Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev

Environment and Additional Topics for UPSC Prelims

UPSC : Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev

The document Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev is a part of the UPSC Course Environment and Additional Topics for UPSC Prelims.
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BIOSPHERE
Biosphere is that part of lithosphere, hydrosphere and atmosphere where plants and human beings live. Biosphere contains all life forms on earth.
The biosphere consists of all the living organisms (the biotic component), energy and physical environment (the abiotic component) and there are continuous interactions between living organisms and physical environment and among the living organisms themselves.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevBiosphere

  • The biosphere consists of two major systems viz.:
    (i) terrestrial biomes systems and
    (ii) aquatic biomes systems
  • The terrestrial biomes systems are further comprised of three subsystems viz.:
    (i) Plant system,
    (ii) Animal system and
    (iii) Soil system.
    These subsystems are intimately interrelated among themselves through the cyclic pathways of movements and transfer of energy and materials.
  • The aquatic biomes systems are also composed of three sub-systems viz. :
    (i) Plant system,
    (ii) Animal system, and
    (iii) Nutrients.
    These three sub-systems of aquatic biomes system of the biosphere are also intimately interrelated through cyclic pathways of movements of energy and matter among themselves.
  • Man depends on biosphere to fulfill many of his needs like food, drugs, clothes, housing, paper and tourism and environment.

ECOLOGY
Ecology can be defined as a scientific study of the interactions of organisms with their physical environment and with each other.
The term ecology is derived from the Greek word ‘oikos’ meaning ‘house’, combined with the word ‘logy’ meaning the ‘science of’ or ‘the study of ’. Literally, ecology is the study of the earth as a ‘household’, of plants, human beings, animals and micro-organisms. They all live together as interdependent components.
A German zoologist Ernst Haeckel, who used the term as ‘oekologie’ in 1869, became the first person to use the term ‘ecology’. The study of interactions between life forms (biotic) and the physical environment (abiotic) is the science of ecology.


ECOSYSTEM
An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with the surrounding physical environment.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevEcosystem and its components

Components of Ecosystem:
There are four basic components of an ecosystem.
(i) The abiotic part, which is the non-living environment.
(ii) The producers or autotrophs, the green plants capable of producing their own food by using the energy of sunlight to make carbohydrates from water and carbon dioxide; this process is called photosynthesis.
(iii) There are the consumers or heterotrophs. These are animals which obtain their food by eating plants or other animals. The heterotrophs in any ecosystem can be divided into groups by their feeding habits:

  • Herbivores eat only living plant material;
  • Detritivores feed on dead plant and animal material;
  • Carnivores eat other animals;
  • Omnivores eat both plant and animal material.

(iv) Decomposers, such as the bacteria and fungi that promote decay.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevRelationship with ecosystem

 

Types of Ecosystem:
Ecosystem varies greatly in size from a small pond to a large forest or a sea. Many ecologists regard the entire biosphere as a global ecosystem, as a composite of all local ecosystems on Earth. Since this system is too much big and complex to be studied at one time, it is convenient to divide it into two basic categories, namely the terrestrial and the aquatic.

1. Terrestrial Ecosystem

  • The ecosystem which is found only on landforms is known as the terrestrial ecosystem.
  • The main factor which differentiates the terrestrial ecosystems from the aquatic ecosystems is the relative shortage of water in the terrestrial ecosystems and as a result the importance that water attains in these ecosystems due to its limited availability.
  • Another factor is the better availability of light in these ecosystems as the environment is a lot cleaner in land than it is in water.
  • The main types of terrestrial ecosystems are the forest ecosystems, the desert ecosystems, the grassland ecosystems and the mountain ecosystems.

2. Aquatic Ecosystem

  • An ecosystem which exists in a body of water is known as an aquatic ecosystem.
  • The aquatic ecosystems are mainly of two types, the freshwater ecosystems and the marine ecosystems.

Energy Flow in Ecosystem:
Sun is the primary source of energy for all ecosystems on Earth. Of the incident solar radiation less than 50 per cent of it is photosynthetically active radiation (PAR). Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.
Plants capture only 2-10 percent of the PAR and this small amount of energy sustains the entire living world. The energy of sunlight fixed in food production by green plants is passed through the ecosystem by food chains and webs from one trophic level to the next. In this way, energy flows through the ecosystem.

