Ecological succession is the process by which the composition or structure of a biological community evolves over time. It is triggered by a disturbance which kills or displaces existing community members. Pioneer species are the first to colonize the disturbed area, improving conditions for subsequent species and facilitating further ecological succession. Over time, the community may progress to a relatively stable climax ecosystem, though disturbances ensure nature remains dynamic. Succession can occur through primary colonization of new areas or secondary regrowth after minor disturbances in previously inhabited areas. Aquatic succession involves sediment filling in bodies of water over time. Fire is a common disturbance supporting fire climax ecosystems through periodic resetting.

1. Ecosystem Response to
Disturbance

2. Themes
II.The Living World
D. Natural Ecosystem Change (ecological succession)

3. Disturbance
• disturbance: a significant change that kills or displaces many
community members

4. Ecological Succession
• ecological succession:
transition from one biotic
community to another
• pioneer species: first to
colonize a newly opened area
• pave the way for other species
by improving conditions for
subsequent species - known as
facilitation

5. Ecological Succession
• climax ecosystem: when
there appears to be a dynamic
balance between all of the
species and the physical environment
• implies more stability than actually
occurs in nature

6. Succession
• succession - existing species taking advantage of available
niches
• disturbance constantly creates gaps or patches in the landscape
• enhances biodiversity

7. Primary Succession
• primary succession:
process of initial invasion
and progression from one
biotic community to the
next

8. Secondary Succession
• secondary succession:
when an area has been
cleared by fire, humans, or
floods and then left alone,
plants and animals from the
surrounding ecosystem may
gradually invade the area
• starts with pre-existing soil

9. Aquatic Succession
• aquatic succession:
when soil particles erode
from the land and settle out
in ponds or lakes, gradually
filling them in
• climax ecosystem may be a
bog or forest

10. Resilience
• resilience: ability of an ecosystem to return to normal after a
disturbance
• resilience mechanisms:
process of
replenishment of
nutrients, dispersion
of plants/animals,
rapid regrowth of
plant cover

11. Fire
• fire climax ecosystems:
ecosystems that depend on fires to
“reset” the ecological
“clock”
• major form of disturbance common
to terrestrial ecosystems
• create a patchwork of meadows and
forests at different stages that lead to
a more diverse environment