There is growing evidence of rapid evolution leading to entangled eco-evolutionary dynamics. However, we are only beginning to address what this implies for maintenance of biodiversity in nature. Community ecology studies how species diversity is maintained in communities despite negative interactions. Separately, population biology studies how phenotypic and genetic variation is maintained in populations despite selection and drift. These two questions are interlinked, but usually addressed independently, not considering the other level. Intriguingly, genetic variation could help maintain species diversity, and reciprocally, diversity could help maintain variation, forming a positive feedback loop. However, this hypothesis has not been empirically tested in complex ecological networks, because maintaining such networks in the laboratory is a major challenge. I propose to experimentally test this hypothesis using a uniquely tractable network of tropical rainforest Drosophila and their parasitoids (6 fly and 5 wasp species), that I developed to allow multigenerational microcosm experiments. We will manipulate species diversity and genetic variation of all species in a factorial design to test the hypothesis. We will then explore the mechanisms of interactions between diversity and variation, focusing on rapid evolution. To link the findings to natural eco-evolutionary dynamics, we will investigate mechanisms maintaining diversity and variation in the wild. Based on the empirical work we will advance eco-evolutionary concepts of organismal diversity and stability. This project will provide a causal test of the interaction between maintenance of diversity and variation, thus linking two key questions in ecology and evolutionary biology. Uncovering the specific coexistence mechanisms will allow us to predict the importance of diversity – variation feedbacks in other systems with important implications for conservation of biodiversity.