Ecology is the study of environmental interactions at the following levels, from least inclusive to most inclusive:

organism, population, community, ecosystem

Explanation: Ecology is the part of the biology in which the study of organism and environment is done along with the relation established between them. This study also includes human,animals and physical surroundings as well. It displays the adaptation and interaction happening in the ecological environment.

The stage/steps of order is followed as organism then population of human, community of them and ecosystem stage respectively .