| 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.
