Chapter # 25
ENVIRONMENTAL BIOLOGY
“The effect of the environment on the
organism is called Environmental biology or Ecology.”
OR “Ecology is the study of
relationship between the organisms and their environment.”
“Okios” means “Home life or place
of living” and “logos” means “Study” The term Ecology was
first introduced by a zoologist Reiter
in 1885.
Ecology was first of all fully defined
by Ernst Hackel in 1869. As living organisms are of two
types, plants and animals ecology is
divided into Plant Ecology and Animal Ecology.
Levels of Ecological organization
Various levels of ecological
organization are as under;
Population:
“A group of individual of the same
species that live in the same area and share the same
resources.” The word population has
been taken from “populous” which means “people”
Population size is the total number of
organisms living in an area.
Community:
A group of different species of plants
and animals living together in the same place is called
Community.
A community is composed of different
populations. A forest with various trees, shrubs, herbs,
animals, insects, birds, and micro –
organisms is considered as a community.
Ecosystem:
A System in which living organisms and
non-living live together and exchange materials
between them is called Ecosystem”
The word ecosystem was first used by
Tansely in 1935. Ecosystem is the basic structural and
functional unit of ecology.
Biomes:
Ecosystem occupying broad geographical
region is called Biome.
Biome is characterized by distinctive
vegetation as grasses, conifers or broad leaved trees etc.
some major biomes of the world are
forest, grassland, desert, tundra etc. combined biomes of
earth together form the planetary
ecosystem.
It extends about 10Km into the
atmosphere and also the same depth in the oceans. It consists of
three parts. (i) Atmosphere (air) (ii)
Lithosphere (earth) (iii) Hydrosphere (water)
Environment:
Everything around the living organisms
such as light, temperature and soil which affect their life
is called Environment.
The environment provides food, water
and shelter to the organisms.
Habitat:
Specific locality with a particular set
of environmental conditions where organisms live is called
habitat.Niche:
The ecological role that a species
plays with in a community is called Niche.”
The term Niche was first used by Jospeh
Grinnell in 1917. The habitat and the niche are closely
related. Niche is the profession and
habitat is the address of an organisms.
APPROACH TO ECOLOGY
There are two approaches to ecology
(1) Autecology
(2) Syechology
(1) AUTECOLOGY:
The study of relationship of a single
population to its environment is called Autecology.
The term Autecology was introduced by
Schroter in 1896. It is also called population ecology. It
involves the study of individual
organisms their life histories and their relationship to their
environment.
(2) SYECHOLOGY:
The study of the relationship of
different communities to their environment is called
Syechology.”
It is also called community ecology.
This term was also introduced by Schroter. In this case we
study the structure, composition,
development and distribution and their relationship to their
environment.
COMPONENTS OF ECOSYSTEM:
Ecosystem consists of two components:
(1) Abiotic Component: Abiotic
components are the non-living materials of ecosystem. These
are the , light, water, Temperature,
Atmosphere, Fire, Soil, Inorganic material, Topographic
factor, Gravity.
Light:
Sunlight is the source of energy for
all ecosystems. Light affects the living organisms in three
ways i.e. quality, intensity and
duration of light.
Light influences the growth and
distribution of organisms. Of the total light reaching the earth’s
surface, only 1% is used in
photosynthesis. Light also control the structural and behavioural
characteristics of the organisms. In
lower organism the locomotion is influenced by light.
Plants growing in weak light do not
develop chlorophyll. Light duration affects the growth and
flowering. Light also play important
role in animals migration. Light also determine the periods
of activity of animals. According to
tolerance to light intensity plants are divided into two
groups.
(a) Heliophytes:
Heliophytes are the light loving
plants. They grow best in high intensity of light. They have thick
cuticle, more branches with short
internodes.
