ADVERTISEMENTS:
Read this essay to learn about ecosystem. After reading this essay you will learn about: 1. Meaning of Ecosystem 2. Nature of Ecosystem 3. Structure 4. Functions 5. Types 6. The Laws of Thermodynamics and Energy Flow 7. Ecosystems Dynamics and Successional Process 8. Ecosystem Disturbance 9. Regulation 10. Material Cycle 11. Productivity 12. Conservation and Management.
Essay Contents:
- Essay on the Meaning of Ecosystem
- Essay on the Nature of Ecosystem
- Essay on the Structure of Ecosystem
- Essay on the Functions of Ecosystem
- Essay on the Types of Ecosystem
- Essay on the The Laws of Thermodynamics and Energy Flow in Ecosystem
- Essay on the Ecosystems Dynamics and Successional Process
- Essay on Ecosystem Disturbance
- Essay on the Regulation of Ecosystem
- Essay on the Material Cycle in Ecosystem
- Essay on the Productivity of Ecosystem
- Essay on the Conservation and Management of Ecosystem
Essay # 1. Meaning of Ecosystem:
ADVERTISEMENTS:
An ecosystem is a functional unit of nature, where living organisms interact among themselves and also with their surrounding physical environment. The term ‘Ecosystem’ was coined by AG Tansley (1935). Ecologist considers the entire biosphere as a global ecosystem comprised of many ecosystems on the earth varying in size from a small pond to a large forest or a sea.
Ecosystem can also be defined as an interactive system, where biotic and abiotic components interact with each other via energy exchange and flow of nutrients. Crop fields and an aquarium are considered as man-made ecosystems.
Essay # 2. Nature of Ecosystem:
Ecosystems consist of living organisms and material environments of soil, air and water, and occur at a variety of scales. As with all systems the ecosystem is composed of a series of inputs, processes or stores and outputs. Although various components within it may change, it is usually maintained in a state of balance, called dynamic equilibrium.
ADVERTISEMENTS:
This stability is due to homeostatic mechanisms, which work rather like the thermostat in a heating system. In an ecosystem, changes thus, may be shown by feedback, which is ability of the output to control the input.
The organisms living on the earth’s surface constitute the biosphere and are found in the air (atmosphere), on land (lithosphere) and in water (hydrosphere). At a global scale, land environments with similar plant and animal communities for natural regions or biomes.
Each biome may be divided, at a variety of scales, into ecological systems or ecosystem. Each ecosystem has a unique range of species forming its biological diversity or biodiversity.
A.G. Transley (1935) defined an ecosystem for the first time as follows-
“A particular category of physical systems consisting of organisms and inorganic components in a relatively stable equilibrium, open and of various lands and sizes”.
However, the current definition is as follows-
“Ecosystem consists of structured webs or systems at a range organism and their material environments of soil, air and water. These components are linked by movements of energy and nutrients”.
Essay # 3. Structure of Ecosystem:
The term ‘structure’ refers to the various components which combine to produce an ecosystem. These may be divided into living or biotic components and non-living or abiotic components. An outline is shown in Fig. 4.1.
The Biotic Component—Producers, Consumers and Decomposers:
The living organisms in an ecosystem collectively form its community or population. Each organism interacts with others forming relatively simple food chains and complex food webs. Each stage in the food chain is called a tropic level. Energy and nutrients pass through the tropic level, as various organisms are in turn eaten by other organisms of higher tropic order.
The producers are the autotrophs, thus forms the first tropic level. These are mainly green plants and photosynthetic bacteria, all of which can carry out photosynthesis. In marine and other fresh water bodies microscopic algae (phytoplankton) as producer.
Producers form the food for the consumers (or heterotrophs). The consumers are of different tiers. Primary consumers or herbivores form the second tropic level, feeding directly on the producers. In land based ecosystems they will include grazing and browsing animals such as antelope, elephant and giraffe, together with plant eating insects and birds.
But in aquatic ecosystems, molluscs such as mussels and zooplankton which feed on phytoplankton are the main primary consumers.
ADVERTISEMENTS:
The third trophic level comprises the secondary consumers or carnivores, which feed on the herbivores. A fourth tropic level, the tertiary consumers, who are also carnivores may occur. Some of the higher level consumers, for example bears, eat both plants and animals, and are called omnivores.
