Biology

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Green House Effect, Ozone Depletion And Its Effects

Green House Effect is a process by which radiant heat from the sun is captured by gases in the atmosphere that increase the temperature of the earth ultimately. The gases that capture heat are called Green House Gases which include carbon dioxide (CO₂), methane (CH₄), Nitrous Oxide (N₂O) and a variety of manufactured chemicals like chloroflorocarbon (CFC).

Increase in greenhouse gases lead to irreversible changes in major ecosystems and climate patterns. For example, coral ecosystem is affected by increase in temperature, especially coral bleaching observed in Gulf of Mannar, Tamil Nadu.

Human activities lead to produce the green house effect by:-

• Burning fossil fuels, which releases CO₂ and CH₄
• Way of Agriculture and animal husbandry practices
• Electrical gadgets like refrigerator and air conditioners release chloro floro carbons
• The fertilizers used in Agriculture which release N₂O
• The emissions from automobiles.

The increase in mean global temperature (highest in 4000 years) due to increased concentration of green house gases is called global warming. One of the reasons for this is over population which creates growing need for food, fire and fuel and considered to be the major cause of global warming.

Effects of Global Warming

• Rise in global temperature which causes sea levels to rise as polar ice caps and glaciers begin to melt causing submergence of many coastal cities in many parts of the world.
• There will be a drastic change in weather patterns bringing more floods or droughts in some areas.
• Biological diversity may get modified, some species ranges get redefied. Tropics and sub-tropics may face the problem of decreased food production.

Sources of Green House Gases Emission (Natural and Anthropogenic)

CO₂ (Carbon dioxide)

• Coal based power plants, by the burning of fossil fuels for electricity generation.
• Combustion of fuels in the engines of automobiles, commercial vehicles and air planes contribute the most of global warming.
• Agricultural practices like stubble burning result in emission of CO₂.
• Natural from organic matter, volcanoes, warm oceans and sediments.

Methane

Methane is 20 times as effective as CO₂ at trapping heat in the atomosphere. Its sources are attributed paddy cultivation, cattle rearing, bacteria in water bodies, fossil fuel production, ocean, non-wetland soils and forest / wild fies.

N₂O (Nitrous oxide)

It is naturally produced in Oceans from biological sources of soil and water due to microbial actions and rainforests. Man-made sources include nylon and nitric acid production, use of fertilizers in agriculture, manures cars with catalytic converter and burning of organic matter.

Global Warming Effects on Plants

• Low agricultural productivity in tropics
• Frequent heat waves (Weeds, pests, fungi need warmer temperature)
• Increase of vectors and epidemics
• Strong stroms and intense flood damage
• Water crisis and decreased irrigation
• Change in flowering seasons and pollinators
• Change in Species distributional ranges
• Species extinction

Strategies to deal with Global Warming

• Increasing the vegetation cover, grow more trees
• Reducing the use of fossil fuels and green house gases
• Developing alternate renewable sources of energy
• Minimising uses of nitrogeneous fertilizers, and aerosols.

Ozone depletion

Ozone layer is a region of Earth’s stratosphere that absorbs most of the Sun’s ultra violet radiation. The ozone layer is also called as the ozone shield and it acts as a protective shield, cutting the ultraviolet radiation emitted by the sun. Just above the atmosphere there are two layers namely troposphere (the lower layer) and stratosphere (the upper layer).

The ozone layer of the troposphere is called bad ozone and the ozone layer of stratosphere is known as good ozone because this layer acts as a shield for absorbing the UV radiations coming from the sun which is harmful for living organisms causing DNA damage. The thickness of the ozone column of air from the ground to the top of the atmosphere is measured in terms of Dobson Units.

The ozone shield is being damaged by chemicals released on the Earth’s surface notably the chloroflorocarbons widely used in refrigeration, aerosols, chemicals used as cleaners in many industries. The decline in the thickness of the ozone layer over restricted area is called Ozone hole.

Ozone depletion in the stratosphere results in more UV radiations especially UV B radiations (shortwaves). UV B radiation destroys biomolecules (skin ageing) and damages living tissues. UV – C is the most damaging type of UV radiation, but it is completely filtered by the atmosphere (ozone layer). UV – a contribute 95% of UV radiation which causes tanning burning of skin and enhancing skin cancer. Hence the uniform ozone layer is critical for the wellbeing of life on earth.

During 1970’s research fidings indicated that man-made chloroflorocarbons (CFC) reduce and convert ozone molecules in the atmosphere. The threats associated with reduced ozone pushed the issue to the forefront of global climate issues and gained promotion through organisation such as World Meterological Organisation and the United Nations.

The Vienna Convention was agreed upon at the Vienna conference of 1985 but entered into force in 1988 provided the frameworks necessary to create regulative measures in the form of the Montreal protocol.

