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 Pioneer community (lichens, mosses) Soil formation (lichens die/ break up rock) Enough soil = grasses out compete lichens Grasses die = more soil = shrubs and weeds take over Increased soil = shallow rooted trees (pine) Increased pine = more shade = favorable for deeply rooted plant (maple/ birch) Climax Community *Climax community is the stable community that results.

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.

04_03_succession.swf

Question: Why are there prescribed burns? Is this a good thing?

Prescribed burns:

Assignment Please complete the following: – Environmental changes and succession worksheet.