Generation Game
The Rules of the Game
You will need pages R2 and R3. Scientists are worried that the
lovable little furry creature, the 'dirty rat' (Rattus
filthicus) is dying out. A careful study of their life-cycle
was made.
This showed:
- One-fifth of the rats die on their first birthday.
- One-fifth of the surviving rats die on their second
birthday.
- All rats surviving then die on their third birthday.
- The female always gives birth to one male and one female
rat at the beginning of her second year of life.
There are only 750 rats left. (250 baby rats, 250 rats between
1 and 2 years old and 250 between 2 and 3 years old; there are
equal numbers of each sex in each group)
When the total population falls below 300, the rats give up in
despair and become extinct. You are going to find the year when
they all die off!
Table 6 on page R2 starts to show the number of rats in each
age group every year for the 10 years.
- Complete the table for the first six years.
Figure 9 on page R3 shows the population pyramids for the
first three years.
- Draw the population pyramids for the next three years.
- Draw a graph to show the total population each year. Use
a scale of 1 cm to represent 1 year along the bottom.
(Make sure that your scale on the bottom goes along to 12
years.)
- Now make a projection for the year in which the rats
become extinct.
You can cheek your projection by continuing Table 6 until the
total population falls below 300.
*Not-so-dirty Rats
The dirty rats decide to improve their public health. As a
result fewer rats die at the end of their first and second years.
Play the generation game with different birth and death rates to
see how they affect population changes.
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