Ecosystems PDF

MODULE 3  Let us a little permit Nature to take her own way; she better understands her own affairs than we. ~Michel de Montaigne CONCEPT OF ECOSYSTEM An ecosystem can be defined as a biological environment consisting o...

MODULE 3  Let us a little permit Nature to take her own way; she better understands her own affairs than we. ~Michel de Montaigne CONCEPT OF ECOSYSTEM An ecosystem can be defined as a biological environment consisting of all the organisms living in a particular area interacting with each other, as well as with all the nonliving, physical components of the environment, such as air, soil, water, and sunlight, exchanging energy and matter. The study of ecosystems is called ecology. The term ecology was coined in 1869 (by Earnst Haekal) much before the term ecosystem. It is derived from the Greek word Oikos (Home) and Logos (study) and so ecology meant the study of organisms in their natural environment or home interacting with their surroundings. The unit of study of ecology was later described by Tansley (1935) as ecosystem. STRUCTURE AND FUNCTION OF ECOSYSTEM Structure of ecosystems – This can be summarized in three ways I. Biotic Components and Abiotic Components II. Trophic relationships I11. Ecological pyramids BIOTIC COMPONENTS Biotic components, or biotic factors, can be described as any living component that affects another organism or shapes the ecosystem. Standing crop is the total above-ground plant biomass on the site at a particular point in time. This includes both animals that consume other organisms within their ecosystem, and the organism that is being consumed. Biotic factors also include human influence, pathogens, and disease outbreaks. Each biotic factor needs the proper amount of energy and nutrition to function day to day. Producers, otherwise known as autotrophs, convert energy (through the process of photosynthesis) into food. Consumers, otherwise known as heterotrophs, depend upon producers (and occasionally other consumers) for food. Decomposers, otherwise known as detritivores, break down chemicals from producers and consumers (usually antibiotic) into simpler form which can be reused.  Abiotic Components – The abiotic components are air, water, salts, light, temperature, nutrients etc. Nutrients such as N, P and Ca, necessary for the growth of living organisms are accumulated in the biomass and the abiotic components like the soil. The amount of these nutrients present in the soil at any given time is known as standing state. Different ecosystems have different standing state of nutrients. The standing state of nutrients may vary at different time even in the same ecosystem.  Trophic relationships - Ecosystems also have a basic structure according to trophic relationships. A Food chain can be defined as a linear series of organisms dependent on each other for food, resulting in the function of transfer of energy in an ecosystem.  Types of food chain: Grazing food chain Detritus food chain Parasitic food chain  A food web can be defined as an interconnected set of food chains in the ecosystem.  As the diversity (e.g. number of species) in the ecosystem increases, the complexity of these food webs also increases and as complexity increases so does stability. E.g. disturbance or extinction of one or two species can be compensated for. In simple food webs or chains, extinction of one species may lead to the collapse of the entire system. Human agricultural ecosystems are good examples of simple, unstable ecosystems. Monocultures of single crop plants consumed by livestock and/or humans are the single food source of insects in the ecosystem making the system unstable and because they are unstable, they require additional energy inputs to prevent them from collapsing e.g. insecticides, herbicides, fertilizers, irrigation water, etc TROPHIC LEVELS Ecosystems have a basic structure according to how different populations acquire energy flow, where energy flow is a function of ecosystems. Trophic levels refer to the respective position of the organisms within ecological food chains or webs.  Composition of Species: For each ecosystem, the species composition in these three basic structural levels of producers, consumers and decomposers will be different.  Ecological Pyramids- Ecological pyramids are graphic representation of the structure of trophic and function of an ecosystem, starting with producers at the base and successive trophic levels leading to the apex. These are mostly upright but can be inverted. Ecological pyramids can be based on three different kinds of information related to the trophic relationships.  Pyramid of numbers – It is based on numbers of individuals in each trophic level. Forest ecosystem MARINE ECOSYSTEM  ANTS TERMITES TREE PARASITIC FOOD CHAIN  Pyramid of biomass – It is based on weight of living material in each trophic level.  