetic, functional and stand structural diversity had both positive and negative effects on EMF, depending on how the EMF index was quantified, whereas soil microbial diversity exhibited a consistent positive impact. Biodiversity indices explained on average 45% (26%-58%) of the variation in EMF, whereas climate and disturbance together explained on average 7% (0.4%-15%). Our result highlighted that the tremendous effect of biodiversity on EMF, largely overpassing those of both climate and disturbance. While above- (β = 0.02-0.19) and below-ground (β = 0.16-0.26) biodiversity had direct positive effects on EMF, their opposite mediating effects (β = -0.22 vs. β = 0.35 respectively) played as divergent pathways to human disturbance impacts on EMF. Our study sheds light on the need for integrative frameworks simultaneously considering above- and below-ground attributes to grasp the global picture of biodiversity effects on ecosystem functioning and services. Suitable management interventions could maintain both plant and soil microbial biodiversity, and thus guarantee a long-term functioning and provisioning of ecosystem services in an increasing disturbance frequency world.
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http://dx.doi.org/10.1111/gcb.15606DOI Listing
June 2021

How complementarity and selection affect the relationship between ecosystem functioning and stability.

Ecology 2021 06 11;102(6):e03347. Epub 2021 May 11.

Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, CNRS, Moulis, 09200, France.

The biotic mechanisms underlying ecosystem functioning and stability have been extensively-but separately-explored in the literature, making it difficult to understand the relationship between functioning and stability. In this study, we used community models to examine how complementarity and selection, the two major biodiversity mechanisms known to enhance ecosystem biomass production, affect ecosystem stability. Our analytic and simulation results show that although complementarity promotes stability, selection impairs it. The negative effects of selection on stability operate through weakening portfolio effects and selecting species that have high productivity but low tolerance to perturbations ("risk-prone" species). In contrast, complementarity enhances stability by increasing portfolio effects and reducing the relative abundance of risk-prone species. Consequently, ecosystem functioning and stability exhibit either a synergy, if complementarity effects prevail, or trade-off, if selection effects prevail. Across species richness levels, ecosystem functioning and stability tend to be positively related, but negative relationships can occur when selection co-varies with richness. Our findings provide novel insights for understanding the functioning-stability relationship, with potential implications for both ecological research and ecosystem management.
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http://dx.doi.org/10.1002/ecy.3347DOI Listing
June 2021

Scaling up biodiversity-ecosystem functioning relationships: the role of environmental heterogeneity in space and time.

Proc Biol Sci 2021 03 10;288(1946):20202779. Epub 2021 Mar 10.

Department of Biology, McGill University, 1205 Dr. Penfield Avenue, Montreal, Quebec, Canada H3A 1B1.

The biodiversity and ecosystem functioning (BEF) relationship is expected to be scale-dependent. The autocorrelation of environmental heterogeneity is hypothesized to explain this scale dependence because it influences how quickly biodiversity accumulates over space or time. However, this link has yet to be demonstrated in a formal model. Here, we use a Lotka-Volterra competition model to simulate community dynamics when environmental conditions vary across either space or time. Species differ in their optimal environmental conditions, which results in turnover in community composition. We vary biodiversity by modelling communities with different sized regional species pools and ask how the amount of biomass per unit area depends on the number of species present, and the spatial or temporal scale at which it is measured. We find that more biodiversity is required to maintain functioning at larger temporal and spatial scales. The number of species required increases quickly when environmental autocorrelation is low, and slowly when autocorrelation is high. Both spatial and temporal environmental heterogeneity lead to scale dependence in BEF, but autocorrelation has larger impacts when environmental change is temporal. These findings show how the biodiversity required to maintain functioning is expected to increase over space and time.
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http://dx.doi.org/10.1098/rspb.2020.2779DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7944106PMC
March 2021

Biotic homogenization destabilizes ecosystem functioning by decreasing spatial asynchrony.

Ecology 2021 06 30;102(6):e03332. Epub 2021 Apr 30.

Centro de Modelación y Monitoreo de Ecosistemas, Facultad de Ciencias, Universidad Mayor, José Toribio Molina 29, Santiago, 8340589, Chile.

