Dispersal-induced resilience to stochastic environmental fluctuations in populations with Allee effect

TL;DR

This paper demonstrates how dispersal in spatially extended habitats can enable populations with Allee effects to persist despite environmental fluctuations, identifying conditions for sustainability and resilience.

Contribution

It introduces a theoretical framework showing dispersal can induce resilience in populations with Allee effects under environmental stochasticity, including the existence of high- and low-density sustainable states.

Findings

Dispersal can prevent extinction in populations with Allee effects under environmental fluctuations.

Maximum extinction threshold occurs at dispersal distances larger than environmental fluctuation synchrony.

Extinction threshold scales with the square root of dispersal rate and inversely with Allee threshold.

Abstract

Many species are unsustainable at small population densities (Allee Effect), i.e., below a threshold named Allee threshold, the population decreases instead of growing. In a closed local population, environmental fluctuations always lead to extinction. Here, we show how, in spatially extended habitats, dispersal can lead to a sustainable population in a region, provided the amplitude of environmental fluctuations is below an extinction threshold. We have identified two types of sustainable populations: high-density and low-density populations (through a mean-field approximation, valid in the limit of large dispersal length). Our results show that patches where population is high, low or extinct, coexist when the population is close to global extinction (even for homogeneous habitats). The extinction threshold is maximum for characteristic dispersal distances much larger than the spatial scale of synchrony of environmental fluctuations. The extinction threshold increases proportionally to the square root of the dispersal rate and decreases with the Allee threshold. The low-density population solution can allow understanding difficulties in recovery after harvesting. This theoretical framework provides a novel approach to address other factors, such as habitat fragmentation or harvesting, impacting population resilience to environmental fluctuations.