Landscape composition and vole outbreaks: evidence from an eight year study of Arvicola terrestris

This study investigates the relationships between landscape composition and the population dynamics of the fossorial water vole Arvicola terrestris. Land use patterns were studied based on agricultural and forestry data from the French Ministry of Agriculture collected in 1955 and 1988. In the Massif Central, France, water vole populations were monitored from 1985 to 1993 by using index methods. Outbreaks of water vole populations occurred in many dispersed epicentres and spread suddenly and widely over > 7500 km 2 . At a regional scale, the fluctuation lasts six years on average with an outbreak period lasting from two to three years. Density variation patterns are positively correlated with the proportion of permanent grassland to agricultural land. A high risk of outbreak is linked to a high proportion of permanent grassland (over 90%), whereas a low risk of outbreak is linked to a proportion of < 80%, Conversely, density variation patterns are negatively correlated with the proportion of temporary grassland to agricultural land and with the proportion of forest to total land in the western (major) part of the study area. Temporary grassland thus appears to be a marginal habitat for water voles and extensive forests could act as a brake on outbreaks. The increase in the area of permanent grassland from 1955 to 1988 was apparently the major cause of chronic high densities of water voles. Therefore, land use and landscape management could be one way to control water vole outbreaks.