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Ecosystem The term ecosystem was coined by A.G. Tansley (1953). Ecosystem is defined as a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment. An ecosystem is a self regulating group of biotic communities of species interacting with one another and with their non-living environment exchanging energy and matter. The term Ecology was coined by Earnst Haeckel (1869). The term ecology is derived from Greek words Oikos (home) and Logos( study). So it deals with the study of organism in their natural home interacting with their environment. The Ecology is also defined as study of the structure and functions of an ecosystem. The ecosystem can be Natural such asforests, grasslands, deserts, and aquatic ecosystems such as ponds, rivers, lakes, and the sea and human modified such as agricultural fields and aquarium.
Structure and function of ecosystem: • Structural features of Ecosystem: Composition and organization of biological communities and abiotic components constitute the structure of an ecosystem. • Biotic component: The plant, animal and microorganism present in an ecosystem forms the biotic component. They are divided based on the way they get their food • Producers: They generate food by their own. They can be Photo autotrophs( mainly green plants) which produces organic matter in presence of sun light through photosynthesis and chemo-autotrophs ( produce organic matter through chemical reaction) such as sulphur oxidizing or reducing bacteria, nitrifiers , methanogens. • Consumers: They get their food by feeding upon either plants or other organisms. They can by divided into a) Herbivores (plant eaters): They feed directly on producers for their food and also known as primary consumers. Ex- rabbit, insects, man.
b) Carnivores ( meat eaters) : They feed on consumers and can be called secondary consumers ( if feeds on herbivores . Example: frog) or tertiary consumers( feeds upon secondary consumers, example: snake, big fish). c) Omnivores: They feed on both plants and animals. Example: Humans, rat, many birds. 3) Decomposers or Saprotrophs: They derive their nutrition by breaking down the dead organic material to simpler organic compounds and ultimately into inorganic nutreints. Examples: Bacteria, fungi and actinomycetes are decomposer. Decomposition is a vital function in nature as without this all the nutrient would be tied up in dead matter and no new life will be produced. Most ecosystem are highly complex and consist of an extremely large number of individuals of a wide variety of species. Some species of plant and animals are extremely rare and may occur only at a few locations. These are said to be endemic to these area.
B) Abiotic component: It include air, water, soil and can be divided into: 1) Climatic component: include, sunlight and shade, average temperature, rainfall, wind pattern, humidity of a particular area. Most of the climatic parameters occurs in the lower atmosphere known as troposphere.
2) Edaphic component: Soil is the major source of mineral nutrients for plants and other organisms. Soil fertility is determined by nutrient availability, the water holding capacity and aeration of the soil. Soil profile: It is the sequence and nature of the horizons (layers) superimposed one above the other and exposed in a pit section dug through the soil mantle. In a longitudinal section of soil, three distinct layers (A, B and C horizons) can be seen. Sometime we also observe O layers which is present above the surface of mineral matrix and mainly composed of fresh or partially decomposed organic matter. The uppermost A : horizon is the most important one in which seeds are grown and from which plants derive nutrition. These are rich in organic matter and show downward loss of soluble salts, clay, iron and know as zone of eluviations. B- horizon : it contains less organic matter and is hence less fertile as compared to horizon A. The chemical leached from A horizon , collects in this zone. Also know as zone of illuviations. C – horizon : which is a mineral layer made of incompletely weathered large masses of rocks.
A horizon: Organic matter, roots, worms, insects, small rock and mineral fragments. Dark in color. B horizon: Some roots and other living organisms, materials leached by water from the A horizon, clay, rock fragments, minerals. Lighter in color than topsoil. C horizon: Weathered parent rock materials leached by water from the B horizon, partly weathered rock fragments. yellowish color.
