Effects of Habitat Loss and Fragmentation on the Behavior and Demography of Gray-Tailed Voles

We monitored the short term behavioral and demographic responses of gray-tailed voles (Microtus canicaudus) to the reduction and fragmentation of their habitat. Our objectives were (1) to test whether animals perished or moved into remaining fragments after 70% of their habitat was removed; and (2) to test the null hypothesis that the social structure and demography of animals would not differ between habitats consisting of one large continuous fragment (625 m²), a mosaic of 25 small fragments (each 25 m²) separated by 4 m of bare ground, and control, unmanipulated habitats (1850 m²). We conducted the experiment in 12, 0.2-ha enclosures planted with alfalfa with four replicates for each of two manipulated treatments and a control. A 70% reduction in habitat did not adversely affect adult survival, reproductive rate, juvenile recruitment, or population size. However, an influx of unrelated females into habitat fragments resulted in decreased juvenile recruitment in those fragments. Voles from cleared habitat moved into the remaining habitat and did not measurably affect the resident population. Similarly, the demography of voles did not differ significantly among the large-fragment, small-fragment, and control enclosures. Peak density estimates based on the amount of habitat in each enclosure were 545 animals per hectare in control, 1056 in large-fragment, and 2880 in small-fragment enclosures. Reduced movement of animals among the small fragments was the most obvious effect of habitat fragmentation. Six percent of females and 15% of males moved among small fragments within a week compared to approximately 60% moving comparable distances in large-fragment and control enclosures. Rates of juvenile dispersal and sexual maturation declined throughout the summer on all treatments, were associated with season and density, and were only marginally associated with habitat loss and fragmentation. We conclude that at the time of habitat removal and fragmentation, populations were small enough to accommodate a 70% reduction in habitat and still continue to increase in numbers. The social system of gray-tailed voles was sufficiently flexible to accommodate an influx of animals to withstand densities> 1000 voles per ha. The behavioral and demographic features of gray-tailed voles are similar to those reported for other small mammals, thus confirming the use of voles for ecological model systems in habitat fragmentation studies.