Cane toads in Australia

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The cane toad (Rhinella marina; formerly Bufo marinus) is an invasive species in Australia. The cane toad is the largest species in the family Bufonidae. Adult cane toads are usually heavy-built and weigh an average of up to 1.8 kg. (4 lbs.). Their size may vary from 15–23 cm.(4–9 in.) and their skin is warty. The coloration on their back and sides may vary from olive-brown or reddish-brown, gray, and yellow while their bellies are semi-yellow or semi-white with darker mottling. Their body is round and flat, has prominent corneal crests, and light middorsal stripes. Their front feet are unwebbed, but their back feet have tough, leathery webbing. Cane toads have short legs and a ridged bony head that extends forward from their eyes to their nose. Behind their ears lie the parotid glands, which usually causes their head to appear swollen. These glands are used for defense against predators. The parotid gland produces milky toxic secretion or poison that is dangerous to many species.[1] This venom primarily affects the functioning of the heart. Envenomation is painful, but is usually not fatal for humans.[2] However, it does have some effects, such as burning of the eyes and hands, and skin irritation.[1]

An adult cane toad (Rhinella marina).

Invasive species[edit]

The cane toad in Australia is regarded as an exemplary case of a "feral species"—others being rabbits, foxes, cats, and Giant Mimosa. Australia's relative isolation prior to European colonisation and the industrial revolution—both of which dramatically increased traffic and importation of novel species—allowed development of a complex, interdepending system of ecology, but one which provided no natural predators for many of the species subsequently introduced. The recent, sudden inundation of foreign species has led to severe breakdowns in Australian ecology, after overwhelming proliferation of a number of introduced species for which the continent has no efficient natural predator or parasite, and which displace native species—in some cases these species are physically destructive to habitat as well. Cane toads have been very successful as an invasive species, having become established in more than 15 countries [3] within the past 150 years. The Australian Government placed cane toads in the Environment Protection and Biodiversity Conservation Act 1999 as a "key threatening process" [4]

Introduction and spread[edit]

A young cane toad.

Native to Central and South America, Cane toads were introduced to Australia from Hawaii in June 1935 by the Bureau of Sugar Experiment Stations in an attempt to control the native grey-backed cane beetle (Dermolepida albohirtum) and Frenchi beetle (Lepidiota frenchi).[5] These beetles are native to Australia and they are detrimental to sugar cane crops, which are a major source of income for Australia. Adult cane beetles eat the crop's leaves, but the main problem is the larvae, who feed on the roots. Adult cane beetles have a heavy exoskeleton and their eggs and larva are often buried underground, making them difficult to exterminate. Furthermore, conventional methods of pest control, such as pesticide use, would eradicate harmless species of insects as well, making it an unsatisfactory method.[6]

The cane toads bred immediately in captivity, and by August 1935 more than 102 young toads were released in areas around Cairns, Gordonvale and Innisfail in northern Queensland. More toads were released around Ingham, Ayr, Mackay and Bundaberg. Releases were temporarily limited because of environmental concerns but resumed in other areas after September 1936. Since their release, toads have rapidly multiplied in population and now number over 200 million and have been known to spread diseases affecting local biodiversity.[7] Unfortunately, the introduction of the toads has not only caused large environmental detriment, but there is also no evidence that they have had an impact on the cane beetles they were introduced to predate. The toads have steadily expanded their range through Queensland, reaching the border with New South Wales in 1978 and the Northern Territory in 1984. The toads on the western frontier of their advance have evolved larger legs;[8] this is thought to be related to their ability to travel farther. As a consequence of their longer legs, larger bodies, and faster movement, about 10% of the leading edge cane toads have also developed arthritis.[9] It is estimated that cane toads migrate at an average of 40 kilometres (25 mi) per year currently.[10]

Ecological effects[edit]

The spread of cane toads in Australia from 1940 to 1980 in five year intervals. They have now reached the state of Western Australia.

