3 Environmental Science : Ecosystem part 2
FUNCTION OF AN ECO-SYSTEM
For a fuller understanding of ecosystems a fuller understanding of their functions
besides their structures is essential. The function of ecosystems includes, the process how
an eco-system works or operates in normal condition.
From the operational viewpoint, the living and non-living components of ecosystem are
interwoven into the fabric of nature. Hence their separation from each other becomes
practically very much difficult. The producers, green plants, fix radiant energy and with the
help of minerals (C, O, N, P, L, Ca, Mg, Zn, Fe etc.) taken from their soil and aerial
environment (nutrient pool) they build up complex prefer to call the green plants as converters
or transducers because in their opinion the terms ‘producer’ form an energy viewpoint which
is somewhat misleading. They contend that green plants produce carbohydrates and not
energy and since they convert or transducer radiant energy into chemical form, they must
be better called the converters or transducers. However, the term’ producer’ is so widely
used that it is preferred to retain it as such.
While considering the function of an ecosystem, we describe the flow of energy and the
cycling of nutrients. In other words, we are interested in things like how much sunlight
plants trap in a year, how much plant material is eaten by herbivores, and how many
herbivores carnivores eat.
Functions of Eco-system
The functions of Ecosystem are as under:
1. Transformation of Solar Energy into Food Energy
The solar radiation is major source of energy in the ecosystem. It is the basic input of
energy entering the ecosystem. The green plants receive it. And is converted into heat
energy. It is lost from the ecosystem to the atmosphere through plant communities. It is
only a small proportion of radiant solar energy that is used by plant to make food through
the process of photosynthesis. Green plants transform a part of solar energy into food energy
or chemical energy. The green plants to develop their tissues use this energy. It is stored
in the primary producers at the bottom of trophic levels. The chemical energy, which is
stored at rapid level one, becomes the source of energy to the herbivorous animals at trophic
level two of the food chain. Some portion energy is lost from trophic level one through
respiration and some portion is transfereed to plant-eating animals at trophic level two.
2. The Circulation of elements through Energy Flow
It is seen that in the various biotic components of the ecosystem the energy flow is the
main driving force of nutrient circulation. The organic and inorganic substances are moved
reversibly through various closed system of cycles in the biosphere, atmosphere, hydrosphere
and lithosphere. This activity is done in such a way that total mass of these substances
remains almost the same and is always available to biotic communities.
3. The Conversion of Elements into Inorganic Flow
The organic elements of plants and animals are released in the under mentioned ways:
(i) Decomposition of leaf falls from the plants dead plants and animals by decomposers
and their conversion into soluble inorganic form.
(ii) Burning of vegetation by lighting, accidental forest fire or deliberate action of man.
When burnt, the portions of organic matter are released to the atmosphere and
these again fall down, under the impact of precipitation, on the ground. Then they
become soluble inorganic form of element to join soil storage, some portions in the
form of ashes are decomposed by bacterial activities.
(iii) The waste materials released by animals are decomposed by bacteria. They find
their way in soluble inorganic form to soil storage.
4. The Growth and Development of Plants
In the biogeochemical cycles are included the uptake of nutrients of inorganic elements
by the plants through their roots. The nutrients are derived from the soil where these
inorganic elements are stored. The decomposition of leaves, plants and animals and their
conversion into soluble inorganic form are stored into soil contributing to the growth and
development of plants. Decompositions are converged into some elements. These elements
are easily used in development of plant tissues and plant growth by biochemical processes,
mainly photosynthesis.
5. Productivity of ecosystem
The productivity of an ecosystem refers to the rate of production i.e. the amount of
organic matter, which is accumulated in any unit time. Productivity is of the following types:
(1) Primary productivity: It is associated with the producers which are autotrophic,
Most of these are photosynthetic, Thus, they are, to a much lesser extent the
chemosynthetic micro organisms. These are the green plants, higher saprophytes
as well as lower forms, the phytoplankton’s and some photosynthetic bacteria. We
can define Primary productivity as “the rate at which radiant energy is stored by
photosynthetic and chemosynthetic activity of producers.” Primary productivity is
further distinguished as:
Gross primary productivity: Gross Primary Productivity is the rate of storage of
organic matter in plant tissues in excess of the respiratory utilization by plants
during the measurement period. This is, thus, the rate of increases of biomass. In
this way, net primary productivity refers to balance between gross photosynthesis
and respiration and other plant losses as death etc.
