Invasive species and range shifts

Thousands of species have been introduced, either deliberately or inadvertently, to Australia and become established in all parts of the country, along our coasts and in the marine environment. Introduced species include agricultural species and domestic animals that benefit our economy, as well as species that are detrimental to the environment. Climate change is increasing the incidence of range shifts, where species change or expand their ranges to cope with changed environmental conditions. These species can act as invasive species in their new ranges.

Introduced species now make up a significant proportion of all species recorded in Australia’s terrestrial bioregions. The largest numbers are recorded in the intensive agricultural regions surrounding the major cities, such as the Sydney Basin, south-east Queensland, the Flinders Lofty Block and the Victorian midlands. We now have more introduced terrestrial plant species in Australia than native ones (Groves et al. 2005). Approximately 2,800 introduced terrestrial plant species have naturalised, and approximately 10% of these are considered invasive plants.

Invasive species are consistently identified as one of the most prevalent threats to Australian wildlife, and their management is a significant economic burden in Australia (Hoffmann & Broadhurst 2016). It is estimated that, since the 1960s, Australia has spent or incurred losses totalling at least $389.59 billion (2017 value) as a result of terrestrial invasive species (Bradshaw et al. 2021). In marine and coastal waters, the vast majority of invasive species are not actively managed.

Invasive species are also having a significant impact on natural heritage, including in a number of Australia’s World Heritage properties (e.g. Macquarie island, Lord Howe Island Group, Wet Tropics of Queensland), although this is an issue that is being addressed, particularly in World Heritage Areas, with some success.

The International Union for Conservation of Nature launched a global register of introduced and invasive species (GRIIS) in 2018 to support national government responses to biological invasions (Pagad et al. 2018). Species verified as non-native to a country are assessed for evidence of impact and may be further designated as ‘invasive’. This information, combined with Australian occurrence records from the Atlas of Living Australia, provides a national framework for reporting on status and trend of introduced species. Using 1980 as a baseline for the total number of species recorded at least once since 1901, anywhere on the Australian continent and remote territories, the aggregated public data record shows that the number of introduced terrestrial species by 2020 had increased by more than 17% since 1980 (i.e. 368 additional species; Figure 20). Over the same period, the number of invasive non-native species increased by 24% (i.e. 26 additional species). Of the naturalised species, around 10% are likely to become impactful invasive species over time (Williamson & Fitter 1996).

Assessment Invasive species and range shifts

2021

Invasive species are one of the most prevalent threats to Australia’s ecosystems and biodiversity. The number of invasive species continues to climb. Some species benefit from background trends pressures such as climate and habitat change. These pressures are also driving changes in the distribution of native species, many of which are moving southwards, resulting in changes to community composition.
Assessments of impact range from low to high
Assessments of trend are deteriorating
Related to United Nations Sustainable Development Goal targets 13.1, 15.8

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Biosecurity and sources of invasive species

Biosecurity is Australia’s first line of defence against species and disease introductions. Overall, the rate of new weed detections is in decline, and the introduction rates for some groups, most notably invertebrates, are also declining in our region compared with other parts of the world, providing indirect evidence of the effectiveness of Australia’s biosecurity system. However, new threats continue to emerge. From 2012 to 2017, biosecurity incursions into Australia increased by almost 50% to 37,014 (CSIRO Futures 2020).

This cumulative burden of new and existing incursions is likely to continue to escalate in future years. A recent study has predicted that the number of established non-native species in Australia is likely to increase by 36% between 2005 and 2050 (Seebens et al. 2021).

More than 250 marine species have been introduced into Australia; however, this is likely to be an underestimate due to a lack of taxonomic clarity and monitoring (see Invasive species management). Only 4 jurisdictions (the Northern Territory, Queensland, Victoria and Western Australia) use active surveillance approaches for marine pests, and hence our capacity to assess the state or trajectory of this pressure is very low.