Pyramid of energy – It is based on energy content of each trophic level. As energy is always lost at each step of a food chain, the pyramid of energy is always upright. The energy loss in the form of heat, respiration etc at each trophic level is as high as 90%, that is only about 10% of the energy is passed on to the next trophic level.  Functions of Ecosystem- Interactions between ecosystem components involve two general processes or functions: 1. Energy flow. 2. Nutrient cycling.  Energy Flow – The fixation of energy and its flow thus obeys the two laws of thermodynamics where the first law states that energy can neither be created nor destroyed. It can only be transformed from one form to another. And the second law states that every transformation of energy is accompanied by a simultaneous degradation of energy from concentrated form to dispersed form. Energy flow is thus a very inefficient process and very little energy is left when decomposers get to it.  There are two important energy flow models. a. Single channel energy flow model- It depicts the energy flow in a grazing food chain which starts from green plants and ends to carnivores passing herbivores.  Y-shaped energy flow model- It was E.P. Odum who noted that food chain may begin with live parts of plants or dead parts of plants parts which led to his conclusion that in nature two basic food chains the grazing food chain and detritus food chain operate, in the same ecosystem. It can be concluded from the energy flow, that shorter the food chain, greater would be the available food energy as with the increase in length of the food chain, there is a correspondingly greater loss of energy.  Nutrient Cycling – Unlike energy, there is no major input of nutrients from outside the ecosystem. Thus, nutrients are used over and over again which would mean that the carbon, nitrogen, etc. atoms in our body have been used over and over again in ecosystems. Major cycles are Nitrogen, Carbon and Phosphorous cycle. Nutrients exist in either a reservoir or exchange pool: reservoir is the storehouse of nutrients. The nutrients in the reservoir are not directly available to organisms in the ecosystem e.g. reservoirs for carbon include limestone, coral reefs, and fossil fuels such as coal and natural gas. Reservoir of phosphorous are rocks, fossils etc. Exchange pool is the source of nutrients in a form that can be taken up by primary producers e.g. carbon in the form of atmospheric carbon dioxide is the exchange pool form.. From Phosphate rocks the phosphorous becomes available as dissolved phosphorous due to erosion. Nutrients tied up in biomass are released by decomposition back into exchange pool.  ECOLOGICAL SUCCESSION Thus Ecological Succession can be elaborately defined as an orderly process of change in the community structure and function with the passage of time, mediated through modifications in the physical environment and ultimately culminating in a stabilized ecosystem known as climax. Types Autogenic succession Allogenic succession  Does ecological succession ever stop?  Process of Succession 1 Nudation- It is the development of a bare area without any life form. The bare area may be caused due to landslides, volcanic eruptions, drought, glaciers, frost, overgrazing, outbreak of diseases, agricultural, industrial activities etc  2. Invasion- It is the successful establishment of one or more species on a bare area through dispersal (by wind water birds etc) or migration, followed by ecesis or establishment. As growth and reproduction start, these pioneer species increase in number and form groups or aggregations.  3.Competition and coactions- As the number of individuals grows there is interspecific and intraspecific competition for space water and nutrition. This influence on each other in a number of ways is called coaction.  4. Reaction- The cause of ecosystem change, is the impact that established species have upon their own environments, sometimes subtle and sometimes overt alteration of one’s own environment. This modification of the environment by established species is called reaction and the modifications are very often such that they become unsuitable for the existing species and favor some new species which replace them. This reaction is what leads to seral communities.  5. Stabilization- The succession ultimately culminates in a more or less stable community called climax which is in equilibrium with the environment owing to full adjustment with the environment, maximum biomass and mutually beneficially linkages with other organisms XEROSERE  Xerosere: Crustose lichen stage- Rocks cannot absorb water and are not in a position to hold nutrients, but the weak acids formed by the pioneer lichens to appear, the crustose lichens like graphis, Rhizocarpum etc corrode the rock surface forming small depressions and release the minerals needed for the growth of these lichens.  