(2) Secondary productivity: These are the rates of energy storage at consumers
level. Since consumers only utilize food materials (already produced) in their
respiration, simply covering the food matters to different tissues by an overall
process. The secondary productivity is not divided into ‘gross’ and ‘net’ amount.
(3) Net Productivity: Net productivity refers to the rate of storage of organic matter not
used by the heterotrophs (consumer) i.e. equivalent to net primary production minus
consumption by the heterotrophs during the unit period. It is thus the rate of increase
of biomass of the primary producers, which has been left over by the consumers.
(4) Stability of Ecosystem: The stability of ecosystems refers to the balance between
production and consumption of each element in the ecosystem. In other words,
balance between input and output of energy and normal functioning of different
biogeochemical cycles and stable conditions of equilibrium as under:-
(i) The Equilibrium Model: The equilibrium model states that an ecosystem,
always tends towards stability. As soon as the community of an ecosystem is
disturbed due to external environmental change, it quickly returns to original
state where as.
(ii) The non-equilibrium model: The non-equilibrium model states that an
ecosystem stability is rarely attained because disturbances caused by frequent
external environmental change do not allow to develop ordered state of species
assemblages in an ecosystem.
DECOMPOSERS
In this world all living organisms require a constant supply of nutrients for growth. The
death and decomposition of plants and animals, with release of nutrients constitutes an
essential link in the maintenance of nutrient cycles. When an organism dies, an initial
period of rapid leaching takes place and populations of macromolecules. The dead organism
is disintegrated beyond recognition. Enzymic action breaks down the disintegrating parts of
the litter. Animals invade and either eat the rapidly recolonized by micro- organisms, and
the litter biomass decreases. It becomes simpler in structure and chemical composition.
Process of Decomposition
The process of decomposition involves three interrelated components, viz.
(i) Leaching (ii) Catabolism, (iii) Comminution.
1. Leaching
Leaching is a physical phenomenon operating soon-after litter fall. Soluble matter is
removed from detritus by the action of water. Sometime over 20% of the total nitrogen
content of litter maybe leached off.
2. Catabolism
The process in a plant or animal by which living tissue is changed into waste products.
3. Comminution
Comminution to make small to reduce to power or minute particles. Comminution
means the reduction in particle size of detritus. During the course of feeding, the decomposer
animals community detritus physically. And utilize the energy and nutrients for their own
growth (secondary production). In due course, the decomposers themselves die and contribute
to the detritus.
Function of Decomposition
The two major functions of decomposition within ecosystems are as under:-
(1) The mineralization of essential elements,
(2) The formation of soil organic matter to inorganic form.
The formation of soil organic matter in nature is a slow process. The decomposition of
any piece of plant detritus may take hundreds of years to complete. However, some residues
of decomposition within this period do contribute to the formation of soil organic matter.
Community of Decomposer Organisms
The community of decomposer organisms includes several bacteria, fungi, protests and
invertebrates. The different species in such a community function in an integrated manner.
For example, a fungus decomposes plant litter and is eaten by an animal. Upon death,
bacteria decompose the animal, and protozoa may eat the bacteria.
Fungi and bacteria are the principal organisms that break down organic matter. Certain
protozoa, nematodes, annelids and arthopods strongly influence their functioning (i.e. of
fungi and bacteria) due to their feeling activities. Microarthopod fauna, comprising mainly
of oribatid mites besides other mites and collembolans, are abundant in most forest, grassland
and desert ecosystem.
Most of these micro-arthropods are predominantly fungal-feeders. They can do as under:
(1) They can decompose substrata.
