Factors that Affect Animal Population Size

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  • 0:03 Animal Population Size
  • 0:31 Light and Nutrition
  • 1:12 Habitat and Niche
  • 2:23 Competition and Predation
  • 3:18 Symbiosis
  • 4:15 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

In this lesson, you will learn about the many factors that may influence animal population size, such as nutrition, competition, and even things like parasitism.

Animal Population Size

Did you know that the nutrition you get as you're growing can affect how big you get? If you have poor nutrition while growing up, you'll be smaller than if you get lots of good nutrition. Nutrition is also one factor in how big or small a whole population of animals can get, not just individuals within that population. Other factors that influence animal population size include water, habitat, competition, predation, and lots more. This lesson will cover them.

Light and Nutrition

The more food and water an animal's population has at its disposal, the more likely it will be bigger in size. Conversely, if there is a drought and plants or water disappear, or the prey that the animals once ate die off, the population size will plummet. Thus, more nutrition means a larger population size.

Light is another key factor in population size. While life can certainly exist and even thrive without light (such as in deep sea vent communities or caves), the more light there is, the higher the abundance of food and prey. This means population sizes will - all else being equal - likely be bigger in areas with more light.

Habitat and Niche

The type of habitat an animal inhabits will also affect the population's size. For instance, animal communities in the arctic or desert regions of the earth differ vastly in size as compared to those in tropical regions, even for the same area of landmass. That's because arctic and desert communities have fewer resources to support larger populations. All of this goes back to the prior section regarding access to nutrients.

But even a particular niche within the same habitat can play a key role in an animal's population size. One extreme example of this occurred roughly 65 million years ago, when pretty much all the dinosaurs died off after a mass extinction event. Even though the dinosaurs died off, other animals, including mammals, that lived in the same exact geographic location still survived. Why? It's because they inhabited a specific niche within that environment. Some animals back then, including small mammals, lived largely underground, and this important factor helped them survive. One population of animals died off (the dinosaurs) and another eventually thrived (the mammals).

Competition and Predation

The type of competition within a community also influences animal population size. If competition for scarce resources like food is high between one population and another, then either both populations will decline or one will increase to the detriment of the other as they take over those scarce resources.

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