PRINCIPLES OF ECOLOGY

UNIT-1

Introduction to Ecology

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What is ECOLOGY?

 – Ecology is the branch of biology that deals with the relationships of organisms to one another and to       their physical surroundings or immediate environment.

– It deals with the interactions between organisms and their natural habitats.

– We (humans) are also a part of the ecosystem and dependent on it for our survival because we too are     after all just one more species on this planet earth.

– The term ecology ("Ökologie") was coined in 1866 by the German Zoologist, Ernst Haeckel (1834–      1919). It was derived in 19th century from the Greek word

“Ökologie” meaning: οἶκος, "house", or "environment"; -lοgίe, "study of”.

– Ernst Haeckel gave the following statement originally in German language, which

says; “By occology we understand the science of economy of the domestic affairs

of organisms. It enquires into the whole relation of animals with their inorganic

and organic surroundings, and above all their friendly and hostile relations with

such animals and plants as they come into directed or indirected contact with or

in short with all the involved interdependence that Darwin designated as the

condition of the struggle for existence”

– Ecology (aka Bionomics) is essentially an interdisciplinary field

incorporating biology, geography and geoscience (earth science).

– Ecology means study of biota, its surrounding environment and their

interactions amongst themselves as well as their physical

surroundings.

– An organism's environment is made up of the living or biotic, and

non-living or abiotic components

– For instance; the study of food chains in wetlands, study of habitats

in deserts, etc.

– This relationship could be between a particular organism with its

environment or between human groups and their physical

environment or between flora and fauna with their physical

surroundings.

 

 

What is an ECOSYSTEM?

– Ecosystem emphasises on the importance of transfers of

Materials and/or energy between similar or different

Organisms and their environment.

– The term "ecosystem" was coined by British ecologist Arthur

Tansley.

– A HABITAT is an ecological or environmental area that is

Inhabited by a particular species of animal, plant, or other

Types of organisms.

– It is made up of physical factors as well as biotic factors

Arthur Tans ley

In the 1890s.

(1871-1955)

– Example of a habitat could be any geographical area or even

As small as inside an organism.

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Historical perspectives of

Ecology

– Ancient Indian writing reflects the reference of ecological

Thoughts like Vedic, Epic, Puranic etc. describe the

Importance of Vayu (air), Jala (water), Desha (topography)

And Kaal (time).

– The inter-relationships between the organisms and their

Environment are described by some outstanding Greek

Scholars like Aristotle, Hippocrates, and Theophrastus etc.

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Historical perspectives of

Ecology….. (contd.)

– Baron A .V. Humboldt (1804) explored the tropical and temperate South

America and published 26 volumes based on the data collected by him.

– Alfred R. Wallace published three books titled (I) The Malaya

Archipelago (ii) the geographical Distribution of Animals and (iii) Island

Life.

– Geoffrey St. Hillarie (1859) first used term ‘ethology’ to refer the study

Of relationship of organisms with their environment.

– St. George Jackson Milvart proposed the term ‘Hexicology’ to refer the

Study of organisms with their relation to environment regarding the

Nature of locality, temperature and amount of light that best suit them

And also their relation with other organisms as enemies, rivals or

Accidental and involuntary benefactors.

– Reiter (1868) first introduce the term ‘Oekologie’ to describe the inter-

Relationship that exist between organisms and their environment.

 

 

Historical perspectives of

Ecology….. (contd.)

– Ernst Haeckel (1869) was a German Biologist and was credited to have coined the term

„Ecology‟ and used it widely in his literature. He also precisely gave its definition.

– Le Coq Sendfner and Kerner introduced for the first time the plant communities as an

Aspect of ecology.

– Karl Mobius (1877) described the Animal communities.

– Schroeder and Kirchner (1896) introduced the term ‘synecology’

– McFadden (1957), a British Biologist laid down the principles governing the relationship

Of plants and animals and their relations to environment.

– K. Frederic’s (1958) defined ecology as ‘the science of living beings as members of the

Whole of nature’.

– F. Faster Darling (1963) defined ecology as „the science of organisms in relation to their

Total environment, and the inter-relationship of organisms inter-specifically and between

Themselves’.

– A.G. Tansley (1935) introduced the term „ecosystem‟ and led to the development of

Concepts of productivity and energy relations in ecology which is now referred to as

Bigeneric approach.

