CL142 Environmental Sciences

Ecology and Ecosystems

 Ecology - Introduction
• The word ecology is derived from two greek
words “oikos” meaning habitation and
“logos” meaning study
• Ecology is the study of interrelationship
between living organisms and their physical
and biological environment
• It is nothing but the study of living organisms
in their natural surroundings
 Objectives of Ecological Study
• The interrelationship between organisms in
population and diverse communities
• The seasonal changes of an organism (annual,
successional etc)
• Behavior under natural conditions
• Functional adjustments of organisms to their
physical environment
• Energy flow in ecosystem
 Objectives of Ecological Study
• Development in the course of evolution
• Development of mathematical models to
relate interaction of parameters and to
predict the effects
 Classification of Ecology
• Ecology can be divided into
1) Autoecology
2) Synecology
 Classification of Ecology
• Autoecolgy deals with the study of individual
organism and its relation with its
surroundings.
Example : A tree in a forest
• Synecology deals with the study of group of
organisms which are associated together as a
unit.
Example : A forest
 Classification of Ecology
• Further sub-division of ecology is based on
following:
1) Based on taxonomic affinities
• Plant Ecology
• Animal Ecology
 Classification of Ecology
2) Based on habitats
Aquatic Terrestrial
Ecology Ecology

Marine Grassland
Ecology Ecology

Fresh
Forest
Water
Ecology
Ecology

Stream Desert
Ecology Ecology
 Classification of Ecology
3) Based on level of organization

