3 Environmental Science : Ecosystem part 1

INTRODUCTION
No life exists in a vacuum. Materials and forces which constitutes its environment and
from which it must derive its needs surround every living organism. Thus, for its survival,
a plant, an animal, or a microbe cannot remain completely aloof in a shell. Instead, it
requires from its environment a supply of energy, a supply of materials, and a removal of
waste products.
For various basic requirements, each living organism has to depend and also to interact
with different nonliving or abiotic and living or biotic components or the environment.
1. Abiotic
The abiotic environmental components include basic inorganic elements and compounds
such as water and carbon dioxide, calcium and oxygen, carbonates and phosphates besides
such physical factors as soil, rainfall, temperature, moisture, winds, currents, and solar
radiation with its concomitants of light and heat.
2. Biotic
The biotic environmental factors comprise plants, animals, and microbes; They interact
in a fundamentally energy-dependent fashion. In the words of Helena Curtis “The scientific
study of the interactions of organisms with their physical environment and with each other,
is called ecology”. According to Herreid II “It mainly concerns with the directive influences
of abiotic and biotic environmental factors over the growth, distribution behaviour and
survival of organisms.
Ecology Defined
(1) Ernst Haeckel (1866) defined ecology “as the body of knowledge concerning the
economy of nature-the investigation of the total relations of animal to its inorganic
and organic environment.
(2) Frederick Clements (1916) considered ecology to be “the science of community.(3) British ecologist Charles Elton (1927) defined ecology as “the scientific natural
history concerned with the sociology and economics of animals.”
(4) Taylor (1936) defines ecology as “the science of the relations of all organisms to all
their environments.”
(5) Taylor (1936) defined ecology as “the science of the relations of all organisms to all
their environments.”
(6) Allee (1949), considered ecology as “the science of inter-relations batwing living
organisms and their environment, including both the physical and biotic
environments, and emphasizing inter-species as well as intra-species relations.
(7) G.L. Clarke (1954) defined ecology as “the study of inter-relations of plants and
animals with their environment which may include the influences of other plants
and animals present as well as those of the physical features.”
(8) Woodbury (1955) regarded ecology as “the science which in investigates organisms
in relation to their environment: a philosophy in which the world of life is interpreted
in terms of natural processes.
(9) A. Macfadyen (1957) defined ecology as “ a science, which concerns itself with the
inter-relationships of living organisms, plants and animals, and their environments.”
(10) S.C. Kendeigh (1961, 1974) defined ecology as “the study of animals and plants in
their relation to each other and to their environment.” Certain modern ecologists
have provided somewhat broader definitions of ecology.
(11) M.E. Clark (1973) considers ecology as “a study of ecosystems of the totality of the
reciprocal interactions between living organisms and their physical surroundings.
(12) Pinaka (1973) defined ecology as “the scientific study of the relationships of loving
organisms with each other and with their environments.” He adds that “it is the
science of biological interactions among individuals, populations, and communities;
and it is also the science of ecosystems-the inter-relations of biotic communities
with their non-living environments.
(13) R.L. Smith (1977), considers ecology as “a multidisciplinary science which deals
with the organism and its place to live and which focuses on the ecosystems.”
ECO-SYSTEM
At present ecological studies are made at Eco-system level. At this level the units of
study are quite large. This approach has the view that living organisms and their non-living
environment are inseparably interrelated and interact with each other. A.G. Tansley (in
1935) defined the Eco-system as ‘the system resulting from the integrations of all the loving
and non-living actors of the environment’. Thus he regarded the Eco-systems as including
not only the organism complex but also the whole complex of physical factors forming the
environment.
HISTORICAL BACKGROUND
The idea of Eco-system is quite an old one. We find in literature some such parallel
terms as (i) biocoenosis (Karl Mobius, 1977), (ii) microcosm (S.A. Forbes, 1887),
(iii) Geobiocoenosis (V.V. Doduchaev, 1846-1903); G.F. Morozov; see Sukachev, 1944),
(iv) hlocoen (Frienderichs, 1930), (v) biosystem (Thienemann, 1939), (vi) bioenert body
(Vernadsky, 1994), and ecosom etc. use for such ecological systems.
The terms ecosystems is most preferred, where ‘eco’ implies the environment, and
‘system’ implies an interacting, inter-dependent complex.
