[IB Biology: Ecological Notes] -------- [Review of Succession]

Ecological 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:

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

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

Factors Affecting the Distribution of :
Animal Species
Plant Species
a) Temperature a) Temperature
b) Water b) Quantity of Light
c) Food Supply c) Water
d) Breeding & Nesting Sites d) soil pH
e) Territory e) Minerals (includes salts)

Changes Which Occur During Succession
Soil Structure:

Early Successional Stages

(Pioneer Plants)

Late Successional Stages

(Climax Community)

Soil Depth
None or Shallow
Organic Nutrients
Moisture Retention
Ability to Recycle Nutrients


(few saprotrophs)


(many saprotrophs)

Ecosystem Structure:    
Plant Size
Large, or a mix from small to large.
Species Diversity
Low: few species
High: many species
Trophic Structure
Mostly producers, a few decomposers .
Many producers, herbivores, carnivores & decomposers.
Ecological Niches
# of Food Web Links
Many: Complex connections between food chains.

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.

Recent Examples & Causes of Extinction:

[Review of Succession]