(b) Sciophytes:
They are shade loving plants. They grow
best in dim light. They have thin cuticle, few branches
with long internodes.Water:
Water is essential for all living
organisms on land. It covers more than 70% of the earth’s
surface. Water acts as a universal
solvent. It is used as a raw material in photosynthesis. It is
most essential for almost all the
metabolic chemical reactions in the body. On the basis of
availability of water the plants are
divided into three groups.
Hydrophytes: Grow in or near water e.g.
Thypha.
Mesophytes: Grow in areas with moderate
water e.g. Crops
Xerophytes: Grow in dry and arid
conditions e.g. Acacia.
Protozoa have contractile vacuoles to
get rid of excess of water. Fished have water proof
exoskeleton which prevent absorption of
water through body surface.
Temperature:
Temperature controls the growth, and
distribution of animals and plants. life functions generally
within a temperature range of 10 – 45
o C.
At 0 o C water freezes in the cells and
the cells rupture. Above 45oC the protoplasm, proteins and
enzymes denature. The temperature at
which the activities of the organisms are at maximum is
called optimum temperature is called
thermal migration.
At high temperature some animals become
inactive called Aestivation. At low temperature some
animals become inactive called
Hibernation. On the basis of temperature tolerance plants are
divided into Megatherm, Microtherm and
Mesotherm. Temperature also determines the breeding
seasons of most animals.
Atmosphere and Wind:
Atmosphere is the gaseous envelop
surrounding the earth. It contain nitrogen (78%) Oxygen
(21%) Co 2 (0.03%). Plants take
nitrogen from the soil in the form of nitrates. CO 2 is used in
photosynthesis as raw material.
Oxygen is required for respiration of
organisms.
Fast moving atmosphere is called wind.
Wind leads to excessive transpiration
which produces desiccation.
It also causes soil erosion and
uprooting of trees.
Wind also help in pollination,
dispersal of sees and fruits.
Soil:
Soil is the upper layer of earth’s
crust. It consists of two layers i.e. topsoil and subsoil. Top soil
is
the surface soil which is 20 – 30 cm
thik. It is dark brown in colour due to the presence of
humans. Topsoil supply nutrients to the
plants. Subsoil lies below the topsoil. It is light brown in
colour and contains large rock
particles. Soil which is good for agriculture is called loam. Soil
is
important to plants because it provide
Anchorage water and nutrients.
Air to roots for respiration.
Inorganic Nutrients:
It includes nitrates, phosphates and
various other salts.
A small portion of these nutrients
available in solution form.
Most of them remain reserved in
rocks.Organism depends on these nutrients for their body
maintenance.
Topography:
Behaviour and structure of earth’s
surface like, hill, slope, elevation is called Topography.
Topography has no direct effect on
organisms. But it modifies other factors like, atmosphere,
temperature. Slope affects the drainage
and stability of soil. Steeper slope support less
vegetation.
At higher altitudes:
Radiation increases, Atmosphere is
thin, Temperature is low, Rainfall is high, and Winds are
strong.
Gravity:
Gravity is the most constant factor
affecting an ecosystem. Plants and animals have some
structural modification to overcome the
pull of gravity. It acts as an external stimulus in the grow
response of plants. Root grows towards
gravity while stem grow away from gravity.
Xylem cells in plant lifting water to
the upper parts of the plants. Birds have light bones and
wings to overcome the gravitational
pull.
BIOTIC COMPONENTS
Biotic components are the living
organisms of ecosystem. These components are of three types;
(i) Procedure
(ii) Consumers
(iii) Decomposer
(i) Procedure:
Green plants are the producers. They
prepare their own food and are called Autotrophs.
Phytoplanktons are the producers of
aquatic ecosystem. Rooted plants are producers of land
ecosystem. A part of this prepared food
is utilized by plant themselves. Remaining part is
utilized by consumers.
