Download Ecology Lesson #6: Succession: The Process of Change

Succession: The Process of Change (See slide show on my website that goes along with these notes)
Also see pages 408-410 in your text.
• succession comes from the Latin, succedere, meaning to follow after
• DEFINITION: the gradual and directional process of species change in a community. Succession
can be thought of as the evolution of a given landscape and the biotic / abiotic factors within that
area
• communities change through time in response to many influences:
ABIOTIC FACTORS
Climatic Events: ice ages, droughts, floods, el nino, global warming
Natural Disasters: fires, tornadoes, hurricanes, earthquakes, floods
Human Activities: urban sprawl, pollution, deforestation, mining
BIOTIC FACTORS: disease, competition, immigration /emigration/ extinction
The rest of the presentation differentiates between primary succession, secondary succession and climax
community.
What is primary succession?
Primary succession – the establishment of living things in an area that was previously lifeless. Pioneer
species, the first species to colonize an area (usually lichens and mosses but sometimes higher plants),
begin the process of soil formation. Pioneer species establish biogeochemical cycles that pave the way for
larger plant species .
*Volcanic eruptions are good examples involving 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. Example: Hawaiian Islands
What is secondary succession, and how does it differ from primary succession?
Secondary succession – the changes and / or replacement of plant and animal species in an area where
food webs and biogeochemical cycles are already well established. Example:CA. Mt.St.Helens eruption in
1980. (State of Washington, USA)
* Secondary succession results in the transition of a community from pioneer species to climax species
(species that define an area)
*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, some prairie plants NEED fire before they can germinate.
*Climax community - a “stage” of succession in which changes are usually slow and subtle but at times
can be extreme. Climax communities are characterized by several dominant species of plant and animal.
Example: the major biomes of the world
TURN OVER
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 sustain itself.
• Disturbances can affect the process of succession at various stages
(primary, secondary or the climax state).