ECOSYSTEM

1. ECOSYSTEM BIODIVERSITY
ECOSYSTEM
The term 'ecosystem' was coined by A.G.Tansley in 1935.
He defined the ecosystem as "the system resulting from the integration of all the living und non-
living factors of the environment'.
The ecosystem is the basic functional unit in ecology; it includes organisms (biotic communities)
and abiotic environment, each influencing the properties of the other and is necessary for maintenance of
life. Ecosystem development is an autogenic process.
Structure and Function of an Ecosystem
The two major aspects of an ecosystem are:
1. Structure
2. Function
 Structure of an Ecosystem
Every ecosystem consists of two basic components. They are
1) Abiotic (non-living) components &
2) Biotic (living) components
1) Abiotic components:
These include non-living things in an ecosystem. These may be categorized into three different
types. They are,
A) Adaphic (soil) factors: includes different types of soils, minerals, rocks, soil pH, etc.
B) Physical or Climatic factors: Rain fall, snow fall, pressure, wind, gaseous elements in atmosphere
etc. and energy (Solar radiation, chemical energy, geo-thermal energy etc.)
C) Chemical Factor:
 Organic : lipids, proteins, carbohydrates and vitamins
 Inorganic: Nitrates, Phosphates, Potassium, Calcium, etc..
2) Biotic components:
These include all living organisms which are present in such ecosystem. These involves plants, trees,
grasses, micro organisms, animals, birds etc. these are also grouped into three types. They are,
Producers: - which prepares their own food material. These are also known as AUTOTROPHS.
E.g. all green plants, some micro organisms etc.
Photoautotrophs: can synthesize food materials in presence of light energy E.g.: Green
Plants
Chemoautotrophs: they can synthesize food material without light energy, depends on
radiant energy (chemicals). E.g. Sulphur bacteria
Consumers:- which depends upon other organisms for their food. These are also known as Heterotrophs.
E.g. All animals.
Heterotrophic component
(Heterotrophic = other-nourishing) in this component, utilization, rearrangement and decomposition of
complex substances predominate. These are macro consumers such as herbivores, carnivores and
omnivores (Photographs) and micro consumers such as decomposers, osmotrophs and saprotrophs.
Heterotrophic organisms, chiefly animals, which ingest other organisms (or) particulate organic

2. matter, are included in this category.
They are of four types viz.,
Herbivores: Plant eaters also known as Primary consumers. Eg- grasshopper, birds, caterpillars
Carnivores: Meat eaters (Eat herbivores or other organisms) also known as Secondary consumers. Eg-
lizards, snakes, lion, eagle etc.
Based on the length of food chain carnivores are Primary carnivores, secondary, tertiary or quaternary
carnivores
Omnivores: Plant as well as meat eaters (Eat both plant and other organisms). Also called as Tertiary
consumers. Eg- Bear, Birds
Detritivores: Feeds on only dead ones. Also called as saprophytes. Eg- Vultures, Hyena, Hawks
D) Decomposers: - which decompose the dead organisms.
E.g. Micro organisms, fungi, etc.
Heterotrophic organisms, chiefly bacteria and fungi, which breakdown complex compounds of dead
organic matter, absorb some of the decomposition products and release inorganic nutrients that are usable
by the producers together with organics.
 FUNCTIONS of ECOSYSTEM
From the functional standpoint an ecosystem may be conveniently analyzed in terms of the following:
1. Food chains, Food webs & Food Pyramids
2. Primary and Secondary Production
3. Energy Flow
4. Nutrient cycles
5. Development and evolution
Thus, in any ecosystem, the structure and function are studied together.
Ecological Energetics
Energy is defined as the ability to do work. The behavior of energy is described by the following laws:
o The first law of thermodynamics states that "Energy is neither created nor destroyed but is
transformed from one type into another " e.g.: sun light.
o The second law states that "no process involving an energy transformation will spontaneously
occur unless there is a degeneration of energy from a concentrated form into a dispersed form".
E.g. Heat dispersion. Further, because some energy is always dispersed into unavailable heat
energy, no spontaneous transformation of energy (light) into potential energy (protoplasm for
example) is 100 percent efficient.
Energy flow
Single - Channel Energy Models
The behavior of energy in an ecosystem can be termed as energy flow due to unidirectional
flow of energy. In an ecosystem, the following aspects are essential in understanding the ecological
energetic.
(i) The efficiency of the producers in absorption and conversion of solar energy.
(ii) The use of this converted form of chemical energy by the consumers.
(iii) The total input of energy as food and its efficiency of assimilation.
(iv) The energy lost through respiration, heat, excretion etc at each trophic level.
(v) Gross production and net production.

