What would happen to the population of an animal if it's food source were added to the food web

The food web (in contrast to the food chain) means that there may be more than one organisms competing for the same prey or food or they may be one organism that preys on many kinds of food etc. It is more complex than the food chain. If the food source of a certain animal was added to the food web, meaning there will be other organisms competing for that food source, then the population of that certain animal will either decrease (if the animal is not fit for the competition of food), or become constant or even rise (if the animal is well suited for the competition).