We used images of an ecosystem to introduce the definition. These smallest units of the biosphere contain both biotic and abiotic factors. List the abiotic factors and indicate the importance that each one plays in the development of the ecosystem. Stress how every organism in the ecosystem depends on every other organism and on the abiotic factors. Harm one organism and you harm them all. Discuss ecological succession, and show the succession of a pond ecosystem into a forest ecosystem over thousands of years. Introduce climax community and how and why climax communities can change.