For example, use the food web of a savannah biome.
Let's say the hippos all disappeared. Because the hippos are prey for the tertiary predators like a hyena, the population of the predators would decrease while the population of the grass increased.
If the predators disappeared the preys' population would spiral out of control and all the primary producers like leaves and grass would become scarce. Additionally, the decomposing carcass of animals like dead predators and prey create food for microorganisms which make fertile soil; thus, causing the land to become barren.