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 voles Microtus canicaudus (Miller, 1897) and recruitment of juveniles in response to relative ab undance 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 territoriali ty. Following a 70% reduction in habitat, territories of females shrun k: from similar to 50 m(2) to < 20 m(2) with no significant difference in pregnancy rates or overall juvenile recruitment compared to contro ls. 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 juven ile recruitment in the presence of adult females but not males suggest s that pup mortality rather than food limitation contributed to reduce d 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 pa tterns of space use, reproductive rates, and juvenile recruitment were more consistent with the pup-defense than the food-defense hypothesis for female territoriality.