(ii) Consumers:
Consumers are mostly animals which get
their food from producer. Consumers are all
heterotrophs. Consumers are of the
following three types:
(a) Primary Consumers: Primary
consumers feed directly on green plants. They are also called
herbivores. The primary consumers of
land ecosystem are insects, cow, rabbits, sheep, and goats.
The Primary consumers of aquatic
ecosystem are mollusks, crustaceans (arthropods) and some
fishes.
(b) Secondary Consumers: They feed on
herbivores and green plants. Secondary consumer
which feed on herbivores is called
carnivores e.g. lion, tiger, hawk etc. some consumers eat both
herbivores, carnivores and green plants
and are called Omnivores.
(c) Tertiary Consumers: These are the
top carnivores. They get their good from primary and
secondary consumers. e.g. lion, tiger,
for, hawks etc.(iii) Decomposers:
They are also called saprophytes or
scavengers. They get their energy from the decomposition of
dead bodies of plants and animals.
Decomposers act as cleaners of ecosystem. Decomposers help
in the recycling of nutrients in the
ecosystem. Bacteria and fungi are chief decomposers of
ecosystem.
CYCLING OF NUTRIENTS IN ECOSYSTEM.
The cyclic movements of chemical
elements of the biosphere between the organism and the
environment are called Biogeochemical
cycles.”
The chemical elements essential for
life in living organisms are called biogenic elements or
nutrients elements. These are of tow
types.
(1) Macronutrients: These nutrients are
needed in large amount like, water, oxygen, nitrogen,
hydrogen.
(2) Micronutrients: these nutrients are
needed in very small amount like , zinc, iron,
molybdenum etc.
NITROGEN CYCLE:
The cyclic movement of atmospheric
nitrogen from air into the soil and back from the soil into
the atmosphere is called nitrogen
cycle.
In the atmosphere nitrogen occurs in
three different states:
(i) Dinitrogen molecule: e.g. N 2
(ii) Nitrogen oxides: e.g. nitrite (No
2 ) and nitrates (No 3 )
(iii) Reduced nitrogen: e.g. ammonia
(NH 3 ) and ammonium (NH +4 )
The chief reservoir of nitrogen is the
atmosphere. In air the nitrogen is about 78%. But it can not
be used in free state by plants or
animals. It cannot be functional unless it is converted into NH 3 .
Most plants absorb nitrogen from oil as
NO -3 .
STAGES OF NITROGEN CYCLE:
Nitrogen cycle complete in the
following way:
(i) Decomposition of dead bodies.
(ii) Nitrogen fixation
(iii) Thunder storms
(i) Decomposition of dead bodies:
Dead bodies are decomposed by fungi and
bacterial into simpler compounds. There are two steps
in this process.
Ammonification: The process in which
the nitrogenous compounds are decomposed by fungi
and bacteria into ammonia (NH3) or
ammonium ion (NH+4) is called Ammonification.
These micro organisms use the protein
and amino acid.
Nitrification: The conversion of
ammonia and ammonium ion into nitrites and nitrate by the
actively nitrifying bacteria is called
Nitrification. Two groups of nitrifying bacteria are
responsible for nitrification.
(a) Nitrosomonas: converts ammonia to
nitrites.(b) Nitrobacter: converts nitrites into nitrates.
Although the plants can utilize
ammonium directly, nitrate is the form in which most nitrogen
moves from the soil into the roots.
(ii) Nitrogen Fixation:
The conversion of atmospheric nitrogen
into simpler compounds, nitrite and nitrate with the help
of some living organisms is called
Nitrogen Fixation.
The organisms which help in nitrogen
fixation are rhizobium bacteria and blue green algae.
There are two types of nitrogen
fixation.
(a) Non – symbiotic nitrogen
fixation
(b) Symbiotic nitrogen fixation.
(a) Non-Symbiotic nitrogen fixation:
This type of nitrogen fixation is carried out by some
bacteria like Azotobacter and
Clostridium, and Nostoc. These organisms live freely in the soil.
They do not form any useful combination
with plants.
