Ocean as an Ecosystem:
The oceans constitute nearly 70 per cent of the earth’s surface. The sea has unusual stability in temperature, salinity and gaseous content.
The upper portion of the oceanic region through which light penetrates is called euphotic zone.
The region of the ocean below the euphotic zone (below 200 metres) is called benthal. It is also known as aphotic zone. This zone is completely fee of photosynthetic organisms.
Thus, different sets of environmental conditions are present in different zones of the ocean and each zone has its own peculiar life form. Planktonic organisms are algae, diatoms, protozoa, small crustaceans and their eggs. The seashore organisms live under variable physical conditions and they are constantly under the impact of waves. Most of them are covered and exposed twice daily by the rise and fall of the tides.
Streams and Rivers:
In the rivers and streams or in the shallow water, the velocity of current is fast to keep the bottom clear. Filamentous algae and fishes are common examples of producers and consumers respectively. In the zone of deep water the velocity of water current is reduced and silt and other loose materials tend to settle at the bottom.
Wet Lands:
These are marshes and swamps which are low lying wet lands and their ecosystems are suitable for ducks and other semi-aquatic animals. Swamps also support large trees and shrubs. They have various types of environmental conditions, both aquatic and semi-aquatic. Aquatic insects, reptiles and birds are common in such regions.
Forest as an Ecosystem:
Forest ecosystem is the best example of a terrestrial ecosystem.
Like other ecosystems, there are two main components of forest ecosystem:
(A) Abiotic component
(B) Biotic component.
(A) Abiotic component:
In a forest ecosystem soil, moisture, air and sunlight form the abiotic or physical component.
(B) Biotic component:
There are three important classes of biotic components:
1. Producers
2. Consumers
3. Decomposers and transformers.
1. Producers:
All the green plants of a forest are producers. They are the main sources of food for all the animals. There are several layers of vegetation in the forest. The plants of top stratum are angiospermous and gymnospermous trees. These plants utilize radiant energy of sun to the greatest extent. Below the level of trees there is layer of shrubs which consume light energy of low intensity coming through trees. Just below the shrubs there are grasses, herbs, lichens and mosses. These also manufacture food. These plants get least light.
2. Consumers:
There are a number of consumers in an old dense forest. Consumers of first order in the forest are grasshoppers, rabbit, deer, monkey, birds and many other wild herbivorous animals which utilize plants directly as their food. Secondary consumers are wolves, pythons, and jackals etc. which consume the flesh of herbivores. Lion, tiger, hawks are the consumers of top level.
3. Decomposers and transformers:
These are micro-organisms, chiefly bacteria and fungi which attack dead bodies of producers and consumers and convert complex organic compounds into simpler inorganic compounds and elements. These free elements again return to the abiotic component and are reutilized by producers in their nutrition.
Artificial Ecosystems:
Gardens, parks, vegetable gardens and agricultural lands are the artificial or man-made ecosystems. A balanced aquarium is also an artificial ecosystem. The space capsule which lasts for limited period is also an artificial ecosystem. For longer journey the spacecraft includes all the basic components of the ecosystem, namely, producers, consumers, decomposers and abiotic components.