UPSC Biology Ecology and Ecosystem Biodiversity Evolution and Ecological Biodiversity

Evolution and Ecological Biodiversity

Category : UPSC








The branch of life science for the study of ‘origin of life’ and evolution of different forms of life on earth was called bio evolution or evolutionary biology by Mayer, (1970). The word evolution means to unfold or unroll or to reveal hidden potentialities. Evolution simply means an orderly change from one condition to another. Evolution is slow but continuous process which never stop.



  • Origin of life is the process by which living organisms developed from inanimate matter which is generally thought to have occurred on Earth between 3800 – 4200 millions years ago. First life evolved 3800-4200 million years back. There are several theories about the origin of life, like big bang theory, theory of special creation, theory of eternity, cosmozoic theory etc.


Chemosynthetic Theory of Origin of Life

The widely accepted theory is the Chemosynthetic theory of origin of life proposed by A.I. Oparin. It states that life has originated on earth through a series of combinations of chemical substances in the distant past. All these processes took place in water.


  • The early atmosphere contained ammonia (\[N{{H}_{3}}\]), water vapour (\[{{H}_{2}}O\]), hydrogen (\[{{H}_{2}}\]), methane

(\[C{{H}_{4}}\]). At that time there was no free oxygen.


Miller and Urey Experiment











Comparative Anatomy and Morphology

  • Different animals and plants show dissimilarities in their structure but in some characters they show similarity. These similarities provide one of the most concluding evidence of organic evolution.
    • Similarities are of two types: homology and



Let us discuss some of the important sources that provide evidences/or evolution.

  • Homologous organs: Homologous organs are similar in origin (or are embryo logically similar) but perform different functions.

For example, the forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.



  • Analogous organs: Analogous organs have different origin but perform similar functions.

For example, the wings of a bird and a bat are similar in function but this similarity does not mean that these animals are more closely related.


Vestigial organs

  • The organs which are present in reduced form and do not perform any function in the body but correspond to the fully developed functional organs of related animals are called vestigial organs.
  • Human body possess about 180 vestigial organs. Some of these are - nictating membrane, muscles of pinna (auricular muscles), vermiform appendix, coccyx, canine teeth, third molars (wisdom teeth), segmental muscles of abdomen, caecum, body hairs, nipples in male and ear pinna.


Theories of Organic Evolution

  • Four main theories to explain theories of evolution are-

(i) Lamarckism

(ii) Darwinisms

(iii) Mutation theory

(iv) Modern concept of evolution (synthetic theory)



  • Theory of inheritance of acquired characters is the first theory of organic evolution proposed by Jean Baptiste de Lamarck (1744-1829). Lamarck coined the terms
  • It states about the internal vital forces, effect of environment and new needs, use and disuse of organs and inheritance of aquired characters. These aquired characters are passed from one generation to another which results in new species.
  • Examples in support of Lamarckism are

Long neck and high fore limb of Giraffe, Aquatic birds stretched their toes and developed web, Snakes lost their legs, Deers became good runners by the development of strong limbs and streamlined body and retractile claws of carnivorous animals.



  • “Darwinism” or “The theory of Natural Selection” was proposed jointly by Charles Darwin and A.R. Wallace. This theory was explained by Darwin in his book ‘On the origin of species by the means of Natural Selection’ (1859).
  • Darwin was influenced by two books-

(i) “Principles of Population” by Malthus.

(ii) “Principles of Geology” by Charls Lyell.


Main features of theory of Natural Selection

  • Over production

- All organisms have capability to produce enormous number of offspring, organisms multiply in geometric ratio.

-   E.g.

(i) Plants produce thousands of seeds.

(ii) Insects lay hundreds of egg.

(iii) One pair of elephant gives rise to about six offspring and if all survived in 750 years a single pair would produce about 19 million elephants. Thus, some organisms produce more offspring and other produce fewer offspring. This is called differential reproduction.


Mutation Theory

  • The mutation theory was put forward in 1901 by Hugo de Vries.
  • The plant on which de Vries had experimented was Oenothera Lamarckiana.
  • Role of mutations in evolution is genetic variations.
  • Mutations are discontinuous variation called sports by Darwin and saltatory variation by
  • Features of mutation theory are-

(i) It forms the raw material for mutation.

