In order for any system to be sustainable (i.e. viable over a long period) all of its components must have a high degree of autonomy. The reason why natural ecosystems are sustainable (if humans don’t destroy them) is because their components such as plants and animals are autonomous. Plants, for example, autonomously photosynthesize and extend their roots to draw nutrients from the soil. Meanwhile, herbivores autonomously nourish themselves by eating plants, and carnivores by eating herbivores etc.