Space use and juvenile recruitment in gray-tailed voles in response to intruder pressure and food abundance

We examined space use by female gray-tailed voies Microtus canicaudus (Miller, 1897) and recruitment of juveniles in response to relative abundance of food and increased intruder pressure following experimental removal of habitat. Our experiment indirectly tested the assumptions of the food-defense and pup-defense hypotheses for female territoriality. Following a 70% reduction in habitat, territories of females shrunk from -50 m to < 20 m with no significant difference in pregnancy rates or overall juvenile recruitment compared to controls. Juvenile recruitment was not adver­sely affected by overall density or the numbers of males sharing a patch, but decreased significantly as the number of unrelated adult females sharing a patch increased. We did not measure infanticide directly, but the decreased rate of juvenile recruitment in the presence of adult females but not males suggests that pup mortality rather than food limitation contributed to reduced juvenile recruitment, We conclude that at high densities, increased intruder pressure from adult females had a greater impact on juvenile recruitment than did food abundance. Thus, our results suggest that patterns of space use, reproductive rates, and juvenile recruitment were more consist­ent with the pup-defense than the food-defense hypothesis for female territoriality.