Female and male mammals have different behavioral strategies for maximizing their reproductive success. Pregnancy and lactation obligate female mammals to provide greater parental investment than males; thus, females compete with each other for food and space to rear their offspring, while male mammals compete with each other for female mates. Therefore, natural selection should favor any behavior among females that increases their access to food and space to rear successful offspring and any behavior among males that increases their access to females. In two enclosure experiments, the gray-tailed vole, Microtus canicaudus, was used as a model species to study (1) the relative influence of male competition versus access to females on space use by males and (2) facultative sex-ratio adjustment at the population level in response to low and high population densities, skewed adult sex ratios, and season. Home-range sizes of male voles did not appear to expand beyond an overlap with about five members of either sex. Intrasexual competition with 3-4 males and/or overlap with five females appear to set the upper limits to home-range size. Space use by males is influenced by intrasexual competition and by access to females with an upper limit of overlap with either sex. Additionally, facultative sex-ratio adjustment in response to changing population densities and skewing adult sex ratios did not occur, but a seasonal effect was detected with significantly more males produced in autumn than in spring. Under the conditions of this experimental study, I was not able to measure sex ratios of individual litters, but if any sex-ratio adjustment occurred in response to densities and adult sex ratios, it was not detectable at the population level. / Graduation date: 1999

Graduation date: 1997

I monitored demography, movement, and reproductive behavior of gray-tailed voles, Microtus canicaudus, in experimental habitat patches with and without corridors. I tested the hypotheses that reproductive rate, juvenile recruitment, and population size and growth rate would be affected negatively by immigrants that were introduced to resident groups (+ male and + female treatments). I hypothesized that "strangers" would commit infanticide thus decreasing juvenile recruitment. Second, I determined if movement corridors facilitated dispersal among habitat patches, thus potentially increasing infanticide, but decreasing reproductive inhibition of opposite-sex relatives by allowing them to separate (corridor treatment). Experiments were conducted in 12 0.2 ha enclosures planted with alfalfa that was fragmented into four patches (each 156 m��) separated by 12.5 m of bare ground. Introduction of unfamiliar conspecifics did not adversely affect reproductive rate, juvenile recruitment, population size, density, or growth rate. Corridors facilitated dispersal movements with males moving more than did females; however, corridors did not result in an even distribution of animals in the four patches. Unconnected habitat patches resulted in female- rather than the typical male-biased dispersal and females dispersed at lower body mass than in controls. Males that did not disperse from their natal patch exhibited a slight delay in sexual maturation. I conclude that movement is deterred in patchy environments, enhanced with corridors, and differentially affects males and females. Behavioral factors that affect an individual's dispersal or reproductive pattern should be considered in landscape planning. / Graduation date: 1997