Sunday, March 6, 2011

How Do Communities Change with Time?

Many things change with time. Your body looks different as you grow older. Rocks and mountains wear away over many years. Communities or organisms can also change with time. As organism interacts with one another and with nonliving things, they sometimes cause changes. The resources are available to the organism changes. As a result the kinds of organism that make up a community also change. In time, the pond community in the picture might become a forest community. Most ponds begin as small bodies of water with small organisms living in them. A young pond usually has a sandy bottom. Algae, Snails, and other small organisms live in the pond. When the organisms die, they sink to the bottom of the pond and decompose. The dead matter builds up and forms a thick, muddy soil. Water plants begin to grow from the muddy soil.  Water plants begin to grow from the muddy soil. The mud provides a home for the new kinds of organism. The drawings show how the pond continues to change over many years. Crayfish, clams and worms from surrounding areas find the pond and burrow in the mud. Small fish from nearby streams enter the pond and feed on the plants. Soon, large fish enter and feed on the small fish. The muddy pond bottom gets thicker as organisms die and sink to the bottom. More kinds of organisms live in the pond as it gets older. Ducks, frogs and taller plants enter the pond. As the muddy bottom continues to rise with dead matter, less water is available for fish. Eventually, all the fish die. The drawings show that the edges of the pond fill up faster than the center of the pond        

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