Vegetation Characteristics of Microtus ochrogaster and M. pennsylvanicus Habitats in East-Central Illinois

Abstract

Vegetation characteristics of Microtus ochrogaster and M. pennsylvanicus habitats in east-central Illinois were analyzed by comparing local distribution of the two species among 128 roadside sites. M. pennsylvanicus was the only species at 41 sites, whereas only M. ochrogaster occurred at 28 sites; both species occurred at two sites. Comparison of the vegetation at 18 M. pennsylvanicus sites and 17 M. ochrogaster sites revealed that M. pennsylvanicus sites were characterized by a greater total vegetation biomass, a higher percent composition of grasses other than Poa and by a lesser amount of Taraxacum than were M. ochrogaster sites. Mean total cover was similar between M. ochrogaster and M. pennsylvanicus sites; mean vegetation ceiling height and litter depth at M. pennsylvanicus sites were nearly twice those at M. ochrogaster sites. Discriminant function analysis indicated that total biomass, percent species composition and structure (mean height) explained 42.8, 48.8, and 57.5%, respectively, of the vegetation variation between M. ochrogaster and M. pennsylvanicus sites. Non- Poa monocotyledonous plants contributed most to the discriminant functions; mean litter height also contributed significantly to the structural model. The structural model was the best predictor of whether a site would be inhabited by M. ochrogaster or by M. pennsylvanicus . We suggest that differential predation risk resulting from difference in nest location (surface and underground for M. pennsylvanicus and M. ochrogaster , respectively) is responsible for the preference of M. pennsylvanicus for dense vegetation habitats and tolerance of M. ochrogaster for sites with more sparse cover.