Activity #3
What’s your trophic level and
ecological efficiency?
1) Use the tables handout from class to collect your dietary data and make
calculations.
2) List food items eaten during breakfast, lunch and dinner on a typical day.
3) In the next column, list the source feeding category for each food item.
4) Next, record the relative serving size or portion of each item. Give a "1"
for small, "2" for medium and reserve "3" for the largest portions. Last
record the predominant trophic level of each food item.
5) Sum all the values for portion sizes; this will be used in the calculation
table.
6) Follow the steps given in the calculation table to derive your trophic level.
7) Use your trophic level value to calculate your ecological efficiency.
Data Collection Table
Meal Item:
Source Ecological
Grouping
Portion
Size
Diet Trophic
Level
Cantaloupe
Producer
2
1
Coffee
Producer
2
1
Milk
Primary Consumer
1
2
Bacon
Primary Consumer
1
2
Pasta
Producer
1
1
Pesto sauce
Producer
1
1
Tuna
Secondary Consumer
3
3
Salad
Producer
1
1
Bread
Producer
1
1
Beer
Producer
1
1
Producer
1
1
Breakfast:
Lunch:
Dinner:
Snacks:
Snickers Bar
Sum of all portion values =
15
Calculation Table for Your Trophic Level
Step A: Add all portion values for each diet trophic level separately. The total of these three values should equal the
sum of all portion values that you calculated above.
Step B: Divide the sum of all portions for each diet TL by the total of all portions to yield the fraction of your diet coming
from each trophic level (B = A ÷ total portions).
Step C: Multiply the fraction by the diet trophic level value to yield the weighted contribution from each diet trophic level
(C = diet TL * B).
Step D: Sum the weighted diet trophic level contributions (i.e. sum all three values under “C”).
Step E: Add one to the value in “D” to get your trophic level (E = D +1).
Diet Trophic Level
{A}
Sum of portions for
each diet TL
{B}
Fraction of total
portions
{C}
Weighted diet TL
contribution
1
10
0.67
0.67
2
2
0.13
0.26
3
3
0.20
0.60
{D}
Average Diet Trophic Level =
(sum weighted diet TL contributions)
1.53
{E}
2.53
Your Trophic Level =
(Average Diet TL + 1)
100
EE = 10
80
(3-TL)
60
Ecological Efficiency (EE)
Ecological Efficiency
(EE)
Ecological Efficiency versus
Trophic Level
10
8
6
4
2
0
2
40
2.5
3
3.5
4
Trophic Level (TL)
20
0
1
My EE = 2.95%
2
3
Trophic Level (TL)
4
Some herbivores are more
efficient than others.
6%
33%
16 %
Thought Questions:
1) How would eating more primary producers change your trophic level and
ecologically efficiency?
2) If you ate more fish (secondary consumers), how would these values
change?
3) Primary production represents an energy resource you consume via your
diet, either directly like a herbivore or indirectly as a carnivore. Fossil fuel
combustion and nuclear power also represent energy resources used by
man. How would total energy use differ for a vegetarian eating exotic
vegetables versus someone who's diet is restricted to local harvests
("bioregional" diet)?
4) How would total energy use differ for someone who's diet is restricted to
processed foods and prepackaged cooking kits versus the individual that
eats the same diet, but makes their meals from scratch?
5) What do you imagine would be the most energy efficient diet?
6) How far are you from that ecologically high efficiency diet and what do you
see as the cost and benefits to your normal diet?