The spatial component of variation in small-mammal abundance measured at three scales

We studied small-mammal populations across a range of spatial scales to det ermine if they exhibited spatial variability that was independent of the di stribution of vegetation. Between 1996 and 1999, systematic livetrapping su rveys were conducted on nested grids at three scales: (1) extent (total are a covered by a grid) = 4900 ha, grain (minimum space between sampling point s)= 1000 m; (2) extent = 306 ha, grain = 250 m; and (3) extent = 31 ha, gra in = 125 m. The four most abundant species were the red-backed vole (Clethr ionomys gapperi), the short-tailed shrew (Blarina brevicauda), the deer mou se (Peromyscus maniculatus), and the woodland jumping mouse (Napaeozapus in signis). Small mammals exhibited spatial population structure over distance s up to 250 m but not over 1000 m. There was a component of this population structure that appeared to be temporally and spatially dynamic, and that w as not correlated with measured vegetation variables. We discuss processes that would create the observed metapopulation structure in seasonal landsca pes.