Types of Species Interactions - Symbiotic Relationships

A Biology post about the types of Species Interactions and the symbiotic relationships we find in ecosystems.

Old Man's Beard - Symbiosis of a Fungus & AlgaOld Man's Beard - Symbiosis of a Fungus & Alga

An ecological community is made up of interacting populations.

Symbiosis is the term used to describe the direct or close relationship between individuals of different species that live together.

There are a few types of species interaction by symbiosis and today we will be taking a look at each of them.

They are:

  • Mutualism
  • Commensalism
  • and Parasitism

As we look at these 3 forms of species interaction, you may be able to recall examples from your own knowledge.

Types of Species Interaction and Symbiosis

Keep in mind that symbiotic relationships usually involve an organism that lives or feeds in or on another organism, sometimes called the host.


As the name suggests, this symbiotic relationship is when both partners, benefit from the relationship.

Partners in this symbiotic relationship may even depend on the relationship to survive.

For example Lichen is a combination of an alga and a fungus.

  • In some cases, their mutualistic relationship allows them to grow on exposed, bare rock - where neither one would survive on its own.

Both the Alga and Fungus play their own part in this symbiotic relationships.

  • The Alga provides food for both organisms through photosynthesis and the fungal partner protects the alga from drying out or blowing away.
  • The fungal also produces an acid that dissolves rock, releasing minerals that are needed by the alga.


Commensalism is another symbiotic relationship - where one partner benefits but the other partner is neither harmed, nor benefited.

Think of the relationship between suckerfish and sharks. The fish holds onto the shark's body and it receives protection and bits of food from the shark.

Yet the shark itself doesn't appear to benefit or suffer from it's relationship with suckerfish.

* Note that scientists believe that this form of symbiosis is probably rare due to the fact that there might actually be a mutualistic relationship between the organisms.


  • The relationship between certain birds and cattle appears to be an example of commensalism.
  • However these birds sometimes pick flies and other insects from the cattle's skin, so is this an example of mutualism?

With instances like that, it may be hard to determine whether both partners benefit from a symbiotic relationship.


A slightly gruesome type of species interaction.

  • Parasitism is a form of symbiosis where one partner, benefits at the expense of it's host.

This makes parasites among the most 'successful' species in the world, they thrive in most parts of the biosphere.

Examples of parasites:

  • Viruses

Various Types of

  • { Worms
  • Unicellular organisms
  • Insects }

I won't insert a picture, but if you dare - google it yourself.

  • Some internal parasites, such as the parasite which causes malaria, interact with their host in a unique survival strategy.

This particular parasite wraps itself in its host's liver cell membranes - to escape detection by the host's immune system.

Parasites have a huge impact on global economy and quality of life, & you can see this with diseases such as malaria, which results in 2-3 million deaths annually.

Other Types of Species Interaction

The 3 types of species interactions covered above are the main types you may come across, and they are examples of symbiosis.

But let's look at a couple more types of species interaction, which you may likely already be familiar with!

Predator / Prey

A predator is a consumer that kills and consumes other organisms, known as prey.


Intraspecific competition is the competition for limited resources among members of the same species.

Interspecific competition is competition between two or more populations for limited resources such as nutrients, light or living space.

Thanks for reading this page on species interactions. I hope it helped to boost your understanding of how species can interact, especially in symbiotic relationships.

What type of species interaction did you find most fascinating? Please comment below!

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