Concepts Of An Ecosystem

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02 Nov 2017

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The wordecology has come to the forefront of human consciousness. It is the branch of science that incorporates the basic concepts of civilization. The term has been introduced by a German scientist Hans Reiter, combining the two words ‘Oikos’ (-house) and ‘logos’ (- to study). Therefore it deals with the study of plants and animal interrelationship and also their relation to the environment. Ernst Haeckel was the first to define ecology as the study of organisms in its natural home. It was Odum (1963) who defined ecology as the study of structure and function of the nature or it is the study of inter- relationships between organisms in relation to their environment. Ecology can be studied as plant and animal ecology. Often the tern ‘bioecology’ is used when we give equal importance to the study of plants and animals.

3.1.1 ECOLOGY AS A DISCIPLINE:

Ecology was regarded as an offshoot of biology as it deals with all forms of life and explores the riddles at various levels of living systems. But presently, it is a multidisciplinary science that requiresinput from the various disciplines like physics, chemistry, biology, geography, geology, economics, international relations, policies, legislation and uses mathematical, statistical and computational tools to explain the naturally observed phenomena with relevance to its varied consequences.

3.1.3 BASIC ECOLOGICAL PRINCIPLES

There are 4 basic principles of ecology, which are as follows:

1. It contains a network of interrelations of its components.

2. These interrelated networks form a structure that comprises abiotic and biotic components.

3. The networks exhibit energy flow and flow of nutrients.

4. Solar energy holds the basic control over the flow of nutrient and energy.

From these principles arise the fundamental ecological concepts like population, community, habitat, territory and ecosystem. Thus through ecology we strive for understanding and explaining the various life processes, adaptation, species distribution and species abundance, the various stages in the development of communities and the material and energy flow through ecosystem.

3.1.4 SCOPES OF ECOLOGY:

It plays significant role in conservation and management of land and its resources like minerals, forests etc; livestocks, water and pisciculture; urbanization and town planning; population control; risk assessment and disaster management.

Ecology can also be studied as

Autecology – when we study individual organisms with its environment, for e.g. study of polulation.

Synecology – when we study groups of organisms in relation to environment, for eg. Community.

3.1.5 SUBDIVISIONS OF ECOLOGY:

There are three levels of integration in ecology-

Individual

Population - group of interbreeding organisms of same species inhabiting a given area. EgHomo sapiens

Community - Group of populations interacting a given habitat.eg. forest floor.

3.2 CONCEPTS OF AN ECOSYSTEM

3.2.1 DEFINITIONS (as defined by various Authors)

Ecosystems were initially defined as "units of the earth’s surface, i.e., the whole system including the organisms and the physical factors that form the environment".(Tansley, 1935).

Later on,ecosystems weregrouped by their structure and function with much stress on integration and interactions. The ecologists were grouped into two - those engaged with quantifying an ecosystem’s input and output relationships (flows of matter and energy; Evans, 1956) and those concerned with particular populations (Levin, 1976).

Populations do react to environmental stimulus and so ecosystems canalsobe defined by biota and by the environment (Chapin et al., 1997).

An ecosystem is the basic functional unit in ecology, as it comprises both organisms and their abiotic environment.Organism cannot exist without their environment. Ecosystem thus symbolizes the highest level of ecological integration and is based on energy. A forest, a lake, a mangrove, paddy field and even laboratory culture can represent ecosystems. Thus an ecosystem is a specific unit of all the organisms inhabiting a specifiedspacethat interacts with the physical element of the environment to producediscrete trophic structure, biodiversity and nutrient cycling. The term ecosystem was first proposed by the British ecologist A.G. Tansley.

3.2.2There are two elementary processes in an ecosystem -the nutrient cycle and the energy flow.

Nutrient cyclecomprisesof the transfer of inorganic substances between living beings and the environment. The plants are able toprepare complexorganic materials from simple raw materials. This organic matter is finally released as raw materials after their death that isrevertedback to the environment.

Continual energy inflow is another fundamental requisite of the ecosystem. Solar energy is trapped by the green plants by photosynthesis. Sun is the ultimate source of energy. Herbivores procure their nutrition and energy from the plants. This energy intake passes on to other organisms.It is in this way the energy gets transferred from one organism to another which is known as energy flow in ecosystem.

3.3COMPONENTS OF ECOSYSTEM

3.3.1 ABIOTIC COMPONENTS

The term abiotic refers to nonliving substances like air, water, land, elements and compounds. These are innate but become a part of biotic world once they enter the body of living organisms. The oxygen required in our metabolism comes from the air we breathe. The hydrocarbons that form our body come from the hydrogen in water and carbon dioxide in air. Most of the necessary elements are found as ores such as calcium in limestone, iron in magnetite etc. the most important aspect of these substances is the entry into living organism and their release from the living organism, i.e. their recycling.

Based on Odum’s classification the abiotic components are grouped into three -

Inorganic – Carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus etc.

Organic – carbohydrates, proteins, fats, vitamins, coenzymes etc.

Climatic factors- light, rainfall, temperature, soil types etc.

3.3.2 BIOTIC COMPONENTS

The diverse groups of living organisms comprise the biotic components. These organisms

interact to allow the unidirectional flow of energy that was fixed by the autotrophs and also the

nutrient cycling. Most of the energy trapped by the autotrophs is lost to the environment as heat.

1. Producers: They are autotrophs ("self-feed"), produce the food and energy they need. Examples: photoautotrophs (all green plants, planktons) and chemoautotrophs (sulfur bacteria)

2. Consumers: These are Heterotrophs that obtain food and energy by feeding on other organisms. Examples- Herbivores, carnivores and parasites. Animals cannot manufacture their own food and are hence dependent on plants and/or other animals. There are three groups of consumers.

Herbivores: Animals that eat plantsonly (or primary consumers).

Carnivores: Animals that eat on other animals.

Carnivores that eat herbivores are secondary consumers.

Carnivores that eat other carnivores are tertiary consumers.

Omnivores: Animals who eat both animals and plants.

Parasites: absorbs energy from living hosts.

Scavengers: eat on dead organisms. Example – vultures; but the largest group of scavengers is the insects.

Decomposers/ Detritivores: Detritus refers to the decaying organic material and can vary fromthe dead carrion to bacteria, organic waste from plants and animals. Heterotrophs that acquire energy from dead or decomposed organic matter (dead remains and wastes) of other organisms are decomposers. It aids in returning the nutrient back to the producers (fungi and bacteria). Detritivores refers to small insects, earthworms, bacteria, fungi. They obtain energy by eating dead plants, animals as well as animal waste. Decomposers, such as bacteria and fungi change the wastes and dead organisms into nutrients that can once again be used by plants and animals.

