Use Slide 14 to prompt students to write down as many observations as they can about how the four ecosystems are alike and different.
- The main thing they should notice is that the relative sizes of ecosystem pools is the same across ecosystems: the largest pool is the soil organic carbon, followed by producers, then herbivores, then carnivores.
- They may also notice that soil organic carbon is the largest pool in the prairie, but the forest has the most organic carbon in producers. You may use this opportunity to talk about how pool sizes are different because of the history of the site (lots of grasses growing and dying increase the soil organic carbon pool) and the size of the organisms that live there (trees versus corn).
- They should also notice that the total organic carbon differs across ecosystems.
- They may also notice that human management produces a somewhat different pattern for the corn field. Humans use fences, hunting, and pesticides to kill or keep out most herbivores (since we want to use the corn for ourselves), so the herbivore and carnivore populations are much smaller than for natural ecosystems.
Use Slide 15 to introduce the ideas differ in the total organic carbon that they can support Students will be explore this idea more deeply more in Lesson 4. Ecologists answer the last question (about why different ecosystems have different amounts of total organic carbon) by identifying limiting factors, including:
- Water (the primary limiting factor for deserts)
- Temperature (the primary limiting factor in Arctic and alpine ecosystems)
- Nutrient availability (the primary limiting factor in rain forests)
This is a good time elicit students’ ideas and questions about what limits organic carbon in different ecosystems. You do not need to teach about limiting factors at this point.
Accommodation: For the information on the final slide, as a class create organic matter pyramids or other bar graphs to show the size of the pools as visuals. Have students describe the organic matter pools in the four ecosystems (desert, forest, corn field, and prairie) including the herbivores, producers, and carnivores that live in each ecosystem.