Question

partial biomass pyramid for a
particular marine ecosystem
shrimp
? kg
zooplankton
20,000 kg
phytoplankton
2,000,000 kg
if the proportion of energy transferred between trophic levels remains relatively constant, which
prediction of the total biomass in the trophic level containing shrimp is most likely correct?
a. 2,020,000 kg
b. 1,980,000 kg
c. 200 kg
d. 20 kg

Explanation:

Step1: Determine energy transfer ratio

In a biomass pyramid, energy transfer between trophic levels is typically about 10% (a common ecological rule). So, the biomass of a higher trophic level is about 10% of the lower trophic level's biomass.

First, find the ratio between Zooplankton and Phytoplankton: $\frac{20,000}{2,000,000} = 0.01$ (which is 1%, wait, maybe my initial thought was wrong. Wait, Phytoplankton is the producer (lowest trophic level), Zooplankton is primary consumer (eats Phytoplankton), Shrimp is secondary consumer (eats Zooplankton). So energy transfer from Phytoplankton to Zooplankton: $\frac{20,000}{2,000,000} = 0.01$ (1%). So if the proportion is constant, then from Zooplankton to Shrimp, it should also be 1% of Zooplankton's biomass.

Step2: Calculate Shrimp's biomass

Zooplankton biomass is 20,000 kg. So Shrimp's biomass should be $20,000 \times 0.01 = 200$ kg. Wait, but wait, maybe the 10% rule? Wait, no, let's recalculate. Wait, 2,000,000 kg (Phytoplankton) to 20,000 kg (Zooplankton): $20,000 / 2,000,000 = 0.01$ (1%). So the transfer efficiency is 1% here. Then Zooplankton (20,000 kg) to Shrimp: 1% of 20,000 is 200 kg. Let's check the options. Option C is 200 kg. Wait, but sometimes the 10% rule is used, but here the ratio between Phytoplankton and Zooplankton is 1%, so we use that constant proportion.

Wait, maybe I made a mistake. Let's do it again. The problem says "the proportion of energy transferred between trophic levels remains relatively constant". So first, find the proportion between Phytoplankton (2,000,000 kg) and Zooplankton (20,000 kg). The proportion is $20,000 / 2,000,000 = 0.01$ (1%). So this is the proportion of energy (and thus biomass) transferred from Phytoplankton to Zooplankton. Now, we need to apply the same proportion from Zooplankton to Shrimp. So Shrimp's biomass = Zooplankton's biomass × proportion. So $20,000 \times 0.01 = 200$ kg.

Step3: Match with options

Looking at the options, option C is 200 kg, which matches our calculation.

Answer:

C. 200 kg