Is it possible for any one population to grow so large it takes over the planet? In this lesson you will learn the answer to that question. You will learn about the limiting factors of population growth and how it controls population numbers.
Trying to Take Over the World
Your little brother Marcus’s 5th birthday is coming up. He has been asking you over and over for an enclosed ant farm that he saw in a catalog. On his birthday you surprise him with the gift he has fantasized about for months.
After he thanks you repeatedly, he tells you why he really wanted the ant farm. Marcus has plans to grow the biggest ant population on the planet right in his bedroom. You immediately feel sad that you brought it for him because you know that his plan will not work. You begin to explain why his plan for an ant population large enough to take over the planet won’t happen, especially from Marcus’s bedroom.
What Is a Limiting Factor?
You try to explain a few basic concepts to Marcus, starting with a limiting factor. Limiting factors are anything that places restrictions on how large a population can grow.
You ask Marcus to tell you some of the things his ants will need in order for them to be healthy and allow their population to grow. After thinking a minute, Marcus says food, water, and space. Very good! You say. Anything that a population needs to survive, thrive, and remain healthy can also be a limiting factor in the growth of that population.
A Population too Large
What will happen to the population of ants on Marcus’s ant farm if they have all of the food and water they need? Well of course the population will grow! However, there is one thing that they will eventually will run out of on the ant farm, and that is space.
Think about the things that can happen to any population when they are over-crowded. Disease is one of the limiting factors that becomes more apparent as a population reaches its environment’s upper limit for that population (its carrying capacity). You ask Marcus what he thinks will happen to his ants as more and more of them start to carry disease. He replies that, some of them will die. Correct, you say.
A Population too Small
You explain to Marcus that as more and more of his ants become sick and die, the population numbers will drop back below their environment’s carrying capacity. Sometimes changes in the environment, disease, and other limiting factors can cause a population’s numbers to drop so low that rapid population growth follows.
No matter what happens in a population, its numbers will drop and sometimes rebound if it reaches the carrying capacity for its environment.
Flows Like a River
As you can see from the explanations above, population is a not a static thing. It does not stay constant.
Environmental changes and limiting factors keep the population from growing out of control, but they don’t keep the population at a constant number. The population of any organism can grow sharply, perhaps because of the introduction of a new food source. The population will then eventually decrease because of other limiting factors. The population could also go through a large decrease because of loss of habitat, say if a shopping mall is built where it used to live. As long as the population of an organism is not driven to extinction, it will continue to rise, fall and flow, like the water of a river, never standing still.
All population numbers are controlled by limiting factors. Limiting factors are environmental factors that keep a population’s numbers from growing out of control. Some examples of limiting factors are food, water, living space, and disease.
The maximum number of any one organism an environment can support is the carrying capacity for that organism. Population numbers are not static; they go up and down based on limiting factors and other environmental occurrences.