The long-term effects of toads on the Australian environment are difficult to determine, however some effects include "the depletion of native species that die eating cane toads; the poisoning of pets and humans; depletion of native fauna preyed on by cane toads; and reduced prey populations for native insectivores, such as skinks." [2]

Precipitous declines in populations of the Northern Quoll (Dasyurus hallucatus) have been observed after toads have invaded an area. There are a number of reports of declines in goanna and snake populations after the arrival of toads.[11] For example, local populations of Varanus panoptes dropped by up to 90% when their habitat was invaded by cane toads.[12] The preliminary risk assessment of cane toads in Kakadu National Park stated that the predation of the cane toad by native wildlife is the greatest risk to biodiversity. Other factors, such as competition with native wildlife for resources, and the predation of the cane toad on native wildlife, were considered much lower risk factors[13] but requiring further study.[14] In the Northern Territory, goanna predation on cane toads has been linked to a rise in the amount of undamaged salt water crocodile eggs.[15] Cane toads were present within a few days of the crocodiles hatching in April 2007.[16]

Numerous native species have been reported as successfully preying on toads. Some birds, such as the Black Kite (Milvus migrans),[17] have learned to attack the toad's belly, avoiding the poison-producing glands on the back of the head. Anecdotal reports in the Northern Territory suggest that a native frog, Dahl's Aquatic Frog (Litoria dahlii), is able to eat the tadpoles and live young of the toad without being affected by the poison that often kills other predators.[18] This may account for slower than expected infestations of toads in certain areas of the Northern Territory, although later research carried out jointly by several Australian Universities casts doubt on these reports.[19] Some snakes have been reported to have adapted smaller jaws so that they are unable to swallow large cane toads which have large quantities of poison.[20]

Another study, however, notes that the cane toad is adapting to a wider environmental range and may in the future be spreading into habitats currently not available.[21]

In 2009 it was found that the native meat ant is immune to the toad's poison and can successfully prey upon young cane toads. Whereas native frogs and toads have natural reflexes to avoid the meat ants, the cane toads do not tend to try to escape the ants, rather standing still when attacked waiting for the toxin to kill the attacker.[22]

Predator effects[edit]

Predators in Australia are not adapted to their toxin, which is the toad's main defense mechanism. Because of this, toads don't tend to hide and are usually targeted by predators, who then expose themselves to the toxic effects.[23] One study suggests Australian reptiles are greatly threatened by invasion of the Cane Toad, more so than any other group [3] Seventy-five species of crocodiles and freshwater turtles were found to be at risk of invasion, and all species studied were found capable of eating a toad large enough to kill them [3] All freshwater turtles and crocodiles are predicted to share part of their future distribution with the invasive species by the year 2030.[3] Australia’s varanids and agamids are also at a great risk.[3] It is reported that one native freshwater turtle species, Myuchelys latisternum (Saw-shelled Turtle) which ranges along rivers and streams from Cape York Peninsula to northern New South Wales, is one of the few native animals which is a successful predator of Cane Toads.[24] The larger the animal, or predator, is the better chance they have of survival, as their body weight effectively dilutes the concentration of the toxin in their body. One native species, the Torresian Crow have learned how to kill and eat Cane Toads without ingesting the poison by flipping it onto its back and using its powerful bill to deliver a lethal blow to the throat where the toad's skin is thinner, giving the crow access to the toad's non-toxic innards.[25]

Most of these predator populations learn not to eat cane toads after an initial drop in population after toad invasion. However, the initial drop in population is often steep and can reduce biodiversity on a population level. One proposed solution is to use "teacher toads", or smaller toads which are less likely to kill predators. These toads would allow predators to learn not to eat the toads while mitigating mortality. Some have even proposed adding some chemical to make the toads distasteful to further discourage predation. These efforts have shown some promising results so far.[23]

Methods to control invasion[edit]

Currently, most attempts to curtail the invasion of cane toads have been unsuccessful. Many of these strategies involve the physical trapping of toads, but these methods also capture unintended native species.[23] Since the largest selective pressure on cane toads currently is intraspecies competition, these physical removals often only improve the conditions for untrapped toads. Also, since migration is high, any area purged of toads would most likely be reinvaded quickly.

Many new ideas have been proposed to control the cane toad population. Some have suggested introducing a native viral or bacterial pest of the toads, but this has potential to once again invade native species. Two similar strategies have been proposed, both of which focus on fecundity. One involves the release of sterile males into the population. These males would compete for resources with other males, while themselves not being able to reproduce. A second strategy would be to insert a gene in female toads which would allow them to only create male offspring. In theory, this would limit the reproductive rates and control the population. It is difficult to determine the efficacy and dangers of these approaches, as these methods have never been attempted, especially on a large scale.[23]

On 13 June 2012 news reports cited a new research breakthrough regarding cane toad control. Research has confirmed that cane toad tadpoles are attracted to the toxin produced by adults and spawn. Tadpoles are believed to cannibalize toad spawn as a food source. Researchers used cane toad toxin to successfully lure cane toad tadpoles, implying that in controlled areas tadpoles could be captured and eradicated.[26]

The RSPCA has guidelines[27] for the humane culling of cane toads. Inhumane ways include spraying with Dettol, Phenyl and using golf clubs, but these are illegal in most states and territories.[citation needed] Due to concerns over potential harm to other Australian wildlife species, the use of Dettol as pest control was banned in Western Australia by the Department of Environment and Conservation in 2011.[28]

In popular culture[edit]

A purse made from a cane toad.

