APES Food for
Thought……Trophic Levels
Homework Discussion
Guinea Hens, Grasshoppers,
Soybeans, and Cows
Let’s look at some energy pyramids
if humans ate grasshoppers instead of
hens
1 human/yr
15 humans/yr
365 hens/yr
3,330,625 gh/yr
3,330,625 gh/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
345 humans/acre/yrs
3,600 humans/acre/yrs
Soy = 200,000 g protein/acre/year
1 cow = 19,000 g protein/acre/yr.
Let’s take a closer look at protein
supplied by cows vs. soybeans
Benefits of eating at a
lower trophic level
Drawbacks 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
•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
Biomagnification of DDT, mercury
Eat Fish????
Top trophic
level results in
a 1/1,000
energy loss
1g
10 g
100 g
1000 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