Indicator: LD-40 Current research into pressures and contributions of naturalised introduced species

Data

Naturalised species thought to be of environmental concern

Terrestrial Animals

Eight naturalised terrestrial animal species are listed as “key threatening processes”. Six of these are mammals and two are invertebrates (both ants). An additional four animal species are listed on the Department of the Environment and Heritage (DEH) website as being of “significant concern”: three more mammals and one amphibian. The nine listed species are:

Cat
Red fox
Rabbit
Goat
Pig
Rat (on small islands)
Red Fire Ant
Yellow Fire Ant
Horse and donkey
Camel
Cane toad

Current research has been compiled under National Threat Abatement Plans for cats, foxes, rabbits, goats and pigs. An advice paper on rats is available.

The two invertebrates, the Red Fire Ant and the Crazy Yellow Ant, have been listed as separate key threatening processes. However, a new Threat Abatement Plan, aimed at Tramp Ants more generally, is currently under development.

The current research that has been compiled on each of these species shows the following.

Rabbits: Rabbits have contributed to the decline in a number of other native plants and animals. There is some evidence that they may have caused the extinction of several small ground-dwelling mammals of Australia's arid lands.

Foxes: Foxes may have played a role in the decline of some species. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Cats: Convincing evidence that feral cats exert a significant effect on native wildlife on the mainland, or in Tasmania, is scarce. There is no evidence of feral cats causing extinctions in mainland Australia or Tasmania.

Goats: Feral goats may be responsible for a variety of impacts on native flora and fauna. Destruction of vegetation is also thought to cause soil erosion. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Pigs: There are few quantitative data on actual environmental impacts of feral pigs. The relationship between feral pig density and level of environmental damage is also unknown. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Rats: Introduced rats are only considered to be a key threatening process on islands of less than 1000 K². When rat numbers are high, the removal of seeds by exotic rats may be a threat to the survival of the plant species concerned. Rats may have had adverse impacts on a number of native species including ground-nesting seabirds, reptiles and molluscs.

Tramp ants: Fire ants have the potential to threaten the survival and abundance of native fauna, particularly invertebrate species. The species occurs mostly in areas of disturbance such as lawns, pastures, roadsides, and agricultural lands or open natural areas such as grasslands or open forests. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Source: Department of the Environment and Heritage 2006, National Threat Abatement Plans, viewed 18 May 2006, http://www.deh.gov.au/biodiversity/threatened/tap/index.html

Threat Abatement Plans

Current research has been compiled for DEH Fact Sheets for cane toads, horses and donkeys, camels and water buffalo.

Horses and donkeys: These species can cause erosion and damage vegetation and waterholes with their hard hoofs, and to introduce weeds through seeds carried in their dung, manes and tails. Feral horses and donkeys may also compete for food and water with native animals. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Camels: Camels are capable of severely damaging native trees when they gather in large numbers. However, at their normal low density, feral camels do not appear to have a major impact. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Water buffalo: This species has been all but eradicated from the wild in Australia. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Cane toads: Cane toads can harm native wildlife by eating small animals and poisoning larger predators that try to eat them. Adult cane toads may compete with native animals for food (particularly insects) and shelter. There does not appear to be any evidence that they have caused or contributed to the extinction of any Australian species.

Source: Department of the Environment and Heritage 2006, Invasive Species, viewed 18 May 2006, http://www.deh.gov.au/biodiversity/invasive/index.html

Invasive Species

Presumably these nine species do not represent a comprehensive list of naturalised animal species. However, compilations of research on the naturalisation and potential impacts of non-mammalian vertebrates and of invertebrates appear to be scarce.

Terrestrial Plants

About 3000 species of non-native plants have established naturalised populations in Australia. Of these, the National Weeds Strategy has identified some twenty species as being “of national significance”. All of these are regarded as posing some threat to endangered species or plant communities.

Weeds impacts (PDF - 41 KB)

The following table lists native species of plant and animal that are believed to be under threat from various introduced plants.

