an unfilled niche would have the known properties of life with resources so bounding that there isn't a strict need for competition for survival. (a brand new uncovered dish of agar media)
a populated biome has an active +- exchange of resources between participants that facilitates the need for competition due to resource bounds. (the rain forest, most of the biological world)
a sterile biome has no known properties of life, and no known participants. The participants that are there struggle to exist or are in some form of stasis to survive the condition. (a brand-new sealed blood vacuum vial.)
as for 'as much as it can support', i'm unaware of how to determine an optimal maxima for biological growth independent of species or environment. Maybe some exotic sphere-packing type idea might work with a reward function for 'resources' ? I don't know.
