What are Ecosystems?

Science, Grade 3


Table Of Contents: What are Ecosystems?

1. Environment
How is the place where a fish lives different from a place where a bird lives? Each kind of living organism needs a certain environment to survive. An organism's environment is everything around it. It is made up of all living and nonliving things in an area.
2. Living and Nonliving Things
The living things in an environment include plants, animals and microorganisms. Nonliving things include air, water, nutrients, soil and climate.
3. What is an Ecosystem?
Everything in nature is connected. An ecosystem is made of all living and nonliving things in an environment that interact with each other. An ecosystem may be as large as a pond or as small as the area under a log in the forest.
4. An Organism's Habitat and Niche
Every organism in an ecosystem has a niche and a habitat. A habitat is the place where an organism lives. It provides food, water and shelter for the organism to survive. A niche is the role that an organism has in an ecosystem.
5. Population and Community
Ecosystems contain populations and communities. A group of living organisms of the same kind living in the same place makes up a population. An ecosystem may include many different populations. All of the populations work together and form a community. The community of living things interacts with the non-living world around it to form an ecosystem.
6. Parts of an Ecosystem
An ecosystem includes soil, atmosphere, heat and light from the Sun, water and living organisms. Soil provides nutrients for the plants. The atmosphere provides oxygen and carbon dioxide for both plants and animals. The Sun provides heat for plants and animals, and light for plants to make food. Water is part of all living organisms; without water there would be no life.
7. How does an Ecosystem Work?
The living organisms in an ecosystem depend on other living organisms but also on nonliving things for survival. For example, in a pond ecosystem, the Sun light helps algae grow. Algae make oxygen for the fish and also provide food for tiny pond organisms. The fish eat the tiny pond organisms, use the oxygen, and give out carbon dioxide which plants need to grow.
8. Kinds of Ecosystems
There are many kinds of ecosystems. Each ecosystem has its own unique group of living and nonliving things. Examples of different kinds of ecosystems include wetlands, coral reefs, prairies, and deserts. Many factors, such as climate, soil and type of water, determine the kinds of plants and animals that can live there.
9. Energy in an Ecosystem
The energy cycle within an ecosystem determines which populations survive and which die. All living things need energy. Ultimately, the Sun is the source of all energy in an ecosystem. Energy flows from the Sun, to producers, then to consumers and finally to decomposers.
10. Producers, Consumers & Decomposers
The living organisms in an ecosystem can be divided into three groups: producer, consumers and decomposers. Producers are living things that make their own food using light energy from the Sun. Consumers are animals that get their energy by eating other organisms. Decomposers are organisms that get their energy by breaking down dead plant and animal matter. Examples of decomposers include mushrooms, bacteria and earthworms.
11. How Do Ecosystems Change?
Ecosystems are always changing. Some changes are so big that an ecosystem can die or change into another kind of ecosystem. For example, if a fire burns most of a forest, its plant life will have to start over again. New growth will start with grass, wildflowers and small shrubs. Soon young trees, or saplings, will sprout, but it will be many years before there will be tall, strong trees standing in that place again.
12. An Ecosystem After a Fire
Another change that may happen because of a forest fire is that certain populations of animals will leave the area to find food and shelter elsewhere. Other populations that depend on those animals for food will also leave or die out. For example, when trees burn, squirrels and birds leave, and foxes and coyotes follow. When the plants start growing back, animals that eat them will start to return to the forest. Over time, if left alone, the forest ecosystem will come back. Life goes on, only now it's in a new kind of environment!