Ecology: Study/Science of Biosphere
Ecology: Study/Science of Biosphere
Ecology: Concepts & Facts
⇒ The term Ecology is the combination of two Greek words, Oikos (= house/habitat/dwelling place) and Logos (= the study/science of). Thus, Ecology is the study/science of the biosphere (dwelling place of organism)
⇒ Ecology is defined as the study of the relationships of organism to one another and to their physical environment.
Ecology is also called Bioecology, Bionomics or Environmental biology.
⇒ There is some controversy about the person who coined the term ‘ecology’. Some scholars think that it was term ‘Oekologie’ H. Reiter who introduced the (= ecology) in 1868; but most of the scholars think that it was German scientist Ernst Hackel (1834-1919) who coined the term oekologie (= ecology) and put the first precise definition and explanation in the year 1869.
American biologist E.P. Odum (1913-2002) wrote in his popular textbook ‘Fundamentals of Ecology’: “The word ‘oekologic’ was first proposed by the Ernst Hackel in 1869. Hackel defined ecology as ‘the study of the natural environment including the relations of organism to one another and to their surroundings’.”
⇒ Ernst Hackel (1834-1919) is known as the father of Ecology (classical period). [According to some scholars, German naturalist Alexander Von Humboldt (17691859) as the father of ecology (classical period)]
E.P. Odum (1913-2002) is known as the father of Modern Ecology (Modern Period).
Ramdeo Misra (1908-98) is revered as the father of Indian Ecology.
Note: In science, the period from the Beginning to 19th century (i.e, the Beginning-19th century) is considered as ‘Classical Period’ and the period from 20th centrury to Till Date (i.e. 1901-Till Date) as ‘Modern Period’.
⇒ Like other fields of learning, the development in the field of ecology have been gradual. Ecology has progressed from Natural History and Biogeography to Ecosystem Ecology. In the last quarter of the 20th century. (i.e 19752000), Global Ecology with an emphasis on biodiversity, climate change and ecological sustainability has been emerged. Global Ecology is a subfield of ecology and it treats ecology at a global scale.
Levels of Ecological Organisation (Ecological Hierarchy)
⇒ Levels of Ecological Organisation or Ecological Hierarchy provides a convenient but a holistic approach to understand ecology which is very complex in nature. It is represented in triangular form in diagram below. In ecology, levels of ecological/biospherical organisation range from organism to ecosphere/biosphere. It is also called Ecological/ Biospherical Hierarchy (Hierarchy means an arrangement into a graded series). Levels of Ecological organisation i.e. Ecological Hierarchy as displayed in diagram (fig. 2) in which seven transcending processes or functions are depicted as vertical components in ascending order.
Note :
1. In Biology, there are 11 levels of organisation :
Cell → Tissue→Organ→Organ system → Organism → Population → Community → Ecosystem → Landscape → Biome→ Biosphere.
The elementary 4 levels (Cell→ Tissue→ Organ → Organ system) of Biological levels of organisation are not included in Ecology. So, there are only 7 levels of organisation in Ecology.
2. Cell is the basic unit to study in Biology, where as organism is the basic unit to study in Ecology. basic unit to
3. There are 3 key levels of Ecological organisation : Organism, Ecosystem & Ecosphere/Biosphere. If we understand these 3 terms (or levels) properly, then the rest 4 terms (or levels) shall be easily comprehensible to us.
4. The Level 1 to Level 3 (organism to community) and the level 4 to level 7 (Ecosystem to Ecosphere/ Biosphere) are loosely synonym to one another; they are almost similar in traits (characteristics), but differ in size and extension. Hence, we can say, organism is the reduced & compressed form of community and community is the enlarged & extended form of organism. Similary, Ecosystem is the reduced & contracted form of dex Biosphere and Biosphere is the enlarged & extended form of Ecosystem. This is the reason that Biosphere is called a ‘giant ecosystem’.
5. Biosphere is synonym of Ecosphere. With name ‘biosphere’ someone may confuse that it is concerned only to biotic/living environment, but it is not so. It is concerned with both biotic/living environment and physical/non-living environment. Similary, with name unecosphere, don’t confuse that it is concerned only to physical environment, but it is concerned with physical environment as well as biotic environment.
