Pond illustrates a small functional ecosystem that is easy to understand. Pond is a place where different plants and animals that are adapted to aquatic environment live. It is also a self -sufficient and self - regulating system, although many ponds dry out occassionally in years of drought or regularly every dry season.
Like all other ecosystems, it has an abiotic and a biotic component and the latter has producers, consumers and decomposers.
If includes water, air, elements, organic compounds of various types. These are mostly in utilizable form. Some of the matters are there which arc not in unavailable form while much of them are in the living organisms occurring there. This component also includes solar radiation falling on the surface of the pond.
These are the algae and other green plants leave growing in the pond. The plants are either rooted to the soil or are found floating in water (phytoplanktons). All these plants produce food through photosynthesis and are responsible for basic food supply to the pond.
Some of the common algal species found floating in pond water are Zygncma, Ulothrix, Spirogyra, Oedogonium, Diatoms, Anabaena.
The aquatic macrophytic populations arc of Typha, Saggitaria, Hydrilla, Vallisnaria, Nelumbo, Eichhornia, Pistia, Azolla, Wolffia, Lcmna etc.
These are largely herbivores feeding directly the plants growing there these are primary consumers, which are divided into Benthos (including insects, crustaceans, mites, fishes, mollusks etc.) and Zooplanktons (including protozoans like Kuglena, rotifers like lirachionus and crustaceans like Cyclops etc.)
The primary consumers are food for another set of organisms, together called as "secondary consumers" e.g. big fish feeding on small fish, beetles feeding upon zooplanktons etc. There may be yet another group constituling "tertiary consumers" which feed on the secondary consumers,
These are, of course, heterotrophs. Majority of them are saprophytes feeding on dead organic matter which they absorb in solution or ingest in very small pieces. The decomposers help release of basic materials for reuse. Important species functioning as decomposers are members of the group of bacteria, fungi or prokaryotes.
Generally speaking the upper layer of a pond is "Productive Zone" of plants and the bottom layer is a "Detritus Zone" of decomposers and these two zones together constitute a balanced ecosystem.