Community Ecology: Definition & Types

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  • 0:02 What Is Community Ecology?
  • 1:15 Predation
  • 2:50 Competition
  • 3:30 Symbiosis
  • 5:02 Lesson Summary
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Lesson Transcript
Instructor: Marta Toran

Marta has taught high school and middle school Science and has a Master's degree in Science Education.

Community ecology looks at the interactions between populations of organisms. Here we explore a polar ecosystem in Greenland to describe what community ecology entails and what it really means to be at the top of the food chain.

What Is Community Ecology?

Nanortalik is the last town in the southern tip of Greenland. It is nestled among glaciers, woodlands and fjords in a strip of land between the Atlantic Ocean and Greenland Sea. The surrounding area is a natural paradise for climbing, kayaking, and watching its undisturbed habitats, or ecological areas that are home to particular types of life. In this case, the Nanortalik is home to beautiful landscapes and many arctic animals like polar bears—which give the town its name, meaning 'place of the polar bears.'

Let's take on the role of community ecologists to better understand life in this polar ecosystem. Community ecologists study how the various species in a community interact with each other. But what is a community?

A community is made up of populations of different species, or animals, plants, fungi, and bacteria, living in the same area. In Nanortalik, the Inuit people share their land with polar bears, whales, seals, marine birds such as puffins, fish, crabs, willow trees, and lichens, among others. Together, these populations form a biological community, interacting and sharing natural resources. But, what are the ways in which these organisms in a biological community interact?


The most obvious form of species interaction is when one species eats another, predation being the technical term for this unfortunate fate. The predator is the organism that does the eating, the prey the one that gets eaten. A simple way to depict who eats what is by drawing a food chain, with the arrows pointing in the direction the food is going, i.e. to the predator. For example, take this food chain found off the shore of Nanortalik. The algae gets eaten by the herring, which in turn gets eaten by the cod, which gets eaten by the seal, which is devoured by the orca.

The organisms at the bottom of food chains (or far left when drawn horizontally), usually plants, are called producers. They produce food by converting carbon in the atmosphere, i.e. through photosynthesis. The herbivores that eat the plants , or the algae in this case, are called primary consumers (like the herring), and the carnivores that eat the primary consumers are secondary consumers (like the cod). Tertiary consumers such as seals eat secondary consumers, and so on. The orca is said to be 'at the top of the food chain' because it has no natural predators. It is considered a quaternary consumer, or top predator.

Food webs, like the one in the picture here, are used to show how the food chains in an ecosystem are interconnected.

For example, from the diagram we can see that the herring mentioned above is also part of other food chains involving the humpback whale or the Greenland shark as secondary consumers.

Another example of a food chain in this ecosystem would be:

algae --> small invertebrates --> sand eels --> Greenland shark --> Orca whale


Another way in which populations within a community interact, without eating each other, is through competition. Two species that share the same diet will compete for their food. From the food web diagram above, we can see that the wolfish, sand eels, cod, and walrus will all be competing for small invertebrates such as crabs, while the krill, herring, and small invertebrates compete for algae.

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