Foliose lichen stage- Lithosere also involves successive changes in animal life. Pioneer stages in animals are few species of mites, spiders and ants, which are exposed to harsh temperatures.  Moss stage- Large sized xerophytic mosses like Grimmia, Tortula shade the Lichens and replace them. Their rhizoids can penetrate deep into the crevices of the rocks, and more of soil and organic matter is added to the soil. During moss stage, many new species of mites, spiders, springtails invade the community.  Herbs stage- The compact mat formed by mosses retains sufficient moisture and especially in rainy season making it possible for seeds of annual grasses and herbs like Poa, Eleucine etc to germinate. Herb stage is invaded by nematodes, mites and various insect larvae  Shrub stage- Xerophytic shrubs like Zizyphus, Rubus etc start invading the area and they soon replace the grasses. Shrubs provide more shade for the sol surface, and the atmosphere becomes more moist due to more of transpiration. Roots of shrubs cause more fragmentation of rocks and there is more accumulation of soil.  Forest stage: - Numerous kinds of animals as snails, wire worm, millipede, mites, ants and amphibians such as frogs, salamander occur. Reptiles which occur there are skinks, turtles and other lizards. Birds such as goose, flycatcher and mammals as shrews, mouse, mole, squirrels, fox and chipmunk occur. HYDRARCH SUCCESSION  Hydrosere / Hydrarch succession Phytoplankton stage- In the initial stage, phytoplankton (cyanobacteria), green algae (Spirogyra, Oedogonium), diatoms etc are the pioneer colonizers.  Rooted submerged stage- Phytoplankton  Zooplankton Fish dead organic matter utilized by bacteria and fungi, and minerals are released after decomposition Nutrient rich mud supports rooted hydrophytes such as Hydrilla, Ceratophyllum etc. It is also inhabited by animals such as may flies, dragon flies etc. and Crustaceans as Daphnia, Cyclops etc.  Rooted floating stage- At the margin of pond grow rooted floating vegetation. Example- Nelumbo nucifera, Monochoria, Trapa etc. In floating stage faunal living space is increased and diversified. Example- frogs, salamander, turtles snakes, diving beetles etc inhabit such conditions.  Reed swamp stage- Gradually, the depth of water decreases due to water evaporation and organic matter decomposition. The reed swamp species are Scirpus, Typha etc  Sedge meadow stage- Mesic (growing in moderate moisture) communities like sedges like Juncus and grasses begin forming a mat like vegetation.  Wood Land Stage- The marshes get dry due to the sunlight and the marshy vegetation disappears. The soil encourages land plants as shrubs and trees.  Forest stage- Depending upon the geographic conditions, different forests like deciduous or tropical forest stage takes over. The once aquatic fauna gets replaced by land animals. ECOTONE, ECOCLINE, EDGE EFFECTS MAJOR TYPES OF ECOSYSTEM  Forest Ecosystems These ecosystems tend to be stable climax community of various strata of trees shrubs herbs climbers and a variety of animals and birds, or they are always moving towards maturity called a climax forest.  a.Tropical Evergreen Rain Forests- Rainfall: Mean annual rainfall exceeds 200 cm - 450cm Temperature: around 22- 30°C Relative humidity: 80- 90%. Major Tree Species: Mahogany, iron wood, teak, ebony, rubber, palm, deodar, Brazil nut, bamboo and cane etc. Leaves are large, long and narrow ending.  The map below shows the location of the world's tropical rainforests. Rainforests cover only a small part of the earth's surface - about 6%, yet they are home to over half the species of plants and animals in the world. Major characteristic features are: (i) Different plant species grow together. (ii) Trees are sky-high and epiphytes are common. (iii) Light cannot penetrate into the lower strata full of undergrowth. (iv) Due to the presence of trees of different height, several canopy also develops. (v) Foliage is leathery in texture. (vi) Parasites, saprophytes, climbers grow luxuriantly.  