Subnote: Keep these concepts well in mind. Don’t take general meaning of these terms, but specific meaning whenever you tackle the questions of Ecology.
⇒ The levels of ecological organisation are briefly described below.
1. Organism: Organism is the basic and smallest unit to study in ecology. Organism means any individual living being/thing, whether of plant or animal. Thus, any living structure (plant, animal, bacterium or fungus) capable of growth and reproduction is called organism. (Note: Virus is not included in constituent parts of organism because they are incapable of autonomous metabolism, growth or reproduction). Organism is an assemblage of organ systems. Similar organism having the potential for interbreeding and producing fertile off-spring constitute what we call species. For example: a rose, an elephant etc.
2. Population: The term population, originally coined to denote a group of people, is broadened to include groups of individuals of any kind of organism. Hence population is a group of individuals of a plant or animal species in habiting in a given area. For example: all individuals of roses in a area, all individuals of elephants in a area etc.
3. Community: The term community is a combination of French word Commune (= a group of people) and noun suffix – ity (= state, condition). Community (sometimes designated as Biotic community) is an assemblage of all the populations occupying in a given area. For example: all population of roses in a area, all population of elephants in a area etc.
4. Ecosystem Ecosystem is the acronym of Ecological system. The system means a set of things that work erotogether. The biological community and the physical environment function together as an ecological system or ecosystem. It is a fundamental functional unit of ecology, because it includes both biotic (living) and abiotic (non-living) environments. For example: Forest, grassland, desert, marine, lake, river, pond; crop field, park, spacecraft, swimming pool, well, aquarium etc.
Ecosystem is not only a middle level but also a very important level of ecological hierarchy. So the structure and functioning of ecosystem shall be discussed in detail in latter part of the chapter ‘Biosphere : A Giant Ecosystem’.
5. Landscape The term landscape, originally referring to a painting and explained as ‘an expanse of scenery seen by the eye as one view’. In ecology, landscape is defined as a heterogenous area composed of a cluster of interacting ecosystem that are repeated in a similar manner throughout. For example: a watershed etc.
6. Biome: The term biome is a combination of Greek word bios (= life) and noun suffix – (o) ma (= mass, growth). A biome is a large regional unit characterised by a major vegetation type and associated fauna found in a specific climate zone.
For example: (a) Terrestrial (land-related) BiomesEquatorial (0°-15° of globe) evergreen forest biome, Tropical (120-25°) rainforest biome, Temperate (45°-66¹/2°) deciduous forest biome etc.
(b) Aquatic (water-related) Biomes Marine (Saltywater) biomes like ocean, sea etc, Freshwater biomes like Lentic (standing water): lakes and ponds, & Lotic (running water): rivers and streams & Wetlands : marshes and swamp forests (like mangrove forest). –
7. Ecosphere/Biosphere: The largest and most nearly selfsufficient ecological/biological system is designated as the Ecosphere/Biosphere. Ecosphere/Biosphere includes all the living organisms interacting with physical environment as a whole to maintain a selfadjusting, loosely controlled pulsating state.
Note : A simple formula to remember levels of ecological organisation (Ecological hierarchy):
Branches of Ecology
⇒ The ecological studies are based on three main aspectslevels of organisation, taxonomic affinities & types of habitat.
⇒ The branches of Ecology are briefly described below:
1. On the basis of levels of organisation : There are two branches of ecology on the basis of levels of organisation Autecology & Synecology.
Autecology: Auto (= on itself)+ Ecology=Autecology.
Autecology is the study of relationship of individual species to its environment. For example: Organism ecology.
Synecology: Syn (= together) + Ecology – Synecology. Synecology is the study of relationship of group of organism and their environment.
Synecology is subdivided into ‘population Ecology’, ‘Community Ecology’, ‘Ecosystem Ecology’ etc.
2. On the basis of Taxonomic Affinities Taxonomy is concerned with the classification of things, especially organisms (plants & animals). For example: Plant Ecology & Animal Ecology.
3. On the basis of Habitat: Habitat is the place where organism live. On the basis of habitat, ecology is divided into two categories
(i) Terrestrial Ecology: For example, Forest ecology, Grassland ecology, Desert Ecology etc.
