Population Dynamics in Ecology: Definition & Concepts

Population Dynamics in Ecology: Definition & Concepts
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  • 0:00 Populations in Ecology
  • 0:56 Stability
  • 1:45 Fluctuation
  • 3:15 Immigration & Emigration
  • 4:11 Metapopulation
  • 4:52 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

In this lesson, we look at how population is an ecological concept just as it is a sociological one. We will look at wildlife populations by comparing them to human social actions and define key concepts for understanding population from an ecological perspective.

Populations in Ecology

Chances are when you hear the word 'population,' you immediately think of the size of a human population. For example, Canada has around 30 million people, China has more than 1.3 billion, or Washington, D.C. has around 600,000. However, the word 'population' can just as easily be used to describe the numbers of other animals as well.

In this lesson, we will look at population as an ecological concept. To do that, we will see what it means for a population to be stable or to be fluctuating, as well as the results of immigration and emigration on a population. (Spoiler alert: there is a difference between immigration and emigration!) Finally, we will examine the idea of a metapopulation, all while referring back to human populations for clarity.


When ecologists say that a population is stable, they are really saying that it is about as big as it's going to get and is not in any foreseeable danger of mass shrinkage. Stable populations are usually a good thing for ecologists to find because that means that the chances of extreme and sudden changes are unlikely.

Remember, too, that everything in ecology is interrelated and can quickly affect other populations. After all, if a population of deer in a given forest is pretty constant, chances are that the bear population is also pretty stable. In humans, a stable population allows for the people who look after our habitats, ranging politicians to farmers, to make sure that there are enough resources to go around.


Fluctuation is what happens when there is no stability. Fluctuation can result in a rapidly growing population or one that can't stop shrinking. In any event, fluctuation means that stability is gone. Let's go back to our example of the deer in the forest. What do you think would happen if the population of deer was to suddenly increase? It could signal that there is more food for the deer in the area, meaning that more fawns are able to reach adulthood.

However, more food for the deer means more food for the local bear population; bears eat deer, so a fluctuation in the deer population often creates the same fluctuation in the bear population. But what happens when the deer run out of food? Their numbers rapidly shrink, but so too does the bear population. However, and why we should care as humans, is that mischievous bears could invade human habitats to access our garbage cans and picnic baskets.

For humans, we are seeing the same thing play out right now. Over the last 80 years, our species' ability to produce more food has meant that the population is growing at a very rapid rate. Some people are afraid of what will happen when our population approaches a point at which we can no longer produce enough food for ourselves. Luckily, not too many of us have to worry about being eaten by bears, so at least we have that going for us.

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