Odam declares the ecosystem to be the basic functional unit in ecology since it includes both the organic and inorganic parts of the biosphere; these influence each other and together provide the conditions necessary for the maintenance of life.
Ecosystems perform the following functions:
1. It allows flow of biological energy, i.e., control the rate of production and respiration of the community.
2. It controls the rate of nutrient cycles, i.e., production and consumption of miner
3. It regulates bath ways, i.e., the environment by organisms and the organisms' environment.
4. It allows circulation of chemical elements along characteristic paths from environment to organism and back to environment.
Chemical elements travel from the environment into the organisms and from the organism into the environment regularly and continuously. Autotrophs plants obtain a number of inorganic nutrients from the environment, which become components of organic matter. From autotrophs a nutrient goes to other living constituents and again in the environment with the help decomposers.
The cycling of materials between the organisms and the non-living environment varies widely in different ecosystems. Chemical elements are not uniformly distributed in the ecosystem. These are found to be present in compartments or pools.
Homeostasis means maintenance of relatively constant conditions either within organisms or within the ecosystem. Homeostasis is achieved by the biotic and abiotic components of the ecosystem.
The decomposition of organic matter by decomposers is an important factor in homeostasis. A delicate balance is also maintained in the natural ecosystems of the world due to constant cycling and recycling of materials.
Different ecosystems exchange biotic and abiotic materials. In an ecosystem, different components, linked together by a web of their dimensional and highly complex interrelation. The autotrophic component includes the autotrophs (green plant), which are capable of fixing the radiant energy of the sun and manufacturing the complex organic food materials from simple inorganic substances.
The plants provide oxygen, food and shelter to animals and animals supply carbon-dioxide to plants and help in dispersal and pollination. Different animals are further interrelated in the food web to becoming the food of another. When plant and animals die, their bodies are broken down by the decomposers and reused by plants.
Energy Flow in the Ecosystem
The behaviour of energy in an ecosystem can be termed energy flow due to one-way flow of energy. The energy used for all plants life processes is derived from solar radiations. The radiant energy of the sun is not uniformly distributed either in space or in time. It is estimated that green plants utilize about 0.02 per cent of the total visible light reaching the surface of the earth.
Much of the visible light coming from the sun is lost by reflection. A very small proportion of radiant energy is transformed into potential or food energy and retained in the plant tissue, 'locked in' with the inorganic elements absorbed by the roots to form new protoplasm. This potential chemical energy becomes the source of energy for herbivores and then carnivores.
The one-way flow of energy, in the communities of the ecosystem, brilliantly demonstrates the operation of the laws of thermodynamics in the living system.
The first law of thermodynamics states that energy can neither be created nor destroyed but it may be transformed from one type into another. The first law can be seen operational in the living systems when we study the energy flow.
The radiant energy of the sun is first converted into electrical energy of agitated electrons in the chlorophyll molecules.
This electrical energy is further converted into chemical energy by the synthesis of complex organic molecules and also by the synthesis of ATP molecules. Heterotrophs feed on the plants and thus the chemical energy flows into the heterotrophs.
The heterotrophs recover the energy stored in the chemical compounds during the final stages of the respiratory process and this recovered energy is stored in the terminal bond of ATP molecules. Heterotrophs feed on the plants and thus the chemical energy flows into the heterotrophs.
The heterotrophs recover the energy stored in the chemical compounds during the final stages of the respiratory process and this recovered energy is stored in the terminal bond of ATP molecules. When the terminal bond of ATP is broken down, the chemical energy will be converted.
The second law of thermodynamics states that during energy transformations a large part of energy is degraded into heat or dissipates.
A simplified energy flow diagram depicting three trophic levels (Boxes numbered 1,2,3) in a linear food chain, I total energy input: LA light absorbed by plant cover, PG gross primary production, A-total assimilation, PN-net primary production, P-secondary (consumer) production, NU-energy not used (stored or exported) NA-energy not assimilated by consumers (egested), R-respiration. Bottom line in the diagram shows the order of the magnitude of energy losses expected at major transfer points, starting with a solar input of 3,000 Kcal per square meter per day. This can be clearly illustrated in living systems by the study of the pyramid of energy.
There is decrease in the availability of energy from the lower to the higher trophic levels. This is due to considerable loss of energy in the form of heat during energy from one organism to another. Thus, energy flow and energy transformations in living systems strictly confirm to the first and second laws of thermodynamics.
Figure 9.4 presents a very simplified energy flow model of three trophic levels, from which it becomes evident that the energy flows from producers to herbivores and then to carnivores.
There is a successive reduction in energy flow whether we consider it in terms of total flow. Thus of the 3,000 kcal of total light falling upon the green plants, approximately 50 per cent (1500 kcal) is absorbed, of which only one percent (15 kcal.) is converted at first trophic level.
Thus, net primary production is merely 15 kcal. Secondary productivity (P2 and P3 in the diagram) tends to be about 10 per cent at successive consumer trophic levels, i.e., herbivores and the carnivores, although efficiency may be sometimes higher, as 20 per cent, at the carnivore level as shown (or P3 = 0.3 kcal.) in the diagram.