In this article we will discuss about the estimation of energy accumulation by producer and consumer.
Estimation of Energy Accumulation by Producer:
Edgar Transeau (1926) made the pioneer venture to estimate the energy accumulation by the primary producers. He based his calculations on an estimated harvest of 10,000 plants (corn) per 10,000 sq. meter of land in one growing season (of about 100 days).
The plants weighed 6000 kg and their chemical compositions were known. He calculated that the corn plants gave 2675 kg of carbon. It is obvious that the carbon entered the plants through photosynthesis and it would be equivalent to 6687 kg of glucose.
This he termed as net production (NP). He further calculated the amount of glucose that had been spent in the metabolism of the plants. This loss due to cellular respiration (R) came to be 2045 kg. Thus according to his calculations the gross production was (NP4-R= 6687 kg + 2045 kg) 8732 kg.
Now it is known that in the production of 1 kg of glucose 3760 kilo calories are needed. So in the gross production of 8732 kg of glucose 33 million kilo calories will be required. He further calculated that 408,000 gallons of water were transpired by the plants and this can be done at the expense of 910 million kilo calories of energy.
The total solar energy available to the corn field was 2043 million kilo calories (Fig. 3.10).
From the above data Transeau calculated the efficiency of energy utilization and that came to be only 1.6 per cent of the total energy available. He was further able to calculate the utilization of energy that has been incorporated.
Calculations of energy utilization by Transeau:
The data calculated by Transeau was well ahead of his time and by the application of the data it has been possible to calculate the gross primary production in kilo calories of the world per square meter per day (Fig. 3.11).
Flow of Energy beyond the Producers:
The autotrophs incorporate and utilize energy. What happens to this incorporated energy (or in other words the fate of the energy beyond the initial trophic level) – is a pertinent question. To provide the answer to this question an analysis of the following data will be of much help. The data was prepared by Raymond Lindeman (1942).
Annual energy budged of Ceder Bog Lake of Minesota estimated by R. Lindeman.
The table shows that in the Ceder Bog Lake of Minesota (Fig. 3.12) there is a gross production (GP=NP+R) is 111 g cal/cm2/yr. with an efficiency of energy capture of 0–I0 per cent. Of this energy 23 4 g cal/cm2/yr. or 21% is consumed in reactions that allow growth, development and reproduction of the autotrophs.
The energy incorporated by the primary producers is lost in various pathways. The major pathways are Herbivory, Decomposition. The left over after the loss has been termed as unutilized. In the Ceder Bog Lake the loss of energy due to Herbivory is 15 g cal/cm2/yr. or 17%. of net autotroph production and the loss due to decomposition is 3 g cal/cm2/yr. or 3.4% of net production.
The rest of the plant material, 70 gcal/cm2/yr. or 79.5% of the net production remains ‘unutilized’ and finally it becomes part of the accumulating, sediments.
Fate of Energy beyond the Primary Consumers:
The herbivores are the primary consumers. In the Ceder Bog Lake the herbivores incorporate as much as 15 g cal/ cm2/yr. of energy. Of this the herbivores lose 4.5 g cal/cm2/yr. or 30% of energy due to metabolic activity. This leaves 10.5 g cal/cm2/yr. of energy available to the carnivores. But this energy is not utilized. It has been calculated that only 3 g cal/ cm2/yr. of the net production (NP) passes to the carnivores.
Again at the level of the carnivore about 60 per cent of the carnivores energy intake is consumed in metabolic activity and the rest 40 per cent becomes the part of the non-utilized sediments. Yearly loss due to decomposition is insignificant.
Nature of Energy Flow in an Autotroph based Ecosystem:
From the calculations made above in the Ceder Bog Lake energy flow several factors of importance emerge out.
These are:
(1) Energy flow is unidirectional:
The energy that is captured by the autotrophs does not go back to solar in put, that which passes on to the herbivores from the autotrophs does not pass back to the autotrophs and so on.
That means the energy progressively passes through different trophic levels in an one way road as the energy is in no case available to the previous trophic level. The danger that lies with any ecosystem is that the system would collapse if the primary energy source (solar radiations) was cut off.
(2) Progressive decrease in energy utilization at each trophic level:
There occurs a progressive decrease in energy at each trophic level. This is largely due to the fact that at each trophic level some energy dissipates as heat in the metabolic activity. The respiratory loss by the autotrophs is 21 %, by the herbivores is 30% and that in carnivores is 60%.