(ii) Aquatic Ecology: For example, Marine ecology, Freshwater ecology etc.
Ecological Factors
⇒ The factors that affect flora and fauna directly or indirectly is called Ecological or Environmental Factors. In short, Ecological factors is known as Eco Factors.
⇒ There are two kinds of ecological factors-Abiotic & Biotic factors.
A. Abiotic Factors
⇒ Non-living factors are called Abiotic factors. For example, light, temperature, humidity (water), wind, topographic (physical features of an area viz. river, mountain etc), edaphic (soil) etc.
1. Light: Light is an important climatic factor. Most of the plants need light for photosynthesis process to make their food. Animal community is dependent on plants for their food. Though the Sun emits a wide spectrum of light, only long waves (infra-red portions of visible light) and short waves (ultra-violet) are important ecologically. By means of light, many animals are able to move about freely and to carry on the necessary activities of life. Ultraviolet light is both beneficial and harmful to animals. Vitamin D is synthesised in the skin and hair under the influence of UV light. However, too much exposure to UV rays may lead to skin cancer (including melonama).
Plants are divided into three types on the basis of Photoperiod (total length of the daily light period to which plants are exposed)
(a) Long-day plants: e.g. Wheat, barley, oat, henbane etc.
(b) Short-day plants e.g. Rice, Soyabean, cotton, sorghum/jowar etc.
(c) Day-neutral plants: e.g. Rose, almost flowers of winter season, sunflower, tomato, chilli, tobacco etc.
In another way, plants are divided into two types on the basis of sunlight –
(a) Photophilous/Heliophilous (Sunlight loving) plants: e.g. Birch, cactus, sugercane, maize etc.
(b) Sciophilous/Heliophobus (Shade loving/Sun fearing) plants: e.g. Fern, several herbaceous plants etc.
2. Temperature: Temperature is the degree of hotness or coldness of a susbstance. Temperature is needed for motion and reproducution of a organism. Total degree of heat received by the plants is called Thermoperiod. Obviously thermoperiodic effects are distinct from photoperiodic effects (caused by duration of light). An average of 10°C to 45°C temperature is essential for biological functioning. Respiratory function of plants increases with rising temperature. On the basis of temperature, plants are divided into four categories
3. Humdity Atmospheric moisture in the form of invisible vapair is called humidity. Humdity plays an important role in life of plants and animals. Proccess such as transpiration, absorption of water etc. are much influenced by humidity.
4. Wind: Wind is an important abiotic eco factor. Wind affects soil erosion, pollination, seeds dispersal etc. According to speed, winds are classified as follows: Breeze-5-50 km/h, Gale-50-100 km/h, Storm – 100-125 km/h, Hurricane More than 125 km/h.
5. Topographic : Topographic factors are concerned with the physical geography of the earth in the area. Height, slope. expose etc. of topography affects plants and animals in many ways.
6. Edaphic (Soil) Man depends on plants and plants grows in soil. Thus soil plays an important role in the life of plants and animals. The constituent parts of the soil are-Soil water (25%), Soil air (25%), Mineral matter (40%), Organic matter or Humus (10%).
B. Biotic Factors
⇒ Biotic factors also affects the life of plants and animals. Under natural conditions, organism live together influencing each other’s life and establish relationship. The common examples of such relationship are given below
1. Symbiosis : Symbiosis means live together. A relationship between two different living being close to one another and depending on each other benefiting from each other in particular ways is known as symbiosis. e.g. Algae and fungus live together and form Lichen (Pronounced as Liken) etc.
2. Parasittism: The relationship between two organism in which one benefits at the expense of the other is called parasitism. e.g. Bacteria, Virus, Cuckoo (Hindi name Koyal, as we know that cuckoos do not build nest their own, but deposit their eggs in the nests of crows) etc.
3. Commensalism: An association between two organism in which one benefits and the other derives neither benefits nor harm is called commensalism. e.g. Remora & Shark (Remora rides under the shark and feeds the leftovers of their host shark’s meals), Tree frog and plants (Tree frog uses plants as their protection), Heron (Bagula) and cattle (cattle egrets eat the insects strirred up by cattle when they are grazing) etc.