Eastern Australia is among 5 global regions considered most vulnerable to the establishment of new invasive species, originating mainly from Asia and America via people, trade and tourism (Bellard et al. 2016). South-eastern Australia is an invasion hotspot, and the rate of biosecurity incursions into Australia has been increasing in recent years. Annually, as at 2018, more than 18,000 vessels, 1.8 million sea cargo consignments, 41 million air cargo consignments, 152 million international mail items and 21 million passengers arrive in Australia, and numbers are growing every year (Inspector-General of Biosecurity 2019b).

Using data collated by the Atlas of Living Australia, it is clear that the numbers of introduced terrestrial species are higher in regions where more land is intensively used. By 2020, the total number of introduced species recorded since 1980 had increased at a greater rate in the extensive use zone (63% increase) than in the intensive use zone (18% increase). Non-native species may benefit from changing climatic regimes, changes in nutrient or water availability, and establishment opportunities following bushfires and other disturbances – for example, widening of transport routes and clearings for powerlines and fire breaks (Abbott et al. 2020, Seebens et al. 2021).

Impacts of invasive species

Invasive species affected the largest numbers of native species at risk of extinction, as listed under the EPBC Act, compared with other threatening processes, affecting 82% (1,257 of 1,533) of threatened taxa in Australia in 2018 (Figure 21). In total, 267 invasive species (207 plants, 57 animals and 3 pathogens) are listed as affecting Australian threatened taxa (Kearney et al. 2018). This includes 230 non-native species (187 plants, 41 animals and 2 pathogens) and 37 problematic native species (20 animals, 16 plants and 1 pathogen). The top 10 threatening terrestrial species are 7 vertebrate animals, 2 plants (blackberry and lantana) and 1 fungus (Phytophthora) that causes disease in plants.

The presence of invasive species can impact Indigenous people’s connection to Country through direct effects on native plants and animals, and all aspects of cultural landscapes, threatening the continuation of cultural knowledge and practices (Ens et al. 2015).

Terrestrial invasive animals

Threat abatement plans under the EPBC Act are in place for key threatening processes arising from feral cats, the European red fox, unmanaged goats, feral rabbits, feral pigs, cane toads, and exotic rodents on offshore islands (see Invasive species management).

The most commonly cited invasive species affecting Australia’s threatened species is the European rabbit (Oryctolagus cuniculus), which threatens 21% (322) of EPBC Act–listed species (Kearney et al. 2018). The feral cat (Felis catus), feral pig (Sus scrofa) and feral goat (Capra hircus) are cited as threatening more than 100 threatened species each. Feral cats are believed to have been a major factor in the extinction of the 30 Australian native mammal species lost since European settlement. There is no effective broadscale control method for feral cats, so they remain a major cause of decline of many Australian mammals (Legge et al. 2017). The feral pig is widely considered as one of the worst invasive species throughout its introduced range, particularly in the tropical north.

Feral vertebrate herbivores and livestock are an important threat to many species and ecological communities, as well as native vegetation broadly. Feral herbivore management is complex because many species have social and cultural value, and some are considered a resource by landowners, recreational and commercial hunters, and Indigenous communities.

Terrestrial invasive plants

Weeds are the most damaging category of pest in agriculture, and can displace native species and contribute to land degradation. Weed control is estimated to impose an overall average annual cost of nearly $5 billion across Australia; control in agricultural areas accounts for the majority of costs. About $300 million is spent each year on public weed control across national parks and Indigenous lands, and on weed research (McLeod 2018). The total annual cost of weeds (revenue loss plus expenditure) to Australian grain growers has been estimated at $3.3 billion (Llewellyn et al. 2016), and across all grain, beef and wool industries is nearly $5 billion (McLeod 2018).

