This document discusses trophic levels in food chains and energy transfer through ecosystems. It defines trophic levels as the position organisms occupy in a food chain based on what they consume for energy. Food chains show the transfer of energy from producers like plants at the first trophic level to primary, secondary, and tertiary consumers at higher levels. Food webs represent multiple interconnected food chains and alternative pathways for energy transfer. There is a 90% loss of energy between each trophic level, demonstrating that less energy is available at higher levels. This energy transfer can be represented by an ecological pyramid that shows decreasing numbers of organisms and available energy as one moves up trophic levels in an ecosystem.

1. Trophic Levels,
Energy transfer
and Pyramids

2. Trophic Levels – is the
position an organism
occupies in a food
chain. It refers to food or
feeding.

3. Food Chain

4. Food Chains
The energy flow from one trophic level
to the other is know as a food chain
Producers are at the first ENERGY LEVEL
Primary Consumers are the SECOND
ENERGY LEVEL
Secondary consumers are at the THIRD
ENERGY LEVEL

5. Trophic Levels (feeding levels)
3
2
1

6. Food Web
Food webs are
multiple food chains.

7. Food Webs
Food webs show
ALTERNATIVE PATHWAYS
other possible pathways
through which an
organism can obtain
energy

8. Food webs

9. Energy Level Producer, primary
consumer, secondary
consumer, tertiary
consumer?
Grass
Mouse
Grasshopper
Frog
Owl
Hawk
1st producer
2nd Primary
consumer

10. Energy Level Producer, primary
consumer, secondary
consumer, tertiary
consumer
Grass 1st Producer
Mouse 2nd Primary consumer
Grasshopper 2nd Primary
consumer
Frog 3rd Secondary
consumer
Owl 3rd
and 4th Secondary and
tertiary consumer
Hawk 3rd Secondary
consumer

12. Transfer of Energy
Energy lost from chain
“link” to “link” is
significant!

13. from grass to sheep, loss is about
90%!
10% Original
Energy! 1% Original
Energy!
100% Energy
Available
HEAT
90%
HEAT
90%

14. Energy lost from one trophic level
(energy level) to the next level can be
represented by a pyramid
PRODUCERS
1° CONSUMERS
2° CONSUMERS
3°
CONSUMERS
4⁰°
CONSUMERS

15. ♦Each level above only gets
10% of the energy from below
− Ex: 10,000 J of producers (plants) only give 10% of
energy to primary consumers
> 1,000 J to primary consumers (snails,
minnows, dragonflies)
> 100 J to secondary consumers (small fish)
> 10 J to tertiary consumers (big fish)
> 1 J to quaternary consumers (fish hawk)

16. ENERGY PYRAMID
10,000 J10,000 J
1,000 J1,000 J
100 J100 J
10 J10 J
1 J1 J

18. Usually no more than 4 trophic
levels since 6th level would have
very little energy to keep it alive

19. Ecological Pyramid
• Which level has the most energy?
• Which level has the most organisms?
• Which level has the least organisms?
• Which level has the least energy?