Answer :
### Question 22
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#### (d) Line Graphs
To draw the line graphs, you will plot time on the x-axis with a range from 0 to 10 years. You will then plot three different curves for each dataset on the y-axis:
- Haplochromis Population (in thousands)
- Biomass (in thousands of arbitrary units)
- Depth of Light Penetration (in arbitrary units)
Make sure to use different styles or colors for each dataset. Label your axes and provide a legend to differentiate between the different datasets.
---
#### (e) Description of Changes
(i) Number of Haplochromis:
- The population of Haplochromis initially increases from year 0 (36,000) to a peak at year 5 (120,000).
- After year 5, there is a sharp decline to year 7 (60,000).
- The population continues to drop to a lowest recorded point (20,000) in year 8.
- It starts to slightly increase again towards year 10 (28,000).
(ii) Biomass of Accumulated Decayed Plant Materials:
- Starts at 100 (arbitrary units) in year 0 and decreases to 64 by year 3.
- From year 3 to year 6, it fluctuates but generally increases, peaking at 102 in year 6.
- A decline follows from year 6 to 94 by year 7.
- It continues to decline to 50 by year 9 and remains constant through to year 10.
(iii) Depth of Light Penetration:
- Begins at 38 (arbitrary units) in year 0, decreases to its lowest at 10 in year 5.
- After year 5, it increases sharply to a peak of 55 by year 8.
- There is another fluctuation where it decreases to 25 and ends at 30 by year 10.
---
#### (f) Explanation of Relationships
(i) Haplochromis Population and Biomass:
- When the biomass initially decreases, the Haplochromis population increases (years 0–5).
- Post year 5, the biomass increases slightly before stabilizing, while the Haplochromis population declines severely. This indicates an inverse relationship where a high biomass may correlate with a lower Haplochromis population perhaps due to competition for resources or increased predation.
(ii) Haplochromis Population and Depth of Light Penetration:
- Depth of light penetration and Haplochromis population seem to have an inverse relation up to a point. As the Haplochromis population reaches its peak, the light penetration is at its lowest around year 5.
- As the Haplochromis population declines, the light penetration depth increases significantly, implying that clearer water might be linked with fewer Haplochromis.
---
#### (g) Other Factors Influencing Haplochromis Population Size
1. Water Temperature
2. Predator Population
3. Food Availability
4. Water Quality
---
#### (h) Explanation of Influences
1. Water Temperature:
- Fish metabolism and breeding cycles are often temperature dependent. Optimal temperatures support active feeding and reproduction, while extreme temperatures can reduce survival rates.
2. Predator Population:
- A high number of predators can directly decrease the Haplochromis population through predation. Conversely, fewer predators allow the Haplochromis population to potentially increase.
3. Food Availability:
- Sufficient food resources support larger populations by facilitating growth and reproduction, while scarcity can limit population size.
4. Water Quality:
- Good water quality supports fish health by reducing stress and disease incidents, leading to a more stable population. Pollutants and poor water quality can lead to fish mortality.
---
#### (i) Estimating Population Size
To estimate the population size of Haplochromis in a small lake over two days:
1. Mark-Recapture Method:
- Day 1: Capture a sample of fish, mark them in a harmless way, record the number, and release them back into the lake.
- Day 2: Capture another sample of fish and record how many of these are marked.
- Use the formula [tex]\( N = \frac{M \times C}{R} \)[/tex] where:
- [tex]\( N \)[/tex] = Total population size
- [tex]\( M \)[/tex] = Number of fish marked on the first day
- [tex]\( C \)[/tex] = Total number of fish captured on the second day
- [tex]\( R \)[/tex] = Number of marked fish recaptured on the second day
---
#### (j) Effect of Dumping Untreated Sewage and Excess Fertilizers
Dumping untreated sewage and fertilizers in the water body would likely cause eutrophication. This process would lead to several ecological consequences:
- Nutrient Overload: Excess nutrients (especially nitrogen and phosphorus) would cause algal blooms.
- Reduced Oxygen Levels: Decomposing algae consume oxygen, reducing availability for other organisms, potentially causing fish kills.
- Degraded Water Quality: Increased organic matter and pollutants can degrade the water quality, affecting the health of aquatic organisms.
- Light Penetration: Algal blooms reduce water transparency, impacting the depth of light penetration and consequently, the aquatic life relying on sunlight.
These effects collectively disrupt the aquatic ecosystem, often leading to reduced biodiversity and altered habitat conditions unfavorable to the Haplochromis population.
