In this term paper we will discuss about the ecosystem. After reading this term paper you will learn about:- 1. Introduction to Ecosystem 2. Meaning of Ecosystem 3. Types 4. Classification 5. Functional Steps 6. Functional Aspects 7. Examples 8. Energy Flow 9. Structural Characteristics.
Term Paper on Ecosystem
Term Paper Contents:
- Term Paper on the Introduction to Ecosystem
- Term Paper on the Meaning of Ecosystem
- Term Paper on the Types of Ecosystem
- Term Paper on the Classification of Ecosystem
- Term Paper on the Functional Steps of Ecosystem
- Term Paper on the Functional Aspects of Ecosystem
- Term Paper on the Examples of Ecosystem Services
- Term Paper on Energy Flow in an Ecosystem
- Term Paper on the Structural Characteristics of an Ecosystem
Term Paper # 1. Introduction to Ecosystem:
Term ecosystem was first of all coined by Arthur G. Tansley (1935). Earlier it was called biocoenosis by Karl Mobius (1877), microcosm while it was called holocoen by Friederichs (1930), biosystem by Thienemann (1939), biogeocoenosis by a Russian ecologist, Sukachev (1944) and Holon by Koestler (1969). According to Odum (1963), the ecosystem is the basic functional unit of ecology in which both biotic communities and a biotic environment influence each other.
The term ecosystem was proposed by Sir Arthur G. Tansley in 1935. Tansley realised that the living organisms and their non-living environment are inseparably interrelated, and interact upon each other.
He, thus, applied the term to a whole community of organisms and its environment working as a single unit. Various other terms were also applied to this concept, but only one earlier term biocoenose has found favour in Europe and Russia.
The ecosystems may be permanent and natural or temporary. Common examples of natural ecosystems are a pond, a lake, a desert, a meadow, a grassland or a forest. A balanced aquarium is also an example of ecosystem. Examples of temporary ecosystems are a protozoan culture medium, a rainfed pond, etc.
The ecosystem maybe as small as a little water in a dish or as large as an ocean or a large forest. Biosphere is considered as a global ecosystem and is formed of all the local ecosystems on Earth.
Term Paper # 2. Meaning of Ecosystem:
A community of organisms that interact with one another and with the environment is called an ecosystem. It is self-sustaining structural and functional unit of the biosphere. Ecosystem (Gr. eco—environment; system = interacting and interdependent complex) is an integrated system resulting from interaction of living and non-living factors of the environment.
In other words, the ecosystem can also be defined as any unit which includes all the organisms (i.e., communities) in a given area, interacts with the physical environment e.g. water, air, soil etc. by means of food chains and chemical cycles resulting in energy-flow, biotic diversity and material cycling.
It is also called ecological system. The variety of animals in the world are not only dependent on one another, but are also dependent upon the physical factors of the environment e.g. soil, water, air and plants.
For this reason, living beings cannot be separated from the non-living things. There is an intimate relationship between the living community and the non-living environment for survival. The inter relationship between organisms and their environment is ecology.
Term Paper # 3. Types of Ecosystem:
There are three types of ecosystem:
I. Marine Ecosystems:
i. The oceans cover about 64.5% of the earth’s surface. The marine environment is characterized by its high concentration of salt (average salinity is 3.5% but it is 5% in Red Sea and 1% in Baltic Sea) and mineral ions. Most dominant ions are sodium (about 10.7%) and chloride (about 19.3%) followed by sulphur, magnesium and calcium.
ii. Salinity of sea water varies at various depths and is minimum near the river mouths and the poles.
iii. The sea is not a single environment. It is subdivided into distinct ecosystems in both abiotic and biotic composition.
iv. Important determinants of marine ecosystems are: depth of water, distance from the shore and drainage of glaciers and rivers.
v. Major limiting factors for the organisms in the ocean are temperature (varies with latitudes and the surface temperature is about 28°C at the equator and below zero near the poles), salinity, mineral salts, pressure, light etc.
vi. Pressure increases with the depth in the ocean at the rate of about of one ton per square inch for every 1800 metres.
vii. of most of marine biomes is 1000 kcal/m2/year so is less than most of terrestrial biomes. The main reason for the low productivity of ocean is low contents of nitrogen and iron, and light which decreases with increasing depth. But coastal biome has high productivity.
