Nov.5 , 2013
- When glaciers receded they left large chunks of ice in the ground which melted and
created kettle lakes
- These lakes fill in, the plants around the edge of the lake begin to build over the
water and enclose the lake
Why do communities change?
Why do some stay the same?
What aspects of communities change?
Perturbations happen all the time. We call them disturbances and they happen all the time.
- Dune blowout (all vegetation will be blown out, sand will replace it)
- Ice scour
Response to disturbance is succession
- A regular sequence of changes in the species composition of a community in a newly
formed or disturbed habitat that progresses to a stable state
- Progresses to a state of no change, will remain in balance for a long time
- A series of stages of community change leading toward a stable state
o Different seres can lead to same endpoint
- There can be other patterns that lead us to stability
- Understand that we can start with an aquatic system, dune grasses or aster-
o There are different ways to get to the same final point Climax community:
- The endpoint of a successional sequence, or sere; a community that has reached a
steady state under a particular set of environmental condition
- Succession in a newly formed or exposed habitat devoid of life
- Ex: Krakatau 1883, huge volcanic eruption, everything covered in ash
- Succession in a habitat that has been disturbed, but in which some aspects of the
- If we can recognize the operation we can understand the changes
- A species increases the probability that….
- Ex: Alder- N-fixing symbiotic bacteria
o Alder makes the soil much richer
o Can end up with a much more complex soil which eventually spruce trees
can survive and germinate and grow
o Presence of one species allows another species to invade
- Ex: Surfgrass
o Green plant that looks like grass
o Can’t invade fresh rocky surfaces, it requires algae first
o When algae is undisturbed there are more seeds
o Algae facilitates the later growth of surfgrass
- Species prevent