Community Ecology - Sem 5th Unit 6th PDF

6.2. Community Dynamics: The gradual change in species composi on and processes of communi es over me is known as ecological succession or community development. Understanding the process, rates and pa ern of ecological succession is important for the management of ecosystems and for understanding vegeta on poten al and dynamic changes in the landscapes. Succession in ecology refers to the process by which the structure of a biological community evolves over me. CAUSES OF SUCCESSION: 1. Disturbance (Natural or Human-Made)  Natural Disturbances: Events like wildﬁres, hurricanes, ﬂoods, volcanic erup ons, and landslides can destroy exis ng ecosystems, crea ng opportuni es for new communi es to establish themselves.  Human-Made Disturbances: Ac vi es such as deforesta on, agriculture, urbaniza on, mining, and pollu on can alter or destroy habitats, leading to secondary succession. 2. Clima c Factors  Changes in Climate: Long-term shi s in temperature, precipita on, and seasonal pa erns can alter the suitability of an area for certain species, promp ng succession.  Microclimate Varia ons: Localized changes in light, moisture, and wind within a speciﬁc area can cause gradual changes in the species composi on of a community. 3. Soil Composi on and Nutrient Availability  Soil Forma on: In primary succession, the absence of soil (e.g., a er a volcanic erup on) means that pioneer species like lichens and mosses need to colonize and contribute to soil forma on before other species can establish.  Nutrient Deple on/Enrichment: Over me, the nutrients available in the soil change due to processes such as decomposi on and nutrient cycling, favoring diﬀerent species and causing shi s in community composi on. 4. Bio c Factors  Species Interac ons: Compe on, preda on, herbivory, and mutualism among species can drive succession. For example, early colonizers may create condi ons (e.g., shading, nutrient accumula on) that facilitate the establishment of later successional species.  Invasive Species: The introduc on of non-na ve species can disrupt exis ng communi es and ini ate a new succession sequence as the ecosystem adjusts to the presence of the invaders. 5. Geological Factors  Tectonic Ac vity: Earthquakes, volcanic erup ons, and mountain forma on can dras cally alter landscapes, crea ng new environments for ecological succession to begin.  Erosion and Sedimenta on: Processes like erosion can strip away soil and vegeta on, while sediment deposi on can create new landforms (e.g., river deltas), both leading to succession. 6. Human Restora on Eﬀorts  Reforesta on and Habitat Restora on: Human eﬀorts to restore degraded environments (e.g., plan ng trees, removing invasive species) can inﬂuence succession by accelera ng or altering natural processes. 7. Ecesis/Con nuing causes  These are the processes such as migra on, ecesis, aggrega on, compe on, reac on, etc., which cause successive waves of popula ons as a result of changes, chieﬂy in the edaphic features of the area. 8. Stabilizing causes  These cause the stabiliza on of the community. According to Clements, climate of the area is the chief cause of stabiliza on, other factors are of secondary value. Types of Succession: 1. Hydrosere Plant successions which begin in ponds, lakes, marshes, or elsewhere in water, are termed hydrarch and diﬀerent stages are called as hydrosere. The water is deep in the middle and becomes progressively shallow towards the bank. 1. Pioneer stage: This is characterized by a bo om barren of plant life. The pioneers include phytoplankton. This consists of microscopic algae, bacteria, diatoms and protozoa. This phytoplankton a er death se les to the bo om. The soils are very much reduced with a pH value of not more than 5. 2. Submerged stage: This stage is found where the water is less than 20 feet deep. The plants are en rely submerged. Prominent submerged plants include pond weeds (Potamogeton), hornwort (Ceratophyllum), eelgrass (Vallisneria), water weed (Elodea), Hydrilla, bladderwort (Utricularia), Chara and Ranunculus. These are all rooted plants. When these plants die, their remains sink to the bo om where they become humus. The humus binds the so muddy soil. These plants also help in deposi ng soil par cles at the bo om. As a result of these reac on the water becomes shallow and the habitat becomes unsuitable for submerged plants, which in turn are replaced by ﬂoa ng plants. 3. Floa ng stage: This stage is present where the water is only 6-8 feet, deep. This stage includes rooted plants with ﬂoa ng leaves like Nyphaea (water lily), Nelumbium, Limnanthemum, Aponogeton, Monocharia, Trap and freeﬂoa ng plants like Pis a, Azolla, Lemna, Spirodella, Wolﬃa, Eichhornia, etc. The water level by now becomes very much decreased, making the pond shallower. By their death and decay humus is formed which results in the higher concentra on of salts and organic ma er and ul mately the water becomes unsuitable for these ﬂoa ng plants which are then replaced by reed swamp plants. 