In up by plants. The nutrients move through

In this lesson, you will learn the definition of ecological imbalance and explore some examples of ecosystems that have shifted to a state of imbalance. Test your new knowledge at the end with a quiz.

How Ecosystems Work

Has your car ever broken down on the side of the road? Often, a car breaks down because one simple part is broken.

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There are many moving parts that make a car work. A spark plug ignites the fuel, wheels move the car forward, and a radiator cools down the engine. In order for a car to work smoothly, all parts need to be intact and in good condition. Just like a car, species living in an ecosystem play an important part in keeping an ecosystem running smoothly. If one species is lost the entire ecosystem can stop working.Ecosystems are organized in a state of balance where species coexist with other species.

If something happens in an ecosystem, it can shift from a state of balance to a state of imbalance. Ecological imbalance is when a natural or human-caused disturbance disrupts the natural balance of an ecosystem. A disturbance is any change that causes a disruption in the balance of an ecosystem.Examples of natural disturbances are

  • Volcanic eruptions
  • Floods
  • Natural fires

Examples of human-caused disturbances are

  • The introduction of a new species
  • Logging a forest
  • Pollution
  • Overhunting of a species

After a disturbance occurs, an ecosystem can recover back to a balanced state. But if an ecosystem has a severe disturbance or is constantly having new disturbances, it may never recover back to a state of ecological balance.

English Ivy

Let’s look at some examples. Here’s a human-caused disturbance: did you know a killer plant has invaded the United States? This killer plant is called English ivy.

Originally from Europe, English ivy was brought here by settlers as a garden plant. With its natural predator thousands of miles away it was able to grow out of control, invading many forests. Now, over a century later, English ivy has grown out of control causing a state of ecological imbalance in many forest ecosystems. It quickly creeps over the forest floor killing native plants. The loss of plants means less food available for mammals, which can cause their populations to drop. Moreover, English ivy climbs up trees weighing them down causing them to collapse.

The loss of trees means less nesting habitat for birds.


Let’s look at one more example. Did you know that salmon have a hidden treasure locked inside their tissues? Born in freshwater streams, salmon migrate hundreds of miles to the ocean. In the ocean, adult salmon munch on a buffet of ocean organisms. As they get fatter and fatter, they store a treasure full of nutrients in their tissues. Salmon carry this treasure of ocean nutrients back to the stream to lay their eggs.

They die soon after. The treasure of nutrients stored inside their dead bodies is unlocked by decomposers. This treasure of nutrients is quickly gobbled up by plants. The nutrients move through the food chain as animals eat the plants.Unfortunately, in many areas, salmon populations are plummeting due to human disturbances. The loss of salmon means that they are no longer carrying a treasure of nutrients from the ocean back to the stream.

This disrupts the balance of the entire ecosystem. Without nutrients, plants do not have food to help them grow. Less plant growth means less food for mammals and insects. Fewer insects mean less food available for birds. The loss of salmon is like an earthquake that violently shakes the entire ecosystem shifting it to a state of ecological imbalance.

Lesson Summary

Let’s review. Ecological imbalance is when a natural- or human-caused disturbance disrupts the natural balance of an ecosystem. The balance of an ecosystem can be disrupted by natural or human-caused disturbances.

If a species disappears or a new species is introduced it can shift an ecosystem to a state of ecological imbalance. Examples are invasive English ivy and dam building or overfishing of salmon.


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