The ocean basins are roughly of the shape of an inverted hat or a wash basin (Fig. 14.35). From the coastline, a gradually sloping region extends for about
160 km into the sea. This zone is called continental shelf and has a depth of 8-200 metres. The slope is hardly 0.1°. The angle of the slopes then abruptly steepens to form the continental slope.
This slope is between 3° to 6°. It is not smooth, have ridges, trenches, basins etc. formed by mud. The continental slope eventually levels off into a more or less horizontal ocean floor (about 6 to 10 km). The depth of ocean floor is in the range of several thousand metres.
On the basis of penetration of sunlight, ocean is divided into three vertical zones:
i. Photic or Euphotic Zone:
It is upper lighted zone upto a depth of about 200 metres.
ii. Aphotic Zone:
This zone gets less light which is insufficient for photosynthesis. It extends upto the depth of 200-2000 meters.
iii. Abyssal Zone:
It is present below 2000 metres and is characterized by perpetual darkness. There are no producers.
Three major environments can be distinguished in ocean basin.
i. Littoral zone, comprising the sea floor from the shore to the edge of the continental shelf;
ii. Benthonic zone formed of sea floor along the continental slope and abyssal plain;
iii. Pelagic zone, consisting of water of the ocean basin. It is again divisible into four sub-zones: epipelagic (in photic zone); mesopelagic (in aphotic zone); bathypelagic (in upper part of abyssal zone) and abyssopelagic (in lower part of abyssal zone).
The organisms of ocean are classified ecologically into three categories:
These are small organisms that float and are drifted passively in surface waters by waves, currents and winds. These do not have organs of locomotion. The planktons include microscopic plants called phytoplanktons (diatoms) and minute animals termed zooplanktons (protozoans, tiny crustaceans, larvae etc.).
These are actively swimming animals found in the surface or deep waters. They have well developed locomotory organs. They feed mainly on planktons or smaller nektons. They include jelly fishes, cuttle fishes, bony fishes, turtles, snakes, seals, whales etc.
These are the bottom dwelling animals that crawl over, burrow into or are attached to the bottom. Crabs, star fishes, brittle stars, sea urchins creep about the bottom. Worms and sea-cucumbers burrow into the soft floor. Sponges, corals, sea pens, tunicates etc. are attached.
II. Freshwater Ecosystems:
There are two main types of freshwater ecosystems:
i. Standing Water Bodies (Lakes and Ponds):
These constitute lentic system. Ponds and lakes are stagnant inland waters. The ponds are small, but very common. They vary greatly in size but always less than one hectare. Small ponds are seasonal but large ones are perennial (at least in their central region). Depth ranges from a few centimetres to about 2 metres.
Though not flowing, the pond water is not motionless. It is slowly circulated by winds. Light penetrates almost to the bottom of ponds. Temperature and distribution of oxygen, carbon dioxide and minerals are informed.
Lakes are often large and deep. They have permanent water. Lakes are classified on the basis of physical factors and productivity.
On the basis of penetration of light, a deep lake is divided in 3 zones:
Upper stratum exposed to solar radiations so is warmer in summer (about 21-22°C) and cooler in winter.
Basal stratum of a lake and is always cool (about 5°C).
Based on productivity, lakes are of two types:
(a) Eutrophic Lakes:
They are relatively shallow but have rich accumulation of organic products and little oxygen (O2 used by decomposers in decomposing the organic wastes). These have rapid circulation of nutrients. Dal lake of Kashmir is a eutrophic lake.
(b) Oligotrophic Lakes:
They are generally deep and often have steep and rocky sides. They are poor in circulating nutrients such as phosphates, calcium and nitrogen.
The physical factors of lakes are dependent on location, latitude, altitude and surrounding biome. For example, some of the lakes like Sambhar lake of Rajasthan contains saline or brackish water.
In fresh water ponds (Fig. 14.36) the flora (autotrophic plants) is constituted by microscopic plants (Chlamydomonas, Chlorella, Spirogyra, Oedogonium, Zygnema, etc.) free floating surface plants (Azolla, Wolfia, Salvinia, Pistia, Lemna, Eichhornia, etc.), suspended plants (Ceratophyllum, Utricularia, Hydrilla etc.) and rooted plants (Vallisneria, Nelumbo, Typha etc.).
Certain rooted but emerged plants like Typha, Sagittaria, Phragmites, etc. also occur. The fauna is constituted by many types of zooplanktons (ciliate and flagellate protozoans, rotifers, minute crustaceans like Daphnia, Cyclops, eggs and larvae of insects like mayflies, dragon flies, damsel files) nektons (insects like water boatman, beetles, water bugs; fishes; frogs; turtles; snakes; tortoises, etc.) and benthos like Hydra, Prawns, crabs, mussels and snails. The study of organisms living in ponds and lakes is called limnology.
ii. Moving Water Bodies (Streams and Rivers):
These constitute Lotic system. These are inland fresh-water bodies with ever-changing and running water. These have well oxygenated water with less minerals and greater availability of sunlight but with no thermal stratification. Temperature of water rises with greater availability of sunlight.
The nature of perennial rivers varies. These are swift- flowing, narrow and cool in upper reaches; wider, slow-moving and with sedimentary bed in middle reaches while are very slow moving and with muddy water in lower reaches.
Moving water bodies differ widely in volume of water, speed of flow of water, oxygen content of water, temperature and many other physical and chemical conditions. The nature of flora and fauna in the rivers and streams depends on the source and land environment through which they pass.
Plants living in streams and rivers are usually attached to surfaces. Animals are mostly strong swimmers. Floating populations of plankton are generally absent in surface water due to rapid water currents. In the middle reaches, the water current becomes slower and river or stream bodies get widened.
The surface gets more of sunlight due to which rate of photosynthesis and biological activity are high. In the lower reaches, the water current further diminishes, but water becomes muddy. This reduces light penetration at the river bed. The nature and composition of fauna in rivers and streams almost resembles with that of lakes.
III. Man-Made Ecosystem:
Man is the dominant organism in planet. He has changed the environment to a far greater extent than any other species. In some instances, the modifications are so profound that we call these Man-made or Artificial ecosystems or anthropogenic ecosystems.
Such ecosystems are of variable stability and duration. These may be terrestrial or aquatic. Familiar examples of man- made terrestrial ecosystems are villages, cities, urban settlements, parks, gardens, orchards and plantations. Large dams, lakes, canals, fishery tanks, reservoirs and aquaria are common examples of man-made aquatic ecosystems.
In the earliest days of evolution, man was not civilized, due to which no changes occurred in surrounding environment. With the passage of time man became civilized and started modifying the surrounding environment for personal benefits.
Most important man-made modifications in the biotic community came with the use of fire, cultivation of plants and domestication of animals. The entire human civilization is supported by agriculture. It is rightly called the backbone of the entire civilization. Broadly, the term agriculture is used to include both animal husbandry and crop production but mainly it is related with crop production.
Human population is increasing day by day. Man has converted very large areas of forests and grasslands into croplands, so as to increase the agricultural produce to support the human population. In these croplands man has planted much selected, mainly herbaceous plants such as cereals, pulses, oil-seeds and forages.
The study of the relation between agricultural crops and environment is called Agroecology. The man-made croplands are generally called Agroecosystems. In a cropland, the physical conditions depend upon latitude, overall climatic and edaphic (soil) factors. The deficiencies in the physical conditions are overcome by artificial irrigation and use of fertilizers and manures.
Usually one crop is raised (Monoculture) in a cultivated field and there is a strong selective pressure to reduce the diversity. However, some weeds and other plants may make their way in the field. Animal population of crop land consists of earthworms, nematodes, domestic animals, pollinators, pests, insects, rodents and many birds.
Some important features of man-made ecosystems are:
(i) They are simple and highly efficient.
(ii) They are not diverse in nature.
(iii) They are not stable though for short period.
(iv) They are more vulnerable to sudden changes due to absence of diversity, stability and self-regulation.
