Australia and Its Exotic Species Introductions

Australia is one of the most diverse and species-rich places on the planet. They have just about every type of habitat you can think of across the continent. It consists of, “About 85 per cent of flowering plants, 84 per cent of mammals, more than 45 per cent of birds, and 89 per cent of inshore, freshwater fish are unique to Australia” (Australia.gov.au). On the other hand, since 1770 more than 3,000 non-native species are known to have been introduced to Australian lands. “These include animals, birds, plants, insects, and other invertebrates, fungi, parasites and marine creatures” says The Australian Academy of Science. Some species have been known to actually have a positive impact on their environment. Dung Beetles for example helped control fly populations in high cattle number areas. Also, exotic earthworms are known to significantly improve the quality of the soil in several urban areas. A few species that have had a negative affect on Australia and are considered to be invasive include the wild brumby, feral camel, European rabbit, European honeybee, and the red fox.

There is one exotic species though that I would like to talk in depth about and that is the arrival of trout. In 1864, brown trout were introduced into the Plenty River in Tasmania. A guy by the name of James Youl who is a pastoralist, was the one responsible for bringing the trout over to Australia. Rainbow trout were introduced a little later as the second trout species in Australian waters in 1894. The introduction of these trout species brought happiness and joy to many anglers. Also, “Ask any avid angler, and the introduction of trout has created many positive economic and social opportunities in Australia” (Australian Geographic). As far as adapting into the environment goes, the trout fit in very well. The waterways are cold just how they like it and can tolerate it.

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Victoria and New South Wales are where the trout call home. They live in places like the Thredbo River, Lake Eucumbene, the Upper Murrumbidgee River and Lake Jindabyne. These rivers and lakes in New South Wales and the high-country streams in Victoria provide the perfect environment for trout. Fishermen from all over travel to these regions for good trout fishing and spending time in the great Australian outdoors.

Now introducing trout did not only bring beneficial impacts, but also negative ones. When exotic fishes were introduced it had a significant impact on the freshwater ecosystems and the native fish. The competition increased within the populations. Brown trout specifically are known to eat small native fish such as the Barred Galaxias and the Mountain Galaxias. In Tasmania, for example, the Pedder Galaxias fish population was wiped out of its natural range because they were eaten by trout. The only fish left of this species lies in another lake where trout are not present. Although trout have quite the dramatic effect on the native fishes, there are no plans to stop stocking them.

Another creature that has had a dramatic effect on Australia is the Cane Toad. Cane Toads are considered to be one of the world’s worst invasive species (The American Naturalist 171, no. 3 (March 2008). In 1935-1937 they were introduced along a 1,200 kilometer (about 745 miles) stretch in Northeastern Australia. Since then they have expanded their range to more than 1.2 million square kilometers (about 463,322 miles). The goal for introducing this species was to help control sugar cane pests. This Central/South American native species not only failed at its attempt to control sugar cane pests, it became invasive and toxic very quickly. It also initiated heavy declines in native species populations.

The reason they spread at such a high rate is because of their rapid mating and deadly toxins. The toads’ mate all throughout the year and the females can have up to thirty thousand eggs at a time. Another thing that has helped them take over is their deadly toxins. Hidden behind the bulbous lumps behind can toads’ eyes are glands that secrete toxins (LiveScience; Brett Israel 2010). With the constant mating and deadly toxins, it seems as though they are impossible to get rid of. Australia has spent 20 million dollars (17 million USD) on toad control, yet they just keep repopulating themselves. The Australians have tried just about everything they can from pesticide spraying which ended up causing cancer in humans, Whack-A-Toad safaris, bait traps and many more. Basically, the people got creative and did whatever they could to take out these toads, but nothing seemed to work. Biologist and cane toad expert Richard Shine of the University of Sydney says that we can’t stop the toads from spreading, but we can do all kinds of things to reduce their numbers and impacts.

