Question 19M.3.HL.TZ1.17b
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.HL.TZ1.17b |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
In Wales, UK, the grey squirrel (Sciurus carolinensis) is an alien species and the red squirrel (Sciurus vulgaris) is endemic. The maps show the distribution of red and grey squirrels in 1945 and 2010.
[Source: © The Red Squirrel Survival Trust]
The niches of the red and grey squirrels overlap. Explain the concept of competitive exclusion with respect to the changes in squirrel distribution shown in the maps.
[3]
a. competitive exclusion states two species that occupy a similar niche in the same location cannot coexist ✔
b. one of the two competitors will always have an advantage over the other ✔
c. leads to extinction/displacement/evolution of the second competitor ✔
d. grey squirrels have replaced/occupied niches formerly occupied by red squirrels
OR
habitats favour the grey squirrel in competition for the niche ✔
e. the niche of one competitor/both competitors becomes narrower ✔
This question was yet another instance where weaker students were disadvantaged by their inability to access the appropriate subject-specific vocabulary. They tended not to use the term “niche” with this question, and too frequently “niche” and “habitat” were confused.
