An ecosystem (EK-oh-sis-tuhm) is made up of groups of living things, and the environment in which they live.  In an ecosystem, the living things are able to get the things that they need in order to survive.  Healthy ecosystems are in balance.  In other words, there is enough food, water, and shelter for all of the species that live within the ecosystem.
    Ecosystems are made up of several different populations.  A population is a group of the same species of plant or animal living together in the same place and time.  Populations live in environments that meet their specific needs.  For example, there are many species of tropical plants and animals that thrive in rain forest ecosystems, but would not be able to survive in other places.
    Plant and animal populations interact with each other in many different ways.  Animals tend to use plants for food and shelter.  Animals carry seeds from place to place, and help to fertilize the soil.  Insects find their food while hiding in or around plants.  Insects also help pollinate plants so that they can grow and produce fruit.  When plant and animal populations work together, they function as communities.  A community is made up of all the the populations found in a specific area.
    Food webs and food chains can be used to illustrate the ways that plants and animals interact within ecosystems.  Each food chain is comprised or made up of three basic parts.  Food chains always begin with a green plant.  These plants are known as producers because they use photosynthesis to make their own food.  The next level is made up of consumers, or animals that eat other plants or animals in order to obtain energy.  The last level of a food chain is made up of decomposers which consume non living things, and help to break down organic material into nutrients for the soil.
    There are many different types of ecosystems.  Ecosystems can be found in tropical rain forests, saltwater marshes, coral reefs, kelp forests, and deep in the ocean.  Each ecosystem is unique, but each also requires a delicate balance between the plant and animal species in order for the ecosystem to remain healthy.  Pollution, rapid deforestation, natural disasters, and slow environmental changes over time can all threaten the health of our earth's ecosystems.  We should do everything we can to preserve nature's delicate balance so that its wonders can be enjoyed by generations to come.
 
 

Teacher Links: http://www.nps.gov/ever/ed/eenone.html
                          http://www.fi.edu/tfi/units/life/habitat/habitat.html