Note- Scavengers and decomposers are also heterotrophs, but in place of consuming living plants and animals they consume detritus.

Detritivores and decomposers nourish at every trophic level.

3.4 STRUCTURE AND FUNCTION OF AN ECOSYSTEM

3.4.1 Structure involves:

1. Composition of biotic community includes species, their numbers, their biomass, life history, distribution in space, etc.

2. Quantity and allocation of non-living materials, such as various nutrients, water, etc.

3. Range or gradient of the existence conditions, such as temperature, light, pH, etc.

Functions of an ecosystem include:

1. Rates of energy flow, i.e. the production and respiration rates of the community.

2. Rates of materials flow or nutrient cycles, such as carbon, nitrogen, phosphorus etc.

3. Biological or ecological regulation includes both regulations of organisms by environment and vice versa.

Thus in any ecosystem, structure and function are intricately associated with each other andto be considered together.

TROPHIC STRUCTURE:

Trophic means ‘to feed’. Trophic structure comprises of the feeding levels or tiers and the

feeding relationships between the ecosystem components. It refers to the pattern of

arrangement in which the organism utilizes the food sources and helps in energy transfer within

an ecosystem. Every ecosystem rests on autotrophs that make organic food for themselves and

other members of the community. Some bacteria are able to utilize chemical energy to make food (chemoautotrophs).Organisms possessing chlorophyll are able to use solar energy through photosynthesis. They use water from the soil and carbon dioxide from the air for photosynthesis to make organic materials like glucose and releases oxygen as a byproduct. Macromolecules like starch, proteins and vitamins are assembled from the simple molecules along with the minerals (sulphur, nitrogen, phosphorus) present in the soil.

Animals consume these plant products and breathe in atmospheric oxygen. They oxidize these

food substances with the help of oxygen and release carbon dioxide and water, a mechanism

known as cell respiration or metabolism. All green plants starting from microscopic plant (phyto

planktons) to the grasses, shrubs, herbs and trees photosynthesize. Two third of all oxygen on

earth is produced by the phyto- planktons.

Trophic Structures can be represented graphically as Food chains, and Food webs and Food pyramids (Ecological Pyramids).

FOOD CHAINS: Food chains illustrate the flow of energy from plant to animal and from animal to animal by the way of eating and being eaten relationship. Plants are the producers as they can manufacturetheir own food in the form of carbohydrates during photosynthesis.Consumers devouron plants and other organisms. Each such step in a food chain is called a trophic level.

A food chain is a straight line sequence of who eats who in an ecosystem. In other words a food chain is a linear sequence of links in a food web beginning with a trophic species that eats no other species in the web and ends with a species that is consumed by no other species in the web. Food chain seems to be simplified abstractions of the food webs in reality, but intricate in their dynamics and implications.

Usually, food chains are restricted within four or five trophic levels. For example, a food chain consisting of a plant, a frog, a snake and finally peacock consists of four levels, whereas, a food chain comprising of grass, a grasshopper, a mouse, a snake and finallyeagle consists of five levels. Thus a food chain can vary in lengths.

Food chains are of two types –

1. Grazing food chain - This type of food chains always begin with autotrophs followed by grazers.

Plants ---------- Deer ----------------- Tiger

2. Detritus food chain – This type of food chains begin with dead matters followed by detritivores.

Leaf litter ---------- bacteria ---------------- protozoa ---------- small fish --------- big fish

2. FOOD WEB

It was Charles Elton who introduces the concept of food web what he referred to as food cycle. Food web refers to a network of interlinked food chains with numerous producers, consumers and decomposers operating simultaneously. It is the actual depiction of the feeding relationships amongst species in a community. It is also a way of displaying how food energy flows between various organisms of a community as a consequence of feeding relationships.In a food web the species are connected by means of arrows called links.

A food chain shows only a partial picture of the food web consisting of a simple, linear series of species (e.g., plant, herbivore and a predator) connected by feeding links. A food chain exhibits linear monophagous pathway and differs from a food web which is actually acomplex polyphagous network of feeding relations that are aggregated into trophic species. A food web aims to portray a more inclusive picture of the feeding relationships.Simply it can be considered as a system of many interrelated food chains occurring within the community. All the species in the same position in a food chain comprise a trophic level within the food web. For example, all of the green plants in the food web are the first trophic level or "primary producer", all herbivores comprise the second trophic level or "primary consumer" and carnivores that eat herbivores comprise the third trophic level or "secondary consumer".

All the organisms in an ecosystem that are the same number of transfer steps away from the energy input into the system.

3.ECOLOGICAL PYRAMID

Trophic structure and trophic function of an ecosystem may be graphically shown by means of ecological pyramids where the producer level forms the base and successive levels form the tiers and make up the apex.

PYRAMID OF NUMBERS

"Pyramid of numbers may be defined as the graphical representation of number of individuals per unit area of the various trophic levels arranged stepwise with producers forming the base and top carnivores the tip".

The shape of the pyramid of numbers may vary from ecosystem to ecosystem.

In grasslandand aquatic ecosystems, autotrophs are present in huge numbers per unit area. They sustain a lesser number of herbivores, which in turn support fewer carnivores.So, the producers are the maximum in number but of smaller body size while, top carnivores are lesser in number and larger body size. Hence the pyramid of numbers is in aquatic and grassland is always upright.

In a forest ecosystem large sized treesbeara larger number of insects which inturn are eaten by frogs, lizards etc.; these are in turn eaten by carnivorous birds like hawks and eagle, which are smaller in number. The pyramid assumes a spindle shape and is known as semi upright pyramid.

In a parasitic food chain, for e.g., a banyan tree provides food to several herbivorous birds. The birds supportand sustain a good number of ectoparasites leading to the formation of an inverted pyramid.

PYRAMID OF BIOMASS

The total quantity of living or organic matter in an ecosystem at any instant is called Biomass. Pyramid of biomass is the graphicalillustration of biomass present per unit area of the various trophic levels, with producers at the base and top carnivores at the tip.

The biomass pyramids makes a trophic level look as if it contains more energy than it does actually. For example, the exoskeletal structures like beak, feathers and skeletons, though constitute the biomass are not consumed by the next higher trophic level.These body parts would be still quantified and shown even though they do not contribute to the overall energy flow.

1. In a land ecosystem, the maximum biomass occurs in producers followed by a progressive decrease in biomass from lower to higher trophic levels. Thus, in a land ecosystem, the pyramid of biomass is upright.

2. In an aquatic ecosystem the pyramid of biomass is either inverted or semi upright.Here the biomass of trophic level depends upon the biotic potential and lifespan of the member.