4. Reed-swamp stage: This stage also called as amphibious stage occurs where the water is 1-4 feet deep and includes the plants which are partly submerged, with their roots at the bo om and their foliage raised above the surface of water. The important plants consis ng this stage include ca ail (Typha), bulrush (Scirpus), reed grass (Phragmites), arrow head (Sagi aria), Rumex etc. These plants cut oﬀ the light from the ﬂoa ng plants and in this way make the water s ll shallower by se ling down the sedimentary materials washed into the lake and by very rapid accumula ons of humus. This changed habitat becomes highly suitable for the growth of plants of next seral stage i.e., marsh-meadow stage. 5. Marsh-meadow stage: This stage includes hydrophytes or water loving plants. The substratum at this stage is hardly covered by 1-2 inches of water, so to say the soil becomes marshy. This is now invaded by numerous species of sedge. Juncus, carice (Carex), spike rush (Eleocharis), Polygonum, etc. Many species of herbs like mint (Mentha), marsh marigold (Caltha), bell ﬂower (Campanula), etc., also occur intermixed with sedges. All these hydrophytes react upon the habitat, raise the surface by binding water carried and wind-borne soil, accumulate plant debris, and transpire enormous quan es of water. This makes the soil more suitable for the mesophytes and terrestrial plants. Under these circumstances, hydrophytes cannot live long, they migrate inward giving room for grasses and woody plants. 6. Woodland stage: If the climate is dry then a grassland develops but under moist climate a woodland is formed containing certain shrubs and small tress. This stage is characterized by the plants that can tolerate water-logged soil around their roots. Shrubby willow (Salix), dog woods (Cornus), bu on bush (Cephalanthus), alder (Alnus), co on wood (Populus), tree willows etc., are the plant species of the woodland stage. These plants by their reac on make the soil unsuitable for themselves and more suitable for shade enduring herbs which grow the trees and shrubs. 7. Climax forest: This represents the ﬁnal stage of hydrarch. It includes mixed forest of alder (Alnus), willow (Salix), co onwood (Populus), elm (Ulmus), ash tree (Fraxinus), oak (Quercus), etc. A er a few genera ons a pure forest oaks or hickories may develop. Fig. Hydrosere Succession 2. Xerosere Succession Xerosere is the sequence of successional stage which occur on bare areas deﬁcient in water. Succession on a bare rock is as follows: 1. Pioneer stage (Crustose lichen stage): The rocky habitat is extremely xeric and hos le. There is no water as the substratum does not absorb rain water. There is no nutrient holding mechanism. When exposed to sun, the surface temperature goes very high. In such a habitat, only the crustose lichens can become pioneer colonies that have ability to bear high degree of desicca on and temperature extremes. These lichens reach the bare rock through wind borne soredia, lichen fragments and spores. The lichens produce carbonic acid which has a corroding eﬀect on rock ma er. Co2 + H2 o→H2 Co3 Generally, species of Rhizocarpon, Rinodena, Lecidea and Lecanora establish themselves on the bare rocks. 2. Foliose Lichen stage: Foliose lichens i.e., those a ached to the substratum at a single point or along a single margin appear as soon as a li le soil has accumulated on the non-weathered por on of rock and in depressions or other slightly less exposed situa ons. They slowly replace the crustose form. These expanding leaf-like thalli may completely over shadow the crustose lichens causing the crustose species to die and decay. Above the foliaceous invaders water has be er chance to collect and to be absorbed. Evapora on is greatly decreased. Wind and water borne lichen fragments and dust par cle lodge and humus is more rapidly accumulated because of its less rapid oxida on. Acid produced by living and decaying plants are constantly ea ng further into the rocks. Indeed, it is possible that change from crustose to foliose lichen is a change of habitat. A er the crustose give away to foliose species such as Dermatocarpon, Parmelia, Umbilicaria, a new type of invaders appears. 3. Moss stage: As soon as suﬃcient amount of soil has accumulated in the minute crevices and depression xerophy c mosses begin to appear. These are common species of Gerimmia, Polytrichum and Tortula. They may have migrated long distances by wind-blown spores that are caught in minute amount of soil and along foliose lichens and germinate there. Their rhizoids compete with those of foliose lichens for water and nutrients. The erect stems of mosses o en exceeded the lichens in heights. The power of withstanding desicca on is almost as marked along these pioneers as among the lichens. These are the most exac ng foliose species that may occur simultaneously or indexed. The mosses may some mes precede foliose lichens. Soil rapidly accumulates among the erect stems as the plant die below and con nue to grow above and build up the substratum and constantly increase their area. The depth of the soil under the cushion like mat is o en one inch or even more. The crustose lichens like Cladonia grow along with mosses. The mosses form thick mats and play a signiﬁcant role in building up thick substratum of soil. Their con nuous growth, death and decay for several years builds up a good soil which is quite ﬁt for the growth of herbaceous ﬂora. 4. Herbaceous Stage: The soil forming and soil holding reac on of mosses are so pronounced that the seeds of some xerophy c herbs especially shortlived annuals are soon able to germinate and grow to maturity. They grow slowly and exhibit stunted growth because the soil is yet not very favourable and lacks nutrients. Drought condi ons also prevail. The roots of these xeric herbs con nue to grow and corrode the rocks. Their dead remains enrich the soil further and more humus collects. Depending upon the plants growing in surrounding communi es the invading herbs are Poten lla, Solidago and Saxifraga. Their growth makes the condi ons less dry. Bacteria, fungi and microfauna appear along with grasses. Their death and decay further add to the soil layers. 5. Shrub stage: Woody shrubs like Rhus glabra, or Rubus and Sassafras invade these areas. Their shade makes the growth of herbs impossible and thus they disappear. The humidity increases and wind velocity is decreased. The addi on of organic ma er to the soil increases water holding capacity of soil, its texture and structure is changed so that the seeds of trees ﬁnd suitable place for growth. 6. Climax forest: The tress which make their appearance are dwarf sized, xeric and grow separated apart. They are however followed by mesophytes as the climate becomes more mesic. Quercus, Tilia are the trees which ﬁnd place in climax communi es. 6.3 Ecosystem: Structure of ecosystem: The structure of an ecosystem is characterised by the organisa on of both bio c and abio c components. This includes the distribu on of energy in our environment. It also includes the clima c condi ons prevailing in that par cular environment. The structure of an ecosystem can be split into two main components, namely: Bio c Components Abio c Components The bio c and abio c components are interrelated in an ecosystem. It is an open system where the energy and components can ﬂow throughout the boundaries. Structure of Ecosystem highligh ng the bio c and abio c factors Bio c Components: Bio c components refer to all life in an ecosystem. Based on nutri on, bio c components can be categorised into autotrophs, heterotrophs and saprotrophs (or decomposers). Producers include all autotrophs such as plants. They are called autotrophs as they can produce food through the process of photosynthesis. Consequently, all other organisms higher up on the food chain rely on producers for food. Consumers or heterotrophs are organisms that depend on other organisms for food. Consumers are further classiﬁed into primary consumers, secondary consumers and ter ary consumers. Primary consumers are always herbivores that they rely on producers for food. Secondary consumers depend on primary consumers for energy. They can either be a carnivore or an omnivore. Ter ary consumers are organisms that depend on secondary consumers for food. Ter ary consumers can also be an omnivore. Quaternary consumers are present in some food chains. These organisms prey on ter ary consumers for energy. Furthermore, they are usually at the top of a food chain as they have no natural predators. Decomposers include saprophytes such as fungi and bacteria. They directly thrive on the dead and decaying organic ma er. Decomposers are essen al for the ecosystem as they help in recycling nutrients to be reused by plants. Abio c Components: Abio c components are the non-living component of an ecosystem. It includes air, water, soil, minerals, sunlight, temperature, nutrients, wind, al tude, turbidity, etc. Func ons of Ecosystem 1. It regulates the essen al ecological processes, supports life systems and renders stability. 2. It is also responsible for the cycling of nutrients between bio c and abio c components. 3. It maintains a balance among the various trophic levels in the ecosystem. 4. It cycles the minerals through the biosphere. 5. The abio c components help in the synthesis of organic components that involves the exchange of energy. Types of Ecosystem: 1. Pond Ecosystem A pond ecosystem is a freshwater ecosystem that can either be temporary or permanent and consists of a wide variety of aqua c plants and animals interac ng with each other and the surrounding aqua c condi ons. The pond ecosystem falls under the category of a len c ecosystem because the water remains stagnant for a longer period. Characteris cs of Pond Ecosystem  The water in the pond ecosystem is stagnant.  Either natural or ar ﬁcial boundaries surround the pond ecosystem.  The pond ecosystem exhibits three dis nct zones, the li oral zone, limne c zone, profundal zone, and benthic zone.  