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Learning About Ecosystems

Bob Bahlmann is the executive director of the education nonprofit Explore the Outdoors and has written a series on wilderness survival.

An ecosystem can be as large as the entire earth or as small as a puddle of water.

An ecosystem can be as large as the entire earth or as small as a puddle of water.

Living (Biotic) or Non-Living (Abiotic) Factors












What Is an Ecosystem?

The word “ecosystem” is short for ecological system. An ecosystem is all the living organisms in an area and how they relate to each other and to non-living things. Most ecosystems need energy from outside the system. For example, our world depends on energy coming into it from the sun.

Natural ecosystems are made up of abiotic (non-living) and biotic (living) factors.

An ecosystem can be as small as a puddle or as large as the entire earth.

An example of an ecosystem could be all the critters living under a big rock or a rotting log. An example of a man-made ecosystem is an aquarium with tropical fish.

Ecosystems feature a dynamic (changing) interaction between plants, animals and microorganisms and their environment. An ecosystem will fail if the organisms do not remain in balance.

No ecosystem can carry more organisms than their food, water, and shelter can accommodate. Food and shelter are often balanced by natural phenomena such as fire, disease, starvation, and predators. Each organism has its own niche or role to play in the ecosystem.


Carrying Capacity Activity

Liebig’s Law of the Minimum

Liebig’s law states that growth is not controlled by the total of the resources available, but by the scarcest resource or “limiting factor.” This limiting factor determines the carrying capacity of an ecosystem.

For example, an animal needs food, water, and shelter to survive. If an ecosystem has enough food for 20 animals, enough water for 35, and enough shelter for 15, that ecosystem will only support 15 animals.

A good way to demonstrate this law is by using an empty cardboard drink carton. Fill the carton with water. The water represents the number of organisms that the carton “ecosystem” can support. Now limit the resources by poking holes in the carton.

Your first hole can be anywhere on the carton and will represent the amount of food available. The second hole represents the amount of water in the ecosystem and the third hole is for the shelter.

Watch the water leak out through the holes and you will see that the level inside the carton will reach the level of the lowest hole. This hole represents the scarcest limiting factor and the water level represents the carton’s carrying capacity.

A Simple Food Web



Biodiversity is the variety of all the living organisms in an ecosystem. A healthy ecosystem will have a wide variety of critters. Within each ecosystem is a web of connections between the organisms and their environment. When an ecosystem is healthy there is a balance between the inhabitants and the resources they need. When something disturbs or removes a part of that balanced ecosystem it effects the balance and can disrupt the ecosystem.

Activity: Study an Ecosystem

Find an ecosystem in your back yard or a nearby park or make a trip to the nearest forest. Select a small area and make a list of all the biotic (living) and abiotic (non-living) factors you see.

Spend half an hour watching the area to see what makes up the ecosystem. Observe how things interact with each other and what types of energy enter the area from outside the boundary.

Even though your ecosystem might be in the middle of a city, you will probably see critters and plants that are similar to the ones you might see in the mountains or desert. Some might be completely different, but some might be exactly the same.


After watching for half an hour you probably think you’ve seen all the organisms in your ecosystem, but there’s still a lot you haven’t seen.

Now it’s time to build a simple scientific tool to see what you might have missed.

Making a Berlese Funnel

The Berlese (pronounced burr-lay-see) funnel trap is named after an Italian entomologist (a scientist who studies insects) who invented the trap more than 100 years ago. Scientists have modified the trap a little but still use it to study very small organisms that live in soil or leaf litter.

Here’s what you will need to build your own Berlese funnel:

One 2 liter plastic soda bottle, a knife or scissors for cutting the bottle, a white paper towel, several paper clips or clothes pins, plastic canvas (available in the craft area of most department stores), a clip-on or gooseneck lamp.

Building your Berlese trap

NOTE: You might want to do this outside on your porch to keep the critters from escaping into your house or classroom.


  1. Cut the top 1/3 off the soda bottle. Save the top.
  2. Moisten the paper towel and place it in the bottom of the bottle. The moisture will attract the critters and the white paper towel will make it easier to see them.
  3. Turn the cut off top of the bottle upside down to make a funnel. Put the funnel into the bottom of the soda bottle. Secure the funnel with paper clips or clothes pins.
  4. Cut the plastic canvas in a circle so it fits into the bottom of the funnel an inch or so above the narrowest part. Use a paper punch or scissors to cut out several of the connecting pieces to make the holes bigger, as shown on the right. this will allow larger critters to move down into the bottle. Put this screen in the bottom of the funnel.
  5. Put a small handful of leaf litter or good garden soil into the top of the funnel. Potting soil that you buy in bags won’t work because it has been sterilized to kill any bugs.
  6. Put your funnel under the light bulb and allow it to warm and dry the leaves or soil.
  7. To observe your live animals more closely, remove the top of the funnel and leaf litter carefully. Quickly cover the bottle with a plastic bag and turn the bottle over. Gently shake the contents into the bag. Close off the bag opening and check out your critters! A magnifying glass will make it easier to see the smaller ones.
  8. When you’re done looking at the members of the ecosystem, take them back outside where you got the leaf litter or soil and turn them loose.

How to Make a Berlese Funnel

Activity: Visit a Man Made Ecosystem

Aquariums are one of the most popular man made ecosystems. Visit a local public aquarium if there is one in your area. If not, see if you can find someone who has one in their home or visit a pet store that sells tropical fish.

Look at the aquarium and determine which are the biotic and abiotic parts of the ecosystem. What external factors (things that come from outside the aquarium) are needed for the ecosystem to survive? What internal factors (things that are produced inside the ecosystem) help the aquarium stay healthy?

Most people really enjoy aquariums and many think they would like to have one of their own. Talk to the owner of the one you visit and ask them about what they need to do to properly care for their aquarium.

Man Made Ecosystems

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.