Calculate the food web efficiency for the following two systems.
Brown food webs start with heterotrophic inputs - usually from organic matter input into the system (waste water or decaying organisms, for example). Green food webs start from autotrophs (called because many of them are green in color, like plants), but still support some level of bacteria that are often consumed as primary production. Determine the FWE for the two food webs and compare, providing some insight into why they might be different.
Brown Food Web Green Food Web
Bacteria biomass (ug/L) 200 30
Phytoplankton (ug/L) 0.5 4
Heterotrophic flagellates (ug/L) 100 0
Ciliates (ug/L) 350 0
Zooplankton (ug/L) 8 60
To calculate the food web efficiency (FWE), we need to determine the trophic level biomasses for each organism in the food webs. The trophic level biomasses represent the energy or biomass at each trophic level.
Trophic levels can be defined as follows:
1. Primary producers: Autotrophs such as phytoplankton
2. Primary consumers: Heterotrophs that directly consume the primary producers, such as bacteria and heterotrophic flagellates
3. Secondary consumers: Heterotrophs that consume the primary consumers, such as ciliates
4. Tertiary consumers: Heterotrophs that consume the secondary consumers, such as zooplankton
For the given brown food web:
- Bacteria biomass: 200 ug/L
- Phytoplankton: 0.5 ug/L
- Heterotrophic flagellates: 100 ug/L
- Ciliates: 350 ug/L
- Zooplankton: 8 ug/L
For the given green food web:
- Bacteria biomass: 30 ug/L
- Phytoplankton: 4 ug/L
- No heterotrophic flagellates, ciliates, or zooplankton
Now let's calculate the FWE for each food web:
Brown Food Web FWE:
Primary production = Phytoplankton biomass = 0.5 ug/L
Heterotrophic biomass = Bacteria biomass + Heterotrophic flagellates + Ciliates + Zooplankton
= 200 ug/L + 100 ug/L + 350 ug/L + 8 ug/L = 658 ug/L
FWE = (Biomass transferred to the next trophic level / Biomass at the previous level) * 100
= (658 ug/L / 0.5 ug/L) * 100
= 131,600%
Green Food Web FWE:
Primary production = Phytoplankton biomass = 4 ug/L
Heterotrophic biomass = Bacteria biomass (no other heterotrophs present in this food web) = 30 ug/L
FWE = (Biomass transferred to the next trophic level / Biomass at the previous level) * 100
= (30 ug/L / 4 ug/L) * 100
= 750%
Comparing the FWE for the two food webs, we can see that the brown food web has a significantly higher FWE (131,600%) compared to the green food web (750%). This indicates that there is a more efficient transfer of biomass and energy between trophic levels in the brown food web compared to the green food web.
The difference in FWE can be attributed to the initial input of organic matter in the brown food web. The brown food web starts with heterotrophic inputs, which provide a higher initial biomass to support the subsequent trophic levels. In contrast, the green food web starts from autotrophs, which have lower biomass compared to the heterotrophic inputs in the brown food web.
Additionally, the presence of other heterotrophs such as ciliates and zooplankton in the brown food web further contributes to higher biomass transfer and efficiency. These higher trophic level consumers help in consuming and transferring the primary production biomass more efficiently.
Overall, the differences in FWE between the two food webs highlight the importance of the initial inputs and trophic interactions in determining the efficiency of energy and biomass transfer in an ecosystem.
