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 gr ay-tailed voles (Microtus canicaudus) to the reduction and fragmentati on of their habitat. Our objectives were (1) to test whether animals p erished or moved into remaining fragments after 70% of their habitat w as removed; and (2) to test the null hypothesis that the social struct ure and demography of animals would not differ between habitats consis ting of one large continuous fragment (625 m(2)), a mosaic of 25 small fragments (each 25 m(2)) separated by 4 m of bare ground, and control , unmanipulated habitats (1850 m(2)). We conducted the experiment in 1 2, 0.2-ha enclosures planted with alfalfa with four replicates for eac h of two manipulated treatments and a control. A 70% reduction in habi tat did not adversely affect adult survival, reproductive rate, juveni le recruitment, or population size. However, an influx of unrelated fe males into habitat fragments resulted in decreased juvenile recruitmen t in those fragments. Voles from cleared habitat moved into the remain ing habitat and did not measurably affect the resident population. Sim ilarly, the demography of voles did no differ significantly among the large-fragment, small-fragment, and control enclosures. Peak density e stimates based on the amount of habitat in each enclosure were 545 ani mals per hectare in control, 1056 in large-fragment, and 2880 in small -fragment enclosures. Reduced movement of animals among the small frag ments was the most obvious effect of habitat fragmentation. Six percen t of females and 15% of males moved among small fragments within a wee k compared to approximately 60% moving comparable distances in large-f ragment and control enclosures. Rates of juvenile dispersal and sexual maturation declined throughout the summer on all treatments, were ass ociated with season and density, and were only marginally associated w ith habitat loss and fragmentation. We conclude that at the time of ha bitat removal and fragmentation, populations were small enough to acco mmodate a 70% reduction in habitat and still continue to increase in n umbers. The social system of gray-tailed voles was sufficiently flexib le to accommodate an influx of animals to withstand densities >1000 vo les per ha. The behavioral and demographic features of gray-tailed vol es are similar to those reported for other small mammals, thus confirm ing the use of voles for ecological model systems in habitat fragmenta tion studies.