Post on 27-Dec-2015
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
agni
ficati
on o
f DD
T, m
ercu
ry
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