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 ==========================================================================
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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Strange & Offbeat ========================================================================== PLANTS_&_ANIMALS Why_There_Are_No_Kangaroos_in_Bali_(and_No_Tigers_in_Australia) Number_Cruncher_Calculates_Whether_Whales_Are_Acting_Weirdly Fossils_Reveal_How_Ancient_Birds_Molted_Their_Feathers_--_Which_Could_Help Explain_Why_Ancestors_of_Modern_Birds_Survived_When_All_the_Other_Dinosaurs Died EARTH_&_CLIMATE Why_There_Are_No_Kangaroos_in_Bali_(and_No_Tigers_in_Australia) Turning_Old_Maps_Into_3D_Digital_Models_of_Lost_Neighborhoods Squash_Bugs_Are_Attracted_to_and_Eat_Each_Other's_Poop_to_Stock_Their Microbiome FOSSILS_&_RUINS Giant_Stone_Artefacts_Found_on_Rare_Ice_Age_Site_in_Kent,_UK How_Urea_May_Have_Been_the_Gateway_to_Life Newly_Discovered_Jurassic_Fossils_in_Texas Story Source: Materials
provided by ETH_Zurich. Original written by Peter Ru"egg. Note: Content
may be edited for style and length.


========================================================================== 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 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230706152402.htm

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