Biology 100/101
Lecture 5: Ecosystems in Time (Succession)
Text readings in Life by Ricki Lewis:
Chapter 42 (Communities and Ecosystems)
Review questions:
Questions 2 and 3, page 870
"To think about":
Question 5, page 870
Web Resources:
Chapter 42 Web Links
Objectives:
After studying this material you should be able to:
- Define the term succession and explain its importance to communities and ecosystems.
- Explain primary succession and give some real world examples.
- Explain secondary succession and distinguish it from primary succession.
- Explain the role of disturbance in natural and managed ecosystems and its relationship to secondary succession.
- Describe the general types of environmental change that occur during succession.
- Explain the role of ecosystem disturbances such as fire as natural and necessary environmental factors in the maintenance of an ecosystem.
- Understand the concept of "global climate change" and that it will lead to successional changes in communities, ecosystems and biomes.
Key Terms:
| succession |
| climax community |
| pioneer species |
| primary succession |
| secondary succession |
| lichen |
Ecological Succession: Some Definitions
- comes from the Latin, succedere, to follow after
- the gradual and directional process of species change in a community
- biotic communities change through time in response to many influences:
- climatic change
- disturbances
- invasion of species from other areas
- Eventually, succession leads to a climax community
Climax community: A community that remains fairly constant in species composition if the land and climate are undisturbed. These are the communities that characterize the various biomes.
Pioneer species: The first species to colonize an area (usually lichens and mosses but sometimes higher plants), beginning the process of soil formation.
What is primary succession?
- the processes and progress involved in changing an area from one lacking any community (no plants, no animals, no insects, no seeds, etc.) to one consisting of individuals, populations, communities, and ecosystems.
- the arrival of life in an area where no community previously existed.
- see page 856, text
-
Primary succession on bare rock. Rocks erode, sand accumulates, decomposition adds organic matter, and voila! soil. As soil continues to form, larger (and woody) plants appear.
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Volcanic eruption is primary succession. Following the eruption, there is no life in the blast zone. Eventually, however,
pioneer species of plants do establish themselves, beginning the course of succession.
-
Primary succession can also occur from man-made structures.
What is secondary succession, and how does it differ from primary?
Secondary succession is the arrival of new species in an area that already has life, such as seen here.
Secondary succession results in the transition of a community from pioneer species to climax species.
Because soil may already be present, the rate of secondary succession is faster than primary succession.
Secondary succession also indicates changes in community composition following disturbances.
-
Floods,
hurricanes, and
fires
are all examples of naturally occurring disturbances. Notice, however, that none of these completely wipes out the life that was in the area.
- Not only do plants and animals survive these disturbances, but some need them to be able to continue to live there. For example, the
red cockaded woodpecker is an endangered species from the Southeastern US that lives only in longleaf pine forests that burn every 2 or 3 years.
Traditional farming involves creating disturbance and then fighting secondary succession.
Plowing is a prime example of disturbance, but it can't eliminate
- underground plant parts
- seeds left in the soil from previous years (even 100 years or more)
- seeds of nearby plants
- seeds blown in from far away
A link to John Deere and his plow
"Weeds" are pioneer species; if farming is discontinued, these colonizing plants will reclaim a field.
A summary of changes that occur during succession:
- Pioneer species colonize a bare or disturbed site. Soil building.
- Changes in the physical environment occur (e.g., light, moisture).
- New species of plants displace existing plants because their seedlings are better able to become established in the changed environment.
- Newly arriving species alter the physical conditions, often in ways that enable other species to become established.
- Animals come in with or after the plants they need to survive.
- Eventually a climax community that is more or less stable will become established and have the ability to reproduce itself.
- Disturbances will start the process of succession again.
What is disturbance? Can it, and should it, be kept out of an ecosystem?
Question: Should fires be intentionally set in (and out of) the national forests?
Web resources:
The global climate is changing. Along with it, expect changes in the natural world.
- The long term trend is one of a slowly increasing mean earth temperature associated with a rapidly increasing level of atmospheric carbon dioxide.
- What effects will global warming have on biome distribution and the plants and animals existing within?
- Satellite images are used to see what changes have occurred. Here's an example showing the deterioration of an arctic ecosystem due to air pollution.
Take me home.
