Nicolas Schtickzelle

Intraspecific trait variation (ITV), potentially driven by genetic and non‐genetic mechanisms, can underlie variability in resource acquisition, individual fitness and ecological interactions. Impacts of ITV at higher levels of biological organizations are hence likely, but up‐scaling our knowledge about ITV importance to communities and comparing its relative effects at population and community levels has rarely been investigated. Here, we tested the effects of genetic and non‐genetic ITV on morphological traits in microcosms of protist communities by contrasting the effects of strains showing different ITV levels (i.e. trait averages and variance) on population growth, community composition and biomass production. We found that genetic and non‐genetic ITV can lead to different effects on populations and communities across several generations. Furthermore, the effects of ITV declined across levels of biological organization: ITV directly altered population performance, with cascading but indirect consequences for community composition and biomass productivity. Overall, these results show that the drivers of ITV can have distinct effects on populations and communities, with cascading impacts on higher levels of biological organization that might mediate biodiversity–ecosystem functioning relationships.