Science 20: Unit D – Living Systems

Changing Populations

Ecological Succession •Ecological succession is a community change

in which new populations of organisms gradually

replace existing ones.

•Succession occurs from natural causes

(competition, fire, earthquakes, etc) or due to man

(logging, mining, farming etc).

Primary Succession

•Primary succession-succession that begins in an

area where there is no existing community.

•Causes of primary succession: volcanic eruption,

glacier retreat.

Primary Succession Animation

•The first group of organisms to

occupy an area in primary

succession is called a pioneer

community.

•Pioneer organisms must be hardy

and able to live on minimal

resources.

•Lichens are pioneer organisms;

humus is the organic component of

soil created from decomposing

organisms.

Steps in Primary Succession:

Glacier Retreats exposing Parent rock

Glacier Retreats exposing Parent rock

Pioneer community (lichens, mosses)

Pioneer community (lichens, mosses)

Soil formation (lichens die/ break up rock)

Soil formation (lichens die/ break up rock)

Enough soil = grasses out compete lichens

Enough soil = grasses out compete lichens

Grasses die = more soil = shrubs and weeds take over

Grasses die = more soil = shrubs and weeds take over

Increased soil = shallow rooted trees (pine)

Increased soil = shallow rooted trees (pine)

Increased pine = more shade = favorable for deeply rooted plant (maple/ birch)

Increased pine = more shade = favorable for deeply rooted plant (maple/ birch)

Climax CommunityClimax Community

*Climax community is the stable community that results.

Primary Succession:

Primary Succession:

• Occurs when water collects in a basin; algae starts to

grow; eggs are planted in water; fish hatch and

attract birds to the water.

• Nutrients from runoff create soil for plants to grow;

plants grow on edge (cattails).

• When lots of plants overtake water = terrestrial

ecosystem.

Aquatic Succession

Secondary Succession•Secondary succession: occurs in an area where an existing community has been partially destroyed.

•Examples: Fires, logging, farming

•Occurs more rapidly then primary succession

•A community that achieves relative stability is called a climax community.

•Climax communities tend to have greater species diversity than the communities that precede them.

http://www.geowords.org/ensci/imagesbook/04_03_succession.swf

Question:

Why are there prescribed burns?

Is this a good thing?

Pre

scribed

b

urn

s:

Assignment

• Please complete the following:– Environmental changes and succession

worksheet.