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← Theoretical B

Q16 — Niche Dimensions and Stipa capillata Drought Adaptation

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Ecology

The “hypothesis of intra-niche dimensions” states that stable coexistence in one ecological niche can be reached if the growth of one species is constricted by one limiting factor and the growth of a neighbour species by another. The balance of limiting factors creates trade-offs, allowing more than one species to occupy different “dimensions” within a niche; otherwise, a more adapted species will completely displace a less adapted one.

In the steppe conditions, Stipa capillata is more resistant to drought compared to other perennial grasses. However, since its root system is weak, it cannot spread vigorously in grasslands with good perennial turf.

Turf is a surface layer of soil, densely overgrown with short herbaceous plants very close to the ground.

A photo of Stipa capillata grass with long, drooping, feathery seed awns, growing among other grasses. Figure 1. Stipa capillata.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Based on the hypothesis, fast-growing plants usually overpopulate nutrient-poor soils.
B. Horses grazing in the meadows of Stipa grass can help increase the number of other plant species in the steppe.
C. Uncontrolled ploughing of steppe areas will lead to a decline in the biomass of Stipa grass relative to other perennial grasses.
D. During the drought season, the biomass of turf may decrease, particularly, owing to the reduced photosynthesis in turf.
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Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF