Influence of Chemical Factors on Palatability of Forage to Voles

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Abstract
Laboratory-feeding trials were used to test the palatability of 15 plant species to two species of voles (Microtus pennsylvanicus and M. ochrogaster) in central Illinois. The intake of different plant species was compared to the chemical composition of plants, as measured by nitrogen, water, fiber, alkaloid, and phenolics, and to selectivity for plants by voles in the field. Palatability of plants varied greatly; some species were ignored but others were consumed heavily. The most palatable plant species in our laboratory trials were those previously reported as species selected for in the field. The relative payabilities of plants were similar for both vole species. Multiple-regression analyses incorporating chemical characteristics for all the plants explained a maximum of 29% of the variance in consumption. However, when only consumed plants were considered, as much as 73% of the variance was explained by nitrogen level and substances that reduce digestibility (fiber and protein-binding phenolics). Plants not eaten by either vole species are known to contain toxic compounds. These results support the hypothesis that food selection by generalist herbivores is a two-step process: plant characteristics that determine which plant species are avoided may differ from characteristics that determine the level of consumption of those eaten.