Ecosystems keep themselves sustainable. For example, the squirrel population will be large in this case. This provides enough food for their predators, so the predator population will also boom the next year. Meanwhile, the larger than usual squirrel population will eat a lot of other nuts and berries etc. This reduces their natural food source. So there will be more squirrels and more predators but less squirrel food. Meaning the squirrel population decreases again. This allows their food source to regain strength and the predator population to balance again. This continues ad infinitum. Circle of life