There are several different groups of secondary and tertiary consumers:
1. Predators are those, which hunt, capture and kill their prey.
2. Carrion feeders consume dead and dying animals.
ADVERTISEMENTS:
3. Parasites live on their host animals.
The decomposers and detrivores form another major component of the biotic structure of an ecosystem. After plants and animals die, they and their waste products arc decomposed by saprophytic microorganisms such as fungi and bacteria. Very small decomposing fragments form detritus, which is then fed on by small animals, detrivores, including earthworms and woodlice.
Abiotic Component or Habitat Concept:
Individuals, species and populations, both marine and terrestrial, tend to live in particular places. These places are called “habitats”. Each habitat is characterised by a specific set of environmental conditions – radiation and light, temperature, moisture, wind, fire frequency and intensity, gravity, salinity, currents, topography, soil, substratum, geomorphology, human disturbances and so forth.
Habitats come in all shapes and sizes, occupying the full sweep of geographical scales. They range from small (microhabitats) through medium (mesohabitats) and large (macrohabitats), to very large (mega habitats).
ADVERTISEMENTS:
Microhabitats are a few square centimeters to a few square meters in area. They include leaves, the soil, lake bottoms, sandy beaches, tall slopes, wall, river banks, and paths. Mesohabitats have areas up to about 10,000 km2; thus is a 100 x 100 kilometer square, which is about a small district.
Each main mesohabitat is influenced by the same regional climate, by similar features of geomorphology and soil, and by a similar set of disturbance regimes. Macrohabitats have area up to about 1, 00,000 km2, which is about the size of a country. Mega habitats are regions more than 1,000,000 km2 in extent. They include continents and the entire land surface of the Earth.
Diverse forms of organisms live in virtually all environments, from the hottest to the coldest, the wettest to the driest, the most acidic to the most alkaline. But there are special requirement for each organisms and also tolerance limits too.
For every environmental factor (viz., temperature and moisture) there is a lower limit below which a species cannot live, an optimum range in which it thrives and an upper limit above which it cannot live.
The upper and lower bounds define the tolerance range of a species for a particular environmental factor (Fig. 4.2). Each species (or race) has a characteristic tolerance range. Stenoecious species have a wide tolerance; euryoeciuos species have a narrow tolerance.
All species, regardless of their tolerance range, may be adopted to the low end (oligotypic) to the middle (mesotypic) or to the high end (polytypic) of an environment gradient (Table 4.1).
Essay # 4. Functions of Ecosystem:
There are two major functions within an ecosystem the transfer of energy through and the recycling of nutrients within the ecosystem.
i. Energy Flows in Ecosystem:
Photosynthesis is the process by which light energy from the sun is absorbed by green plant, cyanobacteria and other photosynthetic bacteria. It is then used to produce new plant cell material, which forms the food source for plant eating animals (herbivores).
Plants are able to convert light energy and inorganic substances (CO2, H2O and various mineral substances) into organic (carbon based) molecules through the process of photosynthesis are called phototrophs or autotrophs.
The basic reaction is as follows:
ADVERTISEMENTS:
6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
Carbon dioxide + Water → Glucose + Oxygen + Water
The energy thus produced in the form of organic molecules by photosynthesis will pass through the food chains and food webs of an ecosystem, with some of it being stored as chemical energy in plant and animal tissue. Some of it will be lost from the system, as respiration (heat energy) and excreta products.
The total amount of energy lost, from all the trophic levels in an ecosystem through respiration, forms the community respiration. Energy is lost at each level in the food chain, with the average efficiency of transfer from plants to herbivores being about 10 per cent and about 20 per cent from animal to animal (Fig.4.3).
As a result of the loss of energy at each transfer between trophic levels, ecosystems are usually limited to three or four trophic levels. The actual number will depend upon the size of the initial autotroph (producer) biomass, and the efficiency of energy transfer between the trophic levels.
ii. Nutrient (Gaseous or Biogeochemical) Cycles:
The nutrients or elements used by all organisms for growth and reproduction are termed essential elements. Among the essential elements some are required in large quantity. They are termed as macronutrients or major nutrients viz., carbon (C), hydrogen (H), Oxygen (O), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sulphur (S).
However, there are about others 30 elements which are also essential but required in small quantity viz., iron (Fe), manganese (Mn), copper (Cu), zinc (Zn) and cobalt (Co) etc. They are called trace elements.
