UNIT 1 ECOLOGY AND ECOSYSTEM

Structure
1.1 Introduction
Objectives
1.2 Ecology
Definition
History of Ecology
Subdivisions of Ecology
Relationship of Ecology with Other Disciplines of Biology
1.3 Environment
External and Internal Environment
Natural versus Artificial (man-made) Environment
1.4 Population
1.5 Community
Types of Community
Growth-form and Structure
1.6 Ecosystem
Components of Ecosystem
Size of Ecosystem
Types of Ecosystem
Natural and Artificial Ecosystem
I 1.7 Biosphere
1.8 Summary
1 1.9 Terminal Questions ,

1.10 Answers

1.1 INTRODUCTION
You have already been introduced to the concepts of environment, ecology, ecosystem,
energy flow and nutrient cycling in the foundation course on Science and Technology. As
you are aware ecology is the scientific study of the reciprocal relationship between
organisms, including microbes, plants, animals as well as man, with their environment. It
deals with the ways in which organisms are moulded by their environment, how they make
use of environmental resources including energy flow and mineral cycling. Everything that
surrounds or affects an organism during its life time is collectively known as its environment '

which comprises both living (biotic) and nonliving (abiotic) components. The extinction of
, many plant and animal species, pollution of the environment and population explosion are
some of the major ecological problems affecting the balance of nature on a global scale. In
order to manage the earth and its life support systems, it is thus imperative to understand its
ecological processes.
In this unit, which is the first unit of the ecology course, we will begin by briefly explaining
some of the basic terms and concepts of ecology. We shall then discuss the comprehensive
definition, history, scope and the various branches of ecology. Besides, we will also describe
the basic features of ecosystem structure and function.
Before starting this unit please go through Units 14 and 15 of the Block 4 (Environment and
Resources) of the foundation course to refresh your memory about ecology. These units will
help you understand the contents discussed in this unit.

t' Objectives
After you have studied this unit you would be able to:
define and use in the proper context terms such as ecology, environment, population,
community, ecosystem and biosphere,
outline the development of the discipline of ecology,
, describe the three main subdivisions of ecology, namely autecology, synecology and
habitat ecology,
I
show with the help of a diagram the interrelationshipbetween ecology and other
biological disciplines,
i
i
Environment and its distinguish between natural and man-made (artificial) environments,
Components , a enumerate the basic numerical and structural attributes of population,
describe the characteristic features of community and distinguish between major and
minor community,
describe the components of an ecosystem.

1.2 ECOLOGY

1.2.1 Definition
Very often a word has a precise well-defined meaning in scientific literature but is loosely
used in everyday language. It is, therefore, necessary for you to be clear about a few
concepts and definitions before we begin the study of ecology.
Ecology is a familiar term today. Although ecological studies have been going on for many
years, however, it is only recently that people have become aware of ecology as a part of
their daily life. These days newspapers and magazines provide ample space to highlight the
nature and the consequences of man's impact on nature -deforestation, soil erosion. the
Bhopal gas tragedy, the Chernobyl disaster, ozone hole, global wanping and many other
problems. Public outcry about slich problems clearly emphasises the relevance of ecology
for our society. Ecology is now a well-developed branch of science having increasing
importance to human welfare and survival.
The term ecology was coined only as late as 1868. It has been derived from two Greek
words namely, 'Oikos' meaning home or estate and 'logos' meaning study. Literally it
means the study of the home or household of nature. Ecology is defined 'as the scientific
study of the relationship of the living organisms with each other and with their
environment.'
Ecological studies are aimed to understand the relationships of organisms with their
environment. This could be best achieved by extensive field observations and experimental
studies to verify the field observations.

