Stability and Structure of Ecosystem!
An organism cannot live in isolation. It needs other organisms, nutrients from its environment, and so on, to survive.
So, nature has provided functional units in which different organisms of a given area can live and interact among themselves and with their surroundings.
An ecosystem is a functional unit consisting of all the living beings of an area and the non-living components of their environment, interacting to form a stable system.
There are different kinds of ecosystems. They can be natural ecosystems such as deserts, grasslands, forests and lakes, or man-made ecosystems such as gardens, aquariums and crop fields. An ecosystem may be as small as an aquarium or as big as an ocean.
A pond is an example of an aquatic ecosystem. All the algae, plants, insects, microorganisms and fish in the pond, and the water and soil of the pond are part of this ecosystem.
The organisms of the pond get everything they need from the pond itself. And they help to keep its water and soil in good condition, replenishing the nutrients they take from them. This makes the ecosystem self-sustaining.
Now let us look at the ecosystem of a garden. In a garden you will find different plants and animals such as bees, butterflies, earthworms, frogs and birds. They depend on each other and on the non-living things like the soil, air and water.
For example, the earthworm gets nutrition from the soil. In turn, they keep the soil fertile. So do certain kinds of bacteria living in the soil. Birds, bees and butterflies get food from the plants in the garden. They help to keep the ecosystem working by helping in the pollination of the plants.
Stability in Ecosystems:
All ecosystems are stable systems. This means that they maintain a natural balance. An ecosystem involves the flows of nutrients and energy (in the form of food). If the organisms Having in an ecosystem use up nutrients, like nitrogen, from their environment, without replenishing them, soon the system will collapse.
However, a balance is maintained between the availability and use of nutrients by recycling them through natural processes. You already know how things like nitrogen and carbon are recycled in nature. A balance is also required to provide different amounts of energy (from food) needed by different organisms.
As we shall see, the numbers of different organisms in an ecosystem are balanced in such a way that each organism gets the required amount of food. For example, in a forest ecosystem, the numbers of the prey (like rabbits) are always more than the numbers of the predator (like foxes), to ensure adequate food for the predator.
Structure of an Ecosystem:
An ecosystem consists of two components-the abiotic component the biotic component (living component).
The abiotic, or nonliving, component consists of the physical environment, nutrients and climatic factors.
The physical environment consists of soil, water and air. Inorganic substances such as carbon dioxide, oxygen, nitrogen, water, phosphorus, sulphur, sodium, potassium and calcium constitute nutrients. Things like sunlight, rainfall, temperature, humidity and atmospheric pressure constitute the climatic factors.
The biotic, or living, component of an ecosystem can be classified on the basis of how the organisms get their food, i.e., whether they are producers, consumers or decomposers.
Producers Organisms which make their own food are called producers:
They are also called autotrophs. (In Greek, autos = self, trophe = nutrition.) All green plants and certain blue-green algae act as food producers in ecosystems.
Consumers Organisms that depend on other organisms for food are called consumers or Heterotrophs:
(In Greek, heteros = other.) All animals which eat plants or other animals are consumers. Bacteria and fungi that depend on dead plants and animals for food are also in a way consumers.
Consumers can be classified as herbivores, carnivores and omnivores. Herbivores eat only plants and plant products. Cows, deer and rabbits are herbivores. Carnivores eat only the flesh of other animals. Tigers, snakes and hawks are carnivores. Omnivores eat plants as well as the flesh of other animals. Man and crow are examples of omnivores.
Sometimes it is useful to classify the consumers in an ecosystem on the basis of ‘who eats whom’. Primary consumers are those who feed directly on the producers (plants). In other words, herbivores are primary consumers. Carnivores who feed on plant-eating animals (herbivores) are secondary consumers.
For example, a grasshopper that feeds on plants is a primary consumer, and the frog that eats the grasshopper is a secondary consumer. The frog could be eaten by a larger carnivore like a snake. A carnivore that feeds on smaller carnivores is called a tertiary consumer. This consumer may be eaten by the largest carnivore, or the top carnivore, of the ecosystem.
The top carnivore is not killed and eaten by other animals of the ecosystem. The top carnivore belongs to a higher order of consumers. For example, a hawk could be the top carnivore of an ecosystem. Other examples of top carnivores are tigers and lions. (Primary, secondary and tertiary consumers are also called consumers of the first, second and third order respectively.)
Decomposers Organisms which feed on dead plants and animals are called decomposers:
Decomposers are also called saprotrophs or saprophytes (in Greek, sapros = rotten). They include bacteria, fungi and worms. Decomposers break down (decompose) the compounds present in dead plants and animals into simpler substances and obtain nutrition from them.
The substances formed in decomposition are released into the soil and the atmosphere. Thus, decomposers play an important role in the recycling of materials, replenishment of the soil’s nutrients, etc. They also clean up our surroundings by decomposing dead organisms and wastes from animals and plants.
Take a large glass bowl or jar and put some soil and aquatic plants in it. Fill three-fourths of the bowl with water and place it near a window through which sunlight comes in. Put some fish in the bowl. You will need to put some fish food in the bowl from time to time. The oxygen needed by the fish will be liberated by the aquatic plants through photosynthesis.
After a few days the water in your aquarium will become dirty. This is because of the waste generated by the fish and the plants. We do not need to clean natural aquatic ecosystems like ponds and lakes. In these, wastes are consumed by decomposers.