Australian flora and fauna threatened by invasive plants
State and Territory	Threatened flora and fauna	Weeds
Tasmania	tussock skink (Pseudemoia pagenstecheri)	gorse (Ulex europaeus)
NSW	zieria prostrata (Zieria prostrata) austral toad-flax (Thesium australe)	bitou bush (Chysanthemoides monilifera ssp rotundata)
NSW	Cumberland Plain Woodland pink pimelea (Pimelea spicata)	bridal creeper (Asparagus asparagoides)
NSW	hairy quandong (Elaeocarpus williamsianus )	lantana (Lantana camara)
NSW and Victoria	mountain pygmypossum (Burramys parvus)	English broom (Cytisus scoparius ssp scoparius) blackberry (Rubus fruticosus L agg)
Victoria	sunshine diuris (Diuris fragrantissima)	Chilean needlegrass (Nassella neesiana)
Victoria	Eltham copper butterfly (Paralucia pyrodiscus lucida)	Cape broom (Genista monspessulana) radiata pine (Pinus radiata) quaking grass (Briza maxima)
SA	common white spider orchid (Caladenia argocalla)	topped lavender (Lavandula stoechas) soursobs (Oxalis pescaprae) St John's wort (Hypericum perforatum) Cape tulip (Moraea flaccida) gorse (Ulex europaeus) hawthorn (Crataegus monogyna) watsonia ( Watsonia meriana var bulbillifera )
SA	Blue gum woodlands (Eucalyptus leucoxylon) Metallic Sun Orchid (Thelymitra epipactoides)	perennial veldt grass (Ehrharta calycina)
Qld and NSW	Richmond birdwing butterfly (Ornithoptera richmondia)	Dutchman's Pipe (Aristolochia elegans)
Qld	aponogeton queenslandicus (Aponogeton queenslandicus)	para grass (Brachiaria mutica) Hymenachne (Hymenachne amplexocaulis)
Qld	jabiru ( Ephippiorhynchus asiaticus australiensis)	Para grass (Brachiaria mutica) Hymenachne (Hymenachne amplexocaulis)
Qld	Brolga Park zieria ( Zieria sp. “Brolga Park”)	Lantana (Lantana camara)
Qld	Proserpine rock wallaby (Petrogale persephone)	pink periwinkle (Catharanthus roseus) rubbervine (Cryptostegia grandiflora)
WA	wing-fruited lasiopetalum ms (Lasiopetalum pterocarpum)	watsonia ( Watsonia meriana var bulbillifera ) blackberry (Rubus aff. selmeri) gladioli ( Gladiolus undulates)
NT	yellow chat (Epthianura crocea tunneyi)	mimosa (mimosa pigra)
ACT and NSW	button wrinkewort (Rutidosis leptorrhynchoides)	introduced pasture grasses

Source: CRC Weed Management 2006, facts and figures - environmental and agricultural weeds, viewed 12 Jul 2006, http://www.weeds.crc.org.au/main/facts_figures.html

Virus, bacteria and fungus

Some bacteria, fungi and viruses are considered to be of environmental concern because of their impact on native species. However, it is often not clear whether these species are endemic or naturalised.

Psittacine beak and feather disease: Psittacine Circoviral (beak and feather) Disease affects the parrot family (psittacines). In circumstances where bird populations have been dramatically reduced, such as in endangered species, the disease may have the potential to cause catastrophic losses. There is no evidence that the disease is a threat to the survival of psittacine species which are not endangered.

Chytrid amphibian fungus: This is an infectious disease affecting amphibians worldwide, including four regions of Australia. It is a highly virulent fungal pathogen of amphibians capable at the minimum of causing sporadic deaths in some populations, and 100% mortality in other populations. It is not currently known whether the fungus is exotic or native to Australia.

Root-rot fungus: A threat of epidemic exists where dominant species of particular plant communities are inherently susceptible to P. cinnamomi root-rot and those communities are in areas where environmental conditions favour the pathogen, resulting in: major disruption of community structure; extinction of populations of some flora species; modification of the structure and composition of ecological communities; a massive reduction in primary productivity; and, for dependent flora and fauna, habitat loss and degradation.

Mundulla Yellows: No data found

Source: Department of the Environment and Heritage 2006, Invasive Species, viewed 18 May 2006, http://www.deh.gov.au/biodiversity/invasive/index.html

Invasive Species

Research separating impact of naturalised species from other environmental influences

There is considerable evidence that naturalised species are most likely to behave invasively in environments that have been modified in ways that favour them while excluding native species.

For example, two Australia Bird Atlas surveys reviewed by Garnett et al. (2002) show that the relative abundance of introduced bird species is a measure of habitat alteration. The highest abundance of introduced bird species occur in the extensively modified parts of south-east Australia and eastern Tasmania where they now make up 15% of all species.

At present there is little research which attempts to eliminate other variables, such as habitat modification, when attempting to assess the impact of naturalised species on native species.

Source: Garnett, S.T, Crowley, G. M. and Barrett, G.B. 2002, Birds, In "Australian Terrestrial Biodiversity Assessment", Commonwealth of Australia, Canberra.

Research into role of naturalised species in ecosystems

Research into the role of introduced populations when they become naturalised into native ecological communities, and studies of the ecological consequences of removing or significantly reducing them, once naturalisation has occurred, also appear to be scarce.

