The eco-system just needs to load one copy of the mesh for each object type and then allocate a few bytes per instance to record location, size, orientation. This is very efficient in memory usage. I don't know exactly how much information is stored for each instance, but it's probably under 1kb, so 100,000 instances will take well under 100MB of RAM to store. The Poser models often come with high resolution texture maps, which take a LOT of memory. A single 4000 x 4000 map will weigh in at about 64MB, and Poser scenes with clothed models can have dozens of maps (at varying resolutions). Even if you make the ecosystem out of an imported Poser model, then the large number of instances add very little to the memory footprint compared to the model itself.

Mark