Ecosystem is the functional unit of nature where living organisms interact among themselves and also with the surrounding physical environment.
The word ecosystem was coined by A.G. Tansley in 1935.
Types of Ecosystem
Terrestrial ecosystem – forest, grassland, desert etc.
Aquatic ecosystem – ponds, lake, river estuary etc.
Crop fields and aquariums are considered as man-made ecosystems.
Structure and Function
Components of ecosystem
Abiotic factors: This ecosystem includes the non–living substances of the environment. Ex: water, soil, air, light, temperature, minerals, climate, pressure etc.
Biotic factors: This ecosystem includes the living organisms of the environment. Ex: plants, animals, bacteria, viruses etc.
The biotic factors of the ecosystem depend on the abiotic factors for their survival.
Stratification is the vertical distribution of the different species occupying the different levels. Eg: trees occur at a higher level than shrubs.
Functions of ecosystem
Productivity
Decomposition
Energy flow
Nutrient cycling
Productivity
$\displaystyle \small \bullet$ A constant supply of sunlight is required for the proper functioning of any ecosystem.
Productivity: Rate of biomass production is called productivity. It is expressed in $\displaystyle \small g^{-2}yr^{-1}$ or $\displaystyle \small (kcal m^{-2})yr^{-1}$.
Primary productivity: The amount of biomass produced per unit area over a time period by plants during photosynthesis. It is expressed as weight ($\displaystyle \small g^{-2}$) or energy ($\displaystyle \small (kcal m^{-2})).
$\displaystyle \small \bullet$ Productivity can be mainly divided into gross primary productivity (GPP) and net primary productivity (NPP).
Gross primary productivity (GPP): Rate of production of organic matter during photosynthesis.
Net primary productivity (NPP): gross primary productivity minus respiratory losses (R).
$\displaystyle \small \bullet$ NPP = GPP - Respiratory losses (R)
$\displaystyle \small \bullet$ NPP is the available biomass for consumption to heterotrophs.
$\displaystyle \small \bullet$ Primary productivity of an ecosystem depends on:
(a) Plant species inhabiting a particular area.
(b) Availability of nutrients.
(c) Photosynthetic capacity of plants.
(d) Variety of environmental factors.
Secondary productivity is defined as the rate of formation of new organic matter by consumers.
$\displaystyle \small \bullet$ Annual net primary productivity of the whole biosphere is about 170 billion tons (dry weight) of organic matter. Of this, despite of occupying about 70% of the surface of earth, the productivity of the oceans are only 55 billion tons.
Decomposition
$\displaystyle \small \bullet$ It is the process in which decomposers breakdown complex organic matter into inorganic substances like carbon dioxide, water and nutrients.
Detritus: dead remains of plants and animals such as leaves, barks, flowers, faecal matter of animals.
Detritivores: the organisms which feed on detritus are called detritivores. Ex. Earthworm, fungi etc.
$\displaystyle \small \bullet$ Steps of decomposition
Fragmentation - Breaking down of detritus into smaller particles by detritivores.
Leaching - Process by which these inorganic matters enter the soil
Catabolism - Process by which detritus is degraded into simpler inorganic substances by bacterial and fungal enzymes
Humification - Accumulation of humus in the soil. Humus is a Dark, Amorphous substance. Humus is resistant to microbial action and decomposes at an extremely slow rate. It acts as a reservoir of nutrients.
Mineralization - Process by which humus further degrades to release minerals into the soil ($\displaystyle \small Ca^{2+}$, $\displaystyle \small Mg^{2+}$,$\displaystyle \small K^{+}$ etc.).
$\displaystyle \small \bullet$ Factors affecting rate of Decomposition
(a) Oxygen availability
(b) Chemical composition of detritus
(c) Climatic factors
(d) Temperature and soil moisture
$\displaystyle \small \bullet$ Decomposition rate is slower, if detritus is rich in lignin and chitin.
$\displaystyle \small \bullet$ It is quicker, if detritus is rich in nitrogen and water soluble substances like sugars.
$\displaystyle \small \bullet$ Warm and moist environment speeds up decomposition, whereas low temperature and anaerobiosis inhibits decomposition and causes the formation of organic materials.
Energy Flow
$\displaystyle \small \bullet$ Plants and other photosynthetic organisms utilize less than 50% of the solar radiation known as the photosynthetically active radiation (PAR).
$\displaystyle \small \bullet$ The plants are able to capture only 2-10% of PAR.
$\displaystyle \small \bullet$ There is a unidirectional flow of energy from sun to producers and then to consumers, hence all the organisms depend on sun for their energy.
$\displaystyle \small \bullet$ In an ecosystem, plants are called producers and all animals depend upon the plants directly or indirectly for their food. Hence, they are known as consumers or heterotrophs.
$\displaystyle \small \bullet$ The animals which eat herbs are called primary consumers or herbivores. Eg: goat.
$\displaystyle \small \bullet$ The animals which eat herbivores are called secondary consumers or primary carnivores. Eg- birds, wolf.
