What term is defined as a stable mix of populations expected in a given area

The term that is asked in this problem would probably be the climax community.

In an environment, there is always that ongoing exchange of majority between the living organisms. This exchange of majority is observable upon plants and animals, but this would only be observable for a course of time. Thus, number of months or years is needed to observe such exchange. Logic would cut to the chase, but observing it with data would suffice for those who are likely to ask. After some more years, decades, or even centuries, an area that has lasted to such extent would achieve a stable mix of populations which is termed as climax community.