A model ecosystem has a gross primary productivity of 6000 kJ in each square metre in a year…
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A model ecosystem has a gross primary productivity of in each square metre in a year. Its plants lose in respiration. The herbivores (T2) eat of the NPP while it is alive. The rest of the NPP goes to the detritus. T2 passes to T3, and T3 passes to T4. The remaining of each consumer level is lost, and of that loss is respired as heat. The other goes to the detritus. T4 is the top level and loses all its energy in the same way. The decomposers give off all the detritus as heat in the end.
- How much of the NPP goes straight to the detritus?
- What is the total energy that reaches the detritus?
- What is the total energy given off as heat?
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The worked solution
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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. GPP , plant respiration , in kJ. passes on. of each loss is respired.
Plan. Find the NPP and the energy of each level. Share each loss between heat and detritus.
Step 1. (a) NPP . T2 , T3 , T4 . The detritus gets straight from the plants.
Step 2. (b) The losses are , and kJ. Their total is . Thirty per cent of is . So the detritus is .
Step 3. (c) The consumers respire . The heat is .
Answer: ; ; .
Check. The total heat equals the GPP, so all the energy is accounted for.
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