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Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity–ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity–productivity relationships. However, the overlooking of the specific role played by key species has limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects. Here, we conducted a grassland diversity–productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production. We grew six plant species in monoculture, as well as in every combination of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half‐density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community‐weighted mean (CWM) of each trait. We further partitioned above‐ground biodiversity effect into complementarity and selection effects. We observed strong positive biodiversity effects on both above‐ground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (Plantago lanceolata) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity–ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

Aim Conservation planning and prioritization generally have focused on protecting taxa based on assessments of their long‐term persistence or on protecting habitats and sites with high species richness. An implicit assumption of these approaches is that species are equally different from each other. We propose metrics for conservation planning and prioritization that include consideration of differences among taxa in their functional characteristics to ensure long‐term maintenance of ecosystem functioning and services. Innovation We define metrics of functional distinctiveness, irregularity and singularity for a species. Functional distinctiveness is the mean distance in trait space of a species to all other species in a community. Functional irregularity is the variation in the proportional distances of a focal species to all other species based on a Hill function. Functional singularity is the product of those two metrics. These metrics can be weighted based on proportional abundance, biomass or frequency of occurrence. The metrics can be used to prioritize particular species for conservation based on their functional characteristics or to identify functionally distinct priority areas for conservation using the mean functional distinctiveness, irregularity and singularity of a set of species in an area. The metrics can be compared to the species richness of that area, thereby identifying areas that might have low species richness, but whose species are especially functionally distinct, providing important information of conservation relevance. Main conclusions Applying these metrics to data on the global distributions of parrots, we identified species that are not of current conservation concern because they are geographically widespread, but which might be prioritized due to their functional singularity (e.g., the scarlet macaw). We also identified areas that are species poor and not generally considered noteworthy for their parrot fauna, but that contain a fauna that is functionally singular (e.g., Chile). Together, these metrics broaden the criteria used for conservation prioritization.

Despite evidence of a positive effect of functional diversity on ecosystem productivity, the importance of functionally distinct species (i.e. species that display an original combination of traits) is poorly understood. To investigate howdistinct species affect ecosystem productivity,we used a forest-gap model to simulate realistic temperate forest successions along an environmental gradient and measured ecosystem productivity at the end of the successional trajectories.We performed 10 560 simulations with different sets and numbers of species, bearing either distinct or indistinct functional traits, and compared them to random assemblages, to mimic the consequences of a regional loss of species. Long-term ecosystem productivity dropped when distinct species were lost first from the regional pool of species, under the harshest environmental conditions. On the contrary, productivity was more dependent on ordinary species in milder environments. Our findings showthat species functional distinctiveness, integrating multiple trait dimensions, can capture species-specific effects on ecosystem productivity. In a context of an environmentally changing world, they highlight the need to investigate the role of distinct species in sustaining ecosystem processes, particularly in extreme environmental conditions.

Aim: Rare species typically contribute more to functional diversity than common species. However, humans have altered the occupancy and abundance patterns of many species—the basis upon which we define \"rarity.\" Here, we use a globally unique dataset from hydrothermal vents—an untouched ecosystem—to test whether rare species over-contribute to functional diversity. Location: Juan de Fuca Ridge hydrothermal vent fields, Northeast Pacific Ocean. Methods: We first conduct a comprehensive review to set up expectations for the relative contributions of rare and common species to functional diversity. We then quantify the rarity and commonness of 37 vent species with relevant trait information to assess the relationship between rarity and functional distinctiveness—a measure of the uniqueness of the traits of a species relative to traits of coexisting species. Next, we randomly assemble communities to test whether rare species over-contribute to functional diversity in artificial assemblages ranging in species richness. Then, we test whether biotic interactions influence functional diversity contributions by comparing the observed contribution of each species to a null expectation. Finally, we identify traits driving functional distinctiveness using a distance-based redundancy analysis. Results: Across functional diversity metrics and species richness levels, we find that both rare and common species can contribute functional uniqueness. Some species always offer unique trait combinations, and these species host bacterial symbionts and provide habitat complexity. Moreover, we find that contributions of species to functional diversity may be influenced by biotic interactions. Main conclusions: Our findings show that many common species make persistent, unique contributions to functional diversity. Thus, it is key to consider whether the abundance and occupancy of species have been reduced, relative to historical baselines, when interpreting the contributions of rare species to functional diversity. Our work highlights the importance of testing ecological theory in ecosystems unaffected by human activities for the conservation of biodiversity.

