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Transcript
LHS Academic Biology Name: Block: ECOSYSTEM CHANGE = SUCCESSION and DISTURBANCES (Major ecology concept #3.) Ecosystems are constantly changing from and then returning to their natural communities. The causes (called disturbances) can be either human changes or natural events. Succession is an ecosystem’s slow and predictable (step by step) return to its natural, native community of species – the Climax Community. (In Pennsylvania, that is a Temperate Deciduous Forest – trees that shed their leaves.) Examples of succession include a shallow lake changing into a forest, and a forest (or field) covered by lava again growing back (in to a forest or field). What is a disturbance? What is succession? Types of Disturbances Human disturbances to an ecosystem include accidental fires, clearing a forest (or plowing over a field) in order to grow crops or to build a highway or housing development. Natural events include floods, earthquakes, lightning strikes and wild fires, mudslides (filling in a pond or covering the ground), and volcanic eruptions. What are examples of a Human Disturbance? What are examples of a Natural Disturbance? LHS Academic Biology Name: Block: Types of Succession Ecological succession is a gradual process of change and replacement of the types of species in a community. There are two types of succession, Primary Succession and Secondary Succession. Secondary Succession The more common type, it occurs on a surface where an ecosystem was disturbed but still contains soil and life in the soil. After most forest fires, plants are killed but their seeds remain in the soil and begin to grow very quickly. The first species to colonize an area after a disturbance are called Pioneer Species. (Plants are usually the pioneer species after secondary succession.) Pioneer species make the ecosystem habitable (livable) for the next community in the process of returning to the original species. Succession ends when the original community of species, called the Climax Community, is reestablished. Primary Succession Much slower than secondary succession, it occurs where there is no soil (such as after a volcanic eruptions or the retreat of a glacier), or on any other surface that has not previously supported life, such as bare rock. (It can take from several hundred to a thousand years to produce fertile soil, naturally.) After primary succession, the pioneer species that colonize bare rock or new soil are usually lichens and bacteria (see first box, on left). LHS Academic Biology Name: Block: Succession Practice What is Primary Succession? What is Secondary Succession? What is a Pioneer Species? What is a Climax Community? What type of succession – Primary or Secondary - is taking place in the pictures, below? 1) This is a former farm field that has been abandoned by the farmer. Succession Type: _______________________________________________ 2) This is a bare rock field from which a glacier receded. Succession Type: _______________________________________________