Aegean region

Islands: Twenty-four different islands representing various sizes, distances from the mainland (continental Greece or Turkey) and geological settings will be studied.

The Aegean archipelago - one of nature’s most active laboratories - is the only area of the world with floral and faunal elements originating from three different geographical regions (Europe, Asia, and Africa). The amazing number of islands (approximately 9,000), the complex geological history, and the high percentages of endemism renders the Aegean as one of the most interesting archipelagoes from a biogeographic and a biodiversity point of view. Islands that have recently become disconnected from each other and from the mainland due to sea level rising — continental shelf islands (sensu Whittaker 1998) — potentially provide the best natural laboratories in which to study the effects of geographical isolation on allopatric speciation via selection and/or genetic drift (Bittkau and Comes, 2005). Such island systems have many of the advantages of oceanic islands, in that they allow insights to be gained into colonization and dispersal among populations within a molecular framework (e.g., Ranker et al., 2000). Furtehrmore, continental island biotas also provide a premier setting for studying the effects of past range fragmentation via geologically dated sea barriers, and thus for testing genetic drift-models of allopatric speciation and non-adaptive radiation (Comes et al., 2008). 

The Aegean Archipelago (Fig. 1) is located between the Greek peninsula in the west and the Turkish coast of Asia Minor in the east. Geographically, it can be roughly arranged into four groups of islands: (i) north Aegean islands; (ii) the east Aegean islands lying off the Turkish coast; (iii) the Cyclades; and (iv) the southern Aegean islands (the ‘Hellenic Arc’ that marks the southern boundary of the archipelago). Located at the margin of the Eurasian and African plates, this area has experienced tremendous geological alterations since the late Tertiary. Connections created opportunities for dispersal, while submergence of land bridges geographically fragmented populations. The entire Aegean region that offers particular promise for phylogeographical studies is characterized by high levels of diversity and endemism and a complex palaeogeographical history, where Plio-/Pleistocene changes in sea level seems be responsible for much of the faunal and floral divergence of insular populations and taxa.

Figure 1: The Aegean region from the Miocene era to present. The maps were drawn based on present geography. The actual positions of landmasses have been constantly changing from the upper Serravalian, due to the fan-like, southwards, expansion of the southern Aegean region.

The Aegean region was part of a united landmass (known as Agäis) during the Upper and Middle Miocene (23-12 Mya). The late Seravallian to early Tortonian (12-8 Mya) tectonic movements probably initiated the modern history of the Aegean region and surrounding areas. These movements caused the break-up of a southern Aegean landmass. At the end of the middle Miocene (12 Mya), the forming of the Mid-Aegean trench (east of Crete and west of Kasos-Karpathos) began and was fully completed during the early late Miocene (10-9 Mya), causing the separation of west Aegean from east Aegean islands. At the end of Miocene, the Messinian salinity crisis (5.96- 5.33 Mya), caused the dried-up of Mediterranean, enabling overland migration between islands as well as from the mainland. Approximately 5.33 Mya, the Strait of Gibraltar reopened and the basin was refilled from the Atlantic Ocean in about 1000 years. At that time, Crete became permanently isolated, from Anatolia to the east and Peloponissos to the west, as well as from the islands of the Southern Aegean arc. Kithira was submerged during the early Pliocene, and did not reemerge until the late Pliocene. Although Karpathos was isolated during the Miocene, it was connected through Rhodes to the Anatolian mainland in the early Pliocene. Karpathos’ connection to Rhodes was broken at some time during the middle or late Pliocene, and it has remained isolated since. In the Pleistocene, all of today’s islands were in the same position as present. Crete, Karpathos and Rhodes remained completely isolated. Despite the lowering of the sea level of about 200 m of today's level during the glacial maxima, the sea between Crete and Cyclades/Peloponissos was not drained during Pleistocene owe to their great depth.