Download Succession - WordPress.com

Name Teacher
Date
j
Principles of Ecology
Succession—Notes—KEY
(**This note guide does not use Managing Our Natural Resources)
Succession: Changes over time
Succession is the orderly, natural changes and species replacements that take place in the communities of an ecosystem.
* Succession occurs in stages that are somewhat predictable.
* Succession is difficult to observe because it takes decades to centuries to see the community succeed from one to
another.
Two types of succession:
1. Primary succession is the colonization of new land that is exposed by avalanches, volcanoes, or glaciers by
pioneer organisms. (Starts from rocks)
2. Secondary succession is the sequence of community changes that take place after a community is disrupted by
natural disasters or human actions. (Start from soil & left over organisms)
Characteristics of primary succession:
1. The first species to colonize an area in primary succession are pioneer species.
2. The final community in succession that is a stable, mature community that undergoes little or no change in
species is called a climax community.
Characteristics of secondary succession:
1. Secondary succession begins in places that have had communities of organisms exist before. They also begin
with soil instead of rock. This means they take less time to change than primary succession.
2. Secondary succession begins with pioneer species and ends with a climax community just like primary
succession communities.
Comparing and contrasting primary and secondary succession:
1. Similarities: Both are changes that occur to whole ecosystems, both begin with pioneer species, and both end
with similar climax communities for a given area.
2. Differences: Primary begins with rocks and no soil while secondary begins with soil left from a previous
community. Secondary has had living things while primary has not had living things. Primary takes longer than
secondary.
Causes of plant succession:
1. Plants immigrate by means of seed dispersal (spread) and then germinate in new locations.
2. Plants compete with each other for light, water, and nutrients. The best “competitor” wins.
3. Site modification: plants add organic matter to the topsoil which alters the soil. This in turn changes the plants
and animals that live in that site.
4. Stabilization: As plants slowly modify the site, this leads to some stable state. Succession “seeks” stability.
Forces that slow or reverse succession: retrogression
*Retrogression can occur in response to fire, overgrazing, introduced species, drought, and other biotic & abiotic factors.
1
End-point of succession (climax community):
1. The mature community that will result from succession is not always predictable.
2. Events such as drought, fire, or grazing during succession may alter the final stable community.
Ecosystem response to disturbance:
1. Some ecosystems are not easily disturbed—they have high inertia. But once disturbed, restoring the ecosystem
is difficult—low resilience. (i.e., tropical rainforest)
2. Other ecosystems have low inertia and high resilience. (i.e., temperate grasslands)
3. This affects the impact of humans on ecosystems, in other words, how fragile an ecosystem is.
*Summary of ecosystem function: Living systems have 6 major features.
 Interdependences (i.e., food webs)
 Limits (i.e., limiting factors and environmental resistance)
 Diversity
 Unpredictability (i.e., succession)
 Resilience: ability to recover from disturbance
 Adaptability: ability to adapt to disturbance (inertia)
2