In this way, it can be said that any unit that includes all the organisms i.e. the
communities in a given area, interact with the physical environment so that a flow of energy
leads to clearly defined trophic structure, biotic diversity and material cycle (i.e. exchange
of materials between living and non-living components) within the system, is known as an
ecological system or eco-system.
Eco-system may be visualized as 3-dimensional cutouts from the ecosphere. All primary
and secondary producers composing the ecosystem are its essential elements. The
unique feature of eco-systems is the maintenance of their chemical state and of their
environment.
Thus an eco-system is an integrated unit, consisting of interacting plants and animals
whose survival depends upon the maintenance of abiotic i.e. physicochemical environment
and gradients such as moisture, wind and solar radiation with its concomitants of light and
heat, as well as biotic structures and functions. The integrated unit may or may not be
isolated but it must have definable limits within which there are integrated functions. The
physiologists study various functions in individual plants or animals, but the ecologists
study them at the eco-system level. A real ecologist endeavors for maintaining holistic or
eco-system perspective of the process being studied by him.
ASPECTS OF ECO-SYSTEM
The eco-system can be defined as any spatial or organizational unit including living
organisms and non-living substances interacting to produce an exchange of materials between
the living and non-living parts. The eco-system can be studied from either structural or
functional aspects.
1. Structural Aspect
The structural aspects of ecosystem include a description of the arrangement, types and
numbers of species and their life histories, along with a description of the physical features
of the environment.
2. Functional
The functional aspects of the ecosystem include the flow of energy and the cycling of
nutrients.
Habitat
The non-living part of the eco-system includes different kinds of habitats such as air,
water and land, and a variety of abiotic factors. Habitat can be defined as the natural abode
or locality of an animal, plant or person. It includes all features of the environment in a
given locality. For example, water is used as habitat by aquatic organisms and it comprises
three major categories-marine, brackish and freshwater habitats. Each of these categories

may be subdivided into smaller unit, such a freshwater habitat may exist as a large lake,
a pond, a puddle, a river or a stream.
The land is used as a habitat for numerous terrestrial organisms. It includes many
major categories of landmasses, which are called biomes. Biomes are distinct large areas of
earth inclusive of flora and fauna, e.g. deserts, prairie, tropical forests, etc. Soil is also used
as a habitat by a variety of microbes, plants and animals.
Abiotic Factors
Among the main abiotic factors of the ecosystem are included the follwing:
(1) The climatic factors as solar radiation, temperature, wind, water currents, rainfall.
(2) The physical factors as light, fire, pressure, geomagnetism,
(3) Chemical factors as acidity, salinity and the availability of inorganic nutrients
needed by plants.
Biotic or Biological Factors
The biological (biotic) factors of ecosystem include all the living organisms-plants, animals,
bacteria and viruses. Each kind of living organism found in an ecosystem is given the name
a species. A species includes individuals which have the following features:
(1) They are genetically alike.
(2) They are capable of freely inter-breeding and producing fertile offsprings.
Relationships
In an ecosystem, there exist various relationships between species. The relationship
may be as under:
(1) Effects
Two species may have any of the following kind of effects:
(i) They may have a negative effect upon one another (competition).
(ii) They may have a neutral effect (neutralism).
(iii) They may have beneficial effect (protoco-operation and mutualism).
(2) Other kinds of Relationship
The species may aggregate, or separate, or show a random relationship to one another.
Population
A population is a group of inter-acting individuals, usually of the same species, in a
definable space. In this way we can speak of population of deer on an island, and the
population of fishes in a pond. A balance between two aspects determines the size of a
population of any given species:
(i) Its reproductive potential,
(ii) Its environmental resistance.
In this way population size is determined by the relative number of organisms added
to or removed from the group as under:
(i) Addition
Recruitment into the population is a function of birth rate and immigration rate.
(ii) Removal
Loss from the population is a function of death rate and emigration.
Factors Regulating Population
Following factors does population regulation:
(i) Physical attributes of the environment (e.g. climate),
(ii) Food (quantity and quality),
(iii) Disease (host-parasite relationships).
(iv) Predation,
(v) Competition (inter-specific and intra-specific).
An ecosystem contains numerous populations of different species of plants, animals and
microbes; all of them interact with one another as a community and with the physical
environment as well. A community or biotic community, thus, consists of the population of
plants and animals living together in a particular place.
Division of Ecosystem
The ecosystem can be divided, from the energetic view point into three types of organisms:
producers, consumers, and reducers. These can be explained as under:
(1) Producer
Photosynthetic algae, plants and bacteria are the producers of the ecosystem; all other
organisms depend upon them directly or indirectly for food.