So overall abiotic component can be divided into: • Physical factors: It include climatic, edaphic, geographical factor such as latitude and altitude, Soil type, water availability, water current etc. The variation in these physical parameter decide the type of ecosystem characteristics. The solar flux, temperature and precipitation pattern shows mark difference in a desert ecosystem, tropical or tundra ecosystem. • Chemical factors: Availability of major essential nutrient such as carbon, nitrogen, phosphorous, level of toxic substances, salts affects the functioning of an ecosystem. Function attributes of an ecosystem: The major functional attributes of an ecosystems are as follows: • Food chain, food webs and trophic structure b) Energy flow • Cycling of nutrients (Biogeochemical cycles) • Primary and secondary production • Ecosystem development and regulation
Food chains:The sequence of eating and being eaten in an ecosystem is known as food chain. All organism, living or dead are potential source of food for some other organism and thus there is essentially no waste in the functioning of a natural ecosystem. Example of food chain: Grass grasshopper Frog Snake Hawk ( Grassland ecosystem) Phytoplankton water fleas small fish Tuna ( Pond ecosystem) Lichens reindeer Man ( Arctic tundra) Each organism in the ecosystem is assigned a feeding level or trophic level depending upon its nutritional status. So in grassland ecosystem grass constitute the 1st trophic level, grasshopper 2nd, frog 3rd and snake and hawk occupy the 4rd and the 5th trophic levels, respectively. The decomposer consume the dead matter of all these trophic level.
In nature we come across two type of food chain in ecosystem: • Grazing food chain: It starts with green plants( primary producer) and culminates in carnivores. Examples: Grass Rabbit Fox Phytoplankton water fleas small fish Tuna ( Pond ecosystem) • Detritus food chain: It start with dead organic matter which the detritivores and decomposer consumes. Partially decomposed dead organic matter and even the decomposers are consumed by detritivores and their predators. Example: Leaf litter algae crabs small carnivorous fish large carnivorous fish (Mangrove ecosystem) Dead organic matter fungi Bacteria ( Forest ecosystem)
Food web: Food chain in ecosystem are rarely found to operate in isolated linear sequence. Rather they are found to be interconnected and usually form a complex network with several linkages and are known as food web. Food web is a network of food chain where different types of organisms are connected at different trophic levels, so that there are number of option of eating and being eaten at each trophic level. Food webs give greater stability to the ecosystem, as if one species become extinct or suffers then the species in the subsequent trophic level are also affected in food chain, however in case of food web effect will be reduced due to presence of other food options.
Significance of food chains and food webs: • Plays significant role in ecosystem as flow of energy and nutrient cycling take place through food chain and food webs. • Food chain and food webs also help in the maintaining and regulating the population size of different animals thus maintain the ecological balance. • Food chain shows a unique property of biological magnification of some chemicals. Pesticides for examples DDT or other chemical which are non-biodegradable in nature. Such chemicals are not decomposed or excrete out so their concentration keep on increasing at each successive trophic level. This phenomenon is know as biomagnification or biological magnification. Trophic structure: The producer and consumer are arranged in the ecosystem in a definite manner and their interaction along with population size are expressed together as trophic structure. Each food level is known as trophic level and the amount of living matter at each trophic level at a given time is known as standing crop or standing biomass.
Top carnivores Top carnivores Lion, Tigers Hawks, other birds Snakes, Foxes Carnivores Frogs, birds Carnivores Herbivores Insects, birds Herbivores Insects Producers Tree Producers Grasses Ecological Pyramids: Ecological pyramids were first devised by British ecologist Charles Elton(1927). Ecological pyramids is graphical representation of trophic structure and function of an ecosystem, starting with producers at the base and successive trophic level forming the apex is known as an ecological pyramid. It is of three types: 1) Pyramid of numbers: It represent the number of individual organisms at each trophic level. It may be upright or inverted pyramid of number depending upon the type of ecosystem and food chain. Example: Forest ecosystem ( narrow on both end and broader in the middle Grassland ecosystem ( upright)
Hyper parasite Fleas, microbes Lice, bugs Parasite Birds Herbivores Trees Producer Tertiary Carnivores Big fish Carnivores Carnivores Small fish Snake, frog, birds Herbivores insect producer Herbivores Squirrel, rabbit, insect Tree, herbs, grasses Producer Pond ecosystem Parasitic food chain( Inverted) 2) Pyramid of Biomass: It is based upon the total biomass (dry weight) at each trophic level in a food chain. It can be upright or inverted. Example: phytoplankton Forest ecosystem
3)Pyramid of energy: The amount of energy present at each trophic level is considered for this type of pyramid. It is always upright, because there is huge loss of energy (about 90%) in the form of heat and respiration at each successive trophic level. Thus at each energy level only 10% of the energy passes on. 0.1 Top carnivores Carnivores(1) Herbivores(10) Producer(100) Pyramid of energy
Flow of energy in an ecosystem: Flow of energy in an ecosystem takes place through food chain and necessary for the sustenance of an ecosystem. In an ecosystem energy flow is always unidirectional unlike nutrient which moves in a cyclic manner in an ecosystem. The energy flow in an ecosystem follows the law of thermodynamics: 1st law of thermodynamics: energy can neither be created nor be destroyed but it can be transformed from one form to another. In ecosystem green plant( producers) transform solar energy to biochemical energy which then travels to other trophic level. 2nd law of thermodynamics: energy dissipates as it is used or in other word it get converted from a more concentrated to dispersed form. In case of food chain also energy dissipate at every trophic level. The main loss of energy takes place through heat and respiration. At every level there is about 90% loss of energy and the energy transferred from one trophic level to another is only 10%.
