Disturbance‐induced emigration: an overlooked mechanism that reduces metapopulation extinction risk

Abstract

Emigration propensity (i.e., the tendency to leave undisturbed patches) is a key life-history trait of organisms in metapopulations with local extinctions and colonizations. Metapopulation models of dispersal evolution typically assume that patch disturbance kills all individuals within the patch, thus causing local extinction. However, individuals may instead be able to leave a patch when it is disturbed, either by fleeing before being killed or simply because the disturbance destroys the patch without causing mortality. This scenario may pertain to a wide range of organisms from horizontally transmitted symbionts, to aquatic insects inhabiting temporary ponds, to vertebrates living in fragmented forests. We generalized a Levins-type metapopulation model of dispersal evolution by adding a new parameter of disturbance escape probability, which incorporates a second source of dispersal into the model: disturbance-induced emigration. We show that disturbance escape expands the domain of metapopulation viability and selects for lower rates of emigration propensity when disturbance rates are high. The fitness gains from disturbance-induced emigration are generally moderate, suggesting that disturbance escape might act more as a complementary dispersal strategy rather than a replacement to emigration propensity, at least for metapopulations that meet the assumptions of the Levins-type model. Yet disturbance-induced emigration may in some circumstances rescue a metapopulation from long-term extinction when the combination of high disturbance rates and low local population growth rates compromises its viability. Further, a metapopulation could persist exclusively by disturbance escape if local carrying capacities are large enough to counterbalance two sources of mortality: mortality driven by disturbance and mortality during dispersal. This study opens two promising research lines: (1) the investigation of disturbance escape in metapopulations of ephemeral habitats with unsaturated populations and non-equilibrium dynamics and (2) the incorporation of information costs to investigate the joint evolution of disturbance escape and emigration propensity.

Quantifying dispersal between two colonies of northern elephant seals across 17 birth cohorts

“…Dispersal and immigration are vital statistics of populations. Besides affecting gene flow and evolution, dispersal regulates metapopulation dynamics, and by overcoming local extinctions it can be crucial in species recovery from population crashes [1][2][3]. The northern elephant seal offers a clear example.…”

Stability of patch‐turnover relationships under equilibrium and nonequilibrium metapopulation dynamics driven by biogeography

“…Thus, patch characteristics affecting turnover under equilibrium may have different effects during nonequilibrium conditions, reducing the ability of models to project future dynamics. As a result, the incorporation of habitat and disturbance dynamics into metapopulation models has been an area of active theoretical development (Hastings, 2003 ; Mestre et al, 2021 ; Ovaskainen & Saastamoinen, 2018 ) and application (Howell et al, 2018 ; Ruete et al, 2014 ; Van Schmidt et al, 2019 ). Nevertheless, field studies that examine the factors affecting turnover during equilibrium and nonequilibrium conditions are lacking.…”

Quantifying dispersal between two colonies of northern elephant seals across 17 birth cohorts

“…Dispersal and immigration are vital statistics of populations. Besides effecting gene flow and evolution, dispersal regulates metapopulation dynamics, and by overcoming local extinctions it can be crucial in species recovery from population crashes (Chilvers & Wilkinson, 2008; Mestre et al ., 2021; Winkler et al ., 2005). The northern elephant seal offers a clear example, because following near extermination by 19 th -century hunters, it readily dispersed to reoccupy its former range (Bartholomew & Hubbs, 1952; Lowry et al ., 2014; Townsend, 1912).…”