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SNC2D
ECOLOGICAL PYRAMIDS
Name: _________________
Introduction: The ecological pyramids of numbers, biomass, and energy provide models for
ecologist to better understand the workings of an ecosystem. You should read p. 37-38
(the sections of Graphing Energy in Ecosystems: Ecological Pyramids)
Objectives: In the following exercise, you will have the opportunity to see the relationship
between the Pyramid of Numbers and the Pyramid of Biomass. You will be able to relate
this exercise to actual habitat.
Materials: this work sheet, food chain simulator, graph paper
Assumptions:
A. One mountain lion eats approximately 510 kg of venison each year as well as
numerous smaller animals. However, the mountain lion will eat only 50% of each
deer he/she kills.
B. One deer eats approximately 1655 kg of vegetation each year in the form of grasses,
nuts and berries.
C. One square kilometer of deer habitat produces 135 kg of deer food each year.
Problems:
1. What is the minimum area (in km2) of habitat is needed to support one deer?
2. How many deer are needed to feed one mountain lion for a year if the deer average
70 kg in weight?
3. What is the minimum area (in km2) of deer-lion habitat is needed to support one
mountain lion?
Procedure:
1. Find the area of Ottawa.
2. Using the answer from problem #3, determine how large an area of Ottawa this
would cover. (This is just to help you get a feel for the relative size of the habitat –
mountain lions really only live in the mountains of the west coast in the Americas.)
3. Fill in the following table for the area you calculated in Problem #3:
Species
Mountain Lion
Deer
Vegetation
Trophic Level
Energy (MJ/yr)
6,360
115,600
914,500
Number of
Individuals
1
Biomass (kg)
67
9,150,000
4. Take a look at the example for the pyramid of energy in Figure 6 on p.37. Notice
that the boxes are scaled so that their size represents the amount of energy. Using
the information from the table above, draw and label a scaled pyramid of energy for
our food chain on your graph paper … your pyramid can be two-dimensional.
5. Use the rest of the information from your table to draw two more pyramids: a
pyramid of numbers and a pyramid of biomass.
6. Write down your answers to Questions 1-9.
7. Open the simulator from the internet. Read through the instructions before you
begin. Note that you can view your simulation three different ways: in terms of
numbers, a graph of the population, and a pyramid of biomass.
8. Start with 20 foxes, 2,000 rabbits, and 50,000 producers. Run the simulator in the
biomass mode. How did the populations of the three trophic levels do? (You may
choose to view a graph of the populations.) Record your findings in the table found
at Question #10 at the end of this worksheet.
9. Reset the simulator. Choose 1 trophic level and change its starting population. Rerun the simulator. What happened to the populations?
10. Repeat step 9 three times and choose 3 different starting population for the same
trophic level you changed.
11. Repeat steps 9 and 10 by changing the starting population of the other two trophic
levels (one trophic level at a time!).
Questions:
1) How large of an area is Ottawa?
2) Does the area needed to support one mountain lion cover:
i. only a small part of Ottawa?
ii. half of Ottawa?
iii. exactly the same size as Ottawa?
iv. an area larger than Ottawa?
3) What type of habitat do mountain lions really live in? Describe 3 biotic and 3 abiotic
conditions of this habitat.
4) What is discontinuous habitat?
5) What effect does this discontinuous habitat have on the deer and mountain lions?
6) How tolerant are deer and mountain lions to human disturbance?
7) How do the shapes of the three pyramids compare?
8) Is it possible to have this pyramid of numbers? Explain.
4th Trophic Level (5
carnivorous birds)
3rd Trophic Level (300
carnivorous insects)
2nd Trophic Level (100,000
herbivorous insects)
1st Trophic Level (500 trees)
9) Is it possible to have this pyramid of energy? Explain.
4th Trophic Level (90 MJ
carnivorous birds)
3rd Trophic Level (1600 MJ
carnivorous insects)
2nd Trophic Level (15,000
MJ) herbivorous insects)
1st Trophic Level (3000 MJ
trees)
10) Record your observations from the simulator here:
Trial
1
2
3
4
5
6
7
8
9
10
11
12
13
Fox
Population
Rabbit
Population
Producer
Population
20
2,000
50,000
Starting
Biomass
Pyramid
Shape
11) What is the affect on the food chain for each of the following changes:
i. Too many secondary consumers?
ii. Too many primary consumers?
iii. Too few primary consumers?
iv. Too many producers?
v. Too few consumers?
A BONUS QUESTION is continued on next page …
Result
12) Below are two pyramids of biomass from two different ecosystems. Based on your
results from the simulator you would expect the ocean ecosystem to be unstable
because of the small amount of producer biomass. How could you explain the fact
that the ocean ecosystem’s biomass can remain stable (unchanging)? How are the
producers in the ocean different from producers on land?
Modified from http://sftrc.cas.psu.edu/LessonPlans/Wildlife/EcologicalPyramids.html