(ii) It appears suddenly and produce their effect immediately.

(iii) Mutations are markedly different from the parents and there are no intermediate stages between the two.

(iv) Mutations can appear in all directions.



Evolution of man probably took place in Central Africa. Human evolution states that human develops from primates or ape like ancestors. Anthropology is the study of human evolution and culture. It deals with the fossils of pre-historic and living man. Homo erectus was the first human to leave Africa and move to Europe and Asia. It had a sloping forehead, flattish face and brain size between 850-1100 ml. These humans exploited more habitats than their ancestors. They were first to use fire.

Homo nenderthals were the first humans to have adopted to life in cold climates of Europe and Asia. They had strong physique and large brain. They more clothes, made a range of tools and used fire to keep warm. They were the first humans to bury their dead.

Homo sapiens or the “modem human” first evolved in Africa. They had a large brain, were considerably intelligent and had developed the ability to use language. Modem man took control of their surroundings as they developed agriculture, societies and technology.


Handy Facts

  • Carolus Linnaeus gave the term ‘Homo Sapiens’.





The term “ecology” was coined in 1866 by German scientist Ernst Hackel. It is study of biota, environment and their interaction. Ecology also provides information about the benefits of ecosystems and how we can use Earth's resources in ways that leave the environment healthy for future generations. Ecology can studied in following head.






                                                                   \[\downarrow \]



\[\downarrow \]                                       \[\downarrow \]                                             \[\downarrow \]                                     \[\downarrow \]


Population ecology

Community ecology

Ecosystem ecology

Behavioural ecology

This is also known as autecology. It is a part of ecology that deals with the variety of species population and their interaction with their environment. It is the study of size of population of species changing over time and space.

This is also known as Bio coenosis. It is the assemblage of two or more different species that occupies same geographical area.

It is a part of ecology that studies biotic and abiotic components of ecosystem and their interaction   of the ecosystem.

It is a part of ecology that deals with the ecological, environment?s developmental, genetic and social influences of species and their responses to the stimuli. It shows the way of such responses that affects the fitness of organism.



  • The term ‘ecosystem’ was proposed by a British ecologist G. Tansley (1953). It represent the basic fundamental, functional unit of ecology which comprises of the biotic community together with its abiotic (non-living) environment. Ecosystem simply means ‘ecological systems’. Ecology is the study of ecosystems.
  • Ecosystem is the functional unit of nature where living organisms interact with each other and with their environment.




  • Ecosystem is normally an open system because there is a continuous and variable entry and loss of energy and materials. Ecosystem is known by different terms i.e., biogeocoenosis or geobiocoenosis or microcosm or ecosom or bio system etc., the whole earth can be called biosphere or ecosphere.


Components of Ecosystem

  • Ecosystem is composed of a variety of abiotic (non-living) and biotic (living organisms) components that function in an interrelated fashion.


Structure and Function of Ecosystem

  • The structure of an ecosystem can be expressed by the following terms -
  • Species compositor: Plant and animal species found in an ecosystem.
  • Stratification: Vertical layers of plants.
  • Standing crop: Amount of biomass.
  • Standing state: Amount of inorganic substances.
  • The proper functioning of an ecosystem takes place through the following processes:
  • Productivity
  • Decomposition
  • Relationship of producers and consumers
  • Flow of energy through different trophic levels, and
  • Cycling of nutrients.



  • Decomposition is the breakdown of complex organic com- pounds of dead bodies of plants and animals into simpler inorganic compounds like \[C{{O}_{2}},\]water & various nutrients.
  • The organisms carrying out decomposition are called decomposers. It includes micro-organisms (bacteria and fungi), detritivores (earthworm) and some parasites.


Process of Decomposition

  • Decomposition is physical as well as chemical in nature and consists of the foil owing processes:


(i) Fragmentation

It is the formation of smaller pieces of dead organic matter or detritus by detritivores. Due to fragmentation, the surface area of detritus particles is greatly increased.


(ii) Catabolism

Chemical conversion of detritus into simpler inorganic substances with the help of bacterial and fungal enzymes is called catabolism.


(iii) Leaching

Water soluble substances (formed as a result of decomposition) are leached to deeper layers of soil.


