Final answer:
The biotic portion of an ecosystem, which includes all the living populations of different species interacting in a physical environment, is correctly referred to as a community. A community involves various interactions such as symbiosis, predation, and competition which are fundamental to the ecosystem's functioning and evolutionary processes.
Step-by-step explanation:
The biotic portion of an ecosystem refers to all the living components within it, which includes the populations of different species. These populations living and interacting with one another in a physical environment form what is known as a community. This is in contrast to the term biodiversity, which represents the variety of life in a particular habitat; the habitat, which is the physical environment where a species lives; or the niche, which is the role a species plays in its ecosystem.
Understanding the community within an ecosystem is essential because it involves the study of various interactions such as symbiosis, predation, and competition, which are critical to the structure and function of the ecosystem. These interactions among species can influence their evolution and help shape the biodiversity of the community.
An ecosystem itself is composed not only of the community of living organisms but also of the abiotic factors like water, sunlight, and minerals. These components are interconnected through the cycles of nutrients and the flow of energy, which makes the ecosystem a complex, functioning unit.
Therefore, when considering the biotic portion of an ecosystem that includes all populations of different species living and interacting in a particular physical environment, the correct term to use is community. This refers to the sum of all these living organisms and their relationships within the ecosystem.