Biodiversity and distribution of earthworms in the biogeographic province of the Levant

Abstract

We are reporting an increase from 30 to 52 identified earthworm taxonomic species, including one subspecies, in the Levant bioregion during the last 20 years. The number of earthworm taxonomic species is still underestimated. We classified the earthworms of the Levantine into three categories: endemic species, autochthonous species and introduced peregrine species. The endemic species might have originated before the Messinian stage (7.5–3.5 mya) of the Miocene. We suggest that certain endemic species underwent speciation (and subsequently disappeared) during interglacial (pluvial) periods. These changes occurred when the Levantine corridor transformed into a “culdesac” pathway due to the southern opening closing off, caused by the retreating steppe zone and its replacement with a gradually expanding open park forest. As for the autochthonous species, they arrived in the Levant coming from different biogeographic regions by means of biological dispersal and did not have enough time to speciate. The fact that autochthonous species of the Afrotropical realm and of southeastern Asia origin are missing indicates that such species either were not able to cross the Sahara Desert, the Himalayan and the Tien-Shan orogens or that they were extinct before the end of the Miocene. The establishment of the introduced peregrine species group in the Levant has been facilitated by the availability of human-constructed niches during the current interglacial.