A comparison of population characteristics and reproductive success of resident and immigrant meadow voles

Abstract

We used a radionuclide technique combined with a minimum-weight criterion to identify resident and immigrant meadow voles, Microtus pennsylvanicus, on an open grid in South Natick, Massachusetts. Using the same techniques with populations on two fenced grids, we calculated an error rate of 7.2% in residency assignment. Immigrants were not a random subset of the resident population. Among immigrant voles the sex ratio was significantly male biased, whereas among residents it did not differ from 1:1. Immigrants had genotypic ratios that differed significantly from those of residents at three of five allozyme loci examined electrophoretically. Although immigrant males resided on the grid significantly longer than resident adult males, they did not differ significantly in reproductive success, maximum weight, or distance moved between trapping periods. Immigrants seemed to be as successful as residents during a period of low or declining density.