Answer:
Population
Step-by-step explanation:
Population refers to the total number of all members of a species occupying a particular area or habitat or region at a given time. Populations are not static but change in size. Populations make up communities. Community comprise of populations of different species of plants and animals that coexist in a given area. Communities make up ecosystem. An ecosystem is a natural unit composed of living and non-living components whose interactions result in a stable self-supporting system. Ecosystems are generally categorized as either aquatic or terrestrial.