1. Ecosystem
Definition- An ecosystem is an interacting system made by all the living and
nonliving objects in a physically defined space.
An ecosystem is a functional unit which comprises all the organisms in a
particular space interacting with one another within the physical environment and
are inter connected by an ongoing flow of energy.
The term ecosystem was proposed by A.G. Tansley in 1935.
It is an "open" system, where energy and matter are transferred in and out.
An ecosystem can vary in the size depending on the nature of community.
Ecosystem components
Ecosystem consists of various non-living (abiotic) and living (biotic) components.
The abiotic components include various physical and chemical factors.
The physical factors having the greatest effect on the ecosystem are light,
temperature, precipitation, air, soil, fire and water.
The chemical factors are pH, salinity, nutrient contents, moisture contents, amount
of toxic substance and level of dissolved oxygen.
The biotic component of an ecosystem are usually classified as autotrophs and
heterotrophs based on the food or nutrition they need to survive.
Autotrophs
Autotrophs are organisms that can produce their own food, using materials from
inorganic sources.
The word “autotroph” comes from the root words “auto” for “self” and “troph”
for “food.”
2. An autotroph is an organism that feeds itself, without the assistance of any other
organisms.
They are the ultimate source of organic compound.
Autotrophs are referred as producers of the biosphere.
There are two kinds of autotrophs - Photoautotrophs and Chemoautotrophs.
Photoautotrophs are those can make organic nutrients through photosynthesis, it is
found in most terrestrial ecosystem e.g. green plants known as producers.
In aquatic ecosystem, most of the producers are phytoplankton consisting of
various species of floating and drifting bacteria and protists.
Chemotrophs are a class of organisms that obtain their energy through the
oxidation of inorganic molecules, such as iron and magnesium.
The most common type of chemotrophic organisms are prokaryotic and include
both bacteria and fungi.
Heterotrophs
Heterotrophs are those organisms which cannot synthesis the organic nutrients the
need and get them by feeding on the tissues of producers or other consumers.
Fungi, animals and most bacteria are heterotrophs.
Heterotrophs can be classified into consumer and decomposer.
Consumers are organisms such as animals that feed on producers and other
consumers. There are several classes of consumers, depending on their food
sources:
Herbivores- feed directly on plants
Carnivorous- feed on animals
Omnivorous- eat both plants and animals
Detritivores eat detritus.
3. Detritus are the dead bodies and waste product of living and one living organism
or simply, decomposing on organic material.
Some heterotrophs consume the dead organic matters and carry out the natural
product process of decomposition they are called as decomposers.
Both decomposers and detritivores derive nutrition from dead organic matters.
The difference is that detritivores actually eats then organic matter and
decomposers secrete enzymes to digest the organic matter and then absorb the
resulting molecules (e.g. bacteria and fungi).
Ecosystem function
All biological bodies require matter for their construction and energy for other
activities, but also for the population and communities that they form in nature.
Ecosystem normally include primary producers, decomposers, detritivores, a pool
of dead organic matter, herbivores, carnivores and parasites plus the physio-
chemical environment that provides the living condition and act both as a source
and sink of energy and matter.
The key functional aspects of the ecosystem are: productivity and energy flow,
nutrient cycling, decomposition and water dynamics.
Productivity
Productivity refers to the rate of formation of biomass in an ecosystem.
It is expressed in units of mass per unit area (or volume) per unit time.
'Productivity' and 'production' are the two interchangeable terms.
Productivity is the rate at which organic matter is created by producers.
4. Biomass is the amount of organic matter present at any given time. It is expressed
as wet or dry biomass.
Dry biomass refers to the mass of living matter after it has been right to a constant
mass.
Wet biomass refers to the mass of living matter including its water content.
The primary productivity is the rate at which biomass produced per unit area by
the primary producers (both photoautotrophs and chemoautotrophs) the term
primary indicates that we are concerned with the first trophic level in the
ecosystem.
The total rate of photosynthesis, including the biomass used up in respiration
during the period of measurement, is referred to as gross primary productivity
(GPP).
The rate of storage of biomass in a plant that exceeds the respiratory used by the
plants during the period of measurement is net primary productivity (NPP).
Concept of trophic level
A trophic level refers to the organisms’ position in the food chain.
The word ‘trophic’ derived from the Greek word meaning to food or feeding. It is
simply a feeding level represented in a food chain.
Producers comprise the first trophic level, followed by primary consumer
(herbivores), then secondary consumers (carnivores feeding on herbivores) and so
on.
There are many organisms not specialized in their diet such as Omnivores, eat
both animals and plants.
5. The number of trophic levels very soon different ecosystem. Generally, its number
is more in aquatic ecosystems than in terrestrial ecosystems.
Food chains
Classic paper by Lindeman (1942) places the foundation of ecological energetics.
He attempted to quantify the concept of food chains and food webs by considering the
efficiency of transfer between tropic levels.
The first trophic level belongs to the primary producer, the second trophic level to
the herbivores (primary consumers) and the higher level to the carnivores
(secondary consumers).
Some consumers occupy a single trophic level. But consumers such as omnivores,
occupies more than one trophic level. The relation between one trophic level and
adjacent trophic level may be described by a food chain.
6. The transfer of food energy from producers (plants) through a series of organisms
that consumes and are consumed, termed as food chain shows the movement of
energy through a system by indicating the path of food from the producer from a
producer to a final consumer.
In general food chains have 3 to 5 trophic links with 15 to 20 species.
The length of food chain also may reflect the physical characteristics of a
particular ecosystem.
A harsh aquatic landscape has a much shorter food chain than a temperate or
tropical one.
