Since the beginning of time, there has been a continuous flow of species in and out of regions that establishes a foundation for ecosystems. When species are introduced into new environments and replicate excessively to interfere with native species, they become invasive. Invasive species refer to those that spread into new areas and pose a threat to other species. Factors contributing to their menacing status include overfeeding native species, lack of predators, and outcompeting native species (Sakai et al., 2001). Invasive species shouldn’t be confused with feral species which are domestic animals that have reverted to their wild state, or pests which are organisms harmful to human activity (Contrera-Abarca et al., 2022; Hill, 1987). Furthermore, not all introduced species are invasive; crops such as wheat, tomato and rice have been integrated with native agriculture successfully. Many species were introduced accidentally and turned invasive; however, some were intentionally introduced to manage other species, and a lack of foresight resulted in detrimental ecological impacts. Each year, invasive species cost the global economy over a trillion dollars in damages (Roth, 2019).

Claimed ecological benefits of invasive species

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Contrary to the name, invasive species could potentially benefit the invaded ecosystem. Herbivores can reap the benefits of the introduced biodiversity, and native plants can increase their tolerance (Brändle et al., 2008; Mullerscharer, 2004). Deer and goats aid in suppressing introduced grasses and inhibit wildfires (Fornoni, 2010). Likewise, species such as foxes and cats have the capacity to regulate the number of rats and rabbits. Furthermore, megafaunal extinction has opened opportunities to fill empty niches, for example, camels could fill the ecological niche of a now-extinct giant marsupial (Chew et al., 1965; Weber, 2017). Thus, studies indicate the possibility of species evolving to fill vacant niches (Meachen et al., 2014). Below, I’ll explore the rise and downfall of invasive species in Australia.  

Cane toad 

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Cane toads are notorious for their unforeseen invasion. Originally introduced as a biological control for cane beetles in 1935, their rookie status was advantageous to their proliferation and dominance over native species (Freeland & Martin, 1985). Several native predators were overthrown and native fauna in Australia lacked resistance to the cane toad’s poison used as a defence mechanism (Smith & Philips, 2006). However, research suggests an evolutionary adaptation to such poison (Philips &Shine, 2006). There isn't a universal method to regulate cane toads, so efforts to completely eradicate cane toads are futile. However, populations are kept low by continuously monitoring areas and targeting cane toad eggs or their adult form. 

Common Myna 

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The origins of Common Myna introduced into New South Wales and Victoria are uncertain; however, it was introduced into Northern Queensland as a mechanism to predate on grasshoppers and cane beetles(Neville & Liindsay, 2011) and introduced into Mauritius to control locust plagues (Bauer, 2023). The Common Myna poses an alarming threat to ecosystems and mankind, its severity is elucidated by its position in the world’s top 100 invasive species list (Lowe et al., 2000). It has spurred human health concerns including the spread of mites and acting as a vector for diseases destructive to human and farm stock (Tidemann, 1998). Myna also has a vicious habit of fostering competition with cavity-nesting native birds, forcing them and their eggs from their nest, however, the extent of this is unclear, and the influence of habitat destruction needs to be considered (Grarock et al., 2013). The impact of this bird lacks empirical evidence, so appropriate management is undecided (Grarock et al., 2012). However, modification of habitats could be advantageous as the Myna impact urban areas more, whereas intervening in their food resources would be rendered useless with their highly variable diet (Brochier et al., 2012).   

Zebra mussels 

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Zebra mussels accidentally invaded Australia's aquatic locality when introduced by the ballast water of cargo ships. From an ecological perspective, Zebra Mussels overgrow the shells of native molluscs and create an imbalance within the ecosystem (Dzierżyńska-Białończyk et al., 2018). From a societal perspective, it colonizes docks, ship hulls, and water pipes and damages power plants (Lovell et al., 2006) Controlling the spread of Zebra Mussels includes manual removal, chlorine, thermal treatment and more.

Control methods 

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It is crucial to deploy preventative methods to mitigate the spread of invasive species before it becomes irreversible. Few known control methods are employed for certain types of animals but with no guarantee of success. Some places place bounties on catching the animals, however, the results of this technique are conflicting. In 1893, foxes were the target of financial incentives, but the scheme was deemed ineffective (Saunders et al., 2010). However, government bounties were introduced for Tasmanian tigers in 1888, which drastically caused a population decline and their eventual extinction (National Museum of Australia, 2019). Similarly, the prevalence of Cane Toads became unbearable, and in response, armies were deployed, and fences in rural communities were funded. Moreover, in 2007, inspired by a local pub’s scheme to hand out beers in exchange for cane toads, the government staged a “Toad Day Out” to establish a bounty for cane toads (Williams, 2011). 

Invasive species are detrimental to ecosystems, whether introduced intentionally or by accident, management of species is still a work in progress.

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