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Read the following passage - AQA - A-Level Biology - Question 10 - 2021 - Paper 1
Question 10
Read the following passage. Lake Malawi in East Africa has more species of fish than any other lake in the world. Many of these species have evolved from a common a... show full transcript
Worked Solution & Example Answer:Read the following passage - AQA - A-Level Biology - Question 10 - 2021 - Paper 1
Step 1
Suggest and explain how this speciation may have occurred.
Answer
Speciation in Lake Malawi can occur due to several factors:
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Geographical Isolation: When the lake's water level fluctuated, it created smaller, isolated pools, preventing different fish populations from interacting. This isolation allows for separate evolutionary paths.
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Different Habitats: The various ecological niches present in the lake (e.g., varying depths, temperatures, and types of substrates) lead to adaptations in fish species to exploit these specific environments.
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Genetic Drift and Natural Selection: Different environmental pressures in isolated habitats cause certain traits to be favored, resulting in adaptive evolution and the eventual emergence of new species.
Step 2
Calculate the mean loss of forest cover in km² per week during this time period.
Answer
To calculate the mean loss of forest cover, we first need to determine the forest area in both years:
- Forest Cover in 1990: 41.4% of 94,800 km² = 39,227.52 km²
- Forest Cover in 2016: 26.4% of 94,800 km² = 25,059.20 km²
Total Loss of Forest Cover = 39,227.52 km² - 25,059.20 km² = 14,168.32 km²
Time Period = 1990 to 2016 = 26 years = 1,352 weeks
Mean Loss per Week = 14,168.32 km² / 1,352 weeks ≈ 10.47 km² per week.
Step 3
Explain why.
Answer
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Increased Eutrophication: The loss of nutrients into Lake Malawi promotes algal blooms, which can reduce oxygen levels, leading to fish kills.
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Habitat Degradation: Excess nutrients can destabilize the aquatic ecosystem, resulting in loss of suitable habitats for fish species.
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Competition: Changes in nutrient levels may benefit certain species over others, leading to decreased populations of less competitive fish.
Step 4
Explain how.
Answer
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Capture and Mark: Researchers capture a sample of fish from the population, mark them in a way that does not affect their survival.
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Release and Recapture: After allowing time for the marked fish to redistribute, a second sample is captured, and the number of marked fish in this sample is recorded.
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Estimation Formula: The estimated population size (N) can be calculated using the formula:
Step 5
Suggest why the mark-release-recapture method can produce unreliable results in very large lakes.
Answer
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Low Recapture Rates: In large lakes, marked fish may be widely dispersed, leading to a lower chance of recapture.
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Migration: Fish may move in and out of the sampling area, complicating population estimates.
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Sampling Bias: Different species may be more or less likely to be captured or marked, leading to skewed results.