4. Predation: Predation is a biological interaction where one organism, the predator, kills and eats another organism, the prey e.g. Grass (prey) & Grass hopper (predator), Small fish (prey) & Large fish (predator) etc.
5. Seprophytism: (Sapro = to decompose). Saprophytism is a mode of nutrition in which organism obtain food from dead organism (non-living organic matterdetritus, organism that feed on dead organismdetritivore/
Glossary (Ecology)
Deep Ecology: The term ‘deep ecology’ was first coined by Norwagian activist and philospher Arnies Naess in 1972. This term is a related to environmentalism. It is considered as a movement or a concept that pleads radical measures to protect the natural environment irrespective of their effects on human welfare. Thus, deep ecology is an ecocentric philosophy or view point of radical environmental movement that considers humans as equal to other organism within the global ecosystem.
The reverse philosophy/view point of deep ecology is ‘shallow Ecology’, It is anthropocentric i.e. human-centric.
Ecosophy The term ‘ecosophy’ was introduced by Arnies Naess. He defined ‘ecosophy’ as a philosophy of ecological harmony or equilibrium in the global natural ecosystem or environmental system.
Ecotone A boundary and/or transition area (zone) between two or more communities or biomes. For example: Estuary (where fresh water and sea water confluent and exchange their water) etc.
Footprint : : The ecological foot print is a method to measure human demand on natural capital. It is expressed as the minimum area of land required to completes sustain the life of a person is called his ecological footprint. It is measured in global hectare (gha). Huminity’s ecological footprint is more than 1.5 that is we require 50% more than the Earth’s are to sustain our consumption of natural resources.
Habitat: The place where an organism lives is called its habitat. For example, the habitat of a whale-Ocean, the habitat of a tiger-forest etc. Habitat also refer to the place occupied by an entire biological community. For example, a large number of species are found in a forest habitat.
Niche : The word Niche is derived from Latin word nidus meaning nest and the word nidus is further converted into French word nicher meaning make a nest. The term Niche was coined by American biologist Joseph Grinnel in 1917. In ecology, Niche means the place of an organism within its community or ecosystem. An ecossytem consists of a number of overlapping and kumineracting niches. A niche is unique for species that means no two species have exact identical niches. Each specie makes or arranges its own distinct nest.
Overshoot : Overshoot means pass swiftly beyond or cross the limit. We are consuming resources faster than they can regenerate and creating waste faster than it can be obsorbed. This is called ecological- overshoot. While this can be done for a short while, overshoot ultimately leads to the drastic depletion of resources on which our well-being depends.
Sere The entire sequence of communities that successively change in a particular area is called ‘sere’. Succession: The successive replacement of communities in an area over a period of time is called ecological succession. Both abiotic and biotic components are involved in such changes. There are two types of succession-Primary and Secondary succession.
Primary Succession : Succession occuring on previously unoccupied sites is called primary succession. For example: Rock out crop, Glacial moraine etc.
Secondary Succession : The reappearance and establishment of communities in the area where once ecological communities existed, but destroyed due to some reasons. For example: Reappearance of forest community in the place of fire-destroyed forest community etc.
Note: The secondary succession starts with the growth of grasses & weeds. Next small plants begin to grow and there after the sequence is similar to that of primary succession.
Transition: The concept of Ecological Transition was first introduced by American anthropologist John W. Bennatt (1915-76) in 1976.
Biosphere: A Giant Ecosystem
What is Biosphere ?
⇒ Biosphere is a combination of two Greek words Bios (=life) and sphaira (=sphere). Biosphere literally means the sphere where life exists. It is the sphere of action between an organism and its environment. Thus, that part of the earth in which living organism are known to exist, comprising the common part of lithosphere, hydrosphere and atmosphere is called Biosphere.
⇒ The biosphere are mostly found in the relatively narrow zones of contact among the lithosphere (exactly, a fraction of crust), hydrosphere (exactly, a limited part of hydrosphere) and atmosphere (exactly, the lower region-troposphere-of atmosphere).
Extension of Biosphere
⇒ The biosphere extends to any place where life of any kind exist.
⇒ According to Irish biogeographer Joy Tivy (1924-95), the ‘Organic world’ or biosphere is that part of earth which containing living organism-the biological inhabited soil (land), air and water.
