How might scarcity of food affect the size of a finch population?

The finch population evolved in response to the scarcity of food by changes in the distribution of its beak size in Galapagos. Some of them migrated to the nearby island and few die especially those whose beak cannot get some food to eat.

Scarcity will affect the finch population because if there is less food for their population they might die or migrate into the place that food is abundant, food is the main source of life in every animal or even humans so this affects the population of the finch. The finch is a population of fifteen species of a passerine bird.