The bio c components of the pond ecosystem occupy diﬀerent levels in the pond ecosystem, therefore, avoiding the compe on for survival. Scavengers and decomposers occupy the bo om level, and ﬁsh occupy the middle level. The plants enclose the pond’s boundaries and provide shelter to small animals and insects.  Pond ecosystems show a wide range of variety in their size. Stra ﬁca on in the Pond Ecosystem Diﬀerent factors such as distance from the shore, penetra on of light, depth of water, plant and animal species, etc. determine the following zones found in the pond ecosystem:  Li oral zone: It is the zone closer to the shore. It contains shallow water and allows easy penetra on of light. Rooted plant species occupy it. Animal species include reeds, crawﬁsh, snails, insects, etc.  Limne c zone: The limne c zone refers to the open water of the pond with an eﬀec ve penetra on of light. This zone is dominated by phytoplankton. Animal species mainly include small ﬁshes and insects.  Profundal zone: The region of a pond below the limne c zone is called a profound zone with no eﬀec ve light penetra on. Some amphibians and small turtles occupy it.  Benthic zone: The bo om zone of a pond is benthic and is occupied by a community of decomposers. The decomposers are called benthos. Abio c Components of the Pond Ecosystem Abio c components are the non-living components of an ecosystem that ma er for the aqua c species’ survival. There are the following main abio c components of a pond ecosystem:  Light: Light serves as a main abio c component required for the photosynthe c ac vi es of the phytoplankton. The li oral zone has the maximum light penetra on, whereas the profound zone has the least light penetra on.  Temperature: As the depth of the pond increases, the temperature of the water gradually decreases due to the gradual decrease in the light penetra on.  Dissolved oxygen: The amount of dissolved oxygen is maximum in the shallow water and gradually decreases while moving from the surface to the depth of the pond.  Dissolved oxygen: The amount of dissolved oxygen is maximum in the shallow water and gradually decreases while moving from the surface to the depth of the pond. Bio c Components of the Pond Ecosystem Bio c components are living components. A wide variety of living components are found in the pond ecosystem can be discussed as follows:  Producers: These include species of rooted, submerged, emerged, ﬂoa ng plants and algae. The most common ﬁlamentous algae found in ponds is Spirogyra. Mougeo a and Zygnema are some other algae found in the pond. Azolla, Hydrilla, Pis a, Wolﬃa, Lemna, Eichhornia, Nymphaea, Potamogeton, Jussiaea, etc., are a few examples of green plants that are found in the pond ecosystem.  Primary consumers: A large popula on of zooplanktons are the main primary consumers. Besides these, small herbivores such as snails, insects, small ﬁshes, tadpoles, and larvae of aqua c animals are the primary consumers o en found in the pond.  Secondary consumers: These include large animal species such as frogs, big ﬁshes, water snakes, crabs, etc. The consumers of the highest order might include mammals like water shrews, water voles, herons, ducks, kingﬁshers, etc.  Decomposers: These include diﬀerent types of bacteria and fungi that feed upon dead and decaying parts of the aqua c species. Food Chain in the Pond Ecosystem  Phytoplankton and algae serve as producers that convert solar energy into chemical energy.  Phytoplankton is being consumed by zooplankton (primary consumers).  The food chain further proceeds with the small pond species that feed on zooplankton.  Small pond species are eaten by large pond species.  A number of bacteria and fungi feed on dead and decaying parts of the animal species and are therefore called decomposers. Decomposers convert the organic ma er (dead plants and animals) into their inorganic components that are again u lised by producers, and hence a con nuous ﬂow of energy is maintained. Fig. Pond Ecosystem 2. Forest Ecosystem: The terrestrial system in which living things such as trees, insects, animals, and people interact is referred to as a forest ecosystem. It is the smaller classiﬁca on of the ecosystem as a whole, which is the biggest func onal unit comprising all the geographical features and living organisms on Earth. There are many diﬀerent kinds of forest ecosystems, and they are categorised according to the local climate, including the amount of rainfall and temperature. Components of Forest Ecosystem 1. Producers: Producers can synthesize their own food by the photosynthesis process. All green plants are considered producers of the ecosystem as they convert sunlight into the chemical energy of food. 2. Primary Consumers: Since the consumers can not prepare their own food, they depend on producers. Herbivorous animals get their food by ea ng the producers (plants) directly. Examples of primary consumers are grasshoppers, deer, etc. 3. Secondary Consumers: Secondary consumers draw their food from primary consumers. 