The Trophic Structure of Ecosystems:

  • The organisation and pattern of feeding in an ecosystem is known as the trophic structure.
  • The levels through which food energy passes from one group of organism to the other group are called trophic levels.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevTrophic levels


FOOD CHAIN
The chain of transformation and transfer of food energy in the ecosystem from one group of organism to another group through a series of steps or levels is called food chain.

Two types of food-chains are recognised:

  • Grazing food-chain: In a grazing food-chain, the first level starts with plants as producers and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level. There is a loss of energy at each level which may be through respiration, excretion or decomposition. The levels involved in a food chain range from three to five and energy is lost at each level.
    The phytoplanktons →zooplanktons →Fish, The grasses →rabbit →Fox are the examples, of grazing food chain.
  • Detritus food chain: This type of food chain goes from dead organic matter into microorganisms and then to organisms feeding on detritus (detrivores) and their predators. Such ecosystems are thus less dependent on direct solar energy. These depend chiefly on the influx of organic matter produced in another system.
    Example: Such type of food chain operates in the decomposing accumulated litter in a temperate forest.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevFood Chain

Food Web:
When the feeding relationship in a natural ecosystem become more complicated, the food chain does not remain simple and linear rather it is also complicated by several inter-connected overlapping food chains. This happens when greater number of species feed on many kinds of prey.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevFood web

Such complicated food chain is called food web.

  • Thus, Energy is passed through the system in food chains and webs. The flow of energy in ecosystems is unidirectional.
  • The important point to note is that the amount of energy decreases at successive trophic levels. The number of trophic levels in the grazing food chain is restricted as the transfer of energy follows 10 per cent law – only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.
  • Storage of energy in the system is shown by the amount of living material in both the plants and animals present. The amount of living material present is called the standing crop.
  • This can be expressed in several ways but is usually shown as biomass (living material) per unit area, measured as dry weight, ash weight or calorific value.
  • Usually the amount of standing crop in each trophic level decreases with each step on the food chain away from the plants. This can be shown diagrammatically by Ecological pyramids.


Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevEnergy flow through different trophic levels

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev

 

Ecological Pyramid
The pyramid shape of decrease of total number of species, total biomass and energy availability with successive higher trophic levels in the food chain in a natural ecosystem is called ecological pyramid.

  • 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
  • Number Pyramid is the pyramid formed by the number of species from one trophic level to higher trophic levels.
  • Biomass pyramid includes the total weight of the organic matter (total biomass) of each trophic level. Thus, the pyramid formed by total biomass at each trophic level is called biomass pyramid.
  • Energy Pyramid is the pyramid representing total amount of energy present at each trophic level of food chain in a natural ecosystem per unit area per unit time. The energy is expressed in kilocalories per square meter per day or per year. (Kcal/m2/day or year)

Any calculations of energy content, biomass, or numbers has to include all organisms at that trophic level. No generalisations we make will be true if we take only a few individuals at any trophic level into account.

  • A given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time.
    Example: A sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.
  • In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores.
    Also energy at a lower trophic level is always more than at a higher level.
  • There are exceptions to this generalisation, for example the number of insects feeding on a big tree.
  • The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton.
  • 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.


Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRev


PRODUCTIVITY
In ecosystems the rate of production of organic matter is known as productivity.
Primary productivity refers to production at the autotroph level, and secondary productivity refers to production at the heterotroph level.
Productivity can be further divided into gross and net:
Gross productivity is the total amount of organic matter produced, and net productivity is the amount of organic matter left after some has been used in respiration.
Primary gross productivity will depend on the efficiency of photosynthesis and the amount of light energy coming into the system. The intensity and duration of sunlight varies globally so that the potential for gross primary productivity will vary greatly with different ecosystems. Secondary productivity will depend on the conversion of plant substances to animal substances. The efficiency of transfer of energy from one trophic level to the next is known as ecological efficiency.
Primary productivity depends on the plant species inhabiting a particular area. It also depends on a variety of environmental factors, availability of nutrients and photosynthetic capacity of plants. Therefore, it varies in different types of ecosystems.
The table below shows representative values for the net productivity of a variety of ecosystems — both natural and managed. These values are only approximations and are subject to fluctuations because of variations in temperature, fertility, and availability of water 

