In short, a niche is comprised of the conditions and resources required for the survival and reproduction of an organism (following G.Evelyn Hutchinson's definition). Another way of thinking about a niche is an organism's relationship to its environment -- what does it need to survive, and how does it make a living?
Food is required for an organism's survival and reproduction, so it can be considered a 'niche dimension'.
Food is required for an organism's survival and reproduction, so it can be considered a 'niche dimension'.