Mating System and Population Fluctuations of the Prairie Vole,Microtus ochrogaster

Abstract

The basic mating system of the prairie vole, Microtus ochrogaster , consists of monogamous breeding units comprised of one reproductive female and male and their offspring. Most surviving young remain at the natal nest; those that do so normally remain non-reproductive. Of 281 total breeding units monitored in free-living populations 50.2% were monogamous. Twenty-seven percent consisted of a single reproductive female that apparently has lost her mate. Theremaining 22.8% of the breeding units included two or more unrelated adults males and/or females (=‘complex’ breeding units). In general, monogamy was the predominant type of breeding unit at the highest (>100 adults/ha) as well as at low (>20 adults/ha) population densities. There was no consistent relationship between the number of residents of a breeding unit and population density. Significantly more young females remaining at the natal nest became reproductive at high rather than at low population densities (77.1 and 17.6%, respectively). Monogamy was prevalent during the winter as well as during the other seasons; however, there were significantly more complex breeding units during the winter than during other seasons. Breeding unit size was significantly larger during the winter than at other seasons. There was no difference in the proportions of breeding unit types or the number of residents of a breeding unit during breeding and nonbreeding seasons. Increased breeding unit size appears related to low temperatures and associated physiological stresses during the winter rather than to population density.