The nutrients required by plants are obtained as inputs either from the atmosphere through various gaseous cycles or in precipitation, or from the soil via the weathering of parent rock, through several biogeochemical or sedimentary cycles. The two types of cycle are interrelated, as nutrients pass from abiotic nutrient stores, such as the soil and the atmosphere, into biotic, plant and animal stores (the biomass).
The nutrients are then recycled, within the ecosystem, following death and decomposition (Fig. 4.4). Nutrients are lost, as outputs, by surface runoff, leaching through the soil profile or the removal of plant, animal, leaf litter or soil material. The concept of the recycling of nutrients between three compartments or stores is shown in Gersmehl’s Model (Fig 4.5).
Some distinctive features of elemental cycles are described separately.
(a) Carbon Cycle:
In the living world carbon is the major element that constitute the organic molecules viz. carbohydrates, protein, fat, vitamin and other secondary metabolites. Carbon is available as gaseous elements in atmosphere as CO2, CO, CH4, C2H2 and various other volatile gas forms. Carbon is also present as carbonate, bicarbonate in water and soil.
Soil also possesses organic carbon originating from decomposition of biomass. Atmospheric carbon dioxide is fixed by green plant through photosynthesis as organic molecules. Carbon dioxide may also be absorbed by water and soil to form carbonate and bicarbonate salt.
Carbon dioxide is formed through organic decomposition, volcanic eruption, burning of fossil fuel or woods or biomass. Over the years, global imbalance in carbon cycle took place. This is primarily due to source sink disharmony. As a consequence global warming associated process accelerated over the years. A simplified model of carbon cycle is shown in Fig. 4.6.
(b) Nitrogen Cycle:
Like carbon, nitrogen is another important essential elements. In atmosphere nitrogen mostly remain as gas viz. N Ξ N, NO2, NO, N2O, NH3 and other nitrogenous volatile gases. In soil and water nitrogen remain as nitrate, nitrite or ammonium salts. Most of the plant absorb nitrogen from soil nitrate or nitrite and then converted to organic forms.
There are a couples of instances, where atmospheric nitrogen is fixed by the nitrogen fixing bacteria in free state or symbiotic association stage with legumes. Organic materials on decomposition releases nitrogen gas and NH3 or nitrate or nitrite into the soil. On fuel burning nitrogen oxide gas also formed and released into the nature. An over view of nitrogen cycle is shown in Fig. 4.7.
(c) Sulphur Cycle:
Sulphur is also another major essential elements. In atmosphere sulphur remain as SO4, SO3, H2S and in other allied forms. In soil and water it remains as- SO4, SO3, HSO3 or insoluble sulphate rich rocks/sediments. Major sources of sulphur is the volcanic eruption or rock disintegrations. Fossil fuel burning leads to SO2 production. A diagrammatic representation of sulphur cycle is shown in Fig. 4.8.
(d) Mineral Cycle:
There are a number of metallic minerals viz, Ca, Mg, Fe, Mn, Zn, Cu, Mb, Ni, Co, Cd etc. which are very essential for life. Most of these minerals are absorbed from soil/water by producer and subsequently they spread to various categories of consumers through food chain.
In the biological forms all the minerals are released to soil by decomposition. Excess quantity of minerals however may be toxic to the life forms. An overview of mineral cycle is shown in Fig. 4.9.
Essay # 5. Types of Ecosystem:
i. Forest Ecosystem:
It is one of the major productive natural terrestrial ecosystems of the world.
The forest ecosystem varies widely in different climatic zones.
A number of climatic, edaphic and physiographic factors regulates the types and composition of forest ecosystem.
The major types of forest ecosystem are as follows:
1. Tropical Rain Forests:
It grows in the regions with plenty of moisture and heat. These forests were located in tropical South America (viz., Amazon river basin), in the East Indies, South East Asia (viz., Malabar Coast of India), in some parts of Africa and North-West Australia. The annual rainfall of the region is fairly high (2000 to 2500 mm) and evenly distributed throughout the year.
There is a very rich floristic and faunistic composition due to moderate temperature, high humidity, better soil nutrient and moisture regime. A typical ram forest has multi-layer component vegetation with well-developed canopy of tall trees (25-40 meter high). The understory vegetation is fairly thick. There are lots of climbers and epiphytes. The net primary productivity is as high as 30 ton per acre per year.
