Azerbaijan lies in the south-east Caucasus. In the east it is washed by the Caspian Sea, while it has long borders with the Russian Federation in the north and with the Islamic Republic of Iran in the south. In the west, Azerbaijan borders Georgia, Armenia, and Turkey. The territory of Azerbaijan divides naturally into five areas: the Greater Caucasus, Lesser Caucasus, Central Plain, Talish Mountains, and Nakhchivan. Azerbaijan is part of the Caucasus Ecoregion, an isthmus between the Black and Caspian seas, which serves as a bridge linking Europe and Asia. The country has rich biodiversity which historically was formed under the influence of the Turanian, Mediterranean, Near East, and European formation centers.