Estimated Net Productivity of Certain Ecosystems (in kilocalories/m2/year) 

15,000

Tropical rain forest

12,000

Coastal marsh

5,000

Temperate deciduous forest

2,500

Ocean close to shore

2,000

Tall-grass prairie

800

Open ocean

500

Desert


Ecological Niche 
The role that an organism takes in the ecosystem is known as its ecological niche. Species vary in the breadth of the roles performed. Some animals are specialists in their feeding habits-such as the koala bear, which eats only eucalyptus leaves—and others are generalists, consuming a wide variety of food.
The majority of animals occupy a broad ecological niche and so are generalists in their feeding habits.

Habitat: The ecological niche of a species may vary through its distribution in relation to its habitat, which is the name given to the place where an organism lives.
Factors such as availability of different foods and competition from other species will influence the role of an individual. Man is an example of this, operating as a herbivore, a carnivore and an omnivore in different places.

Species Structure: The species structure of an ecosystem refers to the numbers of species present, their relative abundance and diversity. Characteristically ecosystems contain a few species that are relatively common, having large numbers in their populations or a large amount of biomass in their standing crop, and a large number of species that are rare. Details about species structure will be taken up in next chapter.

Decomposition: Decomposition is the natural process of dead animal or plant tissue being rotted or broken down.
This process is carried out by invertebrates, fungi and bacteria. The result of decomposition is that the building blocks required for life can be recycled. Some dead animals will be eaten by scavenging animals such as foxes or crows.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevDecomposition cycle in terrestrial ecosystem

  • Those which are not eaten by larger animals are quickly decomposed or broken down into their constituent chemicals by a host of creatures including beetles and their larva, flies, maggots and worms as well as bacteria, moulds and fungi. Collectively these are known as decomposers.
  • The important steps in the process of decomposition are fragmentation, leaching, catabolism, humification and mineralisation.
  • 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 catabolism.
  • It is important to note that all the above steps in decomposition operate simultaneously on the detritus (raw material for decomposition).
  • Humification and mineralisation occur during decomposition in the soil.
  • Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralization.
  • Decomposition is largely an oxygen-requiring process.

The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favour decomposition whereas low temperature and anaerobiosis inhibit decomposition resulting in builds up of organic materials.


BIOMAGNIFICATION
Biomagnification, also known as bioamplification, is the process by which substances become more concentrated in the bodies of consumers as one moves up the food chain (trophic levels).

When chemicals or pesticides are let into rivers or lakes they are consumed by aquatic organisms like fish, which in turn are consumed by large birds, animals or humans. These harmful substances become concentrated in tissues, internal organs as it moves up the food chain.

Following substances have the potential to biomagnify:

  • Polychlorinated Biphenyls used as insulators in transformers and fire retardants.
  • Polynuclear aromatic hydrocarbons which are present in petroleum products.
  • Heavy metals like Mercury, copper, cadmium, chromium, lead, nickel, zinc, tin (TBT or tributyltin).
  • Cyanides used in fishing and gold leaching.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevBiomagnification of DDT

Effects of biomagnification:

  • High concentrations of DDT in some bird species caused failure of eggs by thinning the shells.
  • PCBs can affect the immune system, fertility, child development and possibly increase the risk of certain cancers.
  • Mercury poisoning interferes with the nervous system development in fetuses and young children.

Bioaccumulation v/s Biomagnification:

  • Although sometimes used interchangeably with bioaccumulation, an important distinction between the bioaccumulation and biomagnifications is that bioaccumulation occurs within a trophic level, and is the increase in concentration of a substance in certain tissues (usually in fatty tissue.) of organisms' bodies due to absorption from food and the environment.
  • The longer the half-life of the substance the greater is the risk of poisoning though levels of toxins are not very high in the environment. Bioaccumulation varies between individual organisms as well as between species. Large, fat, long-lived individuals or species with low rates of metabolism or excretion of a chemical will bioaccumulate more than small, thin, short-lived organisms. Thus, an old lake trout may bioaccumulate much more than a young bluegill in the same lake.


NUTRIENT CYCLES
The flow of energy in ecosystems is one-way. In contrast, the nutrients which are needed to produce organic material are circulated round the system and are re-used several times.

