For example: if there is an increase in the prey population, this means that the availability of food increases, and therefore predators will eat more and reproduce, as they reproduce the predator population would increase and since they would be eating the prey population, the prey population decreases, and eventually the predator population becomes large enough and the prey population would decrease and therefore there wouldn't be enough food for predators o rely on and survive, this means that the predator population decreases.
Since the predator population decreases, there wouldn't be any organisms eating the prey, and therefore the prey population reproduces and increases again, this means that the availability of food once again increases for the predators.
Along with predators having more food, an introduction to a new pathogen/ disease (biotic factor), means that the prey population could potentially decrease to an extent where they are no longer able to breed, and therefore the whole population wipes out, and becomes extinct.
This also means that the species relying on that particular species would have lack of food, and this causes affect in the size of the population on another species. ultimately having an affect on the whole ecosystem, due to interdependence