Can environmental factors explain size variation in the common shrew ( Sorex araneus)?

Abstract

Shrews are small mammals with a high metabolic rate and may potentially be greatly influenced by environmental factors. Several studies have indicated both morphological and genetical variation in the common shrew ( Sorex araneus). The aims of this study were to study patterns in size variation and to test which environmental factors influence body size most. Most study sites were located to northern Norway, between 65° and 70°N, one study site in south Norway was also included (60°N). At one site shrews were studied for 10 consecutive years. Three body measurements (body length, tail length and body mass) and two combined estimates (tail proportion and body condition) were compared, where appropriate, among populations (sites), years and months, and along gradients of altitude (habitat), coast–inland and north–south. Effects of summer climate (temperature and precipitation) were also tested. Size variations among populations of common shrews were found in a number of respects; yearly, seasonal, local and regional. Regional variation was most significant, followed by yearly and seasonal variation. The results suggest a strong link between body size and a coast–inland gradient, with smallest shrews (up to 13% smaller) on inland locations. The main differences between coastal and inland sites are lower winter temperatures and less snow cover at inland sites (factors which are also associated with habitat productivity), which could favour smaller shrews with less energetic demands. Most other variation was relatively small (<5%). Most of the results indicate climate and habitat productivity as the most important factors, which may also vary between years at a single site. Bergmanns's rule, Allen's rule or Dehnel's phenomenon were not supported by this study. The insular syndrome was partly supported. Smaller variations in size may only be proximate adaptations to local food supply, but larger variations are likely to be ultimate adaptations.