Between Indonesia’s vast archipelago lies a border that is physically invisible but whose impact is very real. This boundary is so sharp that it separates two different ecosystems as if separated by an invisible wall. This line, called the “biogeographic boundary” in the scientific world, is known as the Wallace Line. So, what is the feature of this line and how was it discovered?
What is the Wallace Line?
Wallace LineIt is an invisible border that crosses over 25,000 islands in the Malay Archipelago. While large Asian species such as tigers, elephants and rhinos live on the western side, once you cross the line you encounter different species of creatures such as marsupials and komodo dragons on the eastern side. So how did this line come into existence and why does it form such a sharp border?
The answer to this question is in the 19th century Alfred Russel Wallace It is based on the discoveries made by a naturalist named. Wallace first described this line in 1859 and investigated the reasons why species were separated by such a clear border.
Wallace’s Great Discovery: The Emergence of the Invisible Line
Alfred Russel Wallace He was an important scientist who discovered the theory of natural selection together with Darwin. During his eight-year research in the Malay Archipelago, he noticed sudden changes in the distribution of species during his travels between islands. During this discovery, while he was bedridden due to malaria, the idea of a line separating living species from their roots appeared in his mind.
Wallace argues that this border is neither a physical nor a visible barrier; However, he noticed that living species did not move beyond a certain line, as if there were a real wall. He examined the known scientific data of the period to make sense of this sharp distribution of species.
Geological History: The History That Shaped Living Species
Although it was not fully known in Wallace’s time, we know today that the distribution of species is a result of geological events. The western islands were once connected to mainland Asia. Therefore, land mammals such as elephants, rhinos and tigers were able to reach these islands.
On the other hand, the islands on the eastern side were the ancient ruins of the Australian continent. Species such as marsupials and komodo dragons evolved here and remained isolated. The Wallace Line formed the boundary of two different biogeographic regions.
Deep Waters and Species Divergence
Although today these islands are surrounded by shallow seas, sea levels were much lower in the geological past. However, there were deeper waters in the area where the Wallace Line was located, making it impossible for land animals to pass from east to west or west to east.
This deep water barrier fed by strong currentsprevented the passage of not only large land mammals but also some small living species such as birds and insects. Thus, as species evolved on both sides of the Wallace Line, completely different ecosystems were formed.
Plate Tectonics: Earth’s Dynamic Surface
Although Wallace understood the biological and geological underpinnings of this invisible boundary, the theory of plate tectonics was not yet known in his time. According to this theory, which was accepted in the 1960s, the surface of our planet is in a constant state of change with the movement of large land masses.
The Malay Archipelago is one of the most tectonically complex regions in the world. The separation of continents, the rise of islands, and the change in sea levels explain the origin of the diversity of life in this region. The Wallace Line is a natural reflection of these geological dynamics.
Invisible Borders Are Not Only Here
Invisible biogeographic boundaries such as the Wallace Line are also found elsewhere in the world. During periods of rising sea levels, the migration of species between continents and island groups was prevented. This has resulted in even more mobile creatures such as birds and insects being unable to cross some boundaries.
Alfred Russel Wallace laid the foundations of biogeography with his discoveries about the distribution of species. The Wallace Line, named after him, proves how dynamic and surprising natural history can be. Today, this invisible line still guides scientists in understanding how ecosystems are shaped.
The Wallace Line is a joint product of both geological history and biological evolution. While this line helps us understand how species are distributed in the world, it also reveals what great secrets nature holds.
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