Tropical Deciduous Forests/ Monsoon Forests Moist/dry deciduous forests. Found a little away from equator, having warm climate, rainfall only during monsoon,(moderate amount of precipitation), ), a large part of year remaining dry and so favoring deciduous trees which lose their leaves in winter. Rainfall: Mean annual rainfall exceeds 100 cm - 250cm Temperature: around 25 - 30°C, lowest10oC. Relative humidity: 80-90%. Drops in winter. Major Tree Species: rose wood, mahogany, ebony, teak, logwood, sal,, sissu, acacia catechu, palash, haldu, neem  Characteristics of Vegetation: (i) Most of the tress are broadleaved and provide hardwood variety. (ii) Trees are so heavy that in most cases they do not float in water. (iii) Several layers are visible in forest, according to height of the trees. Trees with height of 50 meters to 10 meters are common. (iv) Wide variety of climbers, creepers, parasites, epiphytes and saprophytes are common. (v) Thick undergrowth of shrubs, bushes and bamboos are common. (vi) Swampy, marshy areas exhibit mangrove forests, e.g. Sundarbans in West Bengal. Major Tree Species: Among the valuable trees, notable are: mahogany, ebony, teak, logwood, sal,, sissu, acacia catechu, palash, haldu,, margose (neem) etc  Temperate Rain Forests- Rainfall: Mean annual rainfall exceeds 150 cm - 400cm Temperature: During (winter) is quite long and wet not less than 0oC, and during (summer) is short, dry and foggy around 27oC Major Tree Species: pines, firs, redwood, lime, oak, walnut  Found in temperate areas with adequate rainfall dominated by coniferous trees like pines, firs, redwood and also some evergreen broad leaved trees owing to the plentiful rainfall. Temperate rainforests are characterized by mild climates or temperatures. Essentially, these areas do not experience extremely cold or extremely hot temperatures. Temperate rainforests have two different seasons. One season (winter) is quite long and wet, and the other (summer) is short, dry and foggy. Throughout the long wet season, the temperature hardly falls below freezing point, which is 0°C or 32°F. Throughout the short, dry and foggy season, the temperature hardly exceeds 27°C or 80°F. Temperate rainforests are located along some coasts in temperate zones. The biggest temperate rainforests are located on the Pacific coast of North America.  Temperate Deciduous Forests- Temperate deciduous or temperate broad-leaf forests are a variety of temperate forest 'dominated' by trees that lose their leaves each year. They are found in areas with warm moist summers and cool winters favoring broad leaf deciduous trees like oak(Quercus), hickory, poplar etc. Therefore they are more precisely termed as temperate broadleaf forest, and are found in North America, southern South America, Europe, and Asia.  Key Characteristics of Temperate Deciduous "Broadleaf" Forest Deciduous forests have a long, warm growing season as one of four distinct seasons. There is abundant moisture. The soil typically is rich. The leaves dropped from trees provide a steady source of organic material for the soil. Many species live in the soil and break down the organic matter. Tree leaves are arranged in strata: canopy, understory, shrub, and ground. A great deal of light is therefore filtered out before it reaches the ground. With the dropping of their leaves during one season, trees stop photosynthesis and enter a dormant period. Three main types of trees are characteristic of these forests: northern hardwood, central hardwood, and southeast pine and oak. TROPICAL SCRUB FORESTS/ MEDITERRANEAN SCRUB FOREST- Rainfall: 50-100 cm Temperature: 18°C – 25°C. Relative humidity: Only in winter. Dry summer. Major Vegetation: Winter rainfall and dry summer separates Mediterranean vegetation from all other vegetation type. Lush green winter and pale brown summer is typical  Tropical Scrub Forests/ Mediterranean scrub forest- Found in areas where the dry season is very long favouring small deciduous trees and shrubs. Shrubland, scrubland, scrub, brush, or bush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs. Shrubland may either occur naturally or be the result of human activity. Shrublands are dense thickets of evergreen shrubs and small trees. They are most common near the seacoast, and are often adapted to wind and salt air from the ocean. Fire, both natural and human-caused, has played a large role in shaping the ecology of Mediterranean ecoregions. The hot, dry summers make much of the region prone to fires, and lightning-caused fires occur with some frequency The ecoregion covers the semi-arid portions of the Deccan Plateau, extending across the Indian states of Maharashtra,Telangana, Karnataka,Andhra Pradesh, and Tamil Nadu to the Northern Province of Sri Lanka  Climatic Characteristics: (a) Temperature: Average annual temperature varies between 18° – 25°C. Winters receive moderate temperature while summer months remain hot. (b) Rainfall: The peculiar climatic characteristics of Mediterranean climate is manifested by its winter rainfall. The region receives much of its rainfall during winter, summer months remain dry and rainless. Average annual rainfall varies between 50-100 cm. (c) Humidity: This is the only region on earth where winter months remain humid while summer months are dry. Characteristics of Vegetation: Winter rainfall and dry summer separates Mediterranean vegetation from all other vegetation type. Lush green winter and pale brown summer is typical. Though much of the original vegetation has long been destroyed due to ruthless human interference.  