⇒ The average thickness of the biosphere or life supporting layer of the earth consisting of land (soil), water and air is approximately 30 km (= up to 9 km deep in the water + 9 km over the land surface + up to 12 km above in the air rougly).
⇒ Most living organisms actually live within a small area in the biosphere, from 500 metres below the surface of the ocean to 6,000 metres above the sea level.
⇒ The biosphere is absent at extremes of the North & South pole, at the highest mountains and in the deepest oceans, because of existing hostile conditions that do not support life. Occasionally spores of bacteria and fungi do found at great height beyond 8,000 metres, but they are not metabolically active, so they represent dormant life only.
Upper limit (in air)
⇒ The upper limit of the biosphere is determined by availability of oxygen, moisture, temperature and air pressure with increase in height in the atmosphere limits the upper boundary of the biosphere.
⇒ Though NASA has detected the presence of bacteria up to the height of 15 km in the atmosphere, but the lower layer of atmosphere up to a few thousand meters accounts the most of the living organisms because favourable enviornment conditions are available for the growth and development of living organism in the lower part of the atmosphere.
Lower Limit:
(a) Overland: The lower limit of biosphere are determined by the availability of required amount of oxygen and light which can sustain life. Thus, the depth of the biosphere over the land is depth of the deepest roots of the trees or depth up to which can live the burrowing organism or the depth at which lie the parent bed-rocks.
(b) In water: The existence of life has been detected up to a depth of 9 km in the deep oceanic trenches and deep sea plants.
Diagramatic Representation of Biosphere
⇒ Diagramatic representation of biosphere is given below –
⇒ Biosphere is displayed by shaded area of diagram.
⇒ From above-mentioned diagram, it is very clear that biosphere is not a separate or fourth sphere of the earth as many think, but it is the common part of the lithosphere, hydrosphere and atmosphere where life exists.
⇒ Our earth is an unique planet in having a biosphere. Biosphere is a life supporting layer which surrounds the earth and makes life of organism possible without any protective device.
⇒ There are a variety of organism in the biosphere. They are broadly divided into the plants, animals and microbes. More than 3 lacs plant species and 10 lacs animal species known to exist.
⇒ These organism exist in the zones of contact among lithosphere, hydrosphere and atmosphere. There is exchange of matter and energy among these three constituents of physical environments and the organisms in the biosphere.
The Sun: Driving Force of Ecosystem
⇒ The Sun is the primary sustainer of life on the Earth. Energy from the sun flows through materials and living organism and eventually goes back into space as in the form of heat. Only a tiny part of the Sun’s energy falls on earth, but that is enough to keep ecosystem going.
⇒ The Sun is the driving force of an ecosystem. The Sun is the main source of energy which causes changes in the environment. We are very familiar with the day to day changes in weather and seasonal changes in climate. These changes are the result of differences brought in the heating of the earth and its atmosphere by the Sun. Similarly, other enviromental changes occured by the solar energy. A field of wheat, a herd of cattle, a crowd of people and a shoal of fish represent example of solar energy stored in various forms.
Importance of Biosphere
⇒ Though the biosphere is a relatively thin layer of the earth, but it has great significance to our life.
⇒ The biosphere provide a variety of food and also raw materials which provide clothing and shelter and other needs of man.
⇒ Therefore, it is necessary to understand the relationship of organism to one another and to their physical environment.
⇒ Plants, animals and other organism together with the physical environment with which they interact constitute the Ecological system, in short, Ecosystem.
⇒ The term ecosystem was coined by English botanist Arthur Tanslay in 1935.
Types of Ecosystem
⇒ There are two types of ecosystem-Natural/
1. Natural/Non-cultivated Ecosystem:Naturalecosystem is subdivided into two categories Terrestrial (landrelated) and Aquatic (Water-related).
(a) Terrestrial (land-related): For example, Forest, Grassland, Desert etc.
(b) Aquatic (water-related): For example, Salty water (marine, estuary etc.), Fresh water (Stream, Lake, Pond etc.).
