Seasonality shapes the amplitude of vole population dynamics rather than generalist predators

Harry P Andreassen,Kaja Johnsen,Barbara Joncour,Morten Odden,Magne Neby

doi:10.1111/oik.06351

Harry P Andreassen, Kaja Johnsen + Show 3 more

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https://doi.org/10.1111/oik.06351

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Abstract

Seasonality has been suggested as a necessary factor for the initiation of vole population cycles in Fennoscandia. This has been well described for a latitudinal gradient. Here, we used an elevational gradient as a proxy for winter length to study how the length of the winter season correlates with the amplitude of bank vole Myodes glareolus population cycles. In addition, we studied whether the small mammalian generalist predator community present locally could explain any elevational effects. We estimated the population size of 30 local bank vole populations. We found a strong effect of elevation on the amplitude of the population cycle with local populations at around 800 m elevation having 1.5 times greater densities than populations in the valley (ca 300 m elevation). A univariate model with elevation as predictor for amplitude was twice as likely to be the best model than models including generalist predators. Our results fit well with the theories of a positive effect of winter length on the amplitude of vole population cycles in Fennoscandia, irrespective of whether the seasonal effect corresponds to a latitudinal or elevational gradient. The mechanisms may be limited resources during winter rather than generalist predators.

Highlights

Periodic fluctuations in the size of small mammal populations are common in northern ecosystems (Finerty 1980, Krebs 1996, Myers 2018)
In small mammals, increasing amplitude of population fluctuations are associated with a longer winter season (Hanson and Henttonen 1985, 1988) and stronger delayed density-dependence related to winter predation by specialist predators (Stenseth et al 2003)
Our results confirmed our expectations that winter length was positively associated with the amplitude of vole population cycles

Summary

Introduction

Periodic fluctuations in the size of small mammal populations (i.e. population cycles) are common in northern ecosystems (Finerty 1980, Krebs 1996, Myers 2018). These fluctuations tend to have a greater amplitude with increasing latitude. At the other end of the latitudinal gradient, stronger direct density-dependence occurs due to the presence of a larger number of generalist predators further south (Hanson and Henttonen 1985, Bjørnstad et al 1995, Ims et al 2008, Henden et al 2009).

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