3. Single - Channel Energy Models
Fig: Energy flow diagram for a lake (freshwater ecosystem)
Thus, due to one-way flow of energy, the system would collapse if the primary source, the sun, were cut off.
Secondly, there occurs a progressive decrease in energy dissipated as heat in metabolic activities. It is clear that
the energy inflows balance outflows as required by the first law of thermodynamics and energy transfer is
accompanied by dispersion of energy into unavailable heat (i.e., respiration) as required by second law. Further,
there is a successive reduction in energy flow at successive trophic levels. Thus shorter the food chain, greater
would be the available of food energy.
 Y - Shaped Energy Flow Models
Eugene. P.Odum (1983) gave a generalized model of Y-shaped or 2-channel energy flow model applicable to
both terrestrial and aquatic ecosystems as shown in Fig.3.3
Fig : The Y-shaped energy flow model showing linkage between grazing and detritus food chains.
A difference approach for energy inputs, outputs and energy transfers for two interconnected land ecosystems
i.e. two grazing food web and food web are shown in above Fig 3.3.
Universal energy flow model:
However, the below figure presents what might be called a universal model, applicable to any living
component (animal, plant, microorganisms, individual, population or a trophic group). Such a model may depict
food chain or the bio energetics of the entire ecosystem.

4. Fig.3.4 Universal model of energy flow.
In this model, the shaded box labeled ‘B' represents the living structure or biomass of the components.
The total energy input is indicated by 'I' (light for autotrophs and organic food for heterotrophs).
 Food chains, Food Webs and Ecological Pyramids
The transfer of food energy from the producers, through a series of organisms (herbivores carnivores and
decomposers) with repeated eating and being eaten, is known as food chain. In nature, two general types of food
chains are distinguished. They are
1. Grazing food chain
2. Detritus food chain
 Grazing Food Chain
(a) This food chain starts from the living green plants and goes to grazing herbivores and on to carnivores.
CONSUMERS
Fig: Diagrammatic sketch showing the food web in a pond.
(b) Ecosystems with such type of food chain are directly dependent on an influx of solar radiation
Detritus Food Chain
Fig. Example of Detritus food chain.
1. The detritus food chain initiates from dead organic matter into microorganism and then to organisms feeding
on detritus (detritivores) and their predators.

5. 2. This food chain operates in the decomposing accumulated litter in a temperate forest.
3. The best example of a detritus food chain is seen in mangrove ecosystems & forest ecosystem
4. The leaves of mangrove trees fall into the warm, shallow waters. Only 5% of the leaf material will be
removed by grazing insects before leaf fall.
The fallen leaf fragments are acted upon by saprotrophs such as fungi, bacteria, protozoa etc. and colonized
mainly by phytoplankton and benthic algae and later eaten and re-eaten (coprophagy) by a key group of small
animals.
 Food Webs
Food chains in natural conditions never operate as isolated sequences. The linear arrangement of food chains
hardly occurs and they are interconnected under natural conditions thus, there are found alternatives in nature.
In a grazing food chain of a grass land, in the absence of rabbit, grass may also be eaten by mouse. The mouse
may in turn be eaten directly by hawk or by snake first which is then eaten by hawk.
There are five linear food chains in the food web of a grass land
Fig. food web in a grassland ecosystem.
There may be seen five possible food chains interlocked together making the food web.
These five chains are interlinked with each other at different points forming a food web. The food webs are
important in maintaining the stability of an ecosystem in nature. For example, decrease in the population of
rabbit would naturally cause an increase in the population of alternative herbivore, the mouse. This may
decrease the population of the consumer that prefers to eat rabbit.
 Ecological Pyramids
The interaction of the food chain phenomena (energy loss at each transfer) and the size metabolism
relationship results in communities having a definite trophic structure. It is often characteristic of a particular
type of ecosystem (lake, forest, coral reef, pasture etc).
Trophic structure may be measured either in terms of the standing crop per unit area (or) the energy fixed
per unit area per unit time at successive trophic levels. The graphical representation of the trophic structure and
also trophic function is referred to as "Ecological Pyramids". In this the first (or) producer level forms the base

