Microbial ecosystems have tipping points where even small perturbations are enough to cause a collapse, according to a new study. The authors, from the Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg, Germany, describe microbial communities as a network based on cross-feeding, the exchange of metabolic by-products between populations. This network of relationships can collapse abruptly if individual populations are lost, they conclude. This mechanism may explain why microbial diversity is difficult to maintain in the laboratory, the researchers write in the journal PNAS.