Ecosystem
Introduction
An ecosystem can be visualised as a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment
Ecosystem varies greatly in size from a small pond to a large forest or a sea
Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth
Since this system is too much big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely the terrestrial and the aquatic
Forest, grassland and desert are some examples of terrestrial ecosystems; pond, lake, wetland, river and estuary are some examples of aquatic ecosystems
Crop fields and an aquarium may also be considered as man-made ecosystems
We will first look at the structure of the ecosystem, in order to appreciate the input (productivity), transfer of energy (food chain/web, nutrient cycling) and the output (degradation and energy loss)
We will also look at the relationships – cycles, chains, webs – that are created as a result of these energy flows within the system and their inter- relationship
Ecosystem–Structure and Function
In earlier classes, you have looked at the various components of the environment- abiotic and biotic
You studied how the individual biotic and abiotic factors affected each other and their surrounding
Let us look at these components in a more integrated manner and see how the flow of energy takes place within these components of the ecosystem
Interaction of biotic and abiotic components result in a physical structure that is characteristic for each type of ecosystem
Identification and enumeration of plant and animal species of an ecosystem gives its species composition
Vertical distribution of different species occupying different levels is called stratification
For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers
(ii) Decomposition;
(iii) Energy flow; and
(iv) Nutrient cycling
To understand the ethos of an aquatic ecosystem let us take a small pond as an example
This is fairly a self-sustainable unit and rather simple example that explain even the complex interactions that exist in an aquatic ecosystem
A pond is a shallow water body in which all the above mentioned four basic components of an ecosystem are well exhibited
The abiotic component is the water with all the dissolved inorganic and organic substances and the rich soil deposit at the bottom of the pond
The solar input, the cycle of temperature, day-length and other climatic conditions regulate the rate of function of the entire pond
The autotrophic components include the phytoplankton, some algae and the floating, submerged and marginal plants found at the edges
The consumers are represented by the zooplankton, the free swimming and bottom dwelling forms
The decomposers are the fungi, bacteria and flagellates especially abundant in the bottom of the pond