Influence of vole cycles and other environmental factors on pine marten (Martes martes) population dynamics and abundance in southeastern Norway
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The pine marten in Norway lives at the northern edge of their distribution area. At this latitude, regular fluctuations in vole population sizes are common, where the amplitudes get more pronounced with increasing latitude. This dynamic plays an important role in the ecosystem, as voles are prey for many predators, being a major part of the diet for the pine marten. However, the temporal and causal relationship between pine marten and vole fluctuations has received little attention, particularly regarding how vole peaks and lows affect pine marten population dynamics. Using snow tracking indices from previously sampled 618 yearly line transects covering eleven years in Hedmark county, Southeastern-Norway, I estimated the pine marten abundance, and investigated how pine marten abundance responded to vole fluctuations. I studied how these potential co-dynamics behaved in a north-south gradient, including the parameters snow depth and vole abundance (from prior data collections) upon the response variable pine marten abundance from snow tracks (i.e., tracks per km2 ). Pine marten abundance was expressed as binomial in order to reduce noise, and binomial regression models were used with snow depth, vole abundance and human settlement density. In order to test for cyclicity, snow track indices were used in Partial Rate Correlation Function, and the combined residuals was used as a response variable with snow depth, elevation and vole coefficient of variation. I predicted that pine martens were synchronized with vole fluctuations, and that the cyclicity was more pronounced in the northern part of the study area. The results showed that pine marten population size was positively associated with the previous year’s vole abundance and snow depth. A possible explanation can be the pine marten physiology, and adaptation to snow. The pine marten abundance was negatively associated with human settlement density, indicating vulnerability towards anthropogenic impacts. Pine marten population dynamics displayed a strong density-dependent growth pattern and showed no signs of cyclicity. The growth pattern was negatively affected by variation in vole abundance and increased elevation, while positively associated with snow depth, indicating that the population dynamics differs on a north-south gradient. The prediction that the pine marten is cyclic was not supported, albeit it is clear that voles are a vital part of the pine marten diet, it’s life history traits might explain why it is not synchronized with vole fluctuations. Possible explanations here include food caching, shifting to alternative prey and intraspecific regulation mitigating effects of varying access to voles as prey.