Short-term demographic response of the red-backed vole to spruce beetle infestations in Alaska

How small mammals are affected by habitat changes caused by forest insect epidemics is largely unknown. Our objective was to determine the influence of spruce beetle (Dendroctonus rufipennis) epidemics on the dynamics of northern red-backed vole (Clethrionomys rutilus) populations approximately 10 years post-infestation. We conducted a mark-recapture study on northern red-backed voles for 2 field seasons in the Copper River Basin, Alaska, USA, where recent beetle infestations were widespread. Using the robust sampling design, we produced estimates of vole abundance, survival, and recruitment. in 3 locations that varied in their degree of beetle-induced spruce mortality. Vole abundance inversely related to the level of spruce mortality. Vole recruitment showed a larger contribution from both immigration and in situ reproduction in the low infestation site than in the medium and heavy infestation sites. No differences in vole survival were detectable across the 3 locations with varied beetle-induced spruce mortality levels. Measured vole food resources and protective vegetative cover did not vary greatly across infestation levels. Abundance and recruitment parameters indicate a negative change induced by spruce beetle infestations. However, the effect of beetles was not large enough to cause the variation in vole survival. Spruce mortality levels may need to be over 50% before greatly influencing the habitat and the demographics of northern red-backed voles.