1.2.2 History of Ecology

The roots of ecology lie in Natural History, which is as old as human civilisation itself. As a
matter of fact man indulged in ecology in a practical sort of way, though unknowingly, since
early history. In primitive societies every individual was required to have intimate
knowledge of his environment for survival, i.e., of the forces of nature and of plants and
animals around him. Primitive tribes, which were dependent on hunting, fishing and food
gathering needed detailed knowledge of their environment to obtain their sustenance. Later,
the adoption of settled agricultural life further stressed the need to learn practical ecology for
the successful domestication of plants and animals.
Our ancient Indian texts are full of references to ecological principles. The classical texts of
the Vedic period (1500 BC-600 BC) such as the Vedas, the Samhitas, the Brahmanas and
the Aranyakas-Upanishadscontain many references to ecological concepts.
'Caraka' is to be pronounced as The Indian treatise on medicine, the Caraka-Samhita (I st Century AD4th Cenklry AD)
Charaka i.e. T5 and and the surgical text Susruta-Samhita (1st Century AD-4th Century AD), show that people
'Susruta' as Sushruta i.e. during this period had a good understanding of plant and animal ecology. These texts
contain classification of animals on the basis of habit and habitat, land in terms of nature of
soil, climate and vegetation; and description of plants typical to various localities. Caraka-
Samhita contains information that air, land, water and seasons were indispensable for life
and that polluted air and water were injurious for health.
Similar awareness of ecological issues was prevalent in Europe in the 4th Century BC. The
early Greek philosophers were well aware of the importance of environmental studies.
Hippocrates in his work 'On Airs, Waters and Places' stressed the need for ecological
background for medicdl students, as he emphasised the effect of water, air and locality on
health and diseases in man. Aristotle classified animals on the basis of habit and habitat.
Theophrastus (370-250 BC) was the first person to introduce ecological approach long
before the term ecology was coined. He studied plant types and forms in relation to altitude,
moisture and light exposure.
After a gap of several centuries European m W s t s made significant contribution to
ecological thinking. The French Naturalist Georges Buffon (1707-1788) in his book Natural
History (1756) made a serious attempt to systematise the knowledge concerning the relation
of animals to environment.
In the early eighteenth century Anton-van Leeuwenhoek (1632-1723), the microscopist,
pioneered the study of food chain and population regulation which have grown into the
major areas of modern ecology.
It was Hanns Reiter who in 1868 appears to have coined the tern 'ecology' by combining
the two Greek words Oikos (home) and Logos (study). However it was the Gernan biologist
Ernst Haeckel(1866-1870) who for the first time elaborated the definition of ecology as
follows:
"By ecology we mean the body of knowledge concerning the economy of nature -
the investigations of the total relations of animal both to its inorganic and to its
organic environment; including above all, its friendly and inimical relation with
those animals and plants with which it comes directly or indirectly i ~ t contact
o -
m a word, ecology is the study of all the complex interrelations referred to by
Darwin as the conditions of the struggle for existence."
A few year$ earlier to Haeckel, the French zoologist Isodore Geoffroy St. Hilaire and the
English naturalist St. George JacksomMivart had proposed the terns "ethology" and
"hexicology" respectively, which are almost similar to 'ecology'. A British zoologist
Charles Eton (1927) in his pioneering book "Animal Ecology' defmed ecology as scientific
natural history.
The concept of community in ecology was applied by Karl Mobius (1877) to animals.
Whereas Forbes (1887). Warming (1909). Cowles (1899), Clements (1916) and many others
made notable contributions to the study of plant and animal communities.
The concept of 'population' and its several related aspects developed in the early part of the
twentieth century. Mathematical techniques were used for understanding community
ecology. These mathematical and statistical methods have since been applied for an
understanding of population dynamics.
In 1935 a distinguished British botanist, Sir Arthur Tansley introduced the concept of the
ecosystem or ecological system. This was a major development in the history of ecology.
The concept of ecosystem alongwith the ideas on the trophic-dynamic aspect 6f community The IBP is a world-wide plan of
developed by Lindeman (1942), and biogeocoenoses by Sukachev (1944) stimulated study of biological productivity
investigations on the organism -environment complex from a holocoenotic standpoint and and human welfare. initiated by
International council of
led to a major breakthrough in the progress of ecology. Recently, an American ecologist Scientific Unions (ICSU) a non-
Eugene P Odum (1971) has defined 'ecology as the study of the structure and function of governmental organisation in
nature'. Paris. IBP was launched with the
aim of filling in the lacunae in
In India, ecological studies began as elsewhere with the descriptive phase at the end of the the knowledge of certain
nineteenth century. Descriptive accounts of the forests were prepared by the forest officers ecological areas. by means of a
(1875-1929). However, the first comprehensive ecological contribution was made in 1921 co-ordinated comprehensive
by Prof P. Dudgeon of Allahabad University who described the role of environment in the approach including
standardisation of methods to
succession of communities. ensure comparable results. The
By the 1940s there was sufficient ecological infornation of the descriptive and study was divided into 7 sections
depicted below.
observational kind. There was now a need for precise determination of the behaviour and
distribution of plants (individually or in groups) in relation to specific environmental factors. Areas Studied in the IBP
This led to the experimental approach (1940-1965). Extensive synecological studies were Programme
Productivity of terrestrial
canied out on forest and grassland communities and autecological studies on trees, herbs communities
h d grasses under the guidance of Prof. R. Misra, who established a flourishing school of Production process
ecology at the Banaras Hindu University, by the 1960s. Conservation of terrestrial
communities
In the early sixties the need for developing a better understanding of the structure and Productivity of fresh water
function of different ecosystems was considered necessary for the effective management of communities
natural resources. especially in view of the growing human population. hoductivity of marine
communities
With this view, the International Biological Programme (IBP) was launched (1964-1974) Human adaptability
with a focus on the biological basis of productivity and human welfare. Under the aegis of Use and management of
biological resources
this programme, productivity of different terrestrial and aquatic ecosystems was evaluated
apart from studies on human adaptability, conservation of ecosystem and the use of
biological resources.
Envirwment and its Much of the recent interest in ecology stems from the problems caused by rapid population
Components growth and widespread deterioration of environment due to pollution of air, soil and water.
Ecological studies are now increasingly geared to promote conservation and rational
utilisation of natural resources through international efforts such as Man and Biosphere
Programme of UNESCO (MAB), United Nations Conference on Human Environment held
at Stockholm in 1972, United Nations Environment Programme (UNEP), International
Union for Conservation of Nature and Natural Resources, (IUCN) and World Wide Fund for
Nature (WWF). The science of ecology has much to contribute in solving the problems of
environment.

133 Subdivisionsof Ecology

Ecology was earlier divided into plant and animal ecology. However, modem ecology does
not make any such distinction since plants and animals are intimately interconnected and
interdependent amongst themselves and on their environment.
The three main subdivisions of ecology today are given below:
i) Autecology, ii) Synecology, iii) Habitat ecology.

AUTECOLOGY SYNECOLOGY HABITAT ECOLOGY

(study of the ecology (study of the ecology . (descriptive study
of an individual in of groups or communities \of both the organisms
relation to the in relation to their and the kind of the
environment) environment) environment or habitat
where organisms live)

Autcfology Population Community Ecosystem approach

ofa ~ h 3 Y (study of groups of
Species (study of (study of communities together ,

(study of individuals individual with their non-living -

individual of a given communities) environment, interacting
species) - (species) together so as to function
as a system)

i) Autecology: It is the study of individual species or individuals in relation to the

environment. There are two approaches to autecological studies (a) autecology of
species where individual species are studied (b) population ecology where individuals
of the same species are studied.
ii) Synecology: It is the study of the community of living organisms as a unit. The
difference between autecology and synecology could be explained by the following
example. If a neem tree (or several peem trees) or a crow (or several crows) are studied
 in relation to the environment then this would be an autecological study. However, if the E c o k .ndEeosynk~~
study deals with a forest community as a whole in which many different buds, trees and
animals share the same area, then it would be called a synecological approach.
Synecological studies can be of two types. a) community ecology is concerned with the
study of biotic (living) community comprising of interdependent plants and animals in a
particular area, b) ecosystem ecology which is a recent development in ecology. It deals
with the community of living organisms and their environment as an integrated unit of
nature.
iii) Habitat ecology : It is the study of the habitat or environment of organisms and its effect
on the organisms. In this approach different types of habitats such as terrestrial, fresh
water, marine, and estuarine are the focus of study.

