Invasive Species (Australia)

Invasive species cause significant ecological damage in Australia every year. Many of Australia’s native plants and animals are threatened or endangered because of invasive species; they outcompete native species for habitat space and food and in some cases prey directly on native species. For example, European honeybees are threatening to outcompete Australia’s native honeybees, and the brush-tailed bettong is endangered due to predation from European red foxes and feral cats.

While there are numerous kinds of ecological damage caused by invasive species, invasive species also cause economic damage. A study by Hoffmann and Broadhurst published in 2016 reported that economic losses and pest control cost the government an estimated $9.8 billion in the 2001–2002 financial year. This rose to an estimated $13.6 billion in the 2011–2012 financial year.

Overview

Hundreds of species have been introduced to Australia by humans. While the majority are benign, many have proven to be invasive, successfully establishing themselves and causing damage to the native environment. Species that are invasive in Australia include species of plants, freshwater fish, insects, birds, amphibians and mammals. Introduced diseases, fungi and parasites can also be considered invasive and cause serious impacts on native vegetation.

Some species were introduced by accident, like rats and mice that arrived on ships. Other species were introduced deliberately for a variety of reasons. Of these, some species of animal were deliberately released into the wild for food or hunting, such as European red fox. Others were brought as pets, pack animals and domestic livestock. Escaped animals would establish feral populations. Feral animals that are particularly damaging in Australia are cats, pigs, goat, donkeys, camels and horses. Introduced and feral animals cause erosion damage, they eat or trample the endemic plants, and they outcompete or prey on native wildlife. Some invasive species are native to Australia but were moved by humans to places they had never previously occurred. For example, sugar gliders were introduced to Tasmania from Victoria in the 1800s as pets. Sugar gliders escaped and have been predating Tasmania’s birds, contributing to the decline of endangered birds such as the Swift parrot.

Besides animals, there have also been deliberate plant introductions that have led to damaging invasions. A number of plants that were initially used for crops, pasture, erosion prevention or ornamental purposes have been listed by the Australian government as Weeds of National Significance, which collectively cause billions of dollars of damage annually. Weeds are responsible for soil disturbance, land degradation and loss of native plants. Invasive water plants are responsible for eutrophication and changing the conditions of waterways.

There are a number of management methods within Australia designed to eradicate invasive species or stop their spread. Government-sponsored culling programs are used to reduce populations of large mammals. Pigs, donkeys, horses and camels can be culled using helicopters. Animals can also be trapped or baited using poison. Other control methods include the introduction of species-specific diseases. There has been some success curbing rabbit and water buffalo populations with the use of disease.

Two animals that are considered extremely invasive in Australia are cane toads and European red foxes. Cane toads are an ironic example of a species being introduced to control another pest. They were introduced to northern Queensland from Hawaii in 1935 to prey on the larvae of cane beetles that were impacting Australia’s sugar cane crops. Cane toads were ineffective at controlling the beetle population and instead spread throughout the Queensland. They are efficient breeders and can migrate between 40 and 60 km per year. They threaten endemic wildlife by preying upon them and by outcompeting local predators. Furthermore, cane toads produce a toxin that can kill native predators such as birds. Methods used to control the spread of cane toads include trapping, culling and fences to restrict their access to water. The success of these methods has been limited. New methods have been proposed that would rely on sterilisation. Researchers have also tried to find ways of teaching the local wildlife to avoid cane toads by exposing them to smaller volumes of the toxin, allowing predators to learn from their mistakes instead of dying outright. If successful, this would reduce the cane toad’s impact on predators.

Red foxes were introduced from Europe in the 1800s for recreational hunting. Biological characteristics such as lifespan and reproduction meant they spread quickly in their new environment. Originally released in southern Victoria, they spread to New South Wales in 1893, South Australia in 1901, Queensland in 1907 and Western Australia in 1912. The fox is considered to be one of the most widely distributed invasive animals in Australia with a population of more than 7.2 million in 2012. Increased fox populations have corresponded with declines in medium-sized mammals that live on the ground, like numbats, bilbies and quokkas. Foxes have also caused the extinction of the desert rat-kangaroo. Several native species have only escaped extinction because of populations on islands where foxes have not been introduced. Besides hunting, the fox population is also managed through poisoned bait. The most common poison is 1080 (sodium fluoroacetate), although this is not selective and has been found to harm native predators such as the quoll and Tasmanian devil. However, 1080 is effective in south-west Australia since native plants contain the same compound and native animals have developed an immunity. Research suggests that the presence of dingos decreases red fox populations and increases native fauna.

Of the many invasive species in Australia, the cane toad and the European red fox are good examples of the type and extent of damage caused and the difficulties associated with managing Australian invasive species. However, even though there is still a long way to go to manage the impact of invasive species, there have been some success stories. The establishment of parks that focus on weed and animal eradication have led to a rejuvenation of native wildlife. Government funding and dedicated, continuous effort led to the eradication of invasive animals on Macquarie Island and the subsequent recovery of native populations of birds and vegetation. Efforts to remove invasive plants and eradicate foxes and goats from the Coturaundee Nature Reserve led to a recovery of the yellow-footed rock-wallaby.

Bibliography

Biba, Erin. “Inside Australia’s War on Invasive Species.” Scientific American, 9 Jun. 2017. https://www.scientificamerican.com/article/inside-australia-rsquo-s-war-on-invasive-species/. Accessed 29 Dec. 2018.

Braysher, Mike. Managing Australia’s Pest Animals: A Guide to Strategic Planning and Effective Management. CSIRO Publishing, 2017.

Garnett, Stephen, et al., editors. Recovering Australian Threatened Species: A Book of Hope. CSIRO Publishing, 2018.

Heathcote, Angela. “Sugar Gliders an Invasive Species in Tasmania, Scientists Find.” Australian Geographic, 5 Feb. 2018. https://www.australiangeographic.com.au/news/2018/02/sugar-gliders-an-invasive-species-in-tasmania-scientists-find/. Accessed 29 Dec. 2018.

Hoffmann, Benjamin D., and Linda M. Broadhurst. “The Economic Cost of Managing Invasive Species in Australia.” NeoBiota, vol 31, pp. 1-18, 2016.

Leishman, Michelle R., and Vivien P. Thomson. “Experimental Evidence for the Effects of Additional Water, Nutrients and Physical Disturbance on Invasive Plants in Low Fertility Hawkesbury Sandstone Soils, Sydney, Australia.” Journal of Ecology, vol. 93, no. 1, 2005, pp. 38–49.

Miller, Joseph T., et al. “The Evolution and Phylogenetic Placement of Invasive Australian Acacia Species.” Diversity and Distributions, vol. 17, no. 5, 2011, pp. 848–860.

Phillips, Ben L., et al. “Spatial and Temporal Variation in the Morphology (And Thus, Predicted Impact) of an Invasive Species in Australia.” Ecography, vol. 29, no. 2, 2006, pp. 205–212.

Ward-Fear, Georgia, et al. “Using a Native Predator (the Meat Ant, Iridomyrmex Reburrus) to Reduce the Abundance of an Invasive Species (the Cane Toad, Bufo Marinus) in Tropical Australia.” Journal of Applied Ecology, vol. 47, no. 2, 2010, pp. 273–280.

West, Peter. Guide to Introduced Pest Animals of Australia. CSIRO Publishing, 2018.