Density-dependent variation in body mass of voles |
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Authors: | Edda Johannesen Harry P Andreassen |
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Institution: | 1. Institute of Marine Research, Nordnes, P.O. Box 1870, 5817, Bergen, Norway 2. H?yskolen i Hedmark avd Evenstad, 2480, Koppang, Norway
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Abstract: | We studied inter-annual, spatial and sexual variation in the body mass of bank volesMyodes glareolus Schreber, 1780 and grey-sided volesMyodes rufocanus Sundevall, 1846 using live trappings from two grids on the southand north-facing slopes of a mountain valley in Southern
Norway. Variation in spring density of the four populations was consistent with cyclic dynamics (n=7,s-values >0.5). Individuals caught on the south-facing slope were larger than those caught on the north-facing slope. Reproductively
mature bank vole males were smaller than females, whereas reproductively mature grey-sided vole males were larger than females.
Body mass was related to density in both species. In bank voles, we found a direct positive density dependence caused by a
higher rate of survival at higher densities resulting from individual allocation of resources from reproduction to survival
and growth. In grey-sided voles, we found a negative delayed density dependence resulting from grazing on preferred plants
that determined the resource available for individual vole growth the following year. |
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