(v) In a monoculture cropland, the single crop may be totally destroyed by drought, floods, diseases, pests or pathogens. In contrast to this multiple (polyculture) system has scope for many adjustments and substitutions.
Term Paper # 4. Classification of Ecosystem:
Ecosystem has been classified into two factors:
I. Abiotic Factors
II. Biotic Factors.
It is the non-living environment, which holds the biotic community. In any particular environment of a geographical region, the relation and interactions between living and non-living objects are collectively known as Eco-system.
I. Abiotic Factors:
Abiotic factors or components are the non-living components or parts that affect the metabolism and behavior of the organisms in the environment.
Abiotic factors include:
i. Inorganic Components:
Water and mineral salts are inorganic components of eco-system. In addition to these, there are other gaseous elements like O2 (oxygen), N2 (nitrogen), CO2 (carbon dioxide), etc., which are necessary for the nutrition of the plants and respiration of organisms.
ii. Organic Components:
It is the rotten parts of the dead body of plants and animals. The dead body of plants and animals after being decomposed forms urea and humus. These constitute the organic elements of the soil.
iii. Physical Components:
The climate of a particular environment depends on rainfall, air movement, temperature, humidity, amount of sunlight, snow fall, etc.
Condition of soil in any place influences the animals and plants living there.
Sunlight is an important factor as it helps the plants to live and continue the biogeochemical cycles.
The life of animals and plants also depend on the quantity of water, the level of underground water, drainage of excess water and also on the porosity of the soil.
II. Biotic Factor:
Every organism is a part of the eco-system. Plants, animals, microorganisms are all included.
In an ecosystem, the non-living and living components are interdependent. The absence of one affects the other in maintaining their natural activities. The change in plants influences the animals’ character in the eco-system.
Thus, an ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals. For example, if you visit a garden, you will find different plants, such as grass, flower bearing plants like rose, jasmine, sunflower; and animals like frogs, insects and birds. All these living organisms interact with each other.
Their growth, reproduction and other activities are affected by the abiotic components of an ecosystem. So, a garden is an ecosystem. Other types of ecosystems are forests, ponds and lakes. These are natural ecosystems while gardens and crop-fields are human-made (artificial) ecosystems.
Term Paper # 5. Functional Steps of an Ecosystem:
i. Producers or autotrophs convert inorganic compounds like CO2 and H2O into organic compounds like monosugars in the presence of radiant energy of the sun and Mg++ containing chlorophyll by the process of photosynthesis.
ii. Consumers or animals are heterotrophs and consume the producers directly or indirectly so may be herbivorous or carnivorous in their feeding.
iii. Decomposers break down the complex organic compounds of dead bodies of both producers and macro consumers to release inorganic compounds back into the environment by the process of decomposition and mineralisation. These help in material cycling.
iv. In these interactions, there is undirectional flow of energy from lower to higher trophic levels.
Term Paper # 6. Functional Aspects of Ecosystem:
Some of the functional aspects of ecosystem are as follows:
III. Energy flow
Iv. Nutrient cycling.
A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Productivity is the rate of biomass production per unit area over a time period.
It is expressed in terms of g-2 yr-1 or (kcal m-2) yr-1.
Productivity of an ecosystem can be categorized as, primary productivity and secondary productivity.
A. Primary Productivity:
It is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight or energy (kcal m-2).
Primary productivity has two aspects given below:
a. Gross Primary Productivity (GPP):
It is the rate of production of organic matter during photosynthesis. A considerable amount of GPP is utilised by plants in respiration.
b. Net Primary Productivity (NPP):
It is the amount of energy left in the producers after utilisation of some energy for respiration.
Gross primary productivity minus the respiration losses is net primary productivity. It is actually the available mass for consumption by heterotrophs (herbivores and carnivores).
GPP – R = NPP
Where, R = Respiration losses.
Factors Affecting Primary Productivity:
Different factors affecting primary productivity are given below:
a. The plant species inhabiting in a particular area.
b. Environmental Factors:
The various environmental factors also contribute in affecting primary productivity like light, temperature, water and photosynthetic capacity/efficiency of producers.