(2) They can decrease substrata’s mass by leaching soluble intercellular components.
(3) They can do so by oxidation.
(4) They can physically cut in into smaller fragments.
Increased mineralization of nitrogen, phosphorus and potassium has been reported to
be mediated by microarhropods in several studies.
In the same way, the interactions of micro-arthropods with soil fungi are also quite
important in nutrient cycling. Studies of this aspect are made in mycorrhizal fungi and
themicro-arthropods which feed upon these fungi:
(1) It is found that Mycorrhizal pump massive amounts of nutrients form detritus and
represent a sizable nutrient reservoir themselves.
(2) The orbited mites and other micro-arthropods feed on myocardial fungi they act like
herbivorous pests, and can alter nutrient relations/cycling in terrestrial ecosystems.
Table 3.1 : Chief Decomposer Organisms
Division/Class Orders Common Names
Eubacteria Myxobacterales Fruiting bacteria
Cytophagales Gliding bacteria
Spirochaetales Spirochaetes
Actinomycetales Actinomycetes
Cyanobacteria Blue green algae
Myxomycota Slime moulds
Mastigomycotina Chytrids, zoosporic fungi, water moulds
Zygomycotina Mucorales Pin moulds
Eutomophjthorales Entomogenous fungi
Zoopagales Nematode-trapping fungi
Ascomycotina (Several) Yeasts, cup fungi, flask fungi
Basidiomycotina (Several) Ruts, smuts, mushrooms,
Toadstools, bracket fungi, Puffballs etc.
Deuteromycotina Imperfect fungi, puffballs, Pycnidial fungi, etc.
Protozoa Ciliates, amoebas, Flagellates, etc.
Rotifera Rotifers
Nematoda Tricladida Flatworms
Metanemertini Ribbonworms
Annelida Earthworms, leeches
Mollusca Pulmonata Slugs, snails Copepods, amphipods,
Isopods, decapods
Arthropods, Diplopoda Millipedes
Arthropods, Chilopods Centipedes
Arthropods, Insects (Several) Termites, beetles, flies, Moths, ants,
grasshoppers, Cockroaches etc.
Arthropods, Arachnida (Several) Scorpions, sun spiders, Mites, spiders
DECOMPOSERS WITH VARYING RELATIONS
Some decomposer organism’s cannot be assigned a rigid or fixed position in the food
web. Their trophic relations can vary from time to time.
1. Nectroph: Some decomposers are nectrophs. They cause rapid death of the food
source because they have a short-term exploitation of living organism. Nectrophs
include may plant parasitic microbes as well as some herbivores, predators, and
microtrophs (organisms which feed on living bacteria and fungi.)
2. Biotrophs: On the other hand biotopes resort to a long-term exploitation of their
living food resource. For example, root-feeding nematodes and aphids, obligate
plant parasites, e.g., and mycorhizae and root nodules, etc.
3. Saprotophs: The apostrophes utilize food already dead, and most of the decomposers
belong to this category.
Decomposers occupying different trophic levels
There are some such organisms causing decompositions as can occupy various trophic
levels under different conditions. For instance the root parasites like Fusarium and
Thizoctonia are necrotrophs, which often show a saprotrophic tendency. In the same way,
the predators (foxes and kites) sometime behave as saprotrophs. Biotrophs sometime act as
necrotrophs or as saprotrophs.
Soul Invertebrates And Termites
There are some soil invertebrates e.g. earthworms and collembolans distribute organic
matter throughout the soil whereas others e.g. termites and ants, concentrate it at localized
sites around or near the royal chamber or in mounds. The following table shows the estimated
activities of major groups of soil animals.
