3. Ecosystem is the functional unit of nature,
where living organisms interact among
themselves and also with surrounding
physical environment.
Earth is a closed system with respect to
nutrients but an open ecosystem in terms
of energy.
Artificial Ecosystem- Aquarium, Crop fields
4. Structure of Ecosystem
Species composition: Variety of flora
and fauna occurring in an ecosystem.
Stratification: Vertical distribution of
different species occupying different
level is called stratification.
Example: Trees occupy top vertical
strata of a forest, shrubs the second
and herbs and grasses occupy the
bottom layers.
5. Four Key Functions of Ecosystem
Productivity
Decomposition
Energy flow
Nutrient cycling
7. Conversion of inorganic into organic
material by autotrophs with the help of
radiant energy of sun. (Productivity)
Decomposers decompose dead organic
matter into inorganic form so that it could
be reused (Decomposition).
Energy flow occurs at every step of
food chain.
Productivity and decomposition
together ensure nutrient cycling.
Ponds is a Complete Ecosystem.
9. Productivity is the rate of biomass
production in a ecosystem.
Primary productivity is the
amount of biomass produced per
unit area over a time period by
plants during photosynthesis.
It is expressed in terms of gram
per meter square per year (gm-2
yr -1) or kilocalories per meter
square per year (kcal m-2 yr -1).
GPP of an ecosystem is the rate of production
of biomass during photosynthesis.
GPP minus respiration losses is the NPP.
NPP = GPP – R
Note: NPP is available biomass for the
consumption of heterotrophs.
Secondary Productivity: It is the
rate of formation of new biomass by
consumers.
10. Factors Affecting Primary Productivity
1. Solar Radiations:
Sun light is the ultimate source of energy.
Maximum light is available in tropical region whereas polar region
receives minimum light. Due to this, photosynthesis, hence NPP is
highest in tropical region against temperate forests.
In aquatic ecosystem production is less than terrestrial ecosystem. It
is limited by light which decreases with increasing water depth.
2. Temperature: Temperate forests have lesser productivity than
tropical rainforest due to cold climate that severely limits productivity.
11. Factors Affecting Primary Productivity…
3. Moisture: Rain and humidity increase productivity of an ecosystem. It
decreases with water scarcity. Desert have lowest primary production
whereas tropical rainforest have the highest.
4. Nutrients:
Nitrogen is deficient in oceans that limits production of marine
ecosystems.
Desert soils are deficient in nutrients thus are less productive.
Estuaries and coral reefs are highly productive as nutrient supply is rich.
5. Photosynthetic efficiency of producers:
C4 plants are more productive than C3 plants.
Sugarcane is most productive crop being efficient in trapping sunlight.
13. Decomposition
Decomposers breakdown complex organic
matter into inorganic substances like CO2, H2O and
nutrients, the process is called decomposition.
Dead plants remains such as leaves, bark,
flowers and dead remains of animals including
faecal matter constitute detritus which is the raw
material for decomposition.
Decomposition is breakdown of complex organic
matter….can this process be compared with that of
digestion???
14. Steps in Decomposition
1. Fragmentation: Detritivorous (example:
earthworm) breakdown detritus into smaller
particles, the process is called fragmentation.
Earthworms are farmers’ friends…
2. Leaching: Water soluble inorganic
nutrients go down into lower soil horizon and
get precipitated as unavailable salts. The
process is called leaching.
15. Steps in Decomposition…
3. Catabolism: Bacterial and fungal enzymes degrade detritus
into simple inorganic substances, the process is called
catabolism.
4. Humification: It leads to accumulation of dark coloured
amorphous substance called humus that is highly resistant to
microbial action and undergoes decomposition at an extremely
slow rate.
Note: Humus serves as reservoir of nutrients.
5. Mineralisation: Humus is further degraded by some
microbes and release of inorganic nutrients occur by the process
known as mineralisation.
