Final answer:
The word describing the living components within an environment such as mammals, fish, birds, and plants is 'ecosystem,' which includes both biotic and abiotic elements.
Step-by-step explanation:
The word that describes the mammals, fish, birds, and plants that live in an environment is ecosystem. An ecosystem includes all the living things in a particular area, interacting with each other, and with their non-living environments (weather, earth, sun, soil, climate, atmosphere). In an ecosystem, the biotic components are the living creatures that shape the environment, such as mammals, fish, birds, and plants. The structure of an ecosystem is defined by the living organisms and their physical environment.