2. Artificial/Cultivated Ecosystem Human activities may modify or convert natural ecosystem into anthropogenic or man-made ecosystem. Generally, natural forests have been cut and land converted to agricultural system or plantation. Often, dam construction invades submergence of forests and conversion to water reservoires. For example, Crop field, Park, Spacecraft, Swimming pool, Well, Aquarium etc.
Components of Ecosystem :
⇒ An ecosystem consists of both abiotic/non-living and biotic/living components.
1. Abiotic/Non-living Component
⇒ Abiotic components of an ecosystem consist of lithospheric, hydrospheric and atmospheric components, which are generally considered as land / soil, water and air respectively. Actually, chemical substances (whether organic or inorganic) found in land, water and air and other climatic elements (such as light, temperature, rainfall etc.)make together aboitic components of ecosystem.
⇒ In this way, abiotic components of ecosystem is categorized in three categories –
(i) Inorganic Materials: For example, water, oxygen, carbon dioxide and minerals like phosphate, nitrate etc.
(ii) Organic Materials: For example, carbohydrate, fats, proteins, vitamins etc.
(iii) Climatic Elements: For example, light, temperature, rainfall etc.
⇒ The amount of abiotic component that is present at a particular time in a given area is known as ‘standing state’.
⇒ In ecosystem, abiotic matter keeps changing into biotic matter and biotic matter into abiotic matter continuously. This process is called Bio-chemical Cycle.
2. Biotic/Living Component
⇒ Plants together with animals constitute the biotic/ living component of ecosystem.
⇒ The biotic components are broadly divided into two major groups-the producers and the consumers.
(i) The Producers: The producers are organisms which produce their own food from the physical environment. These are called autotrophic [auto (= self) + trophic (= nourishing) = self-nourishing] organisms. Green plants are Primary Producers, as they take simple inorganic substances from their abiotic environment and make complex molecules utilising Sun’s radiant energy. These are the only organisms in an ecosystem that can trapenergy from the Sun and make new organic materials. All other organism in this world are directly or indirectly dependent on the producers for their food. The process used by the producers to convert inorganic materials into organic matters is called photosynthesis. The green plant takes water from the soil, carbon dioxide from the atmosphere and energy from the sun to make a kind of sugar molecule. In the process, it gives out oxygen. The presence of green pigment called chlorophyll in the leaves of plants makes photosyn thesis possible. Hence, we can say that photosynthesis takes place in the leaves of the plants.
In ocean waters, phytoplanktons are primary producers as they produce their own food using solar energy.
Note: During photosynthesis process, 50% of total energy is absorbed by the plants, and at most 5% (i.e. 10% of energy absorbed) of that is converted into organic energy under the most favourable condition. Under the adverse condition the rate of energy conversion decreases. This means 1-10% of absorbed solar energy is converted into organic energy by plants through photosynthesis.
(ii) Consumers: The organisms that depend on other organisms for their food are called Consumers or heterotrophic [Haetero (= other) + trophic (= feeding) other feeding) or Phagotrophs (phago = to devour). Consumers of an ecosystem are categorized into four catergories.
(a) Primary Consumer: An organism that feeds only on plant is called Herbivore or Primary Consumer. For example, rabbit, goat, deer, cow, buffallo etc.
(b) Secondary Consumer An organism that feeds on primary consumers is called (primary) Carnivore (meat-eater) or Secondary Consumer. For example, insect eating frog, mouse eating cat, deer eating fox, edible meat eating man etc.
Omnivore (Herbivore + Carnivore): Some organisms may be omnivore i.e. both herbivore and carnivore. Omnivores are able to eat both plants and animals (e.g. cockroach, rat, pig, fox, bear, human being (man) etc. Whenever they eat plants, they are treated as primary consumers and whenever they eat animals, they treated as secondary consumers. It can be seen in the case of human being (man), when he depends only on plants (such as vegetables, seeds, fruits etc.), he is herbivore or vegetarian and considered as primary consumer, but when he depends only on animals (such as chicken, mutton etc) he is carnivore (meateater) or non-vegetarian and considered as secondary consumer. But, when he depends on both plants and animals, he is omnivore (vegetarian + non vegetarian) and considered as primary consumer together with secondary consumer.
Note: Human being (man) may also be a tertiary consumer when he eats the big fish that eats the smaller fish that eats the algae.
