Microbial ecosystems are commonly modeled by fixed interactions between microbes in steady physiological states, typically the exponential growth state. However, ecological dynamics often feature large self-generated environmental changes which drive microbes through distinct physiological states manifested by very different growth rates. Examples of such dynamics include succession dynamics in nature and simple growth-dilution cycles in the laboratory. Here, we introduce a phenomenological model to gain insight into the dynamic coexistence of microbes due to changes in physiological states in cyclic environments. Our model allows us to bypass specific interactions leading to different physiological states (e.g., nutrient starvation, stress, aggregation, contact-dependent killing, etc.), by considering the growth of each species according to a global ecological coordinate, taken here to be the total community biomass. Analysis of this model provides rigorous, quantitative criteria for the dynamic coexistence of many species in terms of differential species’ dominance (“growth niche”) along the ecological coordinates. Our model shifts the focus of ecosystem dynamics from bottom-up studies based on inter-species interaction to top-down studies based on accessible macroscopic observables such as growth rates and total biomass, thereby allowing quantitative examination of community-wide characteristics.
Host: Walter Goldberger (walter.goldberger@yale.edu)