Drift dynamics in microbial communities and the effective community size

William T. Sloan, Chioma F. Nnaji, Mary Lunn, Thomas P. Curtis, Sean D. Colloms, Jillian M. Couto, Ameet J. Pinto, Stephanie Connelly, Susan J. Rosser

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The structure and diversity of all open microbial communities are shaped by individual births, deaths, speciation and immigration events; the precise timings of these events are unknowable and unpredictable. This randomness is manifest as ecological drift in the population dynamics, the importance of which has been a source of debate for decades. There are theoretical reasons to suppose that drift would be imperceptible in large microbial communities, but this is at odds with circumstantial evidence that effects can be seen even in huge, complex communities. To resolve this dichotomy we need to observe dynamics in simple systems where key parameters, like migration, birth and death rates can be directly measured. We monitored the dynamics in the abundance of two genetically modified strains of Escherichia coli, with tuneable growth characteristics, that were mixed and continually fed into 10 identical chemostats. We demonstrated that the effects of demographic (non‐environmental) stochasticity are very apparent in the dynamics. However, they do not conform to the most parsimonious and commonly applied mathematical models, where each stochastic event is independent. For these simple models to reproduce the observed dynamics we need to invoke an ‘effective community size’, which is smaller than the census community size.
Original languageEnglish
Number of pages11
JournalEnvironmental Microbiology
Early online date8 Mar 2021
Publication statusE-pub ahead of print - 8 Mar 2021


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