Let's start off with an example. Imagine a population of organisms—let's say, deer—with access to a fixed, constant amount of food. When the population is small, the limited amount of food will be plenty for everyone. But, when the population gets large enough, the limited amount of food may no longer be sufficient, leading to competition among the deer. Because of the competition, some deer may die of starvation or fail to have offspring, decreasing the per capita—per individual—growth rate and causing population size to plateau or shrink.
In this scenario, competition for food is a density-dependent limiting factor. In general, we define density-dependent limiting factors as factors that affect the per capita growth rate of a population differently depending on how dense the population already is. Most density-dependent factors make the per capita growth rate go down as the population increases. This is an example of negative feedback that limits population growth.
Hope this helps