III. PYRAMID OF ENERGY

An Ecological Pyramid of Energy is the most practical of the three types, presenting the direct correlation between energy and trophic level. It quantifies the amountof energy in calories at each trophic level. It begins with producers and ends with consumers in the higher trophic levels.It represents the transition of energy from one trophic level to another.

In an healthy ecosystem the energy pyramid will always look like the standard Ecological Pyramid.For the ecosystem to be self sustaining, more energy should be present at lower trophic levels than at higher trophic levels. This help the lower level organisms to maintain a stable population, which would be fed by the organisms at higher trophic levels, thus aiding in transfer of energy up the pyramid.

When energy is transferred to the next trophic level, only about 10% of it is used to assemble bodymass and become stored energy.Rest 90% is lost in metabolism.This is known as Lindemann’s data or 10% law.

The advantages of the Pyramid of Energy:

It takes account of the production rate over a time period as each of the trophic level represents energy per unit area / volume / unit time. An example of units might be - cal /m2/yr.

Two species of same weight may not have the same energy content;so biomass may be misleading but energy is truly comparable.

Not only relative energy flow within an ecosystem can be compared but also different ecosystems can also be compared using energy pyramids.

Energy pyramids can never be inverted.

The input of solar energy can be taken into account.

The disadvantages of the Pyramid of Energy:

To obtain the energy value for a given mass of organism, complete combustion of a sample is required.

Difficulty exists in assigning organisms to a specific trophic level as there is a problem in assigning the decomposers and detritivores to a particular trophic level.

The best way of presenting of the feeding relationships of a community is to do with the help of Energy Pyramids.

3.5ENERGY FLOW IN ECOSYSTEM

All organisms need energy to perform the essential functions such as maintenance, growth, repair, movement, locomotion and reproduction; all of these processes requireexpenditure of energy. In the ecosystem the energy flows from sun to autotrophs, the energy is then transferred to organisms which feed on autotrophs and itself become prey for tertiary consumers.It is the amount of energy that is received and transferred from organism to organism in an ecosystem that modulates the ecosystem structure.

Energy flow is the amount of energy that is transferred through a food chain up the trophic level. Since the energy input, or energy entering the ecosystem, is measured in Joules or calories, the energy flow is also called calorific flow.

The largest source of energy is the Sun. Energy that cannot be utilised in an ecosystem is ultimately lost as heat. Energy and nutrients are transferred through the food chain, when one organism nourishes on another organism. The left over energy in a dead organism is devoured by decomposers. Nutrients arerecycled through an ecosystem but energy is purely lost over time.

Energy flow in an ecosystem would always begin with the autotrophs that trap energy from the sun. Herbivores feed on the autotrophs and transform the energy of the plant into their usable form. Carnivores next feed on the herbivores and, lastly, other top carnivores prey on the carnivores. In each step, energy is passed on from one to the next trophic level and every time some amount of energy is lost in the form of heat into the environment. This happens because each organism must utilize some of the energy they receive from other organisms for their sustenance. The top consumer receives the least amount of energy.

Light and other forms of radiation coming out from the sun strikes the earth 93 million miles distant, providing energy to the air, water and land, warming objects that absorb this energy; i.e., radiant energy is converted to heat energy. Unequal heating causes winds and currents in the air and water; the heat energy becomes kinetic energy. Warming leads to evaporation of water into the atmosphere, setting off the hydrologic cycle. The vaporization of water into the air becomes potential energy that will be converted to kinetic energy when the water begins to flow down. Yet, the most significant solar energy mediated process with respect to living systems is photosynthesis.

SOLAR CONSTANT

The average amount of beaming energy from the sun reaching the Earth's atmosphere is called solar constant with an approximate value 2 calories per minute on each square centimeter of the Earth's upper atmosphere. This value can change as a consequence of Earth's elliptical path. The energy left after reflection by the Earth's surface is known as the net radiation. An astronomical unit is used for doing the calculations of solar constant. Astronomical unit (AU) is the mean distance between the Earth and Sun; One (AU) is equivalent to 149,604,970 kms.

Convection of the air and evaporation are major factors that regulate the temperature of the Earth. The movements of air also allow energy to be given out into the space without whichthe temperature of the Earth would be unbearable due to overheating and life would smother. Suchinteraction is also very useful to maintainthe polar ice caps. On the other hand, a decrease in the solar constant by 2-5% would be sufficient to lead to a second ice age.The uncontrolled burning of fossil fuels can also increase earth’s temperature. The polar ice caps also help in reflecting back part of Earth's radiation which is an essential part in the maintenance of the current climatic conditions.

THE LAWS OF THERMODYNAMICS AS THEY RELATE TO ECOLOGY

The laws of thermodynamics are elemental concepts to all the chemical processes of the universe. They are extremely important in chemistry, physics and many biological concepts as well. The laws state how energy can be transported, which can be applied to ecology as energy transfer is what drives metabolism.

Zeroth Law of Thermodynamics

It is the most understandable of all three laws. It simply states that if the temperature of object X is equal to the temperature of object Y, and the temperature of object Z is equal to the temperature of object Y then the temperature of object Z equals the temperature of object X.

The First Law of Thermodynamics

It states that energy is neither created nor destroyed, but may transformed from one type to another. The total inflow of energy into a system must be equal to the total outflow of energy from the system.

Second Law of Thermodynamics

The randomness or entropyof the universe is always increasing. Energy flow from one trophic level to the next cannot be hundred percent efficient. Energy transfer is always followed by a dissipation of energy into other forms. The second law of thermodynamics certainlyfinds the most application to ecology. The law also suggests a dire that "heat death of the universe" will occur when all the energy of the universe is evenly distributed, although this won't occur for at least 1, 0100 years.

Third Law of Thermodynamics

The Third Law of Thermodynamics simply states that the entropy of the system decreases as the temperature of a system reaches absolute zero (0 K). Precisely, a system at absolute zero is at zero entropy.This is theoretically impossible as because absolute zero is not able to be experimentally reached. This explains the reason why substances turn into gases at high temperatures as entropy increases, and freeze at low temperatures as entropy decreases. Decomposition also has a higher rate at elevated temperatures for the same reason.

PRODUCTIVITY IN ECOSYSTEMS

Energy flow is unidirectional.This is in contrast to the cyclic flow of material in ecosystems. Energy flow includes production, consumption, assimilation, non-assimilation losses (feces), and respiration (maintenance costs)."

In general, energy flow (E) can be defined as the sum total of metabolic production (P) and respiration (R), such that E=P+R.

