In the Death Valley area of Nevada in the USA, there was once a very large lake. Around 20 000 years ago, the lake began to dry out and today it exists only as separate pools. Four species of desert pupfish have been recorded in these pools. Evidence shows that more than 20 000 years ago there was just one pupfish species in the lake system. Fig. 8.1 shows a desert pupfish.
(a)[5]
Explain how the shift from an extensive lake system to only a few pools could have led to the evolution of four new species of desert pupfish.
(b)[2]
State how environmental factors may act as stabilising forces of natural selection in each isolated pool, after the initial evolution of a new species of desert pupfish.
(c)[3]
Suggest what may happen to the desert pupfish if water levels rise and the pools once again become an extensive lake system.
Worked solution & mark scheme
This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “the term allopatric speciation” …