Population dynamics of small rodents in the southern boreal forest as influenced by furbearer harvest

Abstract

:We tested four predictions derived from the hypothesis that the guild of avian and terrestrial predators should regulate small mammal populations at low densities in relatively productive ecosystems of the southeastern part of the North American boreal forest. We estimated the density of two small mammal populations and the abundance of their predators for 3 y in two adjacent areas that differed with respect to trapping of furbearers. We predicted 1) that small mammal densities would not show multi-annual fluctuations in the two areas and 2) that densities would be much lower than peak densities reached by cyclic populations. Due to the harvest of furbearers in one area, we also predicted 3) that population densities and 4) survival of small mammals would be higher in the trapped than in the protected area. In agreement with our first two predictions, densities of the two main small mammal species (southern red-backed vole, Clethrionomys gapperi, and deer mouse, Peromyscus maniculatus) showed little variation between 1998 and 2000 in both areas, and additional data from the two previous years in the trapped area indicated that densities remained relatively stable and low over the 5-y period. However, contrary to our last two predictions, densities of the two most abundant species did not vary between areas, nor did survival rate of red-backed voles, the only species for which this variable could be estimated. Our findings show that the effect of trapping did not cascade down to small mammals. We have some evidence based on snow-tracking data that trapping, which focused on large generalist predators, may have relaxed intra-guild predation on small specialist predators and favoured an increase in abundance of specialist predators. Accordingly, we cannot reject the idea that a predation-based mechanism maintains small mammal densities at relatively low and stable levels in productive forests.