1. Ecological Disturbances and Succession
SC.912.L.17.4 Describe changes in ecosystems resulting from seasonal variations, climate change and succession.
By Dr. Suris Soto

2. What Is Disturbance? A disturbance
Is an event that changes a community
Removes organisms from a community
Alters resource availability

3. Natural Human-Caused Disturbances They are common in ecosystems
Fire
Hurricanes
Floods
Volcanic Eruptions
Are the most widespread agents of disturbance
Usually reduces species diversity
Humans also prevent some naturally occurring disturbances
Deforestation and land cleared
Farming
Urbanization (Developments)

4. Ecological Succession
Is the gradual sequence of community and ecosystem changes after a disturbance
One community of organisms replaces another

5. Types of Ecological Succession:
Primary succession
Occurs where no soil, (barren terrain) exists when succession begins
No pre-existing plant or animal life
Examples: After volcanic eruption, retreating glacier (natural), abandon parking lot (human-caused)
Secondary succession
Begins in an area where soil remains after a disturbance
Some organisms may still be there
Examples: After a flood, hurricane, tornado (natural) or after
land cleared for farming, deforestation (human-caused)

6. Primary Succession ---- No Soil, barren rock
Glacier Retreating
Volcanic Eruption
Abandon parking lot

7. Secondary Succession after a fire
Is a significant disturbance in most terrestrial ecosystems
Is often a necessity in some communities
(a) Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass).
(b) During the burn. The detritus serves as fuel for fires.
(c) After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.
Figure a–c

8. The large-scale fire in Yellowstone National Park in 1988
Demonstrated that communities can often respond very rapidly to a massive disturbance
(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.
(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.
Figure 53.22a, b

9. Secondary Succession

10. Pioneer species
Always the first species to move into a devastated area
Must be able to live on limited resources
Must be able to live in barren rock
They include
Bacteria
Lichens
Lichens are a symbiosis (close relationship) of a fungus and a green algae
Each organisms depends on each other for survival (mutualism)
Fungus anchors lichen to a surface, absorbs water and nutrients, and protects the algae from direct sunlight.
The algae performs photosynthesis to make its own food and also feed the fungus
As lichens grow, they make break down rock , help form soil. When it dies it decomposes enriching the soil.

11. Pioneer species
Mosses
Lichens
Bacteria

12. Primary Succession

13. Climax community Fairly stable community
Marks the end of succession in an area
Organisms present depend on the climate and physical features of the area
Ex. In areas with little rain the climax is a grassland
Nothing lasts forever: A new disturbance can happen at any time
Disturbances in climax communities can lead to secondary succession or primary in the event of volcanic eruption covering the soil with lava, hardened to rock

14. Draw it yourself:

15. Fire Flood Earthquake Change of seasons
Which of the following is not a possible cause of secondary succession?
Fire
Flood
Earthquake
Change of seasons

16. Which of the following is an example of primary succession?
Lichens growing on rocks after a volcanic eruption
Grasses growing after a forest fire
Oak trees replacing pine trees in a forest
Nonnative species introduced into a climax community

17. Which term refers to final forest’s development?
Pioneer forest
Secondary forest
Climax forest
Conifer forest