Organisms in the same ecosystem are all

In the same system, the organisms are interdependent: one is a food source for another, which in turn is a food source for another, etc. this does not end with predators: when they die, their bodies are a food source for very small animals.

Interdependent

Organisms in the ecosystem are interdependent. Ecosystem is encompassing all the life on earth in the physical environment that supports it. In addition, an ecosystem involves both the biological (plants, animals, human beings) and non-biological (land, water, soil, and atmosphere) community which interacts as a system. More importantly, the living things are very dependent on the abiotic community since it cannot survive by itself. Every animal, plant and human needs the primary physiological needs of water, food and shelter provided by the abiotic system.   

It's cell theory. easy name i would think.