The International treaty called the Montreal Protocol (1987) was held in Canada on substances that deplete ozone layer and the main goal of it is gradually eliminating the production and consumption of ozone depleting substances and to limit their damage on the Earth’s ozone layer.

Clean Development Mechanism (CDM) is defied in the Kyoto protocol (2007) which provides project based mechanisms with two objectives to prevent dangerous climate change and to reduce green house gas emissions. CDM projects helps the countries to reduce or limit emission and stimulate sustainable development.

An example for CDM project activity, is replacement of conventional electrifiation projects with solar panels or other energy efficient boilers. Such projects can earn Certified Emission Reduction (CER) with credits / scores, each equivalent to one tonne of CO₂, which can be counted towards meeting Kyoto targets.

Effects of Ozone depletion

The main ozone depletion effects are:

• Increases the incidence of cataract, throat and lung irritation and aggravation of asthma or emphysema, skin cancer and diminishing the functioning of immune system in human beings.
• Juvenile mortality of animals.
• Increased incidence of mutations.
• In plants, photosynthetic chemicals will be affected and therefore photosynthesis will be inhibited. Decreased photosynthesis will result in increased atmospheric CO₂ resulting in global warming and also shortage of food leading to food crisis.
• Increase in temperature changes the climate and rainfall pattern which may result in flood / drought, sea water rise, imbalance in ecosystems affecting flora and fauna.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Ecological Plant Succession – Characteristics, Types and Examples

We very often see that forests and lands in our areas are drastically affcted by natural calamities (Flood, earthquake) and anthropogenic activities (Fire, over grazing, cutting of trees). Due to these reasons all plants of an area are destroyed and the areas become nude. When we observe this area, over a period of a time we can see that it will be gradually covered by plant community again and become fertile.

Such successive replacement of one type of plant community by the other of the same area / place is known as plant succession. The first invaded plants in a barren area are called pioneers. On the other hand, a series of transitional developments of plant communities one after another in a given area are called seral communities. At the end a final stage and a final plant community gets established which are called as climax and climax community respectively.

Characteristics of ecological succession

• It is a systematic process which causes changes in specifi structure of plant community.
• It is resultant of changes of abiotic and biotic factors.
• It transforms unstable community into a stable community.
• Gradual progression in species diversity, total biomass, niche specialisation, and humus content of soil takes place.
• It progresses from simple food chain to complex food web.
• It modifies the lower and simple life form to the higher life forms.
• It creates inter-dependence of plants and animals.

Types of succession

The various types of succession have been classified in different ways on the basis of different aspects. These are as follows:

1. Primary succession:

The development of plant community in a barren area where no community existed before is called primary succession. The plants which colonize first in a barren area is called pioneer species or primary community or primary colonies. Generally, Primary succession takes a very long time for the occurrence in any region.

Example: Microbes, Lichen, Mosses.

2. Secondary succession:

The development of a plant community in an area where an already developed community has been destroyed by some natural disturbance (Fire, flood, human activity) is known as secondary succession. Generally, This succession takes less time than the time taken for primary succession.

Example: The forest destroyed by fire and excessive lumbering may be re-occupied by herbs over a period of times.

3. Allogenic succession

Allogeneic succession occurs as a result of abiotic factors. The replacement of existing community is caused by other external factors (soil erosion, leaching, etc.,) and not by existing organisms. Example: In a forest ecosystem soil erosion and leaching alter the nutrient value of the soil leading to the change of vegetation in that area.

Classification of plant succession

Detailed study of Hydrosere and Lithosere are discussed below:

Hydrosere

The succession in a freshwater ecosystem is also referred to as hydrosere. Succession in a pond, begins with colonization of the pioneers like phytoplankton and finally ends with the formation of climax community like forest stage. It includes the following stages Fig 7.21.

1. Phytoplankton stage:

It is the first stage of succession consisting of the pioneer community like blue green algae, green algae, diatoms, bacteria, etc., The colonization of these organisms enrich the amount of organic matter and nutrients of pond due to their life activities and death. This favors the development of the next seral stages.

2. Submerged plant stage:

As the result of death and decomposition of planktons, silt brought from land by rain water, lead to a loose mud formation at the bottom of the pond. Hence, the rooted submerged hydrophytes begin to appear on the new substratum. Example: Chara, Utricularia, Vallisneria and Hydrilla etc.

The death and decay of these plants will build up the substratum of pond to become shallow. Therefore, this habitat now replaces another group of plants which are of floating type.

3. Submerged free flating stage:

During sthis stage, the depth of the pond will become almost 2-5 feet. Hence, the rooted hydrophytic plants and with floating large leaves start colonising the pond. Example: Rooted flating plants like Nelumbo, Nymphaea and Trapa.

Some free flating species like Azolla, Lemna, Wolff and Pistia are also present in this stage. By death and decomposition of these plants, further the pond becomes more shallow. Due to this reason, floating plant species is gradually replaced by another species which makes new seral stage.

