BBA Environmental Studies Ecosystems Notes in PDF
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UNIT-III
Q. 1 Describe structure and functions of ecosystem.
Ans. ECOSYSTEMS
The term ecosystem was coined by Tansley (1935). Ecosystem is the structural and functional unit of biosphere, comprising living beings and their non-living environment. The ecosystem may be temporary (rainfed pond) or permanent (forest), The size is also variable. It may be like a flowerpot (micro-ecosystem) or ocean (macro-ecosystem).
Structure; The components are of two types:
1. Biotic.
2. Abiotic.
1. Biotic components: These may by plants, animals and microbes ,are known as producers consumers and decomposers, respectively
(a) Producers : These are photo-autotrophs and Chemoautotrophs.
(i) Photoautotrops : These are green plants, Euglena, green sulphur bacteria etc, They can perform phosynthesis and prepare food. They dominate terrestrial ecosystem. All animals and human beings are dependent on them for food.
( ii) Chemoautotrophs :They are iron, sulphur bacteria which release energy during chemicalreaction and prepare organic food. This process is called as chemosynthesis. Producers use CO and release 02. Hence, maintain CO —O balance in nature: They also convert radiant energy of sun into chemical energy and are called as transducers.
(b) Consumers : They are heterotrophs and can not produce food. These are of three types .
(i) Primary Consumers : These are called herbivores and eat plants and their products e.g., cattle, goat, rabbit, rat, grasshopper (terrestrial ecosystem) and snails, tadpols, tortoise, (aquatic ecosystelll) etc.
Elton used the term key industry animals for primary consumers as they convert plant material into animal material.
(ii) Secondary Consumers : These are carnivores which eat herbivores. Cats, d0gs, foxes .called as transduction, are examples of terrestrial ecosystem. Hydra, water bug, frogs, small fish are examples of aquatic ecosystem.
(iii) Quaternary : Largest carnivores are, e.g., lions/tigers on land and whales in aquatic ecosystem, these are also called as top carnivores.
(c) Decomposers (Saprotrophs) : These are bacteria/fungi which derive their food from dead plants and animals and their waste products. These are also called micro consumers(reducers) due to their small size. They add inorganic materials to the environment and help in mineralization.
E.coli, Tapeworm, etc are parasites or consumers and derive their food from them. animals like frog is herbivore at tadpole stage and secondary cousumer at adult stage. Man, ants, etc, are omnivores.
Insectivorous plants (Drosera) act as producer and Some, annuals like trermites, Vultures feed on dead organisms and are called as scavangers (detrivores).
2. Abiotic Components : These include non-living factors the which affect distribution,/structure of organisms, these are as follows
(i) Inorganic substances like carbon, oxygen, nitrogen, CO D, calcium, phosphorus, sulphur and micro-nutrients, etc., occur in form Of’ compounds dissolved in in soil or in free state’
(ii) Organic compounds like lipid, proteins, carbohydrate, nucleic acids, vitamins, humid substances on which all living beings are dependent for their sustenance
(iii) Temperature, light, water, gases, wind, humidity, soil, annuals, etc. are also the part of abiotic component.
Producers : Green plants (herbs, shrubs, trees) photosynthetic, bacteria, cyanobacterias, phytoplankton.
Macro-consumers : They are of four types. They eat or Inject producers directly or indirectly.
(a) Primary consumers (herbivores).
(b) Rabbit, rat, deer, goat, grasshopper, cattle, etc. (terrestrial ecosystem).
(c) Molluscs, Crustacean. (Aquatic ecosystem).
(d) Secondary consumer : primary carnivores feed upon herbivores, snake, wild cat, foxes frogs, centipedes, etc.
(e) Tertiary consumers (secondary carnivores)-wolves.
(f) Quaternary consumers (tertiary carnivores)-tiger, lion, etc.
The decomposers, are essential as they secrete enzymes to digest organic compounds externally, help in mineral recycling and cleaning of environment, e.g., bacteria, fungi.
Functions of ecosystem
(i) Production of food by autotrophs, chemo autotrophs.
(ii) Use of solar energy by green plants.
(iii) Recycling of minerals.
(iv) Help in maintaining CO 2/O2 ratio in atmosphere.
(v) To maintain flow of energy.
(vi) Ecosystem is a discrete structural, functional and life sustaining environmental system.