16. Factors Affecting Decomposition
1. Temperature:
Soil temperature of 25° or more accelerates decomposition.
A low temperature <10° reduces rate of decomposition. As a
result in many temperate forest detritus piles up at ground level.
2. Moisture is essential for decomposition. Decomposition rate is
very low in tropical desert despite presence of favourable
temperature.
3. pH: Neutral and slightly alkaline soils are rich in detrivores and
decomposers.
4. Aerobiosis:
Aerobic conditions are essential for activity of decomposers.
Anaerobic conditions reduce decomposition and cause piling up
of detritus.
17. Factors Affecting Decomposition …
5. Composition of Detritus: Chitin
and lignin are very slow to get
decomposed.
Decomposition of forest litter is a
function of lignin content and climate.
19. Laws of Thermodynamics
First Law of Thermodynamics: Energy is neither created nor
destroyed but can be transferred from one form to another. Example:
Solar energy can be transferred into chemical energy and heat.
Second Law of Thermodynamics:
No energy transformation occurs spontaneously without dissipation
of energy.
Thus in ecosystem transfer of food energy from one organism to
another leads to loss of energy as heat. Due to metabolic activities
only a small fraction of energy is stored in living tissues as biomass.
21. Trophic Levels
Each trophic level has a certain
mass of living material at a
particular time; it is called as
standing crop.
Standing crop is measured as
mass of living organisms
(biomass) or their number in a
unit area.
23. Food Chain
All trophic levels in an ecosystem are
connected by transfer of energy from
one tropic level (example: producers)
to next tropic level (example:
consumers) is called food chain.
GFC extends from producers to
herbivores and carnivores. Cattle
grazing in grasslands, deers browsing
in forests and insects feeding on crops
and trees are examples of GFC.
DFC begins with dead organic matter and
passes through detritus feeding organisms in
soil (example: earth worm) to organism feeding
on detritus feeders.
24. Important Points
In aquatic ecosystem GFC is major conduit for energy flow
whereas in terrestrial ecosystem, larger fraction of energy flows
through DFC.
DFC may be connected to GFC at some levels, i.e. some organisms
of DFC are prey to GFC animals.
25. Food Web
Different food chains are often
interconnected. Example: A
specific herbivore of one food
chain may serve as food of
carnivore of several other food
chains. Such interconnected
matrix of food chains is called
food web.
Food chain is just a concept….it
does not exist in nature.
No energy that is trapped into an organism
remains in it for ever. The energy trapped by
the producer is either passed on to a
consumer or the organism dies. Death of
organism is the beginning of the detritus food
chain.
27. Ten Percent Law
Amount of energy decreases at successive trophic levels.
The energy assimilated by herbivore is used in respiration and a
fraction of unassimilated energy is transferred to decomposers
(example: Faecal matter).
Only 10% of energy is transferred to each trophic level from the lower
trophic level.
Because of tremendous loss of energy at successive higher trophic
levels, residual energy is decreased to such an extent that no further
trophic level can be supported.
Therefore, length of food chains in an ecosystem is generally limited to
3-5 trophic levels.
29. Ecological Pyramids
Trophic structure in ecosystem can be represented by comparing
standing crop (number of individuals or biomass) or energy fixed
per unit area at different trophic levels.
Ecological pyramids are graphic representation of trophic structure
where the basal, mid and top tiers show the parameter value for
producers, herbivores and carnivores in the ecosystem.
Common parameters for constructing ecological pyramids are
number of individuals (pyramid of number), dry weight (pyramid of
biomass), rate of energy flow (pyramid of energy) at successive
tropic levels.
30. Pyramid of Number & Biomass
In most ecosystems, pyramid of number and biomass
are upright, i.e. producers outnumber and outweigh
the herbivores and herbivores outnumber and
outweigh carnivores.
