Evolution of a Fluctuating Population in a Randomly Switching Environment

TL;DR

This paper investigates how environmental and demographic noise influence the evolution and fixation probabilities of competing strains in a fluctuating environment, revealing noise-induced transitions in population size distribution.

Contribution

It introduces a model analyzing the combined effects of environmental switching and demographic noise on population dynamics, highlighting noise-induced phenomena.

Findings

Coupled environmental and demographic noise can increase fixation probability of slower-growing strains.

Population size distribution can be unimodal, bimodal, or multimodal depending on switching rates.

Noise-induced transitions occur when environmental switching rate matches growth rate.

Abstract

Environment plays a fundamental role in the competition for resources, and hence in the evolution of populations. Here, we study a well-mixed, finite population consisting of two strains competing for the limited resources provided by an environment that randomly switches between states of abundance and scarcity. Assuming that one strain grows slightly faster than the other, we consider two scenarios--one of pure resource competition, and one in which one strain provides a public good--and investigate how environmental randomness (external noise) coupled to demographic (internal) noise determines the population's fixation properties and size distribution. By analytical means and simulations, we show that these coupled sources of noise can significantly enhance the fixation probability of the slower-growing species. We also show that the population size distribution can be unimodal, bimodal or multimodal and undergoes noise-induced transitions between these regimes when the rate of switching matches the population's growth rate.