(iv) Humification

If decomposition leads to the formation of colloidal organic matter (humus), the process is called humification. Humus is highly resistant to microbial action and undergoes extremely slow decomposition. It serves as a reservoir of nutrients.


(v) Mineralisation

Formation of simpler inorganic substances (like \[C{{O}_{2}},\] water and minerals) is termed mineralisation.




  • Food chain is an order or sequence of different organisms which are arranged in a way that the food is passed from one type of organism to other organisms such that the organisms of one order or trophic level are the food of the organisms of next order.


Types of food chains

The food chains are of two types, namely:

(i)         Grazing food chain: This food chain starts from plants, goes through herbivores and ends in carnivores, ex- Plant \[\to \] Herbivores \[\to \] Primary Carnivores \[\to \] Sec. Carnivores. This type of food chain depends on the autotrophs which capture the energy from solar radiation.

(ii)         Detritus food chain: It starts from dead organic matter and ends in inorganic compounds. There are certain groups of organisms which feed exclusively on the dead bodies of animals and plants. These organisms are called detritivores. The detritivores include algae, bacteria, fungi, protozoans, insects, millipedes, centipedes, crustaceans, mussels, clams, annelid worms, nematodes, ducks, etc.



  • Food web refers to a group of inter-related food chains in a particular community. Under natural conditions, the linear arrangement of food chain hardly occurs & these remain indeed inter-connected with each other through different types of organisms at different trophic level.
  • Food webs are very important in maintaining equilibrium (homeostasis) of ecosystem.

Example: In a grassland ecosystem

  • Grass \[\to \] Grasshopper \[\to \] Hawk
  • Grass \[\to \] Grasshopper \[\to \] Lizard \[\to \] Hawk
  • Grass \[\to \] Rabbit \[\to \] Hawk
  • Grass \[\to \] Mouse \[\to \] Hawk
  • Grass \[\to \] Mouse \[\to \] Snake \[\to \] Hawk



  • The pyramidal representation of trophic levels of different organisms based on their ecological position is called Ecological pyramids.
  • Three ecological pyramids which are studied are - pyramid of number, pyramid of biomass and pyramid of energy.




  • Ecological succession is the successive development of different biotic communities at the same site. The communities develop one after another till the development of a community which is near equilibrium with the environmental conditions. This is called climax community.
  • Climax community is the stable perpetuating and final biotic community that develops at the end of biotic succession. It has maximum diversity & niche specialization.
  • The first biotic community which invades a base area is called pioneer community. It is characterized by high growth rate and short life span.
  • The transitional communities which develop during the ecological succession or in between the pioneer and climax community are called seral communities.


Types of Succession

  • Succession is of two types: Primary and Secondary.
  • Primary succession: It is the ecological succession occurring in an area where no organisms are found, like bare rocks.
  • Secondary succession: This type of succession takes place in those areas where all the previous biotic communities have been destroyed, e.g.- burned forests, flooded fields.


Hydrach/Hydrosere Succession

  • Hydrosere is a sequence of communities that reflects the developmental stages in a plant succession, which commences on soil, submerged by fresh water.
  • Hydrach succession takes place in wetter areas like ponds, lakes etc. and the successional series progress from hydric to the mesic conditions.


Xerarch Succession

  • Xerarch succession starts in dry areas & the series progress from xeric to mesic conditions.
  • Stages in xerarch occurring on bare rock is called
  • Pioneer of this succession depends on climate. In tropical areas the pioneers are cyanobacteria or blue green algae. In temperate areas, they are crustose lichens.
  • The ecological succession on bare rocks includes the development of following communities -

Crustose lichens \[\to \] foliose lichens \[\to \] mosses \[\to \] grasses \[\to \] shrubs \[\to \] trees.



  • These are the cyclic events by which various nutrients which are essential for the living organisms are transferred from one form to other. During these cycles, the nutrients pass from the biotic components to the abiotic components and vice-versa,; hence these are also called biogeochemical cycles.
  • Two types of nutrient cycles are -

(i) Gaseous cycles (nitrogen, oxygen, carbon cycles)

(ii) Sedimentary cycles (phosphorus, sulphur cycles)

  • In gaseous cycle, the main reservoirs of chemicals are the atmosphere and ocean.
  • In sedimentary cycles, the main reservoirs are soils and rocks.