Table 3.2 : Soil Animals’ Activites
Group (m-2) Density R/Q Production Excretory C/N ratio
Respiratory efficiency products
quotient
Protozoa 0.1-x1000 0.31-0.71 0.34-0.40 Urea ammonia 5
Nematodes 3.9-0-6x106 04.41-0.96 0.04-0.13 Urea ammonia 7.5-12
aminoacids
Annelids 0.650 <0.07 Urea
(eartworms)
Molluscs 0-8500 0.82 Ammonia. urea,
Amino acids
Arthropods
Collembola 700-40,00
Ants, termiter 1000-10,000 Uric acid urates
ENERGY-ITS FLOW IN ECOSYSTEMEnergy-DefinedEnergy can be defined as the capacity to do work, whether that work be on a gross scaleas raising mountains and moving air masses over continents, or on a small scale such astransmitting a nerve impulse from one cell to another.Kinds of EnergyThere are two kinds of energy, potential and kinetic. They can be explained as under:-1. Potential Energy
Potential energy is energy at rest. It is capable and available for work.
2. Kinetic Energy
Kinetic energy is due to motion, and results in work. Work that results from the
expenditure of energy can be of two kinds:
(1) It can store energy (as potential energy).
(2) It can order matter without storing energy.
3. Laws of Thermodynamics
The expenditure and storage of energy is described by two laws of thermodynamics:-
(i) Law of conservation of energy: The law of conservation of energy states that
energy is neither created nor destroyed. It may change forms, pass from one place
to another, or act upon matter in various ways. In this process no gain or loss in
total energy occurs. Energy is simply transferred from one form or place to another.
Two Reactions
There may be either of the two reactions:
1. Exothermic Reaction
When wood is burnt the potential energy present in the molecules of wood equals the
kinetic energy released, and heat is evolved to the surroundings. This is an exothermic
reaction.
2. Endothermic Reaction
In an endothermic reaction, energy from the surrounding may be paid into a reaction. For
example, in photosynthesis, the molecules of the products store more energy than the reactants.
The extra energy is acquired from the sunlight yet there is no gain or loss in total energy.
(ii) Law of Decrease in Energy: The second law of thermodynamics states that on
the transformation of from one kind to another, there is an increase in entropy and
a decrease in the amount of useful energy. In this way, when coal in burned in a
boiler to produce steam, some of the energy creates steam that performs work, but
part of the energy is dispersed as heat to the surrounding air.
Three Sources of Energy
Three sources of energy account for all the work of the ecosystem. These sources are
gravitation. Internal forces within the earth and solar radiation. The last one is significant
for ecosystem. The solar radiation, which originates from sun is the source of energy for lifeand is what sets the ecosystem, besides other natural system.Energy FlowDue to unidirectional flow of energy, the behaviour of energy in ecosystem is calledEnergy Flow. From the energetics point of view, energy flow is explained as under:(i) The efficiency of the producers in absorption and conversion of solar energy.(ii) The use of the above said converted chemical form of energy by the consumers.(iii) The total input of energy in form of food and its efficiency of assimilation.
(iv) The loss caused through respiration, heat, excretion etc.
(v) The gross, net production.
Single Channel Energy Model
Lindemann (1942) was the first to propose the community energetics approach or the
trophic-dynamic model) to ecology, which enables an investigator to compare the relative
rates at which different kinds concerning energy flow through forest ecosystems by the
application of this kind of approach, e.g. by comparing ratios of leaf fall to litter deposition
on the forest floor. His conclusion was that the rates of leaf production are higher and those
of litter accumulation lower, in the tropics than at higher latitudes.
Solar radiation
118, 872
Decom position
3.0 Decom position
0.5
Decom position
(trace)
Not utilised
1.2
Respiration
1.8
Not utilised
7.0
Respiration
4.5
Not utilised
70.0
Respiration
23.0
HERB IVO RES
(G .P.)
15.0
CARNIVO RES
(G .P.)
3 .0
AUTO TRO P HS
G ross production
(G .P.)
111.0
Single channel energy model.
The following conclusion can be drawn from the above figure:
(1) Out of the total incoming solar radiation (118,872 g cal/cm2 /yr), 118,761 gcal/cm2/yr
remain unutilized. In this way, the gross production (net production plus respiration)
by autotrophs comes to be 111 gcal/cm2/yr with an efficiency of energy capture of
0.10 per sent.
