Year 8 Science · Unit 1 · Lesson 24

Population Changes and Introduced Species

Challenge Worksheet

Name

Date

Class

Learning Goals

Construct a multi-step ecological prediction about the consequences of feral cat eradication.
Consider second-order and unexpected ecological effects using food web principles.
Evaluate the complexity of ecosystem restoration using specific Australian species as evidence.

Go Deeper

What if…?

Scenario

Feral cats (Felis catus) are estimated to kill around 1 billion native animals in Australia every year, making them one of the biggest drivers of native mammal extinction. In 2024, the Australian Government committed to a new national feral cat management strategy. Imagine that, through a combination of biological control, baiting and island eradication programs, feral cats were completely removed from mainland Australia over a 20-year period. Consider what would happen next, not just the obvious recoveries, but also any unexpected consequences.

Using what you know from this lesson, predict and explain what would happen to the Australian ecosystem if feral cats were completely eradicated. Your answer should:

Name at least TWO native species likely to recover and explain why.
Name at least ONE species or population that might unexpectedly increase to problematic levels once feral cat pressure is removed (think: what do cats also eat besides native animals?).
Explain how these changes would ripple through the food web.
Discuss whether "eradicating cats" alone would be enough to fully restore the ecosystem.

Challenge4 marks

Show What You Know

1. The concept of "trophic cascade" (from Lesson 22) and "introduced species" (this lesson) are closely related. Using the example of foxes being introduced to Australia, explain how the removal of a single predator from a food web (such as a native predator that would normally control fox numbers) can cascade through the entire ecosystem.

Challenge 3 marks

2. A student argues: "The best way to fix introduced species problems is to introduce another species that preys on them, like introducing a predator to eat cane toads." Evaluate this strategy using at least two specific pieces of evidence from Australian history. Is it a good idea? Why or why not?

Challenge 4 marks

Wrap Up

In one sentence, what was the main idea of this lesson?