The Asian climate helped migrate many animal species to Australia. This is evidenced by the study conducted by researchers at ETH Zurich, and published in Sciences. Why countless species of, venomous snakes, spiny lizards (Moloch horridus), jumping mice (Notomys sp.) or flying foxes found their way from Asia to Australia, and not the other way around, has until now been a mystery. To better understand this asymmetric distribution of vertebrates along the Wallace line, the researchers led Loic PelissierProfessor of Ecosystems and Landscape Evolution at ETH Zurich, has created a new model that combines climate reconstructions with 30-million-year-old plate transitions and a comprehensive dataset of some 20,000 birds, mammals, reptiles and amphibians recorded today in the region.
If you go to Bali, you won’t see a cockatoo, but if you go to the neighboring island of Lombok, you will. The situation is similar for marsupials: Australia is home to many species of marsupials, such as kangaroos and koalas. The further west you go, the rarer it becomes. While there are only two representatives of these typically Australian mammals on the Indonesian island of Sulawesi, in neighboring Borneo you will search for them in vain. Australia, on the other hand, is not home to the typical mammals of Asia, such as bears, tigers or rhinos.
This sudden change in the composition of the animal world caught the attention of the British naturalist and creator of the theory of evolution, Alfred Russel Wallace, who traveled across the Indo-Australian archipelago from 1854 to 1862 collecting animals and plants. He described an invisible biogeographical line that runs between Bali, Lombok, Borneo and Sulawesi and represents the western distribution of Australian fauna.
Biodiversity researchers have long been fascinated by this sudden change in organisms along the Wallace Line. However, how we arrive at these distribution models is not explained in detail. One explanation is plate tectonics. Forty-five million years ago, the Australian plate began moving north and slid under the powerful Eurasian plate. This brought together two landmasses that were previously far apart. It became easier for terrestrial creatures to colonize one continent from another.
The researchers show that adaptation to local range climates is partly responsible for the uneven distribution of representatives of the Asian and Australian fauna on either side of the Wallace line. In addition to plate tectonics, the environmental conditions that prevailed millions of years ago were crucial to the exchange between the two continents. Based on the simulations, the scientists found that animals native to Asia were more likely to cross Indonesian islands to reach New Guinea and northern Australia.
These islands were characterized by a humid tropical climate, in which the animals were comfortable and to which they had already adapted. The Australian fauna was diverse, having evolved in a cooler and drier climate over time, and thus less successful in gaining a foothold on tropical islands than the animals migrating from Asia. The Asian climate therefore favored the organisms that arrived in Australia via the tropical islands in the faunal region known as Wallacea, especially those able to withstand a wide range of climates.
This made it easier for them to settle in the new continent. “Historical context is important for understanding the distribution patterns of biodiversity observed today and this was the missing piece of the puzzle that explains the mystery of the Wallace line.”said the first author alexander scales, Postdoctoral researcher in the Pellissier Group. The findings are important to researchers: “They show that we can only understand current patterns of biodiversity distribution if we take into account geological evolution and prehistoric climatic conditions.”Pellissier said. “Knowing what factors influence exchanges over long periods of time is important for understanding why species can become invasive over more recent timescales. In the current biodiversity crisis, this can help us better assess the consequences of human-caused invasions.”Skeels pointed out.
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