Carbon Cycle

  • Discovered by Joseph priestley and Antoine Lavoisier
  • Carbon is present in carbohydrates, proteins and fats.
  • Carbon is taken up by green plants as \[C{{O}_{2}}\]for photosynthesis.
  • Carbon is present as \[C{{O}_{2}}\] in atmosphere, as graphite and carbonates in rocks and also in fossil fuels (coal, petroleum).
  • Ocean are big reservoirs of carbon.
  • Carbon is released as \[C{{O}_{2}}\] in atmosphere during -

(i)  respiration of plants and animals

(ii) burning of fossil fuels

  • Carbon is also released in atmosphere as methane by rice fields and marshes.


Phosphorus Cycle

  • Phosphorus is an important element for living beings.
  • The cycling of phosphorus between biotic & abiotic components of the environment represent phosphorus cycle.
  • Phosphorus is present in bio membranes (as phospholipids) nucleic acids (as phosphoric acid), nucleotides (as AMP, ADP, ATP etc.) and bones and teeth (as hydroxyapetite).
  • Consumers obtain phosphorus directly or indirectly from plants.
  • Phosphorus is also present in phosphatic rocks.
  • Phosphorus is released during the decomposition of plant and animal remains.
  • The released phosphorus may reach the deeper layers of soil and gets deposited as phosphate rocks.
  • Phosphorus containing rocks are mined for manufacture of fertilizers, which provide an additional supply of an organic phosphates to the abiotic environment.



  • Nitrogen cycle is a cyclic process that involves conversion of elemental nitrogen of atmosphere into simple molecules that enter living beings forming complex molecules. Then these complex molecules are broken down to release nitrogen back into the atmosphere.
  • Earth’s atmosphere has about 78% of nitrogen gas. It forms essential constituents of all living organisms and is essential for many biological processes. It is present in all amino acid, nucleic acid and vitamins.


Broadly, the nitrogen cycle in the biosphere involves five main steps:

Atmospheric nitrogen \[\to \] Nitrogen fixation \[\to \] Nitrogen assimilation\[\to \] Ammonification \[\to \] Nitrification \[\to \] Denitrification


  • Plants cannot absorb nitrogen from the atmosphere. So, how is atmospheric nitrogen then utilized by plants? It is through nitrogen fixation.

(i) Nitrogen fixation: It is the process of converting atmospheric nitrogen into usable forms like nitrates. It is of three types:

  • Biological nitrogen fixation: Certain bacteria and blue-green algae can fix atmospheric nitrogen directly into ammonia that combines with organic acids to form amino acids.
  • Atmospheric nitrogen fixation: During lightning and thunder, the high temperature and pressure in the air convert atmospheric nitrogen into oxides of nitrogen that can dissolve in water to produce nitric and nitrous acids. The nitrogen oxide then dissolve in rain water and pass down as nitrites and nitrates.

(ii) Nitrogen assimilation: Nitrogen assimilation is carried out by plants. Plants cannot absorb nitrogen in its elemental form. It has to be first converted into nitrates for the use of plants by the process of nitrogen fixation. The atmospheric nitrogen after nitrogen fixation gets converted into nitrates which are then absorbed by plants. Nitrate first changes into ammonium state. Ammonium ions combine with organic acids to form amino acids. Amino acids give rise to proteins and nucleotides, which in turn produce nucleic acids.

Animals take organic nitrogen directly or indirectly from plants.

(iii) Ammonification: It is the process of conversion of complex organic compounds like proteins into ammonia, in the presence of ammonifying bacteria or putrefying bacteria.

(iv) Nitrification: It is the process of conversion of ammonia into nitrites and nitrates. Nitrification is brought about by nitrifying bacteria such as Nitrosomonas and Nitrobacter.

(v)  Denitrification: It is the process of conversion of nitrate salts present in the soil and water to gaseous nitrogen which escapes into atmosphere. It takes place with the help of bacteria called Pseudomonas present in water logged soils. Denitrification reduces soil fertility.


Water Cycle (Also known as hydrological cycle)

Water cycle is the cyclic process of water between various components of biosphere especially evaporation of water from sea, falling on land and then flowing back into sea by rivers. Water is not evenly distributed throughout the surface of the earth. Major percentage of the total water on the earth is chemically bound to rocks and does not cycle. Out of the remaining, nearly 97.3% is in the oceans and 2.1% exists as polar ice caps. Thus only 0.6% is present as fresh water (in the form of atmospheric water vapors, ground and soil water). The ice caps and the water deep in the oceans form the reservoir.


