The stratification of a lake can be studied in three zones as follows:

i.The littoral zone and sublittoral zone are the shallow water zone which is penetrated by light. It usually extends about 10 meters downwards. This zone includes plants which are rooted at the bottom but some of them grow above the surface of water. The plants included in this zone are Nymphaea, Hydrilla, Chara, Vallisneria etc. Many unicellular algae like diatoms and Nitella are also seen in this zone. The fauna supported by the plant community of this zone induces fish, frogs, larvae, some bivalves, snails etc.

ii. The limnetic zone : This is the open water zone or surface water area . It is well illuminated and supports floating forms like leaves of rooted plants of the littoral zone, with plankton, nekton and other free floating organisms which are plankton feeders. For example, blue algae, blue-green algae, some protozoans, diatoms, Pistia, Eichhornia and other animals like Cyclops, daphnia, larvae of insects and plankton and nekton eating small fish.

iii. The profundal zone : This is the bottom of a lake where light does not reach. This zone includes consumers and decomposers but not producers. It includes animals like tapeworms, sponges, some clams. Since it contains the dead bodies of plants and animals it has an abundance of decomposers i.e. bacteria and fungi. A few fish also visit this area for eating detritus.

Ponds and lakes in particular show a number of abiotic components like minerals and salts dissolved in water and in the bottom mud and soil. It also shows biotic communities like.

1. Producers, like phytoplanktons, algae, floating plants, and   rooted submerged plants.

2. Herbivores , like larvae of insects and omnivores like frogs.

3. Primary consumers , like zooplankton, snails, worms and crustaceans.

4. Secondary consumers, like aquatic insects, small fishes frogs etc.

5. Tertiary consumers, like large fishes, carnivorous birds which feed on small fishes.

Besides these, there are number of parasites and saprophytes as well as decomposers like fungi and bacteria in this ecosystem.

Communities of a forest: A forest is a large tract of land covered chiefly with trees and undergrowth. The green earth is blanketed with forest wherever there is sufficient moisture and suitable temperature for trees to grow.

A deciduous forest is a biome of abundant rainfall, moderate temperature with warm summers and cold winters, and humid, with rain. The vegetation consists of deciduous trees like oak, elms, and walnut along with low underbushes, vines and scattered evergreen trees. The characteristic animals are deer, fox, bear, flying squirrel, wild cat, small birds, snakes and amphibians. Many insects and other invertebrates are also found taking shelter in decaying logs.

A tropical rain forest is a biome of much rain and constant humidity. There are many species of evergreen trees with large broad foliage leaves continuously growing all the year round. Because the floor is overshadowed by trees it is exceedingly humid and dark and populated by plants requiring minimum light. The characteristic animals are monkeys, amphibians, insects, snails, leeches, scorpions, reptiles and birds.