Our planet is facing significant changes of biodiversity across spatial scales. Although the negative effects of local biodiversity (α diversity) loss on ecosystem stability are well documented, the consequences of biodiversity changes at larger spatial scales, in particular biotic homogenization, that is, reduced species turnover across space (β diversity), remain poorly known. Using data from 39 grassland biodiversity experiments, we examine the effects of β diversity on the stability of simulated landscapes while controlling for potentially confounding biotic and abiotic factors. Our results show that higher β diversity generates more asynchronous dynamics among local communities and thereby contributes to the stability of ecosystem productivity at larger spatial scales. We further quantify the relative contributions of α and β diversity to ecosystem stability and find a relatively stronger effect of α diversity, possibly due to the limited spatial scale of our experiments. The stabilizing effects of both α and β diversity lead to a positive diversity-stability relationship at the landscape scale. Our findings demonstrate the destabilizing effect of biotic homogenization and suggest that biodiversity should be conserved at multiple spatial scales to maintain the stability of ecosystem functions and services.
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http://dx.doi.org/10.1002/ecy.3332DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8244107PMC
June 2021

Agricultural land use and the sustainability of social-ecological systems.

Ecol Modell 2020 Dec 1;437. Epub 2020 Oct 1.

Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, CNRS UMR 5321, 09200 Moulis, France.

Agricultural land expansion and intensification, driven by human consumption of agricultural goods, are among the major threats to environmental degradation and biodiversity conservation. Land degradation can ultimately hamper agricultural production through a decrease in ecosystem services. Thus, designing viable land use policies is a key sustainability challenge. We develop a model describing the coupled dynamics of human demography and landscape composition, while imposing a trade-off between agricultural expansion and in-tensification. We model land use strategies spanning from low-intensity agriculture and high land conversion rates per person to high-intensity agriculture and low land conversion rates per person; and explore their consequences on the long-term dynamics of the coupled human-land system. We seek to characterise the strategies' viability in the long run; and understand the mechanisms that potentially lead to large-scale land degradation and population collapse due to resource scarcity. We show that the viability of land use strategies strongly depends on the land's intrinsic recovery rate. We also find that socio-ecological collapses occur when agricultural intensification is not accompanied by a sufficient decrease in land conversion. Based on these findings we stress the dangers of uninformed land use planning and the importance of precautionary behaviour for land use management and land use policy design.
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http://dx.doi.org/10.1016/j.ecolmodel.2020.109312DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116488PMC
December 2020

Disentangling local, metapopulation, and cross-community sources of stabilization and asynchrony in metacommunities.

Ecosphere 2020 Apr 21;11(4):e03078. Epub 2020 Apr 21.

Department of Biology, McMaster University, 1280 Main Street West, Hamilton Ontario L8S 4K1 Canada.

Asynchronous fluctuations of populations are essential for maintaining stable levels of bio-mass and ecosystem function in landscapes. Yet, understanding the stabilization of metacommunities by asynchrony is complicated by the existence of multiple forms of asynchrony that are typically studied independently: Community ecologists, for instance, focus on asynchrony within and among local communities, while population ecologists emphasize asynchrony of populations in metapopulations. Still, other forms of asynchrony, such as that which underlies the spatial insurance effect, are not captured by any existing analytical frameworks. We therefore developed a framework that would in one analysis unmask the stabilizing roles of local communities and metapopulations and so unify these perspectives. Our framework shows that metacommunity stabilization arises from one local and two regional forms of asynchrony: (1) asynchrony among species of a local community, (2) asynchrony among populations of a metapopulation, and (3) cross-community asynchrony, which is between different species in different local communities and underlies spatial insurance. For each type of stabilization, we derived links to diversity indices and associated diversity-stability relationships. We deployed this framework in a set of rock pool invertebrate metacommunities in Discovery Bay, Jamaica, to partition sources of stabilization and test their dependence on diversity. Cross-community asynchrony was the dominant form of stabilization, accounting for >60% of total metacommunity stabilization despite being undetectable with existing frameworks. Environmental variation influenced types of stabilization through different mechanisms. pH and dissolved oxygen, for example, increased asynchrony by decorrelating local species, while salinity did so by changing the abundance structure of metapopulations. Lastly, all types of asynchrony depended strongly on different types of diversity (alpha, metapopulation, and beta diversity drove local, metapopulation, and cross-community asynchrony, respectively) to produce multiple diversity-stability relationships within metacommunities. Our new partition of metacommunity dynamics highlights how different elements-from local communities to metapopulations-combine to stabilize metacommunities and depend critically on contrasting environmental regimes and diversities. Understanding and balancing these sources of stability in dynamic landscapes is a looming challenge for the future. We suggest that synthetic frameworks which merge ecological perspectives will be essential for grasping and safeguarding the stability of natural systems.
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http://dx.doi.org/10.1002/ecs2.3078DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116476PMC
April 2020

Can biomass distribution across trophic levels predict trophic cascades?

