SPATIAL VARIATIONS IN RARITY IN THE AEGEAN TENEBRIONID BEETLES (Coleoptera, Tenebrionidae)

Abstract

Three measures of species rarity were calculated to investigate possible spatial patterns of variation in tenebrionid community rarity on the Aegean islands. For each species rarity was evaluated as geographic distribution (mean incidence of species on islands in the archipelago), ecological tolerance (total area of the islands occupied) and population density (number of decades of species’ records from 1870 to 2000). In addition, Kattan’s index of vulnerability was computed. These rarity and vulnerability measures were used to construct analogous indexes at community level. Plotting species richness on island coordinates, produced a map where richness decreased in the centre of the archipelago, reaching highest values on peripheral islands. Geographic rarity increased from the centre of the archipelago to periphery. By contrast, ecological tolerance and population density show the following pattern: islands located very close to the Anatolian mainland, as well as those that are clumped, host the most eurytopic and abundant species, while remote southern islands have ecologically specialized faunas with low population density. Vulnerability (i.e. the reverse of Kattan’s index applied to communities) decreased in remote islands, which are usually also the smallest. As a whole the tenebrionid beetles on the Aegean Islands constitute threatened faunal assemblages of great ‘rarity’ under several dimensions, and some islands are especially rich in rare species, deserving special attention in conservation efforts.