Microbial communities

Microorganisms comprise about half of the biomass on our planet and play a key role in the biogeochemical cycling of elements like carbon, nitrogen, and sulfur. Furthermore, due to their small size and short generation time, microorganisms provide ideal model systems for the study of many universal ecological processes.

To understand the population dynamics of microorganisms, we first examine the growth of a single bacterium on a single resource. This illustrates that the population dynamics of microorganisms are intimately connected to the dynamics of their resources. Competition for limiting resources may lead to competitive exclusion of species when resource levels are exhausted below their minimal requirements. Competition may also allow stable coexistence of species if they differ sufficiently in their resource utilization patterns. Some microorganisms affect each other by allelopathic interactions. This chemical warfare between toxic and nontoxic microbes can generate species oscillations, as exemplified by the ‘rock-scissors-paper’ dynamics of Escherichia coli strains. Multispecies interactions in microbial food webs add further complexity to the population dynamics of microorganisms, including chaos. These nonequilibrium dynamics generally favor microbial biodiversity. Yet, despite the astounding complexity of multispecies interactions in microbial communities, the ecosystem functions driven by microorganisms can show remarkable stability.