carnivores herbivores Producer Organic matter Organic matter Organic matter Reuse decomposer Inorganic molecule Inorganic substance Nutrient Cycling: Nutrient cycling is another functional aspect of ecosystem. Nutrient like Carbon, nitrogen, sulphur, phosphate moves in a circular path through biotic and abiotic components and therefore known as biogeochemical cycle. The nutrient too move through food chain and ultimately reach the detritus compartment( containing dead organic matter) where various micro-organism carry out decomposition. In the decomposition process dead organic matter converted into inorganic substances by microbial decomposition which are again used up by plant. Simplified nutrient cycle in ecosystem
The main component of the nitrogen cycle starts with the element nitrogen in the air. • Nitrogen in the air becomes a part of biological matter mostly through the actions of bacteria and algae in a process known as nitrogen fixation. Legume plants such as clover, alfalfa, and soybeans form nodules on the roots where nitrogen fixing bacteria take nitrogen from the air and convert it into ammonium, NH4. The ammonia is further converted by other bacteria first into nitrite ions, NO2, and then into nitrate ions, NO3. Plants utilize the nitrate ions as a nutrient or fertilizer for growth. Nitrogen is incorporate in many amino acids which are further reacted to make proteins. • Ammonia is also made through a synthetic process called the Haber Process. Ammonia may be directly applied to farm fields as fertilizer. Ammonia may be further processed with oxygen to make nitric acid. The reaction of ammonia and nitric acid produces ammonium nitrate which may then be used as a fertilizer.Animal wastes when decomposed also return to the earth as nitrates. • To complete the cycle other bacteria in the soil carry out a process known as denitrification which converts nitrates back to nitrogen gas.
Oxygen Cycle: The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within and between its three main reservoirs: the atmosphere (air), the biosphere (living things), and the lithosphere (Earth's crust).
By far the largest reservoir of Earths oxygen is within the silicate and oxide minerals of the crust and mantle (99.5%). Only a small portion has been released as free oxygen to the biosphere (0.01%) and atmosphere (0.36%). The main source of atmospheric oxygen is photosynthesis, which produces sugars and oxygen from carbon dioxide and water: 6CO2 + 6H2O + energy → C6H12O6 + 6O2 An additional source of atmospheric oxygen comes from photolysis, whereby high energy ultraviolet radiation breaks down atmospheric water and nitrous oxides into component atoms. 2H2O + energy → 4H + O2 2N2O + energy → 4N + O2 The main way oxygen is lost from the atmosphere is via respiration and decay, process in which animal life and bacteria consume oxygen and release carbon dioxide. Chemical weathering of exposed rocks also consumes oxygen. 4FeO + O2 → 2Fe2O3
Primary Production: The rate at which radiant energy is converted into organic substances by photosynthesis or chemo-synthesis by the primary producer. It is also known as gross primary production (GPP). Net Primary Production( NPP) : Some part of the organic matter produce during photosynthesis get used during respiration process to produce energy for the sustenance of the primary producer, so the amount of remaining organic matter left is known as Net primary production (NPP). GPP = NPP + R Secondary Production: The plant energy is used up for producing organic matter of the herbivores which, in turn is used up by carnivores. The amount of energy stored by the herbivores or carnivores( in excess of respiratory loss) is known as secondary production. In other word we can say that energy stored at consumer level for use by the next trophic level is known as secondary production.
