Is the matrix really inhospitable? Vole runway distribution in an experimentally fragmented landscape

Habitat fragmentation is a common feature of modern landscapes, with significant impacts on the population densities of and space use by animals. A frequent model system for studying these effects is that of voles (Microtus spp.) and other rodents in experimentally fragmented grasslands. Design of these study sites is motivated by landscape theory, and often assumes that the matrix between discrete experimental habitat patches is inhospitable to focal species. Our census of M. ochrogaster runways in an experimentally fragmented landscape in eastern Kansas indicates that voles make substantial use of the mowed matrix, and that such use increases with degree of habitat fragmentation. Census season (winter, summer) was also an important predictor of observed runway distributions. Our results suggest that voles may have home ranges that include multiple small fragments and also the intervening matrix, leading to overestimates of population density. While the assumption that the matrix is inhospitable in experimentally fragmented habitats may be justified in many cases, studies using the model system of Microtus spp. or ecologically similar rodents in grasslands should incorporate methods that account for use of the matrix.