1. APES Food for Thought……Trophic Levels
Homework Discussion

2. Guinea Hens, Grasshoppers, Soybeans, and Cows

3. Let’s look at some energy pyramids if humans ate grasshoppers instead of hens
15 humans/yr
1 human/yr
365 hens/yr
3,330,625 gh/yr
3,330,625 gh/yr

4. Which is more efficient to eat?
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
345 humans/acre/yrs
3,600 humans/acre/yrs
Soy = 200,000 g protein/acre/year
1 cow = 19,000 g protein/acre/yr.

5. 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

6. Less arable lands can be used for grazing land

7. Eat Fish???? Top trophic level results in a 1/1,000 energy loss
Biomagnification of DDT, mercury
10 g
100 g
1000 g

8. 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

9. 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