Changes in a community

Ecological succession

(Ecological communities part 3)

Ecological succession:

• Natural, gradual changes in the types of species that live in an area

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• Primary vs. secondary succession

Primary succession

• Occurs in an area with no soil (ie there is bare rock).
• Events that would cause there to be no soil include
• volcanic eruption
• landslide
• glacial retreat

Primary Succession: forest example

Starts on bare rock

Primary Succession

Lichens colonize

Primary Succession

Mosses then grasses and small herbaceous and flowering plants

Primary Succession

Woody shrubs and tree seedlings

Primary Succession

Trees with high dispersal ability and high sunlight tolerance/needs

Primary Succession

Late-successional species become dominant

Climax Community

• A stable group of plants and animals that is the “end” result of the succession process
• Does not always mean big trees
• Grasses in prairies
• Cacti in deserts

Succession of species

lichens & mosses

grasses

trees

bushes & small trees

pioneer species

climax forest

compete well in high sunlight

shade tolerant species

stable community

What causes succession?

• Tolerance of early species
• Facilitation & Inhibition
• early species facilitate habitat changes
• allows other species to thrive that will out-compete (inhibit) the early species

Changes in abiotic factors over time

Soil quantity

Soil quality

Soil water retention

Changes in abiotic factors over time

Light availability

(ground)

Temperature

(ground)

Plant nutrient

avail. (nitrate,

phosphate, etc.)

Changes in abiotic factors over time

Soil quantity

Increases

More detritus increases humus

Provides more area for plants to anchor their roots in

Soil quality

Improves

Gains organic matter

Provides more nutrients for plant growth

Soil water retention

Increases

Increased organic matter retains more water; shading decreases evaporation

More water is available for plants

Changes in abiotic factors over time

Decreases

Light availability

Shading increases over time

Favors shade-tolerant species and inhibits shade-intolerants

Temperature

Decreases

Shading increases over time

Favors heat-intolerant species and inhibits plants that need higher temps.

Nitrogen or phosphorus

Increases

Increased N fixation, Increased decomposition

Favors plants with higher N or P requirements

Secondary succession

• Occurs after a disturbance that leaves the soil (and seed bank within the soil) intact
• Fire
• Massive storm
• Forest clear-cutting
• Death of a large mature tree
• Also occurs in abandoned agricultural fields

Disturbances as natural cycle

• release nutrients
• increases biodiversity

• increases habitats
• rejuvenates community

Fire climax species

Jackpine

adaptations to survive and reproduce in areas that experience frequent fires

Intermediate disturbance hypothesis

Regional diversity

Aquatic succession

• how/why does this happen

over time?

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• oligotrophic, mesotrophic,

eutrophic

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Scenarios

• A massive landslide occurs leaving completely bare bedrock behind.

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• What is the immediate effect on the ecosystem?
• What are the ongoing long-term effects on succession?

2. A forest is completely uprooted by a tornado.

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• What is the immediate effect on the ecosystem?
• What are the ongoing long-term effects on succession?

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