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For a fuller understanding of ecosystems a fuller understanding of their functions
besides their structures is essential. The function of ecosystems includes, the process how
an eco-system works or operates in normal condition.
From the operational viewpoint, the living and non-living components of ecosystem are
interwoven into the fabric of nature. Hence their separation from each other becomes
practically very much difficult. The producers, green plants, fix radiant energy and with the
help of minerals (C, O, N, P, L, Ca, Mg, Zn, Fe etc.) taken from their soil and aerial
environment (nutrient pool) they build up complex prefer to call the green plants as converters
or transducers because in their opinion the terms ‘producer’ form an energy viewpoint which
is somewhat misleading. They contend that green plants produce carbohydrates and not
energy and since they convert or transducer radiant energy into chemical form, they must
be better called the converters or transducers. However, the term’ producer’ is so widely
used that it is preferred to retain it as such.
While considering the function of an ecosystem, we describe the flow of energy and the
cycling of nutrients. In other words, we are interested in things like how much sunlight
plants trap in a year, how much plant material is eaten by herbivores, and how many
herbivores carnivores eat.
Functions of Eco-system
The functions of Ecosystem are as under:
1. Transformation of Solar Energy into Food Energy
The solar radiation is major source of energy in the ecosystem. It is the basic input of
energy entering the ecosystem. The green plants receive it. And is converted into heat
energy. It is lost from the ecosystem to the atmosphere through plant communities. It is
only a small proportion of radiant solar energy that is used by plant to make food through
the process of photosynthesis. Green plants transform a part of solar energy into food energy
or chemical energy. The green plants to develop their tissues use this energy. It is stored
in the primary producers at the bottom of trophic levels. The chemical energy, which is
stored at rapid level one, becomes the source of energy to the herbivorous animals at trophic
level two of the food chain. Some portion energy is lost from trophic level one through
respiration and some portion is transfereed to plant-eating animals at trophic level two.
2. The Circulation of elements through Energy Flow
It is seen that in the various biotic components of the ecosystem the energy flow is the
main driving force of nutrient circulation. The organic and inorganic substances are moved
reversibly through various closed system of cycles in the biosphere, atmosphere, hydrosphere
and lithosphere. This activity is done in such a way that total mass of these substances
remains almost the same and is always available to biotic communities.
3. The Conversion of Elements into Inorganic Flow
The organic elements of plants and animals are released in the under mentioned ways:
(i) Decomposition of leaf falls from the plants dead plants and animals by decomposers
and their conversion into soluble inorganic form.
(ii) Burning of vegetation by lighting, accidental forest fire or deliberate action of man.
When burnt, the portions of organic matter are released to the atmosphere and
these again fall down, under the impact of precipitation, on the ground. Then they
become soluble inorganic form of element to join soil storage, some portions in the
form of ashes are decomposed by bacterial activities.
(iii) The waste materials released by animals are decomposed by bacteria. They find
their way in soluble inorganic form to soil storage.
4. The Growth and Development of Plants
In the biogeochemical cycles are included the uptake of nutrients of inorganic elements
by the plants through their roots. The nutrients are derived from the soil where these
inorganic elements are stored. The decomposition of leaves, plants and animals and their
conversion into soluble inorganic form are stored into soil contributing to the growth and
development of plants. Decompositions are converged into some elements. These elements
are easily used in development of plant tissues and plant growth by biochemical processes,
mainly photosynthesis.
5. Productivity of ecosystem
The productivity of an ecosystem refers to the rate of production i.e. the amount of
organic matter, which is accumulated in any unit time. Productivity is of the following types:
(1) Primary productivity: It is associated with the producers which are autotrophic,
Most of these are photosynthetic, Thus, they are, to a much lesser extent the
chemosynthetic micro organisms. These are the green plants, higher saprophytes
as well as lower forms, the phytoplankton’s and some photosynthetic bacteria. We
can define Primary productivity as “the rate at which radiant energy is stored by
photosynthetic and chemosynthetic activity of producers.” Primary productivity is
further distinguished as:
Gross primary productivity: Gross Primary Productivity is the rate of storage of
organic matter in plant tissues in excess of the respiratory utilization by plants
during the measurement period. This is, thus, the rate of increases of biomass. In
this way, net primary productivity refers to balance between gross photosynthesis
and respiration and other plant losses as death etc.
