Madagascar, located in the Indian Ocean off the east coast of Africa, is the fourth largest island in the world. Its long isolation from neighboring continents allowed the evolution of a distinct communities of plants and animals. It is home to five percent of the world's plant and animal species, 80 percent of which are endemic to Madagascar. some biogeographers refer to the island as the "sixth continent", in recognition of its uniqueness and diversity.
Madagascar and neighboring Indian Ocean islands form a distinctive sub-region of the Afrotropic ecozone, which botanist Armen Takhtajan called the Madagascan Region. The region is characterized by numerous endemic taxa of plants and animals, like the lemurs. Madagascar and the Seychelles are fragments of the ancient supercontinent of Gondwana. As Gondwana began to break up 160 MYA (million years ago), Madagascar broke away first from Africa, and 89 million years ago broke away from India. Many of Madagascar's plant and animal species are of ancient Gondwanian origin. Madagascar remained close to Africa and for a time to India, and some plants and animals were able to cross the straits separating Madagascar from the neighboring continents. The other Indian Ocean islands, like the Comoros and Mascarene Islands, are volcanic islands that formed more recently, and were populated by plants and animals from Madagascar, Africa, and the Seychelles.
Henri Perrier de la Bâthie (1921) proposed division of Madagascar into two distinct floristic provinces. The Flore au vent (windward flora), later called the Région de l'Est (Eastern Region), includes those areas receiving the direct influence of the moist southeast trade winds, which include the eastern coastal region and the central highlands, which run north-south along the spine of the island. The Eastern region also included humid pockets further westward, including Sambirano and Isalo . The Flore sous le vent (leeward flora), now called the Région de l'Ouest (Western Region), lies in the rain shadow of the central highlands. It includes the drier western and southern portions of the Island, as well as the island's northern tip.
The Eastern and Western regions can be further subdivided into seven terrestrial ecoregions. The Eastern region includes two tropical moist broadleaf forest ecoregions, the Madagascar lowland forests along the eastern coastal strip, and the Madagascar subhumid forests which occupies the highlands above 600-800 meters elevation. At the highest elevations, above 2000 meters, the subhumid forests transition to the Madagascar ericoid thickets, a montane grasslands and shrublands ecoregion.
The Madagascar dry deciduous forests , a tropical dry broadleaf forest ecoregion includes western Madagascar and northern tip of the island. Two xeric shrublands regions cover the southwest and south of the island; the dry forests transition to the Madagascar succulent woodlands in the southwest, and the drier Madagascar spiny thickets occupies the southernmost region of the island.
Eight flowering plant families are endemic to Madagascar: Asteropeiaceae , Didymelaceae , Didiereaceae , Kaliphoraceae , Melanophyllaceae , Physenaceae , Sarcolaenaceae, and Sphaerosepalaceae . The Seychelles have one endemic plant family, Mesdusagynaceae , and family Psiloxylaceae is endemic to the Macarene Islands.
Before the arrival of humans, Madagascar was home to six lineages of mammals: lemurs, endemic carnivores, a pygmy hippopotamus, tenrecs, rodents, and bats. The lemurs are thought to be descended from a common ancestor, which crossed to Madagascar over 62 million years ago. Bones of extinct giant lemurs, as large as a gorilla, have been found on the island. Recent DNA evidence suggests that Madagascar's eight endemic carnivores, including the Malagasy "mongooses" (Galidia , Galidictis , Mungotictus , and Salanoia ), fossa (Cryptoprocta ferox), Falanouc (Eupleres goudotii), and Malagasy Civet (Fossa fossana), are descended from a single ancestor which crossed from Africa to Madagascar 18-24 million years ago.
17 species of lemurs, including the giant lemur, together with giant tortoises, the pygmy hippopotamus, and the elephant bird, an enormous flightless bird related to the ostrich, became extinct after the arrival of the human settlers approximately 2000 years ago.
The other islands of the Madagascan region also suffered from waves of extinctions as a result of human arrival on the islands. Numerous bird species, including the famous Dodo of Mauritius, became extinct after human settlers arrived. Most of the islands also had one or more species of giant tortoise before humans arrived; 19 of 20 giant tortoise species are presently extinct, and only the Aldabra Giant Tortoise still survives.
Ecoregions of Madagascar and the Indian Ocean islands
Madagascar lowland forests (Madagascar)
Madagascar subhumid forests (Madagascar)
Madagascar dry deciduous forests (Madagascar)
Madagascar ericoid thickets (Madagascar)
Madagascar spiny thickets (Madagascar)
Madagascar succulent woodlands (Madagascar)
Madagascar mangroves (Madagascar)
Aldabra Island xeric scrub (Seychelles)
Comoros forests (Comoros)
Granitic Seychelles forests (Seychelles)
Mascarene forests (Mauritius, Réunion)
Reference
Yoder, A. D.; Burns, M. M.; Zehr, S.; Delefosse, T.; Veron, G.; Goodman, S. M.; Flynn, J. J. 2003. Single origin of Malagasy Carnivora from an African ancestor. Nature, no. 6924, pp. 734-736.
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Last updated: 10-29-2005 02:13:46
