Year 8 Science · Unit 1 · Lesson 24
Apply Worksheet
Learning Goals
Read the graph
The bar chart below shows estimated rabbit population in Australia at key points between 1860 and 2000. Study it carefully, then answer the questions.
Data: CSIRO estimates, Australian Department of Agriculture.
(a) Describe the trend in rabbit population between 1860 and 1950. What biological factors explain why the population grew so rapidly during this period?
(b) Compare the effect of myxomatosis (1955 bar) with the effect of calicivirus (2000 bar). Which appears more effective at reducing rabbit numbers? What concern might scientists have about the 1980 data point?
(c) Using the concept of population dynamics (birth rate, death rate, and limiting factors), explain why rabbit numbers bounced back between 1955 and 1980 even after myxomatosis killed most of the population.
Real-world context
Cane toads (Rhinella marina) were introduced to Queensland in 1935 to control cane beetles in sugar cane crops. They have since spread across most of northern Australia. As of 2024, climate modelling by the University of Sydney suggests that warmer temperatures caused by climate change could allow cane toads to expand their range southward into coastal NSW and eventually into Victoria, regions where native predators have never encountered the toxic toad before.
(a) Cane toads are toxic to predators who try to eat them. If cane toads expand into southern NSW, predict what would happen to native predator species (such as blue-tongue lizards, monitor lizards and quolls) that have no experience with the toad's toxin. Use the concept of population dynamics in your answer.
(b) If native predator populations decline due to cane toad toxin, predict TWO flow-on effects for the broader food web. Name specific species likely to be affected and explain the food web links.
1. Why is it considered risky to introduce a biological control agent (like myxomatosis or calicivirus) to control an invasive species? What could go wrong?
Wrap Up
In one sentence, what was the main idea of this lesson?