Abstract
AbstractPopulation fluctuations of small rodents are often synchronized over larger areas (>100 km) than what could be explained by dispersal, suggesting that the synchronizing factor is weather‐related and possibly mediated through changes in food quality. Because bank vole (Myodes glareolus) populations usually peak 1 year after peaks in reproduction of the staple winter food plant bilberry (Vaccinium myrtillus), we tested for a possible link between food and spatial synchrony by comparing the synchrony in bank vole population indices and bilberry seed production indices between three study areas across about 20,000 km2 in South Norway during a four decade period (1979–2019). There were subperiods of spatial synchrony and asynchrony between the study areas in the fluctuations of bank vole numbers and bilberry seed production, with the latter part of the study period displaying more pronounced synchrony than the first and middle part. However, with a few marked exceptions, when vole fluctuations were spatially out of phase across study areas so was bilberry seed production. Thus, we conclude that bilberry seed production to a large extent explained the spatiotemporal synchronicity in bank vole population fluctuations. Although bilberry seed production seems to be a causal driver of vole fluctuations, it remains to be seen to what extent the chemical composition of bilberry plants influences vole performance. Finally, certain weather factors may still influence voles directly, or indirectly by triggering bilberry seed production.
Highlights
The high-amplitude multiannual population fluctuations of small rodents in the northern hemisphere are often synchronized over large geographical areas (Angerbjörn, Tannerfeldt, & Lundberg, 2001; Bjørnstad, Stenseth, & Saitoh, 1999; Christiansen, 1983; Krebs et al, 2002; Myrberget, 1973)
Populations of bank vole (Myodes glareolus) in eastern Norway fluctuated in synchrony within a spatial scale of up to 30–40 km during 1990–1994 (Steen, Ims, & Sonerud, 1996), whereas population peaks observed in 2007 and 2014 occurred synchronously in areas situated several hundreds kilometers apart (Andreassen, Johnsen, Joncour, Neby, & Odden, 2020; Selås, 2020; Selås et al, 2011; Wegge & Rolstad, 2018)
Because population peaks of small rodents commonly occur simultaneously over much larger areas than what could be explained by dispersal (Ims & Andreassen, 2005), several authors assume that the synchronizing factor most likely is weather-related (Angerbjörn et al, 2001; Huitu, Laaksonen, Klemola, & Korpimäki, 2008; Koenig, 2002; Krebs et al, 2002)
Summary
The high-amplitude multiannual population fluctuations of small rodents in the northern hemisphere are often synchronized over large geographical areas (Angerbjörn, Tannerfeldt, & Lundberg, 2001; Bjørnstad, Stenseth, & Saitoh, 1999; Christiansen, 1983; Krebs et al, 2002; Myrberget, 1973). Regardless of the causal relationship, spatial synchrony in Myodes vole population dynamics may reflect a similar synchrony in bilberry reproduction, determined by weather factors that act during the flowering cycle of this plant species (Selås et al, 2015). In large parts of Fennoscandia, vole populations have fluctuated with a regular periodicity of 3–4 years (Angelstam, Lindström, & Widén, 1985) These population cycles are usually characterized by a negative autocorrelation at a time lag of 2 years (Hörnfeldt, 1994). Such delayed density dependence has commonly been interpreted as a result of trophic interactions, either between voles and their predators, or between voles and their food plants (Oli, 2019). Our prediction is that the spatial pattern of bank vole synchrony reflects a similar pattern of synchrony in bilberry reproduction
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