4. Reed-swamp stage:

It is also called an amphibious stage. During this stage, rooted floating plants are replaced by plants which can live successfully in aquatic as well as aerial environment. Example: Typha, Phragmites, Sagittaria and Scirpus etc. At the end of this stage, water level is very much reduced, making it unsuitable for the continuous growth of amphibious plants.

5. Marsh meadow stage:

When the pond becomes swallowed due to decreasing water level, species of Cyperaceae and Poaceae such as Carex, Juncus, Cyperus and Eleocharis colonise the area. They form a mat-like vegetation with the help of their much branched root system. This leads to an absorption and loss of large quantity of water. At the end of this stage, the soil becomes dry and the marshy vegetation disappears gradually and leads to shurb stage.

6. Shrub stage:

As the disappearance of marshy vegetation continues, soil becomes dry. Hence, these areas are now invaded by terrestrial plants like shrubs (Salix and Cornus) and trees (Populus and Alnus). These plants absorb large quantity of water and make the habitat dry. Further, the accumulation of humus with a rich flora of microorganisms produce minerals in the soil, ultimately favouring the arrival of new tree species in the area.

7. Forest stage:

It is the climax community of hydrosere. A variety of trees invade the area and develop any one of the diverse type of vegetation. Example: Temperate mixed forest (Ulmus, Acer and Quercus), Tropical rain forest (Artocarpus and Cinnamomum) and Tropical deciduous forest (Bamboo and Tectona).

In the 7 stages of hydrosere succession, stage1 is occupied by pioneer community, while the stage 7 is occupied by the climax community. The stages 2 to 6 are occupied by seral communities.

Significance of Plant Succession

• Succession is a dynamic process. Hence an ecologist can access and study the seral stages of a plant community found in a particular area.
• The knowledge of ecological succession helps to understand the controlled growth of one or more species in a forest.
• Utilizing the knowledge of succession, even dams can be protected by preventing siltation.
• It gives information about the techniques to be used during reforestation and affrestation.
• It helps in the maintenance of pastures.
• Plant succession helps to maintain species diversity in an ecosystem.
• Patterns of diversity during succession are inflenced by resource availability and disturbance by various factors.
• Primary succession involves the colonization of habitat of an area devoid of life.
• Secondary succession involves the reestablishment of a plant community in disturbed area or habitat.
• Forests and vegetation that we come across all over the world are the result of plant succession.

Learninsta presents the core concepts of Biology with high-quality research papers and topical review articles.

Functions Of Ecosystem

The function of ecosystem include creation of energy creation, sharing of energy and cycling of materials between the living and nonliving components of an ecosystem. Before studying the productivity in any ecosystem, we should understand the essential role of sunlight used by producers of the first trophic level. The quantity of sunlight is directly proportional to the production of energy by plants.

Photosynthetically Active Radiation (PAR)

The amount of light available for photosynthesis of plants is called Photosynthetically Active Radiation (PAR) which is from of 400-700 nm in wave length. It is essential for photosynthesis and plant growth. PAR is not always constant because of clouds, tree shades, air, dust particles, seasons, latitudes and length of the daylight availability. Generally plants absorb more blue and red light for efficient photosynthesis.

Of the total sunlight, 34 percent that reaches the atmosphere is reflected back into the atmosphere, moreover 10% is held by ozone, water vapours and atmospheric gases and the remaining 56% reaches the earth’s surface. Out of this 56%, only 2 – 10% of the solar energy is used by green plants for photosynthesis while the remaining portion is dissipated as heat.

PAR is generally expressed in millimoles / square meter / second by using silicon photo voltic detectors which detect only 400 – 700 nm wavelength of light. PAR values range from 0 to 3000 millimoles / square meter / second.

At night PAR is zero and during midday in the summer, PAR oftn reaches 2000 – 3000 millimoles / square meter / second.

Productivity of an ecosystem

The rate of biomass production per unit area in a unit time is called productivity. It can be expressed in terms of gm / m² / year or Kcal / m² / year. It is classified as given below.

1. Primary productivity
2. Secondary productivity
3. Community productivity

1. Primary productivity:

The chemical energy or organic matter generated by autotrophs during the process of photosynthesis and chemosynthesis is called primary productivity. It is the source of energy for all organisms, from bacteria to human.

a. Gross Primary Productivity (GPP)

The total amount of food energy or organic matter or biomass produced in an ecosystem by autotrophs through the process of photosynthesis is called gross primary productivity.

b. Net Primary Productivity (NPP)

The proportion of energy which remains after respiration loss in the plant is called net primary productivity. It is also called as apparent photosynthesis. This the difference between GPP and respiration is known as NPP.

NPP = GPP – Respiration

NPP of whole biosphere is estimated to be about 170 billion tons (dry weight) per year. Out of which NPP of oceanic producers is only 55 billion tons per year in unit time.

