Circle of life

I think it would be a cool addition too see a new system other than regular spawning and breeding for new mobs to enter the world. I think mobs should naturaly breed and eventually die if they don't get enough food or from old age. 

Animals should hunt eachother like in real life to establish an ecosystem. For example if you remove sheep from a biome then the wolf population would deminish since they eat them, and if you bring a wolf to a desert biome it would eventually starve since there isn't any natural prey for them there. 

Or if you bring a few rabbits into a new area eventually that area would be heavily populated with them.

I think this would bring the world to life and make for interessting interactions between mobs.