During the drought of 1977, 84 percent of the medium ground finch population on Isle Daphne Major disappeared. The individuals that survived had deeper beaks and were larger. Given that natural selection favored large individuals with deeper beaks, how can the presence of individuals with small, pointier beaks in 1983 be explained?

+1 vote

 

These islands were colonized from the mainland. These small-beaked individuals must have flown over from Ecuador.

Even though the majority of birds after 1977 had deeper beaks, there was variation in beak size in the population. As seed type and seed availability changed, birds with beaks suited to exploit abundant seeds had higher reproductive success.

Researchers were not measuring juvenile birds in 1977 but did measure juvenile birds in 1983. It is a well-known fact that juvenile birds are small and have small beaks.

These islands must have received immigrants from a neighboring island.

 

asked Dec 28, 2012 in Biology by anonymous
    

1 Answer

+1 vote

 

Even though the majority of birds after 1977 had deeper beaks, there was variation in beak size in the population. As seed type and seed availability changed, birds with beaks suited to exploit abundant seeds had higher reproductive success.

 

answered Dec 28, 2012 by Panda ~Expert~ (1,557 points)

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