Part 3-Lesson 1

Case Study: Becoming a Pest-Rabbits and Cane ToadsPart 3-Lesson 1IntroductionA pest can be defined a number of ways but for us, it is a non-native plant or animal that disrupts or has the capacity to disrupt or alter the natural ecosystem function, composition and diversity of the site it occupies.

Introduction If an organism is brought into a new environment with a lack of predators, competitors and has other members of the same species to mate with, it has the potential to become a pest. The relative importance of each of these factors depends on the nature of the organism and the habitat.

RabbitsEuropean wild rabbits have had the greatest effect on the Australian environment of any introduced species. They first arrived in Sydney in 1788 with Governor Phillips fleet. The rabbits were brought as a source of fresh food and often released when the ships arrive at their desired location.

RabbitsIts believed that the first really successful release of rabbits was in 1859 by Thomas Austin on his property near Geelong in Victoria. He brought 24 wild rabbits from England and set them free with the intention of hunting them for sport.

Rabbits Six years after he released the 24 rabbits he had estimated he had killed 20,000 and had over 10,000 left. In 1866 14,000 were shot on his property.

RabbitsRabbits spread very quickly across the country. The spread was referred to as a grey blanket because of the huge number that covered the land. They migrated to NSW by 1870, Southern Queensland by 1890 and Western Australia and the Northern Territory by 1900.

RabbitsAt one stage there was said to be 100 rabbits for ever man, woman and child in Australia. Rabbits ate everything; bushes, shrubs, grasses and bark. Their effect on the country was devastating.

RabbitsThere was nothing left for grazing animals .The rabbits ate down grasses so far that they killed the roots leaving the soil bare. This affected the native animals and increased rates of erosion. How do you think this affected the economy of the time?

RabbitsBelow is a list of reasons why rabbits were so successful:Were able to adapt to the climates easilyAble to adapt to the habitats easily as many were found in their natural environmentsAbundant sandy soil for warrensCould bread unnoticed because of the shear size of Australian propertiesLittle competition for foodProlific breading animalsFew natural predatorsNeed little water as they absorb most of what they need from their foodRabbitsRabbits were declared vermin in the late 1800s. The government set a bounty on their tails which led to them being hunted, trapped and poisoned in large numbers. A 3200 kilometre rabbit proof fence was built between 1902 and 1907 to try and keep them from entering the cereal growing areas of the south west.

RabbitsThe first successful control program involved the release of a virus called Myoxmatosis which is endemic in South American rabbits and is transmitted by parasites (fleas and mosquitoes). It was released in 1950 and had a 99% mortality rate. The virus reduced the population from 600 million to 100 million in 2 years.

RabbitsRabbit calicivirus disease (RCD) AKA: haemorrhagic disease, is another method of biological control that has been trialled in recent years. This disease is transferred by contact between infected and non-infected rabbits as well as through the faeces of birds which prey on rabbits.

Rabbits This virus escaped from an island off the coast of South Australia and in 1995 was subsequently approved as a biological control. It was released in Western Australia in 1996 and its success is yet to be fully evaluated.

RabbitsMany people made a living out of rabbit hunting during the Great Depression of the 1930s. They also provided a cheap meal for many Australians.

Cane ToadsThe cane toad (Bufo marinus) was introduced into Australia in 1935 in attempt to biologically control the greyback cane and frenchi beetles, pests of sugar cane crops. Cane toads are native to South America and was introduced into Puerto Rico to hold cane pests in check, which allegedly worked pretty well.

Cane Toads102 toads collected in Hawaii, where it had been introdced three years previously, were brought to Australia to a special breeding facility in north Queensland. They were bred and released into the surrounding cane-growing districts.

Cane ToadsBy the next year over 40,000 baby toads had been released around Cairns, Gordonvale, Innisfail and Tully. It was soon apparent that the cane toad was having little effect on the beetles.

Cane ToadsThe greyback beetle live high on sugarcane and rarely come down. Cane toads cannot climb. Frenchi beetles invade the cane fields at a time when the toads are absent because of the lack of protective cover.

Cane ToadsCane toads were however eating other things including honey bees, small reptiles, amphibians and mammals. They rapidly spread down the coast and had reached Brisbane within 10 years of their release in Cairns. They are now the most common vertebrate in some parts of Queensland. In some areas they were as dense as 5000 per hectare.

Cane ToadsThey have migrated west to Kakadu and as far south as Port Macquarie. Their distribution is only limited by the availability of water for breeding. They can even survive in brackish water.

Cane ToadsCane toads are regarded as a pest because of the following factors:They are poisonousThey grow to a large size and can survive away from water for long periodsFemale toads produce a large number of eggs and the tadpoles that hatch from them are poisonousHave very few enemiesThey will eat nearly anything they can put in their mouthCane ToadsCane toads are found in a range of habitats which include forests, wetlands, swamps, farm dams and suburban back yards. The control of cane toads has never been enforced. Recently Brisbane City Council established the Cane Toad Eradication Committee in attempt to control the population.Cane ToadsPeople have been able to benefit from the cane toad. Universities use them for dissections and tests and their skin is a novel type of leather for shoes, handbags and wallets.

Cane ToadsTheir impact on native ecosystems has not been conclusively studied although it is obvious that they displace native amphibians. They do however help some native frogs by eating predators like snakes. The populations of three frog eating snakes: the death adder and two black snakes have declined since their introduction

HomeworkRead pages 197-201 HSC Spotlight TextUpdate electronic vocabularyComplete DOT Point 3.1 and 3.2Case Study: Becoming a Pest-European Carp, Lantana and Salvinia

Part 3-Lesson 2ActivityRead together pages 201-205 Prelim Spotlight TextCompete Activity 4.14 Introduced Species: Its Impact and Control pg 206 HSC Spotlight TextHomework Update electronic vocabularyFinish Activity 4.4 if necessaryComplete DOT Point 4.1-4.4