APES Food for Thought……Trophic Levels

Homework Discussion

Guinea Hens, Grasshoppers, Soybeans, and Cows

Let’s look at some energy pyramidsif humans ate grasshoppers instead of hens

15 humans/yr

3,330,625 gh/yr3,330,625 gh/yr

365 hens/yr

1 human/yr

Sometimes it’s better to compare kg to get a true picture of energy efficiency

Which is more efficient to eat?A human needs 55g protein/day

1 cow = 19,000 g protein/acre/yr.Soy = 200,000 g protein/acre/year

345 humans/acre/yrs3,600 humans/acre/yrs

Let’s take a closer look at protein supplied by cows vs. soybeans

Benefits of eating at a lower trophic level

•Feed more people•Less arable land requires more inputs•More land required to grow meat•Plants convert 1-10% energy of sunlight to edible food

Drawbacks of eating at a lower trophic level

•Supply B-12 in diet•Use less arable lands (steep, rocky) to grow meat•Cows convert 1-10% energy from hay/grain to meat•Source of labor, leather, fertilizer, heat

Less arable lands can be used for grazing land

Eat Fish????Top trophic level results in a 1/1,000 energy loss

Biom

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T, m

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1000 g

100 g

10 g

1 g

Biomagnification vs. Bioaccumulation

Bioaccumulation refers to how pollutants enter a food chain

Biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next

water to zooplankton: 800x zooplankton to fish #1: 31x fish #1 to fish #2: 1.7x fish #2 to gull: 4.8x overall: 202,368x