In this article, I want to walk you through Levels of organization in ecology for UPSC.

Levels of organization in ecology

Ecology is a science that studies the interdependent, mutually reactive and interconnected relationship between the organisms and their physical environment on the one hand and among the organisms on the other hand.

Ecology not only deals with the study of the relationship of individual organisms with their environment, but also with the study of populations, communities, ecosystems, biomes, and biosphere as a whole.

The main levels of organization in ecology are six and are as follows.

  1. Individual
  2. Population
  3. community
  4. Ecosystem
  5. Biome
  6. Biosphere
Levels of organization in ecology


The organism is an individual living being that has the ability to act or function independently. It may be a plant, animal, bacterium, fungi, etc.


A population is a group of organisms usually of the same species, occupying a defined area during a specific time.

The main limiting factors for the growth of a population are abiotic and biotic components.


In ecology, the term community, or more appropriately ‘biotic community, refers to the populations of different kinds of organisms living together and sharing the same habitat.

The characteristic pattern of the community is termed as the structure of the community and is determined by:

  • the roles played by its various populations
  • the range of its various populations
  • the type of area that is inhabited by the populations of the community
  • the diversity of species in the community
  • the interactions between various populations of the community inhabiting the area.

Members of a community also actively interact with their environment. In a community, only those plants and animals survive which are adapted to a particular environment. The climate determines the type of environment, hence, the type of organisms in a community.

For example, it is the climate of the area which determines whether a given area becomes a desert or a forest.

Communities created by human such as lawns or crop communities are such man-made communication are crop communities are relatively simple and consists of only one species as opposed to a natural community characterized by a large number of species.

Man-made communities are very unstable and require a great deal of care and constant manipulation and maintenance.

Types of Community

On the basis of size and degree of relative independence communities may be divided into two types:

Major Community:

These are large-sized, well organized and relatively independent. They depend only on the
sun’s energy from outside and are independent of the inputs and outputs from adjacent

Example: tropical evergreen forest in the North-East.

Minor Communities:

These are dependent on neighboring communities and are often called societies. They are secondary aggregations within a major community and are not therefore completely independent units as far as energy and nutrient dynamics are concerned.
Example: A mat of lichen on a cow dung pad.


An ecosystem is defined as a structural and functional unit of biosphere consisting of a community of living beings and the physical environment, both interacting and exchanging materials between them.

The term ‘ecosystem ‘was coined by A.G. Tansley in 1935. An ecosystem is a functional unit of nature encompassing complex interaction between its biotic (living) and abiotic (nonliving) components. For example- a pond is a good example of an ecosystem.

Ecosystems vary greatly in size and elements, but each is a functioning unit of nature. Everything that lives in an ecosystem· is dependent on the other species and elements that are also part of that ecological community. If one part of an ecosystem is damaged or disappears, it has an impact on everything else. The ecosystem can be as small as a single tree or as large as the entire forest.

Components of an Ecosystem

They are broadly grouped into: 

  1. Abiotic components
  2. Biotic components
Abiotic Components (Nonliving):

The abiotic component can be grouped into the following three categories:

  1. Physical factors: Sunlight, temperature, rainfall, humidity, and pressure. They sustain and limit the growth of organisms in an ecosystem.
  2. Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulfur, water, rock, soil, and other minerals.
  3. Organic compounds: Carbohydrates, proteins, lipids, and humic substances. They are the building blocks of living systems and therefore, make a link between the biotic and abiotic components.
Biotic Components (Living):
  1. Autotrophs/Producers: The green plants manufacture food for the entire ecosystem through the process of photosynthesis. Green plants are called autotrophs, as they absorb water and nutrients from the soil, carbon dioxide from the air, and capture solar energy for this process.
  2. Consumers: They are called heterotrophs and they consume food synthesized by the autotrophs. Based on food preferences they can be grouped into three broad categories. Herbivores (e.g. cow, deer, and rabbit, etc.) feed directly on plants, carnivores are animals that eat other animals (e.g. lion, cat, dog, etc.) and omnivores organisms feeding upon both plants and animals e.g. human, pigs and sparrow.
  3. Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that feed on dead decomposed and the dead organic matter of plants and animals by secreting enzymes outside their body on the decaying matter. They play a very important role in the recycling of nutrients. They are also called detrivores or detritus feeders.
Functions of an Ecosystem

