Biodiversity patterns of terrestrial isopods from two island groups in the Aegean Sea (Greece): Species-area relationship, small island effect, and nestedness

Abstract

Although almost one third of Aegean islands have an area smaller than 1 km2, very few studies have concentrated on this spatial Scale. We investigate biodiversity patterns of terrestrial isopods in 2 island groups (Kalymnos and Astypalaia) of the Aegean Sea, consisting mainly of small islands and characterized by different geological histories, isolation, and species source pools. We focus on the species-area relationship (SPAR), community nestedness and the investigation of the small island effect (SIE) in these island groups. The slopes of the SPARs for terrestrial isopods of the 2 groups are almost identical and place the 2 island groups within the intraprovincial category. The SIE investigated was detected in both island groups, with the Kalymnos group exhibiting a higher upper limit (the island size threshold under which an increase of species number with increase of area in small islands is not observed). Both island groups are highly nested and exhibit similar levels of nestedness. Despite the different geological histories, isolation, and source pools, the 2 island groups exhibit great similarity in all the patterns investigated. The islands studied still "behave" as parts of a continuous land mass, with high numbers of species even on the smallest islands, limited net effects of island size, and significant contribution of the interrelationship between area and environmental heterogeneity to the total species richness.