Food Webs and Energy Pyramids

Food Chains

• A food chain is a simple way to show feeding relationships among organisms.

• It starts with a producer and ends with a final consumer.

Food Web

• In real situations, most animals eat more than one thing.

• A food web show the many complicated relationships among organisms living in a ecosystem

A Food Web

A Food Web

Drawing a Food Web

1. Figure out what eats what2. Decide which trophic level each

organism belongs in3. Place the producers at the bottom of the

web4. Place each organism in a place where it

represents the trophic level 5. Draw arrows pointing from the food to

the eater.

Draw a food web

• Organisms:

algae, protozoan, small fish, large fish, bear, deer, raspberries, rabbit, hawk, grass

raspberriesgrassalgae

rabbitprotozoan

small fish

large fish

bear

deer

hawk

Energy Pyramids

• Energy pyramids help us understand the flow of energy through ecosystems.

Energy Flow through an Ecosystem

When an organism eats:• 60% of the energy is not

used and is passed out as waste.

• 30% used for cellular processes (so the organism can live)

• 10% of the energy is stored in the body ( to make the organism grow and get fat)

Energy flow

• The 10% of the energy of the food consumed by the organism is transferred to the next trophic level.

Creating an energy pyramid

1. Figure out how much energy each level has (remember the 10% rule: only 10% of the energy is passed to the next level)

2. Decide on your scale: make the bottom of the pyramid as large as you can.

3. Figure out the size of each level in your pyramid.

4. Draw it neatly and accurately

Creating an Energy Pyramid

• The producers in an ecosystem contain 50, 000 kJ/m2

• How much energy is available in each of the other trophic levels?

• 2nd trophic level: 50,000 ÷ 10 = 5000 kJ/m2

• 3rd trophic level: 5000 ÷ 10 = 500 kJ/m2

• 4th trophic level: 500 ÷ 10 = 50 kJ/m2

Creating an Energy Pyramid

• Decide how big to make bottom level of the pyramid (make is as big as possible)

• Make each higher level one tenth the size of the one above.

Creating an Energy Pyramid