Environmental Science

ENVIRONMENTAL SCIENCE : ECOSYSTEM 129

On the basis of the studies E.P. Odum pointed out that in nature there are present two
basic food chains in any system:

(1) The grazing food chain beginning with green plant base going to herbivores and
then to carnivores, and
(2) The detritus food chain beginning with dead organic matter acted by microbes,
then passing to detritivores and their consumers (predators).
The figure given below present one of the first published energy flow models as pioneered
by H.T. Odum in 1956.

P 1

P 3 P 1

P PN

Fig. 3.3 First Energy Flow Model (1956)

The above figure illustrates energy flow in a community with a large import and
smaller export of organic matter.

P indicates gross primary production; PN indicates net primary production. P 2.
P 2 ...............P 5 indicate secondary production at the shown levels.

Gross Primary production GPP = Total photosynthetic C fixation Autotrophic Respiration,
RA = GPP-NPP

Net primary Production, NPP-RA

Heterotrophic Respiration, RH = respiration of consumers and decomposers.

Ecosystem Production, NEP = GPP-RE