(2) Secondary productivity: These are the rates of energy storage at consumers
level. Since consumers only utilize food materials (already produced) in their
respiration, simply covering the food matters to different tissues by an overall
process. The secondary productivity is not divided into ‘gross’ and ‘net’ amount.
(3) Net Productivity: Net productivity refers to the rate of storage of organic matter not
used by the heterotrophs (consumer) i.e. equivalent to net primary production minus
consumption by the heterotrophs during the unit period. It is thus the rate of increase
of biomass of the primary producers, which has been left over by the consumers.
(4) Stability of Ecosystem: The stability of ecosystems refers to the balance between
production and consumption of each element in the ecosystem. In other words,
balance between input and output of energy and normal functioning of different
biogeochemical cycles and stable conditions of equilibrium as under:-
(i) The Equilibrium Model: The equilibrium model states that an ecosystem,
always tends towards stability. As soon as the community of an ecosystem is
disturbed due to external environmental change, it quickly returns to original
state where as.
(ii) The non-equilibrium model: The non-equilibrium model states that an
ecosystem stability is rarely attained because disturbances caused by frequent
external environmental change do not allow to develop ordered state of species
assemblages in an ecosystem.
DECOMPOSERS
In this world all living organisms require a constant supply of nutrients for growth. The
death and decomposition of plants and animals, with release of nutrients constitutes an
essential link in the maintenance of nutrient cycles. When an organism dies, an initial
period of rapid leaching takes place and populations of macromolecules. The dead organism
is disintegrated beyond recognition. Enzymic action breaks down the disintegrating parts of
the litter. Animals invade and either eat the rapidly recolonized by micro- organisms, and
the litter biomass decreases. It becomes simpler in structure and chemical composition.
Process of Decomposition
The process of decomposition involves three interrelated components, viz.
(i) Leaching (ii) Catabolism, (iii) Comminution.
1. Leaching
Leaching is a physical phenomenon operating soon-after litter fall. Soluble matter is
removed from detritus by the action of water. Sometime over 20% of the total nitrogen
content of litter maybe leached off.
2. Catabolism
The process in a plant or animal by which living tissue is changed into waste products.
3. Comminution
Comminution to make small to reduce to power or minute particles. Comminution
means the reduction in particle size of detritus. During the course of feeding, the decomposer
animals community detritus physically. And utilize the energy and nutrients for their own
growth (secondary production). In due course, the decomposers themselves die and contribute
to the detritus.
Function of Decomposition
The two major functions of decomposition within ecosystems are as under:-
(1) The mineralization of essential elements,
(2) The formation of soil organic matter to inorganic form.
The formation of soil organic matter in nature is a slow process. The decomposition of
any piece of plant detritus may take hundreds of years to complete. However, some residues
of decomposition within this period do contribute to the formation of soil organic matter.
Community of Decomposer Organisms
The community of decomposer organisms includes several bacteria, fungi, protests and
invertebrates. The different species in such a community function in an integrated manner.
For example, a fungus decomposes plant litter and is eaten by an animal. Upon death,
bacteria decompose the animal, and protozoa may eat the bacteria.
Fungi and bacteria are the principal organisms that break down organic matter. Certain
protozoa, nematodes, annelids and arthopods strongly influence their functioning (i.e. of
fungi and bacteria) due to their feeling activities. Microarthopod fauna, comprising mainly
of oribatid mites besides other mites and collembolans, are abundant in most forest, grassland
and desert ecosystem.
Most of these micro-arthropods are predominantly fungal-feeders. They can do as under:
(1) They can decompose substrata.