(c) Tertiary Consumer: Aconsumer that feeds on secondary consumer is called tertiary consumer. Tertiary consumer includes top/secondary carnivore (e.g. tiger, lion etc). Which can not eat plants but depends only on meat. Top carnivore stands at top level of carnivore and they can not be eaten by other animals.
(d) Quaternery Consumer or Decomposer: A fourth group of consumer feeds on dead or decomposed tissues of plants and animals. They are called Quaternery Consumer or Decomposers or Saprotrophs (Sapro = to decompose) or Detritus feeders/Detrivore e.g. bacteria, fungi (Hindi fafund), termite (Hindi Deemak), maggot, ant earthworm (Hindi jonk), millipede (Hindi Kankhajura), crayfish etc. Apart from getting energy and nutrients from the plants and animals the decomposers convert organic materials into inorganic substances. They release simple substances to the environment as by-products of their metabolism. These are taken up by green plants and help in completing the cycle of soil nutrients. In this way, indefinite cycle goes on.
Note: Bacteria are both decomposer and producer. Virus is not considered as a decomposer because it is neither live nor dead.
Ecological Classification of Plants
On the basis of ecology, Danish botanist Eugenius Warming (1841-1924) classified plants into five classes as follows: Hydrophytes (Hydro (= water) + phytes (= plants)], Mesophytes (Meso = middle), Xerophytes (Xero= dry), Physiologically dry plants in soil and functionally dry plants in soil.
Food Chain
⇒ All organism, including humans need food which provides energy for growth, maintenance and reproduction.
⇒ A part of the energy provided by food is used for biological processes and the rest is dissipated to the environment as heat energy by the process of respiration. Undigest food is excreted and enters the detritus path.
⇒ Food energy passes from plants & planktons to animals in a chain called food chain.
On the land: Food chain is a sequence of organism in a community each of which uses the next lower member of the sequence as a food source, plants & plankons being at the base of sequence on the land surface. The starting point in a food chain is always a green plants.
In the Seas & Oceans: Similarly, there are plankons in the seas and oceans which use sunlight to help them make their food. Fish shellfish and other crustaceans eat the plankon. These animals are eaten by bigger animals such as sharks and whales. Whales are killed by man for meat.
In deep sea and oceans, a different process called chemosynthesis takes place. Here specialized bacteria convert simple compounds from their surroundings into more complex compounds without sunlight. They use instead, a different source of energy. Deep in the Earth’s surface, heat is generated by the decay of radioactive elements. This heat is released at hot water vents in the ocean depths. The bacteria use this geo-thermal energy for chemosynthesis. Later, these bacteria are consumed by many aquatic animals.
⇒ Types of food chain: There are two types of food chain— simple & complex food chain. Complex food chain is also called food web.
1. Simple Food Chain : In a grassland, grass is eaten by grasshopper, grasshopper is eaten by snake and snake is eaten by hawk. This is a simple food chain. Another examples of simple food chain : Insect < Frog < Snake < Hawk; Grass < Rabbit < Fox; Grass < Deer < Lion; Diatom <Crustacean < Herring and so on.
2. Complex Food Chain i.e. Food Web :In cases where some organism eat a variety of other organism, food chain becomes more complex, such complicated network of food chain is called a food web. As a variety of organism live in the ecosystem and there is competition for food among them, food webs are very complex. Realistically, almost all ecosystems have food webs, not merely food chains.
Ecological Pyramid of Trophic (Feeding) Levels
⇒ Each group of organism occupies a trophic or feeding level.
⇒ Trophic levels are classified as follows:
1. First Trophic Level:All green plants and other producers in the ecosystem occupy the first trophic level.
2. Second Trophic Level: Herbivores which feed on plants are placed at the second trophic level.
3. Third Trophic Level: (Primery) carnivores that eat herbivores occupy third trophic level.
4. Fourth Trophic Level: Top/Secondary carnivores that eat carnivore are placed at fourth trophic level.
Ecological Efficiency and 10 Percent Law (Lindeman’s 10% Law)
⇒ The different trophic levels are not equal in terms of energy available, as only a fraction of energy is transferred from lower to higher trophic level.
