Network biogeographical analysis of the central Aegean archipelago

Abstract

Aim Although the factors shaping plant species richness patterns across the islands of the central Aegean are well known, the processes driving the assembly of these island communities remain unclear. To shed light on these processes, we identified biogeographical modules within the phytogeographical area of the Cyclades and tested for nestedness across the islands. Location The Cyclades, Greece. Methods We used a network approach to detect island biogeographical roles and modules, based on a large and detailed database of the Greek endemic plant taxa of the Cyclades, and we tested for nestedness in the island–species matrices. Results The Cyclades were significantly modular and divided into five biogeographical modules. Three of the modules were significantly nested and two displayed all four possible biogeographical roles (connectors, module hubs, network hubs, peripherals). Most of the network's taxa are classified as peripherals and widespread endemics. Main conclusions The borders of the five modules correspond remarkably well to the palaeogeographical and climatic compartmentalization of the Cyclades. The flora of the Cyclades has not yet reached the relaxation phase and the region may act as an ecogeographical filter for the distribution of several plant lineages. Naxos, Milos and Anafi play an important role for the network's connectivity, while at least five adjacent phytogeographical regions affect the distribution patterns of the endemic taxa present in the Cyclades.

Do diversity patterns of the spring-inhabiting snail Bythinella (Gastropoda, Bythinellidae) on the Aegean Islands reflect geological history?

“…The estimated divergence of this clade from the rest of the Aegean lineages occurred 4.85 Mya, which suggested that the Naxos population might possess more relict characters than the Bythinella populations on the geographically close Attica, and Andros and Evvoia. No close relationships were found among the Bythinella from Naxos, Andros and Tinos, as was found for Pseudamnicola (Szarowska et al, 2015), despite the relatively recent connection of all these islands (Kougioumoutzis et al, 2014). Moreover, our Bythinella on Naxos was distinct from all other clades and perhaps reflected the same factors that caused Naxos to be one of the centres of diversity for plants (Kougioumoutzis et al, 2014).…”

“…No close relationships were found among the Bythinella from Naxos, Andros and Tinos, as was found for Pseudamnicola (Szarowska et al, 2015), despite the relatively recent connection of all these islands (Kougioumoutzis et al, 2014). Moreover, our Bythinella on Naxos was distinct from all other clades and perhaps reflected the same factors that caused Naxos to be one of the centres of diversity for plants (Kougioumoutzis et al, 2014). In general, the pattern of interpopulation diversity in Bythinella apparently reflected geological history, particularly the earlier events, much more than that in Pseudamnicola.…”

“…Almost all the hot spots that were identified by Benke et al (2011) were previously described as glacial refugia of Bythinella (Benke et al, 2009;Falniowski et al, 2009b), which strongly suggested that hot spots might reflect glacial refugia. We have no direct evidence that central Greece was another glacial refugium for Bythinella, but this scenario was highly likely because in this region there were the refugia for many plants (Kougioumoutzis et al, 2014), vertebrates (e.g., Weiss & Ferrand, 2007) and invertebrates (Sfenthourakis & Legakis, 2001). …”

“…Based on the geological and climatic events, some key dates can be highlighted as follows: the initiation of the split of the Mid-Aegean Trench (approximately 12 Mya), the end of the split (approximately 9 Mya) and the Messinian Crisis (approximately 5 Mya). Notably, the present geography of the Aegean is no more than 8-6 Kya old (Kougioumoutzis et al, 2014, and references therein).…”

“…In the Late Pleistocene, the eastern Aegean Islands were connected with Anatolia, and the strait between Europe and the Cyclade-mega-island (Cycladic plateau), which connected among others the present Naxos, Paros, Tinos and Andros islands, was rather narrow (Creutzburg, 1963;Douris et al, 2007;Kougioumoutzis et al, 2014).…”