Q. 2. Describle ecological pyramids.
Ans. Ecological Pyramids : The relationship between the various trophic levels of a food chain can be expressed in terms of number/biomass and energy by graphic diagrams, called ecological pyramids.
These are first divided by C.Elton (1927) and are called as eltonian pyramids.
Pyramid of Numbers
It is the graphic representation of the number of individuals of various trophic levels of food chain/ unit area at any time. The base is represented by number of producers and apex is represented by the number of top carnivores. The intermediate consumers are placed in between the two depending upon their relationship in food chain. The number of individuals goes on decreasing from base to top.
Pyramid Of Biomass : The amount of living material present in an organism is called biomass. In terrestrial ecosystem biomass of producers is maximum. The biomass of herbivores is less but their number may be more. The biomass of carnivores show further decrease toward top. So, the pyramid is always upright.
Pyramid of Energy : It is always upright, producers represent maximum energy content. They obtain energy from sun and manufacture food. Herbivores contain less energy as compared to producers, secondary consumers contain still smaller amount of energy and so on.
There is gradual decrease in energy at successive trophic levels.
Energy is maximum at producer level and decreases as one moves to subsequent trophic levels.
Q. 3. Write an essay on functional aspects of ecosystems.
Anse Periodism : In order to discuss vegetational structures, essential and characteristic features were abstracted to a kind of static model. But in this the dynamic, ever changing aspect of physigno my and composition is missing. There is a sharp difference in vegetation on the North and South slopes of Mountain. The North slope .is rather cooler and moisture, many herbs are about to bloom or one in bloom or fruit by late spring. The maximum period of herbaceous activity dries and warms south slope is found during early summer. Because of the vegetational differences between the slopes are largely due to relative density, frequency and cover and not to exclusive presence and one slope and absence on the other. The difference in flowering activity is because of both subtle physiological variations within each species and by subtle but real microclimatological differences between the slopes. Each species has its own characteristic pattern of sequential development and flowering which is attributed to and regulated by the major environmental climatic gradients.
In a deciduous forest biome spring brings release from dormancy and a resurgence of vegetative activity culminating in leafing out in decidous trees. Leaf fall bring the onset Of dormancy and curtailment of activity manifested in leaf colour change and fall. The natural Get Physical phenomenon reach at different intervals and as different species respond differentially to such stimuli, different rhythms would be expected, a prior, among’ different Communities. Photoperiods have major effect on plant behaviour. We may see
(a) The regulatory effect of photoperiod on growth, development and flowering of a single
species and thereby of the community of which it is a part.
(b) The variation existing within widely distributed species regarding the response to
photoperiod and the concomitant effect on the ecosystem of which they are a part.
(c) The diurnal metabolic pattern of an ecosystem
Photoperiodism and Ecotypes
The species has as specific a physiological response to photoperiod as it has a specific morphological adaptation to another environmental parameter. Charles olmsted demonstrated that different population of a common prairie grass known as side-oats grama (Bouteloua curtipendula) did not have identical response to given photoperiods. Long day plants
demonstrate normal vegetative and flowering behaviour only with photoperiods of 14 hours or
onger. Short day plants, functioning normally under 13 hours of light but failing to flower on photoperiods longer than 14 hours. Alpine sorrel (Oxyria digyna) requires 15 hours of light for flowering. There is physiological difference in population at different latitudes. Northern populations have more chlorophyll higher respiratory rates at the same temperature and an attainment of peak photosynthesis at lower temperature.
The ecological races or ecotypes may show little or no morphological difference.
Photoperiodism and Temperature Effects
On a divernal basis, a number of significant periodic phenomenon affect the function of a community. The desert shrubs are differentially adapted to withstand daily changes changes of
550C at the ground surface while simultaneously experiencing little or no change in their deeper
roots and a quite considerable change of about 220C a meter above the ground over to the high
specific heat of water, diurnal temperature changes of such magnitude do not occur in the surface of waters of aquatic ecosystems. Over the period of a year, however, considerable changes in temperature do take place, particularly in the upper waters of temperate ecosystem.
The forces in this series of changes involve the changes in density of water with temperature and the action of wind. Because water is most dense at 40C, warmer and colder water will float on top of a layer of this temperature. After the ice melts the surface water warms to less dense layer immediately beneath it. This overtiming of water, which in the absence of wind, will occur at 40C ultimately results in a temperature that is uniform from top to bottom. Subsequent heating of surface water. Which is accompained by a corresponding decrease in density, results In warmer water at the surface. Wind action results in stirring of the surface water, mixing them to depths according to the strength and direction of wind and relative to exposure or orientation of the system.
