Figure 1. Diversity begets diversity (DBD) and ecological controls (EC) hypotheses illustrated.

Hypothetical microbial communities are illustrated as gray circles containing assemblages of microbial species, shown in different colors. 'DBD' means that the focal species is more likely to acquire diversity – through de novo mutation, invasion of a different strain of the same species, or a combination of both – in a community with high diversity. This is because new niches are created in a more diverse community. By contrast, 'EC' means that the focal species is more likely to acquire diversity through strain invasion or mutation in a community with low diversity. This is because niches remain unfilled in a low-diversity community, while niche space is saturated in a high-diversity community, impeding further diversification.