Question 20N.3.HL.TZ0.18b
| Date | November 2020 | Marks available | [Maximum mark: 2] | Reference code | 20N.3.HL.TZ0.18b |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | List | Question number | b | Adapted from | N/A |
The elimination of wolves (Canis lupus) from Yellowstone National Park in 1926 and their reintroduction in 1995 provided the opportunity to examine ecological interactions with elk (Cervus elaphus). The National Park Service made efforts between the 1920s and 1968 to reduce the size of elk herds by culling (selective killing) because of concerns about overgrazing.
The graphs provide the trends for the numbers of wolves and elk in Yellowstone National Park from 1900 to 2004.
[Source: Ripple, W.J. and Beschta, R.L., 2004. Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems?
BioScience, 54(8), pp.755–766 by permission of Oxford University Press on behalf of the American Institute of Biological
Sciences. Translated and reprinted by permission of Oxford University Press on behalf of the American Institute of Biological
Sciences. Please visit: https://academic.oup.com/bioscience/article/54/8/755/238242.]
List two biotic factors, other than wolf predation or culling, that could affect the elk population.
1.
2.
[2]
a. relative rates of natality;
b. disease/lack of food;
c. competition for the same resources;
d. immigration/emigration/migration;
Many candidates could list two biotic factors, others did not pay attention to "biotic" and included abiotic factors.
