Biotic community refers to populations of various kinds of organisms living together and sharing the same habitat. An ecosystem houses several biotic communities which interact with each other.
For example, populations of different kinds of birds, insects and many other animals on a tree, living in the same environment, mutually sustaining and interdependent. This assembly of different organisms constitutes a biotic community.
Depending on the mode of nutrition, members of a biotic community are categorised into autotrophs, heterotrophs and saprotrophs.
Auto: self; trophos: feeder
All plants (except for a few parasitic plants) can manufacture their own food by the process of photosynthesis. There are certain organisms that do not utilize sunlight yet can manufacture their food by the process of chemosynthesis. Certain bacteria belong to this category.
Since the plants provide food to all the animals directly or indirectly they are also called producers. Autotrophs form the basis of any biotic system as they trap solar energy to manufacture food for all.
In terrestrial ecosystems, the autotrophs are mainly the rooted plants while in aquatic ecosystem, floating plants called phytoplankton and shallow water rooted plants called macrophytes are the examples of autotrophs.
Heteros: other; trophs: feeder
Heterotrophs are called consumers which feed on plants and animals. Consumers include herbivores (that eat plant material) and carnivores (which eat other animals).
Sapros: rotten; trophos: feeder
Saprotrophs, also called decomposers, feed on dead and decaying matter. They break down the complex organic compounds of dead plants and animals into simpler forms and return them back into the environment. Decomposers form an important link between the living and non-living component of the ecosystem. Some bacteria and fungi belong to this category.
Pond is a good example of an ecosystem to understand the concept of abiotic and biotic components and their relationship. A pond has three different layers: top, middle and bottom. All the three layers differ greatly from each other in terms of temperature, light conditions, oxygen content and other factors that affect the lives of the biotic components living in it. The temperature of the water at the top is different from its deeper layers.
Water, dissolved oxygen, carbon dioxide, minerals, soil and stones are the abiotic components. A natural pond also has thousands of different species of plants and animals living together. Some are microscopic, that are too small to be seen with the naked eye while some others are macroscopic. These constitute the biotic component.
Greater the number of species present in the pond, the stronger and healthier it is. Here, living things are born, they live, breathe, feed, excrete, move, grow, reproduce, become food for others and die within the pond.