Succession

11/3

Succession

Succession- the increase in complexity of the structure and species composition of a community over time.

When you have a blank ecosystem what species come colonize first, second, third and finally balance out the system.

Succession

• Succession happens in steps called seral stages.

Primary Succession

Primary Succession- colonization of newly created land.

Examples:• volcanic eruptions• sand dunes• uncovered glacial deposits

Primary Succession

1st things to colonize an area are called pioneer species.

1. ColonizationNo soil at the beginning of primary succession. Colonizers: Lichen, mosses (r-selected)- Drought resistant and help break down rock to

create soil.- When they die they create organic material.

2. Establishment As the soil builds water can be held better and

shallow roots can establish. As these plants die, organic material is added

Establishing species: grasses, small plants, small invertebrates that break down plant matter.

Primary Succession

3. Competition Weathering and rock breakdown create enough

soil for K-selected species. K- selected species start to push out r-selected

colonizers. Competition species: shrubs, shade-intolerant

plants, pine trees.

Primary Succession

4. Stabilization• Soil in now fully established and nutrient rich.

This allows for deep roots and water retention. • Fewer new species are coming in.• Slower growing, less productive, longer life

cyclesStabilization species: (K-selected) shade tolerant

trees, oak, spruce, Douglas fir, maple

Primary Succession

Climax Community –Maximum possible development a community can reach.

• Stable, self perpetuating.• Equilibrium, organisms die at the same rate

they grow. Biomass is stable. • Biodiversity is high, K- selected species with

specific niches are present.

Primary Succession

Secondary Succession

Secondary succession- colonization of already established land.

• Occurs on already established soil. • Seeds can lay dormant • Shortened/ Faster seral stages

Examples:• Fire• Flood• Human activity (clear cutting) (agriculture)• Natural disaster

Disturbance

• Disturbance can send the community back to a previous stage

Changes that occur during succession

• Size of organisms increases• Food webs become more complex• Soil depth increases• Biodiversity increases• NPP and GPP rise and then fall• Production/Respiration ratio falls

Why do these changes occur???