4. Decomposers: The decomposers of the forest ecosystem break down dead plants and animals, returning the nutrients to the soil so that they can be used by the producers. Apart from bacteria, ants and termites are important decomposers in the Amazon rainforest. Millipedes and earthworms also help to break down dead ma er. 5. Nutrient Cycle: The nutrient cycle is cyclic. For the proper func oning of ecosystems, nutrients are required. Carbon, hydrogen, oxygen, and nitrogen cons tute about 95% of the mass of living organisms. About 15 to 20 other elements are also needed in rela vely small amounts. These are recycled repeatedly between the living and non-living components of the ecosystem. 6. Energy Flow: In a forest ecosystem, the grass, which draws its nutri on from sun, soil and water, is eaten by the grasshopper, which in turn is eaten by frogs, snakes, and vultures in succession (diﬀerent trophic levels). In this process of ea ng and being eaten, nutrients are passed from one step to the next in a food chain. The ﬂow of energy that occurs along a food chain is called energy ﬂow. The pyramid of energy represents the total quan ty of energy at each trophic level of a food chain. The ﬂow of energy is always unidirec onal. Characteris cs of Forest Ecosystem 1. Warm temperatures and suﬃcient rainfall are characteris cs of forests, resul ng in the forma on of numerous ponds, lakes, etc. 2. The forest maintains climate and rainfall. 3. The forest supports many wild animals and protects biodiversity. 4. The soil is rich in organic ma er and nutrients, which support the growth of trees. Func ons of Forest Ecosystem 1. Goods Obtained from Forests: There are various types of food products such as honey, wild meat, fruits, mushrooms, palm oil and wine, and medicinal plants obtained from forests. Other than edible parts, we can obtain mber, wood biomass, cork, etc. from forests. The fuel can be extracted from old trees that are buried under the soil. 2. Ecological Func ons: Forests play an important role in maintaining ecological factors such as climate, carbon storage, nutrient cycling, and rainfall. 3. Culture and Social Beneﬁts: The tribal people who live in the forests treat forests as nature goddesses. The tradi onal beliefs and spirituality save wild animals from hunters and cu ng down of trees by urban people. A few modern people visit forests for recrea on. Fig.: Forest Ecosystem 6.4. Ecosystem Func on: 1. Food Chain  All living organisms (plants and animals) must eat some type of food for survival. Plants make their own food through a process called photosynthesis. Using the energy from the sun, water and carbon dioxide from the atmosphere and nutrients, they chemically make their own food.  Since they make or produce their own food they are called producers. Organisms which do not create their own food must eat either plants or animals. They are called consumers.  Some animals get their energy from ea ng plants while other animals get energy indirectly from plants by ea ng other animals that already ate the plants. Animals that eat only plants are called herbivores. Animals that eat both plants and other animals are called omnivores.  Animals that eat only other animals are called carnivores.  Some animals eat only dead or decaying materials and are called decomposers. In the marine food web, special producers are found. They are ny microscopic plants called phytoplankton.  Since the water is the home for these special ny plants; it is also the home for ny microscopic animals called zooplankton. And of course, zooplankton eat phytoplankton. Some mes zooplankton and phytoplankton are collec vely referred to as plankton.  Food chains show the rela onships between producers, consumers, and decomposers, showing who eats whom with arrows. The arrows show the movement of energy through the food chain.  For example, in the food chain shown below, the small ﬁsh (silverside) gets its energy by ea ng the plankton and the large ﬁsh (blueﬁsh) gets its energy by ea ng the small ﬁsh. Finally, the bacteria eats the ﬁsh a er it dies, ge ng its energy from the large ﬁsh. The bacteria also returns nutrients back to the environment for use by the phytoplankton. PHYTOPLANKTON ZOOPLANKTON SILVERSIDE NUTRIENTS BACTERIA BLUEFISH Fig.: Food Chain A classic example of a food chain in an ecosystem  The food chain is an ideal representation of flow of energy in the ecosystem.  In food chain, the plants or producers are consumed by only the primary consumers, primary consumers are fed by only the secondary consumers and so on.  The producers that are capable to produce their own food are called autotrophs.  Any food chain consists of three main tropic levels, viz., producers, consumers and decomposers.  The energy efficiency of each tropic level is very low. Hence, shorter the food chain greater will be the accessibility of food.  Food webs are more complex and are interrelated at different tropic levels.  