Habitat and Interspecific Displacement of Small Mammals in the Netherlands

Abstract

In The Netherlands, 7 species of small terrestrial mammals belonging to 5 genera are so numerous that they often meet in the field. The aim of this study was to assess whether interspecies interaction leads to displacement of species from their favoured habitats. For this purpose, population densities of the species were estimated in 210 localities in which ground-water level, height of herbaceous vegetation and distance from wood edges were accurately measured. The main habitats inhabitated by the various species when distribution is not limited by other species are as follows. All species except Sorex avoid grasslands shorter than 20 cm. Sorex araneus and S. minutus occur everywhere, though more outside than within woods. Microtus agrestis and Micromys minutus avoid woods; in grasslands, they do not react to differences in moisture (ground-water level) or vegetation height. Microtus arvalis occurs only in dry grasslands and presumably avoids woods. Clethrionomys glareolus and Apodemys sylvaticus occur within woods and the adjacent grasslands up to about 30 m from the edges. Tolerance among different species within a locality of co-occurrence was the rule; 6 of the 21 pairwise species combinations were even positively associated; this probably resulted from the presence of unknown environmental characteristics attractive to both. M. arvalis and C. glareolus were negatively associated. Here, we found indirect arguments for the hypothesis that part of the localities were unattractive for only one of these species. Spatial intolerance could be assessed in Microtus arvalis and M. agrestis. When macroallopatric, these live in both tall and short vegetation; however, when in proximity, M. agrestis is restricted to grasslands with tall and M. arvalis to grasslands with short vegetation.