Effects of food addition on the seasonal density-dependent structure of bank vole Clethrionomys glareolus populations

1. Population growth rates of bank vole populations in northern Finland were studied using long-term Capture-Mark-Recapture (CMR) data from two large grids (food-addition and control), in 1982-94. 2. A marked seasonal structure was found for direct density dependence, with a stronger density dependence in summer than in other seasons. There was no detectable evidence of delayed density dependence, consistent with the disappearance of large periodic multi-annual fluctuations. 3. Food-addition resulted in higher densities whereas the effect on the seasonal density-dependent structure was negligible. 4. Stability analysis of the deduced population dynamics model suggests that the dynamics were not affected by food addition. Variation in food resources is therefore unlikely to be a direct cause for multi-annual fluctuations in the studied system. Future studies should aim at linking the seasonal structure in the variation of vital rates to the seasonal structure in population dynamics.