1.2.4 Relationship of Ecology with Other Disciplines of Biology

In order to understand the scope and relevance of ecology let us consider its position in
relation to other biological disciplines, with the help of a diagram in the shape of a cake see
Fig 1.1. . 1

*Y

Others
-
Fig 1.1 :The layered biological cake showing tbe relationshipd ecology with other biological diplines.

This hypothetical biological cake has several horizontal layers representing the 'basic'
divisions of biology, common to all organisms -morphology, physiology, genetics,
ecology, evolution, molecular biology, developmental biology etc. These horizontal layers
are divided vertically into unequal 'taxonomic slices' of biology as well. Each such slice is
labelled by the specific kinds of organism. The thicker slices represent large divisions of
biology and are labelled Zoology, Botany, Bacteriology etc. The thinnq slices are labelled a
Phycology, Ornithology, Protozoology as they deal with specific type of organisms.
Let us consider slice 'A', i.e. ornithology - the study of birds. This slice with its horizontal
layers of molecular biology, developmental biology, genetics, ecology etc. indicates that
there are different approaches to the study of birds. The approach may be molecular or
ecological, or of any other type, or a combination of two or more approaches. The
'biological cake' analogy helps us appreciate that ecology is a basic division of biology.
It is often important to restrict work to certain taxonomic species or groups because
different kinds of organisms require different methods of study. For example, one cannot
study pigeons and bacteria using the same methods. However, the modem ecological
principles have provided many unifying concepts such as energy flow, nualent cycling and
population dynamics for comparing diverse ecosystems.
Environment and its
Components 1.3 ENVIRONMENT

All organisms are intimately dependent on the environment from which they derive their
sustenance. Organisms from virus to man are obligatorily dependent on the environment for
food, energy, water, oxygen, shelter and for other needs. The environment is defined as 'the
sum total of living, non-living components; influences and events, surrounding an
organism'. The relationship and interaction between organism and environment are highly
complex.
For the convenience of study, environment is broadly classified into two components:
abiotic (or non-living) and biotic (or living), as shown in Table 1.1.
Table 1.1 :Components of environment

Abiotic Components I Biotic Components

Energy Green plants

Radiation Non-green plants
Temperature & heat flow Decomposers
Water Parasites
Atmospheric gases and wind Symbionts
Fire Animals
Gravity Man
Topography
Geologic subswtum
Soil

You should realise that the environment is not static. The biotic and abiotic factors are in a
flux and keep changing continuously. The organisms can tolerate changes in environment
within a certain range called 'range of tolerance'.

13.1 Exterrral and Internal Environment

Let us try to understand the concept of environment with some examples. Consider Fig 1.2
Can you identify the environment of a single carp fish in the pond?

FG 13: A pond I
I

Its environment consists of abiotic components sych as light, temperature, water in which
nutrients, oxygen, other gases and organic niatter are dissolved. The biotic environment
consists of microscopic plankton as well as higher plants and animals and decomposers. The
plants are of different kinds such as phytoplankton, partly submerged plants and plants and
trees growing around the edge of the pond. The animals consist of zooplankton, insects,
worms, molluscs, tadpoles, frogs, buds and various kind of fishes. The decomposers are the
saprouophs.
The environment of the fish described above is its external environment. Living organisms
also possess an internal environment, enclosed by the outer body surface. The body surface
acts as an exchange banier between the ex'temal and the internal environment (Fig 1.3a & b b g y and Ecosystem
b). In the case of unicellular organisms however, the boundary of the cell is also the
boundary of the organism. The exchange of materials in single celled organisms is camed
out directly with the external environment to which they are exposed (Fig 1.3a).
/

Reduced c a b n compounds
External Environment (or energy to-synthesize,them)
Usable nitrogen
Exchange of gases Compounds for
protiin synthesis
"Internal Environment"

Inside of cell

of the organlsm Water' balance

Metabolic wastes
~hemicai~n other
d
specific ion exchange

Multicellular Organism Unicellular Organism

a,

Fig 1.3. :I n multicellular organisms except for the celb Fig 13b: Exchanges that are
forming the outer body surface, most cells are exposed to tbe necessary between a living cell and its
internal environment of the organism from whiih they immediate environment.
exchange energy and materials, whereas in unicellular
organisms the cell surface is a b the boundary between .
organism and environment. All exchanges a n made directly
between the cell and the external environment.

The internal environment is relatively stable as compared to the external environment.

