Ecological Succession

Ponder this….

Do communities change?

Ponder this….

Do communities change?

yes, of course

What makes them change?

Ponder this….

Do communities change?

yes, of course

What makes them change?

something about the environment changes, may be huge

or small, natural or man-made, sudden (a disturbance) or

gradual (abiotic factors change as the community

changes)

How do they change?

Ponder this….

Do communities change?

yes, of course

What makes them change?

something about the environment changes, may be huge

or small, natural or man-made, sudden (a disturbance) or

gradual (abiotic factors change as the community

changes)

How do they change?

gradual change over time as species are replaced by other

species

Ponder this….

Do communities change?

yes, of course

What makes them change?

something about the environment changes, may be huge

or small, natural or man-made, sudden (a disturbance) or

gradual (abiotic factors change as the community

changes)

How do they change?

gradual change over time as species are replaced by other

species

For a given area, is change predictable?

Ponder this….

Do communities change?

yes, of course

What makes them change?

something about the environment changes, may be huge

or small, natural or man-made, sudden (a disturbance) or

gradual (abiotic factors change as the community

changes)

How do they change?

gradual change over time as species are replaced by other

species

For a given area, is change predictable?

sort of…. If you could stand in a cleared field in

Alabama for 500 years, what would you expect to see?

disturbance

This change in a

community over

time is called

ecological succession

Ecological Succession

• Definition: a gradual process of change and

replacement of the types of species in a community

• The sequence of changes is somewhat predictable

• May take place over hundreds or thousands of years

Two types of ecological succession

Primary succession: occurs on a surface where

no ecosystem existed before (no soil)

Secondary succession: occurs on a surface where

an ecosystem has previously existed but has been

disturbed (soil is present)

Primary Succession

• On new islands

created by volcanic

eruptions

• On sand dunes

Primary Succession

• Where glaciers have retreated

Primary Succession

• Paved areas that are abandoned

Primary Succession

Begins with pioneer species (defined as the first

species to colonize a disturbed area), like lichens,

that can grow directly on rock; begin the

breakdown of the rock to form soil

Primary Succession

Once rocks begin to weather and crack, soil

forms and small plants can take root

Primary Succession

Larger plants continue to move in until the bare

ground is covered with life

Secondary Succession

Definition: type of ecological succession that occurs on a site

where an ecosystem previously existed (soil is present)

Due to a disturbance to the ecosystem – something upsets the

natural balance

May be natural or man-made (anthropogenic) disturbances

Think of examples of each….

Examples of natural disturbances

tornadoes, floods, trees falling, fire, hurricanes,

disease

Examples of man-made (anthropogenic) disturbances

deforestation, pollution, urbanization, harvesting

‘General Ecology’, D.T. Krohne

Secondary Succession After a disturbance, pioneer species move in,

followed by other species in a somewhat predictable

sequence

Typical stages of secondary succession

in woodlands

• Early: plants typically small with short lifecycles

(annuals, grasses), rapid seed dispersal,

environmental stabilizers (pioneer species)

• Middle: plants typically longer lived, slower seed

dispersal, and usually larger

• Late: plants and animal species are those

associated with older, more mature ecosystem:

larger, slower dispersal, better competitors, slower

growth

• Climax community: final stage of succession that

will last as long as there is no disturbance

• Each stage of succession brings about changes in the ecosystem that enable or prevent certain species from moving in – better soil, less light, more competition as ecosystem matures

• Some changes may help other species – called facilitation (example: dogwood trees grow well under the shade of larger trees)

• Some changes may hinder other species – called inhibition (example: black walnut produces a chemical that keeps other plants from growing near it)

Even though the stages can be generally

predicted, stages of succession can vary,

depending on local conditions

Amount of rain,

temperature, terrain,

latitude, altitude, soil

type, human impact

Succession in two forests: What causes the

difference in these climax communities?

Succession in the boreal forest (for example in Canada) – climax

species are fir, spruce, hemlock

For example,

eastern U.S. -

climax species are

oak, hickory, maple

Even in one location, the climax community

depends on many factors

Current way of thinking: instead of

one stable, final climax community,

there are patches that are constantly

changing within an ecosystem (called

patch dynamics)

Identify the “patches” around SPHS- even

though we are in the “deciduous forest” of

Alabama, it is not that simple….

We can see changes in the animal

communities over time, too

© 2003 John Wiley and Sons Publishers

Fig 10.7 Diagram of bog

succession.

Ecological Succession can occur in

aquatic ecosystems

© 2003 John Wiley and Sons Publishers

Fig 10.8 Graphs

showing changes in

biomass and diversity

with succession.

Changes in Biota

© 2003 John Wiley and Sons Publishers

Fig 10.9 Changes in soil

nitrogen and

phosphorus.

Changes in Abiotic Factors

Conclusions