(2) Consumers
Consumers are herbivorous, carnivorous, and omnivorous animals; they eat the organic
matter produced by other organisms.
(3) Reducers
Reducers are heterotrophic organisms like animals; they are fungi and bacterial that
decompose dead organic matter.
FOOD CHAINS OF FOOD WEB
Species are related by their feeding behaviour in food chains or food webs. There are
two basic types of food chains as under-
(i) The consumer food chain includes the sequence of energy flow from
producer+herbivore+carnivore+reducer;
(ii) The detritus food chain pypasses the consumers, going from producer+reducer.
Basic Theme of Ecosystems
(1) Relationship
The first and foremost theme of an ecosystem in that everything is somehow or other
related to everything else, the relationships include interlocking functioning of organisms
among themselves besides with their environment. Biocoenosis and bioecocoenois are roughly
equivalent to community and ecosystem respectively. Biotopes are the physical environment
in which such communities exist. According to Lamotte (1969), it is this network of multiple
interactions that permits us to define the ecosystem completely. Many ecologists regard
Interdependence as the first basic theme of ecology. Ecosystem includes interacting and
interdependent components that are open and linked to each other.
(2) Limitation
The second basis theme is Limitation which means that limits are ubiquitous and that
no individual or species goes on growing indefinitely. Various species control and limit their
own growth in response to overcrowding or other environmental signals and the total numbers
keep pace with the resources available.
(3) Complexity
Complexity is a third characteristic of any eco-system. The three-dimensional interactions
of the various constituent elements of an ecosystem are highly complex and often beyond the
comprehension on the human brain.
GENERAL CHARACTERISTICS OF AN ECO-SYSTEM
According to Smith following are the general characteristics of eco-system.
(1) The ecosystem is a major structural and functional unit of ecology.
(2) The structure of an eco-system is related to its species diversity; as such the more
complex ecosystem has high species diversity.
(3) The relative amount of energy required to maintain an ecosystem depends on its
structure. The more complex the structure, the lesser the energy it requires to
maintain itself.
(4) The function of the ecosystem is related to energy flow in material cycling through
and within the system.
(5) Ecosystems mature by passing from less complex to more complex states. Early
stages of such succession have an excess of potential energy. Later (mature) stages
have less energy accumulation.
(6) Both the environment and the energy fixation in any given ecosystem are limited.
They cannot be exceeded in any way without causing serious undesirable effect.
(7) Alterations in the environments represent selective pressures upon the population
to which it must adjust. Organisms, which fail to adjust to the changed environment,
must vanish.
To conclude the eco-system is an integrated unit or zone of variable size, it comprises
vegetation, fauna, microbes and the environment. Most ecosystems process a well-defined
soil, climate, flora and fauna and their own potential for adaptation, change and tolerance.
The functioning of any ecosystem involves a series of cycles. These cycles are driven by
energy flow, the energy being the solar energy.
STRUCTURE OF ECO-SYSTEMS
Meaning of Structure
By structure of an eco-system we mean as under.
(i) The composition of biological community including species, numbers, biomass, life
history and distribution in space etc.
(ii) The quantity and distribution of the non-living materials, such as nutrients, water
etc.
(iii) Structure of an ecosystem the range, or gradient of conditions of existence, such as
temperature.
Natural And Function of Structure of Eco-system
The structure of an ecosystem is in fact, a description of the species of organisms that
are present, including information on their life histories, population and distribution in
space. It guides us to know who’s who in the ecosystem. It also includes descriptive information
on the non-living features of ecosystem give us information about the range of climatic
conditions that prevail in the area. From structural point of view all ecosystems consist of
following two basic components:
1. Abiotic Substances (Non-Living Components)
The Abiotic substances include basic inorganic and organic compounds of the environment
or habitat of the organism.
(a) Inorganic Components: The inorganic components of an ecosystem are as
undercarbon dioxide, water, nitrogen, calcium, and phosphate. All of these are
involved in matter cycles (biogeochemical cycles).
(b) Organic Components: The organic components of an ecosystem are proteins,
carbohydrates; lipids and amino acids, all of these are synthesized by the biota
(flora and fauna) of an ecosystem and are reached to ecosystem as their wastes,
dead remains, etc.
(c) The climate, temperature, light, soil etc., are othe rabiotic components of the
eco-system.