2. Secondary productivity

The amount of energy stored in the tissues of heterotrophs or consumers is called secondary productivity.

a. Gross secondary productivity

It is equivalent to the total amount of plant material is ingested by the herbivores minus the materials lost as faeces.

b. Net secondary productivity

Storage of energy or biomass by consumers per unit area per unit time, after respiratory loss is called net secondary productivity.

3. Community productivity

The rate of net synthesis of organic matter (biomass) by a group of plants per unit area per unit time is known as community productivity.

Factors affecting primary productivity

Primary productivity depends upon the plant species of an area, their photosynthetic capacity, availability of nutrients, solar radiation, precipitation, soil type, topographic factors (altitude, latitude, direction), and other environmental factors. It varies in different types of ecosystems.

Concept of trophic level in an ecosystem

(Greek word ‘trophic’ = to food or feeding)

A trophic level refers to the position of an organism in the food chain. The number of trophic levels is equal to the number of steps in the food chain. The green plants (producers) occupying the first trophic level (T₁) are called producers. The energy produced by the producers is utilized by the plant eaters (herbivores) they are called primary consumers and occupy the second trophic level (T₂).

Herbivores are eaten by carnivores, which occupy the third trophic level (T₃). They are also called secondary consumers or primary carnivores. Carnivores are eaten by the other carnivores, which occupy the fourth trophic level (T₄). They are called the tertiary consumers or secondary carnivores. Some organisms which eat both plants and animals are called as omnivores (Crow). Such organisms may occupy more than one trophic level in the food chain.

Energy flow

The transfer of energy in an ecosystem between trophic levels can be termed as energy flow. It is the key function in an ecosystem. Part of the energy obtained from the sun by producers is transferred to consumers and decomposers through each trophic level, while some amount of energy is dissipated in the form of heat. Energy flow is always unidirectional in an ecosystem.

Laws of thermodynamics

The storage and loss of energy in an ecosystem is based on two basic laws of thermo-dynamics.

(i) First law of thermodynamics

It states that energy can be transmitted from one system to another in various forms. Energy cannot be destroyed or created. But it can be transformed from one form to another. As a result, the quantity of energy present in the universe is constant.

Example:

In photosynthesis, the product of starch (chemical energy) is formed by the combination of reactants (chlorophyll, H₂O, CO₂). The energy stored in starch is acquired from the external sources (light energy) and so there is no gain or loss in total energy. Here light energy is converted into chemical energy.

Light energy → chemical energy

(ii) Second law of thermodynamics

It states that energy transformation results in the reduction of the free energy of the system. Usually energy transformation cannot be 100% efficient. As energy is transferred from one organism to another in the form of food, a portion of it is stored as energy in living tissue, whereas a large part of energy is dissipated as heat through respiration. The transfer of energy is irreversible natural process. Example: Ten percent law

Ten percent law

This law was proposed by Lindeman (1942). It states that during transfer of food energy from one trophic level to other, only about 10% stored at every level and rest of them (90%) is lost in respiration, decomposition and in the form of heat. Hence, the law is called ten percent law. Example: It is shown that of the 1000 Joules of Solar energy trapped by producers. 100 Joules of energy is stored as chemical energy through photosynthesis.

The remaining 900 Joules would be lost in the environment. In the next trophic level herbivores, which feed on producers get only 10 Joules of energy and the remaining 90 Joules is lost in the environment.

Likewise, in the next trophic level, carnivores, which eat herbivores store only 1 Joule of energy and the remaining 9 Joules is dissipated. Finally, the carnivores are eaten by tertiary consumers which store only 0.1 Joule of energy and the remaining 0.9 Joule is lost in the environment. Thus, at the successive trophic level, only ten percent energy is stored.

Food chain:

The movement of energy from producers upto top carnivores is known as food chain, i.e., in any food chain, energy flows from producers to primary consumers, then from primary consumers to secondary consumers, and finally secondary consumers to tertiary consumers. Hence, it shows linear network links. Generally, there are two types of food chain, (1) Grazing food chain and (2) Detritus food chain.

1. Grazing food chain:

Main source of energy for the grazing food chain is the Sun. It begins with the first link, producers (plants). The second link in the food chain is primary consumers (mouse) which get their food from producers. The third link in the food chain is secondary consumers (snake) which get their food from primary consumers. Fourth link in the food chain is tertiary consumers (eagle) which get their food from secondary consumers.

2. Detritus food chain:

This type of food chain begins with dead organic matter which is an important source of energy. A large amount of organic matter is derived from the dead plants, animals and their excreta. This type of food chain is present in all ecosystems.

The transfer of energy from the dead organic matter, is transferred through a series of organisms called detritus consumers (detritivores) – small carnivores – large (top) carnivores with repeated eating and being eaten respectively. This is called the detritus food chain.

