Module 8
1. Module 8
1.30. Page 4
Module 8—Populations, Individuals, and Gene Pools
Lesson Summary
In this lesson the following focusing question was examined:
- How do communities and their populations change or remain stable over time?
Communities change over time in the process of succession. Ecological disturbances (both those caused by humans and natural) can destroy communities and return them to rock or to soil. Primary succession begins from bare rock and may be the result of avalanche, rockslide, or glacial melting. Primary successions take a very long time because of the time needed for building soil. The pioneer species of lichens help in this process.
Secondary succession begins from soil, where life still exists as roots, seeds, and other organisms. It occurs after fire has destroyed a community or when human settlements or agricultural fields are abandoned. In either case, a predictable pattern of invasion and replacement of species will occur, ending in a stable climax community.
The species that make up a particular succession are specific to that climate and geography. The first species to invade is the pioneer species, and the last species is the climax species, which the community is named after. Animal species present change in succession as well; as producer species change, so does the presence of animal species that depend on them.
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
climax species: the last species of plant in the succession; is used to name the succession
pioneer species: the first species of plant to invade a cleared site in a succession
primary succession: a succession that begins with bare rock; soil-building organisms (e.g., lichen) are pioneers
secondary succession: a succession that begins with soil
succession: the orderly replacement of one species with another over time; occurs after a disruption, such as fire