Invasive species are a serious threat to endemic Australian species, and an ongoing cost to Australian agriculture. Numerous species arrived with European maritime exploration and colonisation of Australia and steadily since then. There is ongoing debate about the potential benefits and detriments of introduced species; some experts believe that certain species, particularly megafauna such as deer, equids, bovids, and camels, may be more beneficial to Australia's ecosystems than they are detrimental, acting as replacements for extinct Australian megafauna. Management and the prevention of the introduction of new invasive species are key environmental and agricultural policy issues for the Australian federal and state governments. As of 2016 the management of weeds cost A$1.5 billion on weed control and a further $2.5 billion in lost agricultural production over the course of a year.
Causes Both geological and climatic events helped to make Australia's flora and fauna unique. Australia was once part of the southern supercontinent Gondwana, which also included South America, Africa, Arabia, India, Antarctica and Zealandia. Gondwana began to break up 140 million years ago (mya); at 50 mya, Australia separated from Antarctica, and was relatively isolated until the collision of the Indo-Australian Plate with Asia in the Miocene epoch, 5.3 mya. As Australia drifted, it was isolated from the evolutionary pressures in the rest of the world. Other examples of island isolation include Madagascar, New Zealand, Socotra, the Galapagos and Mauritius. The geographic isolation of Australia created a sharp division between Australian fauna and Asian fauna at the Wallace line.
Humans arrived in Australia between 80,000 and 45,000 years ago, living alongside megafauna for 20,000–25,000 years before the megafaunal extinctions that were likely caused by, or partly contributed to by, late Pleistocene climate change; however, the full reason for the extinctions is still unclear and human hunting or habitat changes through fire-stick farming may also have contributed to the extinctions. This left Australia with much of its keystone species extinct, leaving the ecosystems altered and far more vulnerable to invasion. Dingoes probably arrived in Australia between 5,400 and 4,600 years ago, long after the first humans, spread rapidly across the continent and probably contributed to the extinction of even more native species such as the thylacine and Tasmanian devil. The current period of invasive species introduction began in 1788 with the arrival of the first European settlers. The population density in Australia beyond the coastline and major cities has been very low since the arrival of European settlers, and there are large tracts of land where it is very difficult for people to manage even large feral animals like camels, horses, donkeys and water buffalos.
Invasive species
Fungi and bacteria Invasive fungi and bacteria in Australia affect many native plants and animals and agricultural crops. Citrus canker was found twice in the Northern Territory in the 1900s, and was eradicated each time. In 2004, an outbreak of citrus canker occurred in Australia, and many Queensland citrus orchards have been burned to remove the disease. The destruction worked; however, the disease was once again detected in April 2018 and confirmed in May 2018 in Northern Territory and Western Australia. The oomycete Phytophthora cinnamomi, commonly known as wildflower dieback or jarrah blight, has created a massive problem in some types of native vegetation – especially jarrah forest and banksia woodland.
Animals Australia is host to 56 introduced invasive vertebrate animal species. They can be categorised in the following ways:
Invasive – species has a tendency to spread their range into new areas or plague their range Ferals – defined as animals imported for domestic purposes (i.e. pets, recreational use – such as hunting – or beasts of burden) that have gone wild. Pests – animals that have a direct effect on human standard of living or the environment/ecosystems in areas where they are present, have a high rate of reproduction and are difficult to control Animals causing most public concern and economic and ecological damage include:
Control
Various programs exist to control invasive species in Australia. A cane toad control program aims at preventing the spread of the species towards Darwin and Western Australia, and involves trapping. Red Foxes, feral cats, feral dogs and feral pigs are often baited, although the use of 1080 (sodium fluoroacetate) is also known to affect native animals such as the quoll and Tasmanian devil, though the most common and effective method is shooting. 1080 is ideal in the south-west of Australia because a native plant contains the same toxin – therefore most native animals have developed immunity to it. Other species are either open to hunting as a sport (such as the deer) or subject to government sponsored culling programs. Dromedary Camels and Water buffalo are often shot from helicopters.
Bounties Several bounty programs have assisted in the eradication of larger sized pests in Australia. Ironically, many early bounties were paid for the extermination of native species that were considered a pest to farmers. The Tasmanian tiger or thylacine was one such program that caused extinction, whilst the Tasmanian devil, spotted quoll, and Tasmanian wedge-tailed eagle all became seriously threatened by bounties. At various times, bounties have been in place for invasive species such as wild-living domestic dogs (including the dingo) and fox. A beer-for-toads bounty has been publicised for cane toad control in the Northern Territory. In 2002, a Victorian Fox Bounty Trial began to test the efficacy of fox bounties which have been in place intermittently since 1893 (only 30 years after introduction). The study showed no reduction in fox impacts, and that the project may even have been counterproductive. The evaluation also found that a sustained annual reduction of 65% is required to achieve real declines in red fox populations. Feral cat bounties in Queensland have also been considered to counter the growing problem. The dingo is subject to various controversial bounty systems in Australia. The Australian dingo was itself introduced before European settlement, yet has been considered native of the mainland in most cases both the pure breeds and the dingo-dog hybrids are considered pests to livestock.
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