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Ecological Hierarchy

Ecology deals with the interactions of all the various levels of

Biological organization:

– Organisms

– Populations

– Communities

– Ecosystems

– Biomes

The organization at several levels in an ascending order of

Complexity from a simple individual and culminate to a more

Complex biosphere is called ecological hierarchy.

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Ecological Hierarchy

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Ecological Hierarchy

 

 

DIY - 1

EXPLAIN VARIOUS LEVELS OF ECOLOGICAL HIERARCHY.

Key points:

– Individual organism is the basic unit of ecological hierarchy

– Population: Demography, Ecotype, Demes

– Community

– Ecosystem

– Biome

– Biosphere

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SUBDIVISIONS OF

ECOLOGY

Emphasizing on individual organism or groups of organisms

Living in a particular ecosystem: ecology can mainly be

Divided into two types namely:

AUTECOLOGY & SYNECOLOGY

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*term coined by Schrocter &Kirchner 1896

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Laws of

Limiting factors

Liebig’s law of minimum

Shelford’s law of tolerance

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1. Liebig’s law of minimum

(1840)

Liebig’s Barrel

– Liebig’s law is often visualized using the

Example of a barrel

– The capacity of the barrel is limited by the

Shortest section, no matter how tall the

Other sections are!

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Liebig’s law of minimum

– German Biochemist Justus Liebig (1840)

– Studied: the effect of various factors on the growth of plants

– Found: the total yield of crop plants was dependent – not only on the

Nutrients available in large quantities e.g. CO, H O (since they are

2

2

Abundant in environment) – but on the nutrients present in minute

Quantities in the soil e.g. Boron, Zinc, etc.

– Concluded: “the growth of a plant is dependent on the essential nutrient

Present in minimum amount (limiting factor)” OR “growth only occurs at

The rate permitted by the most limiting factor”

– PARAPHRASED: the strength of a chain is determined by its weakest link

Limiting factor: any environmental factor – that by its increase or decrease

Or absence or presence – limits the growth, metabolic processes, or

Distribution of organisms or populations. E.g. in a desert ecosystem, low

Rainfall & high temperature will be the factors limiting colonization.

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Weakness in Liebig’s law

– considered only the effects of nutrient deficiency

– did not take into account + and – synergisms (factors act in

Concert rather than in isolation)

*SYNERGISM: result of an interaction of two or more factors

So that the combined effect is greater (+) or smaller (-) than

The sum of their individual effects

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Two subsidiary principles to

Law of minimum

1. Liebig’s law is applicable under steady-state conditions

Only i.e. when the average inflow of energy & material

Balances the outflow over an annual cycle.

E.g. in a pond, rate of release of CO2 from decaying organic

Matter controls the rate of production = steady state i.e. CO2 is

The limiting factor, provided light, N, P, K are abundant BUT a

Storm might bring excess CO2 into the pond – the rate of

Production is now controlled by rapidly changing

Concentrations & interactions of many other factors as well.

This continues till CO2 becomes limiting again & thus pond is

Again operated by law of minimum.

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2. Factor-Interaction:

– A high concentration/availability/action of some substance,

Other than the minimum one may modify the rate of

Utilization of the latter.

– The organisms may partially substitute the minimum factor

With another closely related factor present in excess.

E.g. when Strontium is abundant, molluscs can partially

Substitute Sir for Calcium in their shells.

E.g. some plants - when grown in shade – require less Zinc than

When grown in full sunlight → a low concentration of Zn in soil is

Less limiting to plants in the shade than in full sunlight.

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Blackman’s law of limiting factor

(1905)

– Proposed by British plant physiologist, Frederick Frost Blackman

– “a process that depends on multiple factors will have a rate limited by the

Pace of the slowest factor”

E.g. Photosynthesis is a biological process that depends on multiple factors

6CO +12H Energy=C H O +6O +6H O

2

2

6 12 6

2

2

CO, H O, and light energy (sunlight) = limiting factors

2

2

Deficiency/less availability of any of them will slower the

Rate of photosynthesis

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2. Shelford’s law of tolerance

(1913)

– developed by American Zoologist

V.E.Shelford

– Success of an organism depends on a complex

Set of environmental conditions (e.g. the

Climatic, topographic, and biological

Requirements of plants and animals) whenever

Levels of these exceed the maximum or

Minimum limits of tolerance of that organism

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– Limit of tolerance/Zone of tolerance: the range

B/w the maximum or minimum limits of

Tolerance i.e. the optimum environmental

Factors that determine success

– range form species to species & w.r.t. different factors

– The range may vary within the same organism, e.g.

