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I was reading Environmental Studies By B. S. Chauhan and there a diagram of a model of transfer of energy.

enter image description here

NU = Not used energy has been shown, energy that was neither stored or exported to the next level.

I wonder what physiological process causes this loss of energy at all trophic levels?

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In this diagram, since this is the only loss between trophic levels (along with respiration and NA within each trophic level), NU represents dead organic matter, that is not transferred along the food chain. In other words, this represents dead leaves that are not eaten by herbivores, hares that die of old age and not predation, and foxes that are killed by falling rocks. So NU is the amount of energy that goes directly into the decomposer community (another flow to decomposers is coming from matter that is excreted by herbivores and predators), since this diagram only includes primary producers, herbivores and predators.

NA, on the other hand, represents energy that is consumed by the next trophic level but not assimilated (Not Aassimilated). So this represents faeces etc.

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  • $\begingroup$ fileunderwater I just had some thoughts I wanted to know what you have to say, I couldn't ping you in Biosphere so I would just address you here. I was wondering do food chain end with a trophic level where the energy content is 0? I think it is possibly never happening (because if an organism feeds on some food it is sure to consume some sugar/fat/protein if the food is not entirely minerals and vitamins) so it is never zero. Besides though food chain theoretically ends with a greater carnivore but there's no terminal organism at the end to eat-to-be-eaten cycle (the food web). .cont.. $\endgroup$ – Tyto alba Jan 10 '17 at 20:18
  • $\begingroup$ So in an aquatic ecosystem where a hawk is supposed to have a very low A it is actually supported by different other food chains, raising its energy content to a sustainable level? $\endgroup$ – Tyto alba Jan 10 '17 at 20:18

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