(3) Biotic Substances (Living Components): This is indeed the trophic structure of
any ecosystem, where living organisms are distinguished on the basis of their
nutritional relationships. From this trophic (nutritional) standpoint, an ecosystem
has two components:
(a) Autotrophic Component of Producers
These are the components in which fixation of light energy use of simple inorganic
substances and build up of complex substance predominate.
(i) The component is constituted mainly by green plants, including photosynthetic
bacteria.
(ii) To some lesser extent, chemosynthetic microbes also contribute to the build up of
organic matter.

(iii) Members of the autotrophic component are known as eco-system producers because
they capture energy from non-organic sources, especially light, and store some of
the energy in the form of chemical bonds, for the later use.
(iv) Algae of various types are the most important producers of aquatic eco-systems,
although in estuaries and marshes, grasses may be important as producers.
(v) Terrestrial ecosystems have trees, herbs, grasses, and mosses that contribute with
varying importance to the production of the eco-systems.
(b) Heterotrophic Component or Consumers
These are the components in which utilization; rearrangement and decomposition of
complex materials predominate. The organisms involved are known as consumers, as they
consume autotrophic organisms like bacterial and algae for their nutrition, the amount of
energy that the producers capture, sets the limit on the availability of energy for the
ecosystem. Thus, when a green plant captures a certain amount of energy from sunlight, it
is said to produce the energy for the ecosystem. The consumers are further categorized as:
(i) Macroconsumers
Marcoconsumers are the consumers, which in a order as they occur in a food chain are,
herbivores, carnivores (or omnivores).
(a) Herbivores are also known as primary consumers.
(b) Secondary and tertiary consumers, if preset, are carnivores of omnivores. They all
phagotrophs that include mainly animals that ingest other organic and particulate
organic matter.
(ii) Microconsumers
These are popularly known as decomposers. They are saprotrophs (=osmotrophs) they
include mainly bacteria, actinomycetes and fungi. They breakdown complex compounds of
dead or living protoplasm, they absorb some of the decomposition or breakdown products.
Besides, they release inorganic nutrients in environment, making them available again to
autotrophs.
The biotic component of any ecosystem may be thought of as the functional kingdom
of nature. The reason is, they are based on the type of nutrition and the energy source used.
The trophic structure of an ecosystem is one kind of producer consumer arrangement, where
each “food” level is known as trophic level.
Standing Corp
The amount of living material in different trophic levels or in a component population
is known as the standing corp. This term applies to both, plants as well as animals. The
standing crop may be expressed in terms
(i) Number of organisms per unit area,
(ii) Biomass i.e.organism mass in unit area, we can measure it as living weight, dry
weight, ash-free dry weight of carbon weight, or calories or any other convenient
unit suitable.
DecomposersIn the absence of decomposers, no ecosystem could function long. In their absence, deadorganisms would pile up without rotting, as would waste products, It would not be longbefore and an essential element, phosphorus, for example, would be first in short supply andthen gone altogether, the reason is the dead corpses littering the landscape would be hoardingthe entire supply. The decomposers tear apart organisms and in their metabolic processesrelease to the environment atoms and molecules that can be reused again by autotrophicpoint of view. Instead they are important from the material (nutrient) point of view. Energycannot be recycled, but matter can be. Hence it is necessary to feed Energy into ecosystemto keep up with the dissipation of heat or the increase in entrophy. Matter must be recycledagain and again by an ecological process called biogeochemical cycle.An IllustrationThe Structure of ecosystem can be illustrated as under with the help of ponds example.1. Abiotic PartThe abiotic or non-living parts of a freshwater pond include the follwing:(i) Water,(ii) Dissolved oxygen,(iii) Carbon Dioxide,(iv) Inorganic salts such as phosphates, nitrates and chlorides of sodium, potassium,and calcium(v) A multitude of organic compounds such as amino acids, humic acids, etc. accordingto the functions of the organisms, i.e., their contribution towards keeping theecosystem operating as a stable, interacting whole.(a) ProducesIn a freshwater pond there are two types of producers,(i) First are the larger plants growing along the shore or floating in shallow, water,(ii) Second are the microscopic floating plants, most of which are algae,These tiny plants are collectively referred to as phytoplankton. They are usually notvisible. They are visible only when they are present in great abundance and given the watera greenish tinge. Phytoplanktons are more significant as food producers for the freshwaterpond ecosystem than are the more readily visible plants.(b) ConsumersAmong the macro consumers or phagotrophas of pond ecosystems include insects andinsect larvae, Crustaces, fish and perhaps some freshwater clams.(i) Primary Consumers: Primary consumers such as zooplankton (animal plankton)are found near the surface of water. Likewise benthos (bottom forms) are the planteaters (herbivores).(ii) Secondary consumers: The secondary consumers are the carnivores that eat theprimary consumers. There might be some tertiary consumers that eat the carnivores
(secondary consumers).