Sulphur Cycle

  • Sulphur is the tenth abundant non-metallic element, which is brittle, tasteless and odorless. It is a component of litamin, protein and hormones and plays very important role in both climate and ecosystem.
  • Its cycle begins with weathering of rocks, due to which sulphur is released in air and converted into sulphate (\[S{{O}_{4}}\]). Later it is taken up by plants, and microorganisms and converted into organic forms, which is consumed by animals and moves into food chain. Dead and decayed organism after decomposition again releases sulphur in atmosphere.



Biodiversity means diversity or heterogeneity at all levels of biological organization, i.e., from macromolecules of the cells to the Biomass. The term Biodiversity was popularized by the sociologist- Edward Wilson.

  • The important levels of biodiversity are: Genetic diversity, Species diversity and Ecological diversity


Genetic Diversity

  • It is the diversity at genetic level, or at subspecies level, i.e. below species level, in a single species.
  • For example there are about 1000 varieties of mango (Mangifera indica) and 50,000 strains of rice.
  • The genetic diversity helps the population to adapt.
  • The low diversity leads to uniformity.
  • The genetic variability is therefore, considered to be the raw material for speciation.


Species Diversity

The measurement of species diversity is its richness, i.e. the number of species per unit area. The greater is the species richness the more will be the species diversity.


Ecological Diversity

It is the diversity at community level. It can be of 3-types


Alpha (\[\alpha \]) diversity

It is the diversity of organisms within the same community or habitat.


Beta (\[\beta \]) diversity

It is the diversity between communities or different habitats. Higher the heterogenecity in the altitude, Humidity and Temperature of a region, the greater will be the dissimilarity between communities, and higher will be the P diversity.


Gamma (\[\gamma \]) diversity

It is the diversity of organisms over the entire geographical area, covering several ecosystems or habitats and various trophic levels and food webs. Such diversity is most stable and productive.


Loss of Biodiversity

  • There is continuous loss of the earth5 treasure of species. For example, the colonization of tropical pacific Islands by human has led to extinction of more than 2000 species of native birds.
  • The Red list of IUCN documented the extinction of 784 species in last 500 years. The last 20 years witnessed the disappearance of 27 species.
  • Some important examples of recent extinctions are. Dodo (Mauritius), Quagga (Africa), Thylacine (Australia), Steller Sea-cow (Russia), and subspecies of Tiger, like ball, javan and Caspian.


Causes of Loss of Biodiversity

The accelerated rate of species-extinction is largely due to human activities. There are 4-major causes, called ‘The Evil Quartet’, for the loss of biodiversity are: Habitat loss and fragmentation, Overexploitation, Invasion of Alien or exotic species and Co-extinctions


Habitat loss and fragmentation

  • The cutting trees, burning of forest, construction of mines, dams, harbors, industries and buildings for human settlement has also affected the biodiversity.
  • The Habitat destruction is the primary and major reason for the loss of biodiversity.



  • Many species - extinction, like that of Stellar sea-cow and Passenger pigeon, in last 500 years, are due to Overexploitation by humans.
  • Ever-increasing need of organism for food and shelter leads to Overexploitation.
  • It includes as overharvesting, overhunting, overfishing etc.


Invasion of Alien or exotic species

When alien species are introduced into an explored area, some of the species turn invasive and cause decline or extinction of indigenous species. For example -

  • Introduction of Nile perch into lake Victoria (E. Africa) led to the extinction of more than 200 species of Cichlid fish in the lake.
  • Introduction of weed species, like Carrot grass (Parthenium), Lantana and water hyacinth (Eicchornia) has posed threat to the native species and damage to environment.



  • Whenever a plant or animal species becomes extinct, its obligatory-associated species also becomes extinct.