Desert
Ecology

Synecology Autoecology

Population Community Ecosystem

Ecology Ecology Ecology
 Ecosystem
• It is made up of two words “eco” meaning
environment and “system” meaning
interacting and independent complex
• It can be defined as the community of
interdependent organisms together with the
environment
• An ecosystem is the basic functional unit of
ecology
 Difference between Ecology and
Ecosystem
• For example, lets say that ecology would be the
study of the students interaction or relationship
with the classroom as a whole. The classroom
being the environment in which the student
lives, the scientific study would said to
be Student ecology and the set of circumstances
surrounding the student in that environment
would be the teacher/teachers, books, other
students, etc and said to be ecosystem.
 Functions of ecosystem
• Major function of ecosystem is to regulate the
energy flow and bio-geochemical cycles on earth
• It provides information about the amount of
available solar energy, mineral elements etc.
• It gives information about relation between
organisms as well as between organism and
abiotic environment
• It gives information about number of producers
and consumers
Structure of Ecosystem
 Structure of Ecosystem
• All ecosystems have two major components:
1) Abiotic Components
2) Biotic Components
 Structure of Ecosystem
Abiotic Components
• The non-living factors or the physical
environment forms the abiotic components
• It includes
1) Physical factors such as climatic conditions
2) Inorganic Substances such as water, minerals etc
3) Organic Substances such as Carbohydrates,
Proteins etc.
 Structure of Ecosystem
Biotic Components
• The living organisms including plants, animals
and micro-organisms present in an ecosystem
are known as biotic components
• They are classified into 3 main categories:
1) Producers or Autotrophs
2) Consumers or Heterotrophs
3) Decomposers or Reducers
 Producers or Autotrophs
• The living organisms which
manufacture their own food
are known as Autotrophs
• For example, plants have
chlorophyll with which they
trap solar energy and
change into chemical energy
• Auto = self, Trophs = feeder
 Consumers or Heterotrophs
• The organisms which
depend on producers
for their food are
known as heterotrophs
• Heteros = other, trophs
= feeder
 Types of Consumers
1) Primary Consumers or first order consumer
or herbivores:
• The animals which feed on plants or the
producers are called herbivores
• Example – Deer, Goat, Rabbit etc.
 Types of Consumers
2) Secondary Consumers or Primary Carnivores
• The animals which feed on herbivores are
called as primary carnivores
• Examples – Cats , Fox, Snake etc.
3) Tertiary Consumers or Third Order Consumers
• These are the large carnivores which feed on
secondary consumers
• Example – Wolf etc.
 Types of Consumers
4)Quaternary Consumers or Fourth Order
Consumers or Omnivores
• These are the largest carnivore which feed on
the tertiary consumers
• Examples – Lion and Tigers
Types of Consumers
 Decomposers or Reducers or
Saprotrophs
• They breakdown the dead organic material of
producers and consumers for their food
• Example – Bacteria and Fungi
• The decomposers are also known as
saprotrophs (sapro = rotten, trophs = feeder)
Structure of Biotic Components
 Energy Flow in Ecosystem
• All organisms need energy to perform the
essential functions such as maintenance, growth,
repair, movement, locomotion, reproduction etc.
• Sun is the biggest source of energy
• In earth’s atmosphere, about 15 x 108 cal/sq.m/
year of energy is present out of which 47 %
reaches the earth surface and only 1-5 % of
energy reaching the ground surface is converted
to chemical energy by green plants
Energy Flow in Ecosystem
 Energy Flow in Ecosystem
• The plants make use of the raw material and
prepare food with the help of energy derived
from sunlight
• Thus energy from the sun enters the
photosynthetic organisms and passes from
one organism to other in the form of food
Energy Flow in Ecosystem
 Energy Flow in Ecosystem
• The flow of energy is unidirectional and non-cyclic
• The flow of energy is governed by law of
thermodynamics which states that:
1) Energy is neither created nor destroyed but is
transferred from one form to another
2) During energy transfer there is degradation of
energy from a concentrated form (mechanical,
chemical etc) to a dispersed form (heat)
 Energy Flow in Ecosystem
• No energy transformation is 100% efficient; it
is always accompanied with loss of energy in
the form of heat
• Heat energy is continuously lost from a
system and therefore should be supplied on a
continual basis
• Shorter the food chain, more will be the
available food energy
 Energy Flow in Ecosystem
• Longer the food chain, more is the
corresponding heat loss in a system
Energy Flow in Ecosystem
 Ecological Pyramids
• Graphic representation of trophic structure
and function of ecosystem, starting with
producers at the base and successive trophic
levels at the apex is known as ecological
pyramid
• They are of 3 types:
1) Pyramids of numbers
2) Pyramids of Biomass
3) Pyramids of Energy
 Pyramids of Numbers
• It represents the number of individual
organisms at each trophic level of a food
chain per unit area at any time
• Generally represented by number per sq.m
• It can be upright or inverted depending upon
type of ecosystem and food chain
Pyramids of Numbers
Pyramids of Numbers
Pyramids of Numbers
 Drawbacks
• The pyramid does not take into account size
of individual organism i.e all organisms are
considered equal in size
• Number of individuals in a trophic level
depends upon the availability of biomass
• For example, a tree supports several insects
but several trees will support a single
elephant or herbivore
 Pyramid of Biomass
• It is based upon the total biomass at each
trophic level in the food chain
• It can also be inverted or upright
• It is represented by grams/ sq.m i.e dry
matter available
Pyramid of Biomass
 Drawbacks
• Each trophic level indicates standing crops
which is different in different seasons for
example, a deciduous tree has more biomass
in spring but less in winter
• Life span of individuals is not taken into
consideration i.e less lifetiem organism may
have higher biomass
• Biomass differs in its energy content in
different oragnisms
 Pyramids of Energy
• In this type of pyramid, the amount of energy
present in each trophic level is represented
• It is presented by kcal/sq.m/year
• Such type of pyramid gives the best
representation and is always upright
• There is always a sharp decline in energy level
at each trophic levels
Pyramids of Energy
Pyramids of Energy
 Advantages
1) Always upright
2) Based on productivity
3) Gives the idea of actual amount of energy
received at each trophic level
• Such type of pyramid gives by far the best
overall picture of functional aspects of
ecosystem
 Bio-geochemical Cycles
• The cyclic exchange of nutrient materials
between living organisms and their non-living
environment is called as bio-geochemical
cycles
• This cycle includes
1) Hydrologic or Water cycle
2) Gaseous cycle
3) Sedimentary cycle
 Bio-geochemical Cycles
• This type of cycle helps us to understand the
flow pattern of various nutrients, gases etc.
