I live on the fringes of the Malay Archipelago. At least that’s what the naturalist Alfred Russel Wallace called it. In his famous book of that name, he wrote:
The Malay Archipelago extends for more than 4,000 miles in length from east to west, and is about 1,300 in breadth from north to south. It would stretch over an expanse equal to that of all Europe from the extreme west far into Central Asia, or would cover the widest parts of South America, and extend far beyond the land into the Pacific and Atlantic oceans. It includes three islands larger than Great Britain; and in one of them, Borneo, the whole of the British Isles might be set down, and would be surrounded by a sea of forests. New Guinea, though less compact in shape, is probably larger than Borneo. Sumatra is about equal in extent to Great Britain; Java, Luzon and Celebes are each about the size of Ireland. Eighteen more islands are, on the average, as large as Jamaica; more than a hundred are larger than the Isle of Wight; while the isles and islets of smaller size are innumerable.
Wallace claimed to have fond a line running through the Malay Archipelago that separates islands with Asian flora and fauna from those with plants and animals more like those of Austalia. This is now called the ‘Wallace Line’. It runs between Bali (on the western, Asiatic side) and the lesser-known nearby island of Lombok (on the eastern side).
Why does the Wallace Line run right between these two nearby islands? Wallace had a theory: it’s because the ocean between them is very deep! Even when sea levels were much lower—for example during the last ice age—and many islands were connected by land bridges, Bali and Lombok remained separate. Indeed, all the islands on one side of the Wallace Line have been separate from those on the other side for a very, very long time.
How long? Maybe forever, since Australia used to be down near Antarctica. I don’t really know. Do you? I’ve brought Wallace’s book to read with me, but that’s probably not the best way to find out. It should be easy to look up.
However, everything gets more complicated when you examine it carefully. Now the Wallace Line is just one of several important lines dividing biogeographical regions in the Malay Archipelago:
Sundaland is the land shelf containing the Malay Peninsula, Borneo, Java, and Sumatra. Sahul, also known as Australasia or simply Australia, is the land shelf containing Australia and New Guinea. Wallacea is a group of islands between Sundaland and Sahul—islands that haven’t been haven’t been recently connected to either of these land shelves.
The Wallace line is the western boundary of Wallacea, separating it from Sundaland. The Lydekker line, named after Richard Lydekker, is the eastern boundary of Wallacea separating it, from Sahul.
Wallacea is the red, heart-shaped region here:
The blue line through Wallacea is called the ‘Weber line’. Max Carl Wilhelm Weber argued that this line, not the boundary between Bali and Lombok, mark the major boundary between Asiatic and Australian organisms.
I bet the real truth is even more complicated.
Anyway, today my wife and I are going to Lombok. We’ll say there until the 21st, based in Senggigi; then we’ll go to Bali and stay in the town of Ubud until the 25th. So, we’ll have a good chance to see the difference between Asiatic and Wallacean flora and fauna.