Saprotrophs
The ecosystem is completed by saprotrophs or decomposer organisms such as bacteria,
flagellage protozoans and fungi, They break down the organic compounds of cells from dead
producer and consumer organisms in any of these ways-
(i) Into small organic molecules, which they utilize themselves, or
(ii) Inorganic substances that can be used as raw materials by green plants.
ECOLOGICAL PYRAMIDS
The main characteristic of each type of Ecosystem in Trophic structure, i.e. the interaction
of food chain and the size metabolism relationship between the linearly arranged various
biotic components of an ecosystem. We can show the trophic structure and function at
successive trophic levels, as under:-
Producers Herbivores Carnivores
It may be known by means of ecological pyramids. In this pyramid the first or producer
level constitutes the base of the pyramid. The successive levels, the three make the apex.
Ecological pyramids are of three general types as under:
(i) Pyramid of numbers: It shows the number of individual organisms at each level,
(ii) Pyramid of energy: It shows the rate of energy flow and/or productivity at
successive trophic levels.
(iii) Pyramid of energy: It shows the rate of energy flow and/or productivity at
successive trophic levels.
The first two pyramids
That is the pyramid of numbers and biomass may be upright or inverted. It depends
upon the nature of the food chain in the particular ecosystem, However, the pyramids of
energy are always upright.
A brief description of these pyramids is as under:
1. Pyramids of numbers
The pyramids of numbers show the relationship between producers, herbivores and
carnivores at successive trophic levels in terms or their numbers.
(i) In a grassland the producers, which are mainly grasses, are always maximum in
number.
(ii) This number shows a decrease towards apex, the reason is obvious, number than
the grasses.
(iii) The secondary consumers, snakes and lizards are less in number than the rabbits
and mice.
(iv) In the top (tertiary) consumers hawks or other birds, are least in number.
In this way the pyramid becomes upright. In a pond ecosystem, also the pyramid is
upright as under:
(i) The producers, which are mainly the phyto-planktons as algae, bacteria etc. are
maximum in number;

(ii) The herbivores, which are smaller fish; rotifers etc are less in number than theproducers;(iii) The secondary consumers (carnivores), such as small fish which eat up each other,water beetles etc. are less in number than the herbivores;(iv) Finally, the top (tertiary) consumers, the bigger fish are least in number.However, the case is not so in a forest eco-system. There the pyramid of numbers issomewhat different in shape:—(i) Producer, here the producers, are mainly large-sized trees, they are less in number,
and form the base of the pyramid.
(ii) The herbivores, which are the fruit-eating birds, elephants, deer etc. are more in
number than the producers.
(iii) Thereafter there is a gradual decrease in the number of successive carnivores.
In this way the pyramid is made again upright. However, in a parasites food chain the
pyramids are inverted. This is for the reason that a single plant may support the growth
of many herbivores. In its turn, each herbivore may provide nutrition to several parasites,
which support many hyperparasites. Consequently from the producer towards consumers,
there is a reverse position. In other words the number of organisms gradually shows an
increase, making the pyramid inverted in shape.
2. Pyramids of biomass
The pyramids of biomass are comparatively more fundamentalism; as the reason is they
instead of geometric factor; show the quantitative relationships of the standing crops. The
pyramids of biomass in different types of ecosystem may be compared as under:
In grassland and forest there is generally a gradual decrease in biomass of organisms
at successive levels from the producers to the top carnivores. In this way, the pyramids are
upright. However, in a pond the producers are small organisms, their biomass is least, and
this value gradually shows an increase towards the apex of the pyramid and the pyramids
are made inverted in shape.
3. Pyramid of energy
The energy pyramid gives the best picture of overall nature of the ecosystem. Here,
number and weight of organisms at any level depends on the rate at which food is being
produced. If we compare the pyramid of energy with the pyramids of numbers and biomass,
which are pictures of the standing situations (organisms present at any moment), the pyramid
of energy is a picture of the rates of passage of food mass through the food chain. It is
always upright in shape.


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