lost niches of extinct Australian megafauna including Diprotodon and Palorchestes, where this may also apply for others (such as cattles and horses and donkeys and deers), and would also drop fire risk, and smaller herbivores such as hog deer or feral goats may also suppress introduced grasses and wildfires. Carnivores such as the red fox or cats may control the number of rats – and rabbits – and eradication of these carnivores may damage native ecosystem indirectly. Economic impact A 2021 study looking at the economic impact of invasive species estimated that invasive species had cost Australian farmers in the past 60 years. with feral cats way ahead of the pack at nearly . Rabbits are next, at around , followed by fire ants, annual ryegrass, pigs, parthenium, foxes, ragwort, cucumis melons, and common heliotrope. World Trade Organisation and Australia's quarantine regulations The World Trade Organisation specified quarantine regulations are weaker than Australia's fairly stringent regulations controlling the importing of raw produce. Following Australia's membership of the WTO, many forms of raw produce once banned have commenced import, with potentially adverse effects and controversy; for example, regarding proposals to import apples from New Zealand or bananas from the Philippines. Australian quarantine regulations such as those limiting banana imports from developing economies have been recognised as protectionist trade barriers by economists including Kevin Fox, head of Economics at the Australian School of Business. The weakening of restrictions on importing raw produce into Australia mandated by the World Trade Organisation Future may pose risks of introducing exotic disease organisms. Case examples include, Chytrid fungus that is threatening numerous Australian frog species with extinction and mass pilchards deaths in the Southern Ocean from 1995 onwards that are suspected to have been caused by a virus that may have been brought in with imported pilchards. See also Invasive species in New Zealand Environmental issues in Australia Fauna of Australia List of invasive plant species in New South Wales References External links Invasive Species Council Full list of noxious weeds in Australia (pdf) CSIRO Cane Toad research page CSIRO Research on Introduced Marine Pests The Cooperative Research Centre for Australian Weed Management CSIRO marine pest fact sheets The Department of Environment and Heritage, Invasive Species Weeds of National Significance The Cooperative Research Centre for Pest Animal Control feral.org.au Rabbit Information Service Fisheries Western Australia – Introduced Marine Species Fact Sheet Agriculture in Australia Biota naturalised