⇒ The percentage of energy transferred from one trophic level to another trophic level is called Ecological Efficiency. The efficiency of energy transfer from one trophic level to another trophic level varies from 5% to 20% depending on the types of organism and environmental conditions.
⇒ The 10% law of transfer of energy was introduced by American ecologist Raymond Lindeman (1915-42) in 1942. In the terrestrial (land-related) ecosystem, only 10% of plant material is eaten by herbivore. That means on an average only 10% of energy is transferred from one tropic level to another trophic level. This means 100 kg of grain is needed to produce 10 kg of meat.
⇒ Such low efficiency is due to the fact that not all the organisms present at one level become easily available as food for the consumers at higher level. Predators may not able to capture all the prey available. Those organism which escape the predators eventually die and they provide food for the decomposers.
⇒ Because ecological efficiency is low, the capacity of ecosystem to support organisms at the higher trophic level is limited.
Energy and Matter Movement
⇒ A model of energy and nutrient movement in the ecosystem is discussed here. The sun provides radiant energy for the producer to manufacture food. The energy is transferred from producer to herbivores and then to the carnivore. Dead or decomposed remains of producers, herbivores and carnivores provide energy for the decomposers.
⇒ While a part (10%) of the food energy consumed is assimilated by organism, rest (90%) of it is dissipated as heat by respiration. Respiration : Respiration process is the reverse of photosynthesis process. In the respiratoin process, the sugar molecule broken down in the presence of oxygen and water into carbon dioxide, energy and water is released. Sugar + Oxygen + Water → Carbon dioxide + energy+ water.
⇒ There is uni-directional flow of energy from the sun until is dissipated as heat into space.
⇒ The movement of nutrient element through various components of an ecosystem is called Bio-geo-chemical cycle.
⇒ The movement of matter in the form of mineral nutrient from the soil to the plants helps in the growth of the plants. These nutrient are consumed by herbivores and carnivores for their growth. When the plants and other organisms die, decomposers like bacteria and fungi feed on them and break then down into inorganic nutrients. These are available in the soil to be recycled by plants. The flow of mineral nutrients through the system is cyclic.
⇒ With respect to matter, the earth is essential a closed system. Matter cannot escape from its boundries. In the words of Physics, energy can neither be created nor destroyed; it can only be transferred one form to another form (Law of conservation of Energy).
⇒ The ecological system maintain its stability by continuous input of energy from the Sun and the cyclic movement of nutrient through the system.
Bio-geo-chemical Cycle
⇒ The term biogeochemical is a contraction/abbreviation that refers to the consideration of the biological, geological and chemical aspects of each cycle.
⇒ Any of the natural cycles by which essential elements of living matter are circulated called Bio-geo-chemical Cycle. For example: Water-cycle, Carbon-cycle Nitrogen cycle, Oxygen-cycle, Phosphorous-cycle etc. Biogeochemistry: It is a branch of science that was founded by Russian geochemist and mineralogist Vladimir Ivanovich (V.I) Vernadsky (1863-1945) in 1926. Carbon-Cycle : An Example of Bio-geo-chemical Cycle
⇒ Carbon dioxide constitutes just 0.03% by volume of the atmosphere, but yet it is vital to life (Note: The percentage of carbon dioxide in the dissolved gaseous state/form present in the water is 0.3%). Plants take carbon from carbon dioxide in the air and they chlorophyll to gather energy from the Sun. From these inputs and water, plants make glucose. In this process of photosynthesis, plants release oxygen. Animals breathe in this oxygen, digest their food thats comes from plants. This is called carbon-cycle. In the words of mathematics:
Photosynthesis process + Respiration process of organism + Combustion process of coal, oil etc. = Carbon-cycle.
⇒ When we burn fossil fuels like coil, oil etc., the carbon in the fuel combines with atmospheric oxygen to form carbon dioxide. This is called combustion process.
⇒ Since we burn a lot of fuel, there is a huge emmission of carbon dioxide. This increase in carbon dioxide concentration upsets the carbon balance in the atmosphere.
⇒ There are not enough growing plants to absorb all the excess carbon dioxide.
⇒ Things become worse when we cut down forests and burn more trees.
⇒ The current excessive level of carbon dioxide however, leads to a higher temperature, global warming and climate change.
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