Wet tropical forest and Estuarine ecosystem are highly productive ecosystem and needed to conserve.
Ecological Succession: Ecosystems are dynamic in nature and often changes its structure and function due to change in the physical environment or change in the biotic composition. Some of these changes are very orderly and can be predicted. During this change process one type of a biotic community is totally replaced by another type of community over a period of time and this transition continue till a stabilized biotic community sets up. This transition process is known as Ecological Succession. Ecological succession is defined as an orderly process of changes in community structure and function with time mediated through modifications in the physical environment and ultimately culminating in a stabilized ecosystem known as climax. Type of succession: • Primary Succession: It start from the primitive substratum, where their was no living matter present before. It is a slow process due to lack of any build up substratum.
Secondary succession: It starts from previously built up substrata where their was presence of living matter before. Due to external factor existing community disappear . These processes are fast. Succession can be autogenic (induced by community itself) or allogenic( due to external factors). Some Definitions: • Pioneer community: The first group of organism established in a particular area is known as pioneer community. • Seral stages or sere: The whole sequence of communities which are transitory between from Pioneer to climax community are known as Seral stages. • Climax community: It is the stabilized community formed in the end of succession process which is in equilibrium with the environment.
Ecological Succession type: Based on the substrata type : • Hydrarch or Hydrosere: It start in watery area like, pond, swamp,bog. 2) Mesarch: starting in the area of adequate moisture. 3) Xerarch or Xerosere: Starting in dry area with little moisture. It can be of following type: • Lithosere: starting on a bare rock • Psammosere: starting on sand • Halosere: starting on saline soil.
Process of succession: Succession take place in a systematic order of sequential steps: • Nudation: It is development of bare area without any life form. This formation can be due to landslide, volcanic eruption (topographic factor), or due to drought, glaciers ( climatic factor) or due to overgrazing, disease outbreak ( biological factor). • Invasion: This is successful establishment of a species in a bare area. It start with migration or dispersal process where seeds, spores reach the bare area through air, water etc. After migration successful establishment of the species( adjustment with the prevailing condition) is know as ecesis. After ecesis , number of species increase in number due to reproduction and come closer to each other a process know as aggregation. 3) Competition and Coaction: As the number of individuals grows there is competition, both inter-specific( between different species) and intra-specific ( within the same species) for space, food and water. Individuals of species affects each other life in various ways and this is known as coaction.
4) Reaction: once the number of species increases, they have a strong influence on the physical environment. The mechanism of the modification of the environment through the influence of living organism in it, is known as reaction. Most of the changes occurs in soil, water, light condition etc. 5) Stabilization: It is the final stage of succession process, where more or less stable community called climax formed which is in equilibrium with the environment. Example of Ecological Succession: 1) Hydrosere (Hydrarch): This type of succession start in a water bodies like pond and culminates in a climax community which is forest. It has following stages: • Phytoplankton stage: These are the pioneer community. Mainly blue green algae, green algae, diatoms and bacteria etc. • Rooted submerged stage: Due to death and decomposition of phytoplankton organic matter start accumulating on the pond subsurface. This new environment is favorable for the growth of rooted submerged hydrophytes like Hydrilla, Elodea etc.
3) Rooted submerged stage: Now the depth of lake reduces to 2-5 feet, favoring the growth of rooted hydrophytes with their large leaves floating on the water surface. Example: Nelumbo, Trapa, Azolla etc. 4) Reed-swamp stage: also known as amphibious stage as the plants of community are rooted but most of it part is in air. Example: Scirpus, Sagittaria etc. 5) Sedge-meadow stage: They form mat like vegetation, results into higher loss of water through evapotranspiration process. The marsh like condition in the previous stage is removed and area with soil moisture left. Example: carex,cyperus etc. 6) Woodland stage: As the marsh land disappear soil become more dry and give rise to vegetation like shrubs( Salix, cornus) and trees ( populus, Alnus). 7) Forest stage: This is climax community. It can developed as tropical rain forest or mixed forest depending upon the climate of the region. Example: Ulmus, Acer and Quercus.
