Prey population size increases when there are enough resources available for food. When prey populations increase, the predator population size also increases, as this means there is more food available for energy. When the predators eat too many of the prey, this can result in a decline in prey population size. Furthermore, declines in prey population size can be due to a lack of food in the ecosystem. Both of these eventually result in a decline in predator population size as their food source is reduced. The prey are then able to grow in numbers as there are less predators eating them. This fluctuation in predator/prey population size results in cycles within a community.