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I remember learning in school many years ago that each level of the food chain is only about 10% efficient. So when an herbivore eats a plant, they get 10% of the energy that the plant had, and a predator eating that animal gets 10% again, and so on. This is similar to the argument of why vegetarianism is much better for the environment, because it requires less energy.

My question is, is there any basis for the 10% figure? I understand that there has to be an energy loss, but how could we know exactly what it is numerically? I would think that with things like the physical activity of the animal, its total life span, its own digestive efficiency, etc. the actual value could be all over the place. Is there any science to support such a precise figure?

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    If that were the case, we would be better of eating grass than beef. In fact, cows are much better than humans in processing foodstuff that is high in cellulose. So it highly depends on the actual food. – Konrad Rudolph Sep 3 '11 at 11:06
  • Is this question about validating the claim or the methodology? – Monkey Tuesday Sep 3 '11 at 13:21
  • by that logic, vegetarians ought to switch to photosynthesis ;-) – vartec Sep 5 '11 at 10:12
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The answer is, no. This is called "Linderman's law of trophic efficiency" (Linderman. 1942), but it is far from a law - the reality is that there is a large variety of trophic efficiencies, and these depend on the type of animal and the food being consumed. Linderman's law is a heuristic tool - a concept useful for teaching not strictly based on fact.

a more detailed explaination:

In a simple system, trophic levels are, e.g. plants, herbivores, and carnivores. There are often more levels in the ocean than on land. For example, crustaceans eat algae, fish eat crustaceans, fish eat fish, sharks eat fish. Or cow eats grass, people eat cow.

The question is, of the available food at one level, how much is converted to growth (and can then become food) at the next level. This is the concept of 'trophic efficiency' accounts for both:

  1. the efficiency at which available resource (food, light) is aquired
  2. the efficiency with which the light / food is converted to growth

Thus, trophic efficiency =

  • (consumed food / available food) x (food allocated to growth / total food consumed) =
  • (food allocated to growth / available food)

If a field produces 100 kg of grass each year, and a sheep living on that field gains 5 kg the sheep has a trophic efficiency of 5%. If a human ate 5kg of sheep, maybe they could gain 100 gm. If a human only ate the grass, they would loose weight and such a food web would not exist in nature.

Even Linderman's original work reports a range of trophic efficienciens among the different trophic levels. In Table IV, efficiency. Note that productivity is the rate of growth (mass/time), not total biomass.

enter image description here

A broad syntheses (Humphreys, 1979) demonstrates that indeed, trophic efficiency is related to the type of food eaten and the physiology of the animal consuming the food.

For example, non-social insects can have > 50% efficiency whereas most mammals, birds, and reptiles have < 5% efficiency (Table 7, P/A% is the metric of interest, N is the sample size):

enter image description here

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    I am a little confused by the definition. Does, say, 10% mean that for every 1kg of food eaten, 100g is put on as body weight? Or that for every 1kg of prey that exists in the environment, the predators that eat them (eventually) weigh 100g? Is all calorific consumption that is converted into movement ("work done") counted as inefficiency? – Oddthinking Sep 3 '11 at 5:11
  • @oddthinking you are correct. your first definition, increase in mass per unit of mass consumed, is for 'assimilation efficiency'. This can be measured for a single organism (and can be > 90% in some cases). Your second definition, increase in mass per unit of available food, is for 'trophic efficiency', which is measured at the ecosystem scale. In both contexts, calories lost via respiration, 'work done', is 'inefficiency', equal to 100% - efficiency %. – David LeBauer Sep 3 '11 at 5:22
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    In that case, I find those figures astonishingly high. (I have no basis to question them, I am just very surprised that a predator could catch more than 50% of the prey AND turn it into biomass so efficiently. It puts the human fear of sharks into sharp relief!) – Oddthinking Sep 3 '11 at 5:34
  • @oddthinking The only predators that have > 50% efficiency are non-social insects ... mammals are < 5%. – David LeBauer Sep 3 '11 at 5:41

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