The introduction and subsequent migration of the cane toad in Australia was popularised by the film Cane Toads: An Unnatural History (1988), which tells the tale with a humorous edge and is often shown in Environmental Science courses. Don Spencer, a popular children's entertainer, sang the song "Warts 'n' All", which was used in the documentary. A longer sequel, Cane Toads: The Conquest, by the same filmmaker, was made in 2010.

Attempts have been made to make use of dead cane toads, which can number in the thousands and cause hygiene problems. This includes processing the carcasses into liquid fertilisers.[29] Their skin can be made into leather, and novelty cane-toad purses made of the fore-body and abdomen are sometimes seen (e.g. see accompanying photo).

In Australian states where the cane toad is common, some 'sports' have developed, such as cane toad golf and cane toad cricket, where cane toads are used as balls. In April 2005, Dave Tollner, a Northern Territory Member of Parliament, called for legalisation of attacks on cane toads. This was criticised by many animal and conservation groups who claim freezing is a more humane way to kill cane toads than hitting them with cricket bats.[30] The short film Cane Toad - What happened to Baz? displays an Australian attitude towards the cane toad. This film won the "Best Comedy" award at the 2003 St Kilda Film Festival.

This was controversial in relation to an ad put out by the Tooheys beer company which showed people from New South Wales standing at the New South Wales-Queensland Border with golf clubs and lights, attracting cane toads just so they could hit them back across the border with the golf clubs.[31][32]

The cane toad has been listed by the National Trust of Queensland as a state icon of Queensland, alongside the Great Barrier Reef, and past icons, the Royal Flying Doctor Service and the backyard mango tree (also an introduced species).[33]

"Cane toad" is also a colloquial term for an inhabitant of Queensland, particularly the state's State of Origin rugby league team members and supporters.[34]

The Cane Toad Times was a satirical humour magazine based in Brisbane, Queensland.

The invasive nature of cane toads was referenced in The Simpsons episode "Bart vs. Australia".[35]

In the video game Ty the Tasmanian Tiger 2: Bush Rescue, cane toads appear as enemies. They wear spiked collars, have poisonous tongues (in contrast to real world cane toads), are about the size of medium-sized dogs, and will chase Ty down upon seeing him.

See also[edit]

References[edit]

