Why would competition be considered a limiting factor within a ecosystem

Answer

The main reason being the amount of food available.

Explanation:

Think of it this way:

If an animal is trying to find food but another species is looking for the same prey then its going to be increasingly difficult for the species to find prey and if there's not enough of the prey species then the population of the predator to go down.

That is why its considered a limiting factor.

its b. greenhouse gasses trap uv rays for heat so that the plants stay alive.