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1.  What you can do
2.  Water
3.  Ecology
4.  Amphibians
5.  Environmental Issues
6.  Keystone species
7.  Get Wet!-
     Field Study Ideas

8.  The Zoo Experience
9.  Frogs & Friends
10. Case Studies
11. Resources
12. Glossary

Case Studies

1. Global Amphibian Decline
2: The Decline of the Leopard Frog
3: The Introduction of the Cane Toad to Australia
4: The Puerto Rican Crested Toad - A Species Survival Plan
5: The Bullfrog - A Species in Decline
6: Blanchard's Cricket Frog

(Level: 7 : 10 acad : 10 appl : 11 appl : 12 acad )

The ecological balance of this island continent was disrupted when the first settlers arrived from Europe, introducing exotic species such as rabbits into the delicate Australian ecosystem. One of the most devastating introductions was the Cane Toad, Bufo marinus.

The introduction of the cane toad into Australia began in the 1930s to biologically control the Grey-back Beetles. The beetles were extremely destructive in the sugar cane fields of northern Queensland. The Cane Toad, native to Mexico and South America, was believed to be the solution to the problem. Despite protests from natural history societies, and naturalists, 101 Cane Toads were released into Australia in 1935.

The repercussions of the introduction began almost immediately in northern Australia. The Cane Toad adapted extremely well to its new environment, and soon spread out of the sugar cane fields. Initially, the Toad was unable to survive the colder temperature in southern Australia, but it slowly adapted. Native wild life were affected throughout the range of the Toad, especially in the paperback swamps. When the Cane Toad is ingested by animals as large as cats and dogs, the poisonous glands behind the head of the toad are lethal. Prior to the introduction, reptiles such as the Red-bellied Snake were thriving. Red-bellied Snakes were an integral part of the ecosystem, as they consumed both rodents and grasshoppers. The snakes began to disappear when the Cane Toad entered the swamps. Remains of the poisonous toad were discovered in the stomach contents of dead snakes. The loss of the snake has resulted in a population explosion of grasshoppers.

Waterfowl, such as Pheasant Caucals, White-faced Herons, and several species of egrets, have been seriously affected by the Cane Toad. The Eastern Swamp Hen was once a common species in the swamps of Queensland. The Cane Toad has interfered with the breeding of the Hen, and the population has declined. Native Australian amphibians have also been threatened by the Cane Toad. The White's Tree Frog has been predated by the toad, and the Green Tree Frog has disappeared from many areas.

The future distribution of the Cane Toad is uncertain. It may be limited by the cooler temperatures in the south, and the lack of breeding ponds in the interior. Unfortunately, there are no natural barriers to prevent the spread of the toad along the northern coast and into the large Kakadu National Park.

The Cane Toad is a classic example of what can occur when an exotic species is introduced into an ecosystem. Species are often introduced into areas where no natural predators exist. This situation has occurred in the wetlands of Ontario where Purple loosestrife is thriving. In some cases, exotic introductions have caused such havoc that a second species is introduced to control the first. Although such mistakes can rarely be corrected, they can be prevented. Through monitoring the species which enter a country, and educating the public, devastating introductions can be reduced.


  1. The introduction of exotic species , either accidental or for biological control of pests, is still occurring. Research the use of exotic species to control the spread of another organism. Is this an effective method to eradicate a pest? Provide an example of a successful and unsuccessful introduction.
  2. Do you feel the introduction of an exotic species is an effective method of controlling agricultural pests? Why or why not?
  3. Can the effects of the Cane Toad on the Australian ecosystem be limited?


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