$\displaystyle \small \bullet$ The animals which eat the primary carnivores are called tertiary consumers or secondary carnivores. Eg: man
$\displaystyle \small \bullet$ Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level.
$\displaystyle \small \bullet$ Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.
$\displaystyle \small \bullet$ Producers belong to the first trophic level, herbivores (primary consumer) belong to the second and carnivores (secondary consumer) belong to the third trophic level.
$\displaystyle \small \bullet$ Food chain is the flow of energy from one trophic level to another trophic level by eating and being eaten.
$\displaystyle \small \bullet$ Types of Food chain
Grazing food chain: Food chain which starts from producers and ends on carnivores through herbivores is called grazing food chain.
Grass --> goat --> man.
Detritus food chain: Food chain which starts from dead organic matter and passes through detrivores to organisms feeding on detrivores is called detritus food chain.
$\displaystyle \small \bullet$ Detrivores are decomposers which meet their energy and nutrient requirements by degrading dead organic matter or detritus, these are also known as saprotrophs.
$\displaystyle \small \bullet$ Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials.
$\displaystyle \small \bullet$ The interconnected matrix of food chain is called food web.
$\displaystyle \small \bullet$ Ten percent law: Proposed by Lindemann in 1942, states that "during transfer of energy from one trophic level to another, only about 10% is stored at higher levels; remaining 90% is lost in respiration (heat)".
Ecological Pyramids
$\displaystyle \small \bullet$ The energy relationship between the different trophic levels is represented by the ecological pyramids.
$\displaystyle \small \bullet$ The base of a pyramid is broad and it narrows down at the apex.
$\displaystyle \small \bullet$ The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.
$\displaystyle \small \bullet$ Types of ecological pyramids
Pyramid of number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number.
Pyramid of biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be of two types:
a) Upright (in case of grassland ecosystem)
b) Inverted (in case of pond ecosystem).
Pyramid of energy: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of flow of energy called pyramid of energy. It is always upright.
Limitations of ecological pyramids
$\displaystyle \small \bullet$ The ecological pyramids do not take into account the same species belonging to more than one trophic level.
$\displaystyle \small \bullet$ It assumes a simple food chain that almost never exists in nature. It does not explain food webs.
$\displaystyle \small \bullet$ Saprophytes are not given a place in ecological pyramids even though they play a vital role in ecosystem.
The word ecosystem was coined by A.G. Tansley in 1935.
Types of Ecosystem
Terrestrial ecosystem – forest, grassland, desert etc.
Aquatic ecosystem – ponds, lake, river estuary etc.
Crop fields and aquariums are considered as man-made ecosystems.
Structure and Function
Components of ecosystem
Abiotic factors: This ecosystem includes the non–living substances of the environment. Ex: water, soil, air, light, temperature, minerals, climate, pressure etc.
Biotic factors: This ecosystem includes the living organisms of the environment. Ex: plants, animals, bacteria, viruses etc.
The biotic factors of the ecosystem depend on the abiotic factors for their survival.
Stratification is the vertical distribution of the different species occupying the different levels. Eg: trees occur at a higher level than shrubs.
Functions of ecosystem
Productivity
Decomposition
Energy flow
Nutrient cycling
Productivity
$\displaystyle \small \bullet$ A constant supply of sunlight is required for the proper functioning of any ecosystem.
Productivity: Rate of biomass production is called productivity. It is expressed in $\displaystyle \small g^{-2}yr^{-1}$ or $\displaystyle \small (kcal m^{-2})yr^{-1}$.
Primary productivity: The amount of biomass produced per unit area over a time period by plants during photosynthesis. It is expressed as weight ($\displaystyle \small g^{-2}$) or energy ($\displaystyle \small (kcal m^{-2})).
$\displaystyle \small \bullet$ Productivity can be mainly divided into gross primary productivity (GPP) and net primary productivity (NPP).
Gross primary productivity (GPP): Rate of production of organic matter during photosynthesis.
Net primary productivity (NPP): gross primary productivity minus respiratory losses (R).
$\displaystyle \small \bullet$ NPP = GPP - Respiratory losses (R)
$\displaystyle \small \bullet$ NPP is the available biomass for consumption to heterotrophs.
$\displaystyle \small \bullet$ Primary productivity of an ecosystem depends on:
(a) Plant species inhabiting a particular area.
(b) Availability of nutrients.
(c) Photosynthetic capacity of plants.
(d) Variety of environmental factors.
Secondary productivity is defined as the rate of formation of new organic matter by consumers.
$\displaystyle \small \bullet$ Annual net primary productivity of the whole biosphere is about 170 billion tons (dry weight) of organic matter. Of this, despite of occupying about 70% of the surface of earth, the productivity of the oceans are only 55 billion tons.
Decomposition
$\displaystyle \small \bullet$ It is the process in which decomposers breakdown complex organic matter into inorganic substances like carbon dioxide, water and nutrients.
Detritus: dead remains of plants and animals such as leaves, barks, flowers, faecal matter of animals.