To protect themselves from the dry summer, vegetation of this area has adopted several devices. Important among these are: 1. Trees are covered by hairs, e.g. Olive trees. 2. Leaves are very thick and skin-like, e.g. Bolen trees. 3. Some trees may adopt wax layers in the leaves. 4. Barks are very thick, e.g. cork and oak. 5. Roots are very long, e.g. grapes.  Evergreen Coniferous Forests(Taiga/Boreal Forests)- Found south of arctic tundra having long cold and dry winters, sunlight being available for a few hours only and summer season being mild and short favoring coniferous trees. The soil gets frozen in winter where only few species can survive. Species diversity is rather low in these forests. (i) Prolonged winter. -10oC (ii) Mild short summer. 15oC (June) (iii) Scanty rainfall. 30-50cm  Climatic Characteristics: The winter temperature remains very low. Sometimes it goes below -10°C. Winter experi- ences heavy snowfall, summer very low snowfall. Annual rainfall varies between 30-50 cm. The major climatic characteristics are: (i) Prolonged winter. (ii) Mild short summer. (iii) Scanty rainfall.  Characteristics of trees: 1. Most of the coniferous forests or Taiga or Boreal forest are evergreen. Forest occurs in places where minimum temperature is above 6°C. 2. The individual trees are cone-shaped as this helps prevent accumulation of snow on the trees. 3. The leaves are leathery and conical. So transpiration can be reduced during summer. 4. Characteristically, most of the coniferous trees are tall and have few branches. 5. Most of the trees are of soft wood variety. This is very useful for production of pulp, paper, newsprint, artificial silk, plywood etc. 6. As the trees are not very dense and evergreen, they do not create good shadow. 7. Same species of trees are found in separate regions.  Grasslands are open areas where grasses or grass-like plants are the dominant vegetation and where there are few trees. Some areas of the grasslands are hot and dry while others may be relatively cool and moist. Many flowering plants, also called forbs, have adapted to the hot, dry climate, completing their cycle of flowering, seed formation and drying out before the hottest part of the summer. Shrubs are also an important component of grasslands, and in some areas they are the dominant plants which have long, deep tap roots that search for water well below the surface. THREE T YPES OF GRASSL ANDS ARE FOUND TO OCCUR IN DIFFERENT CLIMATIC REGIONS Tropical Grasslands - These are known as Savannas, which have tall grasses, scattered shrubs, stunted trees and perennation bulbs, rhizomes, runners etc. The Savanna of India includes narrow lowland ecoregion of the Himalayas, the Ganges and the Brahmaputra River Basin, Little and Great Rann of Kutch and Western Ghats montane rain forests. Areas of high seasonal rainfall support single-story woodlands of tall trees, while lush grasses form the ground vegetation; but, where rainfall is both seasonal and low, the trees consist of stubby xerophilous (dry-loving) shrubs and short, grasses. Savanna covers approximately 20% of the Earth's land area Vervet monkey BABOON PATAS MONKEY GAZELLE ANTELOPE Grey crowned crane White backed vulture Lilac-breasted roller Saddle-billed stork  Temperate Grasslands- In United States and Canada these grasslands are known as prairies, in South America as Pampas, in Africa as Veldts and in central Europe and Asia they are known as Steppes. Temperate grasslands are areas of open grassy plains that are sparsely populated with trees. Temperatures vary with seasons with tornadoes, blizzards, and fires occurring in many temperate grassland regions. Temperate grasslands, however, are located in colder climate regions and receive less precipitation on average than savannas. Most of this precipitation is in the form of snow in temperate grasslands of the northern hemisphere. Temperate grasslands are home to many large and small herbivores. BISON Prairie dogs Badgers Canvasback duck Gadwall Grey partridge  Polar Grasslands- These grasslands are found in Arctic Tundra where the climate is too cold and harsh for trees to grow. A thick layer of ice remains frozen under the surface of soil throughout the year called Permafrost. Only in summers when the sun shine round the clock some annual plants grow and even shallow lakes, bogs etc appear which attract migratory birds. Animals include arctic wolf, weasel, arctic fox, reindeer etc. Artic Hare WEASEL REIN DEER MUSKOX SNOW OWL  DESERT ECOSYSTEM In deserts the amount of water lost to evapotranspiration is much more than the amount of water gained by precipitation. Rainfall-