2) Lithosere: A Xerosere on Rock: It start with bare rock and culminate into a forest stage. Different stages of Lithosere are as follows: • Crustose lichen stage: The lichen are the pioneer community. The substratum is very poor in moisture and organic matter, subjected with extreme of temperature. Examples: Rhizocarpon, Rinodina etc. • Foliose lichens stage: They can absorb more water and retain more water and are able to accumulate dust particle which further help in build up of substratum. Examples: Parmelia, Dermatocapron. • Moss stage : Xerophytic mosses such as Tortula, Grimmia appears after lichens stage. • Herbs stage: due to growth of mosses there is more accumulation of soil.This stage is constituted by shallow rooted grasses such as Aristida,Festuca etc which further replaced by shrubs. • Shrub stage: Species like Rhus, Phytocarpus start growing in the area, which over compete the herbaceous species.
Crustose lichen Foliose lichens Moss
f)Forest stage: This is the climax community for this type of ecological succession. Starting with Xerophytic tree species it changes into mesophytic type and finally into forest type.
ForestEcosystem • Forests are formed by a community of plants which is predominantly structurally defined by its trees, shrubs, climbers and ground cover. • Natural vegetation looks vastly different from a group of planted trees, which are in orderly rows. The most ‘natural’ undisturbed forests are located mainly in our National Parks and Wildlife Sanctuaries. • Each forest type forms a habitat for a specific community of animals that are adapted to live in it. Forest ecosystem has two component: a) abiotic aspects: Include soil type, rainfall pattern in the forest are, light pattern, water amount, temperature condition.
b) biotic aspects: The plants and animals form communities that are specific to each forest type. Plants include the trees, shrubs, climbers, grasses, and herbs in the forest. Animal include the species of mammals, birds, reptiles, amphibians, fish, insects and other invertebrates and a variety of microscopic animals. Forest types in India They can also be classified according to the nature of their tree species – evergreen, deciduous, xerophytic or thorn trees, mangroves, etc. They can also be classified according to the most abundant species of trees such as Sal or Teak forests. In many cases a forest is named after the first three or four most abundant tree species.
Coniferous forest: • grow in the Himalayan mountain region, where the temperatures are low. These forests have tall trees with needlelike leaves and downward sloping branches so that the snow can slip off the branches. • have cones instead of seeds • Trees- Pine, deodar • Animals- Wild goats and sheep, Snow leopard, Himalayan black bear, Evergreen forests: High rainfall areas of the Western Ghats, North Eastern India and the Andaman and Nicobar Islands. There is no dry leafless phase as in a deciduous forest. An evergreen forest looks green throughout the year. Thus very little light penetrates down to forest floor. The forest abounds in animal life and is most rich in insect life. Trees- Jamun, Ficus, Dipterocarpus Animals- Tiger, Leopard, Sambar
Deciduous forests: • are found in regions with a moderate amount of seasonal • Rainfall. Teak tree is one of the dominant tree species in these type of forest • The deciduous trees shed their leaves during the winter and hot summer months. In March or April they regain their fresh leaves just before the monsoon, when they grow vigorously in response to the rains. • Thus there are periods of leaf fall and canopy regrowth. The forest frequently has a thick undergrowth as light can penetrate easily onto the forest floor. Animals- Tiger, Chital, Deer, Trees- Teak, Sal Thorn forests: • Thorn forests are found in the semi- arid regions of India. • The trees, which are sparsely distributed, are surrounded by open grassy areas. • Thorn forest trees have long or fibrous roots to reach water at great depths. These have thorns to reduce water loss through evapotranspiration. • Trees- Babul, Ber, Neem Animals - Blackbuck, Chinkara, Wolf,
Mangrove forests • grow along the coast especially in the river deltas. • These plants are able to grow in a mix of saline and fresh water. • The mangrove trees have breathing roots that emerge from the mudbanks. Trees- Avicenia, Rhizophora Animals- Crocodile, fish, shorebirds – sandpipers Importance of Forests resource: • Consumptive value • Environmental services • Aesthetic and cultural values. Problem associated with the forest resource and its conservation.
