Structure of Ecosystem

Structure of Ecosystem:

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, distinct 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.

Trophic 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 form a food chain. Each step in the food chain represents a trophic level.

The plants represent the first trophic level, the herbivores make the second trophic level, the primary carnivores constitute the third trophic level, and the secondary carnivores, such as large fish, man, etc., constitute the fourth trophic 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.

Trophic structure may be described in terms of living material, called standing crop, found in different trophic 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 to biotic 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, phosphorus and calcium present in the soil at any given time, are called the standing state. The standing states of nutrients differ from one ecosystem to another, or with seasons even in the same ecosystem.