What's your trophic level and ecological efficiency?
(10 Sept 2003)
Data Collection Table
Meal Item:
Source Ecological
Grouping
Breakfast:
Lunch:
Dinner:
Snacks:
Sum of all portion values =
Portion
Size
Diet
Trophic
Level
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
2
3
{D}
Average Diet Trophic Level =
(sum weighted diet TL contributions)
{E}
Your Trophic Level =
(Average Diet TL + 1)
Calculate Your Ecological Efficiency
Ecological Efficiency (EE)
Plug your trophic level value (TL) into the equation on the graph below to determine your ecological
efficiency (EE). The assumption here is that each trophic level above primary producers (TL = 1) is
only 10% efficient in utilizing their food for survival. Note that an herbivore (primary consumer; TL =
2) is 10 % efficient relative to the primary production in the ecosystem. Likewise, a secondary
consumer (TL = 3) is only one percent efficient in using the ecosystem primary production.
10
8
EE = 10 (3-TL) =
6
%
4
2
0
2
2.5
3
Trophic Level (TL)
3.5
4