The ecological causes of functional distinctiveness in communities

Recent work has shown that evaluating functional trait distinctiveness, the average trait distance of a species to other species in a community offers promising insights into biodiversity dynamics and ecosystem functioning. However, the ecological mechanisms underlying the emergence and persistence of functionally distinct species are poorly understood. Here, we address the issue by considering a heterogeneous fitness landscape whereby functional dimensions encompass peaks representing trait combinations yielding positive population growth rates in a community. We identify four ecological cases contributing to the emergence and persistence of functionally distinct species. First, environmental heterogeneity or alternative phenotypic designs can drive positive population growth of functionally distinct species. Second, sink populations with negative population growth can deviate from local fitness peaks and be functionally distinct. Third, species found at the margin of the fitness landscape can persist but be functionally distinct. Fourth, biotic interactions (positive or negative) can dynamically alter the fitness landscape. We offer examples of these four cases and guidelines to distinguish between them. In addition to these deterministic processes, we explore how stochastic dispersal limitation can yield functional distinctiveness. Our framework offers a novel perspective on the relationship between fitness landscape heterogeneity and the functional composition of ecological assemblages

Isoprene emission structures tropical tree biogeography and community assembly responses to climate.

The prediction of vegetation responses to climate requires a knowledge of how climate-sensitive plant traits mediate not only the responses of individual plants, but also shifts in the species and functional compositions of whole communities. The emission of isoprene gas – a trait shared by one-third of tree species – is known to protect leaf biochemistry under climatic stress. Here, we test the hypothesis that isoprene emission shapes tree species compositions in tropical forests by enhancing the tolerance of emitting trees to heat and drought. Using forest inventory data, we estimated the proportional abundance of isoprene-emitting trees (pIE) at 103 lowland tropical sites. We also quantified the temporal composition shifts in three tropical forests – two natural and one artificial – subjected to either anomalous warming or drought. Across the landscape, pIE increased with site mean annual temperature, but decreased with dry season length. Through time, pIE strongly increased under high temperatures, and moderately increased following drought. Our analysis shows that isoprene emission is a key plant trait determining species responses to climate. For species adapted to seasonal dry periods, isoprene emission may tradeoff with alternative strategies, such as leaf deciduousness. Community selection for isoprene-emitting species is a potential mechanism for enhanced forest resilience to climatic change.Financial support for this study was provided to: T.C.T. and S.R.S. by grants NSF-PIRE #OISE-0730305, USDOE #3002937712, NASA #NNX17AF65G and the University of AZ Agnes Nelms Haury Program in Environment and Social Justice; to M.N.S. and S.R.S. by NASA-ESSF #NNX14AK95H; to C.V. by ERCStG-2014-639706-CONSTRAINTS; to I.S. by Grant Agency of the Czech Republic #16-26369S; and to P.M. by NERC # NE/ N006852/1 and ARC #DP170104091

Open Science principles for accelerating trait-based science across the Tree of Life.

Synthesizing trait observations and knowledge across the Tree of Life remains a grand challenge for biodiversity science. Species traits are widely used in ecological and evolutionary science, and new data and methods have proliferated rapidly. Yet accessing and integrating disparate data sources remains a considerable challenge, slowing progress toward a global synthesis to integrate trait data across organisms. Trait science needs a vision for achieving global integration across all organisms. Here, we outline how the adoption of key Open Science principles-open data, open source and open methods-is transforming trait science, increasing transparency, democratizing access and accelerating global synthesis. To enhance widespread adoption of these principles, we introduce the Open Traits Network (OTN), a global, decentralized community welcoming all researchers and institutions pursuing the collaborative goal of standardizing and integrating trait data across organisms. We demonstrate how adherence to Open Science principles is key to the OTN community and outline five activities that can accelerate the synthesis of trait data across the Tree of Life, thereby facilitating rapid advances to address scientific inquiries and environmental issues. Lessons learned along the path to a global synthesis of trait data will provide a framework for addressing similarly complex data science and informatics challenges

Habitat area and climate stability determine geographical variation in plant species range sizes

Despite being a fundamental aspect of biodiversity, little is known about what controls species range sizes. This is especially the case for hyperdiverse organisms such as plants. We use the largest botanical data set assembled to date to quantify geographical variation in range size for ∼ 85 000 plant species across the New World. We assess prominent hypothesised range-size controls, finding that plant range sizes are codetermined by habitat area and long- and short-term climate stability. Strong short- and long-term climate instability in large parts of North America, including past glaciations, are associated with broad-ranged species. In contrast, small habitat areas and a stable climate characterise areas with high concentrations of small-ranged species in the Andes, Central America and the Brazilian Atlantic Rainforest region. The joint roles of area and climate stability strengthen concerns over the potential effects of future climate change and habitat loss on biodiversity

