Lecture #2 Lecture #2 Ecological SuccessionEcological Succession

Unit 7: Ecology

Ecological succession- the regular progression of species replacement over time in a new or disturbed community.

1) Biomass increases over time.

2) An increase in the number & proportion of longer-lived species.

3) Increased species diversity. Succession on Mt. St. Helens

Succession shows some general trends that include:

There are two types of terrestrial succession

1)Primary Succession 2)Secondary Succession

This colonization of new sites by communities of organisms takes

place on bare rock

Primary succession: The establishment and development of an ecosystem in an area that was previously uninhabited

New bare rock comes from 2 sources

1. A volcanic lava flow cools and forms rock

– This is how the Galapagos islands and the Hawaiian islands formed!

New bare rock comes from 2 sources

2. Glaciers retreat and expose rock

How does the process begin?

Pioneer organisms- the first organisms

to colonize a new site – Ex: lichens are the first to colonize lava

rocks

These guys are TOUGH! They thrive where no other species can.

What do they do and what happens next ?

– As lichens add organic matter and form soil, mosses and other plants can colonize and grow.

– As organic matter continues to accumulate, other species move in and change the environment further. First fast growing plants, then slower growing plants.

– Over time, more and more species can find suitable niches and survive.

Primary succession-

Is there an ‘end’ to succession?

Climax Community - a stable, mature

community that undergoes little or nosuccession.

** This is not necessarily a ‘permanent’ community however. What would cause it to change?

Answer: A changing environment!

Secondary succession-

Definition: Sequence of community changes that takes place when a community is disrupted by natural disaster or human actions

• This type of succession occurs in areas where there HAD been previous growth. Because of this, the process is much faster than primary succession.

What can cause secondary succession to

occur? 1) Forest fire

• The regrowth that happens after a fire levels a portion of a forest.

What can cause secondary succession to

occur? 2. Abandoned Agricultural Field • Native plant life from

the areas surrounding the agricultural field reinvade the area.

Secondary succession-

Case Case Study- Study-

YellowstonYellowstone National e National

ParkPark1988 – Park mapshowing areas

(1.6 million acres)

burned by theseries of fires.

Yellowstone National ParkYellowstone National Park1988 fires – The immediate aftermath.

Photo: National Parks Service

Yellowstone Yellowstone National National

ParkPark• One year after the

fires• Note the

appearance of fireweed

Photo: National Parks Service

Yellowstone National Yellowstone National ParkPark

• Ten years after the fires (1998)

Photo: National Parks Service

Yellowstone National Yellowstone National ParkPark

• Twenty years after the fires (2008)

Is the Yellowstone Case study an example

of primary or secondary succession?

Case Study - ChernobylCase Study - Chernobyl

• In April, 1986, a nuclear power plant in the former USSR experienced a core meltdown and a catastrophic release of radioactivity into the environment.

ChernobylChernobyl• Surrounding

towns and villages had to be immediately, permanently abandoned.

Chernobyl – Twenty Years Chernobyl – Twenty Years LaterLater

Chernobyl – Twenty Years Chernobyl – Twenty Years LaterLater

Pripyat town square.

Chernobyl – Twenty Years Chernobyl – Twenty Years LaterLater

Chernobyl – Twenty Years Chernobyl – Twenty Years LaterLater

A local highway.

Is the Chernobyl Case Study an example of Primary or Secondary Succession?

Take 2 minutes to describe what succession is,and to identify the similarities and

differences that exist between primary andsecondary succession.