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## 'Food Web' printed from http://nrich.maths.org/

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A simple ecosystem consists of ample grass, a herd of 50 deer, a nest of 2000 rabbits, a cast of 10 hawks and a sleuth of 5 bears. Deer and rabbits are herbivores, hawks only eat rabbits and bears eat both deer and rabbits.

Draw a food web, showing how the animals in this ecosystem are fed and what the transfer of energy is.

Discuss what would happen to the ecosystem if...

• The deer began reproducing rapidly.
• Some of the rabbits migrated out of the area.
• The bears were hunted by humans.

The average weight of the animals in this ecosystem is given in the table below:

 Animal Weight Deer 150 kg Rabbit 1 kg Hawk 1 kg Bear 500 kg

In the autumn, a bear needs to consume as much as 40kg of food a day as it prepares for its winter hibernation.  A hawk will eat up to 1kg of food at a time, although it can then go without food for a day or two.

Rabbits reproduce quickly: a single female can produce up to 800 children, grandchildren and great-grand children over a season (February to October in the northern hemisphere, July to February in the southern hemisphere).

Is this eco-system sustainable over time?