Download Ecology Lesson #5: Succession: The Process of Change

Ecology Lesson #5: Succession: The Process of Change
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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
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
Primary succession might follow a volcanic eruption
A variety of lichens pictured here grow on bare rock. The
lichens break the rock down to form a soil substrate from
which plants can grow
Primary succession can also occur on man made structures:
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: Mt. St.Helens eruption 1980.
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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.
Flooding along the Mississippi river
Hurricane damage along the Florida Coast
As seen here, controlled fires can be a necessary
measure that directs succession
*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
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
“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 sustain itself.
•Disturbances can affect the process of succession at various
stages (primary, secondary or the climax state).