2. Temperate Forests:
It is primarily a mountainous forest of fairly higher elevation where rainfall is moderate to high, and temperature ranges from 5-20°C. It may be evergreen broad leaved or coniferous or deciduous broad leaved type. The primary productivity is moderate to high. The dominants species were conifers, maple (Acer), Oak (Quercus), Birch (Alnus), Aspen (Populus) Beech (Fagus), Buckeyes (Asculus) and Hemlock (Tsuga) etc.
3. Grassland:
It occupies about 20% of the earth’s land surface, and are of three types viz., Tropical grassland (Savanna), Temperate grassland and Alpine grassland. Each grassland has its own characteristics floral components. Usually, the vegetation is dominated by grasses, legumes and composites. The Alpine grassland is said to be “Tundra”, which is very much lichen rich. Usually the productivity of grassland is fairly low.
4. Mangroves:
This is a specialised vegetation of coastal tidal mudflat. This is distributed in all maritime countries and island states. It has a characteristic dense forest with short height (3-5 meter) trees with elaborate root system, waxy leaves and other xeric features. This is a tropical evergreen forest patch with highly productive ecosystem. Consumer diversity is also fairly high. In India, coastal estuaries have dense mangrove vegetation.
5. Deserts:
These ecosystems are barren or have scanty vegetation consisting mainly of thorny bushes. It receives low rainfall (<500mm per annum), but are not uniform. There are few locations where perennial water sources may be available. The productivity is extremely poor. There are limited and specialised consumers in desert habitats.
Depending on the food availability within different forest ecosystems, the consumer types and their population varies. However, among the terrestrial ecosystems, biological diversity is more pronounced in tropical rain forest and lowest in desert system. Due to varied physiographic and agro climatic zonation, India has almost all categories of forest ecosystem.
ii. Aquatic Ecosystems:
These ecosystems occupy over 70% of the planet earth. In addition to its own productivity these ecosystem plays an important role in the cycling of chemical substances and influences the growth and activities of terrestrial ecosystems.
There are three principal categories of aquatic ecosystems viz., Freshwater (Pond, Lake, Springs or River) ecosystem; estuarine ecosystem (at the meeting point of river and sea); and marine and coastal salt water ecosystem. Each kinds of aquatic ecosystem has it own physical, chemical and biological characteristics.
Primarily inland, fresh water habitats are grouped into two categories:
(a) Lentic habitats (standing water i.e., pond, lake and reservoirs) and
(b) Lotic habitats (running/flowing water i.e., springs and rivers).
Both kinds of fresh water ecosystems differs in their physical characteristics and biotic components. For instance in ponds, lakes and reservoirs, there are three distinct layers shallow water zone (littoral zone), limnetic zone (open water zone) and deep water (pro-fundal zone). But in lotic system, such zonation are not prominent. The flowing water breaks thermal gradient and also helps in mixing of water components (Fig. 4.11).
Fig 4.11: Four major zones of life in a lake
The marine ecosystem of sea has open seas (pelagic environment) and benthic environment (ocean depths) and coastal water (with tidal influences). There are characteristic vegetation with species composition (both producers and different categories of consumers too) (Fig. 4.12).
Fig. 4.12 Major zones of life in an ocean
Among the aquatic ecosystems, estuarine ecosystem is the most productive one and coral ecosystem on coastal littoral zone is the least productive form. An overview characteristics of prominent ecosystems are given in Table 4.2.
Essay # 6. The Laws of Thermodynamics and Energy Flow in Ecosystem:
The application of the two fundamental laws of thermodynamics to energy and matter transformations at the cellular level was discussed over the years through various ecosystem modes.
The First Law (the law of conservation of energy) asserts that in a closed system, energy can nether be created nor destroyed but can only be transformed from one form to another.
Thus, when fuel is burnt to drive a car, the potential energy contained in the chemical bonds of that fuel is converted into mechanical energy to propel the car, electrical energy to ignite the fuel, light to show where you are going and heat to defrost the windscreen.
The key point, however, is that if you could measure the total amount of energy consumed and compare it with the total amounts being produced in these various other forms the two would be equal.
