What would happen to the population of an animal if its food source were added to the food web

Its population would tend to increase, since the existence of an additional food source would mean that the environment can sustain a larger number of mouths to feed. This could potentially lead to further population increases down the line of the food web if the animal is eaten by others. However, it can lead to imbalances if another food source will be completely eradicated because of the large number of this animal.