Conservation means management of human-use of the biosphere so that it may yield greatest long term (sustainable) benefits for the present generation by maintaining its potential to meet the needs and aspiration of future generations. The Conservation of biodiversity can be in situ (on site) or exsitu (offsite)-


In Situ Conservation

  • In such conservation the endangered species are protected in their natural habitat with entire ecosystem.
  • The conservationists, on global basis, have identified certain Biodiversity Hot Spots (with high level of species richness and high degree of endemism).
  • The hot spots are also the regions of accelerated habitat loss. The number of such hot spots is now 34. These hot spots cover only 1 to 2 percent of earth's land area, but according to one estimate, the strict protection in them can reduce the on-going mass extinction by almost 30%.
  • The 3-biodiversity hot spots of India, that cover rich-bio diversity regions, are : Western Ghat, Himalaya and Indo-Burma
  • The in situ conservation, in India, is done through 15-Biosphere reserves, 90-National Parks, more than 450 sanctuaries and several Sacred Groves or the tracts of forests.


Biosphere reserves

They represent natural biomes which contain unique biological communities. They include land as well as coastal environment. Biosphere reserves were created under MAB (Man and Biosphere) programme of UNESCO in 1971. Till May 2000 there were 408 biosphere reserves in 94 countries of the world. In India there are 15 biosphere reserves. There are 3-zones in a biosphere reserve.

  • Core (natural) zone - It is inner most zone which is legally protected and completely undisturbed from human interference,
  • Buffer zone - In this zone limited human activity is allowed for research and education purposes.
  • Transition (manipulation) zone - It is the outermost zone of biosphere reserve in which large number of human activities are permitted, e.g. Cultivation, domestication, harvesting of natural product, grazing, forestry, settlement and recreation etc. In this zone the traditional life style of tribals is protected with their live-stock.


Functions of biosphere reserves

  • For conservation of landscape, ecosystem and genetic resources.
  • For economic development.
  • For scientific research, education and for exchange of information at national and global level.

The list of biosphere reserves of India is given below:

  1. Nilgiri
  2. Nandadevi
  3. Uttrakhand
  4. Nokrek (Meghalaya)
  5. Andamans
  6. Simlipal (Orissa)
  7. Kaziranga (Assam)
  8. Gulf of Mannar (T.N.)
  9. Thar Desert
  10. Sundarbans (W.B.)
  11. Kanha (M.P.)
  12. Runn of Kutch (Guj)
  13. Nicobar
  14. Manas (Assam)
  15. Namdapha (Ar. P.)


National Parks

They are reserved for the betterment of wild life, booth fauna and flora. In national parks private ownership is not allowed. The grazing, cultivation, forestry etc. is also not permitted. The first national park of the world. Yellow stone, in U.S.A., was founded in 1872.

Important state wise national parks of India are –


Jammu and Kashmir

Dachigam, Salim Ali


Kaziranga, Manas



West Bengal



Hazaribagh, Palamau


Corbett ( Hailey ), Nanda Devi, Valley of flowers, Rajaji




Gir, Marine


Sariska, Ranthambore, Desert

Madhya Pradesh

Kanha, Sanjay, Madhav, Panna, Bandhavgarh, Van Vihar, Fossil






Silent Valley, Periyar


These national parks are running Tiger Project also. (The maximum national parks are present in Madhya Pradesh).



In sanctuaries the protection is given to fauna only. The important wild life sanctuaries are Chilka wild life sanctuary (Orissa), Bharatpur Bird Sanctuary (Rajasthan), Sultanpur Bird sanctuary (Haryana) and Jalpara sanctuary (West Bengal). Maximum sanctuaries belong to Andaman and Nicobar.


The Project Tiger was launched in India in year 1973 with the assistance of WWF (World Wild life Fund) after the recommendation of IBWL (Indian Board of Wild Life).


The sacred groves are found in Khasi and Jaintia hills (Meghalaya), Aravalli hills (Rajasthan), Western ghats (Karnataka and Maharashtra) and Sarguja, Chanda and Bastar areas of Madhya Pradesh.


Ex situ Conservation

In such type of conservation the threatened animals and plants are taken out of their natural habitat and are protected in special parks or areas like, Zoological parks, Wild life safari parks and Botanical gardens etc. The ex situ conservation also includes

  • Cryopreservation of gametes of threatened species in viable and fertile form.
  • Fertilization of eggs in vitro and propagation of plants through ‘Tissue culture methods’
  • Preservation of seeds through Seed banks

Other Topics

Notes - Evolution and Ecological Biodiversity

You need to login to perform this action.
You will be redirected in 3 sec spinner