Energy conversions such as these also take place in biological systems. Photosynthetic organisms such as plants capture and transform light energy from the sun and transfer this energy throughout the system subject only to the consequences of the Second Law.
The Second Law asserts that disorder (entropy) in the universe is constantly increasing and that during energy conversions, energy inevitably changes to less organised and useful forms, i.e.. it is degraded Think of this as energy always going from concentrated to less concentrated forms, the least useful (i.e least concentrated) being heat energy.
The consequences of this are very significant biologically Dunn- each conversion stage, some energy is lost as heat.
Therefore, the more conversions taking place between the capture of light energy by plants and the trophic (feeding) level being considered, the lees the energy available to that level. The efficiency of the transfer along food chains is generally less than 10 per cent because about 90 per cent of the available energy is lost or used at each stage.
The study of energy flow is important in determining limits to food supply and the production of all biological resources. The capture of light energy and its conversion into stored chemical energy by autotrophic organisms provides ecosystems with their primary energy source.
Most of this is photosynthetic chlorophyll-based production, the exception being the comparatively limited production of organic materials by chemosynthetic organisms. The total amount of energy converted into organic matter is the gross primary production (GPP) and varies markedly between systems.
However plants use between 15 and 70 per cent of GPP for their own maintenance. What remains is the net primary production (NPP). The total NPP of an ecosystem provides the energy base exploited by non-photosynthetic (heterotrophic) organisms as secondary production.
Heterotrophs obtain the energy they require by consuming and digesting plants (herbivores), by feeding on other heterotrophs (carnivores) or by feeding on detritus, the dead bodies or waste materials of other organisms (detritivores, saprophytes saprozoites)
The energy stored in the food materials is made available through cell respiration. Chemical energy is released by burning the organic compound with oxygen using enzyme-mediated reactions within cells. This produces carbon dioxide and water as waste products.
Energy flow is the movement of energy through a system from an external source through a series of organisms and back to the environment. At each stage (trophic level) within the system, only a small fraction of the available energy is used for the production of new tissue (growth and reproduction), most is used for respiration and body maintenance.
Once the importance of energy flow is appreciated, the significance of energy efficiency and transfer efficiency is more readily understood. Energy efficiency is ‘the amount of useful work obtained from a unit amount of available energy’ and is an important factor for the management and conservation of any biological resource.
The development of most modern intensive agriculture is founded on the principle that increased channeling of energy into a system results in higher yields; however, the energy efficiency is usually less than in more traditional agricultural system
A common ecological measure of efficiency is the trophic-level efficiency, the ratio of production at one trophic level to that of the next lower trophic level. This is never very high and rarely exceeds 10 per cent (the ’10 per cent rule’), more typical values being only 1-3 per cent.
Table 5.1 lists other measures of efficiency often used in ecological comparisons. However, estimates of ecological efficiencies can vary widely between individuals and populations because individuals in a population may live under different ecological conditions.
Essay # 7. Ecosystems Dynamics and Successional Process:
Ecosystem may exist in a relatively stable state or may be subject to change through natural processes or the influence of human activities. In newly created habitat, ecosystem is build up with time through successional process (primary successions). Each stage of successional process is known as sere. There are three major stages in successional process (Fig. 4.14).
Under some circumstances the primary succession may be affected by natural or man made processes, where new community was build up in place of original community. This is secondary successional process.
Within each ecosystem, there are interactions. The levels of interaction in an ecosystem depend upon the size of the various populations at each trophic level, and the links between the populations of each trophic level, and the abiotic environment.
The types of interaction include:
(a) Interactions between organisms and their abiotic environment, and
(b) Interactions between the various organisms in a community (Interspecific and intraspecific).
The major characteristics of stages of ecosystem development are given in Table 4.5.
Essay # 8. Ecosystem Disturbance:
The natural ecosystem may be disturbed in a number of ways viz., natural hazards or man-made activities. Earth quake, volcanoes, cyclone, flood, and landslides are the major natural hazards that damage the natural ecosystem.
Similarly, deforestation, mining, industrialisation, urbanisation, and pollution cause serious threat to the natural ecosystems. Each of the factors of ecosystem damage is interlinked process. Deforestation alone can make a number of ecosystem changes as stated in Table 4.6.
Among the various types of deforestation changes in the globe, the global warming is perhaps most significant change. The felling and burning of the forests is believed to be having a major impact on the climate of the World by increasing levels of CO2 in the atmosphere.
