Energy Pyramids

2.1 Energy Pyramids

Introduction:

The laws of thermodynamics describe the transfer of energy in systems. The first law states that energy is conserved in the system and cannot be created nor destroyed. The second law states that with each transfer, some energy will be lost or dissipated as a less usable form. As energy moves through the trophic levels of an ecosystem, for example, its availability diminishes as it travels from producer to each level of consumer. With each movement up the pyramid, a common rule of thumb is that roughly 90% of the available energy is dissipated.

TROPHIC LEVEL

Secondary carnivore
Primary carnivore
Herbivores
Primary producers

SILVER SPRINGS ENERGY PYRAMID

6 kcal/m²/yr

67 kcal/m²/yr

1,478 kcal/m²/yr

8,833 kcal/m²/yr

Net Production

TROPHIC LEVEL

Secondary carnivore
Primary carnivore
Herbivores
Primary producers

TYPICAL TROPHIC PYRAMID

0.1 kcal/m²/yr

1 kcal/m²/yr

10 kcal/m²/yr

100 kcal/m²/yr

Percent Available Energy

Light
Transmission
Electricity
Coal

LIGHTING ENERGY

0.63 kcal/m²/yr

31.5
kcal/m²/yr

35
kcal/m²/yr

100 kcal/m²/yr

Relative Energy Units

DISPLAY:

Silver Springs Energy Pyramid Typical Trophic Pyramid Lighting Energy

Data for Silver Springs Energy Pyramid from Odum, 1957. Data for Incandescent Light Bulb Energy Pyramid from Huang et al., 2011.

Select the display for the “Silver Springs Energy Pyramid”. The data presented on the diagram come from a study of the productivity of an actual ecosystem in Florida, USA. Hover over each bar to display the exact energy amount associated with each level in kcal/m²/yr.

Question

1. What general trend can you decipher by looking at the pyramid?

The amount of energy in the system stays relatively constant as you move up the pyramid.

The greatest amount of energy lost is between primary carnivore and secondary carnivore.

The amount of energy stays constant after the initial loss between primary producer and herbivore.

The greatest loss of energy occurs between primary producer and herbivore.

Correct.

Incorrect.

Question

2. Determine the total energy lost between the primary producer level and the herbivore level, and between herbivore and primary carnivore. The total energy in kcal/m²/yr lost at the first transition is ____, and at the second transition is ____.

1,478; 67

7,355; 1,411

1,411; 61

1,478; 1,411

Correct.

Incorrect.

Question

3. Determine the percent of energy lost between producer and herbivore as well as between herbivore and primary carnivore. The percent lost between producers and herbivores is____, and the percent lost between herbivores and primary carnivores is____. (Note: To determine the percent of energy lost, first find the difference in the amount of energy between two levels and then divide that number by the amount of energy in the lower of the two levels.)

17%; 9%

83%; 95%

67%; 83%

90%; 90%

Correct.

Incorrect.

Question

4. At what step is the greatest total amount of energy lost?

Between the herbivore and primary carnivore level because this shows the greatest percent loss.

On average only 10% of energy is retained from one level to the next, so the loss is equivalent between all levels.

At the first energy transfer from producer to herbivore.

There is not enough information to answer this question.

Correct.

Incorrect.

Now view the diagram based on the average energy loss of 90% between each trophic level. Select “Typical Trophic Pyramid” from the Display Menu.

Question

5. Assuming that humans are a part of this system and the food energy that nourishes the human population is derived from this system, which level can sustain the greatest population?

Primary producers

Herbivores

Primary predators

Secondary predators

Correct.

Incorrect.

Question

6. If humans are consuming a vegetarian diet, they are consuming organisms that are classified as primary producers. This means that 100% of the energy in the system would be available to feed them. Based on this energy pyramid, what percent of this amount would be available if humans consumed a strictly herbivore based diet?

10%

40%

50%

90%

Correct.

Incorrect.

Question

7. What conclusion can we draw about how the diet decisions of individuals or populations might impact our ability to feed the world?

It does not matter how much animal products are consumed, there will still be the same amount of energy at the primary producer level.

Our diet decisions do not impact food availability because we can always grow more food.

The more the human population consumes food at higher trophic levels, the less food there is to feed our growing population.

Food is grown all around the world and it is impossible to determine how much energy is captured by producers in any given area.

Correct.

Incorrect.

Question

8. Generally the human consumption of animal products is based on herbivores, which occupy the second level of the trophic pyramid. Notable exceptions to this generalization are many of the fish species that are extracted from the ocean for human consumption. For example, tuna are not herbivores but rather top predators. Based on what we know about energy movement through ecosystems, what can we conclude about tuna?

Their populations are necessarily small due to the lack of energy in the ecosystem at that level.

Tuna will always be abundant because 90% of the energy in the ecosystem is available to support their populations.

Tuna may be subject to overfishing due to their naturally small population sizes.

Both the first and third answer choices are correct.

Correct.

Incorrect.

Similar energy pyramids can be created for any transfer of energy. The resulting losses of energy between steps will vary and do not always follow the rule of 90% applied to ecosystems. Select “Lighting Energy” from the Display Menu to show the energy loss from the lighting of an incandescent lightbulb, beginning at a coal-fired power plant.

Question

9. Hover over each level to see the amount of energy available at each step. Which step represents the greatest percent loss of energy? What is the percent loss from the previous step?

Electricity; 98%

Electricity; 35%

Light; 65%

Light; 98%

Correct.

Incorrect.

Question

10. Despite the significant losses in available energy from one step to the next, energy pyramids such as this reveal to us the many places where improvements can be made to increase the efficiency of the system. At which energy transfer could the most energy potentially be saved?

The burning of coal to make electricity, where 65 of the 100 units of energy are lost.

The tranission step, where 31.5% of the energy is lost as heat.

The light step where the efficiency level is 98%.

The light step where 20.9 of the 100 units of energy are lost.

Correct.

Incorrect.

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Chapter 2. Energy Pyramids

2.1 Energy Pyramids

ENERGY PYRAMIDS

TROPHIC LEVEL

SILVER SPRINGS ENERGY PYRAMID

TROPHIC LEVEL

TYPICAL TROPHIC PYRAMID

LIGHTING ENERGY

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