| Date | May 2019 | Marks available | 2 | Reference code | 19M.3.HL.TZ2.6 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Outline | Question number | 6 | Adapted from | N/A |
Question
The shore crab (Carcinus maenas) forages for food in the intertidal zone on rocky seashores. An experiment was carried out to assess predation at specified levels of food abundance. An area of shore was enclosed in a wire cage. All other food was removed from the encaged area except the mussels provided by the investigators. The number of mussels consumed was measured while the crabs foraged at densities of one, two or four crabs per cage.
[Source: reprinted from B D Griffen and D G Delaney, Ecology, 88 (12), pages 3012–3021,
copyright 2007, with permission, the Ecological Society of America]
Suggest a reason for the plateau in the graph when only one crab is present in the cage.
Determine whether foraging by crabs is dependent on number of prey (mussels) or number of predators (crabs).
Outline the role of natural selection in animal behaviour.
Markscheme
a. has eaten its full ✔
b. feeding depends on ratio of predator to prey
OR
when «certain» ratio of predator to prey is reached feeding/graph levels off ✔
c. prefers certain size mussel so only preys on these ✔
[Source: reprinted from B D Griffen and D G
Delaney, Ecology, 88 (12), pages 3012–3021,
copyright 2007, with permission, the Ecological
Society of America]
a. «foraging» depends on number of predators/crabs ✔
b. mean number of mussels/prey consumed per crab decreases as number of crabs increases ✔ Accept vice versa.
c. crabs compete for prey/mussels ✔
d. both «prey and predator» affect foraging success ✔
a. genetically based/innate behavior can be passed on to offspring ✔
b. behavior increases chances of survival and reproduction ✔
c. will increase in frequency/become more prevalent in a population ✔
Examiners report
Most candidates figured out that the plateau occurred when the crab could eat no more but it was more difficult for certain to determine that the foraging depends on the number of predators and to justify it.
Most candidates figured out that the plateau occurred when the crab could eat no more but it was more difficult for certain to determine that the foraging depends on the number of predators and to justify it.
Most candidates could only partly outline the role of natural selection in animal behaviour.
Syllabus sections
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20N.3.HL.TZ0.8b:
Explain how natural selection can cause mate selection behaviour patterns to develop in a species such as eastern bluebirds.
- 20N.3.HL.TZ0.8c: Another type of behaviour is altruistic behaviour. Outline an example of altruistic behaviour.
- 17N.3.HL.TZ0.06a: State the effect of simulated ship noise on foraging behaviour.
-
17M.3.HL.TZ2.7b:
Suggest reasons for the length you stated in (a) being the most common length of M. edulis that C. maenas eat.
- 17M.3.HL.TZ2.7a: State the most common length of M. edulis eaten by the C. maenas population.
-
18M.3.HL.TZ1.7c:
Distinguish between innate behaviour and learned behaviour in the development of birdsong.
- 19N.3.HL.TZ0.7a: Courtship behaviour leads to mate selection. Describe innate behaviour.
-
18M.3.HL.TZ2.8:
Compare and contrast innate behaviour and learned behaviour.
-
20N.3.HL.TZ0.8a:
Evaluate the hypothesis that females prefer to mate with males whose feathers are a brighter blue.
- 19N.3.HL.TZ0.7b: Explain the implications of courtship behaviour in natural selection.
-
19M.3.HL.TZ2.6a.i:
Suggest a reason for the plateau in the graph when only one crab is present in the cage.
-
19M.3.HL.TZ2.6a.ii:
Determine whether foraging by crabs is dependent on number of prey (mussels) or number of predators (crabs).
-
17N.3.HL.TZ0.06b:
Predict the consequences on C. maenas of increasing noise related to human activity.
-
18M.3.HL.TZ1.7d:
Outline an example of a change in animal behaviour as a result of natural selection.
-
18N.3.HL.TZ0.7:
The drawing shows male and female Emperor birds of paradise (Paradisaea guilielmi ) found in Papua New Guinea.
Suggest how the external features and courtship behaviour of these birds of paradise affect reproductive success.