However, it is not absolutely constant. Injury, illness or excessive stress upsets the intemal
environment. For example, if a marine fish is transferred to a fresh water environment, it
will not be able to survive. \

1.33 Natural versus Artificial (Man-made) Environment

The environments discussed so far are, natural environments. In several instances man has
greatly altered the natural conditions and created new situations known as artificial or man-
made environments. Examples of artificial environment are cultivated fields or cities. Let us
see the difference between the natural and artificial environment by considering the city
environment.
The city environment is a product of man's own design. The atmosphere of the city is
generally polluted due to the emission of various gases from factories, motor vehicles and
elect@ power plants. Water is obtained not from streams directly b:~tafter it has been
filtered and disinfected in a water treatment plant. The metabolic wastes and garbage are not
disposed of locally but have to be carried through sewer lines for treatment or for dumping
in a remote place far away from the city. No food is grown in the city but is imported from
rural areas for the city dwellers,
In a city people live in buildings made of bricks, stones and cement. Houses and offices of
well-off people are air-conditioned creating an atmosphere which remains free from the
influence of outside environment. Furthennore, to make life comfortable modem amenities
like fans, fridge, radio, television etc. are installed, requiring electricity which Is generated
by man artificially.
The man-made city environment consumes excessive amounts of energy and materials and
needs constant care, supervision and management to keep it habitable (Fig 1.4).
Environmat .adits
Components Materials

R g 1.4: As eitks grow in size,more food .utertb md eoergy arc dnwn hwn tbe environment md
lam;rscd ameunts d beat and waste arc returned to Uw environment. a) a small town, b) a huge city.

1.4 POPULATION

You must be familiar with the term 'population'. It is one of the most talked about issues of
this century. It is feared that the rapid growth of the world population if allowed to continue,
might outstrip the food supply in the near future. The present high rate of population growth
is a major concern of the governments, scientists and administrators. Have you ever
wondered as to what is meant by population?
Specks is defined as a group of In a technical sense 'population' is defured as a group of freely inte-ng individuals of
Populations consisting of the! same species present in a specific area at a given time. For example, when we say that
sexually or potentially
interbmding organisms of the
the population of a city is 50,000, we mean that there are 50,000 individuals of Homo
same kind, repduaively sapiens in that town.Other living organisms, for example cats and dogs present in the city
i&lleted from other such groups. are not included as they are populations of two different species.
In nature, population of a species is subdivided into a number of local breeding populations
called deme. Demes are geographically separated populations of the same species. For
example, the garden lizards of Qutub Minar. Delhi, form a separate deme from the garden
lizard of Lodi Gardens, Delhi or the garden lizards of Swaraj Bhawan, Allahabad.
.
Yonsequently, in a deme each individual has an equal opportunity of mating with another
individual of the opposite sex, but not with individuals in another deme. Because of frequent
. mating and similar environmental conditions members of a deme resemble each other more
closely.
A population has traits of its own A population exhibits certain characteristicswhich can only be expressed at the population
which differ from those of level and not shared by the individuals of the population. For example, individual organisms
individuals forming a
population. An individual is born
are born, grow and die but characteristicssuch as birth rate, death rate, density are only
once and dies once but a meaningful at the population level.
population continues. perhaps
changing in size depending on The attributes of a population are of two basic types :i) Numerical attributes such as .
h e birth and death rates of the density, natality (birth rate), mortality (death rate), dispersal and ii) structural attributes
population. An individual is like age distribution, dispersion and growth form. Some of the basic attributes of population
female or male, young or old but are briefly described below.
a population has sex ratio and
age structure
a) Numerical attribukx
Density :number of individuals per unit area.
Natality (Birth rate) :the rate at which new individuals are added to a population through
reproduction.
 Mortality (Death rate) :the rate at which individuals are lost from a population by death. , Ecology and Ecosystem
Dispersal :the rate at which individuals of a population emigrate or migrate from an area.
The two contrasting curves of
population growth may be
b) Structural attributes: modified or combined or in
different ways depending on the
Population growth form :refers to the pattern of population growth. There are two basic peculiarities of different
patterns of population growth represented by 'T'and "S" shaped growth curves, see Figure organisms and environment.
1.5 for explanation. Generally the 'J' shaped growth
-
curve is typical of species which
reproduce rapidly and which are
greatly affected by seasonally
fluctuating environmental factors
such as light, temperature and
rainfall. In this type of curve the
population density increases
nipidly in exponential .
(geometric) progression 8, 16,
32.64. 128 etc. manner till a
peak is reached. After this there
is a sudden crash or decline due
to environmental or other factor.
The S shaped or sigmoid growth

-
curve is characteristic of
biological population in general.
Time In this type of curve there is a
slow increase initially in the
Fig 15 :Two t y p e d popuhtlon (Sah.pcd .ad J-&aped) growth curvea population density, followed by
exponential growth (similar to
Dispersion: the pattern of distribution of individuals in space, that of 'J' graph's exponential
Age distribution :the proportion of individuals of different age groups in a population. growth). After this the
population density growth slows
Now you know some of the more important attributes of a population. It is reasonable to down gradually due to increase
in environmental resistance (sum
ask: How populations are studied? Do all attributes have equal importance, or are some total of environmental limiting
more important than others? In analysing population, the main attributes studied is the factor which prevent the biotic
density of the population which depends on four parameters: i) natality, ii) mortality, potential from being realised)
ii) immigration and, iv) emigration (see below) until an equilibrium is reached
and maintained.
Immigration

>-
Natality
+ L
kj.ity :
+ -
Mortality
Active migration is not possible
in plants, though seeds may be
dispersed over long distance by
wind. water and animals.
Emigration

Thus whenever the density of a population falls or rises, we try to find out which of the four
parameters have changed.

