Island Fauna

the fauna of isolated areas of dry land (islands). Island fauna differs essentially from continental fauna in composition and development. The fauna of a particular island is determined first of all by the island’s origin. (Oceanic islands are of volcanic origin and were never attached to the mainland; continental islands were formerly part of the mainland.) Also important is the island’s degree of isolation and its distance from the mainland.

The percentage of endemic animals is high on islands; the older the island, the more endemic forms it has. Large mammals, such as the tamarau and the pony, usually do not reach their fullest possible development on islands. Island birds and reptiles (rails, monitors, turtles) often exhibit insular gigantism. Some birds of oceanic islands, for example, the kiwi, flightless rails, and the Hawaiian cormorant, have lost the ability to fly, and their wings have been reduced. This adaptation is due to the absence of snakes and mammals. Islands have very few or no flying insects, because strong winds transport the insects out to sea.

The characteristics of island fauna are more sharply expressed on oceanic islands that are far from the mainland (for example, Easter Island, the Galápagos Islands, Hawaii, and St. Helena). The fauna on such islands is especially meager, because it consists only of animals that originally came from the mainland or from the closest islands by air or water. An absence of mammals, amphibians, and snakes characterizes oceanic islands and old continental islands. Very intensive species formation occurs on these islands according to the principle of adaptive radiation of certain endemic groups (Hawaiian honeycreepers, ground finches of the Galápagos Islands, tenrecs and lemurs of Madagascar). The characteristics of island fauna are less strongly expressed on continental islands, including the West Indies, Japan, the Malay Archipelago, the British Isles, and Sakhalin. When these islands separated from the mainland, their fauna was already the same as that of neighboring parts of the mainland; it subsequently became more sparse owing to extinction of some species. Species formation is less intensive on these islands than on oceanic islands.

Man effects rapid changes in island fauna: the fauna loses its initial form, particularly on oceanic islands. The fauna of certain isolated mainland areas or areas with unique natural conditions, such as the Crimean Mountains and Kamchatka, has features of island fauna.