(b) Symbiotic nitrogen fixation:
This types of nitrogen fixation is
carried out by the microorganisms like Rhizobium that live
symbiotically in the root nodules of
leguminous plants.
(iii) Thunder Storms:
During thunder storm nitrogen combines
with oxygen to form nitric oxide. This nitric oxide
dissolved in water forming nitrates and
nitric acids. These acids are transferred to the soil by
rain. In the soil these acids combine
with mineral salts to form nitrates which are used by the
plants.
(iv) Dentirification:
Some soil bacterial (pseudomonas) in
the absence of oxygen break down nitrates releasing
nitrogen back into the atmosphere, this
is called denitrification. Oxygen released in the process is
used by bacteria in respiration.
NITROGEN DEPLETION AND ITS REMEDIES:
The lose of nitrogen from the soil is
called nitrogen depletion. It is lost due soil erosion and
activity of some bacteria. Nitrogen
depletion also occurs by the continuous production of crops
in the soil.
Remedies:
Following are few important measures to
overcome the shortage of nitrogen in the soil;
Nitrogen fertilizers should be added to
the soil.
Use of organic manure.
Crop rotation should be practiced.
In rice fields Nostoc are added.
Legumes crops (pea, beans etc) should
be grown.
Farmland may not be cultivated for a
few years.ENERGY FLOW IN THE ECOSYSTEM
Energy is required by all organisms for
their vital activities.
Sun is the main source of energy for
all ecosystems.
Green plants trap the sun energy and
convert it to food.
During this process some of the energy
is lost as heat during respiration.
Plants are eaten by herbivores and the
energy is transferred to them.
Here some energy is also lost as heat
during metabolic process.
Only a small energy is stored in the
body of herbivores.
Then a sequence of eating and being
eaten starts.
Finally the energy reaches the top
consumers.
Top consumers die and are decomposed by
bacteria and fungi.
A small amount of energy is used by
decomposers and rest is lost as heat to the environment.
Thus at each step in the transfer of
energy from one organisms to another a large amount of
energy it lost.
This energy does not return to the
living organisms. The organism must obtain fresh supply of
energy for its use. In ecosystem the
flow of energy occur in only one direction and does not
complete a circle.
INTERACTION AND INTERDEPENDENCE OF
ORGANSISM
Living world needs a regular flow of
energy. Organisms interact and inter-dependence between
organisms may be;
Useful to both partners
One partner get benefit and other is
harmed.
Beneficial for one partner and other
remain unaffected.
Interaction and interdependence between
organisms may be of following type;
(i) Predation
(ii) Parasitism
(iii) Symbiosis
(iv) Grazing
(i) Predation:
When members of one species eat those
of another or same species is called Predation.
An animal that preys on other animals
for food is called predator.
The animal that is caught and eaten is
called prey.
A predator animal is often larger than
its prey. Predators select food on the basis of size and
strength of prey. If prey population
increases it will support more predators. If the prey is killed
in large number, the predator’s
population will also decrease. Predation maintain the biological
fitness of the two populations and
stability of ecosystem.
The presence of prey in an are without
its predator is disastrous.
(ii) Parasitism:
Parasitism is a one sided relationship
between two dissimilar organisms in which one is benefited
and the other is harmed. The organism
which get food, and shelter is called parasite.The organisms which
provide food and shelter is called host. In parasitism the weak takes
benefit
from the strong. The parasite may or
may not harm the host. Diseases in living organism caused
by parasites are called infestation.
Most parasite infect only a specific host. Parasite may be;
Viral Parasites: Such as plant and
animals viruses.
Microbial Parasites: Such as bacteria,
fungi, protozoan etc.
Phytoparasites: Such as plant
parasites.
Zooparasites: Such as animal
parasites.
Ectoparsites: They live outside the
host’s body e.g. leeches
Endoparasites: They live inside the
host’s body e.g. liver, fluke.