There are two main hypotheses:
The first hypothesis is energetic hypothesis, suggests that the length of food chain
is limited by the efficiency of energy transfer along the chain. 10% of energy
stored in the organic matter of each trophic level is converted to the organic matter
and the next trophic level.
The second hypothesis the dynamic stability hypothesis, proposes that long food
chains are less stable than the short chains full stop population fluctuation at lower
trophic level are magnified at higher levels potentially causing the local exist
extinction of top predicted predators. This hypothesis predicts that food chain
should be shorter in unpredictable environments. Most of the data available
supports the energetic hypothesis.
Types of food chains
Grazing food chains
Grazing food chains derive their energy directly from the sun. The grazing food
chain begins with primary producer. Primary consumers or herbivores from form second
link in the grazing food chain. They gain their energy by consuming primary producers.
7. Secondary consumers or primary carnivores the third link in the chain gain their energy
by consuming herbivores. Tertiary consumers or secondary carnivores are animals that
receive their organic energy by consuming primary carnivores.
Detritus food chains
Detritus food chains begin with dead organic matter and go from nonliving
organic matter to microorganisms and then to detritus feeding organisms (detritivores)
and their predators. A large amount of organic matter is contributed by the death of
plant's parts, animals and their excretion products. These types of food chain are present
in all ecosystems.
Detritus food chains are connected to two a grazing food chain. Most of the
natural ecosystem processes have both the grazing and detritus type of food chains. In
terrestrial and shallow water ecosystem grazing food chains dominate because a major
proportion of annual energy flow passes through the through this circuit. In case of tidal
marshes, 90% of the primary production is rooted through the detritus food chains.
Food web
A food web (or food cycle) is the natural interconnection of food chains and a
graphical representation of what-eats-what in an ecological community. Another
name for food web is consumer-resource system. ... Some of the organic matter
eaten by heterotrophs, such as sugars, provides energy.
A food web is similar to a food chain but larger.
8. The diagram combines many food chains into energy relationships among
organisms. Food webs show how plants and animals are connected in many ways.
The arrow points from the organism being eaten to the organism that eats it.
The two extreme categories (trophic levels) are: autotrophs and heterotrophs.
There are different kinds of feeding relations: herbivory, carnivory, scavenging
and parasitism.
Some of the organic matter eaten by heterotrophs, such as sugars, provides energy.
Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes –
from cyanobacteria to giant redwoods, and from viruses to blue whales.
9. Autotrophs and detritus based ecosystem
The autotrophic based ecosystems depend directly on the influx of solar radiation.
They are characterized by a dependence on energy capture by photosynthetic autotrophs
and secondary by the movement of the captured energy through the system via herbivory
and carnivory. A large number of ecosystems function in this way and numerous
herbivorous, carnivorous and omnivorous are dependent on such topic ecosystem.
Some ecosystems depend less on direct solar energy incorporation and more on the influx
of dead organic material or detritus, produced in another ecosystem. Ecosystems such as
caves are completely independent of direct solar energy and our instead completely
energy dependent on the influx of detritus. These entities can be regarded as detritus
based ecosystem.
Ecological pyramid
An ecological pyramid is a graphical representation of the relationship between
different organisms in an ecosystem. Each of the bars that make up
the pyramid represents a different trophic level, and their order, which is based on who
eats whom, represents the flow of energy.
Pyramid of number
The population of each organism in a food chain can be shown in a type of bar
chart called a pyramid of numbers. The bars are drawn to scale – the more
organisms it represents, the wider the bar. The producer in the food chain always
goes at the bottom of the pyramid of numbers.
Foremost ecosystems, like grassland ecosystem, pyramid of number are upright
because numbering of organisms decreases at successively higher trophic level.
However, there are some ecological system for which pyramid of number maybe
inverted for example, if we deploying the number the situation of a single tree
along with its dependent insect population, we would get an inverted and inverted
10. pyramid full stop since the tree is primary producer, it would represent the base of
the pyramid and the dependent phytophagous insect population will represent the
secondary trophic level.
11. Pyramid of biomass
A diagrammatic representation of the amount of organic material, measured in
grams of dry mass per square metre (g m –2
), found in a particular habitat at
ascending trophic levels of a food chain. Biomass decreases at each ascending
level of the food chain.
Generally the biomass of producer is much larger than the biomass of herbivorous
and the biomass of herbivores is much greater than that of carnivores and so on.
In other words, we find that biomass decreases at each trophic level if we move
from producer to the top consumer or carnivorous. Therefore, diagrammatic
representation of biomass of individual belonging to different trophic levels
invariably assumes the shape of an upright pyramid.
It is not always the case coma in some aquatic ecosystems like large lakes and
oceans the pyramid of biomass sometimes assumes and inverted form.
Since microscopic phytoplanktonic algae are the primary producers in the aquatic
ecosystem beginning single-celled organisms they do not accumulate much
biomass and consequently at a given rate the total weight or the standing crop of
phytoplankton is less as compared to herbivores or other consumers.
This is the reason for the base of the pyramid in aquatic ecosystem being smaller
than the upper structure.
12.
13. Pyramid of energy
A pyramid of energy represents how much energy, initially from the sun, is
retained or stored in the form of new biomass at each trophic level in an ecosystem.
Typically, about 10% of the energy is transferred from one trophic level to the
next, thus preventing a large number of trophic levels.
An energy pyramid more accurately reflects the law of thermodynamics, with loss
of energy depicted at each transfer to another trophic level; hence the pyramid is
always upright.
Energy pyramids in the case of aquatic system are also upright even where the
pyramid of biomass is inverted.
In energy pyramids trophic level always has smaller energy content than the tropic
level immediately below it. This is due to the fact that some energy is always lost
as heat in is going from one trophic level to the next. Each bar in the pyramid
indicates the amount of energy utilised at each trophic level in a given time
annually per unit area.
