Pest species and pathogens

2016

Pest plants, pest animals and pathogens have been identified by every state and territory as a key threat to biodiversity generally, and to threatened species specifically. Almost all states and territories also note that data on the distribution and abundance of pest plants and animals, and management effectiveness for these pests are poor. For states that provide assessment grades similar to those used by the Australian Government, the state for pest plants and animals is considered poor to very poor, and the trend is deteriorating (South Australian natural resource management [NRM] report card, Victorian SoE, Australian Capital Territory SoE). Similar concerns have been raised regarding lack of data on pest plants and animals on much of the Indigenous estate. In general, landowners or land managers are legally responsible for the control of pest plants and animals, which can create an onerous demand on resources. In particular, many Indigenous land managers, with the notable exception of Land and Sea Rangers, have inadequate capacity to meet that obligation.

The impact of invasive species is the most frequently cited threat to EPBC Act–listed species. Of the 21 key threatening processes listed under the EPBC Act, 12 describe declines in native species and/or ecological communities caused by 1 or more invasive taxa, including cats, rabbits, goats, rats, cane toads, foxes, feral pigs, gamba grass, escaped garden plants, red imported fire ants and yellow crazy ants. A further 3 are concerned with threats arising from pathogens—the rootrot fungus Phytophthora cinnamomi; psittacine circoviral (beak and feather) disease, affecting endangered parrots; and chitrid fungus disease, affecting amphibians.

In February 2013, novel biota were listed as a key threatening process under the EPBC Act. The key threatening process listing covers 6 major groups of novel biota and associated processes that are affecting biodiversity:

  • competition, predation, or herbivory and habitat degradation by vertebrate pests
  • competition, predation, or herbivory and habitat degradation by invertebrate pests
  • competition, habitat loss and degradation caused by terrestrial weeds
  • competition, habitat loss and degradation caused by aquatic weeds and algae
  • competition, predation, or herbivory and habitat degradation by marine pests
  • mortality, habitat loss and degradation caused by pathogens.

Novel biota encompass those invasive taxa that are separately listed as key threatening processes, as well as other novel biota that are already established in Australia and species with the potential to become invasive in the future.

In April 2014, ‘Aggressive exclusion of birds from potential woodland and forest habitat by overabundant noisy miners (Manorina melanocephala)’ was listed as a key threatening process. The native noisy miner has benefited from extensive fragmentation of woodland habitat with high edge:interior ratios and is considered a pest species. Noisy miners live in large colonies and, in areas where they are abundant, aggressively defend their territory by physically attacking other birds. The abundance of other native woodland birds is demonstrably lower in areas where noisy miners are present, and the effects of the noisy miner are substantially greater than the effects of other recognised threats such as grazing or habitat removal.

Weeds

Since European colonisation, more than 41,000 plant species have been introduced to Australia, and 3175 of these have become naturalised (see the Land report). The vast majority (around 70 per cent) of exotic plant species that have gone on to become serious invaders have been introduced for the horticulture trade or as aquatic ornamental species (Gallagher & Leishman 2014). It is widely understood that the abundance and diversity of native plant species decline in areas where weeds have become dominant. However, there remains a lack of detailed knowledge about the broader impacts of weeds on many ecosystems. Although there is a growing understanding of the economic impact of agricultural weeds, possible social and economic impacts of environmental weeds are generally poorly understood.

Northern Australia floodplain systems, including areas of high conservation significance such as the Kakadu region, are under threat from weeds, especially exotic pasture grasses such as olive hymenachne (Hymenachne amplexicaulis) and para grass (Urochloa mutica), and woody weeds such as giant sensitive plant (Mimosa pigra) and rubber vine (Cryptostegia grandiflora) (DNP 2016). Australian riparian ecosystems suffer from weed invasions throughout Australia where there has been extensive habitat modification to the surrounding areas, or where there is an effective vector for spread of weeds (e.g. the introduction of pasture grasses, such as gamba grass—Andropogon gayanus—in northern Australia). Aquatic weeds such as cabomba (Cabomba caroliniana) and giant salvinia (Salvinia molesta) are not as large a threat, but may be problematic in local regions (e.g. Darwin region).

Woody trees and shrubs are increasingly recognised as serious invaders in Australia. A global survey in 2011 identified Australia as the biogeographic region with the highest number of woody invaders (183 species) (Richardson & Rejmánek 2011).

