THE USE OF FOOD RESOURCES WITH OR WITHOUT KNOWN BY-PRODUCTS BY A CYCLIC POPULATION OF MEADOW VOLES

Results from 3 yr of plant sampling and diet analyses in a cyclic population of meadow voles (M. pennsylvanicus) show that animals use plants with known toxic by-products while the population is in its growth and peak phases: voles from the low density phase of the population almost exclusively eat plants without such by-products. Considering the fact that plants which contain toxic by-products are bad resources for herbivores, while plants which do not are good resources, one can infer that the quantity of good resources available becomes very limited. This explains the appearance of bad resources in the diet at times when the population density becomes very high. There is no evidence in the literature of acute or chronic toxic effects in meadow voles resulting from the ingestion of plants with toxic by-products. At present one can only note the importance of such resources in their diet and speculate on the cost-benefits of such a feeding habit.