Anthropogenic disturbance and environmental factors drive the diversity and distribution of earthworms in São Miguel Island (Azores, Portugal)

Abstract

We present an evaluation of earthworm fauna in São Miguel Island (Azores, Portugal) revealing that it is rich in species in relation to its size and nature. Four families (Acanthodrilidae, Lumbricidae, Megascolecidae and Rhinodrilidae), 15 genera and 27 species were inventoried. About 74% were Palearctic species and 26% were Intertropical, mainly invasive earthworms originating from South-East Asia, of which Amynthas corticis Kingberg, 1867 was most dominant. The first comprehensive checklist of São Miguel earthworms is detailed, and the outdated nomenclature is improved, unifying synonymous taxa such as Lumbricus azoricus Eisen, 1869 and Allolobophoridella eiseni Levinsen, 1884. Seven new earthworm species records are given, highlighting Lumbricus friendi Cognetti, 1904 and Amynthas diffringens Baird, 1869 as cited for the first time in Macaronesia, and therefore expanding their known geographic range to the northern border of this region. Moreover, richness and composition of species were evaluated in relation to environmental and anthropogenic characteristics, including soil properties, altitude, land use intensity or distance to urban nuclei. Our results demonstrated that soil pH affected the establishment of species and that organic matter is positively associated with abundance of some non-native lumbricids (e.g. the anecic Octodrilus complanatus Dugés, 1828) and negatively related to richness and abundance of exotic species such as Amynthas corticis, Amynthas gracilis Kingberg, 1867 and Pontoscolex corethrurus Müller, 1857. Results suggested that land use intensity, represented as five categories ranging from undisturbed sites with native vegetation to sites under intensive agriculture exploitation, is a good predictor of species composition. Higher values of diversity and density of Intertropical species were found in more intensively exploited locations. Moreover, the Palearctic lumbricids, although present in all the disturbance categories tested, were the most diverse group at higher altitudes. The species Dendrodrilus rubidus tenuis Eisen, 1864 and Lumbricus rubellus Hoffmeister, 1843, with narrow distribution range, showed a trend towards natural, non-intensive (NI) and low intensity (LI) systems. Our results indicate that anthropogenic disturbance and altitude are the main drivers of earthworm diversity on the island of São Miguel, making these animals good indicators for land use intensity. Therefore, earthworm surveys may help design conservation programs in protected areas.