Ecosystems are complex dynamic systems. They perform certain functions. These are:

  • Energy flow through the food chain
  • Nutrient cycling (biogeochemical cycles)
  • Ecological succession or ecosystem development
  • Homeostasis (or cybernetic) or feedback control mechanisms

Ponds, lakes, meadows, marshlands, grasslands, deserts and forests are examples of the natural ecosystems. Many of you have seen an aquarium; a garden or a lawn etc. in your neighborhood. These are a man-made ecosystem.

Types of Ecosystems

Ecosystems are classified as follows:

  1. Natural ecosystems
  2. Manmade ecosystems
Natural ecosystems:

Totally dependent on solar radiation e.g. forests, grasslands, oceans, lakes, rivers, and deserts. They provide food, fuel, fodder, and medicines.

Ecosystems are dependent on solar radiation and energy subsidies (alternative sources) such as wind rain and tides. e.g. tropical rain forests, tidal estuaries, and coral reefs.

Man-made ecosystems:
  • Dependent on solar energy. e.g.- agricultural fields and aquaculture ponds.
  • Dependent on fossil fuel e.g. urban and industrial ecosystems.
Productivity of ecosystems

The rate of biomass production is called productivity. The portion of fixed energy, a trophic level passes on to the next trophic level is called production.

Productivity in ecosystems is of two kinds, i.e., primary and secondary.

Green plants fix solar energy and accumulate it in organic forms as chemical energy. As this is the first and
the basic form of energy storage, the rate at which the energy accumulates in the green plants or producers is known as primary productivity.

Productivity is a rate function and is expressed in terms of dry matter produced or energy captured per unit area of land, per unit time.

It is more often expressed as energy in calories/cm2/yr or dry organic matter in g/m2/yr (g/m2 x 8.92 = lb/acre). Hence, the productivity of different ecosystems can be easily compared.

Primary productivity is measured in two ways: Gross Primary Productivity and Net Primary Productivity.

The total solar energy trapped in the food material by photosynthesis is referred to as gross primary productivity (GPP).

However, a good fraction of gross primary productivity is utilized in the respiration of green plants. The amount of energy-bound organic matter created per unit area and time that is left after respiration is net primary productivity (NPP).

Net productivity of energy = Gross productivity — Energy lost in respiration.

The rates at which the heterotrophic organisms re-synthesize the energy-yielding substances are called secondary productivity. Here, the net primary productivity (NPP) results in the accumulation of plant biomass, which serves the food of herbivores and decomposers.

It is notable that the food of consumers has been produced by the primary producers, and secondary productivity depicts only the utilization of this food for the production of consumer biomass. Secondary productivity is the productivity of animals and saprobes in the ecosystem.

Environmental Factors Affecting Productivity in the Ecosystem:

  1. Solar radiation and temperature.
  2. Moisture, i.e., leaf water potential, soil moisture, fluctuation of precipitation, and transpiration.
  3. Mineral nutrition, i.e., uptake of minerals from the soil, rhizosphere effects, fire effects, salinity, heavy metals, and nitrogen metabolism.
  4. Biotic activities, i.e., grazing, above-ground herbivores, below ground herbivores, predators and parasites and diseases of primary producers.
  5. Impact of human populations, i.e., populations of different sorts, ionizing radiations, such as atomic explosions, etc.
  6. In aquatic systems, productivity is generally limited by light, which decreases with increasing water depth. In deep oceans, nutrients often become limiting for productivity. Nitrogen is the most important nutrient limiting productivity in marine ecosystems.

The largeness of primary productivity depends on the photosynthetic capacity of producers and the existing environmental conditions, such as solar radiation, temperature, and soil moisture. In tropical conditions, primary productivity may remain continuous throughout the year, provided adequate soil moisture remains available.

While in temperate regions, primary productivity is limited by the cold climate and a short snow-free growing period during the year.

