Biology 100/101
Lecture 3: Ecosystems in Time
(Print Version)

Announcements &
Assignments

Lecture Objectives

Community Change

Ecological
Succession

Primary
Succession

Secondary
Succession

Disclimax

Succession
Summary

Lecture Syllabus

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Answers to many of these questions can be found on the Text On-Line Learning Center. Select "Student Edition" from the left hand menu, select the text chapter you want, and finally, select either "Testing Your Knowledge" or "Thinking Scientifically". Links to answers can be found on these pages.

You may also ask questions and see answers to your classmates' questions in Web Crossing in the "Talk to Ross and Ed" discussion.

Ecosystems in Time

The content of today's lecture will help you answer question #2 on this assignment:

Take-home Assignment #1, Ecosystems, Biomes, and Succession Due At Lecture Monday, September 19

Objectives:

After studying this material you should be able to:

1. Describe the effects of disturbance, or lack there of, in (natural and managed) ecosystems and explain its relationship to the process of biological succession.
2. Define the term 'invasive species', give an example of an invasive plant or animal and describe its impact on an ecosystem.
3. Distinguish between the terms "primary succession"and "secondary succession" and describe some examples of each.
4. Distinguish between the terms "soil" and "mineral substrate".
5. Describe how pioneer species in primary and secondary succession change nonliving components of an ecosystem (temperature, light, moisture, humidity, mineral substrate, etc.) during the early stages of succession.
6. give an example of disclimax and explain how some ecosystems are maintained in a state of disclimax by natural means or by the intervention of people.

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Key Terms:

Community Change

Community change is initiated by disturbances of all scales:

• fires
• fires and logging
• wind
• floods
• tornadoes
• landslides or avalanches
• volcanoes
• individual tree falls
• agriculture
• land development
• invasion of species from other areas (exotics)
• Invasive Species
• Zebra mussels and their spread: dynamic map,
• Asian Long-horned beetle
• Japanese beetle
• Purple loosestrife
• Kudzu, the vine that ate the South

• climate change
• Climate change predictions for the Midwest
• Climate change, drought and world poverty

• Amazon rainforest picture

Ecological Succession - Overview

From the Latin, succedere, to follow after

"Change in the species composition of a community over time." (Lewis, Life glossary)

• Primary Succession follows the formation of new land surfaces consisting of rock, lava, volcanic ash, sand, clay, or some other exclusively mineral substrate.
• This means that there is NO SOIL present.
• Soil is a mixture of mineral material, decaying organic material, and living organisms.

• Secondary Succession follows the destruction or partial destruction of the vegetation area by some sort of disturbance, like a fire, windstorm, or flood that leaves the soil intact.
• Pioneer species initiate recovery following disturbance in both primary AND secondary successions

Pioneers "pave the way" for later colonists by altering the biotic and abiotic environment:

• soil stabilization
• soil nutrient enrichment (organic matter and biological nitrogen fixation)
• increased moisture holding capacity
• light availability
• temperature
• exposure to wind

Species composition tends towards a Climax Community through succession.

The climax community describes an end product of succession that persists until disturbed by environmental change.

Succession occurs at large scales involving higher plants and animals, but may involve microbial communities on a smaller scale.

Primary Succession

• Illustration of Primary Succession from Department of Geosciences, University of Arizona
• The processes involved in changing an area from one lacking any community (no plants, no animals, no insects, no seeds, AND NO SOIL) to one consisting of individuals, populations, communities, and ecosystems. CAUTION!! The text definition of primary succession is misleading.
• Starts WITHOUT SOIL.

This is the confusing part - there may have been a previous community, but if a disturbance removes or in some way covers the soil so only mineral substrate is left to support pioneer plants we would classify it as Primary succession.

• No organic matter, only mineral material (e.g. sand, bare rock, gravel from glacial outwash, volcanic ash and lava.
• PIONEER PLANTS of primary succession (e.g. lichens and mosses).
• Examples:
• Bare rock
• Succession following volcanic eruption and pioneer species
• Glacier and Glacial retreat
• Man-made structures

Secondary succession

• Illustration of Secondary Succession from Department of Geosciences, University of Arizona
• Follows disturbance of an existing community that removes or damages the vegetation, but does not remove, destroy, or cover the soil.
• Starts WITH SOIL.
• PIONEER PLANTS of secondary succession (the first plants to become established after the disturbance) start from roots or seeds remaining in the soil or from seeds carried in by wind or animals from surrounding communities.
• Faster than primary succession.
• Examples:
• Fires

  • Ponderosa Pine Succession from Arizona State University
  • Fire scar histories
  • Fire and Vegetation Change in Northern New Mexico from Northern Arizona University.
  • Prescribed burning to maintain prairies in a state of disclimax.

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Disclimax

• Disclimax or "disturbance climax" describes a community that is held at an earlier successional stage by repeated but unpredictable disturbances that prevent succession from reaching the climax community that might be expected for the climate of the area.
• The original prairies of Illinois are examples of disclimax communities. The early successional grass and perennial plants are fire tolerant because of their underground roots and stems. Repeated fires destroy shrubs, young trees, and other plants that would change the environment and result in further successional changes that would eventually result in the establishment of a deciduous forest.
• Agricultural practices are essentially an artificial form of maintaining disclimax. Crops like corn and soybeans as well as the common weeds found in agricultural fields have the characteristics of pioneer species and require repeated soil disturbance.
• John Deere and his self-scouring plow
• US Commemorative Postcard
• Secondary succession in abandoned agricultural fields (Buell-Small Succession Study - New Jersey)

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A summary of changes that occur during succession:

• Pioneer species colonize first.
• Pioneer species alter the environmental conditions remaining after the disturbance.
• Eventually new species of plants become established in the conditions altered by the pioneer species and displace the pioneer plants.
• Animals come in with or after the plants they need to survive.
• Further environmental change by the new plants and animals result in the establishment of different species.
• With infrequent disturbance, a stable climax community consisting of plants and animals that can reproduce themselves in the existing conditions will become established.
• Disturbance of the ecosystem will start the process of succession anew.
• In a given area there are usually small patches of land in different stages of succession, depending on the time and severity of the last disturbance. This adds diversity in the types of vegetation and animals living in the greater region.
• Various stages of succession in one area