Aim Rare species make substantial contributions to coastal ecosystem functions. Functional rarity (FR) and phylogenetic rarity (PR) are important features for biodiversity conservation. This work aimed to discuss the necessity and reasonableness of conserving fish FR and PR in coastal seas. Location China. Methods By compiling historical fish investigation data, joint species distribution modelling (JSDM) was applied to model fish communities in coastal China Seas. Biogeographic patterns of FR and PR were explored, and the effectiveness of current MPA networks in terms of match/mismatch with the hotspots of rarity was assessed. Results A total of 44 functionally rare species and 22 phylogenetically rare species were identified. Six of these species were both functionally and phylogenetically rare, and only one was listed as endangered on the Red List of the International Union for Conservation of Nature (IUCN). Functional rarity hotspots covered 10.27% of the coastal areas, which geographically converged in the southern and eastern coast of Taiwan, the Yangtze River Estuary and the Yellow River Estuary. Phylogenetic rarity hotspots only covered 3.06% of the coastal areas, which were sporadically distributed in the coastal East China Sea, the Bohai Sea and the northern Yellow Sea. Current marine‐protected areas (MPAs) only represented 16.16% of the FR hotspots and 20.48% of the PR hotspots, indicating substantial mismatched areas between the MPAs and the hotspots of FR and PR. Main Conclusions Only considering threatened species in conservation practices will omit functionally and phylogenetically rare species because FR and PR are not necessarily correlated with species threat status on the IUCN Red List. Functional rarity hotspots do not necessarily overlap with PR hotspots, and current MPAs mismatch the majority of these areas. We therefore advocate that conservation prioritization and expansion of MPA networks should account for FR and PR both at the species and site levels.

Protected areas (PAs) are pivotal tools for biodiversity conservation on the Earth. Europe has had an extensive protection system since Natura 2000 areas were created in parallel with traditional parks and reserves. However, the extent to which this system covers not only taxonomic diversity but also other biodiversity facets, such as evolutionary history and functional diversity, has never been evaluated. Using high-resolution distribution data of all European tetrapods together with dated molecular phylogenies and detailed trait information, we first tested whether the existing European protection system effectively covers all species and in particular, those with the highest evolutionary or functional distinctiveness. We then tested the ability of PAs to protect the entire tetrapod phylogenetic and functional trees of life by mapping species' target achievements along the internal branches of these two trees. We found that the current system is adequately representative in terms of the evolutionary history of amphibians while it fails for the rest. However, the most functionally distinct species were better represented than they would be under random conservation efforts. These results imply better protection of the tetrapod functional tree of life, which could help to ensure long-term functioning of the ecosystem, potentially at the expense of conserving evolutionary history.

Functionally and evolutionarily distinct species have traits or an evolutionary history that are shared by few others in a given set, which make them priority species for biodiversity conservation. On islands, life in isolation has led to the evolution of many distinct forms and functions as well as to a high level of endemism. The aim of this study is to assess the evolutionary and functional distinctiveness of insular monocotyledons and their distribution across 126 islands worldwide. We show that evolutionary and functional distinctiveness are decoupled but that both are higher on islands than on continental areas. Anagenesis on islands followed by extinctions and/or diversification on the mainland may have led to highly evolutionarily distinct species while functionally distinct species may have arisen from ecological niche shift or niche expansion. Insular endemic species with high evolutionary distinctiveness but not with high functional distinctiveness are significantly range-restricted compared to less distinct species, possibly indicating differences in dispersal potential. By showing that distinctiveness is high on islands and that the most distinct species are range-restricted, our study has important conservation implications. Indeed, islands are among the most threatened systems of the world, and extinctions of the most distinct species could lead to significant loss of phylogenetic and functional diversity.

Background and aims Ultramafic soils have high metal concentrations, offering a key opportunity to understand if such metals are strong predictors of leaf stoichiometry. This is particularly relevant for tropical forests where large knowledge gaps exist. Methods On the tropical island of Sulawesi, Indonesia, we sampled forests on sand, limestone, mafic and ultramafic soils that present a range of soil metal concentrations. We asked how variation in 12 soil elements (metals and macronutrients) influenced leaf stoichiometry and whether stoichiometric distinctiveness (the average difference between a species and all others in a multivariate space, the axes of which are the concentrations of each leaf element) is influenced by increasing soil metal concentrations. Results Positive correlations between corresponding elements in soils and leaves were only found for Ca and P. Noticeably, soil Cr had a negative effect upon leaf P. Whilst most species had low stoichiometric distinctiveness, some species had greater distinctiveness on stressful metal-rich ultramafic soils, generally caused by the accumulation of Al, Co, Cr or Ni. Conclusions Our observation of increased stoichiometric distinctiveness in tropical forests on ultramafic soils indicates greater niche differentiation, and contrasts with the assumption that stressful environments remove species with extreme phenotypes.

