Data Activity - Topic 2.1 - Breeding like rabbits!
Topic 2.1 looks at individuals, populations, communities, and ecosystems. This data activity asks you to consider the rabbit population in Australia, an extreme example of an invasive species exceeding the carrying capacity of the land.
NOTE: This activity is also available as a PDF.
Australia is home to roughly 200 million rabbits, which are not native to the country. The invasive species threatens around 300 kinds of plants and animals, and costs the economy $200 million in agricultural damage each year[1].
This situation can be traced back to just 24 rabbits − in 1859, Thomas Austin, a wealthy English settler, received a shipment of 12 pairs of wild and domestic rabbits from his brother in England.
Rabbits are known for their incredible ability to reproduce for a few reasons:
- Rabbits reach sexual maturity relatively early in their life, typically around 3 to 8 months. Once mature, they have the ability to breed all year round.
- Rabbits are rather promiscuous − they will mate with multiple partners.
- The gestation period for rabbits averages 31 days.
- Rabbits produce large litters, from 4-12 kits (baby rabbits) per litter. However, some breeds have been known to have up to 20 or more kits.
- A single female rabbit can have 6-8 litters in a year.
- rabbits are an example of an r-selected species, able to exploit open niches.
Let's use that knowledge to work out how the rabbit population in Australia grew so quickly.
1. Assume that each of the 12 original female rabbits had 6 litters in the first year, with each litter having 10 kits. Calculate how many rabbits there would be at the end of the year.
2. During that first year, however, some of the new baby rabbits will reach sexual maturity and also be able to have babies. Assume half the babies born are female and all females reach sexual maturity after 6 months. The table below models the situation in the first year.
We can see that the 120 babies born in January will reach sexual maturity in July and then be able to have 600 babies of their own.
Using the data above, calculate how many rabbits there would likely be in total at the end of the first year.
NOTE: The growth becomes even more rapid in the second year as the 600 new babies start reaching sexual maturity. In fact, the total number of rabbits at the end of the second year is 67,344 and at the end of the third year is 1,687,344.
Clearly the situation needed to be controlled. Two main biocontrols have been used in Australia:
- Myxomatosis – The myxoma virus was the first virus to be deliberately introduced to the wild to eradicate an animal. The virus leads to myxomatosis, a disease that only kills rabbits. Although the myxoma virus did lead to the deaths of many of the rabbits in Australia, the rabbits eventually developed an immunity to the virus, rendering it ineffective.
- Rabbit Haemorrhagic Disease (RHD) − This disease is caused by an RNA (ribonucleic acid) virus transmitted by flies, and it can kill rabbits in 48 hours. In 1995, this virus escaped a quarantine facility and made its way to the wild. As with the myxoma virus, the rabbits have begun to develop resistance to RHDV.
The graph below shows the rabbit population in Australia over time and the impact of these two different attempts to control the population.
Rabbit Abundance Index in Australia (1945-2029)
(Index = 100 in 1945)
Source: (PDF) Benefits of rabbit biocontrol in Australia
1. Using the graph above, calculate the change in the Rabbit Abundance Index as a result of the introduction of myxomatosis in 1950.
2. Similarly, calculate the change in the Rabbit Abundance Index as a result of the introduction of RHD in 1995.
3. Investigate other methods used in Australia to control the rabbit population and keep it below the impact threshold.