Changes in Gene Pools 97 KEY TERMS AND IDEAS:

1. The Chatham Island (or black) robin (right) was once common on the Chatham

Islands, but became extinct through most of its range in the 1930s as a result of predation by introduced cats and rats. The population fell to just 5 birds in 1980 and included a single breeding pair. Through captive breeding, the population is now around 250 birds. All of the birds are descended from one female, Old Blue. Its very small population shows very low genetic diversity and there is very high relatedness between the birds. The black robin is listed as critically endangered.

(a) Define the term population bottleneck:

(b) Explain the nature of the population bottleneck experienced by the black robin:

(c) Explain the effect of the bottleneck on the genetic diversity of the black robin population and discuss the likely implications for the persistence of this critically endangered species:

Photo: Dept of Conservation

2. The Wellington tree weta (right) was introduced to Matiu-Somes

Island in Wellington Harbour from Mana Island as part of an ecological restoration programme. A total of 59 weta were introduced over 2 years (1996-1997). The population is now well established.

(a) Define the term founder effect:

(b) Explain why genetic drift is likely to be important in the evolution of the weta population on Matiu-Somes Island: