Migrant Flora and Fauna in Australia

There are some myths that propose Australia was settled with a single migration 60,000 ago and has been disconnected from the rest of the world ever since. According to myth, not only were there no more human migrations to and from Australia, but there was no plant or animal migrations either. In truth, the diversity of foreign flora and fauna in the Australian ecosystem prior to 1788, and prior to 60,000 BC, indicates that not only has there been a long history of biological flow into Australia, there has also been a flow out of it.

 In north Australia, the Boab Tree was a feature of the desert landscape before the arrival of the British. It is a native of Madagascar. In colonial times, a grass known as Kangaroo Grass was common in the landscape. In Africa, its scientific name is Themed triandra and it is the chief feed source for Africa’s grazing herbivores. When British botanist Joseph Banks first explored Australia, he found European plant species such as Couch Grass, Loosestrife, Purslane, and Self-heal. Later botanists have discovered that hundreds of plants found in Australia are also found in Africa and Asia.

It is not clear how the plants spread. Birds have always migrated back and forth between nth Australia and Asia and could have spread seeds. Admittedly Africa is a bit far from Australia for a bird to fly on one stomach so perhaps some seeds might have just been taken by human migrants.

Just as plants have spread, so have animals. The Keelback snake is the only native snake with immunity to the poison of the cane toad. The immunity is a legacy of its evolution in Asia where its ancestor fed upon poisoness toads. The Bush and Water rat are two rodents that are native to Australia, but originally came from Asia around 2,000,000 years ago. How they arrived is a mystery. Perhaps they clung to logs washed out to sea and then onto Australia.

The Dingo is believed to have arrived in Australia around 3,000 years ago. There is a theory that feral cats might have arrived at the same time but either died out or only had a minor presence in what was then a more hostile ecosystem containing Tasmanian Tigers and Tasmanian Devils. In nth America today, the cat is confined to urban areas because it is hunted by the cayote in rural areas. 3,000 years ago, Australia would have been more hostile to the cat than nth America is today.

As well as foreign flora and fauna reaching Australia, Australian flora and fauna has reached foreign countries. The Koa tree in Hawaii is descended from the Australian wattle. Australian Hopbush is found in America, Africa and India. In regards to ajnimals, marsupials are found in Papua New Guinea and Indonesia. In addition, the Komodo Dragon is believed to have evolved in Australia and migrated to island of Komodo 900,000 years ago.

The lengthy flow of flora and fauna back and forth between Australia and other countries pose some questions about why some species took hold but some did not. For example, if prehistory humans brought dogs, rats and even snakes to Australia, why didn’t they bring major agricultural animals such as pigs or chickens? Furthermore, why didn’t they bring a major agricultural crop such as rice, wheat or fruit bearing trees? Even if humans didn’t, why didn’t birds disperse the seeds? If the Boab tree and Kangaroo grass could reach Australia from Africa, why couldn't wheat or rice reach Australia from Asia? If humans brought dogs with them in their canoes from India, why didn't they bring pigs when walking overland from Papua New Guinea?

The answer is that they probably did. At Cuddle Springs in NSW, grinding stones have been found and dated at 30,000 years. The harvesting and grinding was a cultural practice that subsequently died out. Perhaps it died out because rice paddies can’t survive droughts and wheat fields can’t survive either firestick farming or bushfires. Just because rice and wheat didn't exist in Australia in 1788 doesn't mean it wasn't in existence at an earlier time.

Fruit bearing trees would also have struggled to compete. They don’t recover quickly from fire and their lush leaves are prized by Australian fauna that don’t like the toxic eucalyptus. Native fauna would have eaten the trees to extinction. Wheat and rice fields would have likewise struggled in the face of native marsupials that could easily jump fences erected to keep them out.

If pigs had been introduced to Australia and gone feral, they would have had no hope of surviving in an ecosystem containing Tasmanian Devils, Tigers and hunter gatherers. In comparison to a Kangaroo, a pig carries a lot of meat, is slow, cumbersome and is very easy to track. In terms of reward for effort, hunting a pig required far less work and far more reward than hunting a Kangaroo. Both humans and marsupial predators would have favoured it if any went wild. The pig really only survives in Australia today because there are no more hunter gatherers, dingos are shot and the large marsupial predators have gone extinct from the mainland. If the Australian ecosystem was the same as it was 300 years ago, then all feral pigs would quickly go extinct.

