Environmental Science

ENVIRONMENTAL SCIENCE : ECOSYSTEM 127

Trophic levels

Green plants

producers

Consumers

2

Herbivores

NU NA

3

Carnivores

Tota l light

1 and L

heat

3000 — 15000 15 1.5 0.3

R R R

LA PN P 2 P 3

K cal/m /da^2 y

L

PN 1A

A

P 1 P

1

P orG

Fig. 3.2 Energy flow diagram

This is a simplified energy flow diagram

(1) The diagram depicts three trophic levels. Boxes numbered 1, 2, 3 in a leaner food

chain exhibit these.

(2) L. shows total energy input (3000).

(3) LA shows light absorbed by plant cover (1500).

(4) P.G. shows gross Primary production.

(5) A shows total assimilation.

(6) Pn shows net primary production.

(7) P shows secondary (consumer) production.

(8) Nu shows energy not used (stored or exported).

(9) NA shows energy not assimilated by consumers (egested).

(10) R shows respiration.

Some more elucidation of the figure is as under:

(1) The ‘boxes’ represent the trophic levels

(2) The ‘pipes’ depict the energy flow in and out of each level.

Energy inflows balance outflows

The first law of thermodynamics requires it. The energy transfer is accompanied by
dispersion of energy into unavailable heat (i.e. respiration). The second law requires it.