Question

Lake Victoria, shown in the population map above, is the largest lake in Africa and is home to fish called cichlids (pronounced SIK-lids). In the 1950s, a new fish, the Nile Perch, was introduced to Lake Victoria. This map shows the change in the cichlid population since the Nile Perch was introduced.

Use the map above to answer the questions below.

Using a Key: In which year was the number of cichlids the greatest?



Using a Key: How many years did it take for the cichlid population to decrease by 50 percent?



Inferring Relationships: Which fish in Lake Victoria do you think is higher on the food chain—the cichlid or the Nile Perch? Explain your answer.



Identifying Trends: Based on the rate of decrease of cichlids shown on the map, what do you think will happen to the cichlid population by 2050? Explain your answer.

Answer 1

I don’t have the map image you’re looking at. Could you upload it or type the years and the cichlid values shown in the map key (for example: 1950 = 100%, 1970 = 50%, 1990 = 20%, etc.)? With those numbers I’ll give exact answers.

If you can’t upload, here’s how to answer each question and an example based on a typical data pattern:

Steps to use the map/key
- Find the year that corresponds to the largest value on the key — that’s when the cichlid number was greatest.
- To find how many years it took to decrease by 50%, find the year when the population first reaches half of the initial (greatest) value and subtract the earlier year.
- For food-chain inference, identify which species caused the decline and whether it eats the other — the predator is higher.
- For the 2050 prediction, look at the trend (steady decline, rapid drop, leveling off) and extrapolate, giving reasons (predation, habitat change, fishing, conservation).

Example (typical historical pattern)
- Which year had the greatest number of cichlids? 1950 (the year before the Nile Perch became established).
- How many years to decrease by 50%? If the map shows cichlids at 100% in 1950 and 50% in 1970, it took 20 years.
- Which is higher on the food chain? The Nile Perch is higher — it is a large predator that ate many cichlids, causing their decline.
- What will happen by 2050? If the map shows a steady rapid decline, cichlid numbers will likely be extremely low or many species may be locally extinct by 2050 unless strong conservation and control of Nile Perch occur. Reason: continued predation, competition, habitat changes, and overfishing will keep reducing cichlid populations.

Send the map or list the key values and I’ll give exact answers using your map.