How do trophic levels apply to humans?

[semnae]

I'm a college student studying biogeography this semester. I was reading my text, when I came across the 10% rule, which says, "On average, only about 10% of the energy of any trophic level is passed on to the next trophic level." Since humans are omnivorous, we have the option of eating plants, animals, or both. People on the atkins diet take the role of a secondary consumer, while vegetarians take the role of a primary consumer, and people on the food pyramid diet take the role of both. Does this mean that a vegetarian will have more energy than someone on the atkins diet? Will the atkins diet cause people to become lethargic when compared to people on the food pyramid diet? Will vegetarianism cause people to become hyper when compared to people on the food pyramid diet?

[Skye]

The idea is that a large part of the energy taken in by each level of the food chain is expended rather than stored. Only the stored energy is available for the next level to consume. Some grass might take in a million kJ of energy (from the sun), but only a hundred thousand kJ is stored in the grass, the rest is expended in various biological processes. Then cattle might graze on the grass, let's say eat it all. But all the things cows do take up energy too, so only ten thousand kJ of energy is stored in the cow.

 

This doesn't mean you get more energy from eating grass than eating cows. It just means that if you have a certain amount of energy coming into the food chain at the producer level, less of that will carry through to the secondary consumer than the primary consumer.

[Thomas Kirby]

Disclaimer: I am not an expert.

 

The question that Semnae asked is if this ten percent rule means that different diets would give individual humans more or less usable energy. My answer would be that it does not because the percentage of sunlight that is converted to food calories in a trophic level is not related to the number of food calories that a given consumer will eat, or how well that individual will use those calories. Depending somewhat on the individual there is a difference between the diets, but the ten percent rule has nothing to do with that. It doesn't have anything to do with how much a person eats or how much good it does that person.

[Hellbender]

The atkins diet is severly flawed for a numeber of reasons. I have very little background in nutrition or physiology, but last I checked, the amount of carbohydrates in fruits and vegetables is negligable. Eating only bacon and meat is more harmful with the cholesterol and animal fats. Fad diets are usually full of crap. Plus, eating lower on the trophic scale wastes less energy and you get much more out of it. I shouldn't talk though. Although I enjoy a good salad from time to time, I eat primarily meat almost every meal.

[Mokele]

Skye pretty much covered it, as did the other, however, it should be noted that it's not always 10%. The trophic conversion for some snakes is around 50%, and up to 75% in some salamanders. In contrast, not a single mammals studied has topped a measly 5%, because they waste so much energy heating their bodies.

 

Oh, and Hellbender, was that a typo about fruits and vegies? From what I know, they're almost entirely carbs, namely starch and sugar.

 

Mokele

[LucidDreamer]

, but last I checked, the amount of carbohydrates in fruits and vegetables is negligable.

Check again Most fruits are full of fructose and some vegetables, like potatoes, are full of starch. But I agree with you, the atkins diet is not healthy if you consume lots of saturated fats and cholesterol.

Sorry, off topic.

[Hellbender]

True, I guess I mean negligable compared to eating white bread and cake.

[MattC]

There are some excellent replies here, but I'll add a little anyway

 

The 10% rule, which is not exact by any standard, as another poster pointed out, means that a vegetarian diet requires less energy to produce - meaning, a vegetarian eats the same amount of calories, perhaps, but the sun energy required to produce those calories is much less.

 

A cow eats many, many pounds of grains to produce a single pound of meat. Additionally, that grain needs to be transported, except in those relatively rare cases where the cows simply graze (despite what you see in commercials for california cheese, the vast majority of cows are in crowded lots, where there is no grass, just piles of dung, and piles of imported (locally, I imagine) grain food). While transportation costs are not factored into the 10% rule, it's important with regards to humans.

 

 

 

And as far as water goes ....

1 pound of beef requires over 2,000 gallons of water (estimates vary, but the ones not produced by the obviously biased meat industry cite figures in this range, whereas beef producers claim that beef is much more efficient in terms of water; I suspect the actual average amount is significantly higher than 2,000, but I wanted to cite an extremely conservative value)), whereas 1 pound of, say, wheat, takes under 30 gallons of water.

 

That one pound of wheat is a tiny fraction of the amount of grain a cow needs over it's life, up to the point it is ready for the slaughter. Of course, the whole picture is much more complicated, but I hope this helps.

 

So no, a vegetarian needs to eat just as much, possibly more, as meat is chock full of calories, while vegetables are low on calories. Of course, if a meat eater doesn't get his veggies, he gets sick.