• Environment: the natural landscape together with all of its non-human features, characteristics and processes
  • Ecology: Subject which studies the interactions among organisms and between the organism and its physical (abiotic) environment.
  • Biosphere: The biosphere is the biological component (supporting life) of earth which includes the lithosphere, hydrosphere and atmosphere.
  • Habitat: A habitat is a place where an organism makes its home. A habitat meets all the environmental conditions an organism needs to survive. (All habitats are environments, but all environments are not habitats.)
  • Ecosystem: Structural and functional unit of biosphere consisting of community of living beings and the physical environment, both interacting and exchanging materials between them.
  • Ecotone: An ”’ecotone”’ is a transition area between two biological communities, where two communities meet and integrate. E.g. Mangroves represents an ecosystem between marine and terrestrial ecosystem.
  • Niche: Ecological niche is a term for the position of a species within an ecosystem, describing both the range of conditions necessary for persistence of the species, and its ecological role in the ecosystem. Ecological niche subsumes all of the interactions between a species and the biotic and abiotic environment, and thus represents a very basic and fundamental ecological concept.
  • No two species have exact identical niche. Different types of niches are – Habitat niche, Food niche, Reproductive niche, Physical and Chemical niche.
  • Biomes: A biome is a community of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.


Components of an Ecosystem

  1. Abiotic Components
  1. CLIMATIC FACTORS: Rain, Light, Wind, Temperature
  2. EDAPHIC FACTORS: Soil, PH Minerals Topography


  1. Biotic Components
  1. Consumers
  2. Producers
  3. Decomposers




An abiotic factor is a non-living part of an ecosystem that shapes its environment. In a terrestrial ecosystem, examples might include temperature, light, and water. In a marine ecosystem, abiotic factors would include salinity and ocean currents.

  • Affects the kinetic of enzymes and through its basal metabolism, activity and other physiological functions of the organism.
  • Level of thermal tolerance determine, geographical distribution of an organism.
  • Eurythermal (Organism that can tolerate wide range of temperature)
  • Stenothermal (Organism that are restricted to narrow range of temperature)
  • Productivity and distribution of plants is heavily dependent on water.
  • Euryhaline– Organism that can tolerate wide range of salinities (Note: Salt concentration measured in parts per thousand)
  • Stenohaline– Organism that are restricted to narrow range of salinities.
  • Many freshwater animals can’t live for long in sea water and vice versa due to osmotic problem.
Light For Plants: Photosynthesis + Photoperiodic requirement for flowering.

For Animals: Diurnal and seasonal variation in light, intensity and duration (photoperiod) determines animal’s foraging, reproductive and migratory activities. UV component of the spectrum is harmful to many organisms. Not all the colour components of visible spectrum are available for marine plants living at different depths of the ocean. E.g. red, green, brown algae inhabit sea at different depths.

Soil Vegetation in any area are determine by- Soil composition, Percolation and Grain size, Water holding capacity.

Aggregation of soil are determined by: PH, Mineral composition, Topography.



How do organisms living in extreme environment cope or manage with stressful conditions?



  • Homeostasis (maintaining constancy of internal body) by physiological (sometimes behavioral also) like ensuring constant body temperature (Thermoregulation). E.g. in summer outside temperature is more than our body temperature, we sweat profusely. In winter we shiver, which produces heat and raises body temperature.
  • Constant osmotic concentration (Osmoregulation)
  • Success of mammals is largely due to their ability to maintain a constant body temperature.


  • 99% of animals and nearly all plants can’t maintain constant internal environment.
  • Thermoregulation is energetically expensive for many organisms. For e.g. shrews and humming birds.
  • Heat loss and gain is function of surface area.
  • Small animals have larger surface area relative to their volume so they tend to lose body heat very fast when it is cold outside.
  • They have to expend much energy to generate body heat through metabolism – this is the reason small animals are not found in polar regions.
  • In aquatic organisms, the osmotic concentration of the body fluids changes with that of the ambient water osmotic concentration.
  • The organism moves away temporarily from the stress habitat to more hospitable area and return when stressful period is over. E.g. Keoladeo National Park (Bharatpur) Rajasthan, host thousands of migratory birds from Siberia during winter months.
  • Examples of it are important: Siberian Cranes, Amur Falcon, Greater Flamingo


  • Thick walled spores’ formation à In bacteria, Fungi and lower plants.
  • Dormancy à Plants: Reduction of metabolic activity in higher plants in stressful environment
  • Hibernation à Hibernation is when an animal slows its heart rate to save energy and survive the winter without eating much. e.g. bear, bat, rodents etc.
  • Aestivation à Aestivation is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aquatic animals: E.g. Snail, Fish.

