Multiple Phase Transitions Shape Biodiversity of a Migrating Population

TL;DR

This paper explores how migration rates influence biodiversity in microbial populations, revealing multiple phase transitions and critical slowing down phenomena that impact coexistence stability.

Contribution

It introduces a model showing that biodiversity undergoes multiple phase transitions driven by migration rate changes, including reentrant coexistence phases.

Findings

Biodiversity-migration relationship exhibits multiple phase transitions.

Critical slowing down occurs at each transition point.

Fluctuation statistics due to demographic noise can indicate impending extinctions.

Abstract

In a wide variety of natural systems, closely-related microbial strains coexist stably, resulting in high levels of fine-scale biodiversity. However, the mechanisms that stabilize this coexistence are not fully understood. Spatial heterogeneity is one common stabilizing mechanism, but the rate at which organisms disperse throughout the heterogeneous environment may strongly impact the stabilizing effect that heterogeneity can provide. An intriguing example is the gut microbiome, where active mechanisms exist to control the movement of microbes and potentially maintain diversity. We investigate how biodiversity is affected by migration rate using a simple evolutionary model with heterogeneous selection pressure. We find that the biodiversity-migration rate relationship is shaped by multiple phase transitions, including a reentrant phase transition to coexistence. At each transition, an ecotype goes extinct and dynamics exhibit critical slowing down (CSD). CSD is encoded in the statistics of fluctuations due to demographic noise -- this may provide an experimental means for detecting and altering impending extinction.