Source–sink dynamics: how sinks affect demography of sources

Abstract

Models of source–sink population dynamics have to make assumptions about whether, and eventually how, demographic parameters in source habitats are dependent on the demography in sink habitats. However, the empirical basis for making such assumptions has been weak. Here we report a study on experimental root vole populations, where estimates of demographic parameters were contrasted between source patches in source–sink (treatment) and source–source systems (control). In the presence of a sink patch (simulated by a pulsed removal of immigrants), source‐patch populations failed to increase over the breeding season, mainly due to a high spatially density‐dependent dispersal rate from source to sink patches. The per capita recruitment rate was almost two times higher in source–sink than in the source–source systems, but this did not compensate for the loss rate due to dispersal from source to sink patches. Sex ratio in the source–sink systems became less female biased, probably as a result of an enhanced frequency of dispersal movements in females. Good knowledge of the degree of density‐and habitat‐dependent dispersal is critical for predicting the dynamics of source–sink populations.

Causes and consequences of animal dispersal strategies: relating individual behaviour to spatial dynamics

“…In smaller patches with a greater edge to size ratio, individuals are more likely to encounter the edge which may increase the likelihood of leaving the patch (Stamps, Buechner & Krishnan, 1987;Kindvall & Petersson, 2000). In both root voles Microtus oeconomus (Andreassen & Ims, 2001) and field voles, Microtus agrestis (Crone, Doak & Pokki, 2001), dispersal is more common from small patches than from large patches. However contrary to the theory, manipulation of edge to size ratio, while keeping patch size constant, failed to affect emigration in root voles (Gundersen & Andreassen, 1998).…”

“…Several factors have been identified that may covary with patch size, and be responsible for changes in dispersal rate with patch size. Andreassen & Ims (2001) suggested that ' patch-size dependent demography ' might explain greater emigration from small patches. In their study, movement out of a patch was greater when the population density was low and more variable due to demographic stochasticity, both characteristics of small patches.…”

Human-caused mortality influences spatial population dynamics: Pumas in landscapes with varying mortality risks

“…Despite this, the population was a net source because it consistently exported large numbers of recruits to other subpopulations. This illustrates how a failure to account for dispersal can lead to faulty conclusions about the role a population plays in its regional context (Figueira and Crowder, 2006;Griffin and Mills, 2009;Gundersen et al, 2001). In the case of the NGYE, ignoring the contribution via dispersal would suggest the population was a sink, whereas not accounting for immigration would fail to show its own dependence on immigration.…”

The influence of stage-dependent dispersal on the population dynamics of three amphipod species

“…The Wrst consists of the role of densitydependent dispersal, where the number of dispersers is dependent on the density of the source population, allowing species to either increase when rare at the local scale (negative density-dependent dispersal), or reduce a population size if dispersal increases with density (Amarasekare 2004). In the second, the cost of dispersal from sources can cause population growth rates to become negative (Gundersen et al 2001) or even cause local populations to go extinct (Holt 1993). In this article, we present data on three marine amphipod species that suggest that the life history stage in which dispersal occurs can inXuence population dynamics and cause species to become rare or common.…”