Classification of Natural Ecosystem
  1. Terrestrial
    • Forest
    • Grasslands
    • Deserts
  2. Aquatic
    • Fresh Waters
    • Saline Waters
    • Marine Waters
Goods and Services provided by ecosystems include:
  • Purification of air and water
  • Mitigation of floods and droughts
  • Detoxification and decomposition of wastes
  • Generation and renewal of soil and natural vegetation
  • Pollination of crops and natural vegetation
  • Control of the vast majority of potential agricultural pests
  • Dispersal of seeds and translocation of nutrients
  • Maintenance of biodiversity
  • Protection from the sun’s harmful ultraviolet rays
  • Partial stabilization of climate
  • Moderation of temperature extremes and the force of winds and waves
  • Support of diverse human culture
  • Providing aesthetic beauty and intellectual stimulation that lift the human spirit.

Threats to Ecological Goods and Services-

Because of their importance, it is extremely important to reduce the threat of irreversible damage to our ecological systems caused by:

  • Land-use change and irreversible conversion of landscapes and their ecological functions.
  • Disruption of bio-geochemical cycles i.e. nitrogen, carbon, and phosphorus cycles.
  • Disruption of the water cycle and groundwater recharge.
  • Invasion by or the introduction of exotic (non-native) organisms.
  • Toxins, pollutants, and human wastes.
  • Changes in the chemical composition of the atmosphere and ozone depletion.
  • Climate change.

Ecotone is a zone of the junction between two or more diverse ecosystems e.g. the mangrove forests. They represent an ecotone between marine and terrestrial ecosystems. Some more examples of ecotone are grassland, estuary, and riverbank.

Characteristics of Ecotone:
  •  It may be very narrow or quite wide.
  • It has conditions intermediate to the adjacent ecosystems. Hence ecotone is a zone of tension.
  • It is linear as it shows a progressive increase in species composition of one incoming community and a simultaneous decrease in species of the other outgoing adjoining community.
  • A well-developed ecotone contains some organisms which are entirely different from that of the adjoining communities.
  • Sometimes the number of species and the population density of some of the species is much greater in this zone than either community. This is called edge effect. The organisms which occur primarily or most abundantly in this zone are known as edge species. bob world In the terrestrial ecosystem, the edge effect is especially applicable to birds. For example, the density of songbirds is greater in the mixed habitat of the ecotone between the forest and the desert.
Niche and Organism

In nature, many species occupy the same habitat, but they perform different functions. The functional characteristic of a species in its habitat is referred to as “niche” in that common habitat. Habitat of a species is like its ‘address’ (i.e. where it lives) whereas niche can be thought of as its “profession” (i.e. activities and responses specific to the species).

The term niche means the sum of all the activities and relationships of a species by which it uses the resources in its habitat for its survival and reproduction.


A niche is the unique functional role or place of a species in an ecosystem.

A niche is unique for a species while many species share the habitat. No two species in a habitat can have the same niche. This is because if two species occupy the same niche they will compete with one another until one is displaced. For example, a large number of different species of insects may be pests of the same plant but they can co-exist as they feed on different parts of the same plant.

Types of Niche
  1. Habitat niche – where it lives
  2. Food niche – what is eating or decomposes & what species it competes with
  3. Reproductive niche – how and where it reproduces.
  4. Physical & chemical niche – temperature, land shape, land slope, humidity, and other requirements.


The terrestrial part of the biosphere is divisible into enormous regions called biomes, which are characterized, by climate, vegetation, animal life, and general Soil type.

No two biomes are alike. The climate determines the boundaries of the biome and abundance of plants and animals found in each one of them. The most important climatic factors are temperature and precipitation.

Types of Biome


  • Treeless low (less than 1 m) vegetation with short perennials, water frozen.
  • Typical plants include sedges, lichens, mosses, grasses, and dwarf woody plants.
  • Typical animals include snowy owls, musk ox, reindeer, polar bears, and migrant birds.
  • Very cold, often dry climate, but with the permanently frozen ground creating saturated soils during summer months. Arctic Tundra is circumpolar (scanty Antarctic).


