Energy and cycles of energy Biogeochemical cycles and virtually all other processes on Earth are
drive by energy from the sun. The sun acts as a blackbody radiator with an effective surface
temperature of 5780 K (Celsius degrees above absolute zero). It transmits energy to earth as
electromagnetic radiation. The maximum energy flux of the incoming solar energy is at a wavelength
of about 500 nanometers, which is in the visible region of the spectrum. A 1 square meter area
perpendicular to the line of solar flux at the top of the atmosphere receives energy at a rate of 1,340
watts, sufficient, for example, to power an electric iron. This is called solar flux. Energy in natural
systems is transferred by heat, which is the form of energy that flows between two bodies as a result
of their difference in temperature, or by work, which is transfer of energy that does not depend
upon a temperature difference, as governed by the laws of thermodynamics. The first law of
thermodynamics states that, although energy may be transferred or transformed, it is conserved and
is not lost. Chemical energy in the food ingested by organisms is converted by metabolic processes
to work or heat that can be utilized by the organisms, but there is no net gain or loss of energy
overall. The second law of thermodynamics describes the tendency toward disorder in natural
systems. It demonstrates that each time energy is transformed; some is lost in the sense that it
cannot be utilized for work, so only a fraction of the energy that organisms derive from metabolizing
food can be converted to work; the rest is dissipated as heat. Energy Flow and Photosynthesis
Whereas materials are recycled through ecosystems, the flow of useful energy may be viewed
asessentially a one-way process. Incoming solar energy can be regarded as high-grade energy
because it can cause useful reactions to occur, the most important of which in living systems is
photosynthesis. Solar energy captured by green plants energizes chlorophyll, which in turnpowers
metabolic processes that produce carbohydrates from water and carbon dioxide. These
carbohydrates represent stored chemical energy that can be converted to heat and work by
metabolic reactions with oxygen in organisms. Ultimately, most of the energy is converted to lowgrade heat, which is eventually reradiated away from Earth by infrared radiation. 3 Succession
Environment is always kept on changing over a period of time due to (1) variations in climatic and
physiographic factors, (2) the activities of the species of the communities themselves. These
influences bring about marked changes in the dominants of the existing community, which is thus
sooner or later replaced by another community at the same place. This process continues and
successive communities develop one after another over the same area until the terminal final
community again becomes more or less stable for a period of time. It occurs in a relatively definite
sequence. This orderly change in communities is referred as succession. Odum called this orderly
process as ecosystem development/ecological succession. Succession is an orderly process of
community development that involves changes in species structure and communityprocesses with
time and it is reasonably directional and therefore predictable. Succession is community controlled
even though the physical environment determines the pattern. Causes of succession Succession is a
series of complex processes, caused by (I) Initial/initiating cause: Both climatic as well as biotic. (II)
Ecesis/continuing process ecesis, aggregation, competition reaction etc. (III) Stabilizing cause: Cause
the stabilization of the community. Climate is the chief cause of stabilization and other factors are of
secondary value.
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