Food Web

The inter-locking pattern of a number of food chain form a web like arrangement called food web. It is the basic unit of an ecosystem, to maintain its stability in nature. Which is also called homeostasis. Example: In a grazing food chain of a grass land, in the absence of a rabbit, a mouse may also eat food grains. The mouse in turn may be eaten directly by a hawk or by a snake and the snake may be directly eaten by hawks.

Hence, this interlocking pattern of food chains is the food web and the species of an ecosystem may remain balanced to each other by some sort of natural check.

Signifiance of food web

• • Food web is constructed to describe species interaction called direct interaction.
• It can be used to illustrate indirect interactions among different species.
• It can be used to study bottom-up or topdown control of community structure.
• It can be used to reveal different patterns of energy transfer in terrestrial and aquatic ecosystems.

Ecological pyramids

Graphic representation of the trophic structure and function at successive trophic levels of an ecosystem is called ecological pyramids. The
concept of ecological pyramids was introduced by Charles Elton (1927). Thus they are also called as Eltonian pyramids.

There are three types:

1. pyramid of number
2. pyramid of biomass
3. pyramid of energy.

1. Pyramid of number

A graphical representation of the number of organisms present at each successive trophic level in an ecosystem is called pyramids of number. There are three different shapes of pyramids upright, spindle and inverted.

There is a gradual decrease in the number of organisms in each trophic level from producers to primary consumers and then to secondary consumers, and finally to tertiary consumers. Therefore, pyramids of number in grassland and pond ecosystem are always upright.

In a forest ecosystem the pyramid of number is somewhat different in shape, it is because the base (T₁) of the pyramid occupies large sized trees (Producer) which are lesser in number. Herbivores (T₂) (Fruit eating birds, elephant, deer) occupying second trophic level, are more in number than the producers. In final trophic level (T₄), tertiary consumers (lion) are lesser in number than the secondary consumer (T₃) (fox
and snake). Therefore, the pyramid of number in forest ecosystem looks spindle shaped.

The pyramid of number in a parasite ecosystem is always inverted, because it starts with a single tree. Therefore there is gradual increase in the number of organisms in successive tropic levels from producer to tertiary consumers.

2. Pyramid of biomass

A graphical representation of the amount of organic material (biomass) present at each successive trophic level in an ecosystem is called pyramid of biomass.

In grassland and forest ecosystems, there is a gradual decrease in biomass of organisms at successive trophic levels from producers to top carnivores (Tertiary consumer). Therefore, these two ecosystems show pyramids as upright pyramids of biomass.

However, in pond ecosystem, the bottom of the pyramid is occupied by the producers, which comprise very small organisms possessing the least biomass and so, the value gradually increases towards the tip of the pyramid. Therefore, the pyramid of biomass is always inverted in shape.

3. Pyramid of energy

A graphical representation of energy flow at each successive trophic level in an ecosystem is called pyramid of energy. The bottom of the pyramid of energy is occupied by the producers. There is a gradual decrease in energy transfer at successive tropic levels from producers to the upper levels. Threfore, the pyramid of energy is always upright.

Decomposition:

Decomposition is a process in which the detritus (dead plants, animals and their excreta) are breaken down in to simple organic matter by the decomposers. It is an essential process for recycling and balancing the nutrient pool in an ecosystem.

Nature of decomposition

The process of decomposition varies based on the nature of the organic compounds, i.e., some of the compounds like carbohydrate, fat and protein are decomposed rapidly than the cellulose, lignin, chitin, hair and bone.

Mechanism of decomposition

Decomposition is a step wise process of degradation mediated by enzymatic reactions. Detritus acts as a raw material for decomposition. It occurs in the following steps.

a. Fragmentation – The breaking down of detritus into smaller particles by detritivores like bacteria, fungi and earth worm is known as fragmentation. These detritivores secrete certain substances to enhance the fragmentation process and increase the surface area of detritus particles.

b. Catabolism – The decomposers produce some extracellular enzymes in their surroundings to break down complex organic and inorganic compounds in to simpler ones. This is called catabolism

c. Leaching or Eluviation – The movement of decomposed, water soluble organic and inorganic compounds from the surface to the lower layer of soil or the carrying away of the same by water is called leaching or eluviation.

d. Humifiation – It is a process by which simplified detritus is changed into dark coloured amorphous substance called humus. It is highly resistant to microbial action, therefore decomposition is very slow. It is the reservoir of nutrients.

Mineralisation – Some microbes are involved in the release of inorganic nutrients from the humus of the soil, such process is called mineralisation.

Factors affecting decomposition

Decomposition is affcted by climatic factors like temperature, soil moisture, soil pH, oxygen and also the chemical quality of detritus.

