Wallacea

Wallacea

Geography

Wallacea is defined as the series of islands stretching between the two continental shelves of Sunda and Sahul, but excluding the Philippines. Its eastern border (separating Wallacea from Sahul) is represented by a zoogeographical boundary known as Lydekker's Line, while the Wallace Line (separating Wallacea from Sunda) defines its western border.^[2][3]

The Weber Line is the midpoint, at which Asian and Australian fauna and flora are approximately equally represented. It follows the deepest straits traversing the Indonesian Archipelago.

The Wallace Line is named after the Welsh naturalist Alfred Russel Wallace, who recorded the differences between mammal and bird fauna between the islands on either side of the line. The islands of Sundaland to the west of the line, including Sumatra, Java, Bali, and Borneo, share a mammal fauna similar to that of East Asia, which includes tigers, rhinoceros, and apes; whereas the mammal fauna of Lombok and areas extending eastwards are mostly populated by marsupials and birds similar to those in Australasia. Sulawesi shows signs of both.^[4]

During the ice ages, sea levels were lower, exposing the Sunda shelf that links the islands of Sundaland to one another and to Asia^[5] and allowing Asian land animals to inhabit these islands.

The islands of Wallacea have few land mammals, land birds, or freshwater fish of continental origin, which find it difficult to cross open ocean. Many species of birds, reptiles, and insects were better able to cross the straits, and many such 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.^{[citation needed]}

Similarly, Australia and New Guinea to the east are linked by a shallow continental shelf, and were linked by a land bridge during the ice ages, forming a single continent that scientists variously call Australia-New Guinea, Meganesia, Papualand, or Sahul. Consequently, Australia, New Guinea, and the Aru Islands share many marsupial mammals, land birds, and freshwater fish that are not found in Wallacea.^[3]

Biota and conservation issues

Although the distant ancestors of Wallacea's flora and fauna may have been from Asia or Australia-New Guinea, Wallacea is home to many endemic species. There is extensive autochthonous speciation and proportionately large numbers of endemics; the area is an important contributor to the overall mega-biodiversity of the Indonesian Archipelago.^[6]

Fauna includes the lowland and mountain anoa, or dwarf buffalo (Bubalus sp.), and the babirusa, or "deer-pig" (Babyrousa sp.), both found on Sulawesi, among other islands. Maluku shares a number of similar species with Sulawesi, albeit with fewer total, given the differences in size between the two islands—Sulawesi has at least 4,000 recorded terrestrial plant and animal species,^[7] while Maluku has just over 1,000, by comparison. Sulawesi is home to over 2,000 invertebrate species (with over 1,000 known species of arthropod, not including nearly 900 lepidopterans), 100 species of reptiles and amphibians, and 288 bird species. Maluku has around 70 reptile and amphibian, 250 avian, and over 550 invertebrate species. Seram Island is particularly noted for its butterflies and birds, including the Moluccan king parrot. Smaller mammals, including some carnivorans (such as civets), marsupials (such as the cuscus), primates and rodents are common throughout the region.

A large portion of the waters surrounding Wallacea are part of the Coral Triangle, considered to be the richest coral reef and marine ecosystems on earth, with the highest number of species, adding to the total biodiversity of the region.

Wallacea was originally almost completely forested, mostly

Endemism is higher among terrestrial vertebrate species; out of 1,142 species described there, almost half (529) were endemic. 45% of the region retains some sort of forest cover, though only 52,017 km² (15%) is in a pristine state. Of Wallacea's total 347,000 km²-area, about 20,000 km² are protected.[1]

Wallacea is home to 82 threatened and six critically endangered species of terrestrial vertebrates.^{[citation needed]}

Ecoregions

Tropical and subtropical moist broadleaf forests:

• Leti Islands, eastern Barat Daya Islands
  )
• Buru rain forests (Buru
  )
• Bacan Island
  )
• Seram, Banda Islands, Ambon Island, Saparua, Gorong archipelago
  )
• Talaud Islands
  )
• Sulawesi montane rain forests (Sulawesi)

Tropical and subtropical dry broadleaf forests:

• Komodo, Flores, Alor
  )
• Sumba deciduous forests
  (Sumba)
• Timor and Wetar deciduous forests (Timor, Wetar)

Distribution between Asia and Australia

Australia may be isolated by sea, but technically through Wallacea, it can be zoologically extended. Australian Early-Middle Pliocene rodent fossils have been found in Chinchilla Sands and Bluffs Down in Queensland, but a mix of ancestral and derived traits suggest murid rodents made it to Australia earlier, maybe in the Miocene, over a forested archipelago, i.e. Wallacea, and evolved in Australia in isolation.^[8]

A few species of Eucalyptus, a predominant genus of trees in Australia, are found in Wallacea: Eucalyptus deglupta on Sulawesi, and E. urophylla and E. alba in East Nusa Tenggara.^[11] For land snails Wallacea and Wallace's Line do not form a barrier for dispersal.^[12]

References

External links

Wikimedia Commons has media related to Wallacea.

• Conservation International: Wallacea
• "Too Many Lines; The Limits of the Oriental and Australian Zoogeographic Regions", George Gaylord Simpson, Proceedings of the American Philosophical Society, Vol. 121, No. 2 (Apr. 29, 1977), pp. 107–120
• Wallacea Research Group