Interchange of entire communities: microbial community coalescence

•Community coalescence is the interchange of entire microbial communities.•Lack of terminology and concepts have hampered research.•Community coalescence can be addressed with tools including network theory.•Community coalescence likely has important functional and applied consequences.•Empirical research should address factors governing community coalescence.

Microbial communities are enigmatically diverse. We propose a novel view of processes likely affecting microbial assemblages, which could be viewed as the Great American Interchange en miniature: the wholesale exchange among microbial communities resulting from moving pieces of the environment containing entire assemblages. Incidental evidence for such ‘community coalescence’ is accumulating, but such processes are rarely studied, likely because of the absence of suitable terminology or a conceptual framework. We provide the nucleus for such a conceptual foundation for the study of community coalescence, examining factors shaping these events, links to bodies of ecological theory, and we suggest modeling approaches for understanding coalescent communities. We argue for the systematic study of community coalescence because of important functional and applied consequences.