However in certain ecosystems pyramid of number and
pyramid of biomass are inverted. Example: Numerous
small insects may occur on a single tree and in ocean
weight of short lived phytoplankton at a given time is
very less than weight of long lived fish.
33. Pyramid of Energy
Pyramid of energy is always upright.
It emphasises that total energy flow at
successive trophic level always decreases
compared to preceding trophic level as
some of the energy is always lost as heat
at each step.
Therefore, out of 3 kinds of ecological
pyramids, pyramid of energy can be
considered most representative of
functional characteristics.
34. Limitations of Ecological Pyramids
It does not take into account same organism belonging to two or
more trophic levels (e.g., human occupies more than one trophic
levels in an ecological pyramid).
It assumes a simple food chain something that never exists in
nature. It does not accommodate food web.
Decomposers are not given any place in ecological pyramids
even though they play a vital role in ecosystem.
37. Ecological Succession
Biotic communities are dynamic in nature and change with passage of
time.
The successive replacement of communities in an area over a period of
time is known as ecological succession.
Succession occurring on previously unoccupied sites like a bare rock or
newly formed lake is called primary succession.
38. Secondary Succession
Secondary succession occurs in an
area where natural vegetation has been
destroyed or removed. Example:
Succession in forests destroyed by fire
and excessive deforestation.
Since soil is already present, the rate
of secondary succession is much
faster and hence climax is reached
more quickly.
39. Ecological Succession
Communities at early succession stages
have lower total biomass, higher net
productivity, few species, fewer
heterotrophic species and less capacity to
regulate nutrient cycling than the
communities at later successional stages.
Different communities or stages represented by combinations of mosses, herbs,
shrubs and trees replacing one another during succession are called seral
stages or seral communities.
40. Ecological Succession…
The plants that invade a bare land
initially are called pioneer species.
Symbiotic associations (Example:
Lichens) play important role in early
succession.
The terminal stage of succession is
called climax community. It is stable
and does not show changes in species
composition as long as environmental
condition remain the same.
41. The succession occurring in water
bodies like ponds and lakes is called
hydrarch succession.
The succession taking place in area with
low moisture (rock and sand) is called
xerarch succession.
Ecological Succession…
42. Changes during Biotic Succession
Small short lived plants to large long lived plants.
Unstable biotic community to stable biotic community.
Little biodiversity to high degree of biodiversity.
Greater niche specialisation.
Increase in biomass.
43. Changes during Biotic Succession…
Increase in humus content of soil.
Aquatic or dry conditions to mesic conditions.
Simple food chains to complex food webs.
Reduction in productivity.
Reduction in ecological disturbances.
45. Succession on Bare Rocks (Xerarch)
Lower plants like lichens form a crust over bare rocks and
begin to form soil from their organic remains and by
stimulating chemical breakdown of rocks.
Lichens are followed by mosses which speed up process of
soil formation.
Lichens and mosses are pioneer species forming the
pioneer community.
Accumulation of soil particles in lichen- moss carpet
provides suitable substratum for germination of seeds of
herbaceous plants. Gradually more soil is accumulated in it.
Shrubs are invaded followed by trees.
Dead shoots and fallen leaves accumulate and enrich soil.
47. Succession in Aquatic Environment (Hydrarch)
In a pond phytoplankton and zoo-plankton
constitute pioneer community.
Submerged aquatic plants with their roots anchored
in the mud are next to colonise the pond.
Dead remains of these organisms settle at the pond
bottom.
Floating plant species invade the pond.
With the continued siltation, the pond water
gradually rises and water layer becomes shallow
and rich in nutrients. As a result rooted emergent
plants with aerial leaves are able to colonise the
pond.
48. Succession in Aquatic Environment (Hydrarch)
With increased settling of silt and deposition of dead organic matter
derived from floating and rooted species, pond becomes shallower
until it gets transformed into a terrestrial habitat.
Ultimately terrestrial species like grasses, bushes and trees colonise
the pond area and climax community is established.