1.5 COMMUNITY

If you look around yourself you will notice that populations of plants and animals seldom
occur by themselves. The reason for this is quite obvious. In order to survive individuals of
any one species depend on individuals of different species with which they actively interact
in several ways. A population of squirrels would require fruits and nuts for food and trees
for shelter. Even plants cannot exist by themselves; for example, they require animals for
, seed dispersal, pollination and soil microorganism to facilitate nutrient supply to them
through decomposition.
1 In nature 'an aggregation of populations of different species (plant andlor animals) in an A mat of lichen on a rock
1 area, living together with mutual tolerance and beneficial interactions amongst themselves surface or a cow dung pad
1 and with their environment, form a biotic community. covering only a few centimetfes,
a forest or a coral reef extending
Communities in most instances are named after the dominant plant form species. A over a considerable area are all
grassland, for example, is dominated by grasses, though it may contain herbs, shrubs, and examples of communities as
each would contain several
I
t
trees, alongwith associated animals of different species.
interacting and interdependent

i The definition and description of the community so far must have made you aware that the populations of different species
of organisms.
size of a community is not fixed or rigid; communities may be large or small.
Environment and its 1.5.1 Types of Community
Components
On the basis of size and degree of relative independence communities may be divided into
two types:
i) Maor Community :.These are large-sized, well organizedmd relatively independent.
They depend only on the sun's energy from outside and are independent of the inputs and
outputs from adjacent communities. A tropical ever green forest in the North-East of India is
a good example of a major community.
ii) Minor Communities :These are dependent on neighbouring communities and are often
called societies. They are secondary aggregations within a major community and are not
therefore completely independent units as far as energy and nutrient dynamics are
concerned. A cow dung pad would be a good example of such a community.

1.5.2 Growth-form and Structure

In a community the number of species and size of their populations vary greatly. A
community may have one or several species. The environmental factors determine the
characteristic of the community as well as the pattern of organisation of the members in the
community, the characteristic pattern of the community is termed structure which is
reflected in the roles played by various populations, their range, the type of area they
inhabit, the diversity of species in the community and the spectrum of interactions between
them. As a result the structure of community is as follows:
i) Dominance :In each community, a few over topping species are present in greater bulk.
By their greater number or biomass (living weight) the dominant species modify the habitat
characteristic and influence the growth of other species in the community. In most
communities only a single species, being particularly conspicuous, is dominant and in such
case.the community is named after the dominant species, as for example spruce forest
community. In some communities, however, there may be more than one dominant species,
as in oak-fir forest in the west Himalayas.
Relative abundance is a measure ii) Species diversity :An important attribute of a community is its species diversity. The
Of pmportionOf different diversity is calculated both by the number of species (richness) and the relative abundance
species occurring in a
community of each species (evenness). The greater the number of species and more even their
distribution the greater is the species diversity.
It is important to realise that species diversity and dominance are interrelated. Communities
with one or a few dominant species are characterised by low species diversity whereas
communities where no single species is truly dominant and individuals are equally
distributed among all species. are charactensed by high species diversity.
Diversity is also related to the stability of the community. A stable community is one which
is able to return to its original condition after being disturbed in some way. Communities
with high species diversity are comparatively more stable because many alternative
pathways exist in such communities to enable the individuals to obtain the required energy
and nutrients. To put it differently, the presence of a large number of species would mean
that if one species disappears or declines, its function and place can be assumed at least in
part by another. It is now however, increasingly realised that in some situations greater
diversity does not necessarily result in greater stability. Stability is more dependent on the
number of well adapted species than on the total number of species present.
Communities created by man such as lawns, c?ragricultural fields are very unstable and
require great deal of constant manipulation and maintenance.
iii) Mutual interrelationship among individuals of a community : Mutual
interrelationship includes all the direct and indirect effects that organisms have upon each
other. The three relationship which we shall discuss are (a) competition, (b) stratification,
and (c) depkndence.
a) Competition :Demand for a common resource by different organisms results in
competition. Competition between individuals of different species is called interspecific;
when it occurs between individuals of the same species it is called intraspecific.
b) Stratification :Different organisms in a community develop a characteristic pattern of
stratification to minimise competition and conflict among the members of the community.
Plants and animals of each layer differ in size, behaviour and adaptation from those of othei
iayers. Tropical forests represent good example of vertical stratification as shown in the Ecoiogy and Ecosystem
Fig 1.6.

Strata

mttina veaet&on
Fig 1.6 : I n order to avoid competition organlams in a community exhibit vertical stratification, M shown
in a segment of a tropical forest, whkh may have M many an five or six strata or vegetation,
providing a number of habitats for organism.

The tall growing trees form the overstory and modify the light and moisture conditions for
the shorter trees growing under them. These in turn determine the conditions for the ground
vegetation. In moist tropical rain forests upto five distinct strata can be formed.
Competition in the community is not limited within a species. Different species in the
community compete with each other for nutrients, space, light and other resources. Plants
and animals of each layer differ in size, behaviour form and adaptation from those of other
layers. Stratification is a practical strategy to minirnise interspecific competition i.e.
competition between different species. For example, if several different species develop
simultaneously and have similar demands, then they will all survive in approximately equal
numbers and occupy the same position (dominant or not dominant) and layer in the
community. Those species which do not have overlapping requirements will affect each
other much less and hence will occupy different functional positions or sub layers in the
community. For example, consider a tall growing tree which outgrows a potentially short
one under the same conditions. The former occupies a higher level. The tall trees with
widespread canopy dominate the area and influence light and moisture conditions. As a
result the tall trees control the characteristic in a forest community. Only those species of
organisms can survive which can withstand the environmental conditions created by the
dominant species. The community characteristics changes if the dominant species is
eliminated due to some reason. This is because the position of dominance would be assumed
by other species. The non-dominant species present in the lesser strata probably offer little
direct competition to the dominant species. Indirectly, however, they may offer serious
competition to the dominant species in matters of regeneration. For a dominant species to be
successful it should be able to compete with other species during its early phase of growth.
Competition for survival is most obvious between seedlings of different species since all
depend on the same restricted environment.
C) Dependence :In a community there are some species which are wholly dependent on the
dominant member for survival. Bryophytes, thallophytes and a few vascular small plants are
examples of such organisms. These dependent organisms require special conditions such as
shade and moisture provided by the dominant species. The dependent species will die if the
dominant species are eliminated.
Animals in a community are usually dependent on plants. Large mobile animals like deer are
not necessarily limited to a single community. However, several less mobile species are
Envlronmmi m d its definitely restricted to a single community. For example, certain species of insects and birds
Components have specific association with a particular vegetation type.
In addition to the mutual interactions among organisms of a community, they also actively
interact with their environment. In a community only those plants and animals survive
which are adapted to a given environment. The climate determines the type of environment,
and hence the type of organisms in a community. For example, it is the variation in the
climate which determines whether a given area becomes a desert or a forest. The
environment of an area in turn would determine the types of organisms which could survive
there.
iv) Trophic structure :Organisms in a community are closely interrelated with each other
through feeding relationships.
Another aspect which is quite obvious in a community is that in areas of extreme climatic
conditions both species diversity or the number of species are greatly reduced. This is
because only a few species are able to adapt to the difficult environment.
Communities which extend over a considerable area generally have also locally diverse
conditions of soil or topography. Thusin a community local habitats may be supporting
markedly different species which are very different from the general community
composition.
Members of a community share the same habitat and its resources. A community represents
only the living organisms occupying a given area. When both the living and non-living
components are considered as an integrated unit we would be dealing with an ecosystem, a
concept which will be considered in the next subsection.