Novel biota key threatening process

The 2013 recognition of the key threatening process ‘novel biota’ under the EPBC Act specifically highlights the dangers of new genetic material2 of invasive species already present in Australia being introduced. This could increase their potential to become even more invasive, or could change what are now relatively benign exotic species into much more serious invaders of native ecosystems. An example is the introduced perennial pasture species buffel grass (Cenchrus ciliaris), which occurs across much of arid and semi-arid Australia. Buffel grass continues to spread with the aid of new cultivars imported from its native range that have different tolerances to drought and temperature, and different palatability and growth forms. As with other high-biomass invasive grasses (e.g. gamba grass, and perennial mission grass—Cenchrus polystachios syn. Pennisetum polystachion), buffel grass affects biodiversity directly and indirectly through competition, and by increasing the frequency and intensity of fires. These hotter fires can affect groundcover vegetation (including bushfoods that are important to Indigenous communities) and carry into the canopy of keystone arid-zone trees such as river red gums (Eucalyptus camaldulensis), corkwoods (Hakea species) and beefwoods (Grevillea striata), with flow-on effects to other plants and animals. A threat abatement advice for buffel grass was completed in 2015. A threat abatement plan (2012) was developed to reduce the impacts on northern Australian biodiversity of 5 listed introduced grasses: gamba grass, olive hymenachne, para grass, perennial mission grass  and annual mission grass (Cenchrus polystachios syn. Pennisetum polystachion).

The novel biota key threatening process also includes threats from the introduction, or further cultivation, of potentially weedy species for the biofuel industry. Many good candidates for large-scale biofuel production in Australia have ‘weedy’ qualities (e.g. climatic hardiness, high biomass, early reproduction, resistance to pathogens), and many are already damaging invaders of natural systems elsewhere in the world.

Escaped garden plants

In 2014, the Australian Government Minister for the Environment reviewed the EPBC Act–listed key threatening process of ‘loss and degradation of native plant and animal habitat by invasion of escaped garden plants, including aquatic plants’ (listed in January 2010), and concluded that a threat abatement plan was not a feasible, effective or efficient way to abate the process at this time. The minister accepted that the measures in place at national, and state and territory levels provide a framework for a broad range of actions for border protection, and weed management and control. These measures include national biosecurity controls undertaken by the Australian Government Department of Agriculture and Water Resources, such as the weed risk assessment system (to prevent the importation of new plants, including ornamental plants used in the nursery trade, that have a high potential to become weeds), as well as state and territory legislation, policy and programs to address established and emerging weed issues.

Pathogens

In SoE 2011, 3 pathogens of concern were highlighted: chitrid fungus disease (Batrachochytrium dendrobatidis—Bd), myrtle rust (Puccinia psidii) and Phytophthora cinnamomi.

Chitrid fungal disease

The amphibian pathogen Bd has been identified as a leading agent of amphibian declines globally. SoE 2011 highlighted that increased temperatures had been correlated with Bd-driven declines of frogs in Costa Rica. Work in other jurisdictions has been somewhat equivocal on interactions between Bd and temperature. In Australia, work on the interactions between temperature, Bd and other environmental factors is ongoing, and results suggest that complex environmental and ecological interactions influence the likelihood of Bd causing significant ongoing declines (Daskin et al. 2014, Roznik et al. 2015). In 2014, 7   frog species were identified as being at high extinction risk from Bd infection in Australia, and 22 species were assessed as being at moderate to lower risk of extinction. The 7 high-risk species all occur in low absolute numbers in the wild (probably less than 2000 individuals) and, except for the Tasmanian tree frog (Litoria burrowsae), are listed as endangered or critically endangered in state and Australian legislation. Most of the Tasmanian tree frog’s range (predominantly south-west Tasmania) is currently free from Bd. However, Bd is present in Tasmania, including on the fringes of the tree frog’s range, and is predicted to cause major declines in Tasmanian tree frogs, with its spread mediated by other Tasmanian frogs (Voyles et al. 2014). Importantly, of the 7 high-risk species, only 2 occur in Queensland, where most of the Bd-driven extinction and decline has been identified. Of the species at moderate to lower extinction risk from Bd, many are in south-eastern Australia. A national threat abatement plan was published in 2006 and reviewed in 2013, and a new plan was released in 2016.