6. and successive levels (or) tiers make up the apex. Ecological pyramids may be of 3 general types:
1. The Pyramid of Numbers
2. The Pyramid of Biomass
3. The Pyramid of Energy
The pyramids of number and biomass may be upright (or) inverted depending upon the nature of food
chain in the particular ecosystem but the pyramids of energy are always upright.
 Pyramids of Numbers
They show the relationship between producers, herbivores and carnivores at successive trophic levels in terms
of their number. In a grassland ecosystem, the producers which are mainly grasses are always maximum in
number. This number then shows a decrease towards the apex, as the primary consumers (herbivores) like
rabbits, mice etc., are less in number than the grasses. The secondary consumers such as snakes and lizards, are
lesser in number than rabbits and mice. Finally, the top (tertiary) consumers like hawks (or) other birds are least
in number thus, the pyramid becomes upright
Fig. Pyramids of numbers (individuals per unit area) in different kinds of ecosystems / food chains. A -
Grassland ecosystem. B - pond ecosystem, C - forest ecosystem. D - Parasitic food chain (ODUM 1983).
In a pond ecosystem also the pyramid is upright
i) The producers, which are mainly the phytoplanktons as algae, bacteria etc are maximum in number.
ii) The herbivores which includes small fish, rotifers, cladocerans, copepods etc are lesser in number
than the producers.
iii) Secondary consumers (carnivores) such as small fish eating each other, water beetles etc are less in
number than the primary consumers.
iv) Finally, the tertiary consumers i.e., bigger fish are least in number. However, in a
forest ecosystem, the pyramid of number is different in shape
i) The producers, which are mainly large-sized trees are less in number and form the base of the
pyramid.
ii) Primary consumers (herbivores) includes fruit - eating birds, elephants, deer’s etc and they are more in
number than producers.
iii) There is a gradual decrease in the number of successive carnivores, thus making the pyramid again

7. upright.
The pyramids are always inverted in a parasitic food chain. A single plant may support the growth of many
herbivores and each herbivore in turn provides nutrition to several parasites, which support many hyper
parasites. Thus, from the producer towards consumers, there is a reverse position i.e., the number of organisms
gradually shows an increase making the pyramid inverted in shape.
The pyramids of numbers do not give actual picture of the food chain as they are not very functional.
They do not reflect the relative effects of the geometric, food chain and size factors of the organisms. They
generally vary with different communities with different food chains in the same environment. Sometimes, it
becomes very difficult to represent the whole Community on the same numerical scale (as in forests).
 Pyramids of Biomass
They are more fundamental and show the quantitative relationships of the standing crops.
(i) In grassland and forest, generally there is a gradual decrease in biomass of organisms at successive levels
from the producers to the top carnivores. Thus, these pyramids are upright.
(ii) However, in a pond ecosystem, the producers are small organisms and hence their biomass is least. This
value gradually shows an increase towards the apex of the pyramid, thus making the pyramid inverted in shape.
Fig: (A-C). Pyramids of biomass (g dry wt. per unit area) in different kinds of ecosystems. A - grassland, B-
forest, C-pond.
 Pyramids of Energy
The energy pyramids reflect the best picture of overall nature of the ecosystem. In this pyramid, the number
and weight of organisms at any trophic level depends on the rate at which food is being produced but not on the
amount of fixed energy at any level in a given time. Its shape is always upright since in most cases there will be
always a gradual decrease in the energy content at successive trophic levels from producers to various
consumers
Fig. Pyramid of energy (K cal per unit area within unit time) in any ecosystem.