Invasive grasses have been intentionally introduced to Australia since colonisation, mostly to support agricultural enterprises (Cook & Dias 2006, Setterfield et al. 2018). Some species have caused profound ecosystem impacts and conservation challenges (van Klinken & Friedel 2018). The environmental impacts of non-native invasive grasses are expected to continue to increase, with most still having relatively restricted distributions compared with their potential distribution. Invasive weed species impact how Traditional Owners use and manage their land. For example, the invasion of buffel grass (Cenchrus ciliaris) across arid Australia has impacted bush food collection and hunting, access to traditional lands, and ability to conduct traditional fire management. Further, it has had cascading negative effects on cultural transmission to younger generations and maintaining cultural practice.

Five particularly high-impact weed species primarily occur across northern Australia: gamba grass (Andropogon gayanus), para grass (Urochloa mutica), olive hymenachne (Hymenachne amplexicaulis), mission grass (Cenchrus polystachios syn. Pennisetum polystachion) and annual mission grass (Cenchrus pedicellatus syn. Pennisetum pedicellatum) ((TSSC 2021); Figure 22). Together, these grasses have been listed as a key threatening process under the EPBC Act because of their ability to alter nutrient cycling and water availability, and subsequently cause ecosystem degradation, habitat loss and biodiversity decline. Of particular importance is their capacity to increase fuel loads, resulting in intense fires.

Terrestrial invasive insects

Of particular concern are invasive insects, which can enter Australia through multiple pathways. Their association with a wide range of traded products and ability to endure adverse conditions during travel contribute to their invasiveness (McGeoch et al. 2020). Cut flower and foliage imports, along with plant nursery material and timber trade, are high-risk pathways for the introduction of invasive insects. Over the decade to 2017, for example, imports of cut flowers and foliage increased more than 3-fold, and detections of live insects at the Australian border increased from 13% to 58% of consignments (McGeoch et al. 2020).

Border interception records show that the vast majority of interceptions are of invasive invertebrates, such as tramp ants, which are highly invasive, and cause devastating environmental, economic and social impacts. Between 2001 and 2017, 20 serious tramp ant incursions occurred in Australia, including 16 incursions of red imported fire ants (Solenopsis invicta) (Inspector-General of Biosecurity 2019a).

Australia has the highest success rate globally in invasive ant eradications. For example, 5 out of 6 tropical fire ant infestations have been eradicated from Indigenous land in northern Australia, with eradication of the last likely to succeed in the next 12 months. Yellow crazy ants affecting remote Northern Territory communities have been removed from more than 1,000 hectares, with the risk for further spread eliminated (Hoffmann 2019). Some incursions, such as the red imported fire ant (Figure 23), pose such a high risk to people, industry and the environment that costly eradication measures are justified (Jansse 2017).

Diseases

Diseases, fungi and parasites can affect the health of native species, reducing their ability to reproduce or survive. New diseases caused by introduced pathogens are a particular concern for the agricultural and ornamental industries.

Disease can contribute to the decline and extinction of threatened species. For example, chlamydial disease is one of the main factors threatening the long-term survival of the Vulnerable koala (Phascolarctos cinereus). The population of the Endangered Tasmanian devil (Sarcophilus harrisii) has declined by up to 80% since the mid-1990s when the infectious and usually fatal cancer devil facial tumour was first detected. Devil facial tumour has now spread over 80% of Tasmania (Lazenby et al. 2020). One of the most devastating diseases affecting fauna over recent decades is amphibian chytridiomycosis, caused by the fungal skin pathogen Batrachochytrium dendrobatidis; at least 36 species of Australia’s 238 amphibians have declined, and 7 have become extinct due to the disease.

A large number of plant pathogens also occur in Australia. Myrtle rust (Austropuccinia psidii) is an invasive species of rust fungus that affects growing tissues of a wide range of species in the Myrtaceae family, including iconic Australian genera such as Eucalyptus, Corymbia, Melaleuca and Leptospermum. Although the national-scale impacts of myrtle rust are not fully understood, it has been shown to cause dramatic declines in 2 once-common Australian species (native guava – Rhodomyrtus psidioides, and scrub stringybark – Rhodamnia rubescens). These have subsequently been listed as Critically Endangered under the EPBC Act; the native guava is at very high risk of extinction, with only 1 surviving population that does not produce viable seed (Fensham et al. 2020).

Introduced species, diseases, outbreaks of pests and blooms of harmful algae can have substantial impacts on Australia’s marine species and habitats (Hallegraeff et al. 2021, Nowak & Hood 2021), as well as having direct and indirect impacts on human health and wellbeing. Although several major disease outbreaks, such as white spot disease (Queensland) and Pacific oyster mortality syndrome (New South Wales, South Australia and Tasmania), have occurred since 2016, the state of algal blooms, viral diseases, parasitic infections and mass die-offs is generally good and stable (Hallegraeff et al. 2021, Nowak & Hood 2021). Between 2016 and 2021, the overall pressures from diseases and infestations were low, although significant marine fish and other marine animal mortalities due to disease were regularly reported from most jurisdictions (Roberts et al. 2019, Readfern 2020, Young et al. 2020).

Range shifts and extensions

All living organisms have a range of temperatures and other environmental conditions in which they can live. Climate change, particularly in the form of local warming, stimulates and sometimes forces species to move, generally away from the equator towards cooler regions. Movement of native species and the occurrence of vagrants from nearby countries is a regular occurrence in Australia but may be increasing because of climate change (Davis & Watson 2018). As species extend their range poleward, they encounter new ecosystems that may not be used to their presence, changing the composition of communities, which can negatively impact the local ecosystem and cause loss of native species.

In coastal regions of northern Australia, crocodiles, with no natural predators, continue to both expand in numbers and increase their range, moving southwards. At least 198 Australian marine species have undergone long-term shifts in their geographic distributions since 2003, most of which (87.3%) have moved towards cooler waters (Gervais et al. 2021). Australian species such as the long-spine urchin (Centrostephanus rodgersii) can move into new areas and act like invasive or pest species, altering native ecosystems and processes, with economic and social impacts. Significant geographic shifts have occurred in the distribution of marine algae, including pathogenic and harmful algal bloom species. Some species may end up as far away as Antarctica. Rafts of non-Antarctic kelp, for example, carry a vast array of organisms and can drift very long distances into Antarctic waters. Invasive species pose a major risk of establishment in Antarctica and the subantarctic as climate change provides more favourable conditions.

Globally, 25–85% of marine species have been documented to be shifting, but little is known about the cumulative ecosystem-level impacts of multiple shifts. In addition to latitudinal shifts in species distributions, some species are thought to also be retreating to cooler, deeper waters; with increasing tidal height, intertidal species and ecosystems may also be shifting. However, these trends are largely unknown for Australian waters.

Climate change is also affecting the range of many plant species. For example, climate change is predicted to shrink the ranges of the majority of Australia’s eucalypt species over the next 60 years, and approximately 90% of the current areas with concentrations of highly restricted eucalypts is predicted to disappear (or shift location) (González-Orozco et al. 2016). The shrinking and shifting of the geographic ranges of eucalypts are likely to have significant flow-on effects for ecosystem structure and function, including for the many species that depend on eucalypts for food and shelter.

Much of Australia has limited water resources, and thus there is limited scope for freshwater species to move to more favourable conditions. Species losses under future climates are likely to be high, particularly in inland regions of Australia. In south-western Australia, a marked decline in winter rainfall since the 1970s, coupled with extensive habitat loss and fragmentation, threatens species that depend on wetlands and cannot migrate.

Some species might only persist if they can be introduced to wetter areas. ‘Assisted colonisation’ translocates species beyond their native range to mitigate a major threat, but this approach requires detailed risk analysis and should be considered an action of last resort because we cannot accurately predict the consequences of species introductions.