Grassland Ecosystems • rainfall is usually low and/or the soil depth and quality is poor. • The low rainfall prevents the growth of a large number of trees and shrubs, but is sufficient to support the growth of grass cover during the monsoon. • Grassland shows seasonal variation with low productivity during summer and high productivity during rainy • A variety of grasses, herbs, and several species of insects, birds and mammals have evolved so that they are adapted to these wide-open grass covered areas. These animals are able to live in conditions where food is plentiful after the rains, so that they can store this as fat that they use during the dry period when there is very little to eat. • Man began to use these grasslands aspastures to feed his livestock Grassland Types in India: The Himalayan pasture belt extends up to the snowline. The grasslands at a lower level form patches along with coniferous or broadleaved forests
The animals migrate up into the high altitude grasslands in summer and move down into the forest in winter when the snow covers the grassland. • These Himalayan pastures have a large variety of grasses and herbs. Himalayan hill slopes are covered with thousands of colorful flowering plants. There are also a large number of medicinal plants. Terai: • Extends as a belt south of the Himalayan foothills • Terai consists of patches of tall grasslands interspersed with a Sal forest ecosystem. • The patches of tall elephant grass, which grows to a height of about 5m, are located in low-lying waterlogged areas. Scrublands of the Deccan Plateau: • Semi-arid plains of Western India, Central India and the Deccan - covered by grassland tracts with patches of thorn forest. • Several mammals such as the wolf, the blackbuck, the chinkara, and birds such as floricans are adapted to these arid conditions. • The Scrublands of the Deccan Plateau are covered with seasonal grasses and herbs on which its fauna is dependent.
Shola grasslands: • The Shola grasslands consist of patches on hillslopes along with the Shola forests on the Western Ghats, Nilgiri and Annamalai ranges. • This forms a patchwork of grassland on the slopes and forest habitats along the streams and low-lying areas. Grasslands are not restricted only to low rainfall areas. Certain grassland types form when clearings are made in different forest types. • The grasslands are related to repeated fires that do not permit the forest to grow. • Some grass and herb species are more sensitive to excessive grazing and are suppressed if the area is over grazed. • Others are destroyed by repeated fires and cannot regenerate. Thus overused or frequently burnt grasslands are degraded and are poor in plant species diversity. Important of Grassland: • Pasture land 4) habitat for diverse species of insects. • Fodder source • Grass is also used to thatch houses and farm sheds.
Threats to grassland ecosystem: • Over utilization and changes in land use of the ‘common grazing lands’ of rural communities has lead to their degradation. Extinction of their species- Cheetah, Wolf • A major threat to natural grasslands is the conversion of grasslands into irrigated farmlands. In the Deccan, grasslands have been altered to irrigated farms and are now mainly used to grow sugarcane. How can grassland ecosystems be conserved? • Grasslands should not be overgrazed and areas of the grasslands should be either closed for grazing or rotational grazing pattern is established. • Fires must be prevented and rapidly controlled. In hilly areas soil and water management in each micro-catchments helps grasslands to return to a natural highly productive ecosystem. • To protect the most natural undisturbed grassland ecosystems, Sanctuaries and National Parks must be created. Their management should focus on preserving all their unique species of plants and animals.
