A limiting factor is something that restricts organism(s) from increasing their population. If you look at a graph showing the population of a certain organism, you will notice that at a certain amount of their population it stays around the same area. That is known as the carrying capacity. The carrying capacity is there due to the limiting factors, which depends based on the needs of particular organisms. For example, one limiting factor for a certain species might be that the number of predators increased, or there are limited resources available in order to survive.
