Answer:
ecosystem
Step-by-step explanation:
An ecosystem refers to the interaction/relationship between the biotic parts of a habitat with one another and also the abiotic parts. The biotic parts refers to organisms that possess life in them e.g plants, animals, microbes etc while the abiotic parts refers to the inanimate things e.g rocks, sea, land, soil etc.
Therefore, according to this question, an ecologist looking at communities of different species interacting with each other and the abiotic factors of their environment is studying ECOSYSTEM.