In ecology, productivity or production refers to the rate of biomass generation in an ecosystem, usually expressed in units of mass per unit area (or volume) per unit time,let’s say grams / square meters/ day.

Productivity at producer level, such as plants is called primary productivity, while that at consumer levels such as animals is called secondary productivity.

Primary productivity

Primary productivity is the manufacture of new organic materials from inorganic molecules such as H2O and CO2. It is achieved by the process of photosynthesis which utilizes sunlight to manufacture organic molecules such as sugars.A small fraction of primary production is also achieved through chemosynthesis.Organisms responsible for primary production include green plants, phytoplanktons, blue green algae, sulphur bacteria etc.

It is in theoretically possible to calculate the plant’s energy uptake by measuring the amount of sugar produced since all the energy fixed by plants is converted to sugars. This amount is the Gross Primary Production (GPP), because it occurs in the autotrophs or primary producers. More practicaland relevant is the measure of Net Primary Production (NPP).

In ecosystems NPP is the rate at which plants build up dry mass, usually expressed in kg,m-2,yr-1, or as the energy value gained per unit time kJ,m-2,yr-1. This reserve of energy serves as the potential food for consumers up the trophic levels in the ecosystem.

NPP can be measured as the difference between the rate at which plants photosynthesize (GPP) and the rate, which they respire (R).Glucose produced in photosynthesis has two main fates:

a.Some of it provides energy for anabolism such as growth, maintenance and reproduction along with some energy being lost as heat during respiration.

b.The remainder is stored in and around cells and represents the dry mass (NPP=GPP-R).

Factors limiting NPP

Terrestrial factors include:

Sunlight

Heat and temperature

Moisture and water

Availability of nutrients

Aquatic factors include:

Sunlight

Heat and temperature

Availability of nutrients

The Net Primary Production of aquatic ecosystems has been immensely affected by global warming, such as decline of the coral reef due to coral reef bleaching. Coral reef supports one fourth of the marine biota.

Secondary productivity

It is the total amount of chemical energy assimilated by consumer organisms.

Secondary production is the production of biomass bythe consumer organisms in ecosystem.This is the rate at which primary material is made into animal tissue per unit area in a given time.This includes consumption of primary producers by herbivorous or carnivores. Organisms in chargeof secondary production include protozoans, fungi and animals.

Animals do not use all of the biomass they consume. Undigested matter comes out asfaeces. Gross production in animals is equal to the amount of biomass or energy assimilated or simply biomass eaten minusfaecal matter.

Similar to the plants some of the energy assimilated by the animals is used in the cellular processes via respiration the remainder is available for new biomass. This amount is the Net Secondary Production.

So, Net secondary productivity (NSP ) = food consumed - faeces - respiration energy

NSP = GSP- R

I-Total energy input, LA- light absorbed, PG - Gross primary production, PN- Net primary production, A- Assimilation, NU- Energy not utilized, NA- Energy Not assimilated, R- Respiration, P – Secondary Production

BIOGEOCHEMICAL CYCLES

The atoms from diverse elements and compounds can be an entity of both living things like plants and animals, as well as non-living things like water, air, and even rocks. These atoms are recycled in different parts of the Earth over and over again. The term ‘bio’ means living organisms; ‘geo’ means earth which can be extended to air and water; and ‘chemical’ refers to all the elements and compounds in nature. In other words biogeochemical cycle refers to the passage of these chemicals between living and nonliving and back to living.

There are three types of biogeochemical cycles –

Hydrological cycle - Water

Gaseous cycle – The recycling of those elements which spends most of their time in a gaseous form in the atmosphere is known as gaseous cycle. Elements like carbon, nitrogen, and oxygen fall in this category. Carbon generally occurs in the atmosphere in carbon dioxide (CO2), nitrogen as nitrogen gas (N2), and oxygen as oxygen gas (O2).

Sedimentary cycle – The sedimentary cycles are those in which the element is mostly found in a solid form. Phosphorus and Sulphur

WATER CYCLE

Water makes up eighty to ninety percent of all living organisms. Water is one of the main buffers in the living beings and the environment, preventing heat shocks.Our body comprises 70% of water.Water is plentiful, but 97% of this is salt water and 3 % of fresh water. 2% is locked up in icecaps and glaciers; 0.31% is stored in deep groundwater reserves. Less than 0.01 % is available from the rivers and lakes. Water is unique in its properties like latent heat, density etc and an excellent solvent. These properties are attributable to its molecular composition andarrangement.

Water is cycled through the mechanisms of evaporation from exposed surfaces and transpiration from plants into the atmosphere, and precipitation in the form of rain, snow, sleet etc back to Earth. Water evaporates from the exposed surfaces of the Earth's oceans and seas. Approximatelyone thousand gigatonnes of water evaporate from the oceans per day. The average residence time of a water molecule in air is eight days. It is predictedthat 41,000 cubic kilometers of water returns to the sea from the land per year, harmonizing the transfer of water from sea to land.

Water is thought to be the bottomless sink but acute water problem becomes evident due to pollution like acid rain, eutrophication, dam construction, and irrigation and consumption patterns. The uneven distribution of water gives rise to severe conflictsand water war like situation. The problem needs to be addressed and handled carefully.

CARBON CYCLE

Carbon forms the structural element of all living organisms; it exists as coal and limestone deposits in the lithosphere, carbon dioxide in the air and in water.Atmospheric lifetime of Carbon is approximately 9 yrs. Air contains 750 billion tons of carbon in the form of CO2; living plants and animals contain 560 billion tons, buried organic matter in the soil contains about 1400 billion tons, ocean contains 38,000 billion tons as dissolved CO2 and about 11,000 billion tons are trapped in methane. With development and industrialization, burning of fossil fuels increasing, huge amounts of CO2 (22 billion tons/ year) are released. Deforestation adds a further amount of 1.6- 2.7 billion tons. The main reservoirs of carbon are the sedimentary rocks, fossil fuels, oceans and biosphere.

Carbon goes primarily through three cycles with different time constraints:

A long-term cycle involving sediments and the depths of the lithosphere.

A cycle between the atmosphere and the land.

A cycle between the atmosphere and the oceans.

The last two cycles are faster and subject to human intervention.

Carbon Cycle One: Long-term Cycle

This cycleoccurs between atmosphere, oceans, and sediments and entails a slow dissolution of atmospheric carbon and rock carbons via weathering into the oceans. Oceans contain huge deposits of carbon as calcium carbonate deposits. The carbon in the sediments dissolves slowly and some of the sediments are reverted back into the atmosphere through volcanic action. This cycle takes over hundreds of millions of years.

Figure: Carbon Cycle One.

