Extinction dynamics in experimental metapopulations

Abstract

Metapopulation theory provides a framework for understanding population persistence in fragmented landscapes and as such has been widely used in conservation biology to inform management of fragmented populations. However, classical metapopulation theory [Levins, R. (1970) Lect. Notes Math. 2, 75-107] ignores metapopulation structure and local population dynamics, both of which may affect extinction dynamics. Here, we investigate metapopulation dynamics in populations that are subject to different migration rates by using experimental metapopulations of the annual plant Cardamine pensylvanica. As predicted by classical metapopulation theory, connected populations persisted longer than did isolated populations, but the relationship between migration and persistence time was nonlinear. Extinction risk sharply increased as the distance between local populations increased above a threshold value that was consistent with stochastic sim- Science 290, 1360 -1364], a metric that predicts synchronous cycles, indicated that continuous populations should cycle in phase, resulting in an increased extinction risk. Determining empirically the optimal migration level to improve survival chances will be challenging for any natural population. Migration rates that would not increase migration above the threshold value would be ineffectual, but migration rates that would homogenize local densities could increase the risk of coherent oscillations and enhance extinction risk.experimental populations ͉ metapopulation capacity ͉ population coherence ͉ migration ͉ population persistence H abitat fragmentation is implicated in the decline of many endangered wild species (1-4). To offset the problems associated with habitat fragmentation, conservation biologists have called for the construction of corridors to facilitate migration between fragmented habitats (5), but the construction of corridors and their attendant increase in migration rates is not without risks (6). Predicting how migration affects population persistence is important for species conservation. Metapopulation theory provides a framework for understanding population persistence in fragmented landscapes and as such has been used in conservation biology to inform management of fragmented populations. Originally conceived by Levins, metapopulation dynamics are determined by the balance between local colonization and extinction events (7). When colonization events exceed extinctions, metapopulations are predicted to persist, because migration allows an extinct local population to become recolonized (7-9). Absent from this theory is any consideration of how differences in patch suitability (area, distance to other local patches) and local dynamics (such as reproductive rate and intraspecific competition) influence metapopulation persistence. However, recent theoretical work has included more realistic aspects of metapopulations. Hanski and Ovaskainen (10) examine how differences in patch area and in metapopulation structure affect predicted metapopulation persistence ( refs....

A review of extinction in experimental populations

“…This is particularly true of studies in which investigators manually transfer individuals among populations to simulate migration or where populations are simply separated by a partial partition (as in Forney & Gilpin 1989), because individuals that leave one population are assured of joining another population and the chance of unsuccessful migration is absent. Alternatively, this artefact is absent from lab studies such as that by Molofsky & Ferdy (2005) discussed below, where errant migration is allowed.…”

“…In a study with an annual plant, Cardamine pensylvanica, greater connections among subpopulations increased metapopulation persistence (Molofsky & Ferdy 2005). The authors manipulated the degree of migration via seed dispersal by varying the distance between subpopulations.…”

“…experimental manipulation decreased time to extinction). Very few studies have compared experimental results to quantitative predictions of population extinction (Ellner et al 2001;Drake 2006;Fryxell et al 2006; for examples of quantitative comparisons; but see Leslie et al 1968;Molofsky & Ferdy 2005). The lack of quantitative knowledge hampers the application of theory to natural populations.…”

“…High levels of migration between populations should increase extinction risk by synchronizing population fluctuations, increasing the chance that coupled populations will decline simultaneously (Earn et al 2000). (Burkey 1997*;Holyoak & Lawler 1996b*;Dey & Joshi 2006;Molofsky & Ferdy 2005) Decreased genetic variation is hypothesized to increase the probability of population extinction. This may occur through various causes.…”

Overdominant quantitative trait loci for yield and fitness in tomato

“…On one hand, reproductive-isolation mechanisms retard gene flow between divergent populations (30) and maintain coadapted gene complexes that improve fitness. On the other hand, metapopulation theory and practice, focusing on networks of small local populations connected by migration corridors, has established a central role for immigrant alleles in survival (32). An attractive hypothesis is that ODO QTL, which have been selected to improve fitness through heterozygous advantage, can bring balance between the opposing isolation and diversity needs of gene pools.…”