To calculate the food web efficiency (FWE) for the two food webs, we need to understand the flow of energy through the different trophic levels. FWE measures the efficiency of energy transfer from one trophic level to the next within a food web. The formula for calculating FWE is:
FWE = (Energy at the higher trophic level / Energy at the lower trophic level) x 100
Now, let's calculate the FWE for the two food webs:
For the Brown Food Web:
1. Calculate the energy at the lower trophic level (Bacteria biomass):
Energy at lower trophic level = Bacteria biomass (ug/L) x Conversion efficiency of bacteria (assuming 10% efficiency)
Energy at lower trophic level = 200 ug/L x 0.10 = 20 ug/L
2. Calculate the energy at the higher trophic level (Zooplankton):
Energy at higher trophic level = Zooplankton biomass (ug/L) x Conversion efficiency of zooplankton (assuming 10% efficiency)
Energy at higher trophic level = 8 ug/L x 0.10 = 0.8 ug/L
3. Calculate the FWE:
FWE = (Energy at higher trophic level / Energy at lower trophic level) x 100
FWE = (0.8 ug/L / 20 ug/L) x 100 = 4%
For the Green Food Web:
1. Calculate the energy at the lower trophic level (Phytoplankton):
Energy at lower trophic level = Phytoplankton biomass (ug/L) x Conversion efficiency of phytoplankton (assuming 10% efficiency)
Energy at lower trophic level = 4 ug/L x 0.10 = 0.4 ug/L
2. Calculate the energy at the higher trophic level (Zooplankton):
Energy at higher trophic level = Zooplankton biomass (ug/L) x Conversion efficiency of zooplankton (assuming 10% efficiency)
Energy at higher trophic level = 60 ug/L x 0.10 = 6 ug/L
3. Calculate the FWE:
FWE = (Energy at higher trophic level / Energy at lower trophic level) x 100
FWE = (6 ug/L / 0.4 ug/L) x 100 = 150%
Comparing the two food webs, we can observe that the FWE for the Green Food Web is higher (150%) compared to the Brown Food Web (4%). This difference can be attributed to the initial source of energy in the food web. In the Green Food Web, autotrophs (phytoplankton) are the primary producers, which efficiently capture sunlight energy through photosynthesis. This higher energy input at the lower trophic level results in a higher energy transfer to the higher trophic level (zooplankton), leading to a higher FWE. In contrast, the Brown Food Web starts with heterotrophic inputs, which may have lower energy content and, therefore, lower energy transfer to the higher trophic level, resulting in a lower FWE.
To calculate the food web efficiency (FWE) for the two systems, we need to determine the trophic levels and biomass transfers within each food web. The FWE is calculated by dividing the biomass at one trophic level by the biomass at the previous trophic level.
For the Brown Food Web:
1. Autotrophs (Phytoplankton): 0.5 ug/L
2. Heterotrophs (Bacteria): 200 ug/L / 0.5 ug/L = 400
3. Predators (Heterotrophic Flagellates): 100 ug/L / 200 ug/L = 0.5
4. Predators (Ciliates): 350 ug/L / 100 ug/L = 3.5
5. Predators (Zooplankton): 8 ug/L / 350 ug/L = 0.023
FWE for the Brown Food Web:
- Between autotrophs and heterotrophs: 400
- Between heterotrophs and heterotrophic flagellates: 0.5
- Between heterotrophic flagellates and ciliates: 3.5
- Between ciliates and zooplankton: 0.023
For the Green Food Web:
1. Autotrophs (Phytoplankton): 4 ug/L
2. Heterotrophs (Bacteria): 30 ug/L / 4 ug/L = 7.5
3. Predators (Zooplankton): 60 ug/L / 30 ug/L = 2
FWE for the Green Food Web:
- Between autotrophs and heterotrophs: 7.5
- Between heterotrophs and zooplankton: 2
Comparing the FWE of the two food webs, we can see that the FWE for the Brown Food Web is higher than the FWE for the Green Food Web. This indicates that there is more efficient transfer of biomass between trophic levels in the Brown Food Web compared to the Green Food Web.
This difference in FWE can be attributed to the initial input of organic matter in the Brown Food Web, which provides a larger biomass for the heterotrophs to consume. The Green Food Web, starting from autotrophs (phytoplankton), has a smaller initial biomass, resulting in a lower FWE. Additionally, the absence of certain trophic levels (such as heterotrophic flagellates and ciliates) in the Green Food Web also affects the biomass transfers and overall FWE.