Community diversity affects functionality and species sorting during propagation of a natural microbial community

The influence of community diversity on community function has long been a central question in ecology. Particularly, the dynamics over time of this relationship as a function of levels of diversity remains unclear. Natural populations may vary in levels of species diversity, for instance after they experience disturbances that remove significant amounts of their genetic and species variation, including rare but functionally unique guilds. We investigated the influence of diversity on associated community function by propagating natural microbial communities from a traditionally fermented milk beverage diluted to various levels. Specifically, we assessed the influence of less abundant microbial types such as yeast and rarer bacterial types on community functionality and species sorting trajectories over approximately 100 generations. We observed repeatable changes in bacterial community compositions, metabolic profiles, and acidity related to starting diversity levels. The influence of a single ecological guild, yeast in our study, played a dramatic role on function, but interestingly not on long-term species sorting trajectories of the remaining bacterial community. Our results together evidence ecological selection on the microbial communities in our system and suggest an unexpected niche division between yeast and bacterial communities. ### Competing Interest Statement The authors have declared no competing interest.