P. Odum and Howard T. Odum, Fundamentals
of Ecology (Philadelphia: Saunders, 1951).
chapter 2 "Principles and concepts pertaining
to the ecosystem and biogeochemical cycles",
the Odum brothers review the history and significance
of two fundamental ecological concepts. Although
the term "ecosystem" was proposed
by Tansley in 1935, it has older roots in Forbes'
"microcosm" (1887), Vernadsky's idea
of the "biosphere" (1926). Generally,
an ecosystem is 'any area of nature that includes
living organisms and nonliving substances interacting
to produce and exchange of materials between
the living and nonliving parts." These
biotic and abiotic realms influence each other
and are both necessary for the maintenance of
life on Earth. Biogeochemical cycles are the
more or less circular paths of chemical elements,
including all the essential elements of protoplasm,
that circulate in the biosphere from environment
to organisms and back to the environment."
These "inorganic-organic cycles" have
a long history, reaching back to 18th century
chemistry and natural history.