The general layers in the pyramids are the primary producers already mentioned, the herbivores and the carnivores. Throughout the pyramid both scavengers and microscopic decomposers operate. If one of the key members of a food pyramid layer were removed by disease or environmental change the structure would become unstable. The species lying below the vacant slot would increase unchecked to a point where they outran their food supply and their numbers would be controlled by starvation. In reality this seldom happens and another predator soon appears capable of filling the unoccupied niche.