Populations of microorganisms inhabiting a common environment compete for nutrients and other resources of the environment. In some cases, the populations even excrete into the environment chemicals that are toxic or inhibitory to their competitors. Competition between two populations tends to eliminate one of the populations from their common habitat, especially when competition is focused on a single resource and when the populations do not otherwise interact. However, a number of factors mitigate the severity of competition and thus competitors often coexist.