Strategic Environmental Assessment (SEA) of land‐use planning is a major tool to minimize the environmental impact of urbanization. SEA implementation is, however, often based on incomplete biodiversity diagnostics and almost entirely focused on lists of priority species with high conservation value. At the same time, recent studies in Systematic Conservation Planning illustrate how to integrate the multidimensionality of biodiversity on a large scale, such as ecosystem function and species' evolutionary uniqueness, which could broaden the spectrum of stakes for SEA on a regional scale. The objective of this study is to assess the complementarity and feasibility of adopting a multi‐facet approach to define spatial biodiversity priorities and inform regional SEA stakeholders. To do so, we used a spatial prioritization tool based on Species Distribution Models (SDM) to assess four facets of biodiversity (“priority species list”, “threatened species”, “functional distinctiveness” and “phylogenetic distinctiveness”). In a study of three taxonomic groups (Aves, Flora, and Papilionidae) in three regional administrative entities in France, our results confirm the pertinence of different facets of biodiversity to identify new and complementary priority areas for conservation. However, the limited amount of data adequate for SDM may bias the choice of conservation priorities. We conclude on the clear need to promote a holistic approach to biodiversity conservation if we are to correctly reduce the impacts of development projects on a land‐use planning scale. Résumé L'évaluation environnementale stratégique (EES) de l'aménagement du territoire est un outil essentielle pour minimiser l'impact environnemental de l'urbanization. La mise en œuvre de l'EES est cependant souvent basée sur des diagnostics de biodiversité incomplets et non exhaustifs et se concentre généralement sur des listes d'espèces prioritaires à haute valeur de conservation. Dans le même temps, la composante multidimensionnelle de la biodiversité est de plus en plus étudiée à travers des facettes auparavant négligées à large échelle des processus de Planification de la Conservation ; telles que la fonction des écosystèmes et le caractère unique de l'évolution des espèces qui pourrait élargir le spectre des enjeux de l'EES à l'échelle régionale. L'objectif de cette étude est. d'évaluer la complémentarité et la faisabilité d'adopter une approche multidimensionnelle pour définir les priorités spatiales en matière de biodiversité afin d'informer les acteurs régionaux de l'EES. Pour ce faire, nous avons utilisé un outil de priorisation spatiale basé sur les modèles de distribution des espèces (SDM) et considéré quatre facettes de la biodiversité (la “liste d'espèces prioritaires”, les “espèces menacées”, la “spécificité fonctionnelle” et la “spécificité phylogénétique”). A travers l'étude de trois groupes taxonomique (Oiseaux, Flore et Papillons) dans trois intercommunalités françaises, nous confirmons la pertinence d'étudier différentes facettes de la biodiversité pour identifier de nouvelles zones prioritaires complémentaires pour la conservation. Néanmoins, la quantité limitée de données adaptés pour les SDM peut biaiser le choix des priorités de conservation. Nous concluons sur la nécessité évidente de promouvoir une approche holistique de la conservation de la biodiversité si nous voulons réduire correctement les impacts des projets de développement à l'échelle de l'aménagement du territoire. Our study explores the complementarity and feasibility of adopting a multi‐facet approach to define spatial biodiversity priorities to inform regional Strategic Environmental Assessment (SEA) stakeholders. The study was conducted with data for three taxonomic groups in three local administrative entities situated in very different social and ecological contexts. We propose a workflow to help SEA stakeholders define multi‐faceted conservation priorities from open‐access databases. Finally, we provide recommendations for an operational implementation of such tools by SEA stakeholders.

Relatively little attention has been paid to the underlying mechanisms determining the dominance of non-indigenous species (NIS) once established, despite being regarded as a proxy of invasion success and potential impacts in recipient communities. To bridge this knowledge gap, here we evaluate the potential direct and indirect effects of community filters on the dominance of two widespread NIS in the Baltic Sea: Marenzelleria spp. and the round goby ( Neogobius melanostomus ) within their corresponding communities. We applied a structural equation modelling approach to assess the direct and indirect effects amongst multiple abiotic and biotic variables on the relative biomass (as proxy of dominance) of NIS. The biotic variables represented the taxonomic- and functional diversity of the recipient communities, as well as the trait similarity between NIS and native species. We observed a comparable influence of abiotic and biotic drivers on the dominance of both NIS, with biotic variables having a somewhat stronger overall direct effect. Specifically, the dominance of both NIS was similarly affected negatively by the richness and positively by the evenness of the native communities. However, we also detected that both NIS might need different ecological strategies to become dominant in their recipient communities, which underwent similar assembly processes. Such strategies were partly highlighted by the different degrees of trait similarity between each NIS and their respective co-occurring native species. A better understanding of the underlying processes affecting NIS dominance is of high relevance to mitigate potential impacts of NIS once established. Furthermore, the provided approach could be further applied to unveil the potential strategies that NIS might follow in other regions and ecosystem types.