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Interactions within Ecosystems

© Angela Plumb

An ECOSYSTEM consists of the non-living (or abiotic) environment (rocks, soil, water, climate) and the populations of living organisms that reside in that environment. Let us look at how we organize the interactions between living organisms in an ecosystem.

First of all, consider what living organisms need in order to live.

Some of the things they need are food, water, oxygen and a method to remove waste products. Water and oxygen can be obtained from the abiotic environment and waste products can be expelled into the environment. An organism needs to obtain food to convert into energy, and the energy is used in life processes, such as breathing, moving, maintaining organs and reproducing.
So an organism needs to eat food; that same organism could be eaten by another bigger organism. This "who eats whom" can be organized into what is called a FOOD CHAIN.

Here is an example of a FOOD CHAIN:

algae --> krill --> codfish --> leopard seal --> killer whale

Notice that the arrow points from the organism that is being EATEN to the one doing the EATING. These can also be drawn vertically, with algae at the bottom and killer whale at the top.

Now you may wonder, what does algae eat? Or, what eats a killer whale? There are some terms that will help explain our food chain.

A PRODUCER or AUTOTROPH is an organism that produces its own energy using sunlight in a process called photosynthesis. These organisms don't need to eat any other ones. The most common autotrophs are all the plants you see around you. Algae is an autotroph.

A CONSUMER or HETEROTROPH is an organism that needs to eat other organisms in order to obtain energy. They can be classified into three groups: HERBIVORES - only eat plants CARNIVORES - only eat meats OMNIVORES - eat plants and meats What are human beings? Are we herbivores, carnivores or omnivores?

There are some other organisms that are not present in our food chain, but are very important to ecosystems.

A DECOMPOSER is an organism that causes decay by consuming waste and dead bodies. For example, bacteria, fungi and some insects are decomposers. If we didn't have decomposers, every time an animal died, its body would stay around for a long, long time. We wouldn't want to be walking in a forest covered with dead animals, would we?

A SCAVENGER is a carnivore that consumes dead animal flesh, such as a vulture. A scavenger doesn't break down the bones or fur like a decomposer would.

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