Question

Making Conclusions: Find the general location of your community on the map, if shown. Do you live in an area of high population density or low population density? How could your community’s location affect its population density?



A map of a lake victoria

AI-generated content may be incorrect.

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 can’t see the specific map you’re using, so I’ll tell you how to find the answers on the map and give likely answers based on the known history of Lake Victoria.

1) Find your community on the population map (first part of the worksheet)
- How to do it: locate the country/state/region where you live, then find the town/city or the general area on the map. Check the map’s color key or symbols to see whether that area is marked as high or low population density.
- High vs low: urban areas (cities, ports, industrial centers) are usually high population density; rural, mountainous, desert, or isolated island areas are usually low density.
- How location affects population density: proximity to fresh water, fertile land, transport routes (roads/rail/ports), jobs and industry, and climate all increase density; distance from these resources, poor soils, harsh climates, or geographic barriers (mountains, swamps) reduce density.

2) Lake Victoria / cichlid questions
Note: because I can’t view your map, I’ll explain how to read it and give the historically typical answers.

- Using a Key: In which year was the number of cichlids the greatest?
How to read it: find the color or symbol on the key that represents the largest cichlid population, then identify the year on the map that uses that color.
Likely answer: the greatest number was before the Nile Perch introduction (so a year in the 1950s or the earliest year shown on your map).

- Using a Key: How many years did it take for the cichlid population to decrease by 50 percent?
How to read it: find the year where the map’s symbol/color corresponds to half the population level shown for the earliest (greatest) year, then subtract the years.
Likely/historical answer: cichlids declined rapidly after the Nile Perch introduction in the 1950s–1960s; a 50% drop occurred within a couple of decades (roughly 10–20 years) in many parts of the lake.

- Inferring Relationships: Which fish is higher on the food chain—the cichlid or the Nile Perch? Explain.
Answer: The Nile Perch is higher on the food chain. Explanation: Nile Perch are large predatory fish that eat smaller fish (including many cichlid species). The introduction of the Nile Perch caused heavy predation on cichlids, which is why the cichlid population declined.

- Identifying Trends: Based on the rate of decrease shown, what will happen to the cichlid population by 2050?
How to reason: extend the trend shown on the map forward, considering whether the decline is steady, leveling off, or accelerating.
Likely projection: if no strong conservation or control measures are taken, the cichlid population will remain very low in many areas and some species may go locally or globally extinct. With active conservation (habitat protection, invasive species control, captive breeding and reintroduction), some recovery is possible, but full recovery to pre-introduction levels is unlikely without major, sustained intervention.

If you want exact answers tied to your map, upload a photo or give the years and the key values/colors and I’ll read them and give precise year(s) and calculations.