Intraspecific diversity as a major component of biodiversity-ecosystem functioning relationships – iBEF

Understanding the relationships between biodiversity and ecosystem functioning (BEFs) has major implications. Most BEFs studies have focused on mechanisms operating at the interspecific level, although biodiversity also comprises an intraspecific facet that could be important for ecosystem functioning. The main objectives of iBEF are to quantify the influence of intraspecific diversity on ecosystem functions, to unravel mechanisms linking intraspecific diversity to ecosystem multifunctionality and to integrate further intraspecific diversity into the BEF framework and into conservation policies. iBEF focuses on ten species living in river ecosystems and interacting within a trophic network (from producers to secondary consumers). The project combines observational and experimental approaches and is structured into four tasks, each fulfilling ambitious and novel objectives. The first task aims at determining whether intraspecific diversity substantially contributes to ecosystem functioning in the wild. Using observational data in the wild synthetizing local scale measures of intra- and interspecific richness and of environmental conditions, we will quantify the effects of intraspecific diversity on key ecological functions (primary productivity, secondary productivity and nutrient cycling). We will further test how much of the variability in ecosystem multifunctionality is due to direct effects of intraspecific diversity, to direct effects of environmental drivers, and to indirect effects of environmental drivers mediated by intraspecific diversity. The second task aims at establishing the relative importance of intra- vs. interspecific diversity on ecosystem functioning, while controlling for other drivers. We will use mesocosm experiments focusing on five of the ten species and varying simultaneously intra- and interspecific richness to test how much of the variability in ecosystem functioning is due to changes in each of these two facets of biodiversity. The third task aims at determining the relative importance of intraspecific diversity on ecological functions compared to the effect of climate warming. We will use an experimental approach varying both intraspecific richness (in the same five species than in task 2) and water temperature to tease apart direct effects due to warming and intraspecific diversity, as well as indirect effects of warming mediated by intraspecific diversity on ecosystem multifunctionality. Finally, a fourth task will be dedicated to communicate our results to other scientists, but also to environmental managers as our project will inform on how much of ecosystem functions is loss when loosing intraspecific richness, and hence why it is important to conserve this facet of biodiversity. This project will generate novel results that should lead to a major rethinking of the BEF framework that would rest on an integrative view of the relationships between the environmental drivers, intra- and interspecific diversity, and ecosystem functions. The iBEF project will also favour the general acceptance that intraspecific diversity should be preserved and managed efficiently, not only because it is the raw for evolution to occur, but also because its loss would significantly erode the way ecosystems function and the services they provide.