Dispersal was investigated in two open-grid populations of meadow voles, Microtus pennsylvanicus (Ord, 1815) an central Virginia (U.S.A.) from November 1974 to April 1978. "Dispersal" was defined as immigration onto open, occupied population grids. Dispersers were distinguished from residents by weight at first capture. Individuals first captured at weights <30 g were classified as residents; those first captured at >30 g were classified as dispersers. Three independent lines of evidence support the validity of the 30-g criterion for recognizing dispersers in these vole populations. With frequent trapping and high trappability, particularly of young animals, this open-grid method of study offers two advantages in the study of dispersal. First, dispersers identified in this way exist an a biologically realistic environment as they move into or through an established population. Second, time-dependent components of the fitness of these dispersers can be monitored and compared with those of residents occupying the same habitat. Dispersers (immigrants) usually constituted >75% of the minimum number of animals known to be alive in any week. Dispersal occurred continuously and was more important in situ reproduction as a source of new individuals in the population. Using the criterion of a negative correlation between the proportion of the population dispersing (immigrating) and grid population density, dispersal was not positively density-dependent. Although sex ratios of residents did not differ from 1:1, those of dispersers' favored males on both grids. Nevertheless, 42% of all dispersers were female. Dispersers differed from adult (>30 g) residents in that they were (1) significantly heavier than adult residents of the same sex and (2) more often in reproductive condition, both at first capture and later. Thus, dispersers had the potential to contribute more offspring per individual than residents. Dispersers and adult residents had comparable lifespans on both grids. Females had longer lifespans than males. Based these components of fitness, dispersers appeared to be comparable or superior residents. The attributes of the dispersers and the apparent lack of density dependence may be interpreted as evidence of pre-saturation dispersal in these populations.
Original Publication Citation
Dueser, R. D., Wilson, M. L., & Rose, R. K. (1981). Attributes of dispersing meadow voles in open-grid populations. Acta Theriologica, 26(8), 139-162.
Dueser, Raymond D.; Wilson, Marcia L.; and Rose, Robert K., "Attributes of Dispersing Meadow Voles in Open-Grid Populations" (1981). Biological Sciences Faculty Publications. 423.