Question

how do prey affect the size of a predator population?
prey will quite often begin to feed on the predators.
if the population of prey decreases, predators may not have enough food, causing the predator population to decrease.
prey population does not ever effect predator populations as the predators just find other food.

Explanation:

Prey are the food - source for predators. A decrease in prey population means less food for predators, which can lead to a decline in the predator population due to starvation, reduced reproduction, etc. Prey generally do not feed on predators (as they are the ones being preyed upon), and predators cannot always easily find alternative food sources when their main prey population drops.

Answer:

If the population of prey decreases, predators may not have enough food, causing the predator population to decrease.