4
1.6 ECOSYSTEM
Plants, animals and human beings live in association with a wide variety of other plants and
animals. These communities of organisms are not mere ad boc collections of individuals or
populations but they represent a highly ordered dynamic and complex organisation. Such
complex natural organisation with their living and non-living environments that controls
them and from which the living organisms derive their sustenance are technically called as
"ecosystem" or an "ecological system".
The interaction between living organisms and their environment is very much a two way
process: organisms affect and are in turn affected by their surroundings. Professor Arthur
Tansley, a British botanist, in 1935 proposed the term ecosystem and defined it as the
"system resulting from the integration of all living and non-living factors of the
environment". He regarded ecosystem as nQtonly the organism complex but also the whole
complex of physical factors forming the environment.
The concept of this interacting system has proved extremely valuable and the ecosystem is
regarded as a basic unit for ecological studies.

1.6.1 Components of Ecosystem

The components of the ecosystem can be categorised into abiotic or non-living and biotic or
living components;
 Abiotic components :The important abiotic components are
a) Energy : basically from the sun is essential for maintenance of life. In the case of
plants, the sun directly supplies the necessaty energy. Since animals cannot use solar
energy directly they obtain it indirectly by eating plants or animals or both. Energy
determines the distribution-prganisms in the environment.
b) Materials: (a) organic compound\oteins, carbohydrates, lipids, humic substances
which are formed from inorganic into them on
decomposition. (b) inorganic carbon, carbon dioxide,
water, sulphur, nitrates, phosphates, and ions of vari-tals are essential for
organisms to survive.
c) Climatic factors: light, heat, temperature, wind, humidity, rainfall, snowfall etc.
d) Edaphic factors (structure and composition of soil along with its physical and chemical
characteristics) :also exert significant influenceon the organisms.
Biotic components :Biotic components include living organisms comprising plants,
animals and decomposers and are classified according to their functional attributes into
producers and consumers.
a) Roducers -Autotrophs (self-nourishing)are green plants as they synthesise
carbohydrates from simple inorganic raw materials like carbon dioxide and water in the
presence of sunlight by the process of photosynthesis for themselves, and indirectly for other
non-producers. In terrestrial ecosystem, producers are basically herbaceous and woody
plants while in marine and fresh water ecosystems producers are various species of
microscopic algae. Chemosynthetic bacteria are also producers. However, unlike plants
which constitute the major producers, these bacteria, which are found in deep ocean trenches
where sun energy is absent, derive energy by the process of chemosynthesis from the
hydrogen sulphide seeping through cracks in the sea floor.
b) Consumers -Heterotrophs (other nourishing) are incapable of photosynthesis and
depend on organic food derived from animals, plants or both. Consumers can be divided into
two broad groups namely macro and micro consumers. (i) Macro consumers or phagotrophs
feed on plants or animals or both and are categorised on the basis of their food'sources.
Herbivores are primary consumers which feed mainly on plants e.g. cow, rabbit.
Carnivores feed only on animals. Secondary consumers feed on primary consumers e.g.
wolves. Carnivores which feed on secondary consumers are called tertiary consumerse.g.
lions which can eat wolves. Organisms which consume both plants and animals are called
omnivores e.g. men. (ii) Micro consumers -Saprotrophs (decomposersor osmotrophs) are
chiefly bacteria and fungi which obtain energy and nutrients by decomposing dead organic
substances (detritus) of plant and animal origin. Some of the products of decomposition such
as inorganic nutrients released in the ecosystem are reused by producers and thus recycled.
t
Earthworm and certain soil organisms such as nematodes, and arthropods are also detritus
feeders and help in the decomposition of organic matter.

1.6.2 Size of Ecosystem

As you know an ecosystem may be as small and as simple as a cow dung pad or as complex
and large as an ocean or the biosphere itself, comprising a wide variety of species. An
interesting point to observe is that ecosystems occur within ecosystem. To take an example,
cow dung ecosystem may be contained in a forest ecosystem which is contained in the
biosphere.
In some cases, like a pond ecosystem, the boundaries are well defined. In the case of forests,
grasslands and deserts there are no sharp boundaries. These ecosystems often are separated
I , from adjacent ecosystems by a transition zone or a diffused boundary zone called ecotone.
Organisms of adjacent ecosystems intermingle in the ecotone zone; consequently they may
have greater diversity of species than the neighbouring ecosystems.