Ecol Lett 2021 Mar 13;24(3):464-476. Epub 2020 Dec 13.

Theoretical and Experimental Ecology Station, CNRS, Moulis, 09200, France.

The biomass distribution across trophic levels (biomass pyramid) and cascading responses to perturbations (trophic cascades) are archetypal representatives of the interconnected set of static and dynamical properties of food chains. A vast literature has explored their respective ecological drivers, sometimes generating correlations between them. Here we instead reveal a fundamental connection: both pyramids and cascades reflect the dynamical sensitivity of the food chain to changes in species intrinsic rates. We deduce a direct relationship between cascades and pyramids, modulated by what we call trophic dissipation - a synthetic concept that encodes the contribution of top-down propagation of consumer losses in the biomass pyramid. Predictable across-ecosystem patterns emerge when systems are in similar regimes of trophic dissipation. Data from 31 aquatic mesocosm experiments demonstrate how our approach can reveal the causal mechanisms linking trophic cascades and biomass distributions, thus providing a road map to deduce reliable predictions from empirical patterns.
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http://dx.doi.org/10.1111/ele.13658DOI Listing
March 2021

Ecotone formation through ecological niche construction: the role of biodiversity and species interactions.

Ecography 2020 May 13;43(5):714-723. Epub 2020 Feb 13.

Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, UMR 5321, CNRS and Paul Sabatier Univ., Moulis, France.

Rapid changes in species composition, also known as ecotones, can result from various causes including rapid changes in environmental conditions, or physiological thresholds. The possibility that ecotones arise from ecological niche construction by ecosystem engineers has received little attention. In this study, we investigate how the diversity of ecosystem engineers, and their interactions, can give rise to ecotones. We build a spatially explicit dynamical model that couples a multispecies community and its abiotic environment. We use numerical simulations and analytical techniques to determine the biotic and abiotic conditions under which ecotone emergence is expected to occur, and the role of biodiversity therein. We show that the diversity of ecosystem engineers can lead to indirect interactions through the modification of their shared environment. These interactions, which can be either competitive or mutualistic, can lead to the emergence of discrete communities in space, separated by sharp ecotones where a high species turnover is observed. Considering biodiversity is thus critical when studying the influence of species-environment interactions on the emergence of ecotones. This is especially true for the wide range of species that have small to moderate effects on their environment. Our work highlights new mechanisms by which biodiversity loss could cause significant changes in spatial community patterns in changing environments.
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http://dx.doi.org/10.1111/ecog.04902DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116457PMC
May 2020

Context-dependency of tree species diversity, trait composition and stand structural attributes regulate temperate forest multifunctionality.

Sci Total Environ 2021 Feb 14;757:143724. Epub 2020 Nov 14.

CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China. Electronic address:

High species diversity is generally thought to be a requirement for sustaining forest multifunctionality. However, the degree to which the relationship between species-, structural-, and trait-diversity of forests and multifunctionality depend on the context (such as stand age or abiotic conditions) is not well studied. Here, we hypothesized that context-dependency of tree species diversity, functional trait composition and stand structural attributes promote temperate forest multifunctionality including above- and below-ground multiple and single functions. To do so, we used repeated forest inventory data, from temperate mixed forests of northeast China, to quantify two above-ground (i.e. coarse woody productivity and wild edible plant biomass), five below-ground (i.e. soil organic carbon, total soil nitrogen, potassium, phosphorus and sulfur) functions, tree species diversity, individual tree size variation (CV) and functional trait composition of specific leaf area (CWM) as well as stand age and abiotic conditions. We found that tree species diversity increased forest multifunctionality and most of the single functions. Below-ground single and multifunctionality were better explained by tree species diversity. In contrast, above-ground single and multifunctionality were better explained by CV. However, CWM was also an additional important driver for maintaining above- and below-ground forest multifunctionality through opposing plant functional strategies. Stand age markedly reduced forest multifunctionality, tree species diversity and CWM but substantially increased CV. Below-ground forest multifunctionality and tree species diversity decreased while above-ground forest multifunctionality increased on steep slopes. These results highlight that context-dependency of forest diversity attributes might regulate forest multifunctionality but may not have a consistent effect on above-ground and below-ground forest multifunctionality due to the fact that those functions were driven by varied functional strategies of different plant species. We argue that maximizing forest complexity could act as a viable strategy to maximizing forest multifunctionality, while also promoting biodiversity conservation to mitigate climate change effects.
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http://dx.doi.org/10.1016/j.scitotenv.2020.143724DOI Listing
February 2021

Unequal access to resources undermines global sustainability.

