ecosystem l2
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Energy Flow
Lesson Learning Objectives
By the end of the session you will be able to
understand the following
Energy flow in the ecosystem
Food chain
Food web
Ecological pyramids
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Energy Flow
Energy flow is the movement of energy through an ecosystem,through a series of organisms and back to the externalenvironment.
Energy flow through the ecosystem is always UNIDIRECTIONAL.This is governed by laws of thermodynamics
All organisms require energy, for growth, maintenance,
reproduction, locomotion, etc. Hence, for all organisms theremust beA source of energyA loss of usable energyTypes of energy
Heat energyMechanical energyChemical energy
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Energy
All life processes require some form of energy
Nearly all energy comes from the sun and is harnessedby plants through the process of photosynthesis
Most living creatures obtain their energy either byconsuming plants, or by eating organisms that eat plants
The First Law of Thermodynamics
Also called the Law of Conservation of Energy
States that matter can neither be created nordestroyed; the energy needed to do work within an
organism cannot be generated from nothing
Organisms must obtain energy from an outside source,such as through the consumption of plant material or
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The Second Law Thermodynamics
In the universe as a whole, the total amount of energyavailable to do work is declining In other words, the supply of energy to support life is not
limitless
Transformations of energy always result in some loss ordissipation of energyor
In energy exchanges in a closed system, the potential energy
of the final state will be less than that of the initial stateor Entropy tends to increase (entropy = amount of unavailable
energy in a system)
or Systems will tend to go from ordered states to disorderedstates (to maintain order, energy must be added to thesystem, to compensate for the loss of energy)
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Energy flow
This pattern of energy flow among differentorganisms is the TROPHIC STRUCTURE of
an ecosystem.
Producers
Producers Consumers
Decomposers
Heat
Heat
Sun
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Energy flow through ecosystem
SUN
PRODUCERS HERBIVORES CARNIVORES DECOMPOSERS
HEAT
90%
10%
1%
9%
0.9%
0.1%
0.09%
0.01%
0.009%
It is important to note that only one tenth of energy is received from
previous organism.
Less energy is available as we move up.Organisms present on the top of pyramid need more food to meet their
energy.
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ENERGY FLOW
NU =Energy not utilized
R= Respiration
Producers
D E C O M P O S E R S
Herbivores Carnivores TC
NU
NU NU NU
RR R
R
SUN
Refer text book for single channel energyflow
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Primary productivity
Primary productivity (PP) is the rate at which energy
capture by producers. The amount of new biomass (the dry mass of organic
material in the organisms, the mass of water is not usuallyincluded, since water content is variable and contains no
usable energy) of producers, per unit time and space.
PP depends on solar radiation, availability of
water, nutrients, type of plants, chlorophyll
contents etc..
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Gross primary production (GPP): the total amount ofCO2 that is fixed up by plants in photosynthesis.or total amount of energy captured by the plants
Net primary production (NPP): This is the net amountof PP after the cost of plant respiration
= GPP RespirationNet primary production is thus the amount of energystored by the producers and potentially available toconsumers and decomposers.
Net Ecosystem Productivity (NEP): It is the amount ofPP after the cost of respiration by plants, hetertrophsand decomposers,
= GPP Respiration ( RP+RH+RD)
NEP helps to calculate CO2 balance between variousecosystems.
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FOOD CHAINThe transfer of food energy from the source in plants
(Producers) through a series of organisms (Herbivores to
Carnivores to decomposers) with repeated stages ofeating and being eaten is known as food chain.
A sequence of organism, each of which is served assource of food for the next, is called a food chain.