Species like cane toads and trout are not the only ones that have been introduced to Australia. According to ResearchGate, “Over 27,000 exotic plant species have been introduced to Australia, predominately for use in gardening, agriculture and forestry.” Unfortunately, the new plant species have the potential to become weeds and that is the biggest downsides for bringing in these exotic plants. If a species does turn into weeds then it can have a major impact on Australia’s society, economy, and environment. For example, the Boneseed (Chrysanthemoides monifera) is a weed that was introduced to Australia. This South American native plant was brought in and planted as a garden species to stabilize sand dunes. Today it is known to be one of the worst weeds in Australia due to its potential for spread, invasiveness, and impacts on the environment and economy. It has the ability to outcompete other species after fire, regenerate quickly, and establish in areas of native vegetation. It has also posed threats on rare and threatened species like the brittle greenhood orchid which is located in Victoria.

Boneseed grows under a wide range of climate conditions but prefers sandy or medium-textured soils and disturbed situations, particularly near the sea because it tolerates salty conditions (Weed Management Guide 2003). If there were no plans or programs to control this weed, it would spread far outside its current range. It has already threatened much of Southern Australia and Tasmania, and has the potential to invade just about all of Victoria according to a recent climate analysis. Australia though is already on top of trying to control this plant species. The effective controlling measures include hand pulling, herbicide treatment and fire. Boneseed also requires long-term control because they have the potential to regenerate so the plant has to be looked after and treated regularly year after year.

The Boneseed isn’t the only invasive plant species introduced to the continent of Australia. 179 exotic vine species and other climbing plants have established persistent populations in native vegetation all around Australia. Studies showed that the vine species were mostly introduced for ornamental reasons more than any other. Vines have very interesting roles that they play within the ecosystems. They are known to increase tree mortality, also affect transpiration rates and carbon sequestration due to their high canopy to stem ratio. They also have the ability to smother vegetation such as shrubs, trees, or grasses because vines are not self-supportive so they have to rely on those other plants.

The Ipomoea pes-tigridis and Clematis vitalba were the most recently recorded exotic vines in Australia (introduced 5 years ago) (Wiley Online Library 2007) The Ipomoea pes-tigridis is also known as Tiger’s Foot is native to Africa and Asia. They can be found on the edges of the rainforest twining up the large trees and also near roadsides, refuse dumps, and abandoned settlements. They are also considered a weed in Australia. Another exotic vine that was introduced to Australia is the Rubber Vine which is a restricted invasive plant under the Biosecurity Act of 2014. Native to Madagascar, this woody-perennial vine can grow unsupported as a shrub with several stems and climb up trees as tall as 30 meters which is close to 100 feet. It also can not only smother vegetation but it can form dense thickets as well. It is found in central and northern Queensland (Queensland Government 2015). Rubber vines impact biodiversity and impedes stock and native animal movement. In northeastern Australia the plant impact pastoral and conservation areas as well as threaten the waterways, woodlands, and rainforests. They are also poisonous to livestock and present difficulties for mustering stock. There are four ways of controlling this invasive vine, physical control, mechanical control, herbicide control, and biological control. As many impacts and negative effects that this exotic vine species has on the environment and other plant and animal species, it is definitely one that needs to be controlled. If not controlled it could easily have the potential to take over many parts of Australia and destroy precious habitants throughout the territories.

As we have seen there are many, many exotic species that have been introduced to Australia over the last few hundred years. Some have made positive impacts while others have made negative ones. Some of the species arrived accidentally and others were brought over for a specific purpose. It is hard to believe the power that an introduced species can have on new territories. How in such little time the arrival of a species can either destroy anything that comes across its path, or it can have an extremely positive and beneficial impact on the area that it was brought about in. Whether it be brown and rainbow trout that provided good fishing opportunities for anglers as well as social and economic opportunities for Australia, or the rubber vine which had many negative impacts on livestock, native vegetation, and habitats in northeastern Australia, they have all shaped the continent into what it is today. As long as this beautiful country continues to control the invasive plant and animal species as best as they can, then Australia will continue to be one of the most if the not the most biodiverse place on this planet.