1. Ecological Succession
In this presentation you will:
explore how ecological succession can affect species diversity
explore how ecological succession can affect populations
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2. Introduction
Ecological succession is the term given to the progressive, predictable, and long-term changes in the composition of a biological community.
In this presentation you will look at how succession changes the species that inhabit an ecosystem and affect the populations within it.
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3. Ecological Succession
Succession occurs, for example, when areas of bare rock, sand dunes, or open water become oak woodland.
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4. Ecological Succession
Bare rock is first colonized by a pioneer species. Over time this species will change the environment by adding nutrients to the soil.
This makes it easier for new species to colonize and, in turn, makes it a less suitable environment for the pioneer species.
This process continues until an equilibrium in species number is reached and a stable climax community is established.
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5. Question 1
What is the first species to colonize an area where any soil is completely absent, known as?
A) The climax species
B) The pioneer species
C) The primary species
D) The colonize species
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6. Question 1
What is the first species to colonize an area where any soil is completely absent, known as?
A) The climax species
B) The pioneer species
C) The primary species
D) The colonize species
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7. Pioneer Species
Let us look in more detail at how this occurs and how the species change as the succession progresses.
Pioneer species that colonize rock, are organisms that can tolerate hostile conditions and make their own food, for example bacteria and lichens.
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8. Pioneer Species
Some lichens produce chemicals that help to break down the rock surface into small pieces. This helps to create soil.
As the lichens die, they decompose and provide the organic material to help create even more soil.
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9. Annuals and Biennials
As more soil accumulates over time, the area can become home to plant species that thrive on bare ground and nutrient poor soils.
These species have short life spans of one growing season and produce numerous small seeds that are easily dispersed. These are called annuals.   
Clinton & Charles Robertson   
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10. Annuals and Biennials
Annuals are then quickly replaced in the next year by biennial plants (plants with a two-year life span) that are more dominant.      
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11. Perennials
After about 3 or 4 years, the biennial plants give way to perennial herbs and shrubs.
Perennial plants can live for many years and have the ability to reproduce several times over their life spans.
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12. Softwood Trees
After another 10 years or so, the soil is in a much better condition to support larger and more varied plant species.
These may include larger shrubs and small softwood trees.
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13. Softwood Trees
These trees will grow taller and begin to form a canopy. A canopy will reduce the amount of light that can reach smaller species.
The only plants that will thrive near ground level will be herbs and shrubs that are adapted to low light levels.
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14. Climax Community
The conditions closer to the ground will become more humid, and leaf litter will be produced.
This enables hardwood species, such as oak, to begin to grow and develop into a mature woodland.
At this stage, there is a much slower change of the species in the community. This is known as the climax community.
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15. Question 2
After the pioneer species, what is the correct order of plants in a bare rock to oak woodland succession?
A) Biennial plants, perennial plants, annual plants softwood trees, and hardwood trees
B) Annual plants, perennial plants, softwood trees, biennial plants, and hardwood trees
C) Annual plants, biennial plants, perennial plants, softwood trees, and hardwood trees
D) Perennial plants, annual plants, biennial plants, softwood trees, and hardwood trees
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16. Question 2
After the pioneer species, what is the correct order of plants in a bare rock to oak woodland succession?
A) Biennial plants, perennial plants, annual plants softwood trees, and hardwood trees
B) Annual plants, perennial plants, softwood trees, biennial plants, and hardwood trees
C) Annual plants, biennial plants, perennial plants, softwood trees, and hardwood trees
D) Perennial plants, annual plants, biennial plants, softwood trees, and hardwood trees
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17. Question 3 When is the climax community reached?
A) When the speed at which species change increases
B) In the very early stages of succession
C) When the change in species slows and an equilibrium is reached
D) When the change in species is at its most rapid
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18. Question 3 When is the climax community reached?
A) When the speed at which species change increases
B) In the very early stages of succession
C) When the change in species slows and an equilibrium is reached
D) When the change in species is at its most rapid
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19. Primary and Secondary Succession
When ecological succession occurs on land that has not previously been vegetated, it is known as Primary Succession.
Abrupt changes to an ecosystem, such as forest fires, floods, wind storms, and volcanic eruptions, can cause drastic changes to an ecosystem.
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20. Primary and Secondary Succession
Over time, succession may occur to return the area to its mature community. It is usually more rapid than primary succession as there is often some soil to begin with. It is known as Secondary Succession.
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21. Effects on Populations
During succession, each organism changes the conditions slightly which enables the next, new species to survive. In doing this, the size of population of each species will change.
Conditions become less suitable for a particular species, and their numbers decrease. But as the conditions become more suitable for another species, the numbers of that species will increase.
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22. Effects on Populations
Changes in the size of a population of one species will ultimately affect the population size of other species.
For example, small mammals may rely on certain species of plant for food.
As the habitat becomes unsuitable for those plant species, their food source decreases and the population of the mammals will decrease.
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23. Effects on Populations
As the habitat becomes more suitable for larger birds and animals, these may prey on those small mammals, which will also contribute to the small mammal numbers decreasing.
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24. Question 4
Which of the following would cause a reduction in the size of a population?
A) Reduced food sources
B) Increased number of predators
C) Less suitable environmental conditions
D) All of these
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25. Question 4
Which of the following would cause a reduction in the size of a population?
A) Reduced food sources
B) Increased number of predators
C) Less suitable environmental conditions
D) All of these
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26. Summary In this presentation you have seen:
how ecological succession can affect species diversity
how ecological succession can affect populations
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