On differences between human population limits and those of other organisms,
“Both the jayhawk and the man eat chickens; but the more jayhawks, the fewer chickens, while the more men, the more chickens.” – Henry George, in the Criticism section of https://en.wikipedia.org/wiki/Malthusian_catastrophe
“[T]he more men, the more chickens” can pan out in a few different ways, and the pros and cons of those ways will probably write the future history of our population. This highlights a great potential we humans have for bringing about heaven or hell here in Middle Earth. A key metric distinguishing the two: agricultural externalities. The food you eat, where does it come from? How it’s grown, what does that do for all creatures involved and affected?