the law of ecological tithes

today I was trying to explain to nate, my coworker, the law of ecological tithe, or the ten percent rule. our conversation went a little something like this:

[anna] let me teach you a little something about the law of ecological tithes. basically all our energy comes from the sun. the plants use this energy to make their own food, but they are only able to use ten percent of that energy. when something else eats the plant, they can only use ten percent of that energy. so as you go up the food chain, there's less and less quality energy.

[nate] but isn't energy energy? does one have a higher quality than the other?

we debate back and forth regarding energy and calories and such

[anna] I need to bring in my wildlife ecology book. I have cute little drawings to help explain this a lot better.

[nate] yeah. . .

[anna] so you should eat plants to get the highest quality energy. . .

probably some more stuff was said that I can't remember

[anna] you want to get as close to the source as possible.

[nate] so we should eat the sun?

[anna] yes, we should eat the sun.

here is a slightly more sophisticated explanation:

About 10 percent of the usable food energy in one trophic level* is available as usable food energy for organisms in the next higher level. . . With each energy transfer in a food chain, there is a significant "loss" of useable energy. . .

. . . With the energy transfer at each step in a food chain about 10 percent of the energy available is utilized for weight gain, tissue repair or gamete production and about 90 percent of the energy is lost as heat metabolic by-products, feces, etc.

The lengths of food chains are limited by the decreasing amount of energy available as one moves up the food chain. The Second Law of Thermodynamics** helps explain why big, fierce animals are rare.
Fred Montague, WaMakaSkan, 2003.

see, you really do want to eat as close to the source as possible. if you think about it, this really does make a good case for being vegetarian (or at least flexetarian). get the most out of your higher quality, useable energy!

*trophic structure: the different roles organisms play in using energy as it flows through ecosystems. the position an organism occupies in a food chain. producers (green plants) - primary consumers (herbivores) - secondary consumers ( carnivores) - tertiary consumers (carnivores) - quaternary consumers (top carnivores)
**Second Law of Thermodynamics: no energy transformation is ever one-hundred percent efficient. (with each energy transformation a significant amount of concentrated, "high quality" usable energy is "lost" as a less-concentrated, low quality, less usable heat energy.)