Invasive species and pathogens

2011

 

Invasive species are one of the two most frequently cited pressures for EPBC-listed species (the other being fragmentation of habitat).15 Invasive species and pathogens include plants, animals, fungi and a range of pathogenic microorganisms; their significance and impacts are also discussed in Chapter 5: Land.

Weeds

Invasive plants (weeds) affect biodiversity in many ways: they may outcompete native plants, they may reduce or alter the resources available to native animals and they may markedly affect fire regimes. In 2007, more than 2800 of the 27 000 alien plant species that had been imported into Australia had become established in the wild, and that number was growing at around 10 species per year.120 The number is now much higher. As part of the National Land & Water Resources Audit phase II, the jurisdictions mapped 98 major weeds nationally.121 Of these 98 species, 20 are Weeds of National Significance (WoNS). The remaining 78 are either candidate WoNS, on the national environmental alert list, targets for biocontrol (control of an invasive species by other species, usually by the managed introduction of predators or pathogens), or a combination of these three categories.

As with many threatening processes, the mechanisms by which weeds have impacts are poorly defined, and processes for determining which species they affect and their relative importance compared with other pressures are inconsistent and often unclear.88,122 Scott and Grice122 recently reviewed the state of research on weeds in Australia. Since 1995, the number of quantitative studies of the impact of weeds on the Australian environment has more than doubled to more than 70 studies, covering 30 species. Most studies show that weeds reduce plant biodiversity by reducing native species richness and changing community composition and structure. Weed invasion is considered to be a threatening process for one-third of rare species in Australia. Scott and Grice conclude that the measures currently adopted to understand the invasion of weeds in Australia are not at the level required to plan strategies to mitigate the problems they create.

Invasive fungi

Many introduced fungi have become established in Australian ecosystems, especially in soils. Several are known to have become invasive species, and the list is likely to grow in the future as a result of more research and as climate changes. Three invasive fungi are of particular concern nationally: chytrid amphibian fungus (Batrachochytrium dendrobatidis), myrtle rust (Uredo rangelii) and Phytophthora cinnamomi.123

The chytrid fungus124 has been responsible for mass deaths of frogs worldwide and is widespread in Australia. A significant association between amphibian declines in upland rainforests of northern Queensland and three consecutive years of warm weather125 suggests future warming could increase the vulnerability of frogs to the fungus.

Myrtle rust is of particular concern, because it affects a wide range of plant species in the Myrtaceae family of plants, including Australian natives like bottlebrush (Callistemon spp.), tea tree (Melaleuca spp.) and eucalypts (Eucalyptus spp.).126 There are fears that this emerging invasive species could transform the Australian environment in major ways, especially if its impacts are magnified by climate change.

Phytophthora cinnamomi is a rootrot fungus that attacks a range of native plants as well as crops. It is a particular problem in Tasmania and Western Australia, but is more widespread nationally and is likely to become an even bigger problem as soil warms with climate change in the future.127

Invasive animals

The most significant invasive vertebrate animal species are the European fox (Vulpes vulpes), domestic cat (Felis catus), European rabbit (Oryctolagus cuniculus), feral goat (Capri hircus), feral pig (Sus scrofa) and cane toad (Bufo marinus). Significant invertebrate invasive species include the red fire ant (Solenopsis invicta), the yellow crazy ant (Anoplolepis gracilipes) and a range of tramp ant species.128 European wasps, bumblebees and European honeybees are also widely cited species of concern. Asian honeybees are a recent threat that appears to have potential for major impacts (Box 8.5).

Box 8.5 Emerging threats from Asian honeybees

In March 2011, Dr Denis Anderson, a principal research scientist with Ecosystem Sciences, Commonwealth Scientific and Industrial Research Organisation (CSIRO), gave evidence to a Senate Inquiry into our inability to eradicate the Asian honeybee.129

The Asian honeybee, Apis cerana, made a recent incursion into Cairns. The incursion originated in New Guinea, where the bees were introduced in the late 1980s.By the mid-1990s they had become established throughout the whole island of New Guinea, including many offshore islands, and by 2003 had apparently spread 1000 kilometres east to the Solomon Islands. Since 1995, 10 swarms of Asian honeybees have been intercepted and destroyed on vessels at Australian seaports. A further two swarms have penetrated Australia’s quarantine barrier: at Darwin in June 1998 and at Cairns in May 2007. The Darwin incursion was eradicated, but an attempt to eradicate the Cairns incursion is still ongoing. To date, more than 350 colonies of the bee have been detected and destroyed in Cairns.

Not only do these bees compete with native bees, but they can also carry pathogens—including the varroa mite, which is lethal to European honeybees. (European honeybees are the backbone of the Australian honey industry and play a key role in pollinating some crops.) The presence of the bee in Cairns has already led to the suspension of trade in live bees between the United States and Australia, valued at some $5 million annually, and other trade impacts are emerging. If Asian honeybees become widespread as they have elsewhere, there is likely to be a number of major impacts on Australia, including (in order of the most to least importance): the environment and biodiversity, the beekeeping industry, human health and society, pollination and trade.

