Biocenosis or community

The biocenosis or biotic community of an ecosystem is the set of all living beings that live in the  biotope,  among which certain relationships are established.

A population is the set of individuals of the same species that live in a certain place. Living together allows them to feed, defend themselves, reproduce, etc. in better conditions than if they lived in isolation. For example, the population of mallards in a lake.

Therefore, the biocenosis is formed by the set of populations that live in the same place and that are related to each other.