Sci Total Environ 2021 Apr 16;763:142981. Epub 2020 Oct 16.

CNRS - Station d'Ecologie Théorique et Expérimentale, 2 route du CNRS, 09200 Moulis, France. Electronic address:

Within a global society there exist various land use patterns, inequality, and the movement of people and goods. The various practices and behaviours associated with our current society raise questions about the future sustainability of the human population and the natural environment. We derive a simplified model of the global socio-ecological system in an effort to explore the connections between human well-being and land resources, specifically looking at resource accessibility, conservation initiatives and human migration between two economically diverse regions. We find that the spatial aspect of a global system with two distinct regions allows for faster development of technology, higher peaks in population size, greater natural land degradation, and generally speaking lower population well-being in the long-term. The unequal access to resources and differences in technological progress, alter the outcome of land management (i.e., conservation) and social behaviours (i.e., migration). We conclude that any socio-ecological management practices should be conscientious of the diversity in land access, population size, population well-being and development within the global society, as the potential for unintended consequences is high.
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http://dx.doi.org/10.1016/j.scitotenv.2020.142981DOI Listing
April 2021

General destabilizing effects of eutrophication on grassland productivity at multiple spatial scales.

Nat Commun 2020 10 23;11(1):5375. Epub 2020 Oct 23.

Department of Ecology, Evolution, and Behavior, University of MN, St. Paul, MN, 55108, USA.

Eutrophication is a widespread environmental change that usually reduces the stabilizing effect of plant diversity on productivity in local communities. Whether this effect is scale dependent remains to be elucidated. Here, we determine the relationship between plant diversity and temporal stability of productivity for 243 plant communities from 42 grasslands across the globe and quantify the effect of chronic fertilization on these relationships. Unfertilized local communities with more plant species exhibit greater asynchronous dynamics among species in response to natural environmental fluctuations, resulting in greater local stability (alpha stability). Moreover, neighborhood communities that have greater spatial variation in plant species composition within sites (higher beta diversity) have greater spatial asynchrony of productivity among communities, resulting in greater stability at the larger scale (gamma stability). Importantly, fertilization consistently weakens the contribution of plant diversity to both of these stabilizing mechanisms, thus diminishing the positive effect of biodiversity on stability at differing spatial scales. Our findings suggest that preserving grassland functional stability requires conservation of plant diversity within and among ecological communities.
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http://dx.doi.org/10.1038/s41467-020-19252-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7585434PMC
October 2020

Thermal mismatches in biological rates determine trophic control and biomass distribution under warming.

Glob Chang Biol 2021 Jan 16;27(2):257-269. Epub 2020 Nov 16.

INRAE, Aix Marseille Univ., UMR RECOVER, Aix-en-Provence, France.

Temperature has numerous effects on the structure and dynamics of ecological communities. Yet, there is no general trend or consensus on the magnitude and directions of these effects. To fill this gap, we propose a mechanistic framework based on key biological rates that predicts how temperature influences biomass distribution and trophic control in food webs. We show that these predictions arise from thermal mismatches between biological rates and across trophic levels. We couple our theory with experimental data for a wide range of species and find that warming should lead to top-heavier terrestrial food chains and stronger top-down control in aquatic environments. We then derive predictions for the effects of temperature on herbivory and validate them with data on stream grazers. Our study provides a mechanistic explanation of thermal effects on consumer-resource systems which is crucial to better understand the biogeography and the consequences of global warming on trophic dynamics.
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http://dx.doi.org/10.1111/gcb.15395DOI Listing
January 2021

How community adaptation affects biodiversity-ecosystem functioning relationships.

Ecol Lett 2020 Aug 31;23(8):1263-1275. Epub 2020 May 31.

Université Côte d'Azur, INRAE, CNRS, ISA, 06900, Sophia Antipolis, France.

Evidence is growing that evolutionary dynamics can impact biodiversity-ecosystem functioning (BEF) relationships. However the nature of such impacts remains poorly understood. Here we use a modelling approach to compare random communities, with no trait evolutionary fine-tuning, and co-adapted communities, where traits have co-evolved, in terms of emerging biodiversity-productivity, biodiversity-stability and biodiversity-invasion relationships. Community adaptation impacted most BEF relationships, sometimes inverting the slope of the relationship compared to random communities. Biodiversity-productivity relationships were generally less positive among co-adapted communities, with reduced contribution of sampling effects. The effect of community-adaptation, though modest regarding invasion resistance, was striking regarding invasion tolerance: co-adapted communities could remain very tolerant to invasions even at high diversity. BEF relationships are thus contingent on the history of ecosystems and their degree of community adaptation. Short-term experiments and observations following recent changes may not be safely extrapolated into the future, once eco-evolutionary feedbacks have taken place.
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http://dx.doi.org/10.1111/ele.13530DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7116443PMC
August 2020

Organizing principles for vegetation dynamics.

