So here we have a 2-part example problem where part number 1 is here asking us to calculate net production efficiencies or MPE. And part number 2 is down below here asking us to calculate trophic efficiencies or TE values. We need to recall those equations from our previous lesson video, so I'll go ahead and paste those in here into their corresponding sections.
Part number 1 says, a grasshopper's body mass contains a total energy of 600 joules after it has assimilated 4,000 joules of plant matter throughout its lifetime. A praying mantis then consumes the grasshopper and assimilates 475 joules of energy. It then gains 220 joules of biomass.
Part number 1 wants us to calculate the net production efficiency or MPE of both the grasshopper throughout its life and the praying mantis as it eats the grasshopper. Recall from our previous lesson videos that net production efficiency or MPE can be calculated by taking the net productivity of the organism, dividing it by the assimilated energy of the organism, and then multiplying that ratio by 100%. Let's calculate that for the grasshopper throughout its lifetime first. The MPE value is equal to 6004000 multiplied by 100%, which is 15%.
This value represents the net production efficiency of the grasshopper throughout its lifetime. We then do the same calculation for the praying mantis. The MPE for the praying mantis is 220475 multiplied by 100%, giving an answer of approximately 46.32%.
The net production efficiency tells us how efficiently an organism converts its assimilated energy into biomass. For the grasshopper, 15% of its assimilated energy is converted into its own biomass, with the remaining 85% used for cellular respiration. For the praying mantis, 46.32% of its assimilated energy is used in its biomass, with the remaining energy used for its cellular respiration.
Let's move on to part number 2, where we are asked to calculate the trophic efficiency between the primary producers and primary consumers, and between the primary consumers and the secondary consumers. Trophic efficiency is the ratio of the net productivity across trophic levels, calculated by dividing the net productivity of the current trophic level by the net productivity of the previous trophic level, then multiplying by 100%. For the primary producers (tree) and primary consumers (grasshoppers), the trophic efficiency is 6000100000 times 100%, which is 6%.
For the primary consumers (grasshoppers) and the secondary consumers (praying mantis), the trophic efficiency is 10006000 times 100%, resulting in a value of approximately 16.67%.
This concludes this example problem, and I'll see you in our next video.