What is Ecosystem

The word ecosystem was first used in 1935 by A.G. Tansley (a British Botanist and Ecologist) to describe a basic unit of nature. Tansley coined the word as reduction of the term “Ecological system” to Ecosystem. According to him nature works as a system in which organisms and their communities are profoundly influenced by many non living environmental factors and vice versa.

Prior to Tansley many other ecologists had also worked onunderstanding the relationship between living things and their environment, using different terms like habitat, biome, ecological system etc.

Till the use of the term ecosystem, people were studying inter-relationships in nature in separate units either at small level like habitat or at a larger level as biome. Tansley was the first person to look at all these as a functional system. Thus all inter -relationships are studied as parts of the ecological system.

Interdependence among the biotic component

Relationship between biotic component

* What do the arrows in the figure indicate?
* Trace the path from grass to tiger. (You may trace out other paths as well).
* On how many organisms is rabbit dependent? Write their names.
* How many organisms depend on rabbit? Write their names

We know that there is a feeding relationship between plants and animals. Along with this we can see an interdependence between plants and animals for space, reproduction, shelter etc. as well.

*From where does plants get their food?
* Except food what other things do animals need for their survival?

We find that not only the biotic components show interdependence among themselves but also with the abiotic components like air, water, soil, etc.

All the organisms in an ecosystem derive energy from food to live. The sun is the main source of energy for all living things. Plants trap this energy through photosynthesis. Animals do not get energy directly from the sun. Many animals eat plants, which use sunlight to make food. Animals that do not eat plants still indirectly depend on the energy of sunlight as they eat other plant eaters. So energy from sunlight is transmitted to all living things.
When scientists describe the way energy moves through ecosystems, they used the term food chains. Now we have to know about food chain? A Food chain has three levels. At first level several plants, algae etc use sunlight to make their food and are called producers. At second level some animals eat plants and are called Herbivores.

At third level some other animals eat herbivores are called Carnivores. Herbivores and Carnivores are called as “Consumers”.

At every level there are organisms called Decomposers. They feed on wastes, debris of plants and animals or on their remains after they die. They decompose remnants and return nutrients to the soil, for plants to use, as the cycle begins again. Decomposers are also called recyclers

Changes in the ecosystem

Organisms affect their environments to meet their needs. Usually the changes they cause are small and help in keeping the ecosystem stable.
Some changes affect other organisms. As animals eat plants or other animals, they reduce the number of organisms in their habitat.
For example, there are many insects in a bird’s habitat. When a bird eats insects, it helps keep the number of insects from getting too large. This helps keep the bird’s habitat and the whole ecosystem healthy and stable. But when there are too many birds eating insects, they reduce the insect’s population quickly. In due course of time, there will not be enough food for the birds. In this situation some birds leave the area and few younger birds will be born. This brings the ecosystem back into balance.
Ecosystem can also change quickly; powerful storms, earth quakes, fire accidents, tsunami, etc can destroy ecosystems very quickly.
Humans are also instrumental in bringing about changes in ecosystem.