Sunlight is the ultimate source of energy. In aquatic ecosystems, productivity is less than terrestrial ecosystem. Maximum light is available in tropics and poles receive the minimum light.
It regulates the activity of an enzyme. So, optimum temperature is required for proper functioning of enzyme.
Rain (humidity) increases the productivity of the ecosystem. It tends to decrease with the scarcity of water. Therefore, deserts have the lowest primary productivity as soil is deficient in moisture.
iv. Nutrients Availability:
Nutrients are essential for the growth of producers. Thus, greater nutrients ensure greater primary productivity.
v. Photosynthetic Efficiency of Plants:
Photosynthetic Efficiency of Plants (producers) C4– plants are more productive as compared to C3-plants because some plants have more efficiency to trap sunlight. So, they accumulate more productivity.
Annual net primary productivity of whole biosphere is 170 billion tones (dry weight) of organic matter of this, 55 billion tones is contributed by oceans.
B. Secondary Productivity:
It is the rate of assimilation and formation of new organic matter by consumers. It is small as compared to primary productivity and tends to decrease with the increase in the trophic level.
It is the process of breaking down of complex organic matter into inorganic substances like water, carbon dioxide and nutrients.
Detritus is the raw material for decomposition. It includes dead remains of plants (leaves, bark and flowers) and of animals including faecal matter. It is largely an aerobic process, i.e., requires oxygen for its processing.
Different steps involved in the process of decomposition are:
i. Fragmentation is the process of breaking down of detritus into smaller particles.
ii. Leaching is the process by which water soluble inorganic nutrients go down into the soil horizons and get precipitated as unavailable salts.
iii. Catabolism is the process of degradation of detritus into simple organic material by the action of bacterial and fungal enzymes and then their further conversion into inorganic compounds.
iv. Humification is a process that leads to an accumulation of a dark coloured amorphous and colloidal substance called humus which is highly resistant to microbial action and decompose at a very slow rate. It serves as a reservoir of nutrients.
v. Mineralisation is the process of degradation of humus which is further degraded by microbial action and release of inorganic nutrients.
Fragmentation, leaching and catabolism take place simultaneously on the detritus while humification and mineralisation take place during decomposition of soil.
Factors Affecting Rate of Decomposition:
Decomposition is largely an oxygen requiring process. The rate of decomposition is controlled by chemical composition of detritus material and climatic factors.
i. Chemical Composition of Detritus:
The rate of decomposition is slower, if detritus is rich in lignin and chitin, while it is quicker if it is composed of nitrogen and water-soluble substances like sugar.
ii. Climatic Factors:
Temperature and soil moisture are the most important climatic factors that controls decomposition. Warm and moist environment favours decomposition, while low temperature and anaerobiosis, i.e., an anaerobic conditions (unavailabity of oxygen) inhibits decomposition.
III. Energy Flow:
Sun is the only source of energy for all the ecosystems on the earth except for deep sea hydrothermal ecosystem. Of the total incident solar energy, less than 50% is Photosynthetically Active Radiation (PAR). Plants utilise only 2-10% of PAR to sustain the entire living world.
Plants as well as photosynthetic and chemosynthetic bacteria fix sun’s radiant energy to make food from simple inorganic molecules. Thus, are dependent on producers either directly or indirectly for their food. The flows of energy is unidirectional, i.e., it flows from the sun to producers and then to consumers and thus, maintains the first law of thermodynamics.
The energy is transferred in an ecosystem in the form of food which is converted into energy during metabolic process and a very little amount is stored as biomass. This is in co-relation with second law of thermodynamics.
IV. Nutrient Cycling:
The movement of nutrient through various components of an ecosystem is called nutrient cycling, also called biogeochemical cycles.
Organisms need a constant supply of nutrients to grow, reproduce and regulate various body functions and the amount of nutrients, such as carbon, nitrogen, phosphorus, calcium, etc., present in the soil at any given time, is referred to as the standing state.
It varies with the kind of ecosystem and season (bio-living, geo-rocks, air, water).
Nutrient cycles are of two types:
i. Gaseous Cycle:
In this, reservoir is the atmosphere. Nutrient occurs in either gaseous or vapour form. These are comparatively faster than others, e.g., carbon cycle and nitrogen cycle.