Periodism and Metabolism
There are two similar but opposite processes of considerable importance respiration and photosynthesis. All the producers in the system contribute to the total or gross photosynthesis and the consequent output of both stored chemical energy in the form of biomass and the significant byproduct, oxygen. All organism in the system, produces included, utilize this stored
energy and oxygen in metabolic activities associated with growth and reproduction, a complex of events measured as respiration. Photosynthesis is light dependent process. Respiration is not light dependent process. In some plants increasing light intensity increases respiration, a phenomenon called Photorespiration. Where glycolic acid an intermediate product of photosynthesis is oxidized more rapidly by reducing the overall efficiency of photosynthesis. It is important to consider the periodic characteristics of these two opposing metabolic processes, e.g., the studies show that 12 hour photoperiod plants the might time respiration is at a maximum within a few hours of darkness and drops progressively thereafter. Photosynthesis shows a similar pattern during the period of light, reaching its maximum within the first few hours and decreasing thereafter through the remainder of the day.
Q. 4. Define succession. Give an account of hydrosere and xerosere.
Ans. Succession: The replacement of existing plant and animal communities with new ones in an orderly sequence in an area with them due to change in physical conditions is called ecological or biotic succession. The entire series of communities is called as sere. The individual transitional communities as seral communities or seral stage. The first community to inhabit an area is called pioneer community. The succeeding one are called transitional communities and stable community which persists as long as -no disturbance occurs is called
climax community.
Hydrosere: Hydrosere or hydrarch is a succession begins in water. Generally phytoplankton are pioneer colonizers. After their death, population of decomposing organisms like-bacteria and fungi increases in pond mud. This rich mud now supports the growth of rooted hydrophytes like- Vallisneria, Ceratophyllum, Potamogeton on shallow regions where light reaches the bottom in sufficient quantity.
The death of these plants contribute to the enrichment of medium. Now deeper zones are occupied by such plants which are rooted in mud but their leaves reach the water surface and float, e.g., Trapa, Nelumbium, Nymphaea, Aponogeton.
Soon due to evaporation of water and concentration of nutrients mud increases and becomes sufficient to support the growth of free floating plants which are not rooted in mud like- Lemna, Wolffia, Azolla, Pistia, Salvinia. These plants cover the surface of water.
The pond margins are now covered by emergent hydrophytes like Eleocharis, Isoetes, Typha, Cyperus, Polygonum, etc.
Gradually with passage Of time, the slit along with dead organic matter deposits on bottom and helps to raise its level. The raised pond bed or shallow water may cause invasion by reed-s-wamp species in the area. This is replaced by terrestrial and mesic communities as the water evaporates. Climax formation of trees like-salix is found in low lying lands.
Xerosere: Xerosere or xerarch is a succession begins on any kind of dry situation like-sand (psammosere) rock (lithosere) on saline areas (halosere). on rocks successional trends are controlled bv soil formation and its accumulation. On pioneer, colonizers develop in form of lichens and blue-green algae. They grow and multiply in rainy season. Lichens grow on the rock surface. Due to corrosion in the space, thus created, dust and dead organic matter accumulate and provide growth conditions for foliose lichen or mosses.The pioneers are replaced by new arrivals.
The cushion of mosses catches dust and bigger mosses or some pteridophytes like-Selaginella start appearing. Biological activities and due to action of carbonic acid on rock more soil accumulation takes place. Due to decomposition of dead organic matter by microbes, conditions for growth of plants improve.
Many aggressive and hardy grasses weeds and tree seeding grow and form their communities. Finally, trees develop and characteristic forest.
