A study conducted by biologists from Australian National University (ANU) and ETH Zurich in Switzerland may have discovered why Australian marsupials are nearly impossible to find outside of Australia, particularly in the country’s neighboring Southeast Asian region.
Key details: The study, published in Science on July 6, analyzed Wallace’s Line, an imaginary biogeography line coined by British naturalist and explorer Alfred Russel Wallace in 1863 that serves as an evolutionary boundary for the animals on either side.
While traveling across the Malay Archipelago, which consists of 25,000 islands in Australia, Papua New Guinea and Southeast Asia, the British explorer found the type of animals noticeably changing after a certain point.
Uneven distribution: Researchers have also discerned a disparity between creatures on either side, such as goannas and other animals that originated in Asia being found in Australia, and marsupials naturally found in Australia not present in Southeast Asia.
“If you travel to Borneo, you won’t see any marsupial mammals, but if you go to the neighboring island of Sulawesi, you will. Australia, on the other hand, lacks mammals typical of Asia, such as bears, tigers or rhinos,” Dr. Alex Skeels, an evolutionary biologist and biogeographer from ANU, said.
Their findings: The team learned that the uneven distribution of animals between the two sides was due to the dramatic change in Earth’s climate about 35 million years ago, with Skeels noting that Australia was “located much further south and was connected to Antarctica” during that period.
“At some point in Earth’s timeline, Australia broke away from Antarctica and over millions of years drifted north, causing it to crash into Asia,” Skeels explained in a statement published in an Australian National University report, adding that the collision resulted in the formation of volcanic islands, which are now Indonesia.
Further explanation: Skeels also noted that after Australia drifted from Antarctica, the event “opened up this area of deep ocean surrounding Antarctica which is now where the Antarctic Circumpolar Current is,” which, at that time, made the climate much cooler.
The sudden change in climate was not the same on both sides of the imaginary Wallace’s Line. Skeels said that animals and fauna in Asia had already adjusted to the “relatively warm, wet and tropical” climate in the region, while species in Australia evolved in a “cooler and increasingly drier climate over time.”
Differing climate conditions: According to Skeels, the conditions of the two sides at the time meant that Asian species had a much easier time adjusting to the climate in Australia than Australian species adjusting to the climate in Asia.
How they did it: The researchers reportedly used a computer model to simulate how the climate impacted roughly 20,000 species. They also included several factors in their studies, such as dispersal ability, ecological preferences and evolutionary relatedness.
Data for the future: The latest study could potentially predict which species “may be better versed at adapting to new environments, as changes to Earth’s climate continue to impact global biodiversity patterns,” Skeels said.