Hmmm.... You would also want your animal spawning rate equation to take into account the carrying capacity of the map (the max number of animals the map can support) otherwise, you may end up with a map choked to death with animals. (medium sized map can totally support 2^256 deer.) Not only is it unrealistic, it would also cause our game performance to degrade over time. If I can find some old notebooks of mine, I can write up some nifty equations for rate of population growth with the following properties. If the population is ever above the carrying capacity, the population starves till it falls below capacity. (eg, what happens to the lions when people kill half the deer population.) The population grows fastest when it is far below capacity (more resources per member of the population) and slowest when it nears capacity (fewer resources per population) *optional* When the population falls below some critical value, there are no longer enough members to restore the population, it will eventually go extinct. Determining the carrying capacity at any give time would be easy enough I think. For herbivores, we just take the grazing area and multiply it by some constant (1 acre can support 10 deer. If we have 30 acres, our carrying capacity is 300 deer.) Thus when a player builds buildings, he decreases space and lowers carry capacity. Carrying capacity for predators would be easy too, just relate it to the number of prey items avaliable. So when the prey population decreases, the predator population will fall till there are enough prey to support it. With four equation\s, I think we could make a very lifelike predator/prey model emerge in the game.