Biogeochemical cycles (Nutrient cycles)

Exchange of nutrients between organisms and their environment is one of the essential aspects of an ecosystem. All organisms require nutrients for their growth, development, maintenance and reproduction. Circulation of nutrients within the ecosystem or biosphere is known as biogeochemical cycles and also called as ‘cycling of materials.’ There are two basic types,

• Gaseous cycle – It includes atmospheric Oxygen, Carbon and Nitrogen cycles.
• Sedimentary cycle – It includes the cycles of Phosphorus, Sulphur and Calcium Which are present as sediments of earth.
  

Many of the cycles mentioned above are studied by you in previous classes. Therefore, in this chapter, only the carbon and phosphorous cycles are explained.

Carbon cycle

The circulation of carbon between organisms and environment is known as the carbon cycle. Carbon is an inevitable part of all biomolecules and is substantially impacted by the change in global climate. Cycling of carbon between organisms and atmosphere is a consequence of two reciprocal processes of photosynthesis and respiration.

The releasing of carbon in the atmosphere increases due to burning of fossile fuels, deforestration, forest fire, volcanic eruption and decomposition of dead organic matters. The details of carbon cycle are given in the figure.

Phosphorus cycle

It is a type of sedimentary cycle. Already we know that phosphorus is found in the biomolecules like DNA, RNA, ATP, NADP and phospholipid molecules of living organisms. Phosphorus is not abundant in the biosphere, whereas a bulk quantity of phosphorus is present in rock deposits, marine sediments and guano.

It is released from these deposits by weathering process. After that, it circulates in lithosphere as well as hydrosphere. The producers absorb phosphorus in the form of phosphate ions, and then it is transferred to each trophic level of food chain through food.

Again death of the organisms and degradation by the action of decomposers, the phosphorus is released back into the lithosphere and hydrosphere to maintain phosphorus cycle.

Types of ecosystem

Biosphere consists of diffrent types of ecosystems, which are as follows:

Though there are many types of ecosystems as charted above. Only the pond ecosystem is detailed below.

Structure of Pond ecosystem

It is a classical example for natural, aquatic, freshwater, lentic type of ecosystem. It helps us to understand the structure and function of an ecosystem. When rain water gathers in a shallow area, gradually over a period of time, different kinds of organisms (microbes, plants, animals) become part of this ecosystem. This pond ecosystem is a self sustaining and self regulatory fresh water ecosystem, which shows a complex interaction between the abiotic and biotic components in it.

Abiotic components

A pond ecosystem consists of dissolved inorganic (CO₂, O₂, Ca, N, Phosphate) and organic substances (amino acids and humic acid) formed from the dead organic matter. The function of pond ecosystem is regulated by few factors like the amount of light, temperature, pH value of water and other climatic conditions.

Biotic components

They constitute the producers, variety of consumers and decomposers (microorganisms).

a. Producers

A variety of phytoplanktons like Oscillatoria, Anabaena, Chlamydomonas, Pandorina, Eudorina, Volvox and Diatoms. Filamentous algae such as Ulothrix, Spirogyra, Cladophora and Oedogonium; flating plants Azolla, Salvia, Pistia, Wolff and Eichhornia; submerged plants Potamogeton and Phragmitis; rooted flating plants Nymphaea and Nelumbo; macrophytes like Typha and Ipomoea, constitute the major producers of a pond ecosystem.

b. Consumers

The animals represent the consumers of a pond ecosystem which include zooplanktons like Paramoecium and Daphnia (primary consumers); benthos (bottom living animals) like mollusces and annelids; secondary consumers like water beetles and frogs; and tertiary consumers (carnivores) like duck, crane and some top carnivores which include large fish, hawk, man, etc.

c. Decomposers

They are also called as microconsumers. They help to recycle the nutrients in the ecosystem. These are present in mud water and bottom of the ponds. Example: Bacteria and Fungi. Decomposers perform the process of decomposition in order to enrich the nutrients in the pond ecosystem. The cycling of nutrients between abiotic and biotic components is evident in the pond ecosystem, making itself self sufficient and self
regulating.

Based on the factors like distance from the shore, penetration of light, depth of water, types of plants and animals, there may be three zones, littoral, limnetic and profundal. The littoral zone, which is closest to the shore with shallow water region, allows easy penetration of light. It is warm and occupied by rooted plant species. The limnetic zone refers the open water of the pond with an effective penetration of light and domination of planktons.

The deeper region of a pond below the limnetic zone is called profundal zone with no effective light penetration and predominance of heterotrophs. The bottom zone of a pond is termed benthic and is occupied by a community of organisms called benthos (usually decomposers). The primary productivity through photosynthesis of littoral and limnetic zone is more due to greater penetration of light than the profundal zone.

Ecosystem services (Benefits)

Ecosystem services are defined as the benefits that people derive from nature. Robert Constanza et al (1927) stated “Ecosystem services are the benefis provided to human, through the transformation of resources (or Environmental assets including land, water, vegetation and atmosphere) into a flow of essential goods and services”.

