Numerous laboratory studies with at least 12 species of rodents have reported that exposure of females to strange males results in pregnancy disruption or infanticide. The proximate causes and ultimate benefits of these behaviors have been proposed from an evolutionary perspective. To determine if exposure to strange males or females caused pregnancy disruption and (or) infanticide in a resident gray-tailed vole (Microtus canicaudus) population, pregnancy rate and juvenile recruitment were monitored in populations of 12 female and 12 male voles following introduction of unfamiliar adults. These experiments were conducted in 12 0.2 ha enclosures using three treatments and a control. Every 10 days 12 males, six males, or six females were removed and replaced in the three treatments, respectively, or the populations were left unmanipulated in the control (3 replicates/treatment). The time to first parturition, time between parturitions, number of juveniles recruited/parturition, and percent of births followed by lactation did not vary among the controls and three treatments. The only observable effects of treatment were a slight non-significant delay in time to first birth in the 12-male treatment and a slightly significant difference in the number of pregnancies per female. These results do not support previous laboratory studies indicating that exposure to strangers causes pregnancy disruption and (or) infanticide at high rates. Therefore, in field conditions, little evidence was found indicating that female gray-tailed voles' reproductive fitness declines after exposure to strangers. I propose that results from laboratory studies on behavioral aspects of mammals should be validated with field data prior to being extrapolated to natural populations and applied to evolutionary paradigms. / 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