Carbon Cycle Two: Air and Land Cycle

The second cycle between the atmosphere and biosphere may range from days to decades. Carbon dioxide serves as the basic food to the living and thus the biosphere serves asinstrument for this cycling. Plants fix atmospheric carbon through photosynthesis. The chemical may be represented as:

Simple sugars are assimilated to form complex substances like starch and cellulose. Plants are consumed by animals; part of it is respired as CO2 and part turned into animal tissue. When plants and animals die they form detritus and most of it is decomposedinto inorganic forms.Over millions of years, fossil fuels are formed as partially decomposed matter. Combustion of fossil fuels adds CO2 to the air. Respiration of plants and animals also releases CO2 in the air.

Carbon Cycle Three: Air and Sea Cycle

Oceans are vast deposits of carbon. Over thousands of year the carbonates of the rocks dissolve and makes up the oceanic biomass.

The summary of the three cycles is shown in Figure.

NITROGEN CYCLE

Nitrogen is the most abundant element in the air and makes 79% by volume of air. It exhibits various valencies and so may exist as NO, NO2, N2O, N2O3, N2O5, commonly designated as NOx. Nitrogen forms the building blocks of protein monomers - the amino acid and also forms the constituent of bases in DNA and RNA – adenine, guanine, cytosine and thymine.

Nitrogen is almost 79 % of the air. The nitrogen cycle is dominated by the N2 in the atmosphere. Nitrous oxide, NO2 is the second most common form. N2O, commonly known as laughing gas, is a greenhouse gas. Nitrogen is inert and so it offsets the high reactivity of oxygen, the other major constituent of the atmosphere. Nitrogen can form a variety of compounds owing to its variable valencies. For example, it can combine with oxygen in variable proportion to form N2O, NO, NO2, or N2O5.Collectively, these oxides (except for N2O5) are denoted by NOx.

Nitrogen is an essential element for life. Amino acids, the monomer and the building blocks of proteins, contain nitrogen as NH2, the "amino" part of the molecule. The four building blocks or the nitrogenous bases of DNA [Adenine (A), Cytosine (C), Guanine (G), and Thymine (T)] consist of single or double rings of carbon and nitrogen atoms, with various side chains. Nitric oxide acts as a neurotransmitter.

Nitrogen is inert in the air. All living organisms require large amounts of nitrogen. Neither plants nor animals can fix atmospheric nitrogen. Nitrogen from the air is fixed by three processes.

1. By microbes.

2. By Lightning.

3. By Haber’s process

Microbial fixation can be symbiotic or asymbiotic. Symbiotic fixation is between the leguminous plants like peas, beans, alfalfa, clover and the symbiotic bacteria like Rhizobium. Rhizobium traps atmospheric nitrogen, converts it into nitrates and gives it to the plants. The plants give finished food to the bacteria. Aymbiotic fixation is mediated by blue green algae like Nostoc and Anabaena.

Lightning momentarily raises the temperature causing the atomic nitrogen and oxygen to react together form nitrogen monoxide and further into nitrogen dioxides. The oxide dissolves in water to form nitric acid that precipitates down into the soil and water along with rain. This enriches the nitrogen content in the soil as nitrites.

In the industry, Nitrogen and hydrogen is combined under controlled temperature and pressure and in presence of catalyst to form ammonia. The process is known as Haber’s process.

Nitrogen-fixing bacteria on soybean roots

Plants absorb soluble nitrates, along with other minerals, and use them to build up plant tissues. Animals get their nitrogen by nourishing on plants. Plant and animal wastes and their dead remains are transformed into ammonia by the process of ammonification with the help of bacteria like Clostridium. The use of fertilizers like ammonium nitrate is to compensate for the nitrogen deficit in the soil. Ammonia undergoes nitrification in two steps aided by bacteria. Firstly, Nitrosomonasconverts ammonia into nitrite and subsequently Nitrobacter converts nitrite into nitrates. Nitrates can then be absorbed by the plants.Denitrifying bacteria like Bacillus convert nitrates back into nitrogen gas and make it unavailable again.

OXYGEN CYCLE

Oxygenis a basic element of life. It constitutes about 21% of the atmosphere.Oxygen is omnipresent. It also occurs in combined state in the Earth's crust and mantleand in water. Oxygen is highly reactive. Dissolved oxygen in water supports aquatic life. Photosynthesis releases oxygen in the atmosphere whereas respiration, burning or combustion and decomposition utilises oxygen.

SULPHUR CYCLE

Sulphur, a yellow coloured solid chiefly occurs as sulphates in the rocks and as elemental sulphur. Sulphuris one of the essential elementin living organisms. It occurs in three amino acids like methionine, cystine and cysteine. Sulphur in elemental form cannot be utilized by the plants and animals. Sulphur is oxidized to sulphates by bacteria like Thiobacillusthioxidans. Sulphates assimilated by plants are incorporated into amino acids and then to proteins. Plants are consumed by animals who utilize it. Following their death, the organic substrates are oxidized into organic acid and then reduced to H2S by Desulfotomaculum.Sulphatescan also be reduced in the same manner. H2S resulting from suphate reduction and amino acid decomposition is oxidized to elemental sulphur by Purple and Sulphur bacteria.

PHOSPHORUS CYCLE

Weathering of phosphate rock supplies phosphates to the soil. The dissolved phosphorus is absorbed by the plants and animals do obtain phosphorus from the plants. Phosphorus is an essential ingredient to nucleic acids, ADP, ATP, NADP and phospholipids.

Plants and animals during their lifetime excrete and die. Decomposers breakdown the organic phosphates and return phosphorus to the soil. A part of it is leached to the oceans through the rivers and streams and deposited in the shallow sea. A part of these deposits are utilized by marine animals and after their death they contribute to rocks. Weathering may increase the availability of phosphorus to the biotic community. Much of the shallow deposits are lost to the relatively deep sea deposits.

The biogeochemical cycles are an example of the Law of Conservation of Mass, matter is neither created nor destroyed but simply transforms from one form to another.

3.7ECOLOGICAL SUCCESSION

DEFINITION AND CONCEPT

This refers to the sequence of changes that the biotic community goes through as it matures towards a stable condition known as climax. These changes are orderly, progressive and more or less predictable. It involves progressive replacement of one community by another community over time. The term succession was first used by Henry David Thoreau.

Successions which initialize in aquatic habitats like lake,ponds, marshes etc. are called as hydrarch. Various stages of hydrarchdevelopment make uphydroseres. The hydroseres in saline areas are referred to ashaloseres.In arid conditions like sand dunes and bare rocks etc. the term xerarchis often used and the different stages are known asxeroseres. Xeroseresdeveloping on bare rock are termed lithoseres; xeroseres on sand are calledpsammoseres.Succession beginning on interhabitat between water and sand it is termed mesarch.

