Electronic Appendix A: Analysis of early summer abundance of voles
In the main text, we considered vole abundance quantified in autumn when the amplitude of the vole cycle is most pronounced. Here, we briefly explore the patterns of the dynamics based on abundances measured in early summer. Early summer vole abundances were not normally distributed and were square-root transformed in order to approximate normality.
Wavelet analysis of the dynamics of bank and field voles in early summer in
Kirkkonummi showed a pattern that is clearly consistent with the patterns described in the main text regarding the existence of a period of non-cyclic dynamics in the end of the
1990s (Fig. A1). Nevertheless, in terms of abundance in early summer both species were strongly cyclic before the irregularity and also after the irregularity. In particular, the cycles of both vole species returned at the same time and were of approximate the same signal strength (both much lower than in the period before the irregularity).
For the Heinola population, there also was a clear period of non-cyclic dynamics (Fig.
A2). Bank vole dynamics in early spring showed evidence of a shift towards reduced periodicity before the disappearance of cycles (Fig. A2). In addition, early summer abundance of field voles showed strong evidence of cycles before the irregularity, whereas bank vole cycles were proportionally stronger than field vole cycles after the irregularity.
In conclusion, consideration of vole abundance in early summer largely corroborates the main pattern observed in the autumn abundance. (1), Cyclic dynamics temporarily disappeared in the mid 1990s for about 4 – 5 years. (2), Data from the Heinola population
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supports the pattern that after the irregularity, the bank vole cycles were proportionally stronger than field vole cycles whereas this pattern was the converse prior to the irregularity.
FIGURE CAPTIONS APPENDIX A
Fig A1. Wavelet analysis of vole trapping carried out in early summer (June) in the
Kirkkonummi population. Plotted are the wavelet power spectra for the dynamics of
(panel a) the bank vole, and panel (b) the field vole, and (panel c) the cross-wavelet power spectrum for both species. See caption of Fig. 2 for a detailed explanation of these plots.
Fig A2. Wavelet analysis of vole trapping carried out in early summer (June) in the
Heinola population. Plotted are the wavelet power spectra for the dynamics of (panel a) the bank vole, and panel (b) the field vole, and (panel c) the cross-wavelet power spectrum for both species. See caption of Fig. 2 for a detailed explanation of these plots.
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Fig. A1 / Spring vole abundance in Kirkkonummi / Brommer et al.
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Fig. A2 / Spring vole abundance in Heinola / Brommer et al.
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Electronic Appendix B: Wavelet analysis of published data
We analysed published data on vole abundance from eastern central Finland (Korpimäki et al. 2005; Fig. B1). Voles in this population showed a significant 3-year cycle between
1982 and 1993/1994 (Fig. B1). Bank voles showed clear evidence of a period of noncyclic dynamics (Fig. B1a), whereas field vole dynamics in this locality shoed evidence of a shift towards four-year cycles (Fig. B1b). Both species were clearly phase-locked during the entire length of the time series, which is in agreement with the autoregressive analyses by Korpimäki et al. (2005). Interestingly, there is evidence of the three-year cycle returning in 1998 (as well as there being no cycle in the beginning of the study).
However, since these regions are largely outside the cone of influence, solid conclusions cannot be drawn.
Fig B1. Wavelet analysis of data published by Korpimäki et al. (2005, summation of data in their Figs. 1a and 1b) on vole abundance in western-central Finland from 1977 – 2003.
Plotted are the wavelet power spectra for the dynamics of (panel a) the bank vole, and panel (b) the field vole, and (panel c) the cross-wavelet power spectrum for both species.
See caption of Fig. 2 in the main text for a detailed explanation of these plots.
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Fig. B1 /Brommer et al. (electronic Appendix)
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