Ecological Succession

– Syllabus Topics 2.3.5 to 2.3.7Syllabus Topics 2.3.5 to 2.3.7– 2.3.5. Describe the concept and processes of 2.3.5. Describe the concept and processes of

succession in a named habitat. succession in a named habitat. – 2.3.6 Explain the changes in energy flow, gross and 2.3.6 Explain the changes in energy flow, gross and

net productivity, diversity and mineral cycling in net productivity, diversity and mineral cycling in different stages of succession. different stages of succession.

– 2.3.7 Describe factors affecting the nature of climax 2.3.7 Describe factors affecting the nature of climax communities. communities.

Ecological Succession

– orderly process of change over time in a community” (IB definition)

• What is a “community”?

• Sequence of appearance and disappearance of species

• Pattern of colonization and extinction

• Directional, non-seasonal, continuous

• Two types: primary and secondary

Primary Succession

• Occurs after the creation of a new habitat

• e.g. lava flow, glacier retreat, sand dune formation, artificial ponds, artificial reefs

• Areas which have never had organisms growing on them

• Conditions are unfavorable for life at first

Fig. 7-11, p. 156

Exposed rocks

Lichens and mosses

Small herbs and shrubs

Heath matJack pine,

black spruce,

and aspen

Balsam fir,

paper birch, and

white spruceforest

community

Time

Secondary Succession

• Community development in areas that were previously occupied by a community

• Occurs after a disturbance

• e.g. loss of trees by disease, wind or fire; logs clearing areas in intertidal zone; overturning of boulders in intertidal zone

• Conditions are therefore favourable since seeds, spores and even resistant animals or plants may remain and there is often a well developed soil

• More rapid than primary succession

Fig. 7-12, p. 157

Time

Annual

weeds

Perennial

weeds and

grasses

Shrubs

and pine

seedlings

Young pine forest

with developing

understory of oak

and hickory trees

Mature oak-hickory forest

IN YOUR NOTEBOOK…

• Describe the steps you would take to measure PRIMARY succession in the wake of a melting glacier in glacier national park.

• In another paragraph describe what you would do to measure SECONDARY succession in the forest in the abandoned farms of Long Valley.

Why does succession occur?

– Ecosystem changes result from:

– Changes in physical environment - disturbance or creation of new habitat

– Competition between organisms

– Shift in energy flow from production to respiration

How does succession occur?

• Through a series of stages:

– Pioneer species arrive

– Early colonizers with good dispersal mechanisms (r-selected species); fast growth rate; high photosynthetic rate; minimal environmental demands

– Opportunistic organisms settle

– e.g. diatoms, sea lettuce, scotch broom

Stages of Succession• Sere - “set of communities that succeed one another over the

course of succession at a given location” (IB definition)

• process of succession from beginning to end

– Seral stages

• waves of temporary organisms displace pioneer species through competition

– Climax community

– End point of succession

Climax Community

• Most permanent of all the stages

• Stage at which system has reached steady-state equilibrium

• May take 100’s or 1000’s of years to reach this stage

• Difficult to identify

• Determined by climatic or edaphic (soil) factors unless humans maintain an equilibrium at subclimax (e.g. poor soil quality, grazing, preventing forest fires, selective logging)

• During succession species modify the physical environment making it more suitable for new species and less suitable for those already there

• Pioneer species are often poor competitors and are replaced by stronger competitors that have greater environmental demands

• Later communities are often more complex than earlier communities

Changes in Community with Succession

• Biomass

• Size of individuals

• Biodiversity increases then may stabilize or slightly decline as size of individuals increases

• Shift from linear food chains to complex food webs

• Gross productivity (GPP is low initially, rising in the middle stages of succession, then GPP declines again in the climax phase)

More Changes…

– Net productivity from goes from high in the early stages Net productivity from goes from high in the early stages to zero as succession approaches climaxto zero as succession approaches climax

– Initially low amount of energy lost through respiration Initially low amount of energy lost through respiration therefore high NPPtherefore high NPP

• Respiration with shift in community to more Respiration with shift in community to more consumers so net productivity approaches zero as consumers so net productivity approaches zero as Photosynthesis:Respiration ratio (P:R) Photosynthesis:Respiration ratio (P:R) approaches 1approaches 1

– internal cycling of materialsinternal cycling of materials

– mineral cycles become more closedmineral cycles become more closed