Populations/Teacher Notes

Teacher's Notes

Science Book: living environment page 56 Topic: Animal populations and ecosystems

Introductory Activity - BRAINSTORM - whole class

Q. What factors affect animal population numbers in the wild?

Probe – positive and negative factors Responses – food availability, pollution, weather conditions, water levels, disease, predators, etc Encourage pupils to build on what others have said and to say whether they agree with peer comments (building dialogue skills).

Introductory Activity - LOOKING AT GRAPHS - pairs/groups

Project or print the two graphs in figures 19 & 20. Teacher note: see text between and after the graphs. Look at the graphs of human and great tit populations and discuss:

Q. Tell the story of the graphs; what do they show?

Q. What factors might explain the changes in numbers over time?

Brief plenary.

Activity 3 - CASE STUDY

Case study of rabbits grazing on the North and South Downs of England (whole class teaching and discussion). Teacher note: see text p. 58-61 Show Fig. 22 Colonising chalk downlands and talk through it using Q&A. E.g.

Why might ground be completely bare? (clearing for agriculture, over-grazing, fire, volcano, quarrying) What happens over time?

Introduce succession as a predictable sequence of change. Point to grassland, shrubland, woodland. Chalk grassland would become woodland if left… why hasn’t that happened in the Downs?

What is the role of the rabbit (or sheep)? Grazing prevents trees developing… Why do farmers and vegetable growers install rabbit-proof fences? Why do certain plants increase and others decrease in number when rabbits are present?

Human intervention: tell the story of myxomatosis and its devastating effect on the rabbit population. (Play the song “Bright Eyes” if you want!) Explain that it ultimately died out. What other animals might have been negatively affected by the virus? Why? - predators of rabbits, grassland dwelling birds, rabbit hole inhabitants What animals might have been positively affected by the virus? - competitors What happens when there are no animals grazing? Discuss the positive effects of grazing – biodiversity.

The above Qs can be discussed in groups to get pupils thinking.

Activity 4 - CONCEPT MAP - Whole class

see Fig. 24 mapping interrelationships between rabbits and other organisms on downland

This could be done on the IWB as it exploits the interactive nature of the technology. Provide each organism as a labelled object on the board. Ask pupils to suggest links. You may want them to work on this in groups at tables first (using paper or min-whiteboards), with one group then demonstrating their representation on the IWB, for constructive critique and extension by others.

Introduce the notion of natural selection after this. Teacher note 1 – p.62.

Q. What other examples of natural selection can you think of? Managing the downlands - Teacher note 2 – p.62.

Conclusion: change in ecosystems upsets the whole balance… fragility and instability How much interference should humans make to protect one species or habitat?