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La Wallacea est une zone biogéographique qui comprend l'ensemble des îles situées, au delà de Java et de Bornéo, entre l'Asie du Sud-Est et l'Océanie proche. Elle correspond aux zones qui n'ont pas pu être complètement occupées par des mammifères placentaires, en raison de leur isolement géographique et de la profondeur de l'eau qui les entoure (alors que Sumatra, Java et Bornéo ont été rattachées au continent pendant de longues périodes, notamment quand le niveau de la mer était plus bas). Zone de transition, elle doit son nom au paléontologue britannique Alfred Wallace, co-découvreur au XIXe siècle avec Charles Darwin de la théorie de l'évolution.
Elle comprend les îles de Nusa Tenggara, qui incluent Lombok, Komodo, Florès et Sumba; Timor; Sulawesi (les Célèbes); les îles Moluques du nord North Maluku, comprenant Halmahera; et l'essentiel de la province des Maluku (Moluques), hormis les îles Aru Islands, qui se situent sur la plaque australienne. Elle couvre une superficie de 347 000 km².
à traduire de l'anglais : The boundary between Sundaland and Wallacea follows the Wallace Line, named after the naturalist Alfred Russel Wallace who noted the differences in mammal and bird fauna between the islands either side of the line. The Islands of Sundaland to the west of the line, including Java, Bali, Borneo, share a similar mammal fauna with East Asia, including tigers, rhinoceros, and apes. During the ice ages, sea levels were lower, exposing the continental shelf that links these islands to one another and to Asia, and allowed Asian land animals to inhabit these islands. Similarly, Australia and New Guinea are linked by a shallow continental shelf, and were linked by a land bridge during the ice ages, and Australia and New Guinea share many marsupial mammals and land birds. Wallacea contains few land mammals, who find it difficult to cross open ocean. Many bird, reptile, and insect species were better able to make the crossing, and many species of Australian and Asian origin are found there. Wallacea's plants are predominantly of Asian origin, and botanists include Sundaland, Wallacea, and New Guinea as the Floristic province of Malesia.
Although the distant ancestors of Wallacea's plants and animals may have been from Asia or Australia-New Guinea, Wallacea is presently home to many endemic species. Because many of the islands are separated from one another by deep water, there is tremendous species diversity between islands as well. Conservation International has designated Wallacea as a biodiversity hotspot.
Wallacea was originally almost completely forested, mostly tropical moist broadleaf forests, with some areas of tropical dry broadleaf forest. The higher mountains are home to montane, and subalpine forests, and Mangroves are common in coastal areas.
According to Conservation International, Wallacea is home to over 10,000 plant species, of which approximately 1500 (15%) are endemic. Endemism is higher among terrestrial vertebrate species; of 1142 species found there, almost half (529) are endemic. Most of Wallacea was originally forested; 45% retains some sort of forest cover, and only 52,017 km², or 15 percent, is in a more or less pristine state. Of Wallacea's total area of 147,000 km², only 20,415 km² are protected. Wallacea is home to 82 threatened and six critically endangered species of terrestrial vertebrates.
Tropical and subtropical moist broadleaf forests
Tropical and subtropical dry broadleaf forests
Conservation International: Wallacea