TYPES OF SUCCESSION

PRIMARY AND SECONDARY SUCCESSION

Primary succession: Primary succession is a "change in vegetation which occurs on previously barren terrain" (Barnes et al. 1998). Primary succession is the series of community changes on an entirely new habitat never been inhabited before. So, if succession proceeds from a nude area i.e. area that is devoid of organisms or an area unchanged by organisms, is known as primary succession. Such habitats are generally newly exposed or deposited surfaces.

EXAMPLES OF PRIMARY SUCCESSION

1. Glaciation (Continental glaciers & Alpine glaciers) - Plants and other life colonize the bare rock.

2. Volcanic Lava Flows - Hawaii.

3. Volcanic Explosions –Iceland Volcanic eruptions, Mt. Pinatubo, Mt. St. Helens, Mt. Kilimanjaro

4.Raising sea floor by faulting

5. Elevated sand banks and sand dunes

6. Quarried rock fronts.

7. Landslips

After volcanic eruption or glaciations, the pioneers colonize the barren land, along with weathering facilitates pedogenesis or soil formation through interaction with the surface. Their interaction also adds organic debris to the surface.

Secondary succession: "Secondary succession occurs after a disturbance disrupts ecosystem processes and removes part of the existing biota" (Barnes et al. 1998). Forest depletion, floods, fire and wind can all culminateinto secondary succession. It takes place on previously colonized, disturbed and damaged habitat. It proceeds from a state where other organisms are still present such as seeds, left over stumps and root system and the effects are obvious. Vegetation recovery followed by forest fire is an example of secondary succession. Since the soil is already developed, vegetation was already present, vegetation transformation occurs quickly and rapidly.

EXAMPLE OF SECONDARY SUCCESSION

Tree felling, clearance of woodland

Forest fires.

AUTOTROPHIC AND HETEROTROPHIC SUCCESSION

The succession can be distinguished into autotrophic and heterotrophic succession. The autotrophic succession is marked by early and sustained dominance of autotrphic organisms. It begins in mainly inorganic environment. The heterotrophic succession is marked by an early dominance of heterotrophs and this begins in primarily organic environment. The end product of succession is called the climax community.

AUTOGENIC AND ALLOGENIC SUCCESSION

Successional change can be caused by endogenous or exogenous factors depending upon whether the change is brought about by the actions of the plants by themselves or by outside factors. Changes caused by endogenous factors or internal factors are termed autogenic, whereas changes caused by exogenous factors or external factors are termed allogenic. Primary succession is the typicalcase of autogenic change, in that the vegetation is partly the reason for the development of soils. On the other hand, allogenic succession is determined by periodic disturbances.

GENERAL PROCESS OF ECOLOGICAL SUCCESSION (MECHANISM OF SUCCESSION)

Process of primary succession occurs through a number of sequential steps, which follow one another.

1) Nudation -is the development of anexposed area without any form of life.It may be due totopographical factors (soil erosion, landslide, earthquake etc.) or climatic factors (glaciers, hailstorm, fire etc.) or even biotic factors (human activities, epidemics etc.). Plants who will be able to arrive and colonise will survive. They must be able to thrive and withstand the conditions at the new place in order to survive. They are known as pioneers. For example moss and lichens are lithophytes that colonise on the bare rocks.

2) Invasion–refers to the successful founding of a species in a bareor exposed area, which happens in three steps.

i) Migration - reaching of seed or spores in such a bare area through agents like wind, water etc.

ii) Ecesis- or 'establishment' involves the adaptation of the migrated species with the existing conditions of the area. The pioneers after arrival modify the environment. The old ones are replaced by the new ones, the roots penetrate deeper and deeper breaking the particles, increasing the water retention capacity and making enough space for others to move in.

iii) Aggregation–After establishment, the organisms multiply and grow in number through reproduction.

3) Competition and co-action–Intraspecific and interspecific competition begins as the plants increase in number for food and space. Larger and tall plants grow and overshadow the smaller ones. The species enters into various types of interactions.

4) Reaction–the living organisms modify the environment and new seral stage replaces the existing community. The process is repeated.

5) Stabilization–When the community becomes stabilized with the climatic conditions of a given area, it is said to be the final or terminal community often known by the name of climax. This community is in equilibrium with the prevailing conditions of a given area. The climax dominates for a long time except for catastrophic condition. Succession may be arrested by several factors and thus the progress into the climax community may be inhibited. Sometimes this arrested development leads to subclimax like condition. If the arresting phase prolongs a completely different type of vegetation might develop.

3.8 GENERAL CLASSIFICATION OF ECOSYSTEMS

TERRESTRIAL ECOSYSTEMS

Terrestrial ecosystem refers to the interaction between living organisms and nonliving objects on land masses like islands and continents. It covers 28 % of the Earth’s surface. They differ from aquatic ecosystems because aquatic habitat is the prime requisite of aquatic ecosystems. The dominant species here are the pteridophytes, angiosperms, gymnosperms, burrowing organisms like annelids, insects, reptiles, birds and mammals.

Classification of Terrestrial Ecosystems

Terrestrial ecosystems are classified into several types. Major types are:-

GRASSLAND ECOSYSTEM(Temperate and Savannah):

It consists of various types of grasses predominantly. Temperate grasslands are known asthe Pampas in South America, the prairies in North America, the Murray-Darling Basin in Australia, the Steppes in Central Asia, and the Veld in Africa.

Summersare warm and humid. The climate is much cooler than the savannahs with an average temperature of 18 o C in summer and 10 o C in winter.

The primary producers are the grass. Numerous animals including hares, deer, Saiga antelopes, foxes, gophers, sheep, goat, cow, wild dogs and bisons are found in the temperate grasslands.

FOREST ECOSYSTEMS

Forests cover approximately 30% of land and 9.4% of all the planet earth. It refers to thesection of land that is thickly covered with trees may be defined as a forest. They are also known as woods, weald or woodlands. A forest ecosystem is a terrestrial unit of living organisms that exhibits unique environment and many small undefined micro environmental conditions within that covers broad to very small areas. The environmental "common denominator" of forest community is thetree and obeysall the ecological cycles of energy, water nutrients flow.There is substantial amount of detritus and huge number of decomposers.Fire is another limiting factor in the forest. Many plants develop adaptations to regrow even after fire events. For example the presence of thick bark, dormant buds at the base of the trunk and epicormic buds under the bark. If the leaf canopy is removed they are stimulated to spring up. The treecover generally reaches at least 2 meters height at maturity.

