Life History Variation in Maturation in Fluctuating Meadow Vole Populations (Microtus Pennsylvanicus)

Publisher Website
Google Scholar
Abstract
Successful maturation on the natal area may vary as a function of sex, density, and season in voles and may affect sex ratio manipulation by breeding females. To determine how these factors interact in a microtine population, I live-trapped two Microtus pennsylvanicus populations for five years with two different types of traps. I caught large numbers of young shortly after weaning and determined whether they successfully entered the breeding population. Few males matured on the natal grid (12.2%, N = 1179), with only 3% maturing in the year of birth and 9% maturing the next year. More females matured on the grid (29.8%, N = 1207), with 22% maturing in the year of birth and 8% maturing the next year. Males had the highest probability of entering the breeding population if they were born late in the year and delayed maturation until the next year; females showed the opposite pattern. Maturation on the natal grid in the year of birth during the spring-early summer period was density-independent in males, but strongly density-dependent in females. I found no support for the Trivers-Willard hypothesis that the sex ratio of recruits should be biased to favor the sex most likely to enter the breeding population (daughters early in the breeding season and sons later on): at all times independent of season, a 1:1 sex ratio was observed. I found no support for cockburn''s inbreeding avoidance hypothesis that maturing males should move shorter distances from their natal site at high than at low density to avoid inbreeding; females did move shorter distances at high density.