i would say it means how would organisms would react in an ecosystem. think of everyday life in your backyard perhaps. the grass uses the energy from the sun to grow. another organism, lets say a horse, eats the grass as a main source of food. lets say another grass eater lives there too-like a cow. the cow and the horse would naturally compete as they both rely on the same food source, and the same living space that is close to that food source, and so on as you move up in the food chain.