Temperate and Tropical Forests

Tropical forests are found near the equator. The distinctiveness lies in the and presence of only rainy and dry season lack of winters. Tropical forests may be tropical rainforests and tropical deciduous forests.

Temperate forests lie between the polar and tropical regions in the Northern and Southern Hemispheres. They exhibit a modestand reasonable climate.Temperate forests can be classified into deciduous, coniferous and broadleaved evergreen forests. The types of trees serve as basis for classification. Temperate forests are abode to many animal species, including rabbits, mountain lions, giant pandas, bears, kookaburras etc.

Forests ecosystems are dynamic and constantly changing community. Forests are valued for social, environmental, cultural and economic factors.Forests provide wood and non-timber products and services; plays key role in combating climate change, contributes to our economy and provides excellent opportunities for recreation and tourism.

IMPORTANCE OF FORESTS

Over 1.6 billion people worldwide are dependent on the forests directly for their livelihoods - food, clothing, shelter and traditional medicine.

Forest based industries gives employment to over60 million people worldwide.

They are important source of raw materials like timber and non-timber products. Timber products consist of lumber, pulp and paper and other wood-based products. Approximately, three billion people worldwide are dependent onfuelwood for heating and cooking. Forests provide medicines,saps, spices,rubber, and oils are also an important part of the forestry industry. Berries, nuts, seeds, mushrooms etc are edible.

Tress removes carbon dioxide through photosynthesis and gives out plentiful of oxygen thus purifying air. Forests capture and store enormous amounts of carbon dioxide –which helps mitigating climate change. Carbon offsetting service provided by tropical forests may be value up to $140 billion per year.

Trees provide shade in the summer and protects from the wind in the winter.

Tree roots playa vital role in soil binding thus preventing soil erosion by wind or rain.

Forests also play an important role in scavenging pesticides, fertilizers and other pollutants from local water bodies.

Forests form the habitatfor about 90% of the world’s terrestrial organisms.

Forests are aesthetically beautiful.

In many religions, trees are considered to be sacred and important parts of local tradition and mythology.

DESERTS ECOSYSTEM

Deserts are usually hot during the day and cold at night.Deserts generally occur in the heart of the continents and usually occur between 25 to 40 o north and south latitude. Deserts have extreme temperatures. Deserts may range from hot and dry deserts to cold deserts. Plants and animal life vary from desert to desert. During the day the temperature may be as high as 50°C, whereas night temperatures may fall to below 0°C. Rainfall is less than 250 mm per year and can be unpredictable. Animals and plants that reside in deserts have adapted to live in these adverse conditions.Major plants are the shrubs that are hardy and resistant to droughts such as sagebrush and cactus. The major fauna in deserts include desert lizards and snakes, Foxes, Dama, Gazelles etc.

Three factors cater to the formation of deserts:

existence of high pressureresulting in cloud-free conditions

cold ocean currents

mountain ranges to create rain shadows areas

A few of the world's deserts are - Sahara Desert, Sonoran Desert, Atacama Desert, TharDesert, Gobi desert etc.

AQUATIC ECOSYSTEM

Aquatic ecosystems commonly refer to interaction of living organisms and non-living entities in oceans, seas, lakes, streams, marshes and ponds.An aquatic ecosystem can be marine and freshwater ecosystems. The primary habitat in this case is water.

•Marine Ecosystems

•Freshwater Ecosystems

MARINE ECOSYSTEMS

Marine ecosystems cover approximately 71 percent of the earth’s surface. Diverge habitats ranging from coral reefs to estuaries, open pelagic sea to the deep benthic and abyssal region,and make up this largest aquatic ecosystem in the planet. Prime examples of marine ecosystems include:

•Oceans and Seas: Characterized by the presence of salt water this ecosystem is further divided into important oceans and smaller seas. The five major oceans are Pacific Ocean, Indian Ocean, Arctic Ocean, Atlantic Ocean and Southern Ocean, Red Sea, Caspian Sea, Black Sea etc.

•Intertidal zone: The area which remains underwater at high tide conditions and becomes terrestrial at low tide is referred to as the intertidal zone. Wetlands, rocky cliffs and sandy beaches all fall under intertidal zones.

•Estuaries: Areas between river and ocean environments those are prone to tides and inflow of both freshwater and saline water. Estuaries are extremely rich and diverse. Due to this inflow, estuaries have high levels of nutrients. Estuaries are also known as inlets, lagoons, harbors etc.

•Coral Reefs: Referredto as the "rainforests of the sea". They are mounds found in marine waters as a result of accretion of calcium carbonate deposited by marine organisms like corals and shellfish. Coral reefs form the most speckled marine ecosystems in the planet, but comprise less than one percent of the world’s ocean. Nonetheless, reefs support around 25 percent of marine animals including varieties of fishes, sponges and mollusks.E.g. - Great Barrier Reef.

Common species found in marine ecosystems include:

•Marine mammals such as seals, dolphins, whales and manatees.

•Different species of fish including halibut, sea horse, mackerel, sardine, flounder, salmon, dogfish, sea bass, etc.

•Organisms such as brown algae, diatoms, corals, mollusk, echinoderms, etc.

Presently, marine ecosystems are susceptible to environmental problems such as climate change, pollution and overfishing.

FRESHWATER ECOSYSTEMS

Freshwater ecosystems cover only 0.8 percent of the earth’s surface is covered by them. The water is non-saline. Approximately 41 percent of the earth’s fishes are found in freshwater ecosystems.Freshwater ecosystems faces danger because of the rapid extermination rates of several invertebrates and vertebrates, mainly because of pollution, overfishing and other harmful activities of the ecosystem.

Types of freshwater ecosystems are:

•Lotic ecosystems - Lotic ecosystems refer to the rapid flowing waters that movesunidirectionally.Rivers and streams are the best examples, which harbor several species of insects, crustaceans, snails, slugs and fishes. Crayfish, crabs, clams and limpets, crocodiles and fishes are commonly found in streams and rivers. Mammals such as beavers, otters and river dolphins also dwell in lotic ecosystems.

•Lentic ecosystems: Lentic ecosystems refer to still or stagnant waters such as lakes and ponds. Ponds and lakes supports a variety of organisms including algae, rooted plants and floating- plants, crabs, shrimps, crayfish, clams, frogs, salamanders, alligators and water snakes.

