Tuesday, June 23, 2009


An ecosystem is an area on the Earth that is a community of living organisms and their surrounding environment. Every person, animal, plant, rock, stream, and piece of land belongs to one or more ecosystems. For example, imagine an ecosystem made up of a freshwater pond that serves as a home for frogs, lily pads, fish, cattails, dragonflies, algae, and protozoa. Each of these organisms, along with its sources of food, sediments, nutrients, and the water itself, is a part of the pond ecosystem, which functions as a unit or a single community. Ecosystems on Earth are incredibly diverse, both in size and in form-a large city that contains millions of people, their homes, and a built-up landscape is an urban ecosystem, while a small wildlife preserve within that city serves as a natural ecosystem.

Much like a person, an ecosystem has a given level of health. A healthy ecosystem performs many valuable functions, such as flood control, water purification, seed dispersal, pollination, pollutant removal, nutrient cycling, and habitat provision. These functions are beneficial to both humans and other inhabitants of ecosystems. Consider the value of one wetland ecosystem that helps remove toxic substances from drinking water, provides a nursery for baby fish, and supplies shelter for clams and mussels-and these are only a few of the services provided by this ecosystem. Many ecosystems experience the effects of disturbances. These disturbances can be caused by human actions, such as bulldozing a forest to build a highway, or they can be a result of natural events, such as soil erosion from heavy rains. Disturbances often decrease the ability of an ecosystem to provide valuable function, and thereby decrease the health of the ecosystem. A feature of ecosystems, from the smallest backyard to the entire globe, is that they tend to be resilient. Given time, ecosystems can often recover from disturbances, maintain their health, and continue to provide the functions necessary to sustain life on Earth.
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