The most likely entry and exit point into and out of Australia was over the Wallace Line in Indonesia. This is a stretch of deep water that separates the zoological regions of Asia from those of Australia and Papua New Guinea. During past ice ages, the Australian continent (Sahul) extended close to the line. It would have been quite easy for flora and fauna to be washed from one side of the line to the other; however, unless they had some comparative advantage, they would have quickly died out or struggled to find a mate.

The Wallace Line - A stretch of deep water that separates the zoological regions of Asia from those of Australia and Papua New Guinea. Although the deep water makes migration more difficult, elephants, pigs and Homo erectus made it across prior to the emergence of Homo sapiens.

Sahul – The land mass that comprised PNG and Australia during the last ice age. Australia is not as isolated as some people believe.

While the Wallace Line marks a distinct difference in Asian and Australian zoological regions, fauna far greater in size than rats and snakes have made it across. Homo erectus made it across at least 850,000 years ago. By making the crossing, Homo erectus entered into the Australian zoological region. Species of elephants also made the crossing; however, they became dwarfed and then went extinct. Perhaps the elephants made it into Australia as well. If so, they would have been hunted by the marsupial lion (Thylacoleo carnifex), which had a bite more powerful than the sabar-toothed tiger.

In other parts of Indonesia, pigs, monkeys, and bats have been found to be endemic on islands that have never had less than 100km of open water seperating them from other islands. If these had made a 100km crossing in other parts of Indonesia, it is likely they would have made it across the Wallace Line as well.

The history of flora and fauna migration to Australia shows that Australia has never really been as isolated as some people believe it to be. In turn, the lack of isolation demostrates that Australian ecosystems have never been as weak as some people believe them to be. For example, in 1923, Albert Le Souef, curator of Taronga Park Zoo, wrote:

"when animals of this class (marsupials) suddenly find themselves placed in competition with such advanced forms as the Fox, the Cat, and the Rabbit - types far ahead of them on the evolutionary scale - it is ...inevitable that they should go down before the invader."

If feral fauna and flora has taken over Australia today it is not because the Australian ecosystem is fragile or because marsupials are inferior to more advanced animals like the Fox or Cat, it is because something has changed in the ecosystem that has made it less capable of dealing with invasive species. Specifically, mainland Australia has lost its dominant predators. Furthermore, human activity has changed and changed in a way that helps new arrivals at the expense of the old ones.

The long existence of foreign flora and fauna also undermines ideological desires to speak of “native” ecosystems. For tens of thousands of years, new species have been entering Australia and existing species have been dying out. The Australian ecosystem in 1788 was not like it was in the year 0 and nothing like it was 60,000 years ago. Like all ecosystems, the Australian ecosystem has been in a constant state of change.

Activity 1 – Migration

Understanding how species migrate

The following species appeared to have arrived in Australia without any aid from humans. Speculate how they could have arrived (consider maps during the last ice age, tsunamis, birds etc):

Boab Tree
Bush rat (Bogol)
Water Rat
Keelback Snake
Kangaroo Grass

 

Activity 2 – Extinction and change

Activity purpose – Understand how niches are open and closed by changes in the food web

Cats, dogs and pigs thrive in the bushland today; however, only dogs existed in the bush prior to 1788.

1. Create a list of predators for cats and pigs prior to 1788
2. List some of the things that cats and pigs would have eaten in Australia prior to 1788
3. Look at the map of Sahul during the last ice-age. If pigs were in the PNG part of Sahul at the time, what barriers may have prevented them reaching Australia?
4. Indonesia is a tsunami-prone region. Comment on whether you think it would be possible for many species to move between Sunda and Sahul on the floating debris caused by a Tsunami. (Research where any animals were found floating out at sea after recent tsunamis in Japan and Indonesia.