•Wetlands: Wetlands include swamps, boglands and marshes, where the water is usually of shallow depth.They are regions between land and water. Wetlands are excessively diverse and harbors numerous animals and plant speciessuch as black spruce, sundry, water lilies, mangrove, goran, tamarack. Various species of reptiles and amphibians, birdsand mammals are found in wetlands. Eg – Sundarban, Rashikbeel, Bhitorkanika, Vembanadetc

3.9INTRODUCTION, TYPES, CHARACTERISTIC FEATURES, STRUCTURE AND FUNCTION OF THE FOLLOWING ECOSYSTEM:-

3.10SPECIES INTERACTIONS IN ECOSYSTEMS

The fundamentallife processes such as growth, nutrition and reproduction depend extremely on the interactions between individuals of same species (intraspecific) or of different species (interspecific).Some of the interactions or associations are beneficialto each other and some areharmfulor some may be neutral. The various types of possible interactions/associations can be:

A. Neutral B. Benificial C. Harmful

A. Neutralism the most familiar type of interspecific interaction where neither population affects the other. The interactions are said to be indirect or incidental.

B.  Beneficial Association/Interactions:

1. Proto-cooperation: It is mutually beneficial non obligatory association between two species.For example - Birds removing pests from the bodies of bovine animals etc. in absence of interaction, the bird have the option of finding alternative food sources and so do the bovine does not depend upon the birds to survive.

The Crocodile bird (Pluvianusaegyptius) often goes inside the mouth of the crocodile and feed on parasitic leeches. In this way the bird procures its food and the crocodile is relieved of the blood sucking parasites.

Mutualism (Symbiosis):It is mutually beneficial, absolutely obligatory association between two species.

Example –The association between bees and flowers; bee gets food in the form of nectar, flowers gets its pollen transported by the bee to areas. Without the flower the bee was not able to collect pollen and the plant would not have its pollination that will affect its survival ability.Benefit in the term of nutrients exchange is often termed as "syntrophism".

Lichen (association of algae with fungus) is the association in which algal partgets protection and simple nutrients provided to it by the fungal hyphae.The fungus obtains and use CO2 released by the algae during the process of photosynthesis.

Microorganisms may also form symbiotic relationships with plants. An example is the nitrogen fixing bacteria, Rhizobium-legume association; the plant is benefited by getting readily available nitrate released by the bacterial partner, whereas Rhizobium is getting protection and finished food from the plant. A similar type of interaction is theAnabaena-Azolla, theassociation,extremely important in paddy fields, where nitrogen is often a limiting nutrient.Symbiosis betweenactinomycetes,Frankiawith the roots of Casurina and Alnus (non-legumes) is very common in temperate forest.

Another type of symbiotic association which exists between the fungus and the roots of higher plants calledMycorrhiza. The fungus gets essential organic nutrients and protection from the plants. The plants uptake phosphorus, nitrogen and other inorganic nutrients made available by the fungus.

Zoochlorella lives on the outer tissues of sponges. The alga prepares food and gives 02. In turn the host provides with the matrix and nitrogenous wastes.

Commensalisms: In this association where one organism/partner is benefited and the other partner remains unaffected.

For example, many fungi are capable of degrading cellulose to glucose, which is used by many bacteria.

Remora attaches to shark and is taken to new feeding places and also food pieces falling from the sharks prey serve as food to the Remora.

Epiphytes growing on trees for mechanical support, hardly affect the trees.

Red billed ox-pecker (Buphaguserythrorhynchus) often feeds on the ectoparasites like lice, ticks and mites etc on the skin of rhinoceros.

Hermit crab (Eupagurusprideauxi) is found to live inside the empty shell of gastropods and allows sea- anemone (Adamsiapallicata) to fix on its shell. The sea- anemone provides camouflage (protective colouration) and defend the crab from its enemies , while crab helps in the fast transit of the sea anemone and provides new feeding grounds.

Scavenging: is a direct food linked interspecific interaction in which the scavenger or saprobiontconsumes the dead bodies of other animals, either died naturally or is killed by some other animals.Scavengers sanitize the environment and the available food is ultimately disposed ofso that a major part of nutrients enter the nutrient recycling process. Animals such as vultures, foxes, hyenas, etc. are natural scavengers. Dogs, crows and ants are infrequently seen to do the work of scavengers.

C.Negative (Harmful) Associations/Interactions:

1. Antagonism/ Ammensalism: The relationship in which one species is inhibited by another species in the same environment. The inhibition may be direct or indirect; very common for the production of antibiotics. The phenomenon of antagonism may be of three types, i.e. antibiosis, competition and exploitation.

In the process of antibiosis, the antibiotics or metabolites synthesized by one organism inhibits the growth and survival of another organism. Bacillus secreting an antifungal agent inhibits the growth of several soil fungi.

2. Competition:Active competition may exist among the organisms for available nutrients and space. The limiting food and space may result in favoring one species over another. Hence, competition can be defined as "the injurious effect of one organism on another because of the removal of some resource of the environment". For example, tiger and leopard competing with each other for preying upon deer.

4. Parasitism: A heterospecific association where one organism lives inside or on the body of another for food and shelter. The parasite is dependent on the host and forms metabolic relationship with the host. So,in this host -parasite relationship, one (parasite) is benefited while other (host) is adversely affected, although not inevitably killed. Parasite can be ecto- or endoparasite.E.g. leech, Ascaris, Fasciola.

5. Predation: Predation is an association / exploitation in which predator organism kills and feeds on the pray organism. Generally, the predator is stronger and stout as compared to the prey. E.g.Tiger predating on a deer.

3.11ECOSYSTEM SERVICES

Ecosystem function is the ability of the ecosystem to provide goods and services through natural processes to satisfy human needs, either directly or indirectly.Ecosystem functions are apprehended as a subset of ecosystem structures and function. Natural processesare the result of complex relations between living organisms and the physical and chemical components of ecosystems through the universal driving forces of matter and energy.

There are four primary groups of ecosystem functions

(1) Regulatory functions: refers to the capacity of the natural and semi- natural ecosystems to regulate life support systems like photosynthesis, respiration and ecological processes like nutrient cycles, energy flow, evaporation, precipitation etc. This in turn helps to provide fresh air water and land for our sustenance.

(2) Habitat functions: Natural ecosystems provide shelter and substrate to the wildlife.It contributes to the conservation of biological diversity at all levels as well as to the evolutionary process.

(3) Production functions: The vital process like photosynthesis enables the autotrophs to trap solar energy and convert it into food. These are then consumed and utilized by the secondary organisms for their survival and a variety of other functions.

(4) Information functions: Human evolution took place in the wild and nature serves as the reference point for the multidimensional development of a person. The beauty, serenity and diversity in nature provides excellent platform for spiritual enrichment, intellectual development, recreation etc.

The ecosystem function moves toward a holistic view of the natural goods and services,  

which is shown in Table -

 



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