Desert ecosystem • Desert and semi arid lands are highly specialised and sensitive ecosystems that are easily destroyed by human activities. • The species of these dry areas can live only in this specialised habitat. Desert ecosystem in India: • Deserts and semi arid areas are located in Western India and the Deccan Plateau. The climate in these vast tracts is extremely dry. There are also cold deserts such as in Ladakh, which are located in the high plateaus of the Himalayas. • The most typical desert landscape that is seen in Rajasthan is in the Thar Desert. This has sand dunes. There are also areas covered with sparse grasses and a few shrubs, which grow if it rains. In most areas of the Thar, the rainfall is scanty and sporadic. In an area it may rain only once every few years. In the adjoining semi arid tract the vegetation consists of a few shrubs and thorny trees such as kher and babul
The Great and Little Rann of Kutch are highly specialized arid ecosystems. In the summers they are similar to a desert landscape. • However as these are low-lying areas near the sea, they get converted to salt marshes during the monsoons. • During this period they attract an high number of aquatic birds such as ducks, geese, cranes, storks, etc. • Desert and semi arid regions have a number of highly specialized insects and reptiles. The rare animals include the Indian wolf, desert cat, desert fox and birds such as The Great Indian Bustard and the Florican. • Some of the commoner birds include partridges, quails and sandgrouse. How are desert and semi-arid ecosystems used? • Areas of scanty vegetation with semi-arid scrubland have been used for camel, cattle and goat grazing in Rajasthan and Gujarat. • Areas that have a little moisture, have been used for growing crops such as jowar, and bajra. • The natural grasses and local varieties of crops have adapted to growing at very low moisture levels. These can be used for genetic engineering and developing arid land crops for the future.
What are the threats to desert ecosystems? • Conversion of these lands through extensive irrigation systems has changed several of the natural characteristics of this region. The canal water evaporates rapidly bringing the salts to the surface. The region becomes highly unproductive as it becomes saline. Example: The Indira Gandhi Canal • Pulling excessive groundwater from tube wells lowers the water table creating an even drier environment. How can desert ecosystems be conserved? • Desert ecosystems are extremely sensitive. Their ecological balance that forms a habitat for their plants and animals is easily disturbed. • Desert people have traditionally protected their little water resources. The Bishnois in Rajasthan are known to have protected their Khejdi trees and the blackbuck antelope for several generations. • There is an urgent need to protect residual patches of this ecosystem within National Parks and Wildlife Sanctuaries in desert and semi arid areas.
The Pond ecosystem • The pond is the simplest aquatic ecosystem to observe. • There are differences in a pond that is temporary and has water only in the monsoon, and a lake that is an aquatic ecosystem throughout the year. • Most ponds become dry after the rains are over and are covered by terrestrial plants for the rest of the year. • When a pond begins to fill during the rains, its life forms such as the algae and microscopic animals, aquatic insects, snails, and worms come out of the floor of the pond where they have remained dormant in the dry phase. • Gradually more complex animals such as crabs frogs and fish return to the pond. The vegetation in the water consists of floating weeds and rooted vegetation on the periphery which grow on the muddy floor under water and emerge out of the surface of the water.
As the pond fills in the monsoon a large number of food chains are formed. • Algae is eaten by microscopic animals, which are in turn eaten by small fish on which larger carnivorous fish depend. These are in turn eaten by birds such as kingfishers, herons and birds of prey. • Aquatic insects, worms and snails feed on the waste material excreted by animals and the dead or decaying plant and animal matter. • The temporary ponds begin to dry after the rains and the surrounding grasses and terrestrial plants spread into the moist mud that is exposed. Animals such as frogs, snails and worms remain dormant in the mud, awaiting the next monsoon.
Lake Ecosystem: Euphotic zone ( High productivity) Aphotic zone (little productivity) Lakes are big fresh water bodies with standing water. They are divided into shallow water zone called Littoral zone, an open water zone where effective penetration of solar light takes place called Limnetic zone and deep profundal zone with no penetration of light. Lakes shows thermal stratification during the summer period: Epilimnion( warm surface layer) and Hypolimnion ( Cold, bottom layer). In between there is thermocline( region of sharp drop in temperature).
Lakes can be Oligotrophic (low nutrient concentration), mesotrophic and eutrophic( high nutrient concentration especially nitrogen and phosphate) River ecosystem: It’s a lotic ecosystem, where water flow downward from mountain highland and flowing through the plain fall in the sea. River ecosystem have two type of production: autochthonous( production within the stream) and allochthonous( supplied from terrestrial sources).