The colonisation of land plants usually progresses from margins
towards the centre of the pond area.
Note: Climax stage reflects highest level of vegetation and associated
fauna that can be supported under the given environment conditions.
50. Biogeochemical / Nutrient Cycling
Movement of nutrient elements
through various components of an
ecosystem is called nutrients cycling.
Nutrients cycling involves biological,
geological, and chemical processes and
thus, these nutrient circuits are also
known as biogeochemical cycles.
51. Biogeochemical / Nutrient Cycling
Functions of reservoir is to meet the deficit which occurs due
to imbalance in the rate of influx and efflux.
Standing state is amount of inorganic nutrients found in an
ecosystem.
Amount of inorganic nutrients varies in different kind of
ecosystem and also on seasonal basis.
Environmental factors such as moisture, pH, temperature etc.
regulate rate of release of nutrients into the reservoirs.
52. Standing Crop Standing State
Standing crop is amount of
biomass present in an ecosystem
at a given time.
Standing state is amount of
inorganic nutrients found in an
ecosystem at a given time.
It represents the entire living
matter.
It represents part of non-living
matter.
Continuous synthesis and
consumption of biomass occur in
an ecosystem.
It circulates between living and
non-living components of the
ecosystem.
53. Nitrogen Cycle
The process of conversion of atmospheric nitrogen to water soluble forms of
nitrogen is termed as nitrogen fixation.
Nitrogen exists as two nitrogen atoms joined by very strong triple covalent
bond (N N)
In nature, lightning and ultraviolet radiation provide energy for conversion of
nitrogen to nitrogen oxides. This is called atmospheric nitrogen fixation.
Industrial combustions, forests fires, automobile exhausts and power
generating stations are also sources of atmospheric nitrogen oxides.
Biological fixation of nitrogen is done by bacteria.
57. Symbiotic Biological Nitrogen Fixation
Rhizobium has symbiotic relationship with root nodules of several
legumes such as sweet pea, lentils, garden pea, etc.
The nodules are small outgrowths on roots.
The central portion of root nodules is red due to presence of leg
haemoglobin.
The enzyme nitrogenase is highly sensitive to oxygen, thus requires
anaerobic conditions.
To protect these enzymes, nodules contain an oxygen scavenger called
leg-haemoglobin.
60. Phosphorus Cycle
Phosphorus is major constituent of biological membranes,
nucleic acids and cellular energy transfer systems (ATP, GTP).
Many animals also need large quantities of phosphorus to make
shells, bones and teeth.
Natural reservoir of phosphorus is rock which contains
phosphorus in form of phosphates.
When rocks are withered into some amount of phosphates
dissolved in soil solution is absorbed by roots of plants.
61. Phosphorus Cycle…
Fungi associated with plant roots (Mycorrhiza) facilitate transfer
of phosphates from soil to plants.
Herbivores and other animals obtain phosphorus from plants.
Waste products and dead organisms are decomposed by
bacteria releasing phosphorus into soil
When phosphates are lost to deep sea, they may be recycled
through the activities of sea birds that eat fishes and other
animals that feed in deep waters. Example: Pelicans.
63. Carbon Cycle
Carbon constitute 49% of dry weight of organisms which is next
to water.
Out of total quantity of global carbon, 71% carbon is found
dissolved in oceans. This oceanic reservoir regulates amount of
CO2 in atmosphere.
Fossil fuel also represents a reservoir of carbon.
64. Carbon Cycle …
A considerable amount of carbon returns to atmosphere as CO2
through respiratory activities of organisms.
Decomposers also contribute substantially to CO2 pool by their
processing of waste materials and dead organic matter of land
or ocean.
Some amount of fixed carbon is lost to sediments and removed
from circulation.
Human activities have significantly influenced carbon cycle.
Rapid deforestation and massive burning of fossil fuel have
increased the rate of release of CO2 into atmosphere.
