| Date | November 2020 | Marks available | 3 | Reference code | 20N.3.HL.TZ0.18 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Outline | Question number | 18 | Adapted from | N/A |
Question
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.]
Outline the changes in elk population between the years 1930 and 2004.
List two biotic factors, other than wolf predation or culling, that could affect the elk population.
1.
2.
Markscheme
a. between 1930 and 1968 the numbers were reduced;
b. after 1968/in the 1970s the numbers increased;
c. in 1990s1995 the numbers decreased again;
d. lowest in 1968 and highest in 1990;
a. relative rates of natality;
b. disease/lack of food;
c. competition for the same resources;
d. immigration/emigration/migration;
Examiners report
The majority of candidates had no difficulty outlining the changes in elk population.
Many candidates could list two biotic factors, others did not pay attention to "biotic" and included abiotic factors.
Syllabus sections
- 18M.3.SL.TZ2.8c: Outline the concept of an emergent property.
- 17N.3.HL.TZ0.17a.ii: Outline a reason for organisms seldom occupying their entire fundamental niche.
- 18M.3.HL.TZ2.16c.i: Outline how factor Y affects the species from January to April.
- 18M.3.HL.TZ2.16b: State the month where the population reaches its maximum.
- 17N.3.HL.TZ0.17a.i: Define fundamental niche.
- 20N.3.HL.TZ0.18b: List two biotic factors, other than wolf predation or culling, that could affect the elk...
- 18M.3.HL.TZ2.16a: Distinguish between fundamental niche and realized niche.
- 18M.3.HL.TZ1.14a: The sea star Pisaster ochraceus is identified as a keystone species in the Pacific...
- 19N.3.SL.TZ0.13a: Explain why some biologists think protecting keystone species would help preserve biological...
- 17M.3.HL.TZ2.15a: State the type of interaction that occurs between Zooxanthellae and reef-building corals.
- 19N.3.HL.TZ0.14c: Explain why some biologists think protecting keystone species would help preserve biological...
- 19N.3.SL.TZ0.12a: Outline how these results indicate that blackberry distribution is limited by light intensity.
- 17M.3.SL.TZ1.13a: State the relationship between Zooxanthellae and coral reef species.
-
18M.3.SL.TZ1.13a:
Distinguish between fundamental niche and realized niche.
- 17M.3.SL.TZ2.17c: Researchers have argued that S. geminata is a keystone species in the corn agricultural...
- 16N.3.SL.TZ0.11c: Describe how the distribution of Chthamalus and Balanus is affected when both are present.
- 16N.3.SL.TZ0.14a: Outline the trend in the number of people with malaria during the period when the use of...
- 16N.3.SL.TZ0.11a: Distinguish between a fundamental niche and realized niche.
- 18M.3.HL.TZ2.16c.ii: Suggest, with a reason, what factor Y could be.
- 20N.3.SL.TZ0.12c: Other than position in the tree, suggest two ways in which the niches of the warblers in the...
- 19M.3.HL.TZ1.17a.ii: Suggest two possible reasons for the change in distribution. 1. 2.
- 19M.3.SL.TZ1.10c: With respect to this food chain, outline what is meant by a keystone species.
-
18M.3.SL.TZ1.15:
Discuss how abiotic factors can affect the distribution of species in an ecosystem.
-
18M.3.HL.TZ1.14b:
Outline one example of mutualism.
- 19M.3.HL.TZ1.17a.i: Outline the changes of distribution of the grey squirrel from 1945 to 2010.
- 20N.3.SL.TZ0.12a: Distinguish between the distribution of D. tigrina and that of D. coronata.
- 18N.3.SL.TZ0.15b: Deduce the effect of bleaching on corals.
- 19M.3.HL.TZ1.17b: The niches of the red and grey squirrels overlap. Explain the concept of competitive...
- 18M.3.HL.TZ2.15b: Describe how the sea otter indirectly affects seagrass.
- 20N.3.SL.TZ0.12d: The diagram shows the realized niches of the five species of warbler. Suggest how the...
-
20N.3.HL.TZ0.15b:
Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.
- 18M.3.HL.TZ2.15a: Identify which of the types of interaction shown in the key occur between crabs and seagrass.
- 17M.3.SL.TZ1.13b: Describe the exchange of materials between the coral’s polyps and Zooxanthellae.
- 17M.3.SL.TZ2.14: Paramecium aurelia and Paramecium caudatum are single cell organisms. They were grown...
- 18M.3.SL.TZ1.13b: Outline the impact of competition on the niche of an organism.
- 18M.3.SL.TZ1.13c: Outline the characteristics of keystone species in an ecosystem.
- 18N.3.SL.TZ0.15a: State the trend in temperatures from 1982 to 2014.
-
16N.3.HL.TZ0.14:
Cryptococcus neoformans and the closely related species Cryptococcus gattii are human fungal pathogens. The reproduction of these yeast species on increasing concentrations of pigeon droppings (PD) was examined to determine whether they occupy the same or different ecological niches. The results for reproduction are expressed as a percentage relative to the control.
Suggest how this experiment shows that pigeon droppings represent a realized ecological niche for C. neoformans and a fundamental (but not a realized) niche for C. gattii.
- 19N.3.HL.TZ0.16b: Suggest one reason for leaving natural corridors between different natural reserves.
-
17N.3.SL.TZ0.15:
Explain reasons for differences in the realized niche and fundamental niche of an organism.
-
17N.3.HL.TZ0.17b:
Describe the relationship between Zooxanthellae and reef-building coral species.
- 17M.3.SL.TZ1.13c: State one limiting factor on Zooxanthellae which affects coral reef formation.
- 19N.3.SL.TZ0.13b: Compare and contrast fundamental and realized niche of a species.
- 19N.3.HL.TZ0.14d: Outline what is meant by the niche concept.
