Succession

Succession

• Gradual change in species occupying an area, due to changes in 1 or more abiotic or biotic factors favoring some species over another.

Primary Succession

• Gradual establishment of an ecosystem where one did not exist before (Ex: on bare rock).

• Examples:

• Primary Succession on a Sand Bar

• Primary Succession on a Rock

Secondary Succession

• Gradual reestablishment of an ecosystem from an area where it previously existed.

• Examples: old farm lands, after a fire or natural disaster

Pioneer species

• Plant or animal species that are the first to occupy a newly exposed or disturbed area.

• Examples: lichens, moss

Climax species

• Last stage of succession. One in which populations of all organisms are in balance w/ each other & existing abiotic factors.

• Examples: Old Growth Forest

Changes Which Occur During Succession

• Soil Structure changes:

• Ecosystem Structure changes:

Soil Structure changes

Early Successional Stages

(Pioneer Plants)

Late Successional Stages

(Climax Community)

Soil Depth

None or Shallow Deeper

Organic Nutrients

Few Numerous

Moisture Retention

Poor Good

Ecosystem Structure changes

Plant Size Small Large, or a mix from small to large.

Early Successional Stages

(Pioneer Plants)

Late Successional Stages

(Climax Community)

Species Diversity Low: few species High: many species

Trophic Structure Mostly producers, Many producers,

herbivores a few decomposers carnivores & decomposers

Ecological Niches Few Many

# of Food Web Links Few Many; Complex connections between food chains.

Factors Affecting the Distribution of :

Plant Species

a) Temperature

b) Water

c) Quantity of Light

d) soil pH

e) Minerals (includes salts)

Animal Species

a) Temperature

b) Water

c) Food Supply

d) Breeding & Nesting Sites

e) Territory

Competitive Exclusion Principle

• When 2 species compete very directly for resources, one eventually excludes the other from the area.

Biodiversity

• In the natural world, all living species, ecosystems, and genetic diversity within the species.

– Known Species: 1.75 million plants, animals & microbes.

– Estimated totals: 4-112 million unidentified species.

Extinction

• Death of all members of a species. All the genes of the species are lost forever.

Does the picture below represent primary or secondary succession? • Explain how you would know before

clicking.

Primary succession occurs in areas where no well developed soil exists (bare rock, desert sands, or very fire sterilized soils as examples). Secondary succession occurs in places where well-developed soils already exist.

Explain why primary succession takes

longer to occur than secondary succession.

Primary succession takes longer to occur than secondary succession because:– soil which is ready for plants to grow in does not

exist yet. – Plants are not able to grow well on bare rock,

desert sands, or on soil sterilized by extremely hot fires.

– It thus takes years to centuries longer then for primary succession to occur

– secondary succession occurs faster because the soil already exists and is ready for new plant life.

• Explain how you would know before clicking.

In this example, what are 2 examples of pioneer plants?

The 2 examples of pioneer plants are the lichens & mosses.

How do the pioneer plants change the landform so other plants can live there?

• Answer before clicking.

The pioneer plants change the landform so other plants can live there by adding soil to the rock (as they die and decay) and also by physically breaking down the rock into smaller particles (the beginning of soil).

Explain how the “heath mat” might change the landform so that Jack pine and black

spruce can live there.

The heath change the landform by adding to the depth of soil and the nutrients found there. This occurs as the leaves of the heath drop to the ground and decay. In addition, the roots help break rock and thicker soil up. The result is that the soil soon becomes deep enough for the young trees to live there.

Why aren't the heath able to live there forever?

The heath are unable to live there forever because when the trees begin to get big, they change the habitat further. They do this by stealing water and nutrients from the smaller heath, and more importantly, by shading the heath so it doesn't receive enough sunlight.

What is the last stage of succession called?

• Note that this is the stable, unchanging stage where only a large change (like disease or fire) reverts succession back to an earlier stage.

The climax community. In Pacific Northwest forests, the climax community is known as old growth forest. Note that climax is the most correct term for all habitats when speaking of the final successional stage.

Why does the climax or last stage of succession not change into a different successional stage unless a

major change occurs? • Because the plants that live there are adapted to

living under those environmental conditions. • In this case, the fir, spruce, and birch trees all

are tall as adults so they easily can get plenty of sunlight. In addition, all have wide-ranging root systems to find water and minerals.

• More importantly, their seedlings need shade (not light) to survive. Since all these conditions are met, the older climax species are constantly replaced by their same species.

Does this diagram illustrate an example of primary or secondary succession?

Explain how you would know.

Primary succession.

Primary succession occurs in where no developed soil exists (at the area with exposed rocks below).