Detritivores: the organisms which feed on detritus are called detritivores. Ex. Earthworm, fungi etc.
$\displaystyle \small \bullet$ Steps of decomposition
Fragmentation - Breaking down of detritus into smaller particles by detritivores.
Leaching - Process by which these inorganic matters enter the soil
Catabolism - Process by which detritus is degraded into simpler inorganic substances by bacterial and fungal enzymes
Humification - Accumulation of humus in the soil. Humus is a Dark, Amorphous substance. Humus is resistant to microbial action and decomposes at an extremely slow rate. It acts as a reservoir of nutrients.
Mineralization - Process by which humus further degrades to release minerals into the soil ($\displaystyle \small Ca^{2+}$, $\displaystyle \small Mg^{2+}$,$\displaystyle \small K^{+}$ etc.).
$\displaystyle \small \bullet$ Factors affecting rate of Decomposition
(a) Oxygen availability
(b) Chemical composition of detritus
(c) Climatic factors
(d) Temperature and soil moisture
$\displaystyle \small \bullet$ Decomposition rate is slower, if detritus is rich in lignin and chitin.
$\displaystyle \small \bullet$ It is quicker, if detritus is rich in nitrogen and water soluble substances like sugars.
$\displaystyle \small \bullet$ Warm and moist environment speeds up decomposition, whereas low temperature and anaerobiosis inhibits decomposition and causes the formation of organic materials.
Energy Flow
$\displaystyle \small \bullet$ Plants and other photosynthetic organisms utilize less than 50% of the solar radiation known as the photosynthetically active radiation (PAR).
$\displaystyle \small \bullet$ The plants are able to capture only 2-10% of PAR.
$\displaystyle \small \bullet$ There is a unidirectional flow of energy from sun to producers and then to consumers, hence all the organisms depend on sun for their energy.
$\displaystyle \small \bullet$ In an ecosystem, plants are called producers and all animals depend upon the plants directly or indirectly for their food. Hence, they are known as consumers or heterotrophs.
$\displaystyle \small \bullet$ The animals which eat herbs are called primary consumers or herbivores. Eg: goat.
$\displaystyle \small \bullet$ The animals which eat herbivores are called secondary consumers or primary carnivores. Eg- birds, wolf.
$\displaystyle \small \bullet$ The animals which eat the primary carnivores are called tertiary consumers or secondary carnivores. Eg: man
$\displaystyle \small \bullet$ Based on the source of their nutrition or food, organisms occupy a specific place in the food chain that is known as their trophic level.
$\displaystyle \small \bullet$ Each trophic level has a certain mass of living material at a particular time called as the standing crop. The standing crop is measured as the mass of living organisms (biomass) or the number in a unit area.
$\displaystyle \small \bullet$ Producers belong to the first trophic level, herbivores (primary consumer) belong to the second and carnivores (secondary consumer) belong to the third trophic level.
$\displaystyle \small \bullet$ Food chain is the flow of energy from one trophic level to another trophic level by eating and being eaten.
$\displaystyle \small \bullet$ Types of Food chain
Grazing food chain: Food chain which starts from producers and ends on carnivores through herbivores is called grazing food chain.
Grass --> goat --> man.
Detritus food chain: Food chain which starts from dead organic matter and passes through detrivores to organisms feeding on detrivores is called detritus food chain.
$\displaystyle \small \bullet$ Detrivores are decomposers which meet their energy and nutrient requirements by degrading dead organic matter or detritus, these are also known as saprotrophs.
$\displaystyle \small \bullet$ Decomposers secrete digestive enzymes that breakdown dead and waste materials into simple, inorganic materials.
$\displaystyle \small \bullet$ The interconnected matrix of food chain is called food web.
$\displaystyle \small \bullet$ Ten percent law: Proposed by Lindemann in 1942, states that "during transfer of energy from one trophic level to another, only about 10% is stored at higher levels; remaining 90% is lost in respiration (heat)".
Ecological Pyramids
$\displaystyle \small \bullet$ The energy relationship between the different trophic levels is represented by the ecological pyramids.
$\displaystyle \small \bullet$ The base of a pyramid is broad and it narrows down at the apex.
$\displaystyle \small \bullet$ The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.
$\displaystyle \small \bullet$ Types of ecological pyramids
Pyramid of number: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of number called pyramid of number.
Pyramid of biomass: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of biomass called pyramid of biomass. It can be of two types:
a) Upright (in case of grassland ecosystem)
b) Inverted (in case of pond ecosystem).
Pyramid of energy: The relationship between producers and consumers in an ecosystem can be represented in the form of a pyramid in terms of flow of energy called pyramid of energy. It is always upright.
Limitations of ecological pyramids
$\displaystyle \small \bullet$ The ecological pyramids do not take into account the same species belonging to more than one trophic level.
$\displaystyle \small \bullet$ It assumes a simple food chain that almost never exists in nature. It does not explain food webs.
$\displaystyle \small \bullet$ Saprophytes are not given a place in ecological pyramids even though they play a vital role in ecosystem.
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