In September, 1997, the issue of tropical rainforest destruction was brought to the attention of the World’s community, when it was combined with two other environmental concerns.
A major pollution incident covering large areas of south east Asia and centred on Indonesia and Malaysia, occurred due to the burning of large areas of rainforest in Indonesia. The burning became uncontrollable, as the area was already being affected by a drought, thought to be the result of the El-Nino (effect in the Pacific Ocean).
The high smoke levels trapped gases, including carbon monoxide, nitrous oxide, sulphur dioxide and ozone, specially in urban areas such as Kuching and Kualalumpur, producing a dangerous photochemical smog.
Essay # 9. Regulation of Ecosystem:
Most organisms live in a variable environment within the environment thus leading to maintain a relatively constant internal environment within the narrow limits required by cells. That cells by some means regulate the internal environment relative to the external one. Organisms have to regulate their body temperature, pH, water, and amount of salts in fluids and tissues, to maintain a few- factors.
Because they take in substances from the environment and use them in cellular chemical reactions, they also have to discharge both excessive intake and waste products of metabolism to the environment to maintain a fairly constant internal environment. The maintenance of these conditions within the tolerance limits of die cells is called homeostasis.
Homeostasis involves the feeding of environmental information into a system, which then responds to effects of the input from or changes in external conditions. An example is temperature regulation in humans. The normal temperature for humans is 37°C (98.6°F).
When the temperature of the environment rises, sensory mechanisms in the skin detect it and send a message to the brain, which acts (involuntarily) on the information and relays the message to the effector mechanisms that increase blood flow to the skin and induce sweating. Water excreted through the skin evaporates, cooling the body.
If the environmental temperature falls below a certain point, a similar action in the system takes place, this time reducing blood flow and causing shivering, an involuntary muscular exercise producing more heat. This type of reaction, which halts or reverses a movement away from a set point, is called negative feedback.
If the environmental temperature becomes extreme, the homeostatic system breaks down. If the environmental temperature becomes too warm, the body is unable to lose heat fast enough to hold the temperature at normal. Body metabolism speeds up, further increasing body temperature, eventually ending in heatstroke or death.
If the environmental temperature drops too low, metabolic processes slow down, further decreasing body temperature, eventually resulting in death by freezing. Such situation in which feedback reinforces change, driving the system to higher and higher or lower and lower values, is called positive feedback.
The idea of homeostasis at the level of the individual can be extended to higher levels: the population, involving intrinsic regulation of size, and the ecosystem, encompassing such functions as nutrient cycling. All involve the concept of a system.
What is a system? A system is a collection of interdependent parts or events that make up a whole. For example, a radio consists of various transistors, transductions, wires, a speaker, and control knobs, among other things. Each part has a specific function, yet the expression of the role of each depends upon the proper functioning of all the other parts.
The whole system fails to function unless there is some kind of input from the outside on which the system can act to produce some kind of output. For the radio the outside input is electrical energy, on which the system acts to pick up certain radio waves, which are transmitted as an output-sound. Thus, all the parts of the radio function as a total system.
There are two basic types of systems: closed and open. A closed system is one in which energy but not matter is exchanged between the system and environment. The radio is a closed system, and so is Earth. Its only input is energy from the sun. An open system is one in which both matter and energy are exchanged between it and the environment.
Open systems can be cybernetic systems, that have a feedback system to make them self-regulating (Fig. 4.15). To function in such a manner, the cybernetic system has an ideal state, or set point, about which it operates. In a purely mechanical system, the set point can be fixed specifically. Consider a dehumidifier set for a humidity level of 50 per cent.
When the humidity of the air in a room exceeds 50 per cent, the switch on the dehumidifier turns on and a fan starts to pull air over the refrigerated coils on which the water condenses to be carried away through a hose or pipe. When sufficient water has been wrung out of the air, the dehumidifier shuts off. The feedback of information on humidity causes the dehumidifier to turn off—a negative feedback mechanism.
Living systems are cybernetic systems that can function at various levels but are always regulated by living organisms. The difference between living and mechanical systems is that in living systems the set point is not firmly fixed. Rather, organisms have a limited range of tolerances, called homeostatic plateaus, within which conditions must be maintained.
