1. Chapter 3 COMMUNITIES

2. A. Community All populations of organisms living in a defined area. Habitat - the physical place where an organism lives. What is habitat of a koala? Niche - the resources (biotic & abiotic) an organism uses for survival, growth and reproduction. What is niche of a koala?

3. Life in a Community Various combinations of abiotic and biotic factors interact in different places around the world. The result is that conditions in one part of the world are suitable for supporting certain forms of life, but not others.

4. Limiting factors Factors that affect an organism’s ability to survive in its environment, such as the availability of water and food, predators, and temperature, are called limiting factors. A limiting factor is any biotic or abiotic factor that restricts the existence, numbers, reproduction, or distribution of organisms.

5. Ranges of tolerance The ability of an organism to withstand fluctuations in biotic and abiotic environmental factors is known as tolerance. Limits of Tolerance Organisms absent Organisms infrequent Greatest number of organisms Organisms infrequent Organisms absent Zone of intolerance Zone of Physiological stress Optimum range Lower limitUpper limitRange of tolerance Population Zone of Physiological stress Zone of intolerance

6. Ecological Succession Ecologists refer to the orderly, natural changes and species replacements that take place in the communities of an ecosystem as succession. As succession progresses, new organisms move in. Others may die out or move out. There are two types of succession— primary and secondary.

7. Primary succession Occurs in an area where no community previously existed. Caused by volcanoes, road cuts & glaciers. Takes hundreds of years for a climax community to develop.

8. Primary succession The first species to take hold in an area like this are called pioneer species. An example of pioneer species is a lichen, which is a combination of small organisms.

9. A stable, mature community that undergoes little or no change in species is a climax community. Secondary successionClimax community Primary succession

11. Secondary succession Occurs in an area where a community is disturbed but not decimated (some soil & life remain). Caused by fires, hurricanes & agriculture. Pioneer species are herbs & weeds. Occurs faster than primary succession. Few communities ever reach true climax conditions.

12. Section 3.1 Summary – pages 65-69 Formation of Climax Community