Minor Species as the Dominant Rodents in an Oldfield
Rose, Robert K., Ford, Linda J., The American Midland Naturalist
In this report of substantial syntopic populations, southern bog lemmings (Synaptomys cooperi) and woodland voles [Microtus (Pitymys) pinetorum] were the co-dominant rodents in a grassy oldfield in the absence of the large-bodied species of rodents common to the region. Southern bog lemmings achieved densities of 14 ha^sup -1^ on one grid and woodland voles had a peak density of 32 ha^sup -1^ on the other. Both species bred at high levels during the 18-mo study, including during the winter months.
Despite broad distributions in eastern North America, southern bog lemmings (Synaptomys cooperi) and woodland voles [Microtus (Pitymys) pinetorum] are less studied than other arvicoline rodents, primarily because their populations are patchy, often intermittently present, and usually low in density. Rarely is either species abundant in association with larger rodents, except in eastern Kansas (Gaines et a?, 1977), where S. cooperi coexists in moderate densities with prairie voles (M. ochtogaster) in oldfields. Elsewhere southern bog lemmings occupy variable and often woridy habitats with herbaceous ground cover (Connor, 1959; Kirkland, 1977; Linzey, 1984; Rose, 2006) . Woodland (or pine) voles also are found in a range of habitats, usually in forests and in low numbers (e.g., Hamilton, 1938; Benton, 1955; Stickel and Warbach, 1960). An example of their occasional presence in non-forest habitat was documented in a 28-mo study in eastern Virginia (Green and Rose, 2009) , in which four woodland voles were recorded along with 513 hispid cotton rats (Sigmodon hispidus), 135 meadow voles (Microtus pennsylvanicus) , 129 eastern harvest mice (Reithrodontomys humulis), 45 house mice (Mus musculus), and 21 marsh rice rats (Oryzomys palustris) in an oldfield dominated by grasses and invading loblolly pine (Pinus taeda) trees.
Woodland voles reach their highest densities in apple orchards (e.g., >96 ha^sup -1^ in Pennsylvania, Anthony et al., 1986), where they often kill mature trees by eating the bark from root systems. Although studied extensively as economic pests in orchards (e.g., Benton, 1955; Valentine and Kirkpatrick, 1970), few investigations of woodland vole populations have been conducted in natural plant communities, the most notable being in oak forests by Goertz (1971) in Oklahoma and Miller and Getz (1969) in Connecticut. Our 18-mo study was conducted in a grassy oldfield with 2-3 y-old pine seedlings.
Herein, we evaluated the population dynamics and ecology of southern bog lemmings and woodland voles as the dominant rodents in the absence of the larger and usually dominant oldfield meadow voles, cotton rats, and rice rats in our region.
MATERIALS AND METHODS
THE STUDY SITE
Located 1 km west of Great Dismal Swamp National Wildlife Refuge, a 50,000-ha forested swampland in Suffolk, Virginia, the ca. 100-ha site was in early serai stages after logging of the loblolly pines (Pinus taeda) and sweet gums (Liquidambar styradflua). After die stumps and woody debris were bulldozed into parallel windrows 40-m apart, loblolly pine seedlings were planted mechanically in the peaty soils, leaving deep furrows mat filled with water in winter and sometimes after heavy rains. Besides die 2-3 y-old pine seedlings and colonizing grasses (Panicum sp., Unióla, oüiers), sedges (Carex sp.), and soft rushes /uncus effuses and/, tenuis), small sweet gums and inkberry bushes (Ilex glabra) also were present.
Two rectangular grids were set between the windrows >100 m from the edge of the field. The two trap grids were 15 X 6, with 7.6 m intervals; Row 4 was a null row because no traps could be placed where the logging debris formed the windrow. The effective trapping area of the grids was 0.554 ha, using die inclusive boundary strip mediod of Stickel (1954). One modified Fitch live trap (Rose, 1994) was placed at each coordinate for a total of 75 traps on each grid. …