  • All natural elements are capable of being absorbed by plants, usually as gases from the air or as soluble salts from the soil, but only oxygen, carbon, hydrogen and nitrogen are needed in large quantities. These substances are known as macronutrients and form the basis of fats, carbohydrates and proteins.
  • Other nutrients, such as magnesium, sulphur and phosphorus are needed in minute amounts and are known as micronutrients.
  • Nutrient cycles can be presented in the framework of a model in which each cycle has a reservoir pool, which is a large, slow-moving non-biological component, and an exchange pool, which is a smaller, more active portion where the nutrient is exchanged between biotic and abiotic parts of the ecosystem. There are two basic types of cycle, gaseous ones, in which the reservoir pool is the atmosphere, and sedimentary ones, in which the reservoir pool is the Earth's crust.
  • Another name of nutrient cycling is biogeochemical cycles (bio: living organism, geo: rocks, air, and water).

Water Cycle:

  • Water undergoes a cycle from the ocean to land and land to ocean.
  • The hydrological cycle describes the movement of water on, in, and above the earth.
  • The distribution of water on earth is quite uneven. Many locations have plenty of water while others have very limited quantity.
  • The hydrological cycle is the circulation of water within the earth’s hydrosphere in different forms i.e. the liquid, solid and the gaseous phases.  

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevWater cycle

About 71 per cent of the planetary water is found in the oceans. The remaining is held as freshwater in glaciers and icecaps, groundwater sources, lakes, soil moisture, atmosphere, streams and within life. Nearly 59 per cent of the water that falls on land returns to the atmosphere through evaporation from over the oceans as well as from other places. The remainder runs-off on the surface, infiltrates into the ground or a part of it becomes glacier.


Carbon Cycle:  Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevCarbon cycle

  • Carbon cycle is mainly the conversion of carbon dioxide.
  • This conversion is initiated by the fixation of carbon dioxide from the atmosphere through photosynthesis.
  • Such conversion results in the production of carbohydrate, glucose that may be converted to other organic compounds.
  • Some of the carbohydrates are utilised directly by the plants itself.
  • During the process, more Carbon dioxide is generated and is released through its leaves or roots during the day.
  • The remaining carbohydrates not being utilised by the plant become part of the plant tissue.
  • Plant tissues are either being eaten by the herbivorous animals or get decomposed by the microorganisms.
  • The herbivores convert some of the consumed carbohydrates into carbon dioxide for release into the air through respiration.
  • The micro-organisms decompose the remaining carbohydrates after the animal dies.
  • The carbohydrates that are decomposed by the micro-organisms then get oxidised into carbon dioxide and are returned to the atmosphere.

The Phosphorus Cycle:

  • Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevPhosphorous cycle
  • The phosphorus cycle is an example of a sedimentary cycle which is easily disrupted.
  • Phosphates in the soil are taken into plants for protein synthesis and are passed through the food chains of ecosystems.
  • When plant and animal bodies and their excretory products decompose, the phosphorus is released to the soil where it can either be taken back into plants or washed out by rainfall into drainage systems which ultimately take it to the sea.
  • If this happens it will be incorporated in marine sediments and so lost from the exchange pool.
  • One important route for the rapid return of phosphorus from these sediments occurs where there are upwelling ocean currents. These bring phosphorus to the surface waters, where it is taken into marine food chains.
  • The depletion of phosphorus from the exchange pool is compensated very slowly by the release of the element from the phosphate rocks of the reservoir pool. This occurs by the process of erosion and weathering.
  • The phosphorus cycle can be easily disrupted by the use of phosphate fertilisers in modern agriculture.
  • Most manufactured phosphate fertilisers are produced from phosphate rocks but are rapidly lost from the exchange pool to marine deposits as they are easily leached from the soil.

