EFFECTS OF ADULT SEX RATIOS ON RECRUITMENT OF JUVENILE GRAY-TAILED VOLES, MICROTUS CANICAUDUS

Abstract

Juvenile recruitment, growth, survival, and time to sexual maturation of rodents are all negatively affected by high densities of adults. But whether density of males, of females, or total density of adults has the greatest effect on juveniles is not known. We maintained populations of gray-tailed voles, Microtus canicaudus, in 0.2-ha enclosures with densities of 30 males, 10 females (male-biased); 20 males, 20 females (control); and 10 males, 30 females (female-biased) breeding adults. With juvenile recruitment, population densities increased to 180 voles/enclosure (700 voles/ha) in male-biased enclosures and 200 voles/ enclosure (1,000 voles/ha) in control and female-biased enclosures. Recruitment, growth, and survival of either sex juvenile were not affected negatively by adult males but recruitment and time to sexual maturation of young females were negatively affected by high densities of females. Reduced juvenile recruitment was likely due to neonatal death before emergence from nest. We conclude that females have a greater negative effect on juvenile recruitment and reproductive development than do males. This difference was slight, however, and under normal densities of wild populations probably has minimal impact on vole demography. words: gray-tailed voles, infanticide, recruitment, sex ratios, sexual maturation, territoriality