---
#### (d) Line Graphs
To draw the line graphs, you will plot time on the x-axis with a range from 0 to 10 years. You will then plot three different curves for each dataset on the y-axis:
- Haplochromis Population (in thousands)
- Biomass (in thousands of arbitrary units)
- Depth of Light Penetration (in arbitrary units)
Make sure to use different styles or colors for each dataset. Label your axes and provide a legend to differentiate between the different datasets.
---
#### (e) Description of Changes
(i) Number of Haplochromis:
- The population of Haplochromis initially increases from year 0 (36,000) to a peak at year 5 (120,000).
- After year 5, there is a sharp decline to year 7 (60,000).
- The population continues to drop to a lowest recorded point (20,000) in year 8.
- It starts to slightly increase again towards year 10 (28,000).
(ii) Biomass of Accumulated Decayed Plant Materials:
- Starts at 100 (arbitrary units) in year 0 and decreases to 64 by year 3.
- From year 3 to year 6, it fluctuates but generally increases, peaking at 102 in year 6.
- A decline follows from year 6 to 94 by year 7.
- It continues to decline to 50 by year 9 and remains constant through to year 10.
(iii) Depth of Light Penetration:
- Begins at 38 (arbitrary units) in year 0, decreases to its lowest at 10 in year 5.
- After year 5, it increases sharply to a peak of 55 by year 8.
- There is another fluctuation where it decreases to 25 and ends at 30 by year 10.
---
#### (f) Explanation of Relationships
(i) Haplochromis Population and Biomass:
- When the biomass initially decreases, the Haplochromis population increases (years 0–5).
- Post year 5, the biomass increases slightly before stabilizing, while the Haplochromis population declines severely. This indicates an inverse relationship where a high biomass may correlate with a lower Haplochromis population perhaps due to competition for resources or increased predation.
(ii) Haplochromis Population and Depth of Light Penetration:
- Depth of light penetration and Haplochromis population seem to have an inverse relation up to a point. As the Haplochromis population reaches its peak, the light penetration is at its lowest around year 5.
- As the Haplochromis population declines, the light penetration depth increases significantly, implying that clearer water might be linked with fewer Haplochromis.
---
#### (g) Other Factors Influencing Haplochromis Population Size
1. Water Temperature
2. Predator Population
3. Food Availability
4. Water Quality
---
#### (h) Explanation of Influences
1. Water Temperature:
- Fish metabolism and breeding cycles are often temperature dependent. Optimal temperatures support active feeding and reproduction, while extreme temperatures can reduce survival rates.
2. Predator Population:
- A high number of predators can directly decrease the Haplochromis population through predation. Conversely, fewer predators allow the Haplochromis population to potentially increase.
3. Food Availability:
- Sufficient food resources support larger populations by facilitating growth and reproduction, while scarcity can limit population size.
4. Water Quality:
- Good water quality supports fish health by reducing stress and disease incidents, leading to a more stable population. Pollutants and poor water quality can lead to fish mortality.
---
#### (i) Estimating Population Size
To estimate the population size of Haplochromis in a small lake over two days:
1. Mark-Recapture Method:
- Day 1: Capture a sample of fish, mark them in a harmless way, record the number, and release them back into the lake.
- Day 2: Capture another sample of fish and record how many of these are marked.
- Use the formula [tex]\( N = \frac{M \times C}{R} \)[/tex] where:
- [tex]\( N \)[/tex] = Total population size
- [tex]\( M \)[/tex] = Number of fish marked on the first day
- [tex]\( C \)[/tex] = Total number of fish captured on the second day
- [tex]\( R \)[/tex] = Number of marked fish recaptured on the second day
---
#### (j) Effect of Dumping Untreated Sewage and Excess Fertilizers
Dumping untreated sewage and fertilizers in the water body would likely cause eutrophication. This process would lead to several ecological consequences:
- Nutrient Overload: Excess nutrients (especially nitrogen and phosphorus) would cause algal blooms.
- Reduced Oxygen Levels: Decomposing algae consume oxygen, reducing availability for other organisms, potentially causing fish kills.
- Degraded Water Quality: Increased organic matter and pollutants can degrade the water quality, affecting the health of aquatic organisms.
- Light Penetration: Algal blooms reduce water transparency, impacting the depth of light penetration and consequently, the aquatic life relying on sunlight.
These effects collectively disrupt the aquatic ecosystem, often leading to reduced biodiversity and altered habitat conditions unfavorable to the Haplochromis population.