Carbon constitutes 49% of dry weight of organisms and it is next only to water. About 71% carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere. The fossil fuels also represent reservoir of carbon.
Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. 4 x 1013 kg of carbon is fixed in the biosphere through photosynthesis annually. Decomposers also contribute substantially to CO2 pool by their processing of waste materials and dead organic matter of land or oceans.
Carbon dioxide is returned to the atmosphere via respiratory activities, burning of wood, forest fire and combustion of organic matter, fossil fuels and volcanic activity are additional sources for releasing CO2 in the atmosphere. Human activities have influenced the carbon cycle, e.g., deforestation and burning of fossil fuels lead to increase in the release of carbon dioxide in the atmosphere.
ii. Sedimentary Cycle:
In this, reservoir is the earth’s crust. Nutrient occurs in non-gaseous form. These are comparatively slower than gaseous cycles, e.g., phosphorus cycle and sulphur cycle. Environmental factors like temperature, pH, soil nature and moisture can regulate the rate of release of nutrients. The function of the reservoir is to meet the deficit, which occurs due to imbalance in the rate of influx and efflux.
Phosphorus is a major constituent of biological membranes, nucleic acid and cellular energy transfer systems. Animal shells, bones and nails are all made up of phosphorus only. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
From rocks, it goes to soil solution, there it is absorbed by the plant roots, and finally animals and herbivores obtain phosphorus from those plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.
Term Paper # 7. Examples of Ecosystem Services:
I. Services (Benefits) of a Healthy Forest Ecosystem:
(i) The forests provide food in the form of roots, tubers, leaves and fruits especially for the tribals.
(ii) The forests provide fuel in the form of wood for cooking and keeping warm. Over 1000 million tonnes (more than 80% of total fuel) of wood is used as fuel in the world.
(iii) Forests provide timber for building purposes of houses, ships, railway sleepers, sport goods, agricultural tools, toys, etc.
(iv) Forests also provide a number of useful products like camphor, essential oils, tannins, dyes, gums, resins, soap substitutes, drugs, etc.
(v) These keep the environment cool by regulating transpiration and precipitation.
(vi) Plants produce oxygen during photosynthesis for respiration of animals.
(vii) These provide shelters to a variety of animals and plants (e.g. mosses, ferns etc.)
(viii) These prevent soil erosion by binding the soil particles and regulating the floods and wind velocity so help in conservation of soil.
(ix) These also have aesthetic, cultural and spiritual importance.
II. Services Provided by Watersheds:
A watershed is an area of high land from which water flows under gravity into river or sea. It has a well defined topographic boundary with only one outlet of wafer. The watersheds supply water for irrigation, hydropower generation, transportation, vegetation growth and reducing the chances of floods and droughts. So watersheds improve the economy of the region.
Other sources of ecosystem services are wetlands, wild life, mineral resources, energy services, etc.
Price Tag on Ecosystem Services:
Robert Constanza et.al. have recently put price tags on nature’s life- supporting services. It is proposed an average price tag of US$ 33 trillion a year on these fundamental ecosystem services which is nearly three times the value of the global gross national product (GNP).
Out of the total price tag on various ecosystem services, the soil formation accounts for about 50%; recreation services for about 10%; nutrient cycling for about 10%; 6% for climatic regulation; 6% for wild life management; etc.
But as these ecosystem services are free so these are taken for granted and most of societies believe in anthropogenic world view which states that success and healthy economy of mankind depend upon how nicely man derives benefits from nature.
So the human beings are over-exploiting the natural resources and polluting the environment. It is being further compounded by population explosion. These human acts are very dangerous and may lead to environmental crisis which may threaten even the existence of mankind.
So there is an urgent need of developing the essence of environmental ethics and Eco-centric worldview m the human beings. This view states that the natural resources are limited and the success and healthy economy of mankind depend upon the healthy environment.
The environmental ethics include the human obligations towards the environment and demand that man should learn to live as a part of nature and not as a master of nature. They must make sincere efforts to renew the natural resources so that sustainable development is achieved.
