| Date | November 2017 | Marks available | 3 | Reference code | 17N.2.SL.TZ0.1 |
| Level | Standard Level | Paper | Paper 2 | Time zone | Time zone 0 |
| Command term | Identify | Question number | 1 | Adapted from | N/A |
Question
Define the term carrying capacity.
Identify three reasons why carrying capacity can be difficult to estimate.
Markscheme
the maximum number of individuals/load of a species that can be sustainably supported by a given area/habitat/environment OWTTE;
NB. Definition needs to make clear that cc is associated with a single species. This means that: “The maximum number of a species that can...etc” is acceptable, but “the maximum number of species that can…” is incorrect, and should not be credited.
Generally:
there are many different potential limiting factors for natural populations;
populations’ needs may change through time due to genetic changes/evolution;
environmental conditions may change eg climate change/introduced species;
it takes extensive/long-term study to identify a precise relationship between a species and given environmental factor;
For human populations:
human populations exploit/depend upon a far greater range of different resources than most other species;
(human ingenuity) humans are able to substitute one resource/material for another;
variations in lifestyle/culture/economic status between human populations mean different resources/amounts of resources are used/needed;
the importation of resources from other ecosystems/regions can offset a lack of resources in an area;
technological developments cause changes in resources required/available over time;
Award [1] for each correct reason identified, up to [3 max]
Do not credit responses addressing changing population size (has no influence on carrying capacity).
Examiners report
Although, in other contexts, allowances are made for linguistic imperfections, for the purpose of a “define” question, language does need to be precise. For example, in response to this question the phrase “maximum number of a species” means something quite different to “maximum number of species” …and many responses used the latter concept which is incorrect. Similarly, a number of responses omitted the key element of “sustainably” (i.e. as in “…can be sustainably supported”)
Candidates often found one valid difficulty in estimating carrying capacity but few went further. A significant minority confused the estimation of carrying capacity, with the estimation of population size.
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.
- 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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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.
