Adapted from http://www.science.org.au/nova/001/001print.html accessed 20/6/2012
| Year | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| Rabbits per kilometre | 120 | 100 | 20 | 25 | 20 | 35 | 28 | 45 | 50 | 60 | 75 | 60 | 60 | 80 | 110 |
| Rabbits per hectare | 12 | 10 | 2 | 2.5 | 2 | 3.5 | 2.8 | 4.5 | 5 | 6 | 7.5 | 6 | 6 | 8 | 11 |
- Graph the rabbit density per hectare. How do you explain the apparent existence of half rabbits in years 4, 6 and 8? (Hint 10,000 square metres = 1 hectare)
- In which year do you think a biological control agent was released? Explain
- Why did the scientists count the rabbits at the same time every year? Suggest reasons why the results might have been different if they had counted rabbits in early summer rather than early autumn.
- How do you explain the fluctuations in rabbit numbers between years 4 and 8?
- How do you explain the increase in rabbit numbers in years 13, 14 and 15?
- A new biological control agent is introduced after year 15 and rabbits become scarce. What do you think the farmer can do to make sure that rabbit numbers stay low?
Transmission of myxoma virus depends on mosquitoes or fleas probing through a virus-rich lesion, virus adhering to the mouthparts of the insect vector and being inoculated into another rabbit next time the vector feeds. Virus strains that allow the rabbit to survive in an infective state for longer periods have a selective advantage over highly lethal virus strains because they are transmitted more efficiently. Natural selection also allowed some rabbits with resistance to myxomatosis to survive infection and breed, thus passing on their resistance genes.
- When the myxoma virus was released in Australia in 1950 it was estimated that in some places 90 per cent of the rabbits died within 3 or 4 weeks.
a) Explain why, almost 50 years later, we still have a rabbit problem.
b) What could be done to prevent the same thing happening with the calicivirus?
c) Why does a lethal virus have less selective pressure than one that enables its host to remain infective for longer periods
of time?
- To date, the best spread of the calici virus and most effective killing of the rabbits have been recorded during the breeding season of rabbits. Explain why.
The calicivirus controversy: a role play
Use role play to simulate a meeting of concerned people in an area where rabbits are a problem. Representatives could include a grazier, an animal liberationist, a geneticist, a politician, an environmentalist, a zoologist and/or botanist, and a veterinarian.Teachers notes
The following 'position statements' might help students get started.
Grazier: I have 1.5 million rabbits on my property and soon I will be unable to make a living. I have tried many control methods but the problem is too big. Shooting only gets rid of a small number of rabbits; many rabbits are now immune to myxomatosis; ripping up or bulldozing a warren costs $20 to $40 per warren; poisons are expensive. If I could get hold of an infected carcass, I would get it onto my property as soon as possible.
Botanist: Rabbits graze on small shrubs and trees as well as grass. Trees and shrubs in inland Australia have only been able to grow and survive to reproduce during two periods in Australia's history: once before rabbits were introduced and once just after myxomatosis was introduced. Scientists are now worried that the remaining seeds are close to their limit of viability.
Zoologist: Over 25 per cent of the native mammals have disappeared in areas that are heavily infested with rabbits. Rabbits are very efficient grazers and also destroy habitats that may be necessary for the survival of some small mammals. Zoologists are concerned about the viability of these small mammals.
Politician: The Akubra hat industry forms part of my constituency. It takes fur from 13 rabbits to make one Akubra hat. If the Australian rabbit population is decimated, the Akubra industry will have to import rabbit fur from elsewhere. However, as a Senator, I also represent graziers who are demanding the release of the virus to save their properties from being denuded by rabbits.
Environmentalist: My organisation is very concerned that if the rabbit population is decimated, foxes will prey on small native mammals instead, thus endangering the survival of the native mammals. On the other hand I also appreciate that rabbits have a destructive effect – on plants and on species of animals that depend on the plants for food and shelter.
Geneticist: Is it possible that the rabbit calicivirus disease is capable of infecting animals other than the rabbit? Viruses are known to mutate quite readily, and a mutation might allow the virus to jump between species.
Veterinarian: There are vaccines currently available in Australia that will protect inoculated rabbits from contracting the disease. We need to run an advertising campaign to tell people that they can have their pet rabbits inoculated against the virus. The government should pay for this campaign and for the cost of the inoculations out of the money that is made from the increased productivity of the farms.
Animal liberationist: My organisation is opposed to the human species modifying the environment to suit itself. Other species in this world are equally important and we should not destroy the rabbit population of Australia.
To make the best use of role-play activities:
- have a clear idea of the desired outcomes;
- help students by ensuring that they have adequate information and that they understand the likely attitudes of the people they are representing.
Always leave time at the end of the lesson for debriefing. Debriefing can include questions that help students to distinguish between the simulation and reality, and between their own attitudes and those they acted out during the role play. In addition, you could tell students the desired outcomes and then they could discuss how effective they think the activity was. Debriefing helps to ensure that any antagonisms developed during the role-play do not continue after the lesson.