Changes in Ecosystems:Ecological Succession

EQ: How do communities change over time?

Succession is…

• a series of predictable changes in types of species that occurs in a community over time

• Two types: primary and secondary

Primary Succession• Occurs on surfaces where no soil exists

• Events which expose bare rock:

– volcanoes

– flooding

– glaciers

• Begins with arrival of organisms such as lichens that do not need soil

• Lichen are the pioneer species (first organisms to arrive in an area)

Primary Succession • Soil starts to form as lichens, weathering,

and erosion break down rocks into smaller pieces

• When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil

• Over time, the soil layer thickens, and grasses, wildflowers, and other plants begin to take over

Primary Succession

• In time insects, birds, and mammals move in

• What was once bare rock now supports a variety of life, including trees

Secondary Succession• Occurs in an area with soil that contains

seeds, spores, roots, or other plant parts

• Events that destroys most of an ecosystem • forest fire• harvesting • Hurricane

• Happens faster and weeds are a typical pioneer species in secondary succession

http://www.ux1.eiu.edu/~cfruf/bio3002/secondary_succession.htm

Secondary Succession

Climax Community

• Mature community made up of plants and animals

• Does not always mean big trees– tall grasses in prairies– cacti in deserts

• Species can continue to change in response to climate and other factors

Succession: starting over

Primary• No soil is available

and must be created by pioneer species

• Lichens are usually the pioneer species

• Usually the result of a volcano or glacier

Secondary• Soil is still available

and pioneer species can take root

• Weeds/plants are usually the pioneer species

• Usually the result of a forest fire or hurricane