Over-Exploitation: How Humans Affect Ecosystems By Decreasing Species Populations

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  • 0:07 Definitions
  • 1:09 Overfishing
  • 2:03 What Happens With Overfishing?
  • 3:03 Direct Ecosystem Effects
  • 3:53 Lesson Summary
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Lesson Transcript
Instructor: Laura Enzor

Laura has a Master's degree in Biology and is working on her PhD in Biology. She specializes in teaching Human Physiology at USC.

In this lesson, you'll learn how humans overexploit or overharvest species. You will discover the primary way in which humans are responsible for overfishing. You will also learn about how this negatively impacts ecosystems.


Humans often take too many of one species from their natural habitat. Typically, this involves a species used as a food source. When a species is harvested, or taken at a rate faster than the population can compensate for, the population is listed as overexploited, or overharvested. Think of this like a full cookie jar in a room full of hungry people. The more people that take cookies, the fewer are left in the jar. It takes time to bake more cookies, and if the cookies in the jar are eaten faster than they can be made, soon you run out of cookies!

When the population numbers of a species decline to the point where the animal or plant could possibly go extinct, or cease to exist, the organism is classified as endangered. Removing a species from their natural habitat can be detrimental. Not only does this threaten the biodiversity, or the variation of life within an ecosystem, but is also disrupts the balance of the ecosystem itself.


The best example of overexploitation of a resource is overfishing. Humans have caused the population decline of hundreds of species by overfishing or overharvesting them. When certain species of animals are considered especially tasty, or are considered a delicacy, the demand for those species goes up. Unfortunately, this typically means that those species are overharvested or overfished without regard to population numbers or how it will affect the ecosystem if they no longer exist. Two examples of fish species which have been overfished are bluefin tuna and sharks. Bluefin tuna are prized for their meat for sushi (the record is a single fish selling for over $1 million!), and sharks are harvested for their fins to make shark fin soup. Without their fins, the sharks cannot swim, and they drown.

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