An Experimental Test of the Island Colonization Survival Model: Bank Vole (Clethrionomys glareolus) Populations with Different Demographic Parameter Values

Demographic properties of a colonizing species have been predicted to be decisive for colonization success, during the initial stages of an island colonization. This paper tests the importance of the ratio natality to mortality in a propagule. Experimental introductions were performed on twenty islands in the Stockholm Archipelago, with voles from Northern and Southern Sweden. Earlier studies have shown several demographic parameters, such as litter size and juvenile mortality, to be different for the two provenances. A stochastic simulation model was used to predict extinction pro- babilities for differently sized propagules, based on demographic stochasticity. Northern voles were predicted to go extinct on 16% of ten islands; the observed proportion was 30%. Southern voles were predicted to fail on only 1% of their ten islands, and no extinction was observed. The difference in colonization success was caused by demographic differences, mainly a high adult mortality among Northern voles. Propagule size (ten or twenty) had no effect on colonization success.