| Date | November 2019 | Marks available | 3 | Reference code | 19N.1.SL.TZ0.3 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Explain | Question number | 3 | Adapted from | N/A |
Question
Figure 9(a): Fact file on the round goby (Neogobius melanostomus)
- An invasive species from Asia.
- First discovered in the St Lawrence River in 1990.
- Females lay eggs three times a year; up to 5000 eggs at a time.
- Young fish mature quickly.
- Can eat up to 4000 eggs of other fish in 15 minutes.
- Aggressively defend the best egg-laying sites, out-competing the native mottled sculpin (Cottus bairdii).
- Eat invasive zebra mussels.
- Eaten by native fish, such as lake trout and yellow perch.
Figure 9(b): Pictures of the round goby and mottled sculpin
Using Figures 9(a) and 9(b), identify one feature of the round goby that shows it is an r-selected species.
With reference to Figure 9(a), outline how the round goby both positively and negatively affects the St Lawrence River ecosystem.
With reference to Figure 9(a), explain why the realized niche of the mottled sculpin has changed in recent years.
Markscheme
frequent egg laying (3 times per year);
many eggs laid at one time (5000);
young fish grow quickly / early maturity.
Positive [2 max]:
provide additional food source for native fish (e.g. yellow perch);
eat other invasive species, such as the zebra mussel.
Negative [2 max]:
increased competition for food, outcompeting native fish;
outcompetes the native mottle sculpin for the best egg-laying sites;
outcompetes native species which may become extinct;
eat other fish eggs, reducing populations/biodiversity;
introduce disease, reducing populations/biodiversity.
Accept any other reasonable response.
Do not accept only ‘outcompetes native species’, for credit must be linked to competition for food, egg laying sites or species extinction.
Do not accept ‘aggressively takes the habitat of native species’.
resources declined due to competition with round goby;
competition for/loss of nesting sites;
loss of food resources due to additional competition;
realized niche has changed because of impacts of climate change affecting temperature.
Examiners report
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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18N.1.SL.TZ0.5:
With reference to Figures 9(a) and 9(b), describe one abiotic change and one biotic change in a beaver meadow community undergoing succession.
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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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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.
