Interactions in Ecosystems: Types & Examples

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson we'll be learning about different types of interactions in ecosystems. We'll look at different types of symbiosis as well as predator prey relationships and examples of each.

What Are Ecosystems?

Take a look outside. Even if you live in a city, chances are there are a variety of living things right outside your window. Grass, trees and flowering plants dot the landscape. Birds fly in the trees, looking for insects to eat. This collection of organisms is called an ecosystem.

An ecosystem is the collection of both living and non-living things in an area. The sunlight, rocks, soil and rainfall are all part of your outdoor ecosystem as well.

Ecosystems become more complicated in wild areas untouched by humans. Millions of species interact in these complex ecosystems living in balance together. Tropical rainforests such as the Amazon basin contain millions of different species, all reliant on each other and non-living factors in their environment.


The interactions between these living things can be divided into several categories. Some organisms live in symbiosis, a long lasting ecological relationship between two organisms. Although we usually think of both organisms benefiting in symbiosis, there are other types of symbiosis as well. Let's look at each one in detail next.


Mutualism occurs when both organisms benefit from an interaction. You can think of mutualism as you helping a friend study for a test. You get to review the material (teaching is one of the best ways of learning!) and your friend gets the help they need. One example of mutualism in natural ecosystems is a symbiotic organism called a lichen.

Lichen are composed of algae or cyanobacteria and fungi living in mutualism

Lichen are a collection of fungi and algae or cyanobacteria. They are the first colonizers of new ecosystems, such as the bare rock created by lava flows. The fungi provides a sheltered environment for the algae or bacteria, which normally need aquatic conditions to grow.

The algae and cyanobacteria are photosynthetic, meaning they can make their own food from sunlight. The algae or bacteria share this food with the fungi and the fungi protect them. Thus, both organisms benefit.


Sometimes one organism benefits from an interaction, but the other gets nothing. This is called commensalism. This would be like if you gave your notes from class to a friend to study. You get nothing, but your friend benefits by having excellent notes to learn from.

If we leave the classroom and travel into the tropical ocean, we find an example of commensalism in the interaction between sharks and remora.

A remora rides along the belly of a whale shark

Remora are also known as suckerfish. They live in warm tropical seas and live in commensalism with sharks and other large, marine animals. The remora attaches to the shark to catch a ride with its suckers. Usually the shark or other animal doesn't get anything from the remora. But, they aren't hurt by the remora either.


Unfortunately, sometimes one organism gets the short end of the stick. Parasitism is when one organism benefits, but the other is harmed. This would by like your classmate stealing your finished exam and turning it in as their own. Your grade suffers and theirs is benefited.

Most of us are familiar with parasites already. If you've ever gone swimming in a lake or river you might be familiar with a parasite called a leech. Leeches are invertebrate worms that contain suckers in place of a mouth. Their suckers attach to an unsuspecting victim to suck their blood, stealing nutrients. Clearly, blood loss is not optimal for the leech's victim, but the leech benefits by getting food.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account