The word ‘ecology’ can simply be defined as the study of plants and animals in relation to their environment. Ecology is derived from a Greek word Oikos which means home or a dwelling place. In other words, ecology can be defined as a field of study which deals with the relationship of living organisms with one another and with the environment in which they live. Ecology is often described as environmental biology.

Ecology is divided in two main branches:

Autecology: Autecology is concerned with the study of an individual organism or a single species of organism and its environment. For example, the study of a single rat and its environment.

Synecology: Synecology is concerned with the study of the inter-relationships between groups of organisms or species of organisms living together in an area. For example, the study of different organisms in a river in relation to their aquatic environment.


There are some important concepts commonly used in the study of ecology which enable one to understand the subject matter. Some of these ecological concepts include:

Atmosphere: The atmosphere is the gaseous portion of the earth. It is a layer of gases surrounding the earth. Over 99% of the atmosphere lies within 30km of the earth surface. It contains 0.03% carbon dioxide, 78% nitrogen, 21% oxygen and 0.97% rare or inert gases.

Biosphere or Ecosphere: The biosphere or ecosphere is the zone of the earth occupied by living organisms. It is a layer of life which exists on the earth surface. The biosphere is a narrow zone where complex biological and chemical activities occur. It can be found on air, land, soil and water. It provides habitat for organisms like animals, micro-organisms and plants.

Biotic Community or Biome: A biotic community is any naturally occurring group of different organisms living together and interacting in the same environment. A biome is the largest community of organisms, e.g. rain forest and Guinea savanna.

Ecological Niche: Ecological niche refers to the specific portion of a habitat which is occupied by a particular species or organism. Every organism is adapted to a specific place, and plays a role in that community e.g. it feeds on some organisms/serve as food for others, it derives/ obtains nutrients from its habitat/ returns nutrient to its habitat, it is either a producer or a consumer. The sum total of all these roles for any given organism is referred to as ecological niche. For example, a caterpillar and an aphid which live on the same plant can occupy different positions or ecological niches on the plant. The caterpillar lives mainly on the leaves and feeds on them while the Aphid lives on the young shoot and sucks sap from it. Although both organisms live on the same habitat, each has its own living space and source of food.

Ecosystem: It’s a natural unit, made up of living organisms and their non-living components interacting together to produce a stable system. An ecosystem refers to a community of plants and animals functioning together with their non-living environment. In other words, ecosystem consists of the living factors (plants and animals) interacting with the non-living factors in an environment.

Community: This refers to a group of plants and animals that occupy a given area and are adaptable to the conditions of their environment. They are interdependent, i.e. depend on one another and can continue to live successfully and reproduce new offspring.

Climax Community: Climax community is established when a stable or unchanging community is attained in ecological succession. The community is in equilibrium with the environment. The vegetation reaches its highest development. The same species of animals, plants or organisms re-occur from year to year.

Environment: The environment includes all the factors external and internal, living and non-living factors which affects an organism.

Habitat: Habitat is defined as a place or home within an environment where an organism naturally lives or dwells. Habitat is also defined as an area occupied by a biotic community. In other words, habitat is any environment in which an organism lives naturally. It is the natural home of an organism. For example, the habitat of the fish is water.

The various types of aquatic habitat (i.e. live in water) such as lagoons, lakes, oceans, ponds, rivers, seas, streams and terrestrial habitat (live on land) e.g. desert, forest and savanna.

Every habitat is affected by some environmental factor(s)/ biotic and abiotic factors.

Habitat may be terrestrial e.g. desert/ grassland/ Savanna/ Tropical rain forest/ any suitable example, or aquatic, e.g. arboreal trunks/ lake pond/ leaf surface/ ocean/ or any suitable example.

Hydrosphere: Hydrosphere is the liquid or aquatic part of the earth or living world. It covers 70% of the earth crust. It holds water in various forms – gases (water vapour), liquid (water) and as solid (ice). Examples of hydrosphere are lake, oasis, ocean or sea, ponds, pools, rivers, spring and streams.

Lithosphere: The lithosphere is the solid portion of the earth. It is the outermost layer or zone of the earth crust. It is made up of rocks and mineral materials, and it also represents 30% of the earth surface. The outermost layer of the landmass is made up of loose rock materials like soil, sand and gravel. Lithosphere forms the basis of all human settlement.

Population: Population is defined as the total number of organisms of the same species living together in a given area at a given time. For example, the total number of tilapia fish in a pond constitutes the population of Tilapia fish in that habitat. 


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