Predator prey population links

Level 5

Curriculum area - Science

Outcomes

Students:

• Identify the cyclic nature of population numbers in an area and relate this to available food supplies.
• Use evidence to draw conclusions.

Materials and preparation

The African food web displayed with the cut-outs on a whiteboard, Australian cut-outs and the information table below to use in Part 2

Method

Part 1 - African food web

Conduct a guided class discussion to explore the growth spurt that occurs annually in this food web, along the following lines:

When the rains arrive in Africa, soon after the grasses are in abundance. What effects would this have on the animals of the ecosystem? (The herbivores that fed on the grasses can take advantage of the food supply and grow and reproduce. This in turn provides a greater food supply for the carnivores.) However this lush growth does not last for the whole year but occurs in an annual cycle.

How could the animals that feed off the grass cope with the different conditions - abundance and poor supply of grass at different times of the year? Also what methods do the carnivores use to cope with the corresponding flow-on food supply effects through the web. (Some animals such as crickets are short lived so they can live and reproduce in the short time that the grass is available. Some animals such as reptiles hibernate or go into dormancy during times of short food supply.)

'What about long-lived mammals, what options would they have?' (migration)

Part 2 - Australian food web

Display a food chain showing grass, kangaroos and dingo.

Present the information and table below to the students. The students plot the animal numbers against time and answer the questions.

A university student was studying the animals in the Grant Memorial National Park. Following are the numbers of kangaroos and dingoes that were recorded visiting a watering site in the middle of the park over two years.

Convert the figures into a line graph by plotting the animal numbers on the vertical axis against time on the horizontal axis. Plot the kangaroo numbers and the dingo numbers on the same graph but use different colours for each line.

What patterns can be seen in the graph? Suggest reasons for any patterns.

Is there any relationship between the kangaroo and the dingo numbers? If so, account for this.

The park management have decided to stop a rabbit prevention program because it is too expensive. What effect could this have on the dingo population and why?

Extension

Identify the reasons for the absence of large migratory populations in Australia.