Abstract
Vole population cycles are a major force driving boreal ecosystem dynamics in northwestern Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predictability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze‐thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live‐trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different elevations (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes.
Highlights
Small mammal populations in the northern hemisphere often show cyclic dynamics in their abundance (Hanski, Hansson, & Henttonen, 1991; Kendall, Prendergast, & Bjornstad, 1998; Steen, Yoccoz, & Ims, 1990)
Our objective was to understand the role of three key extrinsic factors as explanatory factors explaining or contributing to winter crashes in the bank vole
The reduced environmental stability at low elevations relative to high elevations was pronounced in the 2013/2014 winter, when the low elevation sites experienced a mild mid-winter warming that did not occur at high elevations
Summary
Small mammal populations in the northern hemisphere often show cyclic dynamics in their abundance (Hanski, Hansson, & Henttonen, 1991; Kendall, Prendergast, & Bjornstad, 1998; Steen, Yoccoz, & Ims, 1990). Population cycles are characterized by a low, increase, peak, and crash phase, each lasting approximately 1 year (Andreassen et al, 2013). The crash phase may occur during the breeding season (Andreassen et al, 2013; Stenseth & Ims, 1993), but more often is observed during winter (Hansson & Henttonen, 1985; Krebs & Myers, 1974). Winter climate and snow or icing conditions may directly or indirectly affect vole population dynamics
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