Biology 9700 · AS & A Level · Evolution

Evolution — practice question

The orca, Orcinus orca, has the broadest range of any aquatic mammal and occurs in almost every sea and ocean. Orca are social mammals and usually live in groups, although group size varies. Several distinct forms of orca exist, and these are classified as the same species. However, there is evidence that sympatric speciation is taking place. In the Northeast Atlantic Ocean there are two distinct forms of orca: Type 1 and Type 2. Type 1 orca feed mainly on fish, whereas Type 2 orca feed mainly on aquatic mammals such as seals. Fig. 2.2 shows where Type 1 orca and Type 2 orca have been seen in the Northeast Atlantic Ocean. Orca are not restricted to only these regions, and some groups travel very long distances.
(a(i))[1]

With reference to Fig. 2.2, explain why the speciation taking place in the orca is called sympatric speciation.

(a(ii))[3]

Suggest examples of behavioural separation that would help produce sympatric speciation in Type 1 orca and Type 2 orca.

(c(i))[1]

With reference to Fig. 2.2, explain why the speciation taking place in the orca is called sympatric speciation.

(c(ii))[3]

Suggest examples of behavioural separation that would help produce sympatric speciation in Type 1 orca and Type 2 orca.

(b)

In the Southern Ocean, which surrounds Antarctica, there are three distinct types of orca: Type B, Type C and Type D. Fig. 2.3 shows the locations around Antarctica where Type B orca, Type C orca and Type D orca have been observed.

(b(i))[1]

With reference to Fig. 2.4, state one way in which the Type D orca is different from both the Type B orca and the Type C orca.

(b(ii))[3]

Phenotypic differences between Type D orca and the other types of orca shown in Fig. 2.4 may have come about through genetic drift, including the founder effect. Suggest how genetic drift could lead to phenotypic differences between Type D orca and the other types of orca shown in Fig. 2.4.

(c)[2]

In the future, the different types of orca may be classified as separate species. If this happens, some of the newly classified species will have very small population sizes. Suggest two factors, other than population size, that should be monitored when assessing the conservation status of any newly classified species of orca.

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