Invasive species affecting inland aquatic environments

A wide range of invasive species affect inland aquatic environments, including non-native freshwater fish species (which represent more than a quarter of the total number of fish species in river systems), feral pigs, the cane toad, red-eared slider turtles and around 10 major invasive plant species nationally (see Chapter 4: Inland water for details).

3.9.5 Marine invasive species

Many marine pests are introduced to Australian waters in ballast water discharged by commercial shipping, biofouling on hulls, aquaculture operations and aquarium imports, as well as marine debris and ocean currents.130 Viruses and a range of invertebrates, including starfish, algae, plankton, molluscs, crustaceans and worms are of high concern in some regions but not others (see Chapter 6: Marine environment for details).

Jurisdictional reporting on invasive species and pathogens

The Assessment of Australia’s terrestrial biodiversity 2008 concluded that data on invasive species is poor nationally but good for some case studies.15Table 8.22 summarises reports from Australian states and territories on invasive species and pathogens.

Table 8.22 Effects of invasive species on biodiversity reported in recent state of the environment reports by the states and territoriesa
Jurisdiction/scale Summary
ACT A wide range of pest plants is established in the territory and some have harmful impacts on native vegetation and biodiversity. Especially after the 2003 fires, control of pest plants, such as exotic grasses, woody weeds, willows and blackberry, continues to be a major task for land managers
Established pest animals include mammals (feral cats, goats, pigs and deer, as well as foxes, rabbits, wild dogs and small numbers of feral horses), fish (carp, oriental weatherloach, redfin, goldfish), birds (common myna, common blackbird, common starling) and insects (European wasp)
Under continuing dry conditions, management of eastern grey kangaroo populations on some land in the ACT has become a contentious issue
NSW Pressures are generally increasing, especially in fragmented landscapes
Invasive species form the second most pervasive threat to native vegetation, affecting 90% of all classes, an increase from 75% in 2006. This threat has intensified due to invasion and establishment of weeds and diseases in new areas
Invasive species, especially foxes and cats, and habitat loss are the two major threats to vertebrate fauna
NT Although native plants dominate most of the landscape, exotic plants are now a major component of some environments, with 13 of the 20 WoNS either already found in the territory or representing a serious threat: alligator weed, athel pine, cabomba, olive hymenachne, lantana, mesquite, mimosa, parkinsonia, parthenium weed, pond apple, prickly acacia, rubber vine and salvinia
Many exotic animal species present serious threats to native species and environments. Cattle and feral animals, such as camels, donkeys, pigs, horses and buffalo, can cause widespread damage through fouling waterholes, selectively grazing and damaging vegetation, spreading declared weeds or ecologically invasive plants, trampling the nests of ground-dwelling animals, and causing erosion
Some feral animals have direct impacts on native species: foxes and feral cats contributed to the extinction of Central Australian mammals and continue to impact a range of other species; competition from rabbits is thought to have caused the demise of the burrowing bettong; poisoning by cane toads appears to have led to local extinctions of the northern quoll; and infestations of crazy ants and big-headed ants have caused significant losses in invertebrate diversity
These threatening processes operate across lands of all tenures
Qld Terrestrial pest animals and invasive terrestrial plants (weeds) cost the state at least $110 million and $600 million a year, respectively
Invasive animals and plant pests have become established in inland waters, but there are no recorded established invasive marine pests
SA Invasive species, including vertebrates, invertebrates, plants, algae and fungal, bacterial and viral pathogens, pose current and potential threats in terrestrial, riparian and marine environments statewide. Some invasive species can irreversibly transform ecosystems by changing water, nutrient, soil and/or fire cycles
Invasive animal species are estimated to be common and widespread over the following percentage areas of SA: rabbits 86%, foxes 56%, feral deer 1%, feral camels 35%, feral goats 11%, wild dogs (including dingoes) 48%, feral cats 60% and starlings 11%
Abundance of rabbits, feral cats, camels and feral goats is increasing; abundance of foxes is decreasing and feral pigs is stable; marine pests are stable; distribution of feral olives and silverleaf nightshade is increasing; distribution of blackberry is stable; boneseed is declining
The total cost of weeds is over $600 million per year
Tas Weeds are among the most serious threats to Tasmania’s natural biodiversity. In 2007, around 30% of the 2626 known plant species in the state were weeds. Several diseases of plants are having major impacts: the introduced soilborne rootrot disease Phytophthora (cinnamon fungus) is a major threat to the health of native vegetation; the naturally occurring pathogenic  fungus myrtle wilt attacks mature myrtle beech trees; and Armillaria rootrot fungus attacks eucalypts
There are limited data for introduced animal species and native animal diseases. Of 447 introduced animal species, 34 vertebrates and 13 invertebrates are considered key environmental pests. Cats are a major problem, and foxes have been introduced recently and are spreading. Introduced invertebrates pose a significant but unknown threat to plants, animals and ecosystems. Introduced diseases are also affecting native animals (Tasmanian devils, platypus, seals and other mammals, frogs and birds)
Vic The total cost of pest species is around $900 million per year
Exotic species represent around 30% of the state’s flora (this is 1.7 times the number in 1984)
Foxes and rabbits are widespread, but wild dogs and feral pigs are absent or unknown over large areas. Wild dogs occur mainly in East Gippsland and the north-east, as well as in the southern Mallee, while feral pigs are localised to relatively small areas, mostly in the east. Pest animals are monitored locally but no statewide data exist
WA More than 1200 recognised weed species occur in the state, with the Swan Coastal Plain and the Jarrah Forest in the south-west having the highest number (700–800 identified species)
11 of the 20 WoNS are present and an additional 7 weed species pose an imminent threat
The distribution and abundance of cats and pigs increased between 2000 and 2005, and the population of camels in the central deserts is large and rapidly increasing. Improved monitoring is needed to determine the extent and density of introduced animal species
National See Box 8.6