Nat Plants 2020 05 11;6(5):444-453. Epub 2020 May 11.

Ministry of Education Key Laboratory for Earth System Modeling, Department of Earth System Science, Tsinghua University, Beijing, China.

Plants and vegetation play a critical-but largely unpredictable-role in global environmental changes due to the multitude of contributing processes at widely different spatial and temporal scales. In this Perspective, we explore approaches to master this complexity and improve our ability to predict vegetation dynamics by explicitly taking account of principles that constrain plant and ecosystem behaviour: natural selection, self-organization and entropy maximization. These ideas are increasingly being used in vegetation models, but we argue that their full potential has yet to be realized. We demonstrate the power of natural selection-based optimality principles to predict photosynthetic and carbon allocation responses to multiple environmental drivers, as well as how individual plasticity leads to the predictable self-organization of forest canopies. We show how models of natural selection acting on a few key traits can generate realistic plant communities and how entropy maximization can identify the most probable outcomes of community dynamics in space- and time-varying environments. Finally, we present a roadmap indicating how these principles could be combined in a new generation of models with stronger theoretical foundations and an improved capacity to predict complex vegetation responses to environmental change.
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http://dx.doi.org/10.1038/s41477-020-0655-xDOI Listing
May 2020

Community efficiency during succession: a test of MacArthur's minimization principle in phytoplankton communities.

Ecology 2020 06 17;101(6):e03015. Epub 2020 Mar 17.

Centre for Geometric Biology, School of Biological Sciences, Monash University, Melbourne, Victoria, 3800, Australia.

Robert MacArthur's niche theory makes explicit predictions on how community function should change over time in a competitive community. A key prediction is that succession progressively minimizes the energy wasted by a community, but this minimization is a trade-off between energy losses from unutilised resources and costs of maintenance. By predicting how competition determines community efficiency over time MacArthur's theory may inform on the impacts of disturbance on community function and invasion risk. We provide a rare test of this theory using phytoplankton communities, and find that older communities wasted less energy than younger ones but that the reduction in energy wastage was not monotonic over time. While community structure followed consistent and clear trajectories, community function was more idiosyncratic among adjoining successional stages and driven by total community biomass rather than species composition. Our results suggest that subtle shifts in successional sequence can alter community efficiency and these effects determine community function independently of individual species membership. We conclude that, at least in phytoplankton communities, general trends in community function are predictable over time accordingly to MacArthur's theory. Tests of MacArthur's minimization principle across very different systems should be a priority given the potential of this theory to inform on the functional properties of communities.
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http://dx.doi.org/10.1002/ecy.3015DOI Listing
June 2020

Scaling-up biodiversity-ecosystem functioning research.

Ecol Lett 2020 Apr 29;23(4):757-776. Epub 2020 Jan 29.

Centre for Biodiversity Theory and Modelling, Theoretical and Experimental Ecology Station, CNRS, 2 route du CNRS, 09200, Moulis, France.

A rich body of knowledge links biodiversity to ecosystem functioning (BEF), but it is primarily focused on small scales. We review the current theory and identify six expectations for scale dependence in the BEF relationship: (1) a nonlinear change in the slope of the BEF relationship with spatial scale; (2) a scale-dependent relationship between ecosystem stability and spatial extent; (3) coexistence within and among sites will result in a positive BEF relationship at larger scales; (4) temporal autocorrelation in environmental variability affects species turnover and thus the change in BEF slope with scale; (5) connectivity in metacommunities generates nonlinear BEF and stability relationships by affecting population  synchrony at local and regional scales; (6) spatial scaling in food web structure and diversity will generate scale dependence in ecosystem functioning. We suggest directions for synthesis that combine approaches in metaecosystem and metacommunity ecology and integrate cross-scale feedbacks. Tests of this theory may combine remote sensing with a generation of networked experiments that assess effects at multiple scales. We also show how anthropogenic land cover change may alter the scaling of the BEF relationship. New research on the role of scale in BEF will guide policy linking the goals of managing biodiversity and ecosystems.
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http://dx.doi.org/10.1111/ele.13456DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497049PMC
April 2020
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