Summary of assessment: Invasive vertebrate pests cause decline in the population size and distribution of many threatened species, making local extinctions likely in the absence of effective control measures. In particular, rabbits are having an adverse impact on the species through direct competition and habitat destruction.
The Committee judges that this threatening process is adversely affecting many listed threatened species.
Competition, predation or herbivory and habitat degradation by invertebrate pests Of the invasive invertebrates in Australia, seven are nominated by the IUCN as among 100 of the world’s most invasive species. These include Argentine ant (Linepithema humile), big-headed ant (Pheidole megacephala), common wasp (Vespula vulgaris), yellow crazy ant (Anoplolepis gracilipes), flatworm (Platydemus manokwari), electric ant (Wasmannia auropunctata), and red imported fire ant (Solenopsis invicta) (Lowe et al., 2000).
If introduced to Australia the Asian gypsy moth (Lymantra dispar) has the potential to have wide-ranging impacts on threatened species and ecological communities. The Asian gypsy moth has polyphagous larvae (feeds on many types of plants) and has been shown to feed on a wide variety of Australian native trees including many endemic species with restricted distributions such as the endangered Eucalyptus gunnii subsp. divaricata from Tasmania (Matsuki et al., 2003). If introduced this moth could have severe consequences on native vegetation, and fauna species’ food supply and habitat.
The European wasp (Vespula germanica), and the English wasp (Vespula vulgaris) were first recorded in Tasmania in 1959 (Goodisman et al., 2001) and 1995 (Matthews, 2000) respectively. European and English wasps are voracious predators with selective appetites, and cause serious impacts on native species by preying on them and out-competing them for food (Matthews, 2000; Goodisman et al., 2001). Wasps also compete with insectivorous and nectivorous birds that depend on insects to feed nestlings. If wasps become established in the vicinity of the Tasmanian nesting areas of the nationally listed critically endangered Neophema chrysogaster (orange-bellied parrot) and endangered Lathamus discolor (swift parrot) they could threaten their reproductive success.
Feral honey bees (Apis mellifera) and bumblebees (Bombus terrestris) have had a major impact on native bees and native Australian plants through disrupting their breeding and seeding systems and on native birds and animals, through competing for nectar and occupying tree hollows (Paton, 1996). Asian honeybees (Apis cerana) detected in Cairns in 2007, if it establishes in Australia is likely to have a significant impact on native species. Asian honey bees are recorded from other countries as hollows and nesting cavities in trees and also build up rapidly competing vigorously for nectar and pollen resources (QDPI&F, 2010).
Feral honey bees are having an impact on all obligate hollow nesting birds in south west of Western Australia (Johnstone and Kirkby, 2007). Bumblebees have naturalised in Tasmania after a suspected deliberate introduction from New Zealand for horticultural purposes (Semmens et al., 1993; Hingston, 2006). In Tasmania bumblebees are active at low temperatures and compete with native bees and nectivorous birds. If bumblebees were to be introduced to mainland Australia they would pose a threat particularly in Western Australia to the critically endangered native bee Neopasiphae simplicior as well as native bird species by competing for pollen, nectar and habitat (Hingston and McQuillan, 1998).
In Australia, ants are the dominant terrestrial invertebrate, occurring in all habitats and fulfilling a crucial role in the environment as predators, prey, pollinators, seed dispersers and soil aerators (Lach and Thomas, 2008). Invasive ant species, such as the red imported fire ant, electric ant, Argentina ant and big-headed ant, have a major impact on native ant species by displacing them and out-competing them for resources (Lach and Thomas, 2008; Callan and Majer, 2009). Replacement of native species by invasive exotic ants impacts on biodiversity by not fulfilling the roles of the native ants and changing the environment. Invasive ant species also impact on other wildlife, such as quail and turtles, by attacking them and their nests (Moloney and Vanderwoude, 2002).
Two invasive exotic ant species are listed as KTPs under the EPBC Act including ‘The reduction in the biodiversity of Australian native fauna and flora due to the red imported fire ant, Solenopsis invicta (fire ant)’ and ‘Loss of biodiversity and ecosystem integrity following invasion by the Yellow Crazy Ant (Anoplolepis gracilipes) on Christmas Island, Indian Ocean'.
For this nominated group of novel biota that impact on biodiversity, yellow crazy ant is provided as one example to further detail the impact of invertebrate pests.
Yellow crazy ant (Anoplolepis gracilipes) The yellow crazy ant has been introduced across the tropics and subtropics as a by-product of human commerce. It invades urban, agricultural and native ecosystems where it can have catastrophic impacts. These impacts include decimation of endemic species, changed habitat structure and resource availability, loss of biodiversity and altered ecosystem processes (Abbott, 2005). The primary threatening process from the yellow crazy ant results from its propensity to establish large populations, rapid spread, association with outbreaks of scale insects, and its broad foraging range and generalist feeding habits.
The yellow crazy ant is known to kill invertebrates, reptiles, hatchling birds and small mammals. On Christmas Island the yellow crazy ant is an environmental pest that directly threatens the conservation value of this isolated oceanic island. A number of species of endemic fauna including land crabs, mammals, birds, and reptiles are at risk either directly through predation or indirectly through habitat alteration or resource depletion (DEWHA, 2005d).
The yellow crazy ant is an aggressive opportunist species capable of invading and rapidly colonizing a wide range of both disturbed and undisturbed habitats. On Christmas Island, supercolony formation by the yellow crazy ant has resulted in the local extirpation of the endemic Gecarcoidea natalis (red land crab) (Abbott, 2005). An estimated 15–20 million red crabs have been killed since crazy ant supercolonies were first noted in 1989 (O’Dowd et al., 1999). Elimination of this keystone species from large areas of the island has resulted in a rapid shift in forest structure and composition. Mutualism between the yellow crazy ant and introduced or cryptogenic scale insects can also result in scale insect outbreaks and dieback of the forest canopy. Ant invasion causes major alterations in composition and structure of the forest.
On Christmas Island, yellow crazy ants cause a “state change” in the rainforest ecosystem. By eliminating the red land crab, which is the major seed, seedling and litter consumer in the island rainforest, the yellow crazy ant affects the rate of seedling recruitment and litter breakdown, altering the recruitment dynamics of rainforest trees and almost certainly changing patterns of nutrient availability (O’Dowd et al., 2001, pp 447–450). Outbreaks of sap-sucking scale insects associated with yellow crazy ants stress trees and lead to decreased seed production and high mortality in some canopy species. Furthermore, seed dispersal by endemic birds such as Zosterops natalis (Christmas Island white-eye), Turdus poliocephalus erythropleurus (Christmas Island thrush) and Chalcophaps indica natalis (Christmas Island emerald dove), may be compromised in yellow crazy ant supercolonies.
The endemic red land crab provides ‘biotic resistance’ to a wide range of potential alien invaders. Extirpation of the red crab from the ecosystem in areas of yellow crazy ant supercolonies facilitates ‘follow-on’ invasions of the giant African land snail (Achatina fulica) and a variety of environmental weeds (O’Dowd et al., 1999; Abbott, 2005). Table 2 shows species listed as nationally threatened under the EPBC Act that have yellow crazy ant listed as a threat to their ongoing survival.
Table 2: EPBC Act listed species that list yellow crazy ants as a threat.