Stock a pond with plants and animals, press play and watch ten seasons go by. Can you keep the food web in balance?
THE POND FOOD WEB
Plants are the producers. They make food from sunlight. Every other living thing in the pond depends on them.
Arrows show where the food (energy) goes. At each step up the web, much of the energy is used up for living and moving, so there are fewer hunters than hunted.
Take out a hunter, and the plant-eaters can multiply until they strip the pond of plants. Then they starve too.
An invader with no hunters can take over. Fertiliser washing in feeds algae, which shade out the plants.
This game is a simple model with round numbers. Real ponds are more complicated, but they follow the same rules.