Hawks don’t restrict their food to snakes, snakes eat animals other than mice, and mice eat grass as well as grasshoppers, and so on.   2. Food Web:  Charles Elton presented the food web concept in year 1927, which he termed as food cycle.  Charles Elton described the concept of food web as:  The carnivore animals prey on the herbivores.  These herbivores obtain the energy from sunlight.  The later carnivores may also be preyed upon by other carnivores.  There are chains of animals that are related together by food, and all are dependent on plants.  A food web is a graphical depiction of feeding connections among species of an ecological community.  The food web is an illustration of various techniques of feeding that links the ecosystem.  The food web also explains the energy flow through species of a community as a result of their feeding relationships.  All the food chains are interconnected and overlapping within an ecosystem and they constitute a food web.  In natural environment or an ecosystem, the relationships between the food chains are interrelated.  The web like structure if formed with the interlinked food chain and such matrix that is interconnected is known as a food web.   Hence, a web like structure is formed in place of a linear food chain. 3. Ecological Pyramid  Ecological pyramids are the graphical representations of trophic levels in an ecosystem. The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.  The pyramid includes a number of horizontal bars presenting specific trophic levels.  Flow of energy through the food chain, enters at the base of the food chain, by photosynthesis in primary producers, and then moving up the food chain to higher trophic levels.  The transfer of energy from one trophic level to the next is not efficient.  The three ecological pyramids that are usually studied are (a) pyramid of number; (b) pyramid of biomass and (c) pyramid of energy. 1. Pyramid of number:  In this type of ecological pyramid, the number of organisms in each trophic level is considered as a level in the pyramid. The pyramid of numbers is usually upright except for some situations like that of the detritus food chain, where many organisms feed on one dead plant or animal. Pyramid of number- upright: grassland ecosystem  In this pyramid, the number of individuals is decreased from lower level to higher trophic level.  In grass ecosystem, at base (lowest trophic level) grass is present in plentiful amount.  The next higher trophic level is primary consumer i.e. herbivore (example – grasshopper).  The next energy level is primary carnivore (example: rat). The number of rats are less than grasshopper, because, they feed on grasshopper.  The next higher trophic level is secondary carnivore (example: snakes). They feed on rats.  The next higher trophic level is the top carnivore. (example – Hawk). Fig.: Pyramid of number- upright: grassland ecosystem 2. Pyramid of biomass:  In this particular type of ecological pyramid, each level takes into account the amount of biomass produced by each trophic level. The pyramid of biomass is also upright except for that observed in oceans where large numbers of zooplanktons depend on a relatively smaller number of phytoplanktons. Pyramid of biomass: upright for terrestrial ecosystem  The pyramid of biomass on land contains a large base of primary producers with a lesser trophic level present on top.  The biomass of next trophic level from base, i.e., primary consumers is less than the producers.  The biomass of next higher trophic level, i.e., secondary consumers is less than the primary consumers.  The top, high trophic level consists very less amount of biomass. Fig.: Pyramid of Biomass 3. Pyramid of energy:  Pyramid of energy is the only type of ecological pyramid, which is always upright as the energy flow in a food chain is always unidirectional.  Also, with every increasing trophic level, some energy is lost into the environment.  The primary producers like the autotrophs contain more amount of energy available.  The least energy is available in the tertiary consumers.  An energy pyramid represents the amount of energy at each trophic level and loss of energy taking place during transfer to another trophic level.  Eg.: Suppose an ecosystem receives 1000 calories of light energy in a given day.  Green plants utilise only a small portion of that absorbed energy, out of which the plant uses up some for respiration and of the 1000 calories, only 100 calories (10%) are stored as energy rich materials.  Now, suppose an animal eats the plant containing 100 calorie of food energy, that animal uses some of it for its own metabolism and stores only 10 calorie as food energy.  A lion that eats that animal gets an even smaller amount of energy.  Thus, usable energy decreases while passing from sunlight to producer to herbivore to carnivore. Therefore, the energy pyramid will always be upright. Fig.: Pyramid of Energy

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