Intraspecific competition is when organisms of the same species compete with each other for the same resources. It can cause a cyclical change in population size around the ecosystem’s carrying capacity — where the population grows, shrinks, grows, and so on. This is because the population of a species increases when resources are plentiful. As the population increases, more organisms will compete for the same amount of space and food. Eventually, these resources become limiting. If the population grows beyond the carrying capacity, there won’t be enough resources for all the organisms and the population will begin to decline.
A smaller population then means that there’s less competition for space and food, which is better for growth and reproduction — so the population starts to grow again.