Diapause à Zooplankton species in lakes and ponds- a stage of suspended development.


  • Adaptation is any attribute of the organism (Morphological, Physiological, Behavioral) that enables organism to survive and reproduce in its habitat. Adaptedness is the state of being adapted: the degree to which an organism is able to live and reproduce in a given set of habitats
  • Example: Kangaroo rat in North American Deserts: in absence of water, has ability to meet its requirement through internal fat oxidation and has ability to concentrate its urine.


Morphological Adaptations:
  • Desert plants have thick cuticle on their leaf surface and stomata arranged in deep pits to minimize water loss through transpiration.
  • Some desert plants like Opunita have no leaves and photosynthetic function is taken over by flattened stems.
  • Mammals from colder climates have shorter ears and limbs to minimize heat loss. This is called Allen’s Rule.
Physiological Adaptations E.g. altitude sickness: Our body compensate low Oxygen availability by increasing red blood cell production, decreasing the binding affin ity of hemoglobin and by increasing breathing rate.
Biochemical Adaptation: Many fish and invertebrates live at great depths in the ocean, where pressure could be >100 times than the normal atmospheric pressure that we experience.
Behavioural Adaptations E.g .Lizard they bask in the sun when body temperature drops, but moves to shade when ambient temperature starts increasing.





  • Producers are organisms that create food from inorganic matter.
  • Example: Plants, lichens and algae, which convert water, sunlight and carbon dioxide into carbohydrates.
  • Consumers have to feed on producers or other consumers to survive.
  • If they feed on the producers, the plants, they are called primary consumers, and if the animals eat other animals which in turn eat the plants (or their produce) they are called secondary consumers.
  • The consumers that feed on herbivores are carnivores, or more correctly primary carnivores (though secondary consumers). Those animals that depend on the primary carnivores for food are labelled secondary carnivores.
  • Example: Deer, Bear, Human beings, etc.
  • An organism that primarily feeds on dead organisms or the waste from living organisms.
  • Detritivores: Some organisms perform a similar function as decomposers, and are sometimes called detritivores.
  • The difference lies in the way decomposers and detritivores break down organic material. Detritivores must digest organic material within their bodies in order to break it down and gain nutrients from it.
  • Decomposers do not need to digest organic material internally in order to break it down.
  • Scavengers: Scavengers are the first to arrive at a dead organism’s remains. It includes lions, jackals, wolves, raccoons, and opossums.
  • Example: Bacteria, fungi


Vertical distribution of different species occupying different levels is called stratification. (For example, trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bottom layers.)


  • Four basic components of ecosystem– (i) Productivity; (ii) Decomposition; (iii) Energy flow; and (iv) Nutrient cycling.


(i) Productivity:

  • The rate of biomass production is called productivity.
  • Primary production is defined as the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis.
  • Gross primary productivity of an ecosystem is the rate of production of organic matter during photosynthesis.
  • A considerable amount of GPP is utilized by plants in
  • Gross primary productivity minus respiration losses (R), is the net primary productivity (NPP). GPP – R = NPP.
  • Secondary productivity is defined as the rate of formation of new organic matter by consumers.


(ii) Decomposition:

  • Decomposers break down complex organic matter into inorganic substances like carbon dioxide, water and nutrients and the process is called decomposition.
  • The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralization.
  • Detritivores (e.g., earthworm) break down detritus into smaller particles. This process is called fragmentation
  • By the process of leaching, water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.
  • Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is called as
  • All the above steps in decomposition operate simultaneously on the detritus
  • Humification and mineralization occur during decomposition in the soil
  • Humification is accumulation of a dark colored amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. It colloidal in nature it serves as a reservoir of nutrients.
  • Humus is further degraded by some microbes and release of inorganic nutrients occur by the process known as mineralization



(iii) Energy Flow:

  • There is unidirectional movement of energy towards the higher trophic levels and its dissipation and loss as heat to the environment.
  • Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR)
  • Plants capture only 2-10 per cent of the PAR and this small amount of energy sustains the entire living world.
  • The green plant in the ecosystem-terminology are called producers. e.g. phytoplankton, algae and higher plants.
  • All animals depend on plants (directly or indirectly) for their food needs. They are hence called consumers and also heterotrophs.
  • A trophic level is the representation of energy flow in an ecosystem.


