Additive effects of climate and vegetation structure on the altitudinal distribution of greater white-toothed shrews Crocidura russula in a Mediterranean mountain range

Environmental variation along geographic gradients determines the distribution of animals and plants trough both direct and indirect effects. We analyze the relative contribution of climate and vegetation structure variations along a Mediterranean altitude gradient on the patterns of abundance and occurrence of the greater white-toothed shrew Crocidura russula, a generalist small mammal whose distribution is constrained by cold conditions. Sampling was performed from February 1995 to July 1997 on nine plots covering a wide altitudinal gradient (540–1550 m?a.s.l.). Structural equation models for the direct and indirect effects of climate and vegetation on shrew density and occupancy rates showed a stronger effect of vegetation structure (53 %) than direct climate effects (38 %) on shrew distribution. Shrews were more abundant in the warmer lowland sites, but were able to colonize highland cold areas by selecting habitats with well-developed understory vegetation (low shrubs or bracken). Vegetation effects were additive to climatic restrictions, seemingly providing more favorable microclimatic, and presumably food, conditions under shrub cover. Results indicate that predictions of range changes for shrews under climate change scenarios may underestimate expected range expansions under the current conditions of general land abandonment and shrub encroachment.