| Date | November 2018 | Marks available | 2 | Reference code | 18N.1.SL.TZ0.5 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Describe | Question number | 5 | Adapted from | N/A |
Question
Figure 9(a): Fact file on beaver’s role in the ecosystem
- Beavers build dams with sticks, creating ponds and slowing the flow of rivers.
- Beaver ponds:
- are less suitable for river fish, for example brook trout
- provide new habitats for aquatic plants, for example bullhead lily, dragon fly larva, bullfrogs and
other fish, for example pearl dace.
- Dam may cause floods; if water covers the roots of river-edge trees, the trees may die and provide
more nesting sites for birds. - Marsh forms at the edge of beaver ponds.
- Grasses and sedges colonise the nutrient-rich silt at the bottom of the former pond, creating a beaver
meadow. - Beaver meadows have more light penetration, higher soil moisture, more nitrogen and a different
vegetation from that of the adjacent river-edge forest. - Dams may collapse because of heavy rains or spring melt, or if beaver is killed by a predator.
© International Baccalaureate Organization 2018
Figure 9(b): The succession of ecosystems caused when a beaver dam is built across a river
With reference to Figures 9(a) and 9(b), describe one abiotic change and one biotic change in a beaver meadow community undergoing succession.
Markscheme
This question requires “Resource Booklet - Nov 2018 SL paper 1”, available under the "your tests" tab > supplemental materials.
Biotic [1 max]:
increase in small bushes followed by trees / reforestation / plant diversity increases;
increase in (mammal) species more adapted to forests;
increase in animal diversity / increase in predation due to greater animal diversity;
Abiotic [1 max]:
reduction in soil moisture (as water is taken up by trees);
reduction in soil nitrogen / reduction in soil nutrients;
reduction in light penetration;
reduced temperature ranges due to greater shade in day;
increased humidity due to transpiration by trees/water channel/creation of river;
Do not accept only “change in vegetation/creation of new vegetation area”.
Do not accept “increase in water turbidity” as meadow is not a water body.
Examiners report
Very few candidates correctly described changes in two suitable factors. Most candidates described changes linked to a river system that was being dammed rather than a beaver meadow undergoing succession. Some students did not know the difference between biotic and abiotic factors.
Syllabus sections
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15M.2.SL.TZ0.2b.ii:
Explain how predation may lead to long-term population decrease or extinction of the prey species.
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15N.1.SL.TZ0.2b.i:
Identify one abiotic factor which may affect the population of insects in a forest.
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19N.1.SL.TZ0.2e:
Suggest why the St Lawrence River beluga whale population has not recovered despite being given protected status in 1983.
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16M.1.SL.TZ0.1d:
Oystercatchers and avocets both feed on small animals in the mud of the wetlands. State the most likely relationship between these two species.
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19M.2.SL.TZ0.5a:
Identify four impacts on an ecosystem that may result from the introduction of an invasive species of herbivore.
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17M.2.SL.TZ0.1e.ii:
Outline how this relationship may be of benefit to the populations of both species.
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19N.1.SL.TZ0.2b:
Using Figure 7, state the St Lawrence beluga whale population in 1920 and 1940.
1920:
1940:
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15M.2.SL.TZ0.2a:
Outline the similarities and differences between predation and competition.
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18M.2.SL.TZ0.5a:
Distinguish between the terms niche and habitat with reference to a named species.
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14N.2.SL.TZ0.2a:
Distinguish between negative and positive feedback using examples from environmental systems.
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18N.1.SL.TZ0.10c:
With reference to Figure 10(b), explain the threats to the future existence of a small and sustainable population of wolves as a result of their protection in limited area.
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17N.2.SL.TZ0.1a.ii:
Identify three reasons why carrying capacity can be difficult to estimate.
- 17M.2.SL.TZ0.1e.i: State the relationship between large and small fish in Figure 1.
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19N.1.SL.TZ0.2c:
Calculate the percent decrease in beluga whale numbers from 1920 to 1940.
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19M.1.SL.TZ0.5:
With reference to Figure 4(d), suggest the impact on the marine food web if tuna numbers were to decline.
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19N.1.SL.TZ0.3c:
With reference to Figure 9(a), explain why the realized niche of the mottled sculpin has changed in recent years.
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16M.1.SL.TZ0.1a:
Define the term species.
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19M.2.SL.TZ0.5b:
Explain how both positive and negative feedback mechanisms may play a role in producing a typical S population growth curve for a species.
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15M.2.SL.TZ0.2b.i:
Explain how predation may lead to stability in a population of the prey species.
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15M.2.SL.TZ0.1d:
Evaluate the possible use of grass carp in controlling the growth of water hyacinth in Inle Lake.
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15N.1.SL.TZ0.2c:
Distinguish between a mutualistic relationship and a parasitic relationship.
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14N.1.SL.TZ0.2c:
Using Figure 1 below, calculate the annual rate of population increase for elephants in Zimbabwe from 1985 to 2005.
Figure 1 Elephant Population: Kenya compared to Zimbabwe, 1973 – 2011
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16M.2.SL.TZ0.3a:
Outline the role of limiting factors in S and J population curves.
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16N.2.SL.TZ0.1f:
Justify whether or not Mesquite should be cleared from the Swakop River Valley.
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16N.2.SL.TZ0.1e:
With reference to the data in Figure 4(b), suggest two conclusions which can be drawn from the camera trap data.
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15N.1.SL.TZ0.2a.ii:
Identify two possible reasons why species B and C were not present in the litter layer when it was resampled six months later.
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17N.2.SL.TZ0.1a.i:
Define the term carrying capacity.
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14M.1.SL.TZ0.1a.iv:
Identify two possible effects of removing trout on this ecosystem.