ACT = Australian Capital Territory; NSW = New South Wales; NT = Northern Territory; Qld = Queensland; SA = South Australia; Tas = Tasmania; Vic = Victoria; WA = Western Australia; WoNS = Weeds of National Significance

a Sources are the same as for Table 8.5

Invasive species affect all tenures. In New South Wales, for example, it is estimated that around 18% of national parks are affected by weeds and 36% by pests.35Figure 8.15 shows the coincidence between invasive species and threatened species across Australia (compare Figure 8.15 with Figures 8.5, 8.6, 8.8 and 8.9).

Examples of the impacts of invasive species are given in Box 8.6.

No institutions currently conduct ongoing assessments of the impacts of weeds on biodiversity, but data are collected and action taken in particular cases where the impact can be mitigated or where important assets are threatened.120 The National Weed Incursion Plan (NWIP) is an operational plan and guideline for managing national responses to weed incursions.137 Application of the NWIP is triggered by the detection of a high-risk weed species. The NWIP sits within the Australian Biosecurity System (AusBIOSEC) framework and provides the essential steps required to execute a response to a high-risk weed incursion.

Box 8.6 Impacts of invasive species

Biodiversity benefits from managing feral animals

Removing grazing livestock, trapping feral predators and building feral-proof enclosures are proving to be highly valuable mechanisms for halting local biodiversity decline. Australian Wildlife Conservation enclosures have shown 4–7-fold increases in targeted marsupial populations at the 5000-hectare Yookamurra and 8000-hectare Scotia sanctuaries in South Australia, and at the 40 000-hectare Mornington Wildlife Sanctuary in the Kimberley, after the removal of introduced herbivores.a, 131. These examples show that active land management can increase the diversity and abundance of small mammals. Mornington Wildlife Sanctuary is the only protected area in northern Australia where a recovery in mammal populations has been recorded. Similar observations are seen for island introductions for northern quolls onto Astell and Pobassoo islands in the Northern Territory132 and bandicoots onto Faure Island off Western Australia.a. Feral trapping has also led to significant, but so far limited, local successes in marsupial populations through the ‘Ark’ projects in Victoriab,133 and the Western Shield Fauna Recovery program in Western Australia.134

Rabbit grazing and native shrub regeneration

Several studies have shown that even quite low rabbit population densities can significantly prevent native shrub regeneration. Recruitment of arid zone acacias and other arid zone shrubs is significantly affected by low post-myxomatosis135 and post-rabbit calicivirus disease136 population densities to the point where near nil recruitment was observed.

The Australian Terrestrial Biodiversity Assessment 200815 commissioned eight case studies to show the effects of invasive species and pathogens on biodiversity, and to highlight examples where the threats are expanding and impacting on relatively common species. The key messages from these case studies were as follows:

Invasive species and pathogens represent one of the most potent, persistent and widespread threats to Australian biodiversity. They have both a direct negative impact on species and communities through losses and extinctions, and an indirect impact on ecosystems and biodiversity through ecological changes brought by those losses and extinctions.

  • Invasive species and pathogens alter entire ecosystem compositions and have directly led to extinctions in most bioregions of Australia.
  • These losses include loss of entire species from mainland Australia and their contraction to neighbouring islands where the particular invasive threat is not established.
  • Establishment and persistence of invasive species and pathogens are promoted by a range of other threats, including fire, all forms of disturbance and climate change.
  • There are major gaps in our understanding of the impacts of invasive species and pathogens on biodiversity.

The interaction between invasive species and other pressures not only make it very difficult to assess separately the impact of invasive species, but also means that strategies to address invasive species are unlikely to succeed unless they also address other interacting pressures.

Cork S (2011). Biodiversity: Invasive species and pathogens. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/8-biodiversity/3-pressures/3-9-invasive-species, DOI 10.4226/94/58b65ac828812