Efectos de la estructura forestal sobre la ab undancia del topillo rojo Myodes glareolus (Schreber, 1780) en un encinar de la Garrotxa (NE Catalunya)

Abstract

The bank vole Myodes glareolus (Schreber, 1780) is a small Eurosiberian forest rodent that lives in the northern third of the Iberian Peninsula. Within its European distribution range, the bank vole is known to prefer forested areas with extensive plant cover (i.e., herbs and shrubs) that provide refuge and food. However, there is a lack of data on its environmental requirements in the Mediterranean, which constitutes the southernmost limit of its distribution. This study analyzed the influence of forest structure on bank vole abundance in a holm-oak forest in La Garrotxa (NE Catalonia, Spain). A total of 34 rectangular plots each containing 8 Sherman traps (4 x 2) were constructed in zones with different structures within the same forest patch. These plots were sampled for 3 consecutive days in winter 1999. The forest structure enabled the definition of two groups of plots based on cluster analysis: 1) one group of 17 plots (type 1) with large oaks and a smaller density of trunks, with a great amount of herbaceous vegetation and shrubs; and 2) a group of 10 plots (type 2), with small oaks and a high density of trunks, with very poor undercover. A third experimental group was added (n = 7 plots), consisting of plots with a structure similar to the type 2 plots, and that were cleared by removing bushes and small trees. A total of 32 different individuals were captured, and analysis of variance demonstrated that the density of bank voles was 9 times higher in type 1 plots than in type 2 plots, whereas there were no captures in type 3 plots. These results indicate microhabitat preferences that are similar to those already known in more northern populations, and that lead to the selection of forest patches with extensive shrub and herbaceous cover.