Myrtle rust

The invasive myrtle rust was detected in Australia in New South Wales in 2010. The rust spread rapidly, becoming established in natural ecosystems throughout coastal New South Wales and south-east Queensland by mid-2011, and in far north Queensland by mid-2012. By 2015, it was established, with more limited distribution, in Victoria, Tasmania and the Northern Territory (Carnegie et al. 2015). There are now 232 species known as hosts because of natural infection in Australia (all but 18 are native to Australia) and another 115 hosts recorded from artificial inoculation only (Carnegie et al. 2015). Australia is floristically dominated by the family Myrtaceae, which is a core component of our vegetation and a key driver of ecological processes. As well, many industries rely on Myrtaceae species, such as the forestry, nursery, essential oils and cut flowers industries. P. psidii has been listed as a key threatening process to the natural environment in New South Wales. In 2014–15, the Threatened Species Scientific Committee considered a public nomination to list ‘exotic rust fungi of the order Pucciniales that are pathogenic on plants of the family Myrtaceae’ as a key threatening process under the EPBC Act. The committee decided that such pathogens are encompassed within the existing ‘novel biota and their impact on biodiversity’ key threatening process.

Phytophthora

A national threat abatement plan for disease in natural ecosystems caused by P. cinnamomi came into force on 31 January 2014. The area of native vegetation affected by P. cinnamomi exceeds 1 million hectares in Western Australia, many hundreds of thousands of hectares in Victoria and Tasmania, and tens of thousands of hectares in South Australia (DoE 2014a). South Australia reports that P. cinnamomi is becoming more widespread in that state.

Other pathogens

Another pathogen highlighted in jurisdictional reports is psittacine circoviral (beak and feather) disease, which affects native parrots, including some threatened species (NSW EPA 2012). This disease is listed as a key threatening process under the Threatened Species Conservation Act 1995 (NSW) and was listed under the EPBC Act as a key threatening process in 2001. A national threat abatement plan was published in 2005 and automatically repealed on 1 October 2015. Nonstatutory threat abatement advice is currently being developed.

A pathogen affecting one of Australia’s iconic species, the Tasmanian devil, is highlighted in Box BIO4.

Pest animals

The most frequently cited invasive vertebrates in state and territory reports are cats, foxes, wild dogs, camels, deer, goats, rabbits, pigs and cane toads. Threat abatement plans under the EPBC Act are in place for feral cats, the European red fox, unmanaged goats, feral rabbits, feral pigs, cane toads, and exotic rodents on offshore islands. A National feral camel action plan (DSEWPaC 2010) and a National wild dog action plan (WoolProducers Australia 2014) are in place for these established pests of national significance in accordance with the Australian Pest Animal Strategy.

Many states note that there are insufficient data to assess the abundance and trends of most invasive animals. However, many invasive animals do appear to be increasing in their distribution and abundance—for example, South Australia reports increases in the distribution of cats, rabbits and foxes, although camels  are decreasing because of significant control efforts. The Northern Territory also reports significant declines in camels as a result of the Australian Feral Camel Management Project between 2009 and 2014. In New South Wales, foxes, cats, goats, rabbits and pigs occur so extensively throughout the state that there is limited potential for further expansion. These species are listed as key threatening processes under the New South Wales Threatened Species Conservation Act 1995.

The pressure that has contributed the most to mammal extinction in Australia and is contributing to the decline of the highest number of threatened mammals is predation by feral cats and red foxes (Woinarski et al. 2014; Table BIO2). It is also a threat affecting most of the species of near threatened mammals identified in The action plan for Australian mammals 2012. The feral cat occurs throughout Australia and on many of its territorial islands; it inhabits deserts, savanna grasslands, urban and agricultural lands, and temperate and tropical woodlands. Cats are listed as a key threatening process under the EPBC Act. A recent continental-scale analysis of the diet of feral cats recorded 400 vertebrate species that feral cats feed on or kill in Australia (Doherty et al. 2015). These include 123 birds, 15 reptiles, 58 marsupials, 27 rodents, 5 bats, 21 frogs and 9 medium-sized and large exotic mammals. Cats also consume a wide range of insects, spiders, scorpions, centipedes and crustaceans. Cats were recorded to consume or kill 28 species on the Red List of the International Union for Conservation of Nature (IUCN); 17 of the consumed species identified are also listed under the EPBC Act. Reducing the impact from cats is considered an essential action for the conservation of Australian birds and mammals (Woinarski et al. 2011, 2014; Garnett et al. 2011).

Poisoning by the invasive cane toad (Rhinella marina) is a major threat to 4 species of threatened mammal. The cane toad has had a significant impact on populations of the northern quoll (Dasyurus hallucatus) in northern Australia (Woinarski et al. 2014). Scientists have also recorded marked declines during the past 5 years in many iconic, and culturally and ecologically significant reptile species across northern Australia because of poisoning by cane toads (Shine & Wiens 2010, Fukada et al. 2016). For example, 35 years of surveys of the Australian freshwater crocodile in the Daly River in the Northern Territory reveals that the density of crocodiles decreased by nearly 70 per cent between 1997 and 2013 following invasion by the cane toad between 1999 and 2003 (Fukada et al. 2016).

