Living ecosystem

Related:
* Artificial life
* Biological simulation

This generally means no animal is "respawned" out of the blue: they are born, grow up and breed. If whole herds are slaughtered from an area, it may take significant time for a herd to migrate to the area from elsewhere, if there even are any left out there.

Often this process works at extremely high speed compared to what it would take in reality, but some games may actually work in such a heightened speed that there's no need for additional speed up for the breeding.