The Australian Cane Toad Essay Research Paper — страница 2

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to feed on toads or on their internal organs. Behavior and Breeding Cane toads are highly adaptable, both in terms of survival and reproduction. They are much more tolerant than other Australian frogs and can survive and breed in somewhat salty water. In Australia, giant toads normally breed from June to January, but they have been found in breeding condition throughout the year. Cane toads usually begin breeding in their second summer, when they are about 75 mm long. The cane toad needs only a small pool of water for breeding. The males fertilize the eggs as they are laid. Male toads will attempt to mate with anything resembling a female toad – living or dead. As many as 35,000 eggs may be produced by each female, thus giving the species a high breeding potential. Cane toad

eggs are blackish in color and are deposited in long jelly like strings onto plants, rocks or debris near water. The spawn consists of long double chains of black eggs about 1 mm in diameter enclosed in a transparent cover. Embryos begin hatching within 48 hours; after several days, the tadpoles begin feeding, and the tail grows proportionately larger and hind limbs develop. In three days, the eggs hatch into small (3 cm) jet black tadpoles – unlike those of any native frog. These tadpoles become toadlets unusually early, so they are out of the water and hopping around faster than most other frogs. Cane toad tadpoles differ further from most species in that they occur in massive numbers and frequently form dense aggregations in shallow water. B. marinus adapted well to the

Australian environment. So well that they are moving closer to the wetlands of Kakadu National Park, which includes the Katherine Gorge. District park manager John De Koning says wildlife like crocodiles, goannas, and snakes will be threatened by the arrival of the non-native pest, even though they have only found a few so far. “We came across one large female, this was right on the very southern eastern edge of the Nitmiluk National Park. We came across one female and we could hear several males in the distance.” The natural rate of spread of the cane toad is now 30-50 km/year in the Northern Territory and about 5 km/year in northern New South Wales. Finally, because their diet is so variable, they do not need to expend much energy searching for food. They can just sit in a

convenient spot, and gobble up anything that wanders by. In urban areas, they are often seen gathered around street lamps eating insects attracted by the light Defense One of the most important factors in the success of the cane toad is that they are highly poisonous to eat, at every stage of their life cycle. All frogs and toads may have enlarged chemical-secreting glands at particular points on their bodies, or small glands spread over the whole skin. The cane toad is one such amphibian. These secrete white venom when the animal is handled or threatened. The eggs and tadpoles are also poisonous and can cause cardiac arrest and death. A cane toad’s reaction to a threat is to turn side-on to its attacker so that the venom glands face them. The glands on the cane toad’s

shoulders are also capable of oozing venom or even squirting it over a distance of up to 2m. Animals picking up a cane toad and receiving a dose of venom may die within fifteen minutes. This venom is composed mainly of cardioactive (affecting the heart) substances. The biggest danger to humans is that the venom could come in contact with the eyes, where it causes intense pain and temporary blindness. Under pressure cane toads can shoot their venom a short distance. This substance may be splashed into a person’s mouth or eyes as they attempt to kill the toad. Since the poison can be absorbed into the system through mucus membranes, without ever being swallowed. Therefore, the mouth, eyes, and nose should always be rinsed thoroughly if contact with venom occurs. Experiments and

observations indicate that a variety of native animal life are extremely susceptible to the many poisons in the cane toad’s venom. These include avid frog eaters such as the Tiger and Red bellied Black Snakes and the quolls. In areas where toads appear, there has been a subsequent decline in populations of these types of native animals, although more research is needed in this field. Research and Control “The CSIRO Australian Animal Health Laboratory (AAHL) at Geelong is a high security microbiological facility, purpose designed and operated to undertake research into viruses, bacteria, fungi and parasites which are exotic and do not occur in Australian domestic or wild animals.” It is the only laboratory of its kind in Australia where studies on these exotic