1.6.3 Types of Ecosystem

Basically ecosystems are of two types : terrestrial and aquatic. If you travel from plains to
the mountains in the Himalayas, you notice significant changes in the landscape. Deserts,
! grasslands, crop fields, forests and glaciers represent different terrestrial ecosystems.
Oceans, estuaries, mangroves, coastal marshes, rivers, lakes, ponds and swamps are
examples of aquatic ecosystem.
Environment and its Ecosystems can also be grouped into two categories, namely natural and artificial or man-
Components made as shown below:
Subdivisions of Ecosystems
ECOSYSTEM
I

Natural Ecosystem Artificial Ecosystem

(Man modified ecosystem)
TaAstrial I (cultivated field,
city, village)
(Tundra, forest.
grassland)
1
Fresh Water Marine
(Sea. ocean)

Lotic lo low in^water) Lentic (stagnant water)

(River. stream) (Lake, pool, ditch, marshes)

1.6.4 Natural and Artificial Ecosystem

i) Natural ecosystems are those which are mostly free from human disturbances, such as
tropical forests, grasslands, oceans, lakes and deserts.
ii) Artificial or man-modified ecosystems are formed as a result of human modification of
the natural ecosystems. For example, man has transformed natural forests and
grasslands into crop fields. An extreme example of an artificial ecosystem is a city.
Increasing human interference has destroyed many natural ecosystems and replaced
them with artificial ecosystems,'such as crop fields, urban centres and industrial
estates.
All ecosystems are fully integrated with the neighbouring ecosystems and communicate with
each other in varying degrees through the import and export of both energy and nutrients.
Materidnument cycling is An ecosystem is a dynamic system characterised by energy flow and nutrients cycling.
exchange and recycling of Substances constantly flow through it, and there are sufftcient supplies of energy within the
minerals and chemicals between
ecosystem to allow for this flow to take place. See Fig 1.7. Ecosystems also possess
living and non-living
components of the ecosystem. considerable self-regulating ability, called homeostasis. due to which they tend to recover
from minor perturbations.
-

Fig 1.7 : A d i m illusbating the manner in which nutrients cycle through an ecosystem. Energy does
not cycle because d l that is derived from the sun eventually dissipates as heat.

y by the ................................ of the

biotic community.
 1.7 BIOSPHERE

Biosphere is that part of the earth where life can exist. It is a narfqy layer around the surface
of the earth. If you visualise the earth to be the size of an apple the biosphere would be as
thick as its skin.
As you can see in Fig 1.8 the biosphere extends from the floor of the ocean some 11,000
metres below the surface of the earth to the top of the highest mountains, or about 9,000
metres above the sea level. Its most densely populated region is just above and below the sea
level.

Fig 1.8 : Vertical dimensions of the biosphere. Life exists from the highest mountain peaks to the depths
of the ocean. Life at the extreme is however, rare. Most organisms are limited to a narrow region
depicted here between 6000 metres above sea level and 200 metres below sea level.

Biosphere represents a highly integrated and interacting zone comprising of atmosphere

1I (air), hydrosphere (water) and lithosphere (land) as you can see in Fig 1.9.

/ Life inthe biosphere is abundant between 200 metres (660 feet) below the surface of the
1 ocean and about 6,000 metres (20,000 feet) above sea level as shown in Fig 1.8.
Biosphere is absent at extremes of the North and South poles, the highest mountains and the
deepest oceans, since existing conditions there do not support life. Occasionally spores of
fungi and bacteria do occur at great height beyond 9,000 metres, but they are not
metabolically active, and hence represent only dormant life.
Environment and its
Components .

1.9 : The b i i rdds at tk intemctbn d l k b p k e , atmosphere and hydrosphere. As shown

here the Moclpbm is e n e r g i d by sunlight.

The energy required for the life within the biosphere comes from the sun. The nutrients
necessaj for living organisms come from air, water and soil and not from outside. The same
chemicals are recycled over and over again for life to continue. Living organisms are not
uniformly distributed throughout the biosphere. Only a few organisms live in the polar
regions, while the tropical rain forests have an exceedingly rich diversity of plants and
animals.

1.8 SUMMARY
In this unit you have studied the following:
Ecology : the study of relationship of living organisms to one another and to their
environment.
History of ecology from primitive man to the present time with special reference to the
development of ecology in India.
- The subdivision of ecology into (i) autecology -study of individuals or populations of
a single species with respect to their environment, (ii) synecology -study of interacting
population of different species, (iii) habitat ecology - which deals with the study of
habitat and the organisms within it.
The relation of ecology with other biological fields such as botany, zoology,
protozoology etc.
The environment, which consists of biotic, abiotic factors, influences and events
surrounding the organisms and may be artificial or natural, external or internal.
Population :a group of sexually or potentially interbreeding organisms of the same
species which has attributes of two basic types (i) numerical attributes-density,
natality (birth rate), mortality (death rate), dispersal and (ii) structural attributes like age
distribution, dispersion and population growth form.
Community is a localised group of several populations of different species and,may be
classified into major and minor communities.
Community attributes consist of growth form and structure: dominance, species
dirersity, mutual interrelationship among members of a community and trophic
structure.
 Ecosystem, which is a localised group of community and their physical environment Ecology and Ecosystem
maintained on energy flow and nutrient cycling.
Components of ecosystem such as i) abiotic or non-living environmental factors: energy,
materials, climate. and edaphic factors ii) biotic or living environmental factors: plants,
animals and decomposers.
Natural ecosystem which is unaltered or only slightly altered by man, and artificial
ecosystem which is a result of major alterations of natural ecosystem by man.
Biosphere, which contains all the living organisms on earth, together with their
interaction with global physical and chemical environment, and maintains a system of
energy use and material cycling. This system runs on energy from the sun which after
use is given up in space as low grade heat.
-
1.9 TERMINAL QUESTIONS

1) Fill in the blanks choosing the appropriate words:

a) Biosphere consists of ....................... , ....................... and ........................
b) The density of population ....................... with increase in mortality and
emigration.
C) The living organisms in a forest form a ....................... community.
d) The density of population ....................... with increase in natality and
immigration.
e) The community of organisms on a log form a ....................... community.
minor, lithosphere, major, atmosphere, increases, decreases, hydrosphere
2) Label the hypothetical cake diagram showing the relationship of ecology with other
biological disciplines.

