Plasmids are circular DNA molecules independent of the bacterial chromosome that can be transferred horizontally between bacteria in an autonomous manner. As such, they are the main vector for horizontal gene transfer between bacteria. In particular, they are responsible for the rapid dissemination of many antibiotic resistance genes, as well as some virulence genes. Plasmids are therefore a threat to our healthcare systems, and it is essential to better understand their eco-evolutionary dynamics. Having established that there is a wide diversity of plasmids, just as there can be a great diversity of interacting species in communities, we propose to apply the theories and concepts of community ecology to bacterial plasmids. In particular, we develop models of competition between plasmids to illustrate how the three main theories of biodiversity (ecological niche partitioning theory, neutral biodiversity theory and emergent neutrality theory) can be applied to plasmids.