The Nitrogen Cycle:

  • The nitrogen cycle is an example of a gaseous type.
  • It is probably the most complete of the nutrient cycles.
  • The reservoir pool is the atmosphere and the exchange pool operates between organisms and the soil.
  • Atmospheric nitrogen in the reservoir pool cannot be used directly by most plants. It has to be made into a chemical compound such as a nitrate before it is available to the exchange pool.
  • Nitrates in the soil are absorbed by plants and pass through food chains.
  • Ultimately they are released as ammonia when organic material is decomposed.
  • The ammonia is changed back to nitrates by the action of bacteria.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevNitrogen cycle


  • If the nitrates are not reabsorbed by plants they may be lost from the exchange pool in two ways: first, by leaching from the soil to shallow marine sediments (in this case they may be returned in the droppings of marine birds in the same way as phosphorus); second, nitrates may be lost from the soil by being broken down by denitrifying bacteria, and the nitrogen contained in them being released to the atmosphere.
  • The conversion of gaseous nitrogen to nitrate occurs in two main ways. Some can be fixed by electrical action during thunderstorms, but most is converted by nitrogen-fixing organisms. These are mostly bacteria, algae and fungi, and either operates by themselves in the soil or in an association with a plant, particularly those in the legume family, such as clover.

The Oxygen Cycle:

  • The cycling of oxygen is a highly complex process. Oxygen occurs in a number of chemical forms and combinations.
  • It combines with nitrogen to form nitrates and with many other minerals and elements to form various oxides such as the iron oxide, aluminium oxide and others.
  • Much of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis and is released in the atmosphere through transpiration and respiration processes of plants.

Other Mineral Cycles:

  • Other than carbon, oxygen, nitrogen and hydrogen being the principal geochemical components of the biosphere, many other minerals also occur as critical nutrients for plant and animal life. These mineral elements required by living organisms are obtained initially from inorganic sources such as phosphorus, sulphur, calcium and potassium.
  • They usually occur as salts dissolved in soil water or lakes, streams and seas. Mineral salts come directly from the earth’s crust by weathering where the soluble salts enter the water cycle, eventually reaching the sea.
  • Other salts are returned to the earth’s surface through sedimentation, and after weathering, they again enter the cycle. All living organisms fulfil their mineral requirements from mineral solutions in their environments. Other animals receive their mineral needs from the plants and animals they consume. After the death of living organisms, the minerals are returned to the soil and water through decomposition and flow.

SUCCESSION

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevStages of forest succession

  • The species structure of an ecosystem will not be constant.
  • There will be changes in the types of plants and animals living there as conditions are ameliorated by the organisms themselves. Typically there will be a sequence of different assemblages of species, each known as a seral stage or sere; each seral stage will alter the environment slightly.
  • New species will migrate into the area as conditions change to those which they can tolerate.
  • Change of community structure due to environmental change through time in this way is called succession. Succession is an orderly process involving predictable changes in species structure leading to a stable, self perpetuating community, called the climax.
  • There are two main types of succession, primary and secondary.
  • Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before.
    Example: a newly quarried rock faces or sand dunes. The establishment of a new biotic community is generally slow. Before a biotic community of diverse organisms can become established, there must be soil. Depending mostly on the climate, it takes natural processes several hundred to several thousand years to produce fertile soil on bare rock.
  • Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat.
    For example, after felling of trees in woodland, land clearance or a fire. Since some soil or sediment is present, succession is faster than primary succession.

Sere:
Succession is directional. Different stages in a particular habitat succession can usually be accurately predicted. These stages, characterised by the presence of different communities, are known as 'seres'. Communities change gradually from one sere to another.

Climax:

  • The seres are not totally distinct from each other and one will tend to merge gradually into another, finally ending up with a 'climax' community.
  • The community developed at the end of succession is called climax vegetation or climax community.
  • Succession will not go any further than the climax community. This is the final stage. This does not however, imply that there will be no further change. When large organisms in the climax community, such as trees, die and fall down, then new openings are created in which secondary succession will occur.
  • At any time during primary or secondary succession, natural or human induced disturbances (fire, deforestation, etc.), can convert a particular stage of succession to an earlier stage.
  • Also such disturbances create new conditions that encourage some species and discourage or eliminate other species.
    Example: Grass ecosystems are an early stage of succession in regions where the mature ecosystems are forests. However, grass ecosystems are climax ecosystems in grassland regions, where there is not enough rainfall to support a forest. Desert ecosystems are climax ecosystems where there is not enough rainfall even for grassland. In some cases, there is enough rainfall for grass, but overgrazing can change the grassland to desert.


