New earthworm records for Macaronesia with observations on the species, ecological characteristics and colonization history

Field surveys have provided new earthworm records for Madeira and Porto Santo, subtropical islands part of central-eastern, oceanic Macaronesia, belonging to three families: Acanthodrilidae, Lumbricidae and Megascolecidae; although we found no evidence of endemic or native species. The first records from Macaronesia of Dendrobaena pseudohortensis, Dendrodrilus rubidus tenuis and Octolasion cyaneum are included, increasing their known distribution. Eight peregrine species are cited for Porto Santo (no previous records) and eight for Madeira, mostly of Palaearctic origin; their introduction is presumed not to have occurred before humans arrived on the islands. The number of introduction events emerges as the most consistent predictor of the establishment of invasive species. The new data presented contribute to a better understanding of the earthworm colonization and the primary factors that determine the present distribution patterns of species are discussed. Human activity appears to be a strong influence on the distribution of the newly recorded species throughout the study area. We also make some ecological observations: soil pH and organic matter as variables influence the spatial ordination of some earthworm species. Affinities are evident with the Canary Island fauna and to a lesser extent with that of continental areas west of the Strait of Gibraltar and within the Mediterranean basin. The diversity of earthworm communities is linked with the arrival of European colonists and agro-commercial activities, which began almost six centuries ago. It is anticipated that the number of earthworm species will continue to increase, since introductions from other parts of the world are highly probable.