|
CROSSING THE LINE
BALI, Indonesia
The "Wallace line" separates two major ecological realms and it would be difficult to find two more distinct natural regions. On the western, Balinese side, the Indo-Malayan realm is home to elephants, rhinos, wild cattle, primates of all descriptions (including the famous orangutan), jungle cats like tigers and clouded leopards, pigeons and hornbills. But once you cross the line to Lombok and the Austro-Malayan realm in the east you'll see none of the Indo-Malayan animals. Instead you'll find creatures that are never found in Bali and west - marsupials like the koala and kangaroos (including a rare tree kangaroo on the island of New Guinea), cockatoos, parrots, birds of paradise, bowerbirds, strange creatures like the platypus and numerous varieties of cactus and eucalyptus. While today it seems obvious that these two realms are distinct, in the mid 19th century scientists were still trying to put order into the natural world. Alfred Russel Wallace deduced the existence of a line, or barrier, because of his extensive collecting. Having no income except for the specimens he sent back to his beetle agent Samuel Stevens in London, Wallace trapped and classified 125,660 specimens, including some 900 new species of beetles, 200 new species of ants, 50 new species of butterflies, and 212 new species of birds. In 1859, while still in Indonesia, he tried to make sense of his collections. "To define exactly the limits of the two regions where they are (geographically) most intimately connected," Wallace wrote, "I may mention that during a few days' stay in the island of Bali I found birds of the genera Copsychus, Megalaina, Tiga, Ploceus, and Sturnopastor, all characteristic of the Indian region [now generally called the Indo-Malayan Realm] and abundant in Malacca, Java, and Borneo; while on crossing over to Lombock [now Lombok], during three months collecting there, not one of them was ever seen; neither have they occurred in Celebes [now Sulawesi] nor in any of the more eastern islands I have visited. Taking this in connexion with the fact of Cacatua, Tropidorhynchus, and Megapodius having their western limit in Lombock, we may consider it established that the Strait of Lombock (only 15 miles wide) marks the limits and abruptly separates two of the great Zoological regions of the globe…. the western and eastern islands of the [Indonesian] Archipelago, as here divided, belong to regions more distinct and contrasted than any other of the great zoological divisions of the globe. South America and Africa, separated by the Atlantic, do not differ so widely as Asia and Australia: Asia with its abundance and variety of large Mammals and no Marsupials, and Australia with scarcely anything but Marsupials; … Asia the poorest tropical region in Parrots, Australia the richest: and all these striking characteristics are almost unimpaired at the very limits of their respective districts, so that in a few hours we may experience an amount of zoological difference which only weeks or even months of travel will give us in any other part of the world." Wallace also noted that there are great physical similarities between the two realms (both realms have rich tropical rainforests, for example), and theorized that the explanation for the existence of completely different species must be found in some other natural cause - changing sea levels due to climate change and deep oceanic trenches. As recently as 10,000 years ago Singapore, Java and Bali were not islands, but part of a large, more-or-less contiguous Asian land mass. In fact in those days it would have been possible to walk from Kuantan to Kuching, Bangkok to Brunei, or Singapore to Surabaya. In a similar fashion, on the eastern side of the Wallace line, one could have walked from Lombok to Sumbawa to Moyo, the island where Amanwana is located, all the way to Australia. (The "line" concept isn't foolproof -- Amanwana, and nearby Komodo island, lie in a curious middle ground, called Wallacea, where Asian and Australian biogeographical zones overlap). And in-between, then and now, lies the deep and treacherous Lombok Straits. But the low sea level was just part of a long cycle of shifting coasts. When the great polar ice caps melted, as they have some twenty times over the past two million years, the subsequent raising of the sea flooded most of the land, isolating the large islands of Borneo, Sumatra, and Java, along with thousands of smaller islands. Today the sea level is about as high as it has ever been, and Southeast Asia has only half as much land as it had when the poles were at their iciest. Nevertheless, sea levels remain strikingly shallow. If you take a cruise on your vacation, ask the captain to show you his charts so you can see how shallow the seas still are today. On the Southeast Asian (Balinese) side of the Wallace line, on what is called the Sunda Shelf, if you pick your route carefully you could scuba dive from Singapore to Bali without ever going deeper than about 40 meters. Then you get to the treacherously deep (200-300 meter) Lombok Straits. Then at Lombok on the east the oceanic shelf becomes shallow again and you can put on your scuba gear once more and wind your way to Australia, again rarely going deeper than about 40 meters. Wallace's observations about sea level changes also led to novel thoughts about how species evolve, a problem that had challenged naturalists, philosophers and theologians for centuries. He developed, independently of Charles Darwin, the theory of natural selection. Some people say that well-connected UK-based Darwin stole the idea from poor unheralded Wallace who was isolated in malarial Indonesia, but that's another story.
|