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Ecological Succession • A gradual process of change and replacement of some or all of the species in a community. • Succession may take 100’s to 1000’s of years Primary Succession • Occurs on a surface where no ecosystem existed before. Ex. On a rock, sand dune, retreating glacier, newly formed island, sidewalk cracks • It can take 1000’s of years for fertile soil to form • Pioneer species such as bacteria and lichens colonize rock surfaces What is a lichen? • A lichen is an important pioneer in primary succession • It is composed of a fungi and algae working together • Algae photosynthesizes, fungi absorb nutrients from rock and holds water. • Together they break down rock • Soil accumulates as dust particles trapped in cracks in rock • Lichens decompose providing food for mosses Examples of Primary Succession Plants colonize cracks in the sidewalk Primary succession – plants take over an abandoned home http://www.worldwithoutus.com/multimedia.html Secondary Succession • Occurs on a surface where an ecosystem had previously existed • Faster than primary succession • Occurs in ecosystems that have been disturbed or disrupted by humans, animals or natural processes ex. Floods, earthquakes etc. • Pioneer species are the first to colonize the land • Pioneers make the ground suitable for other species • Eventually a final and stable climax community appears. The Role of Fire in secondary succession • Fires caused by lightening and man maintain communities in chaparral, temperate forest and southern and western pine forests. • Plants in these communities have adapted to fire • Seeds of some species will not germinate till after fire • Minor fires help reduce dead wood that may lead to larger fires • Some animal species depend on fire, they feed on new shoots after the fire Fire on the prairie • Prairies produce large amounts of plant material • Dead plants do not decompose quickly and form dense mats on the ground • This makes it hard for new shoots to grow and grazers to graze • Fire releases nutrients and lets new shoots access sunlight Is this an example of primary or secondary succession? • http://www.wiley.com/college/strahler/0471 480533/animations/ch23_animations/anim ation1.html • http://www.history.com/content/life_after_p eople