Gene flow in natural populations may be strongly influenced by landscape features. The integration of landscape characteristics in population genetic studies may thus improve our understanding of population functioning. In this study, we investigated the population genetic structure and gene flow pattern for the common vole, Microtus arvalis, in a heterogeneous landscape characterised by strong spatial and temporal variation. The studied area is an intensive agricultural zone of approximately 500 km2 crossed by a motorway. We used individual-based Bayesian methods to define the number of population units and their spatial borders without prior delimitation of such units. Unexpectedly, we determined a single genetic unit that covered the entire area studied. In particular, the motorway considered as a likely barrier to dispersal was not associated with any spatial genetic discontinuity. Using computer simulations, we demonstrated that recent anthropogenic barriers to effective dispersal are difficult to detect through analysis of genetic variation for species with large effective population sizes. We observed a slight, but significant, pattern of isolation by distance over the whole study site. Spatial autocorrelation analyses detected genetic structuring on a local scale, most probably due to the social organisation of the study species. Overall, our analysis suggests intense small-scale dispersal associated with a large effective population size. High dispersal rates may be imposed by the strong spatio-temporal heterogeneity of habitat quality, which characterises intensive agroecosystems.

Spatial genetic structure of a small rodent in a heterogeneous landscape.

Short-term effects of farming practices on populations of common voles

The impacts of rodents in both developing and developed countries are legendary. Myths and dogma about rodents and their population outbreaks abound. They are imbedded in the culture and language of many societies. In many instances, it is the acceptance of these outbreaks by society that is our greatest challenge. The reason these episodic outbreaks become etched in the socio-cultural psyche from the sparsely populated uplands of Laos to the considerably more affluent agricultural lands of Europe is that the impacts are often staggering - economically, socially, and even politically. The book is a collation of contributions from Asia, Africa, Oceania (Australia and New Zealand), Europe, and North America. The advent of ecologically based rodent management has stimulated the progress summarized in this book. The contributions provide a modern appraisal to an age-old problem through a better understanding of the mechanisms that lead to rodent outbreaks, why rodent population numbers increase under different circumstances, and the impact of outbreaks in a range of different agroecosystems and native forests in different parts of the world. This is an encouraging progress report driven by scientists passionate about rodents, about people, about conservation, and about improving our knowledge of these species and the ecosystems they inhabit. And, in a novel twist, there is an appendix of recipes for preparing rat meat. You will be more than tempted to try one of these dishes the next time you travel in Asia or Africa.

Rodent Outbreaks: Ecology and Impacts

Common voles (Microtus arvalis) are common small mammals in some European landscapes. They can be a major rodent pest in European agriculture and they are also a representative generic focal small herbivorous mammal species used in risk assessment for plant protection products. In this paper, common vole population dynamics, habitat and food preferences, pest potential and use of the common vole as a model small wild mammal species in the risk assessment process are reviewed. Common voles are a component of agroecosystems in many parts of Europe, inhabiting agricultural areas (secondary habitats) when the carrying capacity of primary grassland habitats is exceeded. Colonisation of secondary habitats occurs during multiannual outbreaks, when population sizes can exceed 1000 individuals ha(-1) . In such cases, in-crop common vole population control management has been practised to avoid significant crop damage. The species' status as a crop pest, high fecundity, resilience to disturbance and intermittent colonisation of crop habitats are important characteristics that should be reflected in risk assessment. Based on the information provided in the scientific literature, it seems justified to modify elements of the current risk assessment scheme for plant protection products, including the use of realistic food intake rates, reduced assessment factors or the use of alternativee focal rodent species in particular European regions. Some of these adjustments are already being applied in some EU member states. Therefore, it seems reasonable consistently to apply such pragmatic and realistic approaches in risk assessments for plant protection products across the EU.

Common vole (Microtus arvalis) ecology and management: implications for risk assessment of plant protection products.

Small mammals in agricultural landscapes: Opposing responses to farming practices and landscape complexity

This study aimed to reveal changes in spatial behaviour of common voles (Microtus arvalis) after alteration of their habitat by farming practices. Radio-collared common voles were tracked before and after mulching, mowing, harvesting wheat, and ploughing in the flood plain of the river Unstrut in central Germany. Voles undisturbed by agricultural practices were tracked on a mulchland, an abandoned pasture, and a cattle pasture. There was a large decrease in home-range size after harvesting wheat (96%, P<0.001). Changes after mowing (–74%, P=0.06) were almost significant whereas changes after mulching were not (+14%, P=0.60). On the cattle pasture we found a decrease in home-range size (42%, P=0.03) possibly due to increased spatial activity of cattle in autumn. There was a positive correlation of home-range size and vegetation height for plots with and without farming activity but no correlation with vegetation cover, population density, and breeding. Radio-collared common voles did not show evasive movements and farming practices did not cause a shift of centres of activity. Common voles clearly reacted to sudden changes in vegetation height, which may indicate an immediate response to predation risk.

Nadine Hempel

Papers

Effects of farming practices on spatial behaviour of common voles