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.

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 ✔

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.