Q. 5. Describe flow of energy in the living world.
Ans : Flow of Energy in the Living World
The radiant energy that originates in thermonuclear reactions in the sun streams reaches to earth in the form of light (and other forms of radiation) and sustains all living organisms. Over the entire globe about 25% of the incoming solar radiation is scattered or reflected by the atmosphere back into space. This fraction of arriving solar energy is lost to the earth. Another 25% is absorbed by the atmosphere. The remaining 50% that manages to reach the earth’s
surface, some 45% of the total is absorbed as heat by lands or oceans; 5% (of the total) is reflected back into space; 24% is consumed in promoting water evaporation and related meteorological (weather) phenomena. A very small fraction drives the wind and waves. An even smaller fraction is captured by the leaves of green plants. Indeed, the total solar energy reaching on earth per year is said to equal 1,73,000x 1012 watts. Of this, only 40 x 101 watts is used in photosynthesis. It is noteworthy that both the atmosphere and earth’s surface reflect a significant fraction Of the incoming solar radiation. Bare ground and rocks reflect a much larger portion of the incident radiation than green fields and forests, which are more absorbent. Recently satellite engineers have acquired the capacity to estimate on a global scale the total mass of green plants and by inference terrestrial photosynthesis with a high level of resolution.
Flow of energy through different trophic levels
1. Sunlight is trapped by autotrophs which prepare food through photosynthesis. 2. This energy is taken by herbivores, then carnivores and top carnivores. 3. Large amount of energy is lost at each tropic level. Only 10% of energy is passed fromone trophic level to other, i.e., (Lindmann)
Autotrophs— Herbivores—Carnivores-» Top Carnivores
100% 10% 1% 0.1%
4. Energy lost due to heat Or respiration can not be transferred to any organism.
5. Decomposition of dead plants and animals releases chemical energy.
6. In shorter food chain, more energy is available in comparison to longer food chain.
7. The energy always flows undirectionally i.e., from autotrophs to herbivores to berbivores to carnivores.
Q. 6. Describe the sulphur cycle.
Ans. Sulphur Cycle: Sulphur is an important part of some amino acids, It is absorbed by plants as sulphates. Its main source is earth’s crust.
The sulphur is released back to soil by decomposition. Microbes convert sulphur to sulphates. In Marshes under anaerobic conditions, sulphur may be converted to sulphides by bacteria. Sulphides may be oxidized to sulphates. Sulphur may be added to atmosphere as oxides (SOO) due to burning of fossil fuels or by volcanic activities or smelting of sulphur ores and factories.
Q. 7. Describe oxygen cycle.
Ans. Oxygen Cycle
Oxygen is an important essential element. It is found as O2 in atmosphere and as compounds like H2O and CO2.
Utilization : O2 is used by animals for respiration. Oxygen is utilized during combustion and oxidative weathering of rocks.
Release of Oxygen
(i) Oxygen is released during photosynthesis.
(ii) Oxygen is released as C02 during decay of dead organic matter by microbes.
(iii) Oxygen and carbon cycles are completely dependent on one another.
(iv) Oxygen is converted to 03 (ozone) and protects earth from ultraviolet rays.
Q. 10. Describe Nitrogen cycle.
Ans. Nitrogen Cycle
Nitrogen is an important constituent of proteins, nucleic acids, etc.
Nitrogen Fixation : Largest reservoir of nitrogen (79%) is atmosphere but it can not be utilized by plants directly unless it is fixed. 150-750 mg/m2/yr. nitrogen is usually fixed by Rhizobium, Azotobacter, Clostridiurn, Anabaena, Tolypothrix. Some amount of nitrogen is fixed by electro-chemical and photochemical methods (35 mg/m2/yr.). Some nitrogen is fixed by chemical fertilizer factors (Haber’s process).
Uses of Nitrogen : Plants take nitrates from soil. Animals eat plants and proteins are converted into animal proteins are converted into animal proteins. The break down of proteins into urea, uric acid or ammonium compounds. In soil or water, decomposition of wastes takes place and nitrogen is changed to free nitrogen.
Decomposition : It takes place by actinoinyceces, ammonifying bacteria, nitrifying bacteria (Nitrosomonas, Nitrobacter) and denitrifying bacteria (Pseudomonas).
Q. 11. Describe Water Cycle.
Ans. Water Cycle : Water is an important constituent of living cells. Water may exist in gaseous, liquid or solid state.
In global water cycle, water evaporates from water bodies (oceans, rivers, lakes) and forms
clouds. The water vapour in clouds cools and condenses to form ram or snow. The water may fall directly to oceans or may flow to oceans through rivers or underground water. Some water of landmass may seep in as ground water. Some water may remain as perenial snow on mountain peaks or m polar regions.
In smaller cycle, the environmental water moves in living organisms and back to environment. Aquatic animals take water directly and give it back through excretion, etc. Land ammals take water directay or as food from plants or other animals. In case of plants, water is absorbed by roots and returned to atmosphere through transpiration.
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