Ecological Succession

Ecological Succession

• Process by which communities in a particular area change over time

• Early communities modify the environment causing change to occur

• This affects biological community as well– How?

• Each successive (new) community is more favorable for new species

• Changes in stages until a climax community is established

Composition of the community changes with time

Past Community

PresentCommunity

Future Community

Some species in the past community wereout-competed, and/or did not tolerate alteredabiotic conditions

Modifies such abioticfactors as:•Light intensity•Wind speed•Air Temperature•Soil composition•Light quality•Wind direction•Soil water•Humidity

Changes allow newspecies to becomeestablished.

Primary Succession

• Regions with no existing community• Bare rock• Receded glaciers• Volcanic regions• Krakatoa, Glacier Bay

Lichens, bryophytesAnd annual herbsBare Rock

Grasses and Small shrubs

Fast growing trees

Slower growing broadleaf species

Climax Community

100-200 years

Pioneer Species

First organisms to live in a new community. Usually brought in by

wind or animals

Secondary Succession

• Takes place after a land clearance– Fire, landslide, forest clearing

• Soil is already there

• More rapid than primary

Primary bare earth

Open pioneer community (annual grasses)

Grasses and low growing perennials

Scrub: shrubs and small trees

Young broad- leaved woodland

Mature woodland mainly oak

1-2 years 3-5 years 16-30 years 31-150 150+

Climax Community

Gap Succession

• In a forested area with a thick canopy

• Reduced light on soil

• When a tree falls sunlight fills forest floor

• New communities are formed

Wetland Ecological Succession

• In open body of water, aquatic plants are introduced

• Increase in aquatic plants causes sedimentation• Swamps may occur and in warmer months may

dry off• May lead to EUTROPHICATION

– More production (photosynthesis)– Lead to reduced oxygen and fish kills– Natural and anthropogenic– Type of pollution

Aerial view of Lake 227 in 1994. Note the bright green colour caused by algae stimulated by the experimental addition of phosphorus for the 26th consecutive year. Lake 305 in the background is unfertilized.