I've seen the word population most commonly used in the context of the magnitude of a community or group e.g. "The population of the United States is 320 million". I have also seen it used to simply refer to the collective e.g. "The immigrant population of X experience low levels of racism."
Which is the primary or original meaning: magnitude or collective noun?
Edit: So, etymology suggests that the collective noun is the original meaning. When did it change in popular use?