The interaction of the food chain phenomena (energy loss at each transfer) and the size metabolism relationship results in communities having a definite trophic structure, which is often characteristics of a particular type of ecosystem (lake, forest, coral reef, pasture etc.). The trophic structure may be measured and described either in terms of the standing crop per unit area or in terms of fixed per unit area per time at successive trophic levels. Trophic structure and also trophic function may be shown graphically by means of ecological pyramids in which the first of producer level forms the base and successive levels the tiers which make up the apex.
Actually, the pyramids of number do not give the actual picture of the food chain as they aren’t very functional. They do not indicate the relative effect of the geometry, food chain and size factors of the organisms. They generally vary with different communities with different types of a food chain in the same environment. It becomes sometimes very difficult to represent the whole community on the same numerical scale.
They are comparatively more fundamental, as they instead of a geometric factor, shows qualitative relationships of the standing crops. These pyramids of biomass in different types of the ecosystem are shown below. In grassland and forests, there is generally a decrease in biomass of organisms at successive levels from the producers to the carnivores. The pyramids are upright, however in ponds, the producers are small organisms, their biomass is least and this value gradually shows an increase towards the apex of the pyramid, thus, made the pyramids inverted.
There are the three types of ecological pyramids, the pyramids of energy give the best picture of overall nature of the ecosystem. Here, number and weight of organisms at any level depends not on the amount of fix energy any one time in the level just below but rather on the rate at which food is being produced. The pyramid of energy is a picture of the rates of passage of food mass through the food chain. In shape, it is always a gradual decrease in the energy content at successive tropics levels from the producer to various consumers.
The species structure includes not only the number and kinds of species but also diversity of species i.e. the relation between species number and individuals or biomass and the dispersion/spatial arrangement of individual of each species present in the community.
The structure and function of an ecosystem can be seen as the maintenance of the flow of minerals and energy from biotic (living) and abiotic (non-living) components in a self-sufficient system. Nutrient cycles flow closely parallel the routes of energy flow in case of biotic (living) components while differs in abiotic (non-living) components but differ in being conservation, that is, nutrient cycles are concentrated in chemical elements being drawn from finite pools being largely within the ecosystem. The mineral elements taken up from the environment (soil, rock or atmosphere) by the green plants (also microbes) are again returned to the environment. In this taking and returning process of minerals, there involves a number of organisms as well as some physiochemical phenomena that make together as an orderly operating cycle. Thus, the movement (export and import) of minerals is accomplished by the operation of different chemical cycles that keep on passing the materials back and forth between organism and in their environment.
The life on earth depends on the availability of the energy, circulation of elements which the organisms require for their growth and development. There are two types of nutrients: a) macronutrients and b) micronutrients.
Macronutrients include elements and their compounds that play a key role in the protoplasm and are required in larger quantities such as carbon, nitrogen, oxygen, potassium, calcium, magnesium etc.
The micronutrients and their compounds are required in all small quantities. For example; iron, zinc, copper, molybdenum, boron etc. If they are in excess, may cause harmful effects in plants.
The nutrient flow has a specific pattern. The flow is from non-living (abiotic) to living (biotic) and back to the non-living in more or less circular path called biogeochemical cycle. Thus, cycles are of two types; gaseous type and sedimentary type.
Sedimentary cycle usually involves two phases
The important role in mineral cycling is played at one end by green plants which take up the materials and the other end by decomposers which release the materials for reuse. Air and water play an important role in cycles. The whole chain of life depends on “continuous, fixation and never ending cycling of materials to and through the ecosystem and transfer of energy.
E.p., Odum. Fundamentals of Ecology. USA: W.B Saunters Company, n.d.
Jr., Miller G.T. Living in the Environment. Belmont, California,USA: Wadsworth Publishing Company, 2003.