The introduced black rat has contributed to the extinction of several mammal species through predation, competition or disease transmission: the Lord Howe long-eared bat (Nyctophilus howensis); 2 Christmas Island rats (Maclear’s rat—Rattus macleari, and the bulldog rat—Rattus nativitatis); and some island subpopulations (e.g. spectacled hare wallaby—Lagorchestes conspicillatus, and golden bandicoot—Isoodon auratus in the Montebello Islands). It is considered a major threat for a number of other threatened species identified in The action plan for Australian mammals 2012. Predation by the black rat has also contributed to the historical extinction of several island bird species, including the robust white-eye (Zosterops strenuus) on Lord Howe Island. It continues to be a pressure on island populations of birds, including the scarlet robin (Petroica boodang) on Norfolk Island and island thrush (Turdus poliocephalus erythropleurus) on Christmas Island.

The control of dingoes (Canis lupus dingo) and their impact on biodiversity continue to create debate in both the scientific literature and the mainstream public discourse. Dingoes are cast as having positive and negative effects on biodiversity in Australian ecosystems. It is generally recognised that dingoes play an important role as an apex predator, and may have some role in changing pest–predator impacts in the ecosystem by preying on other predators or by competing with them for resources. One review of 31,000 dingo diet records in the literature found that less than 1 per cent contained any evidence of cat consumption; however, it is important to note that this is not a measure of the overall effects of competition for resources, or other indirect impacts, such as changes in the behaviour of pests and predators to avoid being active when dingoes are active (Glen 2014).

Dingoes are also important in the spiritual and cultural practices of some Indigenous peoples. Furthermore, they are gaining importance as an element of wildlife that attracts tourists, with potential flow-on economic benefits.

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Invasive species affecting inland aquatic environments

The Inland water report describes the observed extent of some invasive species affecting aquatic environments, including the freshwater fish common carp (Cyprinus carpio) and eastern gambusia (Gambusia holbrooki), and 2 new (2012) aquatic Weeds of National Significance—sagittaria/arrowhead (Sagittaria platyphylla) and water hyacinth (Eichhornia crassipes).

In Australia, the introduction, stocking and translocation of fishes may threaten biodiversity. Since the mid-1800s, introductions of species for recreation and food, escapes from captivity of ornamental species, and releases of fish for pest control have all increased the number of exotic species established in the wild. Currently, around 43 freshwater fish species have established wild populations, 34 of which continue to spread (Harris 2013). However, uncertainty surrounds this number—survey data are scarce, and not all aquatic ecosystems have been surveyed.

In the Murray–Darling Basin, the condition of fish communities, including the proportions of non-native species in terms of abundance and biomass, was a foundation for river health assessments in the Sustainable Rivers Audit (Davies et al. 2010). Sampling yielded 38 species, 10 of which were introduced, and constituted 43 per cent of individual abundance and 68 per cent of total biomass. Non-native species rivalled or outnumbered natives in 9 of the 23 Basin valleys, with common carp, eastern gambusia and goldfish (Carassius auratus) present throughout. Carp were overwhelmingly dominant, representing 87 per cent of non-native fish biomass and 58 per cent of total fish biomass. Non-native fish species also outnumber native species in some other, mostly densely populated, catchments (e.g. in the south-west of Western Australia).

Some frog species, such as the bell frogs and grass frogs (Litoria aurea, L. castanea and L. raniformis), are potentially threatened by eastern gambusia. Eastern gambusia is also the primary threat to the endangered (critically endangered in the IUCN Red List) red-finned blue-eye (Scaturiginichthys vermeilipinnis) and probably a significant threat to the Edgbaston goby (Chlamydogobius squamigenus—endangered in Queensland, vulnerable in Australia). These 2 fish species are also threatened by feral pigs damaging the small, shallow, spring-fed waterholes in which they live, and by invasive para grass.

Marine invasive species

The Marine environment report includes a description of invasive species affecting marine environments. The report highlights that the number of introduced pests is increasing in marine environments, but that their impacts and trend are highly uncertain. Widespread marine invasive species include the New Zealand screw shell (Maoricolpus roseus) and the northern Pacific starfish (Asterias amurensis). Despite concentrated efforts to develop monitoring systems, ongoing monitoring of marine pests is limited, so any failure of Australia’s national and local prevention arrangements is likely to be detected first as a new established invasion.

Cresswell ID, Murphy H (2016). Biodiversity: Pest species and pathogens. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/biodiversity/topic/2016/pest-species-and-pathogens, DOI 10.4226/94/58b65ac828812