(2) They can decrease substrata’s mass by leaching soluble intercellular components.
(3) They can do so by oxidation.
(4) They can physically cut in into smaller fragments.
Increased mineralization of nitrogen, phosphorus and potassium has been reported to
be mediated by microarhropods in several studies.
In the same way, the interactions of micro-arthropods with soil fungi are also quite
important in nutrient cycling. Studies of this aspect are made in mycorrhizal fungi and
themicro-arthropods which feed upon these fungi:
(1) It is found that Mycorrhizal pump massive amounts of nutrients form detritus and
represent a sizable nutrient reservoir themselves.
(2) The orbited mites and other micro-arthropods feed on myocardial fungi they act like
herbivorous pests, and can alter nutrient relations/cycling in terrestrial ecosystems.
Table 3.1 : Chief Decomposer Organisms
Division/Class Orders Common Names
Eubacteria Myxobacterales Fruiting bacteria
Cytophagales Gliding bacteria
Spirochaetales Spirochaetes
Actinomycetales Actinomycetes
Cyanobacteria Blue green algae
Myxomycota Slime moulds
Mastigomycotina Chytrids, zoosporic fungi, water moulds
Zygomycotina Mucorales Pin moulds
Eutomophjthorales Entomogenous fungi
Zoopagales Nematode-trapping fungi
Ascomycotina (Several) Yeasts, cup fungi, flask fungi
Basidiomycotina (Several) Ruts, smuts, mushrooms,
Toadstools, bracket fungi, Puffballs etc.
Deuteromycotina Imperfect fungi, puffballs, Pycnidial fungi, etc.
Protozoa Ciliates, amoebas, Flagellates, etc.
Rotifera Rotifers
Nematoda Tricladida Flatworms
Metanemertini Ribbonworms
Annelida Earthworms, leeches
Mollusca Pulmonata Slugs, snails Copepods, amphipods,
Isopods, decapods
Arthropods, Diplopoda Millipedes
Arthropods, Chilopods Centipedes
Arthropods, Insects (Several) Termites, beetles, flies, Moths, ants,
grasshoppers, Cockroaches etc.
Arthropods, Arachnida (Several) Scorpions, sun spiders, Mites, spiders
DECOMPOSERS WITH VARYING RELATIONS
Some decomposer organism’s cannot be assigned a rigid or fixed position in the food
web. Their trophic relations can vary from time to time.
1. Nectroph: Some decomposers are nectrophs. They cause rapid death of the food
source because they have a short-term exploitation of living organism. Nectrophs
include may plant parasitic microbes as well as some herbivores, predators, and
microtrophs (organisms which feed on living bacteria and fungi.)
2. Biotrophs: On the other hand biotopes resort to a long-term exploitation of their
living food resource. For example, root-feeding nematodes and aphids, obligate
plant parasites, e.g., and mycorhizae and root nodules, etc.
3. Saprotophs: The apostrophes utilize food already dead, and most of the decomposers
belong to this category.
Decomposers occupying different trophic levels
There are some such organisms causing decompositions as can occupy various trophic
levels under different conditions. For instance the root parasites like Fusarium and
Thizoctonia are necrotrophs, which often show a saprotrophic tendency. In the same way,
the predators (foxes and kites) sometime behave as saprotrophs. Biotrophs sometime act as
necrotrophs or as saprotrophs.
Soul Invertebrates And Termites
There are some soil invertebrates e.g. earthworms and collembolans distribute organic
matter throughout the soil whereas others e.g. termites and ants, concentrate it at localized
sites around or near the royal chamber or in mounds. The following table shows the estimated
activities of major groups of soil animals.
