There are many different organisms and many different habitats in which organisms live. Most of these ecosystems have taken hundreds or thousands of years to develop. The fact that there are so many varieties of life and ecosystems means there is biodiversity on the earth (bio means "life" and diversity means "differences").
Out of all the species of life that have lived on the earth, scientists believe that most have become extinct. It is also believed that much of this extinction occurred during five periods in the earth's history. While no one knows exactly what happened during these periods to cause these mass extinctions, it was likely a combination of environmental factors.
Today, as humans alter ecosystems, scientists are looking into the effects of habitat changes on biodiversity. Changes range from loss of forest cover, to over harvesting of certain species, to accidental (or intentional) introduction of non-native organisms. In some cases, as ecosystems change and certain species are lost through extinction, it may begin a chain of events that leads to extinction of several other organisms. Extinctions lead to a loss of biodiversity, something that cannot be recovered in thousands of years.
As the human population grows, it is necessary for people to be aware of the need for biodiversity, and to include this idea in planning for the future. While we know that extinction is a natural occurrence, we must think about how our actions will affect this process.
Assign students to groups of two. Provide each group with a piece of string and a data collection sheet. Make sure all strings are the same length. Have each group of students proceed to a different area of the school yard. Have the students lie the string on the ground in a straight line. Record all living organisms that can be found under the line. This will include ants, worms, grass, and weeds. Remind the students about the things they cannot see, such as bacteria, fungi, and other microscopic plants and animals. Record the total number of species found at each location. Encourage students to discuss what differences were found and possible explanations for the differences.
Discuss these additional questions: