During the drought of 1977, 84 percent of the medium ground finch population on daphne major disappeared. the individuals that survived had beaks that were deeper and larger than the beaks of individuals who did not survive.
given that natural selection favored large individuals with deeper and larger beaks, how can the presence of individuals with small, pointier beaks in 1983 be explained?
a) 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.
b) these islands were colonized from the mainland. these small-beaked individuals must have flown over from ecuador.
c) even though the majority of birds after 1977 had deeper and larger beaks, there was still 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.
d) these islands must have received immigrants from a neighboring island.