First model – proposed by Jude (1940) and Lindemann (1942).
Later on more sophisticated models proposed, by Odum (1957), Teal (1957) and Mann (1969).
Model proposed by Mann (1969) is shown in Fig. Two principles apply in it:
According to laws of thermodynamics, energy can be up taken only once, no scope of up taking energy for second time in any system
On the other hand, materials in ecosystem move in cyclic fashion, they can be up taken and re-uptaken several times in ecological system.
Odum (1957) measured energy flow at different trophic levels in Silver Spring, a river in Florida.
- Annual incident solar radiation (L) is 7.1 × 106 kJ/m2
- Macrophyte community absorbed (LA) 24% of incident radiation: 17.2 × 105 kJ.
- Gross productivity (PG) was 5% of absorbed radiation: 8.7 × 104 kJ
- Energy flow in base of trophic pyramid (PG/L) = 1.2%
- Respiratory loss is 57.5% of PG = 5.0 × 104 kJ.
- Net productivity becomes 3.7 × 104 kJ.
- Transformation of energy at production level (Pt/At) = 0.42
- From net productivity, large amount flows downstream
- At primary consumer level, energy stored = 1.4× 104 kJ.
- In it 2.0 × 103 kJ/m2 comes from out side ecosystem
- Flow of energy from primary productivity to primary consumer [It/(It-1)] = 16%
- 11% of energy stored at primary consumer level (1.4 × 104 kJ), transferred to secondary consumer level (1.6 × 103 kJ).
- From this (1.6 × 103 kJ) only 6% (47.9 kJ) transferred to top consumer crocodile.
So, in conclusion it can be said that 88% of PG utilized for self regulatory function of ecosystem and 12% is lost as detritus in downstream.
Transfer of energy from one trophic state to another in different ecosystems varies according to structure of organisms.
|Trophic state||Cedar Bog Lake||Lake Mendota||Silver Spring|
|Primary consumer (%)||13.3||8.7||16|
|Secondary consumer (%)||22.3||5.5||11|
|Top consumer (%)||–||13||6|