Tim Newcomb
Mon, July 24, 2023
Patchareeporn Sakoolchai - Getty Images
The Wallace Line runs through Asia and Australia, and shows an incongruity in the dispersion of animal species on either side.
Researchers have known about the differences in the animals for over 150 years, but have only just now released a theory as to why they exist.
Colliding continents could be to blame for some animal species failing to adapt to changing climates.
The imaginary Wallace Line in Southeast Asia and Australia isn’t so fictional for the differing animal species living on either side. The line—named after British naturalist Alfred Russel Wallace—serves as a boundary, and each side of that boundary plays host to very different types of animals.
For over 150 years, scientists didn’t have an explanation as to why the line exists. Why would two regions in close geographic proximity have such different animal populations? For example, why does a koala live in Australia, but not in the Philippines? Or, why can we find kangaroos in Papua New Guinea (and Australia), but not in Malaysia? And why do some animals buck that trend, like the enjoyably named kookaburra, which can be seen throughout both Asia and Australia?
Now, we may finally have an answer. A new paper published in Science claims that, tens of millions of years ago, shifting plate tectonics forced a dramatic swing in Earth’s climate and produced what have come to know as the Wallace Line.
According to the biologists at The Australian National University and ETH Zurich, the Wallace Line was caused by Australia breaking away from Antarctica millions of years ago, drifting north, and ramming into Asia.
“That collision gave birth to the volcanic islands that we now know as Indonesia,” Alex Skeels of Australian National University says in a press release. The creation of the Indonesian islands produced stepping stones for animals from Asia to reach New Guinea and northern Australia.
But the research still shows that far more groups of Asian animals made the move to Australia than vice versa. That’s why the researchers believe the Wallace Line answer comes from more than just moving Earth, but in a climate change shift. The team says that when Australia broke free from Antarctica, a dramatic climate change came with it. This cooled and dried continents and led to a mass extinction event.
“When Australia drifted away from Antarctica, it opened up this area of deep ocean surrounding Antarctica which is now where the Antarctic Circumpolar Current is,” Skeels said. “This dramatically hanged Earth’s climate as a whole. It made the climate much cooler.”
Somehow though, according to the latest theory, Indonesia remained relatively warm, wet, and tropical. So, Asian animals that were well-adapted to and comfortable in the conditions could easily hop from Asia to Australia. “This was not the case for the Australian species,” Skeels said. “They had evolved in a cooler and increasingly drier climate over time and were therefore less successful in gaining a foothold on the tropical islands compared to the creatures migrating from Asia.”
That migration pattern still plays out in today’s distribution of species. “If you travel to Borneo, you won’t see any marsupial mammals, but if you go to the neighboring island of Sulawesi, you will,” Skeels said. “Australia, on the other hand, lacks mammals typical of Asia, such as bears, tigers, or rhinos.”
Millions of years of climate history, the authors claim, could help predict which species can better adapt to the modern world’s changing environments.
The Wallace Line runs through Asia and Australia, and shows an incongruity in the dispersion of animal species on either side.
Researchers have known about the differences in the animals for over 150 years, but have only just now released a theory as to why they exist.
Colliding continents could be to blame for some animal species failing to adapt to changing climates.
The imaginary Wallace Line in Southeast Asia and Australia isn’t so fictional for the differing animal species living on either side. The line—named after British naturalist Alfred Russel Wallace—serves as a boundary, and each side of that boundary plays host to very different types of animals.
For over 150 years, scientists didn’t have an explanation as to why the line exists. Why would two regions in close geographic proximity have such different animal populations? For example, why does a koala live in Australia, but not in the Philippines? Or, why can we find kangaroos in Papua New Guinea (and Australia), but not in Malaysia? And why do some animals buck that trend, like the enjoyably named kookaburra, which can be seen throughout both Asia and Australia?
Now, we may finally have an answer. A new paper published in Science claims that, tens of millions of years ago, shifting plate tectonics forced a dramatic swing in Earth’s climate and produced what have come to know as the Wallace Line.
According to the biologists at The Australian National University and ETH Zurich, the Wallace Line was caused by Australia breaking away from Antarctica millions of years ago, drifting north, and ramming into Asia.
“That collision gave birth to the volcanic islands that we now know as Indonesia,” Alex Skeels of Australian National University says in a press release. The creation of the Indonesian islands produced stepping stones for animals from Asia to reach New Guinea and northern Australia.
But the research still shows that far more groups of Asian animals made the move to Australia than vice versa. That’s why the researchers believe the Wallace Line answer comes from more than just moving Earth, but in a climate change shift. The team says that when Australia broke free from Antarctica, a dramatic climate change came with it. This cooled and dried continents and led to a mass extinction event.
“When Australia drifted away from Antarctica, it opened up this area of deep ocean surrounding Antarctica which is now where the Antarctic Circumpolar Current is,” Skeels said. “This dramatically hanged Earth’s climate as a whole. It made the climate much cooler.”
Somehow though, according to the latest theory, Indonesia remained relatively warm, wet, and tropical. So, Asian animals that were well-adapted to and comfortable in the conditions could easily hop from Asia to Australia. “This was not the case for the Australian species,” Skeels said. “They had evolved in a cooler and increasingly drier climate over time and were therefore less successful in gaining a foothold on the tropical islands compared to the creatures migrating from Asia.”
That migration pattern still plays out in today’s distribution of species. “If you travel to Borneo, you won’t see any marsupial mammals, but if you go to the neighboring island of Sulawesi, you will,” Skeels said. “Australia, on the other hand, lacks mammals typical of Asia, such as bears, tigers, or rhinos.”
Millions of years of climate history, the authors claim, could help predict which species can better adapt to the modern world’s changing environments.
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