ECOLOGICAL SUCCESSION Baker High School生态继承贝克高中.pptVIP

ECOLOGICAL SUCCESSION Ecosystems tend to change with time until a stable system is formed. The stable system that will form depends on climatic limitations. Ecological Succession The replacement of one community by another until a stable stage is reached is called ecological succession. Climax Community The final stage of succession is called the climax community. The climax community in New York State is an oak-hickory forest or a maple-beech forest. Primary Succession Primary succession occurs where there was no previous community, such as on bare rock or sand. Primary succession begins with pioneer organisms. Pioneer Organisms Pioneer organisms can tolerate extreme conditions: hot and cold; dry and wet. Moss, dune grass, and lichens are pioneer organisms. Lichens Lichens are algae and fungus growing together in a mutualistic relationship. Algae make the food; fungus anchor and capture water. Pioneer organisms Soil is produced over hundreds of years by pioneer organisms. These organisms break apart rock, add humus as they die and decompose, and hold water This allows other organisms to grow there. Succession occurs BECAUSE Each community changes the conditions so that they are more favorable to other organisms that replace them. For example, some types of trees need a lot of sun and their saplings cannot grow under the shade of their own species. They will be replaced by the types of trees whose saplings can grow in shade of other trees. Secondary Succession When a community is disrupted and succession occurs again, it is called secondary succession. Disruption may be from fire, farming, wind, foresting Secondary Succession The community begins again where the former community was disrupted. Soil is already present. A community is still undergoing succession As long as the species keep changing: Here, the plants growing under the pine trees are NOT small pine trees, so the species will be changing as the old pine trees fall. Climax Community The same climax