Answer:Key points
In nature, population size and growth are limited by many factors. Some are density-dependent, while others are density-independent.
Density-dependent limiting factors cause a population's per capita growth rate to change—typically, to drop—with increasing population density. One example is competition for limited food among members of a population.
Density-independent factors affect per capita growth rate independent of population density. Examples include natural disasters like forest fires.
Limiting factors of different kinds can interact in complex ways to produce various patterns of population growth. Some populations show cyclical oscillations, in which population size changes predictably in a cycle.
Introduction
All populations on Earth have limits to their growth. Even populations of bunnies—that reproduce like bunnies!—don't grow infinitely large. And although humans are giving the idea of infinite growth a run for its money, we too will ultimately reach limits on population size imposed by the environment.
What exactly are these environmental limiting factors? Broadly speaking, we can split the factors that regulate population growth into two main groups: density-dependent and density-independent.
Density-dependent limiting factors
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.
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