Missions

This postdoctoral project aims to test two complementary hypotheses:
1. A minority of species account for the majority of ecosystem functioning, in line with the Pareto principle;
2. Functionally original species - i.e. those with unique combinations of traits - have disproportionate effects on certain ecosystem processes.

Activités

The main objectives are:
1. Conduct a critical synthesis of existing approaches that distinguish between species-specific effects and those linked to overall biodiversity.
2. Develop a conceptual and/or methodological framework, grounded in existing literature, to empirically test the impact of species (or groups of species) on ecosystem functioning.
3. Test the Pareto hypothesis using ~20 existing datasets covering a range of taxonomic groups (plants, microorganisms, animals), ecosystem processes (including multifunctionality), and spatial scales (local to regional). The goal is to quantify the proportion of species responsible for the bulk of observed functioning.
4. Identify the key species highlighted by this approach, analyzing their location in functional trait space, the proportion of functional space they occupy, and their degree of functional distinctiveness.

Compétences

We seek a curious, creative, and rigorous researcher with a strong background in functional ecology and an interest in conceptual, quantitative, and interdisciplinary approaches (e.g., biogeography, evolutionary ecology, genetics). An interest in methodological and statistical development is a plus. Critical thinking, autonomy, and openness are highly valued.

Contexte de travail

Which species, and what proportion of them, matter for ecosystem functioning?

Scientific Context
The role of biodiversity in regulating ecosystem functioning is now well established, supported by both experimental and theoretical approaches. But how much of this biodiversity is truly involved in these processes? Is it the full set of species present, or rather a small subset - possibly even a single species - exerting a disproportionate influence?
Although various theoretical frameworks aim to disentangle collective (i.e. overall diversity) from specific (i.e. individual species) effects, species-specific contributions are still often treated as residual noise and rarely examined systematically.
Could the Pareto principle (or 80/20 rule), widely used in economics and management, also apply to ecology - i.e. could 20% of the species account for 80% of ecosystem functioning? While this hypothesis holds major theoretical and applied implications, it has rarely been tested in ecological contexts. It directly challenges how we prioritize conservation and management: should we aim to protect all biodiversity, or focus on the few key species that drive most ecosystem processes?
Conceptual Framework: Functional Traits and Functional Distinctiveness
Functional trait-based approaches offer a powerful lens to explore these questions. They will be used to determine how much of the functional space is occupied by the species most strongly influencing ecosystem processes.
A central concept will be that of functional distinctiveness: identifying species that are the most atypical in a multidimensional trait space. We will test whether such functionally original species also exert disproportionate ecological effects.
This research is embedded in the broader work of the international working group FREE (Functional Rarity in Ecology and Evolution) (https://www.fondationbiodiversite.fr/la-frb-en-action/programmes-et-projets/le-cesab/free/), funded by the French Foundation for Biodiversity Research (FRB) via the CESAB initiative and coordinated by Cyrille Violle (CNRS) and Lucie Mahaut (INRAE). The recruited postdoctoral fellow will be fully integrated into this dynamic international network and is expected to play an active and leading role in its activities.
A key conceptual challenge will be to determine whether some species have major effects due to unique traits not captured by standard trait datasets. Addressing this paradox will represent an original contribution of the project.

Research Environment
The postdoctoral researcher will be hosted by the ECOPAR group at the Centre for Functional and Evolutionary Ecology (CEFE) in Montpellier, led by Cyrille Violle. ECOPAR specializes in plant functional ecology but also works on other taxa (microorganisms, birds, fish), notably through the FREE project. The project includes a strong synthesis component, with opportunities for empirical extensions depending on the candidate's interests. The team also has recognized experimental expertise, opening potential for experimental testing of hypotheses.

