Biogeographical zonation of the western Iberian Peninsula on the basis of the distribution of earthworm species

We used TWINSPAN and CANOCO to the biogeography of the western Iberian Peninsula on the basis of the distribution of earthworms among ninety areas of Galicia, Portugal, Asturias, Leon, Zamora, Salamanca, Caceres, Badajoz and Huelva. This part of Iberia is clearly divisible into a Eurosiberian Region in the north and west and a Mediterranean Region in the south and east. For earthworm faunas, however, the limit between these regions is considerably further south than is conventionally accepted on the basis of Rivas Martinez' (1987) vegetation-type classification. Species characteristic of the Eurosiberian Region include Dendrobaena madeirensis, D. octaedra, Allolobophora caliginosa and various species of the genus Lumbricus. Within this region the earthworm fauna of Asturias is clearly distinct from that of Galicia and northern Portugal. Species characteristic of the Mediterranean Region include Allolobophora caliginosa, A. chlorotica and A. rosea, but inventories from this region are most easily identified by the absence or scarcity of those species characteristic of the Eurosiberian Region. Many areas show intermediate characteristics between the two major regions, and in some cases one region 'intrudes' into the other.