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Difficulty: MediumEnergy Flow, Food Chains, and Ecological Pyramids

In a terrestrial grassland ecosystem, the total energy fixed by green plants (producers) is measured at 20000 kJ m−2 yr−120{}000\text{ kJ m}^{-2}\text{ yr}^{-1}. According to Lindeman's 10%10\% law of ecological efficiency, what amount of energy will be available to the secondary consumers in this ecosystem?

  1. A
    2000 kJ m−2 yr−12{}000\text{ kJ m}^{-2}\text{ yr}^{-1}
  2. 200 kJ m−2 yr−1200\text{ kJ m}^{-2}\text{ yr}^{-1}Answer
  3. C
    20 kJ m−2 yr−120\text{ kJ m}^{-2}\text{ yr}^{-1}
  4. D
    20000 kJ m−2 yr−120{}000\text{ kJ m}^{-2}\text{ yr}^{-1}

Answer

The amount of energy available to secondary consumers is 200 kJ m−2 yr−1200\text{ kJ m}^{-2}\text{ yr}^{-1}.
Secondary consumers occupy the third trophic level. Beginning with 20000 kJ m−2 yr−120{}000\text{ kJ m}^{-2}\text{ yr}^{-1} at the producer level, primary consumers (level 2) obtain 10%10\% of this energy (2000 kJ m−2 yr−12{}000\text{ kJ m}^{-2}\text{ yr}^{-1}). Secondary consumers (level 3) retain 10%10\% of the energy from primary consumers, which equals 200 kJ m−2 yr−1200\text{ kJ m}^{-2}\text{ yr}^{-1}.

Step-by-Step Solution

1
Identify the trophic level of secondary consumers.
Producers belong to Trophic Level 1, Primary Consumers to Trophic Level 2, and Secondary Consumers to Trophic Level 3.
Energy flows sequentially from producers to consumers across discrete trophic steps.
2
Calculate energy available at Trophic Level 2 (Primary Consumers).
20000 kJ m−2 yr−1×0.10=2000 kJ m−2 yr−120{}000\text{ kJ m}^{-2}\text{ yr}^{-1} \times 0.10 = 2{}000\text{ kJ m}^{-2}\text{ yr}^{-1}.
Approximately 10%10\% of net primary production is assimilated by herbivores, while 90%90\% is lost as metabolic heat and unconsumed waste.
3
Calculate energy available at Trophic Level 3 (Secondary Consumers).
2000 kJ m−2 yr−1×0.10=200 kJ m−2 yr−12{}000\text{ kJ m}^{-2}\text{ yr}^{-1} \times 0.10 = 200\text{ kJ m}^{-2}\text{ yr}^{-1}.
Applying the 10%10\% transfer efficiency once more determines the energy incorporated at the carnivore/secondary consumer level.

Key Concept

10% Law of Energy Transfer across Ecological Trophic Levels
Estimated Time:1m 15s
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Topics

Energy Flow, Food Chains, and Ecological Pyramids

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