1. Lecture #3 Ecological Pyramids and the 10% Rule
Unit 8: Ecology

2. Ecological pyramids
Food Chains can also be represented by an ecological pyramid by arranging the organisms at various trophic levels diagrammatically.
Notice that there are many more producers than consumers.
Each trophic level consists of organisms that get their energy in the same way.

3. How is Energy Moved and Utilized in Ecosystems?
Ecology
4/23/2017
How is Energy Moved and Utilized in Ecosystems?
Trophic levels are ‘steps’ in the transfer of energy or matter within a food web.
The efficiency of energy transfer between different levels puts a limit on the number of trophic levels in an ecosystem.
G. Podgorski, Biol. 1010

4. Reminder from last time………..

5. What happens to the other 90%?
The ‘Rule of 10’
10% Rule (Energy / Biomass) - as an organism
consumes another organism, only about 10% of
the energy in the food becomes part of the
consumers body.
 This 10% is all that is available to the next trophic level when one organism consumes another.
What happens to the other 90%?

6. Answer: In every energy transfer, 90% of the energy is lost to the environment as heat, due to the various metabolic processes of the consumer.

7. The 10% rule is WHY the shape of an ecological pyramid is a ‘pyramid’
Explanation- At each
trophic level, the energy
stored by the organisms
in a level is about 1/10th
of that stored by the
organisms in the
level below.

8. Let’s Review……..
What determines the width of each block in an ecological pyramid?

9. Answer
The width of each ‘block’ is determined
by the amount of energy or biomass stored in
organisms at that trophic level.

10. 2. The width of the block also shows you the relative population size of the organisms present at each level (Ex: there tends to be more zebra than lions in the savannah)
3. The width of the block can give you an indication of the biodiversity that exists at that tropic level. Example - there tends to be more types of primary consumers than Secondary consumers, etc.)

11. This limits the number of trophic levels.
Ecology
4/23/2017
Only 10% of the Energy Present in Organisms of One Trophic Level Is Captured by Organisms of the Next
This limits the number of trophic levels.
G. Podgorski, Biol. 1010

12. Take 2 minutes to summarize the 10% rule and how it limits the number of trophic levels in an ecosystem.

13. Ecological pyramid- a diagram that shows the relative amount of energy or matter contained within each trophic level in a given food chain or food web.
There are 3 Types
Energy pyramids
Biomass pyramids
Numbers pyramids

14. Energy Pyramids These pyramids are used to show the
transfer of energy from
one level to another in
a food chain.
Calories are the unit of energy that is used.

15. Biomass pyramid A biomass pyramid shows the mass of
living tissue (biomass)
within each trophic
level.
Kilograms or grams are the unit of mass that is commonly used

16. Biomass Distribution

17. Numbers Pyramid
A numbers pyramid shows the total number of individuals in an ecosystem at each feeding level during one year.

18. Exceptions to the rule……
Sometimes, the # of
individuals in a trophic
level does not reflect
the amount of energy
that is present in a level.
Example: In a forest,
there are more insects
feeding on trees than
the trees they feed on.

19. In that instance, ecologists would use a
biomass pyramid rather than a numbers
pyramid to reflect the amount of
energy present in each trophic level.

20. What is a vegetarian diet more common in the developing world?
If you are the leader of a remote village in the developing world and had 100,000 lbs of grain with which to feed your (starving) people, would it make more sense to feed the grain directly to your people, or to cattle, which you could then feed to your people? Assume that every person in your village weighs 100 lbs.

21. How many people would this support for a year?
1,000 lbs of people
10,000 lbs of cattle
100,000 lbs of grain
10 people could survive for a year if the food was handled in this way

22. How many people would the grain support if it were fed directly to the people?
10,000 lbs of people
100,000 lbs of grain
100 people could be kept alive for 1 year if the food was handled in this way!

23. Take 2 minutes to summarize the information that can be learned through studying ecological pyramids, and why it is energetically your ‘best bet’ to feed from lower trophic levels.