  • Dense evergreen needle-leafed forest.
  • Typical plants include white spruce, black spruce, and jack pine.
  • Typical animals include moose, black bears, wolves, and migrant birds.
  • Cold winters with deep snow, but longer growing season than the tundra. The warm-month average temperature is greater than 100 C. Periodic fires are common.


  • Dense forest with thin, broad, deciduous leaves; or rainforests typically dominated by conifers. Tall trees with single boles creating deep shade. Understories are often sparse.
  • Typical plants include maples, oaks, elms (deciduous) spruce or araucaria (rainforest).
  • Typical animals include deer and squirrels.
  • Freezing winters and warm, wet summers and a longer growing season than the boreal forest.


  •  Treeless vegetation less than 1 m high.
  • Typical plants include grasses and members of the sunflower family. Woody plants predominate in steppes.
  • Typical animals include large grazing ungulates such as horses, buffalo, and rhinoceros.
  • Cold or warm winters with growing seasons moisture too dry for trees; fires every 1- 5 years.


  •  Sparse drought-resistant vegetation, typically spiny and with tiny leaves and photosynthetic bark.
  • Typical plants include cactuses, acacias, and short-lived annuals.
  • Typical animals include reptiles and ground-dwelling rodents.
  • Precipitation is low (less than 250 mm/yr) and evapotranspiration high (more than 250 mm/yr). Temperature is generally high. Fires generally are rare due to low biomass.


  •  Thorny forest, woodlands, or scattered trees, many of which loose leaves during the dry season.
  • Typical plants include acacias and grasses.
  • Typical animals include giraffes and elephants.
  • Warm frost-free winters, hot usually-wet summers, and a pronounced dry season. Fire and grazing are important vegetation-forming processes.


  •  Dense tall evergreen forest.
  • Typical plants include strangler figs and tree ferns.
  • Typical animals include snakes and birds.
  • Mild frost-free winters and summers with year-round rain.

Aquatic systems are not called biomes; however, they are divided into distinct life zones, with regions of relatively distinct plant and animal life. The major differences between the various aquatic zones are due to salinity, levels of dissolved nutrients; water temperature, depth of sunlight penetration.

Types of Aquatic Ecosystem:

  1. Fresh Water Ecosystem- The freshwater ecosystem is classified as lotic (moving water) or lentic (still or stagnant water). The lotic water system includes freshwater streams, springs, rivulets, creeks, brooks,
    and rivers. Lentic water bodies include pools, ponds, some swamps, bogs, and lakes. They vary considerably in physical, chemical, and biological characteristics.
  2. Marine Ecosystem Nearly three-quarters of the earth’s surface is covered by the ocean with an average depth of 3,750 m and with salinity 35 ppt, (parts per thousand), about 90 percent of which is sodium chloride.
  3. Estuaries –  Coastal bays, river mouths, and tidal marshes from the estuaries. In estuaries, freshwater from rivers meets ocean water and the two are mixed by the action of tides. Estuaries are highly productive as compared to the adjacent river or sea.


The biosphere is a part of the earth where life can exist. The biosphere represents a highly integrated and interacting zone comprising of the atmosphere (air), hydrosphere (water) and lithosphere (land).

It is a narrow layer around the surface of the earth. If we visualize the earth to be the size of an apple the biosphere would be as thick as its skin.

The biosphere is absent at extremes of the North and South poles, the highest mountains and the deepest oceans since existing hostile conditions there do not support life. Occasionally spores of fungi and bacteria do occur at a great height beyond 8,000 meters, but they are not metabolically active, and hence represent only dormant life.

Living organisms are not uniformly distributed throughout the biosphere. Only a few organisms live in the Polar Regions, while the tropical rain forests have an exceedingly rich diversity of plants and animals.

Reference: Shankar IAS Book (Environment)

Newest Most Voted
Inline Feedbacks
View all comments

Sir you are amazing


thans for giving me the my matter for art interegation

Sohini Paul

The pdf is so helpful and the content is so compact. Easy to understand, thanks a lot.

yusuf lamis

I really found it very relevant and useful


Very nice notes I got this very useful

Juno Fujiwara

Huh. This is pretty helpful. Thank you for this.