Producers serves as the primary source of energy and constitute the first trophic level The detritus food chain (DFC) begins with dead organic matter.
Energy for the grazing food chain is obtained directly from the sunlight. Energy for the detritus food chain is obtained from the organic debris
In an aquatic ecosystem, GFC is the major conduit for energy flow. In a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC




A food chain is a linear flow of energy and nutrients from one organism to another. A food web can be termed as the combination of many different food chains and the relationship that exists between each organism.
A food chain represents only one part of the food or energy flow and reflects a simple and isolated relationship. It shows all possible transfers of energy and nutrients. Food web provides more than one alternative for food to most organisms in an ecosystem and therefore increases their chance of survival.


  • Steps of trophic levels expressed in a diagrammatic way are referred as ecological pyramids.
  • The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top-level consumer.
  • The three ecological pyramids that are usually studied are (a) pyramid of number; (b) pyramid of biomass and (c) pyramid of energy.

Pyramid of Numbers:

  • Pyramid of numbers represents the total number of individuals of different species (population) at each trophic level, can be:
  • Upright– number of individuals is decreased from lower level to higher trophic level, can be seen in the grassland ecosystem and pond ecosystem
  • Inverted– number of individuals increased from lower to higher trophic level. e.g. Tree ecosystem.

Pyramid of Biomass:

  • Pyramid of biomass is usually determined by collecting all organisms occupying each trophic level separately and measuring their dry weight. Each trophic level has a certain mass of living material at a particular time called the standing crop. Pyramid of Biomass can be:
  • Upright: For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level on top.
  • Inverted: Many aquatic ecosystems, the pyramid of biomass may assume an inverted form. (In contrast, a pyramid of numbers for the aquatic ecosystem is upright)

Pyramid of Energy:

Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step.



Non degradable pollutants move from different trophic level. Non-degradable (persistent) is which cannot be metabolized by living organisms. E.g. Chlorinated Hydrocarbons.


Bioaccumulation There is increase in concentration of a pollutant from the environment to the first organism in a food chain.
Biomagnification Increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolized or excreted. Ex: Mercury and DDT.


  • Organisms are interlinked with each other. The interaction is fundamental for the survival of organism and functioning of ecosystem.
  • Interspecific interactions arise from the interaction of populations of two different species.
  • They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.
Type Sp.1 Sp. 2 Examples



+ + Mutualism is defined as an interaction between individuals of different species that results in positive (beneficial) effects on per capita reproduction and/or survival of the interacting populations.

  • Lichens represent an intimate mutualistic relationship between a fungus and algae or cyanobacteria
  • Mycorrhizae are associations between fungi and the roots of higher plants.
  • Mutualistic relationship between fig tree and wasp.

Competition is the struggle between two organisms for the same resources within an environment.

  • It is generally believed that competition occurs between closely related species.
  • But this is not entirely true. Firstly, totally unrelated species could also compete for the same resource.
  • Resources need not be limiting for competition to occur; in interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species.
  • E.g. Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island



+ Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey.

  • Biological control methods adopted in agricultural pest control are based on the ability of the predator to regulate prey population.
  • Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator.
  • Predators also help in maintaining species diversity in a community


+ Parasitism is a symbiotic relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life

  • Many parasites have evolved to be host-specific (they can parasitize only a single species of host) in such a way that both host and the parasite tend to co-evolve.
  • Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population density
  • Ectoparasites-Parasites that feed on the external surface of the host organism. E.g. Lice, Cuscata plant.
  • Endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.
  • Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host and lets the host incubate them E.g. Koel

+ 0 Commensalism is a long-term biological interaction in which members of one species gain benefits while those of the other species neither benefit nor are harmed.

  • An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
  • The cattle egret and grazing cattle
  • Sea anemone that has stinging tentacles and the clown fish that lives among them.

0 Amensalism meaning, an ecological interaction between two species, but in this association among organisms of two different species, one is destroyed or inhibited, and other remains unaffected.

  • The bread mould fungi Penicillium produce penicillin an antibiotic substance which inhibits the growth of a variety of bacteria.
  • A large tree shades a small plant, retarding the growth of the small plant.
Neutralism 0 0
  • True neutralism is extremely unlikely.



The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling. Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, water). Nutrient cycles are of two types:

  1. Gaseous – Reservoir for gaseous type of nutrient cycle (e.g. nitrogen, carbon cycle) exists in the atmosphere
  2. Sedimentary– For the sedimentary cycle (e.g. Sulphur and phosphorus cycle), the reservoir is located in Earth’s crust.


