Patterns of resource use, food quality, and health status of voles (Microtus pennsylvanicus) trapped from fluctuating populations.

Recent studies suggest that diet quality is responsible for differential survivorship of vole cohorts (Boonstra and Boag 1987) and spacing behavior of females (Ims 1987). These phenomena have been related either to a lack of or a deterioration in the quality of the preferred food. To test this hypothesis, we compared foods habits, food quality and health status of meadow voles (Microtus pennsylvanicus) from high and low population density phases. In this study, seven plant species represented the main food items used on a regular basis and biomass values of preferred species decreased with browsing pressure. In addition, food quality of the main dietary items changed between phases forcing females to adjust their feeding strategy accordingly. Health of voles changed also opening the way to speculations on competition for high quality food resources and survivorship.