Ecosystem.

http://www.britannica.com/EBchecked/topic/178597/ecosystem

• ecosystem, the complex of living organisms, their physical environment, and all their interrelationships in a particular unit of space.
• A brief treatment of ecosystems follows. 
• An ecosystem can be categorized into its abiotic constituents, including minerals, climate, soil, water, sunlight, and all other nonliving elements, and its biotic constituents, consisting of all its living members. Linking these constituents together are two major forces: the flow of energy through the ecosystem, and the cycling of nutrients within the ecosystem.

 A food chain in the ocean begins with tiny one-celled organisms called diatoms. They make their own food from sunlight. Shrimplike creatures eat the diatoms. Small fish eat the shrimplike creatures, and bigger fish eat the small fish.

Figure 2: Transfer of energy through an ecosystem. At each trophic level only a small proportion of energy (approximately 10 percent) is transferred to the next level.