High Activity in Bank Voles in Relation to Colonization Ability

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Abstract
Experimental introductions of bank voles in the Stockholm archipelago revealed great differences in colonization ability betwewen voles from northern and southern Sweden. The differences were due to the higher adult mortality of northern voles. Food shortage, predation and emigration are discussed as agents of adult mortality. Northern voles consume more food than southern voles do, but since no density dependent mortality was observed, the food shortage hypothesis is not supported. Differences in activity were recorded in the laboratory, the northern voles being more active. This fact could cause higher levels of emigration in northern voles. A higher locomotory activity also entails higher predation susceptibility. As the most common predator on these islands, the adder uses olfactory cues in its active hunting; a more active vole is easier to find, because it leaves more scent trails. A seemingly subtle behavioural difference between two populations of the same species may thus influence the colonization ability.