kAngaroos and Cockatoos are synonymous with Australian, tigers and Asian orangutans. Both continents are rich in biodiversity, which is also very unique. A simple and popular way to understand these “independent greatness” is the shape of the Wallace line.
What is the Wallace Line?
In the late 19th century, British naturalist Alfred Russel Wallace noticed a dramatic change in the composition of the organism when it moved from Asia to Australia, New Guinea and other nearby islands. He placed an invisible obstacle in the ocean, later called the Wallace Line, running between Bali and Lunpok, hitting north between Borneo and Sulawesi, and then south of Mindanao. To him, the line was like a fence between different species of animals on both sides.
Wallace and others conducted eight years of field surveys to carefully map lines across many kilometers, a process to lay the foundations of modern biogeography: the study of how species are distributed and how they get there.
Over the years, the series has attracted considerable research interest. “The Wallace Line… is partly associated with evolution. You’re not anywhere else on Earth to see such a dramatic shift in such a narrow distance. ” said Jason R. Ali, honorary associate researcher at the Senckenberg Nature Research Society in Germany.
What did Wallace discover in Sulawesi?
At the closest place, Borneo and Sulawesi are 20 kilometers apart, but they support very unique plants, mammals and birds. Wallace is even more confused about Sulawesi. It is one of the largest islands on the archipelago and is home to other parts of the planet, including the tarsiers (tarsiidae), the lowlands Anoa (Bubalus depressicornis) and the Mountain Anoa (Bubalus earlieresi), all of which are of Asian origin. However, Sulawesi is also home to Australian marsupials, such as the dwarf (Strigocuscus celebensis).
The island frustrated Wallace, who repeatedly reselled his boundaries because he wasn’t sure it belonged to Asia or Australia. He wrote in 1876 that the animals here showed “affinity” to Africa, India, Java, the Maru Islands, New Guinea and the Philippines.
Why do Sulawesi species come from both sides of the line, while most others don’t? Wallace has been deducing the basic answers these years ago, but over time it has been more in-depth research.
What do you say about the ancient past?
The line is part of the Malay Islands, a geologically complex area with over 25,000 islands.
Wallace believes that if some of the islands in the past are connected to the Asian continent, it can explain the animal distribution in Sulawesi. As the islands rupture and drift, the ancestral species on each island became isolated and independently developed, creating the Wallace saw in the 19th century. Since then, the researchers have extended this understanding by continuing it in time. Millions of years ago, Australia broke down and separated from Antarctica. In the cracks of growth, the oceans appeared, and the deep water flow cooled the earth.
At the same time, Australia went north to Asia and established the Indonesian volcanic island. Various studies have found that monsoons, droughts and sea level changes between these islands have stimulated island species to adapt to their new conditions and diversify until recently four million years ago.
The movement in the mainland is part of the puzzle. A study published in 2023 reveals another study when scientists look closely at how species on Wallace Line are related. They analyzed data on 20,000 species of birds, mammals, reptiles and amphibians. They found that despite global cooling, the tropical islands of Malay remain warmer and wetter than Australia. As a result, the Asian fauna uses these islands as stones to set foot on Australia, while Australian species develop with cool gases, striving to span islands in Asia. “Species in Asia can migrate through the routes filled with rainforests, because the ecosystems are similar to their origins,” Ali said. “Australian species can only enter Asia along the southern route, Timor and nearby islands. This road has appeared long after (just a few million years ago), making immigration of Australian species more challenging.”
Is it important to do it?
By combining insights from multiple disciplines, the above research helps explain Wallace’s discovery, making the line reveal that this line is phantom: it is visible, but the real reason for its existence is rooted in deeper facts in nature.
Today, even the newer tools have been added to the older tools to further elucidate the biogeography of the region. “We are understanding what adaptability allows species to move across the region through advanced evolutionary modeling and computer simulations,” said Alexander Skeels, a postdoctoral researcher at the Australian National University in Canberra.
Today, factors that affect species dispersion and settlement still make sense today.
India-Malayan Islands face one of the highest rates of habitat destruction in the world. Understanding its biography for ecologists to predict how species will cope with their home loss, exacerbated by the effects of climate change.
“New technology is helping us understand that the lines that separate Asia and Australia may be simplifying the story,” Skyles said. Ali responded to him, saying that repainting the Wallace line or any other line would be “fruit”.
“Different datasets and methods will reveal different results. These boundaries will always be blurry. Instead of redrawing the lines, it is no longer the focus, but rather how these species will be affected by habitat destruction in the future,” Ali added.
Rupsy Khurana is the head of science communication and outreach at the National Center for Biological Sciences in Bangalore.
publishing – March 5, 2025 at 08:30 am
