Gene flow and population structure of a common agricultural wild species (Microtus agrestis) under different land management regimes.

The impact of landscape structure and land management on dispersal of populations of wild species inhabiting the agricultural landscape was investigated focusing on the field vole (Microtus agrestis) in three different areas in Denmark using molecular genetic markers. The main hypotheses were the following: (i) organic farms act as genetic sources and diversity reservoirs for species living in agricultural areas and (ii) gene flow and genetic structure in the agricultural landscape are influenced by the degree of landscape complexity and connectivity. A total of 443 individual voles were sampled within 2 consecutive years from two agricultural areas and one relatively undisturbed grassland area. As genetic markers, 15 polymorphic microsatellite loci (nuclear markers) and the central part of the cytochrome-b (mitochondrial sequence) were analysed for all samples. The results indicate that management (that is, organic or conventional management) was important for genetic population structure across the landscape, but that landscape structure was the main factor shaping gene flow and genetic diversity. More importantly, the presence of organically managed areas did not act as a genetic reservoir for conventional areas, instead the most important predictor of effective population size was the amount of unmanaged available habitat (core area). The relatively undisturbed natural area showed a lower level of genetic structuring and genetic diversity compared with the two agricultural areas. These findings altogether suggest that political decisions for supporting wildlife friendly land management should take into account both management and landscape structure factors.