In the 1970s for 551 days the Galapagos islands received no rain. Plants withere
ID: 216688 • Letter: I
Question
In the 1970s for 551 days the Galapagos islands received no rain. Plants withered and finches on the island grew hungry. The tiny seeds the medium ground finches were accustomed to eating grew scarce. Medium ground finches with larger beaks however could take advantage of alternate food sources because they could crack open larger seeds. The smaller - beaked birds couldn't do this, so they died of starvation. In 1978 scientists returned to the Galapagos to document the effect of the drought on the next generation of medium ground finches. They measured the offspring and compared their beak size to that of the previous (pre drought) generati ons. They found the offsprings' beaks to be 3 to 4% larger than their grandparents'.
The relationship observed between the beak size of ground finches and a drought condition is an example of what type of population change? Be as specific as possible
Explanation / Answer
The observations and the data they collected the grants concluded that evolution by natural selection has occurred in the medium ground finch population. The increase in the average beak size of the offspring was a direct result of the change in the food supply during the drought. Beak size is an inherited trait in the finch population under study. Birds that could eat larger, tougher seeds survived and reproduced during the drought. Beak size varies among the birds in the finch population under study.