Patialparasites: They spend only a part
of their life cycle as parasite.
Permanent parasites: They spend their
entire life as parasite.
(iii) Symbiosis:
Symbiosis is an association between two
dissimilar organisms which live together for mutual
benefit. Symbiosis means “living
together”
This type of association may be
continuous or transitory obligate or facultative. There are two
types of symbiosis. (a) Mutualism
(b) Commensalism
(a) Mutualism: The symbiotic
association in which both the partners get benefit and neither can
survive without the other is called
Mutualism.
Following are some of the examples of
mutualism.
Root Nodules: in root nodules of
legume plants nitrogen fixing bacteria (Rhizobium)
live. The bacterial fix atmospheric
nitrogen for the roots. The root provide food and
shelter to the bacteria.
Pollination: Certain insects such
as bees and butterflies get food from the nectar of plants
and in return bring about cross
pollination.
Lichens: The symbiotic association
between algae and fungi is called lichen. The fungus
absorbs water and minerals. Algae
prepared food by photosynthesis. Neither of the two
can grow independently.
Cellulose Digestion: A flagellate
protozoan Trichonympha lives in the intestine of wood
eating termites where it digests
cellulose. The protozoan gets food and shelter from
termite. A similar relationship occurs
between cow and bacteria.
(b) Commensalism:
In this type of relationship only one
partner get benefit while the other member neither benefited
nor harmed. Following are same of the
examples of commensalism.
Epiphytes: Epiphytes are the plants
growing on other plants. They use other plants only
as support. Tree is neither harmed nor
benefited.
Barnacles and whales: Barnacles
attached to the backs of whales and turtles, get a free
ride to better feeding places.
Crabs and Sea mussels: certain
crabs live in the mantle cavities of sea mussels for
protection.
Sharks and Remoras: Remoras are
small fish which attached to the body of shark. As
the shark feeds, the remoras pick up
the scraps. The remoras benefit from this
relationship the shark is not affected
at all.(d) Grazing:
Grazing is the relationship between
herbivores and the grasses of grassland. Animals that feed on
grasses are called grazers. Cows,
sheep, horses etc, are all grazers.
Significance: Grazing is useful as well
as harmful. Some of its effect is as under. Grazing help is
shaping the grassland ecosystem.
Grazing removes the seeding and reduces the competition in
grassland. It provides secondary
productivity like meat and milk from the sheep, goat etc.
Overgrazing destroys the grassland
ecosystem and converts it to desert. Trampling by grazing
animals make the soil compact and makes
it unsuitable for vegetation.
SUCCESSION:
A long term process of gradual changes
in the community structure over a period of time is
called Succession.
The term succession was first used by
Hult in 1885. Cowles in 1899 laid the foundation of
successional studies. Clements
elaborated the principles and theory of succession. Succession is
unidirectional process. Succession is
initiated by hardy invaders called pioneers.
These species are gradually replaced by
others. In succession the final stable and mature
community is called climax.
Causes of Succession:
The causes of succession may be;
Climatic: Such as flood, fire,
erosion, volcanic activity.
Biotic: such as activity of
organisms like overgrazing, human activities.
All these causes destroy the existing
populations in an area.
TYPES OF SUCCESSION:
The succession may be of the following
two types.
Primary Succession
Secondary Succession
Primary Succession:
The succession occurring for the first
time on an originally bare area is called primary
succession. It start on bare rock,
river delta, glacial debris etc.
Secondary Succession:
The kind of succession occurs in the
area where the vegetation has been destroyed is called
secondary succession. It usually starts
after forest fire, cutting of the trees, flood and erosions.
The pace of the secondary succession is
faster than the primary succession.
Depending on the habitat succession may
be.
Hydrosere: Succession that starts in
aquatic environment
Mesosers: Succession that starts in
area with sufficient moisture.
Xerosere: Succession that starts on a
dry soil or habitat.
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