If environmental conditions exceed the operating limits of the system, it goes out of control. Instead of negative feedback governing the system, positive feedback takes over, with a movement away from the homeostatic plateau that can ultimately destroy the system.
Most of the ecosystem have an unique properties of resilience except the ecoflagile ecosystem. A overview resilience in ecosystems are given in Fig. 4.16. 
The systems approach is especially important to ecology, particularly to an understanding of the function and structure of ecosystems. This approach utilizes the construction of models that represent the real system or parts of the system for the purpose of experimentation.
Essay # 10. Material Cycle in Ecosystem:
Matter in organisms and ecosystems serve two functions:
1. First, matter can serve to store chemical energy as carbohydrate, protein and fats.
2. Second, matter can serve to make up physical structures that support the biochemical activities of life.
Life is only possible with molecules that intercept and transform energy from one form to another. Life also requires molecules that contain and provide the physical and chemical environment necessary for those energy transforming processes.
As molecules are formed and reformed by chemical and biochemical reactions within an ecosystem, the atoms that compose them are not changed or lost. Matter can thus be conserved within an ecosystem, and atoms and molecules can be used and reused or cycled within ecosystems.
Atoms and molecules move through ecosystems under the influence of both physical and biological processes. The pathways of a particular type of matter through the earth’s ecosystem comprise a material cycle (may also be referred to as biogeochemical cycle or nutrient cycle).
The living world depends on the flow of energy and the circulation of matter through ecosystems. Both influence the abundance of organisms, the rate of their metabolism, and the complexity and structure of the ecosystem. Energy and matter flow through the ecosystem together as organic matter; one cannot be separated from the other (Fig. 5.14).
The link between energy and matter begins in the process of photosynthesis. Solar energy is utilized in the fixation of CO2 into organic carbon compounds. Organic matter, the tissues of plants and animals, is composed not only of carbon, but a variety of essential nutrients.
There are two types of material Cycle—the gaseous cycle and the sedimentary cycle. In the gaseous cycle, the element or compound can be converted to a gaseous form, diffuse through the atmosphere, and they arrive over land or sea, to be reused by the biosphere, in a much shorter time.
The primary constituents of living matter—carbon, hydrogen, oxygen and nitrogen—all move through gaseous cycle. In the sedimentary cycle, the compound or element is released from rock by weathering, then follows the movement of running water either in solution or as sediment to the sea.
Eventually, by precipitation and sedimentation these materials are converted into rock. When the rock is uplifted and exposed to weathering the cycle is completed (Fig. 5.15).
Essay # 11. Productivity of Ecosystem:
The productivity of an ecosystem refers to its autotrophs or primary producer’s ability to produce organic matter, normally in the form of organic materials. As such, it depends upon the level of photosynthesis, which in turn reflects the levels of available solar energy (light), temperature, moisture, nutrients and carbon dioxide.
Productivity can be expressed as either gross or net primary productivity. Gross primary productivity (GPP) is a measure of the total amount of energy fixed by the primary producers.
Net primary productivity (NPP) is the GPP minus respiration (the amount of energy converted to heat or used in life processes by the producers):
NPP = GPP – respiration.
The NPP is the rate of accumulation of living material, in a given area, over a certain period of time and is normally expressed, in gms per square meter per year (g/sq.m/yr.) The productivity varies widely with different ecosystem conditions (Biomass). The details of productivity in major terrestrial ecosystems (biomes) are given in Table 4.3.
Essay # 12. Conservation and Management of Ecosystem:
Human activities, specially habitat destruction for agriculture, industrialisation and urbanisation, the introduction of non-endemic or alien species, and air, water and land pollution have caused a large number of plant animal extinctions. This situation compelled to make conservation and management of ecosystems.
Management of ecosystems represents people’s attempts to effect change in plant and animal systems, which may be beneficial and constructive, rather than destructive to their environment. However, for successful management, it is necessary to fully understand the workings of ecosystems, the likely causes and effects of change and the concept of sustainable yield. Several national and international actions was undertaken for protection of ecosystem vis-a-vis species and habitats protection.
These are as follows:
1. International and national conservation legislations implementation (Table 4.7).
2. The creation of protected habitats.
3. The establishment of a global monitoring system of endangered species.
In Rio Earth Summit (1992) focus was also given on conservation of biological diversity of the world. 
