Final Report Summary - TANDEM (Trait diversity: assemblage of communities and their feedbacks to Ecosystem Multifunctionality) The main objective of this proposal was to advance towards a more complete incorporation of the functional component of biodiversity into theoretical and applied models of future biodiversity changes. To do that, it was proposed to study the processes shaping species coexistence, the effects of diversity on ecosystems functioning and the role played by different traits and by phylogenetic differences on the assembly processes of plant communities across environmental and disturbance gradients.Functional diversity is being increasingly recognized as the facet of biodiversity that is more tightly linked to ecosystem functioning. However, functional diversity itself is a complex concept, embracing many aspects of the distribution of functional traits within and among biological communities (such as the average values, the variance, or the range). This complexity has led to the development of a myriad of indices to estimate functional diversity, including different conceptual approaches, which complicate the selection, use and fully understanding of the characteristics of these indices by users. Moreover, many of these indices systematically ignore intraspecific variability in trait values, despite its crucial importance in some ecological and evolutionary processes, and only perform well at a single spatial scale, but cannot be scaled up or down easily. In the TANDEM project, we have devised and developed a unifying framework for functional diversity. This framework is based on the concept of Trait Probability Distributions (TPD), and can accommodate all the existing indices of functional diversity. In addition, the TPD framework permits the inclusion of intraspecific variability in trait values in a very intuitive way. Most importantly, it allows for seamless transitions between scales, resulting in a framework that can be used to analyse data from the intraspecific scale to the global scale. This framework has been published in Trends in Ecology & Evolution.A second part of the project consisted in the establishment of a field experiment to test the effects of the relative importance of functional and phylogenetic diversity on the coexistence of species and the functioning of ecosystems. For this, we established a common garden experiment including monocultures of 19 coexisting species from Czech wet meadows, as well as several communities of 6 species representing orthogonal combinations of these components of diversity, under different levels of fertilization. Additionally, in order to test if more diverse communities are less likely to become invaded by other species because they leave fewer resources available to potential invaders, we weeded one part of each plot. We also measured different parameters related with ecosystem functioning, such as the decomposition rates of leaves, plant biomass, or soil nutrients cycling. Our results show that more diverse communities were less susceptible to invasion, with the traits of the dominant species being an important determinant of susceptibility to invasion. We also found that the decomposition of overyielding into functional complementarity and sampling effects depended on the considered factors (functional and phylogenetic diversities, and nutrient availability). Our results indicate that plant diversity plays an important role on ecosystem functioning, but it depends strongly on the environmental context.The final part of the Project aimed at achieving a better understanding of how functional and phylogenetic diversity change across ecological gradients. In this sense, we have first developed a method to decouple functional and phylogenetic diversity (published in Methods in Ecology and Evolution). In addition we have gathered vegetation and trait information spanning a large gradient across Europe (>4500 sampling points). An initial analysis of part of this data has revealed that the vulnerability of the functional diversity of weed communities to the loss of species increases drastically at the first stages of agricultural intensification. This result, published in Functional Ecology, can be directly translated into improved management practices for agricultural systems.