Study on ecosystem services acts as an effective tool for gaining knowledge on ecosystem benefis and their sustained use. Without such knowledge gain, the fate of any ecosystem will be at stake and the benefits they provide to us in future will become bleak.

How do anthropogenic activities affect ecosystem services?

Now, we all exploit the ecosystem more than that of our needs. The Millennium Ecosystem Assessment (2005) found that “over the past 50 years, humans have changed the ecosystem more rapidly and extensively than in any comparable period of time in human history, largely to meet rapidly growing demands for food, fresh water, medicine, timber, fier and fuel.”

The varieties of benefis obtained from the ecosystem are generally categorized into the following four types

Generally the following human activities disturb or re-engineer an ecosystem every day.

• Habitat destruction
• Deforestation and over grazing
• Erosion of soils
• Introduction of non-native species
• Over harvesting of plant material
• Pollution of land, water and air
• Run of pesticides, fertilizers and animal wastes

How to protect the ecosystem?

It is a practice of protecting ecosystem at individual, organisational and governmental levels for the benefis of both nature and humans. Theats to ecosystems are many, like adverse human activities, global warming, pollution, etc. Hence, if we change our everyday life style, we can help to protect the planet and its ecosystem. “If we fail to protect environment, we will fail to save posterity”.

Therefore, we have to practice the following in our day today life:

• Buy and use only ecofriendly products and recycle them.
• Grow more trees
• Choose sustained farm products (vegetables, fruits, greens, etc.)
• Reduce the use of natural resources.
• Recycle the waste and reduce the amount of waste you produce.
• Reduce consumption of water and electricity.
• Reduce or eliminate the use of house-hold chemicals and pesticides.
• Maintain your cars and vehicles properly. (In order to reduce carbon emission)
• Create awareness and educate about ecosystem protection among your friends and family members.

Ecosystem Management

It is a process that integrates ecological, socio economic and institutional factors into a comprehensive strategy in order to sustain and enhance the quality of the ecosystem to meet current and future needs.

Ecosystem management emphasis on human role in judicious use of ecosystem and for sustained benefis through minimal human impacts on ecosystems. Environmental degradation and biodiversity loss will result in depletion of natural resources, ultimately affecting the existence of human.

Strategy of ecosystem management

• It is used to maintain biodiversity of ecosystems.
• It helps in indicating the damaged ecosystem (Some species indicate the health of the ecosystem: such species are called a flagship species).
• It is used to recognize the inevitability of ecosystem change and plan accordingly.
• It is one of the tools used for achieving sustainability of ecosystem through sustainable development programme (or projects).
• It is also helpful in identifying ecosystems which are in need of rehabilitation.
• It involves collaborative management with government agencies, local population, communities and NGO’s.
• It is used to build the capacity of local institutions and community groups to assume responsibility for long term implementation of ecosystem management activities even after the completion of the project.

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Structure Of Ecosystem

Ecosystem comprises of two major components. They are:

(i) Abiotic (non-living) components:

It includes climatic factors (air, water, sunlight, rainfall, temperature and humidity), edaphic factors (soil air, soil water and pH of soil), topography (latitude, altitude), organic components (carbohydrates, proteins, lipids and humic substances) and inorganic substances (C, H, O, N and P). Abiotic components play vital role in any ecosystem and hence the total inorganic substances present in any ecosystem at a given time is called standing quality (or) standing state.

(ii) Biotic (living) components:

It includes all living organisms like plants, animals, fungi and bacteria. They form the trophic structures of any ecosystem. On the basis of nutritional relationships, trophic levels of an ecosystem have two components.

• autotrophic components and
• heterotrophic components.

1. Autotrophic components:

Autotrophs are organisms which can manufacture the organic compounds from simple inorganic components through a process called photosynthesis. In most of the ecosystems, green plants are the autotrophs and are also called producers.

2. Heterotrophic components:

These organisms which consume the producers are called consumers and can be recognized into macro and micro consumers. Macroconsumers refer to herbivores, carnivores and omnivores (primary, secondary and tertiary consumers).

Microconsumers are called decomposers. Decomposers are organisms that decompose the dead plants and animals to release organic and inorganic nutrients into the environment which are again reused by plants. Example: Bacteria, Actinomycetes and Fungi.

The amount of living materials present in a population at any given time is known as standing crop, which may be expressed in terms of number or biomass per unit area. Biomass can be measured as fresh weight or dry weight or carbon weight of organisms. Biotic components are essential to construct the food chain, food web and ecological pyramids.

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Dispersal of Seeds and Fruits

Both fruits and seeds possess attractive colour, odour, shape and taste needed for the dispersal by birds, mammals, reptiles, fish, ants and insects even earthworms. The seed consists of an embryo, stored food material and a protective covering called seed coat.