Depending on the life stage (larval vs. adult)

– Still organism may fail to survive because of

Biological interactions (competition / predation)

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Zone of

Intolerance

Zone of

Tolerance

– The zone unfavourable – The zone favourable for

For the growth &

Development of an

Organism

The growth &

Development of an

Organism

– No species grow here

– Abundant species grow

Here

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Zone of tolerance is

Subdivided into:

1. Optimum zone:

Between the minimum

& maximum, allows

Maximum growth &

Development of the

Organism

2. Critical minimum

Zone: the lowest limit

Of tolerance zone,

Below which the

Organisms’ growth is

Restricted

3. Critical maximum

Zone: the highest limit

Of tolerance zone,

Above which the

Organisms’ growth is

Restricted

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Lower limit of

Tolerance

Upper limit of

Tolerance

/

/

Stress zone

/ Critical

Minimum

Zone

Stress zone

/ Critical

Maximum

Zone

Species abundant

No species

Few species

Few species

No species

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Subsidiary principles to

Law of tolerance

1. Organisms have wider range of tolerance for one

Factor, narrow for another

2. Organisms with wider range of tolerance are more

Widely distributed

3. When one factor is not optimum, organism may

Reduce its limits of tolerance for other factors

– E.g. when N2 in soil is limiting (low), resistance of grass to

Drought is reduced – more water is required to prevent

Wilting

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4. Sometimes, organisms may not be living at the optimum range

Of one factor, but other factors are important here

– Cord grass (Spartan alterniflora) grows in marshes because it can

Extrude salt from its leaves better than rooted marsh plants (though it

Can grow better in freshwater).

5. Limits of tolerance for reproductive individuals are narrower

Than for non-reproducing ones

– E.g. adult Cypress tree (Morpankhi/Vaidya) can grow on dry land/

Submerged in water but can reproduce only in moist, unfolded

Grounds

– Adult blue crabs can tolerate brackish waters or freshwaters with high

Chloride & are found upstream. BUT larvae cannot live in such waters.

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Relative degree of tolerance

Factor

Narrow tolerance wider tolerance

Prefix ‘steno’ =

Prefix ‘euro’ =

Narrow

Wide

Temperature

Water

Stenothermal

Eurythermal

Stenohydric

Euryhydric

Salinity

Stenohaline

Euryhaline

Food

Stenophagic

Steno-euryeious

Eurypahgic

Eury-euryeious

Habitat selection

These terms apply to the organism, population, community as well as to ecosystem levels.

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Factor compensation

– Organisms possess capacity to modify the physical

Environment

– This helps reduce the effect of any factor

– Thus genetically differentiated subspecies

Develop in response to a particular set of

Environmental conditions = ECOTYPES

– Ecotypes have optima & limits of tolerance adjusted to

Local conditions

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Combined concept of

Limiting factors

– The presence or success of an organism depends upon a

Complex of factors. Any factor which approaches or

Exceeds the limits of tolerance may thus become the

‘Limiting factor’

– The concepts that combine the law of minimum & law of

Tolerance:

1. In nature, organisms are limited by the quantity &

Variability of materials for which there is a minimum

Requirement

2. There are limits of tolerance of the organisms for other

Components of the environment also

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Why to study these laws?

Understanding these laws helps

– To study complex ecosystems

– To discover the probable weak links & focus

Attention on the most critical/limiting factors

– To careful study of factors that are variable in the

Environment e.g. O2 is often variable in water, so

Might become ‘limiting’ for aquatic organisms

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– All the possible factors are not equally important.

The weak links may be identified

– A ‘variable’ factor for which an organism has

‘definite/narrow’ limits of tolerance requires special

Attention

– e.g. O2 on land is adequate & not variable BUT in water,

Relatively scarce & often variable

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EFFECT OF

PHYSICAL

FACTORS:

TEMPERATURE

LIGHT

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DIY

Explain how the physical factors viz. light

And temperature affect the growth &

Development of animals living in an

Environment.

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