  1. ^ a b "Honolulu Zoo Cane Toad". 
  2. ^ a b "Cane Toad Bufo marinus". 
  3. ^ a b c d e http://search.proquest.com/docview/862947521/fulltext?accountid=4117
  4. ^ http://www.environment.gov.au/biodiversity/invasive/ferals/cane-toads.html
  5. ^ Clarke, G. M., Gross, S., Matthews, M., Catling, P. C., Baker, B., Hewitt, C. L., Crowther, D., & Saddler, S. R. 2000, Environmental Pest Species in Australia, Australia: State of the Environment, Second Technical Paper Series (Biodiversity), Department of the Environment and Heritage, Canberra.
  6. ^ http://australianmuseum.com/Cane-Toad
  7. ^ "Institute for Molecular Bioscience, Killing off the cane toad". Retrieved 2006-12-06. 
  8. ^ "Toxic Toads Evolve Longer Legs, Study Says. 15/02/06. National Geographic News". Retrieved 2006-05-19. 
  9. ^ Henry Fountain (16 October 2007). "Arthritis Fails to Slow Invading Toads in Australian Fields". NY Times. Retrieved 2007-10-27. 
  10. ^ Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books. p. 112. ISBN 0-7301-0468-0. 
  11. ^ Mayes, P.J.; Thompson, G. G. and Withers P.C. (2005). "Diet and foraging behaviour of the semi-aquatic Varanus mertensi (Reptilia: Varanidae)" (PDF). Wildlife Research 32: 67–74. doi:10.1071/WR04040. 
  12. ^ J. S. Doody et al (2007): A Preliminary Assessment of the Impacts of Invasive Cane Toads (Bufo marinus) on Three Species of Varanid Lizards in Australia. Mertensiella 16 (Advances in Monitor Research III), S. 218-227
  13. ^ "SSR164 - A preliminary risk assessment of cane toads in Kakadu National Park". Retrieved 2006-05-22. 
  14. ^ Boland, C. R. J. (2004). "Introduced cane toads Bufo marinus are active nest predators and competitors of rainbow bee-eaters Merops ornatus: observational and experimental evidence". Biological Conservation 120 (1): 53–62. doi:10.1016/j.biocon.2004.01.025. 
  15. ^ "Cane toad impact will boost croc hatchling numbers, researchers say". Retrieved 2006-10-15. 
  16. ^ "Cane Toads Present for Croc Hatching". 
  17. ^ Mitchell, D.; Jones, A. Hero, J.-M. (1995). "Predation on the Cane Toad (Bufo marinus) by the black kite (Milvus migrans)". Memoirs - Wueensland Museum 38: 512–531. 
  18. ^ "NT frog 'eats' Cane Toad. 15/15/2004. ABC News Online". Retrieved 2006-05-09. 
  19. ^ ."Team Bufo: About Us". 
  20. ^ Phillips, Ben L.; Shine, Richard (December 2004). "Adapting to an invasive species: Toxic cane toads induce morphological change in Australian snakes". PNAS 101 (49): 17150–17155. Bibcode:2004PNAS..10117150P. doi:10.1073/pnas.0406440101. PMC 535375. PMID 15569943. 
  21. ^ Urban, Mark C.; Ben L. Phillips; David K. Skelly; Richard Shine (2007). "The cane toad's (Chaunus Bufo marinus) increasing ability to invade Australia is revealed by a dynamically updated range model". Proceedings of the Royal Society B: Biological Sciences 274 (1616): 1413–9. doi:10.1098/rspb.2007.0114. PMC 2176198. PMID 17389221. 
  22. ^ Sweeney, Claire (31 March 2009). "Killer ants are weapons of mass toad destruction". The Times (London). Retrieved 2009-03-31. 
  23. ^ a b c d http://www.canetoadsinoz.com
  24. ^ Ryan, Michelle, General Editor. (2000). Wildlife of Tropical North Queensland: Cooktown to Mackay. Queensland Museum. ISBN 0-7242-9349-3. p. 198.
  25. ^ Katrina Bolton (2007-09-15). "Toads fall victim to crows in NT - ABC News (Australian Broadcasting Corporation)". Abc.net.au. Retrieved 2011-11-12. 
  26. ^ Sarah Zielinski (15 June 2012). "The Reluctant Toad Killer". Science 336 (6087): 1375–7. Bibcode:2012Sci...336.1375Z. doi:10.1126/science.336.6087.1375. PMID 22700900. 
  27. ^ http://kb.rspca.org.au/What-is-the-most-humane-way-to-kill-a-cane-toad_299.html
  28. ^ Narelle Towie (23 May 2009). "Cane toad poison banned". Perth Now. Retrieved 2 February 2013. 
  29. ^ "Toads as Fertilizer - DirtDoctor.com - Howard Garrett". Retrieved 2006-06-07. 
  30. ^ "Cane toad clubbing sparks controversy". Retrieved 2006-06-20. 
  31. ^ "Vulgar, Violent Ads". Retrieved 2009-07-20. 
  32. ^ Squires, Nick (8 June 2007). "Cane Toad Golf Out of Bounds". The Daily Telegraph (London). Retrieved 2009-07-20. 
  33. ^ "National Trust Queensland National Icons". Retrieved 2006-10-17. 
  34. ^ "Australian slang terms - Koalanet.com.au". Retrieved 2010-04-02. 
  35. ^ Mirkin, David (2005). The Simpsons season 6 DVD commentary for the episode "Bart vs. Australia" (DVD). 20th Century Fox. 

Further reading[edit]

  • Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books. ISBN 0-7301-0468-0. 
  • Barker, J.; Grigg, G.C.; Tyler, M.J. (1995). A Field Guide to Australian Frogs. Surrey Beatty & Sons. ISBN 0-949324-61-2. 
  • Lawson, Walter J. (1987). The Cane Toad, Bufo marinus: A Bibliography (AES working paper). School of Australian Environmental Studies, Griffith University. ISBN 0-86857-247-0. 

External links[edit]