In any food chain energy flows from producers toherbivores to carnivores
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Types of Food Chain Grazing Food Chain: Starts from green plants and goes to
herbivores to carnivoresExample : Grassland & Forest ecosystem(i) Grass Rabbit Fox Tiger
(ii) Grass Grasshopper Frog Snake Hawk
Detritus Food Chain: Starts from dead organic matter and aretaken by their predators
Example: Mangrove ecosystem
Fallen leaves & dead plants Soil mites Insects Fish
Mapple leaves cricket birds hawk
orMapple leaves earth worms shrew owl
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Food chain
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Terrestrial food chain A marine food chain
Producers
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Food Web
A food web is a network of crossing, interlinked foodchains which include primary producers (e.g., grass) anda variety of consumers (e.g., birds) and decomposers(e.g., bacteria, fungi, insects)
or
Complex network of many interconnected food chainsand feeding relationships; a group of interconnecting
food chains
Food web - Establishes pathways by which
nutrients flow through the ecosystem, eventuallyreturning to the physical environment
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Energy Flow and Trophic Structure
Trophic structure An Organisms feeding status in an ecosystem can be
expressed as its trophic level Organisms that obtain their energy from the same
type of source occupy the same trophic level. Each feeding level within an ecosystem represents a
trophic level. Organisms at the top trophic level are not eaten by
any other organisms. Productivity is highest at the lowest trophic level.
Green plants belong to first trophic level, producers. The energy is then utilized by the herbivores which is
the second trophic level. Herbivores are in turn eaten by the carnivores, which
is the third trophic level.
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Trophic level
4
3
2
1
Feeding strategy
Secondary carnivore
Carnivore
Herbivore
Autotroph
Grazing food chain Decomposer food chain
Cricket
Maple tree leaves
Owl
Shrew
Earthworm
Dead maple leaves
Coopershawk
Robin
Trophic levels
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Ecological Pyramids
The graphical
representation ofamount of energy
stored in the bodies of
living things is calledecological pyramids
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The standing crop, productivity, number oforganisms, etc. of an ecosystem can beconveniently depicted using pyramids, wherethe size of each compartment represents the
amount of the item in each trophic level of afood chain.
The general representation of a pyramid is asfollows
producers
herbivores
carnivores
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Types of Ecological Pyramids
Ecological pyramids
are of three types
Pyramid of numbers
Pyramid of energy
Pyramid of biomass
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Pyramid of numbers A pyramid of numbers indicates the number of
individuals in each trophic level.
It may be upright or inverted
Since the size of individuals may vary widely andmay not indicate the productivity of that individual,pyramids of numbers say little or nothing about
the amount of energy moving through theecosystem.
# of producers
# of herbivores
# of carnivores CHP
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Inverted pyramids
Parasitic food chain shows inverted pyramidsof nos.
Parasite, microbes
Herbivores, birds
Producers, trees
And also pond ecosystem shows inverted pyramid of biomass
Fish
Insects
Phytoplanktons
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Pyramid of energy
A diagram that shows the amount of energythat moves from one feeding level to another
A pyramid of energy depicts the energy flow,or productivity, of each trophic level.
Due to the Laws of Thermodynamics, each
higher level must be smaller than lowerlevels, due to loss of some energy as heat(via respiration) within each level.
producers
herbivores
carnivores
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Note that pyramids of energy and yearly biomassproduction can never be inverted, since this wouldviolate the laws of thermodynamics.
Pyramids of standing crop and numbers can be inverted,since the amount of organisms at any one time does notindicate the amount of energy flowing through the
system.
E.g., consider the amount of food you eat in a yearcompared to the amount on hand in your pantry.
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Pyramid of Biomass
If the biomass produced by a trophic level issummed over a year (or the appropriate completecycle period), then the pyramid of total biomassproduced must resemble the pyramid of energyflow, since biomass can be equated to energy.
producers
herbivores
carnivores
Yearly biomass production(or energy flow) of:
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Significance of Food Chain and Food Web
Energy flow and nutrient cycling take place through foodchain and food web which is the key factor to sustain life
on earth. Help to maintain and regulate population size all types of
species .
Help to maintain ecological balance
Food chain shows a unique property ofBIOMAGNIFICATION. Non biodegradable material
( such as pesticides, heavy metals & chemicals etc..) are
accumulated in higher trophic levels.
Example. Biomagnification of DDT
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