1. Ecosystems Unit Activity 2.3 Biomass Patterns in Ecosystems
Carbon: Transformations in Matter and Energy
Environmental Literacy Project Michigan State University
Ecosystems Unit Activity 2.3 Biomass Patterns in Ecosystems
Discuss carbon pool sizes in different ecosystems.
Use Lesson 2.3 Comparing Different Ecosystems Presentation to compare Sunny Meadows to different ecosystems.

2. The Meadow Simulation
Take out your completed 2.2 Meadow Simulation Worksheet
What was the maximum biomass of foxes that you observed at the end of the 100-year simulation (any trial)?
What was the maximum biomass of rabbits that you observed at the end of the 100-year simulation (any trial)?
Discuss results of the Meadow Ecosystem investigation.
Ask students to take out their completed 2.2 Meadow Simulation worksheet. Open 2.3 Biomass Patterns in Ecosystems PPT.
Use slide 2 to discuss the maximum biomass of foxes and rabbits that students observed in any trial of the investigation. Make sure that they recognize that many different initial settings lead to the same final outcomes (maximum biomass of foxes = 9 and maximum biomass of rabbits = 90).

3. Results of the Meadow Simulation
What was the maximum biomass of grasses that you observed at the end of the 100-year simulation (any trial)?
Why did the greatest grass biomass occur when the foxes and rabbits died off?
Use slide 3 to discuss the maximum biomass of grasses that students observed in any trial of the investigation. Make sure that students recognize that the maximum grass biomass was observed when the rabbits died out, since there were no herbivores to eat the grass.

4. Meadow Simulation Class Results: What initial biomass settings lead to the highest fox biomass?
Initial settings
100 years later
Foxes biomass
Rabbits biomass
Grass biomass
Initial settings
100 years later
Foxes biomass
Rabbits biomass
Grass biomass
Discuss the initial settings that resulted in the highest fox biomass at the end of the simulation.
Use slide 4 to record the data (initial and final biomass of grasses, rabbits, and foxes) from at least 3 groups. Students should recognize that many different initial settings lead to the same outcome. Ask students to share their ideas about how different initial settings could lead to the same outcome.
Initial settings
100 years later
Foxes biomass
Rabbits biomass
Grass biomass

5. Discussion Questions
In any trials did you get foxes completely die out? How do we explain this?
If grasses, rabbits, and foxes all survived for 100 years, the final biomass of each population at the end of the simulation was always the same. How do we explain this?
Use slide 5 to ask In any trials did you get foxes completely die out? How do we explain this?
Make sure that students recognize that if the rabbits do not have enough food (grasses) that they die off, which in turn removes the food source for the foxes, which causes them to die off.
Ask If grasses, rabbits, and foxes all survived for 100 years, the final biomass of each population at the end of the simulation was always the same. How do we explain this? Help students to recognize that foxes eat rabbits and rabbits eat grasses. If all three populations are going to survive then the biomass of grasses must be greater than the rabbits, and the biomass of the rabbits must be greater than the foxes.

6. Complete the Evidence-Based Arguments Tool
Students complete the Evidence-Based Arguments Tool.
Display slide 6. Pass out one copy of 2.3 Evidence-Based Arguments Tool for Ecosystems to each student. Review the Tool directions. Instruct students to use their data from the 2.2 Meadow Simulation worksheet as well as what they learned from today’s class discussion to complete the tool
Give students about 5-10 minutes to complete the process tool.

7. Conclusion #1
The biomass diagram that represents the maximum fox and rabbit biomass in the meadow resembles a pyramid. How do we explain this?
Use slides 7 and 8 to review the two main conclusions that students should have on their Evidence-Based Arguments Tool.
The biomass diagram that represents the maximum biomass of all three populations resembles a pyramid (this diagram is also called the biomass pyramid). Ask students to share their ideas about why so much grass biomass is necessary to support so few foxes. They will learn more about this in the next lesson.

8. Conclusion #2
Only three final biomass diagrams are possible in the meadow ecosystem. How do we explain this?
There are three possible final biomass diagrams that could occur in the meadow ecosystem (the biomass pyramid with all three populations, rabbits and grasses only, and grasses only). Students will not have observed rabbits and grasses only in the simulation and may need help thinking about how this could occur (if the rabbit population dipped so low that the foxes died out, but there were still a few rabbits left to reproduce and repopulate the meadow).

9. Biomass Patterns in Ecosystems
So far we have identified an important pattern in the biomass of different populations in an ecosystem: Producers > herbivores > carnivores We also found that there is a specific biomass of each population that the meadow can support. This is called the carrying capacity. What determines the carrying capacity for each population?
Conclude the discussion of the meadow ecosystem and connect it to future lessons.
Use slide 9 to summarize the key idea that the biomass of producers > biomass of herbivores > biomass of carnivores. Introduce the term carrying capacity and ask What determines the carrying capacity for each population? Make sure that students recognize that resource availability (in this case, the food source) determines the carrying capacity for each population in an ecosystem.

10. Unanswered question
What are the processes that cause the biomass pyramid?
This will be the focus of the next lesson.
Use slide 10 to emphasize that the biomass pyramid is an important pattern in ecosystems, but that we have not yet explained what causes this pattern. That will be the focus of lesson 3.