TRY plant trait database – enhanced coverage and open access

Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

The return of the variance: intraspecific variability in community ecology

International audienceDespite being recognized as a promoter of diversity and a condition for local coexistence decades ago, the importance of intraspecific variance has been neglected over time in community ecology. Recently, there has been a new emphasis on intraspecific variability. Indeed, recent developments in trait-based community ecology have underlined the need to integrate variation at both the intraspecific as well as interspecific level. We introduce new T-statistics ('T' for trait), based on the comparison of intraspecific and interspecific variances of functional traits across organizational levels, to operationally incorporate intraspecific variability into community ecology theory. We show that a focus on the distribution of traits at local and regional scales combined with original analytical tools can provide unique insights into the primary forces structuring communities

Early positive biodiversity effects on total biomass in experimental tree seedling assemblages with and without water limitation

[Questions]: While positive effects of tree diversity on tree community biomass have often been reported in mature stands, the debate on whether diversity effects may be detectable at the seedling level persists, with opposing outcomes found so far. We still lack a comprehensive evaluation of the biodiversity effects (so- called ‘comple-mentarity’ and ‘selection’ effects), as well as the phenotypic drivers at play, underly-ing early-community biomass. Even less is known about whether such biodiversity effects may change under water- limited conditions.[Location]: Seeds from four tree species coexisting in a Mediterranean forest (Spain).[Methods]: We built experimental tree seedling assemblages with three diversity lev-els — monocultures, two- species and four- species mixtures — and under two soil moisture conditions. We quantified the extent to which species richness, species identity, community-weighted mean (CWM) and functional dissimilarity (FD) influ-ence complementarity and selection effects. We computed CWM and FD for seven functional traits related to water and light acquisition; and we calculated the comple-mentarity and selection effects from above- and below- ground biomass measures at the community level.[Results]: Our results showed that complementarity drove the greater biomass in more diverse assemblages at the seedling stage. This pattern was largely favored by a par-ticular species, Quercus faginea, with distinct phenotypic traits (great height, lateral ramification and root biomass with high dry matter content), which induced a positive effect of CWM on community biomass. Moreover, our study showed that the water deficit limited the production of above- ground biomass without interacting with the community’s species richness.[Conclusion]: Our study provides evidence that positive biodiversity effects on com-munity biomass occur early, at the seedling stage, and it highlights the essential role that certain tree species play from their initial development stages by favoring spatresource partitioning. Our work motivates future studies to apply integrated ap-proaches in assessing both the community-wide and species-specific effects to understand the biodiversity–biomass relationship.This work was supported by the Spanish-funded project REMEDINAL-3CM (S2013/MAE-2719). CCB is supported by a postdoctoral fellowship of the Ramón Areces Foundation. BC thanks Coordenação de Aperfeiçoamento de Pessoal de Níıvel Superior - CAPES [DOC- PLENO - Programa de Doutorado Pleno no Exterior (grant Agreement No 99999.001266/2015-02) for a research scholarship. CV was supported by the European Research Council (ERC) Starting Grant Project ‘Ecophysiological and Biophysical Constraints on Domestication in Crop Plants’ (grant ERC- StG -2014- 639706-CONSTRAINTS).Peer reviewe

Multifaceted functional diversity for multifaceted crop yield: Towards ecological assembly rules for varietal mixtures

International audience1.Ecological theories suggest that higher plant genetic diversity can increase productivity in natural ecosystems. So far, varietal mixtures, that is, the cultivation of different genotypes within a field, have shown contrasting results, notably for grain yield where both positive and negative mixing effects have been reported. Such discrepancy between ecological theories and agronomical applications calls for a better understanding of plant–plant interactions in crops.2.Using durum wheat Triticum turgidum ssp. durum as a model species, we investigated the effect of functional trait composition on productivity and grain quality of varietal mixtures by growing 179 highly diverse genotypes in pure stands and 197 two‐way mixtures in field conditions. We quantified the agronomic performance of the mixtures relative to their components grown in pure stands on two variables related to productivity, vegetative biomass yield and grain yield, and one variable related to grain quality, grain protein content. We then analysed the relationship between the relative performance of the mixtures and their functional composition that we characterized with trait means and trait differences on 19 above‐ and below‐ground traits. 3.We found that biomass and grain yield increased by 4% overall in mixtures relative to single varieties, but that mixing effects were non‐significant for grain protein content. The combined effects of trait means and trait differences explained 12%, 17% and 22% of the variability of relative grain yield, biomass yield and grain protein content, respectively, with different traits affecting productivity and grain quality. Clustering varieties into functional groups allowed us to identify the most beneficial associations for multifaceted agronomic performance.4.Synthesis and applications. Functional traits explained a significant part of the relative agronomic performance of mixtures compared to monocultures (12%–22%, depending on the yield component). They can thus serve as a basis to identify groups of varieties whose combinations are expected to generate positive mixing effects, especially for productivity, and without compromising grain quality. Selection could then target convergence between groups for some traits and divergence between groups for other traits using empirically derived relationships between functional traits and agronomic performance as a guideline