Some work was done in the late 1980s, early 1990s, on the relationship between naturalised predator and prey species. Existing research agrees that rabbits provide between 70 and 90 per cent of the diet of foxes and wild cats. Pech et al (1992) found that foxes can regulate rabbit populations. In another study by Newsome and Coman (1989), after a crash in the rabbit population, cats and foxes were removed in one area and left in another area. In the area where they were removed, rabbit numbers increased eightfold in 12 months.

Source: Pech R P, Sinclair A R E, Newsome A E and Catling P C, 1992, Limits to predator regulation of rabbits in Australia: evidence from predator removal experiments, Springer-Verlag.

Source: Newsome A E & Coman B J 1989, Some introduced mammalian pests of the Mallee, proceedings of the National Mallee Conference.

There has been little investigation of the role of naturalised prey species in the diet of native predators, or of the role of naturalised predators in regulating native prey species, especially in areas where native predators have declined. One exception was a Birds Australia study, commissioned by DEH in 1998, of the impact on birds of prey of the reduction of rabbit populations, due to the introduction of Rabbit Calicivirus Disease (RCD). Controlling for seasonal influences, the study showed that, in all monitored areas where RCD had been successful in reducing rabbit populations, there was also a decline in all birds of prey populations - not just rabbit eating birds of prey. This implied that prey switching by the rabbit eaters had caused a substantial reduction in all available prey. However, no studies were undertaken of the impacts on native prey populations.

Source: Birds Australia 1998, Monitoring the impact of rabbit calicivirus disease on the abundance, movements and concentrations of Australian Birds of Prey.

Studies of more complex ecosystem effects of naturalisation processes are even more rare. A recent report prepared for DEH under the Natural Heritage Trust, by the Victorian Department of the Environment and Sustainability and CSIRO Sustainable Ecosystems, reviewing the evidence of the interactions between cats, rabbits and foxes, found that, “the impact of changes in predators and their primary prey on native mammal species has been the focus of few experimental studies. Studies that have discussed the role of foxes and feral cats in regulating rabbit populations have largely not investigated the benefits or costs of predator control to native species. Other studies that have investigated the impact of fox and cat control on native mammal species have reported benefits from pest control; however, there are many acknowledged limitations of these studies. While several studies have reported that fox removal has benefited a range of native species, many have not assessed pre-control population parameters, do not have control sites, are not replicated, and have not attempted to test alternative hypotheses to predation, such as competition by herbivores.”

Source: Robley, A, Reddiex, B, Arthur T, Pech R, and Forsyth, D 2004, Interactions between feral cats, foxes, native carnivores, and rabbits in Australia, Department of Sustainability and Environment, Melbourne.

Interactions between feral cats, foxes, native carnivores, and rabbits in Australia (PDF - 904 KB)

What the data mean

Research and abatement action in relation to naturalised animal species appears to have focused on a very small selection of highly visible and predominantly mammalian species. The collated evidence of the adverse impacts of these species is often surprisingly inconclusive.

There seems to be relatively little research available on naturalised invertebrates and non-mammalian vertebrates. Tramp and cane toads are notable exceptions.

A relatively small selection of a very wide range of naturalised plant species are identified as being of environmental concern, although, as for animals, studies generally do not control for other factors that may be influencing the expansion of some species and accompanying decline of others, or for the adverse impacts of removing species once they have become naturalised.

Very few of a wide range of bacteria, fungi and virus, existing at large in Australia, appear to have received much attention and, where they have, it is not always clear whether these species are native or introduced.

Studies aimed at isolating the impacts of naturalised species from the impacts of other environmental pressures, and studies of the interactions and interdependencies between native and naturalised species, are extremely rare.

Data Limitations

In the absence of more meaningful indicators and data on the actual effects of introduced species on the environment, collated research is the only source of insight available into the ways in which naturalised species are likely to affect native Australian ecological communities.

Indicators need to be developed that will enable assessment of the actual pressures, if any, being exerted by naturalised populations on ecological communities, controlling for other pressures such as natural fluctuations, habitat modification, pollution, and climate change. Indicators are also needed for assessing the pressures which may be exerted on ecosystems by the removal of a species once it has become naturalised.

Ways of collecting and collating these data at the continental level would then be needed in order to make a meaningful assessment.

Issues for which this is an indicator and why

Land - Direct pressure of human activities on the land - Species introduction and species change

To learn whether naturalised populations are exerting pressure on the terrestrial systems that maintain the condition of the land, it is necessary to eliminate any extraneous pressures which may be the common cause of both the proliferation of the introduced species and any contemporary damage to ecosystems. Current research into the both the role and pressures on naturalised species may provide some useful insights into the kind of indicators and data that are needed to inform on this issue.