Question 20N.3.SL.TZ0.12
| Date | November 2020 | Marks available | [Maximum mark: 7] | Reference code | 20N.3.SL.TZ0.12 |
| Level | SL | Paper | 3 | Time zone | TZ0 |
| Command term | Distinguish, Outline, Suggest | Question number | 12 | Adapted from | N/A |
Ecologists studied the distribution of five species of insectivorous wood warblers of the genus Dendorica living on different parts of coniferous trees in mature forests.
Distinguish between the distribution of D. tigrina and that of D. coronata.
[1]
a. D. tigrina lives higher in the tree than D. coronata;
b. D. coronata occupies a greater area/height range than D. tigrina;
c. D. tigrina found in the outer regions and D. coronata found on the inside;
Accept vice-versa.
Overall, well answered.
Outline the principle of competitive exclusion.
[2]
a. no two species can occupy the same niche;
b. competition between them would cause one species to drive the other out
OR
one of the two species would need to adapt and evolve accordingly;
When describing competitive exclusion many candidates simply described competition. Some mentioned habitat rather than niche.
Other than position in the tree, suggest two ways in which the niches of the warblers in the ecosystem may differ.
1.
2.
[2]
a. different food/prey;
b. different predators;
c. active at different times of the day;
d. present at different times of the year;
e. different nest sites;
f. different temperatures;
Do not accept “different habitats”.
The diagram shows the realized niches of the five species of warbler. Suggest how the fundamental niche of D. castanea might differ from its realized niche.
[2]
a. the realized is the actual niche and the fundamental is in the absence of competition;
b. with no competition the D. castanea would have a larger habitat/more food
OR
D.castanea could occupy the niches currently occupied by the other warbler species;
Accept named species.
Weaker candidates gave incomplete or confused suggestions in differentiating between the realised and fundamental niche.