Carbon Cycle:

  • 71 per cent carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere.
  • Atmosphere only contains about 1 per cent of total global carbon.
  • Carbon cycling occurs through atmosphere, ocean and through living and dead organisms.
  • A considerable amount of carbon returns to the atmosphere as CO2 through respiratory activities of the producers and consumers.
  • Decomposers also contribute substantially to CO2 pool by their processing of waste materials and dead organic matter of land or oceans.
  • Human activities have significantly influenced the carbon cycle. Rapid deforestation and massive burning of fossil fuel for energy and transport have significantly increased the rate of release of carbon dioxide into the atmosphere.


Nitrogen Cycle:

  • Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls and many of the vitamins
  • Plants compete with microbes for the limited nitrogen that is available in the soil. Thus, nitrogen is a limiting nutrient for both natural and agricultural ecosystems.
  • Nitrogen exists as two nitrogen atoms (N2) joined by a very strong triple covalent bond (N ≡ N).
  • In nature, lightning and ultraviolet radiation provide enough energy to convert nitrogen to nitrogen oxides (NO, NO2, N2O).
  • Industrial combustions, forest fires, automobile exhausts and power-generating stations are also sources of atmospheric nitrogen oxides.
  1. Step 1: N2 Fixing ➔ Nitrogen → Ammonia or Ammonium Ions
  2. Step 2: Nitrification ➔ Ammonia or Ammonium Ions (bacteria: Nitrosomonas and/or Nitrococcus) → Nitrite (Nitrobacter)→ Nitrate
  3. Step 3: Ammonification ➔ Dead Matter + Animal Waste (Urea, Uric Acid) → Ammonia or Ammonium Ions
  4. Step 4: Denitrification ➔ Nitrate (bacteria: Pseudomonas and Thiobacillus) → Nitrogen


Sulphur Cycle:

  • In Sulfur cycle, there is a circulation of sulfur in various forms through nature. Sulfur occurs in all living matter as a component of certain amino acids.
  • It is abundant in the soil in proteins and, through a series of microbial transformations, ends up as sulfates usable by plants.
  • The Sulphur reservoir is in the soil and sediments where it is locked in organic (coal, oil and peat) and inorganic deposits (pyrite rock and Sulphur rock) in the form of sulphates, sulphides and organic Sulphur.
  • It is released by weathering of rocks, erosional runoff and decomposition of organic matter and is carried to terrestrial and aquatic ecosystems in salt solution.
  • The Sulphur cycle is mostly sedimentary except two of its compounds, hydrogen sulphide (H2S) and Sulphur dioxide (SO2), which add a gaseous component.
  • Sulphur enters the atmosphere from several sources like volcanic eruptions, combustion of fossil fuels (coal, diesel etc.), from the surface of the ocean and gases released by decomposition.


Phosphorus Cycle:

  • Phosphorus is a major constituent of biological membranes, nucleic acids and cellular energy transfer systems.
  • Many animals also need large quantities of this element to make shells, bones and teeth.
  • The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
  • When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants.
  • Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate-solubilizing bacteria releasing phosphorus.
  • Unlike carbon cycle, there is no respiratory release of phosphorus into atmosphere.


  • The gradual and fairly predictable change in the species composition of a given area is called ecological succession.
  • The first plant to colonize an area is called the pioneer community.
  • The final stage of succession is called the climax community.
  • A climax communityis the final stage of succession, remaining relatively unchanged until destroyed by an event such as fire or human interference. This is a community that is in near equilibrium with the environment.
  • The entire sequence of communities that successively change in a given area are called


Primary succession:

  • Primary succession takes place an over where no community has existed previously. E.g. rock outcrops, newly formed deltas and sand dunes, emerging volcano islands and lava flows, glacial moraines etc.
  • In primary succession on a terrestrial site, the new site is first colonized by a few hardy pioneer species that are often microbes, lichens and mosses.
Secondary succession:

  • Secondary succession begins in areas where natural biotic communities have been destroyed such as in abandoned farm lands, burned or cut forests, lands that have been flooded.
  • Since some soil or sediment is present, succession is faster than primary succession.



  • Succession of plants is called hydrarch or xerarch, respectively.
  • Hydrarch succession takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
  • As against this, xerarch succession takes place in dry areas and the series progress from xeric to mesic conditions.
  • Hence, both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).



Autogenic and

Allogenic succession:


● When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession, while change brought about by outside forces is known as allogenic succession.

● Autogenic succession is driven by the biotic components of an ecosystem.

● Allogenic succession is driven by the abiotic components (fire, flood) of the ecosystem.


Autotrophic and Heterotrophic succession


● Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession and the ones in which the heterotrophs are greater in quantity is known as heterotrophic succession.


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