Environmental factors influencing the distribution of Arvicola scherman (Shaw, 1801) at the southwestern edge of its distribution

Abstract

During 2008, damage to pastures in the eastern mountains of the province of Lugo (NW Spain) was detected, probably due to an increase in populations of Arvicola scherman (Shaw, 1801). Due to the scanty information available on this species in the area we conducted a study with the following main aims: i) to predict the current geographic distribution of the species, ii) identify the environmental variables that may determine their geographic distribution, iii) verify interannual variations in abundance and iv) develop a risk map of populations outbreaks. A total of 280 grassland fields were sampled in which species abundance was evaluated by using presence signs (earth tumuli or mounds), and subsequently an abundance index was estimated. The MAXENT programme developed a potential distribution map using the variables: potential evapotranspiration, water balance, altitude and average annual values of temperature and precipitation. The species was found only in the eastern mountains at altitudes of more than 700 m. Altitude and water balance were the variables that best predicted the presence of the species. Furthermore, a significant difference in the relative abundance between 2008 and 2010 was found, suggesting that the species may experience strong demographic fluctuations in the study area. Probably, the increase in grasslands over the last 40 years may have favoured the expansion and abundance of the species in the study area.