Key References
Bannar-Martin, K. H., Kremer, C. T., Ernest, S. K. M., Leibold, M. A., Auge, H., Chase, J., Declerck, S. A. J., Eisenhauer, N., Harpole, S., Hillebrand, H., Isbell, F., Koffel, T., Larsen, S., Narwani, A., Petermann, J. S., Roscher, C., Cabral, J. S., & Supp, S. R. (2018). Integrating community assembly and biodiversity to better understand ecosystem function: The Community Assembly and the Functioning of Ecosystems (CAFE) approach. Ecology Letters, 21(2), 167–180. https://doi.org/10.1111/ele.12895
Brun, P., Violle, C., Mouillot, D., Mouquet, N., Enquist, B. J., Munoz, F., Münkemüller, T., Ostling, A., Zimmermann, N. E., & Thuiller, W. (2022). Plant community impact on productivity: Trait diversity or key(stone) species effects? Ecology Letters, 25(4), 913–925. https://doi.org/10.1111/ele.13968
Cadotte, M. W., Carscadden, K., & Mirotchnick, N. (2011). Beyond species: Functional diversity and the maintenance of ecological processes and services. Journal of Applied Ecology, 48(5), 1079–1087. https://doi.org/10.1111/j.1365-2664.2011.02048.x
Dee, L. E., Cowles, J., Isbell, F., Pau, S., Gaines, S. D., & Reich, P. B. (2019). When Do Ecosystem Services Depend on Rare Species? Trends in Ecology & Evolution, 34(8), 746–758. https://doi.org/10.1016/j.tree.2019.03.010
Dee, L. E., Ferraro, P. J., Severen, C. N., Kimmel, K. A., Borer, E. T., Byrnes, J. E. K., Clark, A. T., Hautier, Y., Hector, A., Raynaud, X., Reich, P. B., Wright, A. J., Arnillas, C. A., Davies, K. F., MacDougall, A., Mori, A. S., Smith, M. D., Adler, P. B., Bakker, J. D., … Loreau, M. (2023). Clarifying the effect of biodiversity on productivity in natural ecosystems with longitudinal data and methods for causal inference. Nature Communications, 14(1), Article 1. https://doi.org/10.1038/s41467-023-37194-5
Delalandre, L., Gaüzère, P., Thuiller, W., Cadotte, M., Mouquet, N., Mouillot, D., Munoz, F., Denelle, P., Loiseau, N., Morin, X., & Violle, C. (2022). Functionally distinct tree species support long-term productivity in extreme environments. Proceedings of the Royal Society B: Biological Sciences, 289(1967), 20211694. https://doi.org/10.1098/rspb.2021.1694
Díaz, S., Lavorel, S., de Bello, F., Quétier, F., Grigulis, K., & Robson, T. M. (2007). Incorporating plant functional diversity effects in ecosystem service assessments. Proceedings of the National Academy of Sciences, 104(52), 20684–20689. https://doi.org/10.1073/pnas.0704716104
Garnier, E., Cortez, J., Billès, G., Navas, M.-L., Roumet, C., Debussche, M., Laurent, G., Blanchard, A., Aubry, D., Bellmann, A., Neill, C., & Toussaint, J.-P. (2004). Plant functional markers capture ecosystem properties during secondary succession. Ecology, 85(9), 2630–2637. https://doi.org/10.1890/03-0799
Jaillard, B., Deleporte, P., Isbell, F., Loreau, M., & Violle, C. (2021). Consistent functional clusters explain the effects of biodiversity on ecosystem productivity in a long-term experiment. Ecology, 102(9), e03441. https://doi.org/10.1002/ecy.3441
Loreau, M., & Hector, A. (2001). Partitioning selection and complementarity in biodiversity experiments. Nature, 412(6842), 72–76.
Mahaut, L., Fort, F., Violle, C., & Freschet, G. T. (2020). Multiple facets of diversity effects on plant productivity: Species richness, functional diversity, species identity and intraspecific competition. Functional Ecology, 34(1), 287–298. https://doi.org/10.1111/1365-2435.13473
Norkko, A., Villnäs, A., Norkko, J., Valanko, S., & Pilditch, C. (2013). Size matters: Implications of the loss of large individuals for ecosystem function. Scientific Reports, 3(1), 2646. https://doi.org/10.1038/srep02646
Pigot, A. L., Dee, L. E., Richardson, A. J., Cooper, D. L. M., Eisenhauer, N., Gregory, R. D., Lewis, S. L., Macgregor, C. J., Massimino, D., Maynard, D. S., Phillips, H. R. P., Rillo, M., Loreau, M., & Haegeman, B. (2025). Macroecological rules predict how biomass scales with species richness in nature. Science, 387(6740), 1272–1276. https://doi.org/10.1126/science.adq3278
Violle, C., Thuiller, W., Mouquet, N., Munoz, F., Kraft, N. J. B., Cadotte, M. W., Livingstone, S. W., & Mouillot, D. (2017). Functional rarity: The ecology of outliers. Trends in Ecology and Evolution, 32(5), 356–367. https://doi.org/10.1016/j.tree.2017.02.002

Contraintes et risques

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