BIOTIC POTENTIAL
(i) Populations vary in their capacity to grow. The maximum rate at which a population can increase when resources are unlimited and environmental conditions are ideal is termed the population's biotic potential. Each species will have a different biotic potential due to variations in:

  • The species' reproductive span (how long an individual is capable of reproducing)
  • The frequency of reproduction (how often an individual can reproduce)
  • "Litter size" (how many offspring are born each time)
  • Survival rate (how many offspring survive to reproductive age)

(ii) There are always limits to population growth in nature. Populations cannot grow exponentially indefinitely. Exploding populations always reach a size limit imposed by the shortage of one or more factors such as water, space, and nutrients or by adverse conditions such as disease, drought and temperature extremes.
(iii) The factors which act jointly to limit a population's growth are termed the environmental resistance.


CARRYING CAPACITY
For a given region, carrying capacity is the maximum number of individuals of a given species that an area's resources can sustain indefinitely without significantly depleting or degrading those resources. Determining the carrying capacities for most organisms is fairly straightforward.

  • For humans carrying capacity is much more complicated. The definition is expanded to include not degrading our cultural and social environments and not harming the physical environment in ways that would adversely affect future generations.
  • For populations which grow exponentially, growth starts out slowly, enters a rapid growth phase and then levels off when the carrying capacity for that species has been reached.
  • The size of the population then fluctuates slightly above or below the carrying capacity. Reproductive lag time may cause the population to overshoot the carrying capacity temporarily.
  • Reproductive lag time is the time required for the birth rate to decline and the death rate to increase in response to resource limits.
  • An area's carrying capacity is not static. The carrying capacity may be lowered by resource destruction and degradation during an overshoot period or extended through technological and social changes.


ECOSYSTEM SERVICESChapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevEcosystem servicesEcosystem services are the benefits people obtain from ecosystems. These include provisioning, regulating, and cultural services that directly affect people and supporting services needed to maintain the other services.

The Millennium Ecosystem Assessment (MA) was initiated in 2001 by United Nations. The objective of the MA was to assess the consequences of ecosystem change for human well-being, the scientific basis for action needed to enhance the conservation and sustainable use of those systems and their contribution to human well-being.


ECOTONE
An ecotone is a transitional area between two different ecosystems, such as a forest and grassland.

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevEcotone

  • It has some of the characteristics of each bordering biological community and often contains species not found in the overlapping communities.
  • An ecotone may exist along a broad belt or in a small pocket, such as a forest clearing, where two local communities blend together.
  • An ecotonal area often has a higher density of organisms of one species and a greater number of species than are found in either flanking community.
  • Some organisms need a transitional area for activities such as courtship, nesting, or foraging for food.
  • Ecotones also appear where one body of water meets another (e.g., estuaries and lagoons) or at the boundary between the water and the land (e.g., marshes).

Edge Effect

Chapter -1- Biosphere And Working of Ecosystems , Environment and Disaster Management UPSC Notes | EduRevEdge effect

  • Ecotones often have a larger number of species and larger population densities than the communities on either side.
  • This tendency for increased biodiversity within the ecotone is referred to as the "edge effect."
  • Those species which occur primarily or most abundantly in the ecotones are called "edge" species.

Home Range

  • The home range of an animal is the area where it spends its time; it is the region that encompasses all the resources the animal requires to survive and reproduce.
  • Competition for food and other resources influences how animals are distributed in space. Even when animals do not interact, clumped resources may cause individuals to aggregate

Other Important Terms

  • Hologenic: Those animals which take their food through their mouths, such as big animals.
    Examples: Elephants, Cows, Camels, etc.
  • Parasites: Those animals which depend on other animals for their food and life.
  • Autecology: The study of relationship of individual species with the environment.
  • Synecology: The study of plant communities in relation to their habitats of a given ecosystem.

UPSC QUESTIONS RELATED TO ABOVE TOPICS 
1. The states of Jammu and Kashmir, Himachal Pradesh and Uttarakhand are reaching the limits of their ecological carrying capacity due to tourism. Critically evaluate. (GS paper 1, 2015)
2. Write in detail on the concept of biosphere as an ecosystem. (Geography Mains 2002)
3. Discuss the concept, components and functioning of an ecosystem. (Geography Mains 2001/200 words)
4. Define ecosystem and describe briefly its various components. (Geography Mains 1994)
5. Write short note on ecosystem. (Geography Mains 1986/200 words).

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Environment and Disaster Management UPSC Notes | EduRev

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