Size variation in the Northern white-breasted hedgehog Erinaceus roumanicus: latitudinal cline and the island rule

Abstract

We explored patterns of size variation for mainland and island populations of Erinaceus roumanicus. Size was expressed either as the condylobasal length of the skull or as the first eigenvector obtained from a principal components analysis of a correlation matrix with four cranial variables. Both estimators were highly correlated. The pattern of size variation across Europe was a smooth cline, with the largest hedgehogs in the south. Furthermore, size correlated positively with temperature and negatively with summer precipitation. Regression model of the mainland hedgehog size against eight climatic variables significantly overestimated size in three out of four insular populations. Insular hedgehogs tended to be smaller on remote islands and larger on islands close to the coast, their putative source of colonization. We suggest that the major driving force determining size of mainland hedgehogs might be seasonality in resource availability. Size adjustment in island hedgehogs, however, was mainly concordant with the island rule which predicts convergence towards a size of approximately 100 g. The insular response was not uniform and large size close to the mainland is possibly a result of frequent introductions.