MSGID: 1:317/3 64a79520   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Why there are no kangaroos in Bali (and no tigers in Australia)    
      
     Date:   
         July 6, 2023   
     Source:   
         ETH Zurich   
     Summary:   
         Researchers are using a new model to clarify why millions of years   
         ago more animal species from Asia made the leap to the Australian   
         continent than vice versa. The climate in which the species evolved   
         played an important role.   
      
      
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   FULL STORY   
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   If you travel to Bali, you won't see a cockatoo, but if you go to the   
   neighbouring island of Lombok, you will. The situation is similar with   
   marsupials: Australia is home to numerous marsupial species, such as   
   the kangaroo and the koala. The further west you go, the sparser they   
   become. While you will find just two representatives of these typically   
   Australian mammals on the Indonesian island of Sulawesi, you will search   
   in vain for them on neighbouring Borneo. Australia, on the other hand,   
   is not home to mammals that you will typically find in Asia, such as   
   bears, tigers or rhinos.   
      
   This abrupt change in the composition of the animal world already caught   
   the eye of the British naturalist and co-discoverer of evolutionary   
   theory Alfred Russell Wallace, who travelled through the Indo-Australian   
   Archipelago from 1854 to 1862 to collect animals and plants. He described   
   an (invisible) biogeographical line running between Bali and Lombok   
   and Borneo and Sulawesi that marked the westernmost distribution of   
   Australian fauna.   
      
   Fascinating change of wildlife Biodiversity researchers have long   
   been fascinated by this abrupt change of creatures along the Wallace   
   Line. How these distribution patterns came about, however, has not yet   
   been clarified in detail.   
      
   One explanation is plate tectonics. Forty-five million years ago, the   
   Australian Plate began to drift northwards and slid under the mighty   
   Eurasian Plate. This brought two land masses closer together that had   
   previously been far apart. It became easier for land creatures to colonise   
   one continent from the other. Tectonic movements also gave rise to the   
   creation of countless (volcanic) islands between the two continents,   
   which animals and plants used as stepping stones to migrate westwards   
   or eastwards.   
      
   More Asian animals in Australia than vice versa But why more species   
   found their way from Asia to Australia -- countless poisonous snakes,   
   thorny lizards (Moloch horridus), hopping mice (Notomys sp.)  or flying   
   foxes bear witness to this -- than the other way round has been a mystery   
   until now.   
      
   In order to better understand this asymmetrical vertebrate distribution   
   along the Wallace Line, researchers led by Loi"c Pellissier, Professor   
   of Ecosystems and Landscape Evolution at ETH Zurich, have created a new   
   model. It combines reconstructions of the climate, plate displacements   
   between 30 million years ago and the present day and a comprehensive   
   data set for around 20,000 birds, mammals, reptiles and amphibians that   
   are recorded in the region today.   
      
   Climates in areas of origin decisive In the latest issue of Science,   
   the researchers now show that adaptations to the climates in the areas   
   of origin are partly responsible for the uneven distribution of Asian   
   and Australian faunal representatives on both sides of the Wallace Line.   
      
   In addition to plate tectonics, the environmental conditions that   
   prevailed millions of years ago were decisive for the exchange between   
   the two continents. Based on simulations, the researchers found that   
   animals originating from Asia were more likely to "hop" across the   
   Indonesian islands to reach New Guinea and northern Australia.   
      
   These islands featured a tropically humid climate, which they were   
   comfortable with and had already adapted to. The Australian wildlife was   
   different, having evolved in a cooler climate that had become increasingly   
   drier over time, and was therefore less successful in gaining a foothold   
   on the tropical islands than the fauna migrating from Asia.   
      
   The Asian climate thus favoured creatures that reached Australia via the   
   tropical islands of the faunal region known as Wallacea, especially those   
   that could tolerate a wide range of climates. This made it easier for them   
   to settle on the new continent. "The historical context is crucial for   
   understanding the biodiversity distribution patterns observed today and   
   was the missing piece of the puzzle explaining the enigma of Wallace's   
   line," says first author Alexander Skeels, a postdoctoral researcher in   
   Pellissier's group.   
      
   Competitive advantages for tropical species Traits of species that evolved   
   in tropical habitats include faster growth and higher competitiveness   
   to enable them to withstand the pressure of coexistence with many other   
   species. In harsher climates, such as the colder and drier regions of   
   Australia, organisms usually have to evolve special adaptations to cope   
   with drought and heat stress. These include behavioural adaptations   
   such as nocturnal activity and physiological adaptations to minimise   
   water loss.   
      
   "Many Australian frogs bury themselves in the ground and remain dormant   
   for long periods for this reason," Skeels points out. "Something that is   
   rare in tropical frogs."  The findings are important for the researchers:   
   "They make it clear that we can only understand today's distribution   
   patterns of biodiversity if we include the geological development   
   and climatic conditions of prehistoric times in our considerations,"   
   says Pellissier.   
      
   The heritage of long past epochs has shaped the patterns of biodiversity   
   right up to the present. It also helps us to understand why more species   
   are found in the tropics today than in temperate latitudes. "To fully   
   understand the distribution of biodiversity and the processes that   
   maintain it in the present, we need to find out how it came about,"   
   says the researcher.   
      
   Learning to understand invasive species This is especially true in   
   biogeography because the exchange of species between continents continues   
   to take place regularly and at an alarming rate today as humans move   
   animals and plants around the planet. These species can become invasive   
   on other continents and harm the ancestral fauna and flora. "Knowing   
   the factors that influence exchange on long time scales is important   
   to understanding why species can become invasive on more recent time   
   scales. In the current biodiversity crisis, this can help us to better   
   assess the consequences of human-induced invasions," Skeels emphasises.   
      
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   provided by ETH_Zurich. Original written by Peter Ru"egg. Note: Content   
   may be edited for style and length.   
      
      
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   Journal Reference:   
      1. A. Skeels, L. M. Boschman, I. R. McFadden, E. M. Joyce, O. Hagen, O.   
      
         Jime'nez Robles, W. Bach, V. Boussange, T. Keggin, W. Jetz, L.   
      
         Pellissier. Paleoenvironments shaped the exchange of terrestrial   
         vertebrates across Wallace's Line. Science, 2023; 381 (6653):   
         86 DOI: 10.1126/science.adf7122   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230706152402.htm   
      
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