As seeds contain miniature but dormant future plants, their dispersal is an important criterion for distribution and establishment of plants over a wide geographical area. The dissemination of seeds and fruits to various distances from the parent plant is called seed and fruit dispersal.

It takes place with the help of ecological factors such as wind, water and animals. Seed dispersal is a regeneration process of plant populations and a common means of colonizing new areas to avoid seedling level competition and from natural enemies like herbivores, frugivores and pathogens.

Fruit maturation and seed dispersal is inflenced by many ecologically favourable conditions such as Season (Example: Summer), suitable environment, and seasonal availability of dispersal agents like birds, insects etc.

Seeds require agents for dispersal which are crucial in plant community dynamics in many ecosystems around the globe. They offer many benefis to communities such as food and nutrients, migration of seeds across habitats and helps spreading plant genetic diversity.

Dispersal by Wind (Anemochory)

The individual seeds or the whole fruit may be modified to help for the dispersal by wind. Wind dispersal of fruits and seeds is quite common in tall trees. The adaptation of the wind dispersed plants are

• Minute seeds: Seeds are minute, very small, light and with inflted covering. Example: Orchids.
• Wings: Seeds or whole fruits are flattened to form a wing. Examples: Maple, Gyrocarpus, Dipterocarpus and Terminalia
  

Feathery Appendages:

Seeds or fruits may have feathery appendages which greatly increase their buoyancy to disperse to high altitudes. Examples: Vernonia and Asclepias.

Censor mechanisms:

The fruits of many plants open in such a way that the seeds can escape only when the fruit is violently shaken by a strong wind. Examples: Aristolochia and Poppy

Dispersal by Water (Hydrochory)

Dispersal of seeds and fruits by water usually occurs in those plants which grow in or near water bodies. Adaptation of hydrochory are:-

• Obconical receptacle with prominent air spaces. Example: Nelumbo.
• Presence of firous mesocarp and light pericarp. Example: Coconut.
• Seeds are light, small, provided with aril which encloses air.Example: Nymphaea.
• The fruit may be inflted. Examples: Heritiera littoralis.
• Seeds by themselves would not flat may be carried by water current. Example: Coconut
  

Dispersal by Animals (Zoochory)

Birds and mammals, including human beings play an effient and important role in the dispersal of fruit and seeds. They have the following devices.

(i) Hooked fruit:

The surface of the fruit or seeds have hooks,(Xanthium), barbs (Andropogon), spines (Aristida) by means of which they adhere to the body of animals or clothes of human beings and get dispersed.

(ii) Sticky fruits and seeds:

• Some fruits have sticky glandular hairs by which they adhere to the fur of grazing animals. Example: Boerhaavia and Cleome.
• Some fruits have viscid layer which adhere to the beak of the bird which eat them and when they rub them on to the branch of the tree, they disperse and germinate. Example: Cordia and Alangium

(iii) Fleshy fruits:

Some flshy fruits with conspicuous colours are dispersed by human beings to distant places after consumption. Example: Mango and Diplocyclos.

Dispersal by Explosive Mechanism (Autochory)

Some fruits burst suddenly with a force enabling to throw seeds to a little distance away from the plant. Autochory shows the following adaptations.

Mere touch of some plants causes the ripened fruit to explode suddenly and seeds are thrown out with great force. Example: Impatiens (Balsam), Hura.

Some fruits when they come in contact with water particularly after a shower of rain, burst suddenly with a noise and scatter the seeds. Examples: Ruellia and Crossandra.

Certain long pods explode with a loud noise like cracker, scattering the seeds in all directions. Example: Bauhinia vahlii (Camel’s foot climber).

As the fruit matures, tissues around seeds are converted into a mucilaginous fluid, due to which a high turgor pressure develops inside the fruit which leads to the dispersal of seeds. Example: Ecballium elatrium (Squirting cucumber) Gyrocsrpus and Dipterocarpius.

Human aided seed dispersal Seed Ball:

Seed ball is an ancient Japanese technique of encasing seeds in a mixture of clay and soil humus (also in cow dung) and scattering them on to suitable ground, not planting of trees manually. This method is suitable for barren and degraded lands for tree regeneration and vegetation before monsoon period where the suitable dispersal agents become rare.

Advantages of seed dispersal:

• Seeds escape from mortality near the parent plants due to predation by animals or getting diseases and also avoiding competition.
• Dispersal also gives a chance to occupy favourable sites for growth.
• It is an important process in the movement of plant genes particularly this is the only method available for self-fertilized flowers and maternally transmitted genes in outcrossing plants.
• Seed dispersal by animals help in conservation of many species even in human altered ecosystems.
• Understanding of fruits and seed dispersal acts as a key for proper functioning and establishment of many ecosystems from deserts to evergreen forests and also for the maintenance of biodiversity conservation and restoration of ecosystems.