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Ecological scientists study organism-environment interactions across ecosystems of all sizes, ranging from microbial communities to the Earth as a whole.
Scientists estimate that there are between five to fifty million species of organisms on Earth, of which less than two million have been officially named (May 1988). Many organisms are small: including microbes that inhabit almost every crevice of the Earth; tiny worms that help build soils; and insects that spend their entire lives in tree tops.
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