Noise-driven oscillations in microbial population dynamics

TL;DR

This paper investigates how demographic noise and unbalanced removal rates can induce sustained oscillations in microbial populations, both single-species and multi-species, under natural environmental conditions.

Contribution

It introduces a model showing that demographic noise can sustain oscillations in microbial populations with unbalanced biomass and substrate removal rates, extending understanding of natural microbial dynamics.

Findings

Deterministic models predict damped oscillations in large populations.

Demographic noise sustains oscillations in small populations.

Oscillations can occur in multi-species microbial ecosystems.

Abstract

Microbial populations in the natural environment are likely to experience growth conditions very different from those of a typical laboratory xperiment. In particular, removal rates of biomass and substrate are unlikely to be balanced under realistic environmental conditions. Here, we consider a single population growing on a substrate under conditions where the removal rates of substrate and biomass are not necessarily equal. For a large population, with deterministic growth dynamics, our model predicts that this system can show transient (damped) oscillations. For a small population, demographic noise causes these oscillations to be sustained indefinitely. These oscillations arise when the dynamics of changes in biomass are faster than the dynamics of the substrate, for example, due to a high microbial death rate and/or low substrate flow rates. We show that the same mechanism can produce sustained stochastic oscillations in a two-species, nutrient-cycling microbial ecosystem. Our results suggest that oscillatory population dynamics may be a common feature of small microbial populations in the natural environment, even in the absence of complex interspecies interactions.