Table 3.2 : Soil Animals’ Activites
Group (m-2) Density R/Q Production Excretory C/N ratio
Respiratory efficiency products
quotient
Protozoa 0.1-x1000 0.31-0.71 0.34-0.40 Urea ammonia 5
Nematodes 3.9-0-6x106 04.41-0.96 0.04-0.13 Urea ammonia 7.5-12
aminoacids
Annelids 0.650 <0.07 Urea
(eartworms)
Molluscs 0-8500 0.82 Ammonia. urea,
Amino acids
Arthropods
Collembola 700-40,00
Ants, termiter 1000-10,000 Uric acid urates
ENERGY-ITS FLOW IN ECOSYSTEMEnergy-DefinedEnergy can be defined as the capacity to do work, whether that work be on a gross scaleas raising mountains and moving air masses over continents, or on a small scale such astransmitting a nerve impulse from one cell to another.Kinds of EnergyThere are two kinds of energy, potential and kinetic. They can be explained as under:-1. Potential Energy
Potential energy is energy at rest. It is capable and available for work.
2. Kinetic Energy
Kinetic energy is due to motion, and results in work. Work that results from the
expenditure of energy can be of two kinds:
(1) It can store energy (as potential energy).
(2) It can order matter without storing energy.
3. Laws of Thermodynamics
The expenditure and storage of energy is described by two laws of thermodynamics:-
(i) Law of conservation of energy: The law of conservation of energy states that
energy is neither created nor destroyed. It may change forms, pass from one place
to another, or act upon matter in various ways. In this process no gain or loss in
total energy occurs. Energy is simply transferred from one form or place to another.
Two Reactions
There may be either of the two reactions:
1. Exothermic Reaction
When wood is burnt the potential energy present in the molecules of wood equals the
kinetic energy released, and heat is evolved to the surroundings. This is an exothermic
reaction.
2. Endothermic Reaction
In an endothermic reaction, energy from the surrounding may be paid into a reaction. For
example, in photosynthesis, the molecules of the products store more energy than the reactants.
The extra energy is acquired from the sunlight yet there is no gain or loss in total energy.
(ii) Law of Decrease in Energy: The second law of thermodynamics states that on
the transformation of from one kind to another, there is an increase in entropy and
a decrease in the amount of useful energy. In this way, when coal in burned in a
boiler to produce steam, some of the energy creates steam that performs work, but
part of the energy is dispersed as heat to the surrounding air.
Three Sources of Energy
Three sources of energy account for all the work of the ecosystem. These sources are
gravitation. Internal forces within the earth and solar radiation. The last one is significant
for ecosystem. The solar radiation, which originates from sun is the source of energy for lifeand is what sets the ecosystem, besides other natural system.Energy FlowDue to unidirectional flow of energy, the behaviour of energy in ecosystem is calledEnergy Flow. From the energetics point of view, energy flow is explained as under:(i) The efficiency of the producers in absorption and conversion of solar energy.(ii) The use of the above said converted chemical form of energy by the consumers.(iii) The total input of energy in form of food and its efficiency of assimilation.
(iv) The loss caused through respiration, heat, excretion etc.
(v) The gross, net production.
Single Channel Energy Model
Lindemann (1942) was the first to propose the community energetics approach or the
trophic-dynamic model) to ecology, which enables an investigator to compare the relative
rates at which different kinds concerning energy flow through forest ecosystems by the
application of this kind of approach, e.g. by comparing ratios of leaf fall to litter deposition
on the forest floor. His conclusion was that the rates of leaf production are higher and those
of litter accumulation lower, in the tropics than at higher latitudes.
Solar radiation
118, 872
Decom position
3.0 Decom position
0.5
Decom position
(trace)
Not utilised
1.2
Respiration
1.8
Not utilised
7.0
Respiration
4.5
Not utilised
70.0
Respiration
23.0
HERB IVO RES
(G .P.)
15.0
CARNIVO RES
(G .P.)
3 .0
AUTO TRO P HS
G ross production
(G .P.)
111.0
Single channel energy model.
The following conclusion can be drawn from the above figure:
(1) Out of the total incoming solar radiation (118,872 g cal/cm2 /yr), 118,761 gcal/cm2/yr
remain unutilized. In this way, the gross production (net production plus respiration)
by autotrophs comes to be 111 gcal/cm2/yr with an efficiency of energy capture of
0.10 per sent.
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