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TWENTY-FIVE YEARS OF POPULATION FLUCTUATIONS OF MICROTUS OCHROGASTER AND M. PENNSYLVANICUS IN THREE HABITATS IN EAST-CENTRAL ILLINOIS

Abstract Populations of 2 species of arvicoline rodents, the prairie vole (Microtus ochrogaster) and meadow vole (M. pennsylvanicus), were monitored monthly in alfalfa, bluegrass, and tallgrass prairie habitats in east-central Illinois from 1972 through 1997. Alfalfa provides very high-quality preferred food and poor vegetative cover for both vole species, whereas bluegrass provides intermediate food and vegetative cover. Preferred food resources were very low, especially for M. ochrogaster, and vegetative cover was very dense in tallgrass prairie. Maximum and mean population densities of M. ochrogaster were highest in alfalfa, intermediate in bluegrass, and lowest in tallgrass prairie. Populations of M. ochrogaster displayed synchronous 3- to 4-year multiannual cycles in all 3 habitats. Cycles were most pronounced in alfalfa, less pronounced in bluegrass, and barely discernible in tallgrass prairie. Food availability seems more important than vegetative cover for the success of M. ochrogaster. Densities of M. pennsylvanicus generally were very low in bluegrass and alfalfa habitats, both of which contained an abundance of preferred food plants. When M. pennsylvanicus was present in abundance in these 2 habitats, populations displayed annual or erratic fluctuations. Densities of M. pennsylvanicus were much higher in tallgrass prairie than in the other 2 habitats. Although vegetative cover seems more important than food availability for the success of M. pennsylvanicus, no evidence existed for population cycles in tallgrass prairie. We found no synchrony among population fluctuations of the 2 species of voles in the 3 habitats.