Past, growth and persistence of source-sink metapopulations

TL;DR

This paper develops criteria for the persistence and growth of source-sink metapopulations modeled as graphs, considering stochastic dispersal and reproduction, with extensions to variable environments and specific graph structures.

Contribution

It introduces a novel approach to analyze source-sink metapopulations using graph theory and stochastic processes, providing explicit criteria for persistence and growth.

Findings

Persistence criteria depend on dispersal and reproduction balance.

Metapopulation growth rate can be explicitly characterized.

Dispersal can enable survival even when all patches are sinks.

Abstract

Source-sink systems are metapopulations of patches that can be of variable habitat quality. They can be seen as graphs, where vertices represent the patches, and the weighted oriented edges give the probability of dispersal from one patch to another. We consider either finite or source-transitive graphs, i.e., graphs that are identical when viewed from a(ny) source. We assume stochastic, individual-based, density-independent reproduction and dispersal. By studying the path of a single random disperser, we are able to display simple criteria for persistence, either necessary and sufficient, or just sufficient. In case of persistence, we characterize the growth rate of the population as well as the asymptotic occupancy frequencies of the line of ascent of a random survivor. Our method allows to decouple the roles of reproduction and dispersal. Finally, we extend our results to the case of periodic or random environments, where some habitats can have variable growth rates, autocorrelated in space and possibly in time. In the whole manuscript, special attention is given to the example of regular graphs where each pair of adjacent sources is separated by the same number of identical sinks. In the case of a periodic and random environment, we also display examples where all patches are sinks when forbidding dispersal but the metapopulation survives with positive probability in the presence of dispersal, as previously known for a two-patch mean-field model with parent-independent dispersal.