Invasive Species: Cane toads are native to South America, occupying rainforests such as the Amazon and even semi-arid environments. Outside of South America, cane toads have been introduced to several countries around the world where they have become invasive. While they have been introduced to Florida, Cuba Hawaii the the Philippines, the most well known introduction was in Australia in 1935. Cane toads were originally introduced as a pest control, to feed on the cane beetle (Dermolepida albohirtum) which had devastated sugar cane crops. Unfortunately, the cane beetle resided off the ground while the cane toad was purely terrestrial so the two species rarely came across one another. A hundred and two cane toads were introduced from Hawaii to Gordonvale Queensland, without any natural predators however, their population became inflated as they moved across the Australian continent. Cane toads produce a potent poison in their skin that would harm any animal that attempted to eat it. This poison has caused the deaths of thousands of native Australian animals and even the local extinction of some such as the Merten's water monitor (Varanus mertensi) in some surveyed sites. On top of this, cane toads are ferocious predators and will feed on anything that will fit in their mouth including small mammals and other amphibians.
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Poison: Cane toads have caused a number of issues when introduced to Australia, a large issue being their poison. Produced from the paratoid glands behind the eye, toads produce a number of toxins as a defense. Of these is bufotoxin, a cocktail of chemicals, many unique to toads and some unique to specific species. For cane toads, their bufotoxins contain Bufagin which attacks the cardiac muscles, affecting the heart when ingested. When predators in Australia attack these toads, they often get a mouthful of these toxins leading to death. This has affected animals such as the northern quoll, various predatory birds, lizards and several snakes. One snake in particular, the red-bellied black snake (Pseudechis porphyriacus) have actually evolved to feed on the snakes. By adapting a smaller mouth, they are unable to feed on larger toads which contain more poison, instead only feeding on smaller individuals which contain a survivable amount of the poison.
Sources:
Griffiths, Anthony D., and J L. McKay. "Cane Toads Reduce the Abundance and Site Occupancy of Merten's Water Monitor (Varanus mertensi)." Wildlife Research, 26 Feb. 2007, www.publish.csiro.au/WR/WR07024. Accessed 22 June 2022. Phillips, Ben L., and Richard Shine. "An Invasive Species Induces Rapid Adaptive Change in a Native Predator: Cane Toads and Black Snakes in Australia." The Royal Society Publishing, 21 Mar. 2006, royalsocietypublishing.org/doi/abs/10.1098/rspb.2006.3479. Accessed 22 June 2022. Rodriguez, Emily. "Bufotoxin." Encyclopedia Britannica, 28 Nov. 2018, www.britannica.com/science/bufotoxin#ref114979. Accessed 22 June 2022. "The Biological Effects, Including Lethal Toxic Ingestion, Caused by Cane Toads (Bufo marinus) - 12 April 2005." Australian Government, Department of Agriculture, Water and the Environment, 12 Apr. 2005, www.awe.gov.au/environment/biodiversity/threatened/key-threatening-processes/biological-effects-cane-toads. Accessed 22 June 2022. "The Cane Toad (Bufo marinus) - Fact Sheet." Australian Government, Department of Agriculture, Water and the Environment, 2010, www.awe.gov.au/biosecurity-trade/invasive-species/publications/factsheet-cane-toad-bufo-marinus. Accessed 22 June 2022. |