Ecosystem L2

8/4/2019 Ecosystem L2

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Dr. Sunita Nair / IT B 01.08.11


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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

otherDr. Sunita Nair/ IT B 01.08.11


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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)

Dr. Sunita Nair/ IT B 01.08.11


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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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Ecosystem L2

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