Structure and Function of Ecosystem
Structure:
As described earlier, biotic and abiotic components are physically organised to provide a characteristic structure of the ecosystem. Important structural features are:
i) Species composition and ii) Stratification
For example, some ecosystems, such as tropical rain forests, show a canopy of tall plants and a large number of biological species. On the other hand, a desert ecosystem shows a low discontinuous layer of herbs or small shrubs which consist of less number of species and extensive bare patches of soil.
In the forest, tallest trees, influence the under storey plants and ground vegetation. The plants form more or less, district strata or storeys on vertical as well as in horizontal planes, which is characteristically known as stratification. The individuals of different layers represent different species of plants.
Tropic levels: There is another way to depict the structure of ecosystem through food relationships of producers and consumers. Trophic or food structure of ecosystem is based on the existence of several trophic levels.
The energy in a community is passed from one organism to another in feeding patterns. These patterns of energy transference together from a food chain. Each step in the food chain represents a trophic level. The plants represent the first tropic level, the herbivores make the second tropic level, the primary carnivore constitute the third tropical level, and the secondary carnivores, such as large fish, man, etc., constitute the fourth tropic level of an ecosystem. Thus energy from the sun enters the living world through photosynthetic organisms and passes open from one organism to another in the form of food.
Tropic structure may be described in terms of living material, called standing crop, found in different tropic levels at a given time. The standing crop is commonly expressed as the biomass of organisms per unit area. The biomass is defined as the total weight of dry matter(dry weight) present in the ecosystem at any one time.
Nutrients are required for the proper growth and development of living organisms. They flow from abiotic components and back to the non-living component again in a more or less cyclic manner. This is known as biogeochemical cycle or inorganic-organic cycle. The amounts of nutrients, such as nitrogen, phosphorous and calcium present in the soil at any given time, is called the standing state. The standing states of nutrients differ from one ecosystem to another, or with seasons even in the same ecosystem.
Functions of ecosystem
An ecosystem is a discrete structural, functional and life sustaining environmental system. The environmental system consist of biotic and abiotic components in a habitat. The synthesis and perpetuation processes involves energy exchange and this energy comes from the sun in the form of light or solar energy. Thus, in any ecosystem, there are three functional components:
i) Inorganic constituents(i,e, air,water and minerals)
ii) Organisms(i,e., plants, animals and microbes), and
iii) Energy input which enters from outside(i,e., sun).
These three interact and form an environmental system. Inorganic constituents are synthesized into organic structures by the green plants through photosynthesis and solar energy is utilized in the process. Green plants become the source of energy of renewals(herbivores) which, in turn become source of energy for the flesh eating animals. Animals, all types grow and add organic matter to their body weight and their source of energy is complex organic compound taken as food. They are known as secondary producers. All the living organisms, whether plants or animals in an ecosystem have a definite life span after which they die.
The dead organic remains of plants and animals provide food for saprophytic microbes, such as bacteria, fungi, and many other animals. The saprobes ultimately decompose the organic structure and break the complex molecules and liberate the inorganic compounds into their environment. These organisms are known as decomposers.
During the process of decomposition of organic molecules the energy which kept the inorganic components bound together in the form of organic molecules gets liberated into the environment as heat energy. Thus, in an ecosystem energy from the sun, the input is fixed by the plants and transferred to animal components.
The ecosystem operating in different habitats, such as deserts, forests,grasslands and seas are independent on one another. The energy and nutrients of one way find their way into another, so that, ultimately all parts of the earth are interrelated, each comprising a part of the total system that keeps the biosphere functioning.
i) Reception of radiant energy sun.
ii) Manufacture of organic materials from inorganic ones by producers.
iii) Consumption of producers by consumers and further elaboration of consumed materials
iv) After the death of producers and consumers, complex organic compounds are degraded and finally converted by decomposers and converters into such forms as are suitable for re utilization by producers