3) State the difference between naturcu and artificial ezosystems in five lines and give
examples.

1 4) State the difference between macroconsumers and microconsumers in five lines.

Environment and its
Components
5) Given below are important ecological terms and their definitions. What you have to do
ir this exercise is to match the appropriate definition in column I1 with the ecdogical
terms in column I. Write the number of the appropnate match in the given box.

W m nI Column XI

1) b10gy [ 1 It is an assemblage of population of different

species inhabiting a particular area. living
together with mutual tolerance and beneficial
interactions amongst themselves and with their
environment. '
2) Community 1 It is defined as the scientific study of the
relationship of living organisms with each other
and with their envimnment.
3) Ecosystem [ 1 It is defined as a gmupof organisms of the same
species occupying a particular area,' a1 a particular
time, capable of mating freely.
4) Population [ 1 It is a unit consisting of a community in a given
area interacting with the physical environment so
that a flow of energy leads to closely defined
hophic structure, biotic diversity and material
cycling within the system. .

6) Describe in brief the contributions of ancient Greek philosophers in the development

of ecology.

7) State the various definitions of ecology given by the following ecologists.

a) Ernst Haeckel
.................................................................................................................................. c..,.....

/ ...........................................................................................................................................
/'

b) Charles Elton

...........................................................................................................................................
C) Eugene P. Odum

...........................................................................................................................................
8) Outline the divisions of ecology.
9) Answer very briefly the following questions:
a) What do you understand by dominant species?

b) What is species diversity?

.........................................................................................................................................

.........................................................................................................................................
c) What do you-understand by relative abundance?

10) What are the vertical limits of the biosphere?

..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
..........................................................................................................................................
........................................................................................................................................

1.10 ANSWERS

Self-assessmentQuestions
1) The Caraka-Samhita and Susrura-Sarnhita have sufficientmaterial to indicate that
people during this period had a good understanding of animal and plant ecology. Both
the Caraka-Samhita and Susruta-Samhita classif) animals on the basis of habit and
habitat, land on the basis of nature of soil, climate and vegetation. Plants typical to
various localities are also described. In addition the Caraka-Samhitas contain
information that air, land, water and seasons were indispensable for life and that
polluted air and water were injurious to health.
2) a) autecological, b) synecological, c) ecosystem.
3) Environment is defined as the sum total of living, non-living components, influences
and events surrounding an organism. The environment external to an organism is its
external environment and the environment enclosed within the body of an organism or
in a living cell is r e f d as internal environment
4) a) False, b) True, c) False, d) False, e) True, f) True, g) False, h) False.
5) a) saprotrophs, b) animals, c) producers, d) cycle, flows, e) ecosystem, d) ecotone.

Terminal Questions
1) a) Atmosphere, lithosphere, hydrosphere; b) decreases; c) major; d) inmses;
e) minor
2)

.Ad
I 'layers'

HorizonW layers

r-y

3) Natural ecosystems are those which are undisturbed or relatively undisturbed by

humans, such as a natural forest, an eshlary, whereas artificial ecosystem are those
ecosystems which have been significantly altered by humans or created with specific
objectives such as wheat field, tea garden, lawn.
4) Both are heterotrophs, but while macroconsumers feed on living plants or animals or
both for obtaining nourishment, microconsumers decompose dead bodies of plants and
animals and obtain energy from the decomposition of the dead bodies.

6) The early Greek philosophers were well aware of the importance of environmental
studies. Hippocrates in his work on airs, waters and places, stressed the need for
ecological background for medical students as he explained the effect of water, air and
locality on health and diseases on man. Aristotle classified animals on the basis of
. habit and habitat. Theophrashs studied plant types and forms in relation to altitude,
moisture and light exposure and is regarded as the first person to introduce the
ecological approach long before the term ecology was coined.
7) a) Ernst Haeckel defined ecology as the body of knowledge concerning the economy
of nature -the investigations of the total relations of animal both to its inorganic
and to its organic environment, including above all, its friendly and inimical
relation with those animals and plants with which it comes directly or indirectly
into contact -in a word, ecology is the study of all the complex interrelations
referred to by Darwin as the conditions of the struggle of existence.
b) Char1es Elton has defmed ecology as scientific natural history.
c) Eugene Odum has defmed ecol6gy as the study of the structke and function of
nature.
8) The divisions of ecology.

AU~COUK;Y SYNECOLOGY HABITATE C O ~ Y

(Study of the (Study of the (Descriptive study of born
ecology of an ecology of p p s the organisms and
individual in or communities in the kind of the envimnment
relation to the relation to their or habitat where organisms live)
environment) environment)
I I
7 7
Autecology Population Community . E-@= a~pr~rd
1
or a speck Eedogy ECohJY
(Study of (Study of (study of (st& of groups of
individual individuals individual ccmununities together with
given species) of a given communities) their non-living envimnmmt,
species) interacting together so as to
function as a system)

9) a) In a community dominant species are a few overtopping species which by their

greater bulk mod@ the habitat characteristics they occupy and influence the
growth of other species of the community.
b) Species diversity is a measure of the number of species (richness) and the relative
abundance of each species (evenness).
C) In a community different species vary in their abundance. Relative abundance is a
measure of relative proportion of different species in a community.
10) The vertical limits of the biosphere extend from 9000 metres above sea level to the
floor of the ocean which is 11 0 0 metres below the sea level.