Term Paper # 8. Energy Flow in an Ecosystem:
It is determined by two basic laws of thermodynamics:
First law of thermodynamics states that energy is neither created nor destroyed, but can be transferred from one component to another, or transformed from one state to another.
Second law of thermodynamics states that every energy transformation involves degradation or dissipation of energy from a concentrated to a dispersed form due to metabolic functions, so that only a small part of energy is stored in the biomass. So they need a constant supply of energy so as to counter the universal tendency towards increasing disorderliness.
Sun is the only source of energy for all the ecosystems of Earth. About 55-60% of the solar energy is absorbed in the atmosphere and about 35% of it is used in heating the water and land. Light falling on the plants is trapped by the producers in the presence of Mg++-containing green pigment called chlorophyll and is used in assimilating the organic food called glucose by the process of photosynthesis. By photosynthesis, radiant energy of sunlight is transformed into potential energy of foodstuffs.
Evidences show that only a part of energy is trapped by the producers while the rest of energy is dissipated. The energy conserving efficiency is 1.15% for grasslands, 0.9% for Savannah, 0.8% for mixed forest 5% for modern crops and 10-20% for sugarcane field, (with maximum energy conserving efficiency). The green plants or producers breakdown a part of organic food in respiration to obtain chemical energy for various body functions and overcoming entropy.
Dissipation of energy occurs as heat. The remaining energy is used in the synthesis of plant biomass called net photosynthesis which is then available to the next trophic level of food chains. This loss is not due to the inefficiency of the photosynthetic mechanism of the plants but due to the operation of second law of thermodynamics. The total biomass manufactured by plants during photosynthesis is called gross primary productivity of an ecosystem and is symbolized as PG.
On average, it is about 1-5 per cent energy of incident radiations, i.e. 2-10 per cent of photosynthetic active radiation (PAR). A part of it is used by the plants themselves for respiration (R) (0.2 to 1% of incident radiations), while the remaining biomass is called net primary productivity (PJ. It is also called apparent photosynthesis. On average, it is about 0.8-4 per cent energy of incident radiations, i.e. 1.6 – 8 per cent of PAR.
So it can be represented as:
PN = PG – R
Energy Flow Model:
Different components for a universal model (Fig. 14.12) of energy flow are:
LA = Light absorbed by plant cover.
L1 = Input or ingested energy.
NU = Not Used.
NA = Not assimilated
A = Assimilated energy.
P = Production.
R = Respiration.
B = Biomass
G = Growth.
S = Stored energy
E = Excreted energy.
When a herbivore eats a plant, then it digests and oxidizes the ingested food to liberate energy which is equal to that used in synthesizing the organic biomass by the plant. Some of the released energy is lost as heat while only a part of energy is used in building the biomass of the herbivore, called gross secondary productivity.
The same is repeated when the herbivore is eaten by a primary carnivore and so on. At each transfer, about 80-90% of potential energy is dissipated as heat while only 10-20% of energy is available to next trophic level. Thus, there is a decline in the amount of energy passing from one trophic level to the next trophic level. The study of energy transfer was called bioenergetics.
Secondary productivity tends to be about 10 per cent at the herbivore level, although efficiency may be higher, as 20 per cent at the carnivore level (Fig. 14.13 & 14.14).
So regarding the energy flow, an ecosystem is characterized by:
i. Unidirectional flow of energy.
ii. Decrease in useful energy.
iii. Return of radiant energy of sun to non-living system as heat.
Term Paper # 9. Structural Characteristics of an Ecosystem:
Interactions of biotic and abiotic components of an ecosystem result to its physical structure which is characteristic for each type of ecosystem.
Important physical structural features of an ecosystem are:
i. Species Composition:
Different ecosystems have different kinds of species composition so have different physical appearance (called physiognomy) e.g. a tropical rainforest is dominated by broad-leaved evergreen trees so giving the appearance of a tall plant canopy. Conversely, a desert has very scanty flora and fauna so shows a low and discontinuous herb layer. Vegetation is less and separated by extensive bare patches of soil.
Trophic (food) structure of an ecosystem is indicated by food relationships of different trophic levels of a food chain. It can also be described in terms of the amount of living material (called standing crop) present in different trophic levels.