Diversity patterns and biogeography of Diaptomidae (Copepoda, Calanoida) in the Western Palearctic

Diaptomid copepods are an important component of biodiversity in inland aquatic ecosystems worldwide but to date little is known about the historical and ecological factors that determined their current distribution. In the present paper, a critical review of the available literature on diaptomid species distribution in the Western Palearctic was performed, and a biogeographical analysis was carried out on the roles that spatial, current environmental, and historical (paleoclimatic) factors played on their actual distribution in this large area. The results show a clear pattern of colonization which is only partially overlapping what has been recently proposed for other terrestrial and aquatic taxa. Disentangling beta diversity into its turnover and nestedness components, we hypothesized a complex post-glacial pattern of recolonization of the higher latitudes, encompassing the importance of extra-Mediterranean refugia in the West (due to mountain chains which represent effective barriers for recolonization coming from the Italian and Iberian peninsulas) and a more typical pattern of post-glacial recolonization from southern refugia in the East, where mountain chains are north–south oriented and therefore less effective as barriers.