The following stacked column chart shows the number of animal species in the IUCN Red List, by class, over time.
- (i) What does the number 14,234 on the top of the column 2019 represent?
- (ii) Approximately how many reptile species were in the list in 2016?
- (iii) Which class(es) of species have seen a relatively small increase in count between 2007 and 2019?
Step-by-step solution
Idea: In a stacked column, the number on top is the total of all the pieces. A single class’s count is the length of its piece: top of the piece minus bottom of the piece.
(i) What does the number 14,234 on the top of the column 2019 represent?
- The 2019 column is all the classes stacked together, so 14,234 is the total number of animal species of all classes on the Red List in 2019.1 mark
(ii) Approximately how many reptile species were in the list in 2016?
- In the 2016 column the reptile piece (second from the bottom) runs from about 1,100 to about 2,200. Its length is about 2,200 − 1,100 = 1,100 species (a reading between 1,000 and 1,200 is fine).1 mark
(iii) Which class(es) of species have seen a relatively small increase in count between 2007 and 2019?
- Compare each piece’s length in 2007 and 2019. Mammals (about 1,100 → 1,250) and birds (about 1,200 → 1,450) hardly change. Reptiles, insects, molluscs and fish each grow by about 1,000 or more; others by about 800; amphibians by about 400. So mammals and birds have the smallest increase.1 mark
Check: Reptiles in 2007 were only about 400, so their rise to about 1,400 by 2019 is one of the largest, which is why they are not in the answer to (iii).
Answer to write in the exam
(i)
Height of the full column = sum of all classes
∴ 14,234 = total number of animal species on the list in 2019
(ii)
Reptile piece in 2016: from ≈ 1,100 to ≈ 2,200
Length ≈ 2,200 − 1,100 = 1,100
∴ About 1,100 reptile species
(iii)
Mammals ≈ 1,100 → 1,250; birds ≈ 1,200 → 1,450
Reptiles, insects, molluscs, fish: increase ≈ 1,000 or more
∴ Mammals and birds show a relatively small increase
Common mistakes that cost marks
- Reading the top of the reptile piece (about 2,200) as the number of reptiles. The count is the length of the piece.
- In (i), saying 14,234 is the number of fish or of the top piece. It is the total of the whole column.
- In (iii), comparing the positions of pieces instead of their lengths.
How this can come in the exam
In a stacked column, a piece starts at 3,000 and ends at 4,800. The quantity it represents is
- 4,800
- 3,000
- 1,800
- 7,800
Show answer
(C) 1,800
Length = 4,800 − 3,000 = 1,800.
Try one yourself
In a stacked column for a library, the fiction piece runs from 0 to 1,200, non-fiction from 1,200 to 2,000 and magazines from 2,000 to 2,300. How many books of each kind are there, and what is the total?
Show answer
Fiction 1,200, non-fiction 2,000 − 1,200 = 800, magazines 2,300 − 2,000 = 300; total 2,300.
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