1. Limits on Energy Transfer and Ecological Pyramids
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2. Learning Goals and Success Criteria
I will learn about the limits on energy transfer in an ecosystem.
I can produce an ecological pyramid to represent the energy transfer within an ecosystem.

3. spruce tree → deer → wolf
Trophic Levels
One way to group living things is by the amount of energy they gain from their food.
Trophic Level – the position that an organism occupies in its food chain
You can determine to what trophic level an organism belongs by looking at its food chain:
spruce tree → deer → wolf

4. Limits on Energy Transfer
Energy is constantly being changed from one form to another in an ecosystem.
Consider:
spruce tree → deer → wolf
Energy transfer starts when plants convert light to sugar. However not all the chemical energy that a plant creates is available to the animal that eats it. WHY?

5. Limits on Energy Transfer
The tree needs and uses some of that energy to stay alive and grow
The deer does not eat all parts of the tree
Therefore, only about 10% of the energy that the tree creates is available to the deer.
Even less energy is available to the wolf because:
The deer uses energy to grow, look for food, hide from predators, mate, and feed its young
The wolf does not eat the fur or hooves of the deer

6. Limits on Energy Transfer
On average, only 10% of the energy available at one trophic level will be passed on to the next.
The further up a food chain you travel, the less energy that is available. This sets a limit on the number of trophic levels in a food chain.

7. Ecological Pyramids
Graphs called pyramids can be used to represent energy flow in food chains – allows us to compare ecosystems.
Pyramid of Energy
measures the amount of energy available at each trophic level

8. Ecological Pyramids

9. Ecological Pyramids Pyramid of Numbers
counts the number of organisms at each trophic level
usually same shape as pyramid of energy – WHY?
If there’s less energy available at higher levels, fewer organisms can be supported. The snake has to eat 10 mice to gain just as much energy that one mouse gained from 1 insect.

10. Ecological Pyramids Pyramid of Biomass
the mass of dry tissues in plants and animals at each trophic level