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

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. 

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.

it's c. (to reduce the greenhouse effect/carbon gasses)