Living things, whether plants or animals, continually interact with their surroundings in many ways. All of the organisms in a given area, plus the nonliving things in that area like water, soil, and air, comprise an ecosystem. The word ecosystem is a combination of the phrase "ecological system," and was coined in 1935 by A.G. Tansley, a British plant ecologist.
There are three major parts of an ecosystem: (1)the soil, rock, or bottom sediment on which the living matter rests or is attached, (2) the water and air above the bottom layer that provides the ecosystem's climate, and (3) the plants, animals, and microorganisms that live within the habitat. An ecosystem can be any size--from the Amazon basin of South America to a backyard pond where frogs and other creatures live. Some may contain thousands of species of plants and animals and may have very complex interactions. It may be stable for thousands of years, or it can change over time due to natural events like fires, floods, landslides, or the actions of man.
The living things, or organisms, in an ecosystem are composed of three different types: (1) producer organisms are mainly the green plants that convert solar energy to the chemical energy of carbohydrates, fats, and proteins through the process of photosynthesis, (2) consumer organisms obtain their nutrients by eating producer organisms or other consumer organisms; an example would be an earthworm, bird, or raccoon, and (3) decomposer organisms obtain their energy and nutrients by breaking down organic matter; examples are fungi and bacteria. Decomposers often work in sequence to reduce organic material into simple inorganic (mineral) substances, which are then available again to producer organisms. This cycle, from producer to comsumer to decomposer and back to the producer demonstrates the essential, cyclical property of a stable ecosystem.
Another way to view the cyclic property of an ecosystem is as a food chain. An example is the food chain where sunlight allows the growth of a plant, which is then eaten by a field mouse, which is then consumed by a weasel, whose remains are converted to mineral matter by bacteria after it dies. At any point in a food chain, less energy or nutrients are available than at the previous point--any individual utilizes about 90% of the energy they ingest in the simple processes of living, and only the small remainder goes to their tissues. This explains why plants are necessarily more common than mice, why mice are more common than weasels, and so forth. Any ecosystem consists of many food chains, all linked together in complex ways. Ecologists call such a system a food web.
Competition and cooperation are important forces in any ecosystem. Each species occupies its own individual place in the ecosystem and is part of the food web, but it inevitably encounters other species as it tries to stay alive. This overlap is an important contributor to the complexity of an ecosystem, or its biodiversity. Some ecosystems contain a simgle species that, at any given time, is dominant in that ecosystem, due to their number, their size, or their behavior. An example is the sugar maple tree in the eastern part of North America, whose abundance often determines the character of the forest community where it resides.
Another example of a dominant species in many ecosystems is, of course, man. Because of their intelligence humans have learned how to dominant and exploit many natural ecosystems to their own advantage. However, this dominance often results in the destruction of an ecosystem, as man produces waste products like air pollution, water pollution, and radioactive waste that is not useful to the ecosystem's cyclical well-being. Because humans have been able to protect themselves from other predators (consumers), their population is not in control. Human pollution and overpopulation are ultimately behind the destruction of ecosystems, and, sometimes, the plant and other animal species that reside there. It is estimated that about one-fifth, or 20%, of the native plants in the United States are in danger of extinction. While there is no agreement on how many of earth's animal species are now extinct due to the actions of man, it is thought that at least thousands have either been eliminated completely or are in danger of becoming extinct.
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