needed for development of life
• It also helps us to understand the relative
importance of a particular member or process
in the cycle
 Carbon Cycle
• Carbon in the form of carbon-dioxide is taken up
by green plants as raw material for photosynthesis
• The organic matter synthesized are passed from
producers to consumers
• During respiration, plants and animals release
carbon back to the surrounding as carbon-dioxide
• The dead bodies of plants and animals as well as
the body waste which accumulates carbon
compounds are decomposed by micro-organisms
and releases carbon-dioxide
Carbon Cycle
 Nitrogen Cycle
• Nitrogen is present in atmosphere in large
amounts (78%) and is fixed either by process of
lightening or biologically by some bacteria
• The biological fixation of nitrogen is 20 times
more than the non-biological methods
• Nitrogen is taken up by plants and passes through
food chain
• Decomposers convert the nitrogen in dead
tissues to nitrites and nitrates which are again
used by plants
Nitrogen Cycle
 Nitrogen Cycle
• Nitrification: Nitrifying
bacteria oxidizes
ammonia to nitrite and
then to nitrate
• Denitrification: Under
anaerobic conditions,
denitrifying bacteria
converts nitrate to
nitrogen gas
 Phosphorous Cycle
• Phosphorous is the main constituent of ATP
and ADP and is very essential for the growth
of plants
• Many rocks contain phosphates
• Due to weathering, it becomes available to
plants
• After death of plants and animals, their waste
is decomposed by micro-organisms releasing
phosphates to soil
Phosphorous Cycle
Phosphorous Cycle
 Sulphur Cycle
• Sulphur occurs in free or combined state
• It is an essential element for living organisms
for synthesizing amino-acids, vitamins etc.
• Burning of fossil fuels and volcanoes releases
hydrogen sulphide and sulphur dioxide gas
which comes in the form of sulphuric acid as
rain forming sulphate compounds
• Some sulphates is also released into soil by
weathering of rocks
Sulphur Cycle
 Food Chain
• In food chain, each organism eats the smaller
organism and is eaten up by the larger organism
• All these organisms are interlinked with each
other and constitute an ecosystem
• The different levels of a food chain are known as
trophic levels
• Each food chain has three main trophic levels:
Producer level, Consumer level and Decomposer
level
Food Chain
 Food Chain
• If any of the intermediate stage of food chain
is removed, the succeeding links of food chain
will be affected
• It is estimated that only 10% of the potential
energy of previous trophic levels is made
available to next trophic level
• Thus, shorter the food chain more will be the
available energy
 Types of Food Chain
1) Predator food chain or Grazing food chain
• Such type of food chain starts from producer
and ends with higher consumer level
• In every trophic level, the size of organism
increases while their number decreases
Predator food chain or Grazing food
chain
 Types of Food Chain
2) Parasitic food chain
• This type of food chain starts with big hosts
and ends with parasitic organisms
• Example:
Cow Worm Protozoa
 Types of Food Chain
3) Saprophytic or Detritus food chain
• This type of food chain starts from dead organism
and ends with decomposers such as bacteria
• Example:
Dead organism Fungi Bacteria
 Food Web
• Various food chains are often interlinked at
different trophic levels to form a complex
interaction between species from view point of
food
• This network like interaction is called food-web
• The food web provides more than one
alternatives of food to most of the organisms in
an ecosystem and therefore, increases their
chances of survival
Food Web
 Symbiosis
• It is a biological relationship in which two
species live in close proximity to each other
and interact regularly so as to benefit one or
both the organism
• It is of two types:
1) Mutualism: When both partners benefit
2) Parasitism: When only one partner benefits
 Types of Ecosystem
1) Forest Ecosystem
• Forest ecosystem have predominance of
trees with large number of species of herbs,
shrubs, climbers and a variety of animals and
birds
• Depending upon climatic conditions forest
can be of different types
 Forest Ecosystem
Types of forests:
1) Tropical rainforests (No dry season)
2) Tropical deciduous forests (Average Rainfall)
3) Tropical scrub forests (Hottest season)
4) Temperate rainforests (Broadleaf with heavy
rainfall)
5) Temperate deciduous forest
6) Evergreen coniferous forest (Woody plants with
normal temperature)
Forest Ecosystem
 Desert Ecosystem
• These ecosystem occurs in regions
where evaporation exceeds precipitation
• Rainfall is less than 25 cm per year
• They have species of various diversity
and consist of drought resistant plants
 Desert Ecosystem
• Deserts are of 3 types:
1) Tropical Deserts (Driest and Hottest) like
Sahara Desert
2) Temperate Deserts (Day as summer and
night as winters) like Mojave Desert
3) Cold Deserts (Cool winters and warm
summers) like Gobi Desert
 Desert Ecosystem
• Desert plants and animals have adaptations
for conservation of water
• Many plants have scaly leaves to reduce loss
of water due to transpiration
• Leaves have thick cuticles
• Desert animals like insects , reptiles have
thick covering to minimize loss of water
 Desert Ecosystem
• Abiotic Components – Temperature is high
and rainfall is low
• Biotic Components
1) Producers – A few species of grass, cactus etc
2) Consumers – Insects, Reptiles, Camels, Birds
etc
3) Decomposers – Few species of fungi and
bacteria with thermophilic nature
Desert Ecosystem
 Aquatic Ecosystem
• On the basis of salinity, aquatic ecosystem can
be freshwater ecosystem and marine
ecosystem
• Freshwater ecosystems can be further divided
into:
1) Lentic (Still like pond, lakes)
2) Lotic (Free flowing like rivers)
 Lake Ecosystem
• Lakes have been found to exhibit distinct
zones of biological activities, largely
determined by availability of light and oxygen
• The most important biological zones are:
1) Euphotic Zone
2) Littoral Zone
3) Benthic Zone
 Zones in Lake Ecosystem
1) Euphotic Zone: Upper layer of water through
which sunlight can penetrate. All plant
growth occurs in this zone.
2) Littoral Zone: The shallow water near the
shores in which rooted plants exist
3) Benthic Zone: Bottom sediments in a lake
comprise this zone. Dead organisms are
decomposed in this zone.
Lake Ecosystem
 Stratification in Lakes
• The lakes show stratification based on
temperature difference
• During summer, the top water becomes
warmer than the bottom waters
• Therefore, only warm layer circulates without
mixing with the colder layers thus forming
distinct layers
 Stratification in Lakes
1) Epilmnion : warm,
lighter, circulating
waters
2) Hypolimnion :cold,
viscous, non-circulating
bottom layers
3) Thermocline: In
between two layers
where there is sharp
drop of temperatures
Pond Ecosystem
 Components of Pond Ecosystem
• Abiotic Components – Temperature, Light, several
inorganic materials
• Biotic Components –
1) Producers – Submerged green plants, free
floating plants etc.
2) Consumers –
• Primary Consumers - Zooplankton like ciliates,
flagellates etc.
• Secondary Consumers – Fish and Insects
• Tertiary Consumers – Large fishes
 Components of Pond Ecosystem
3) Decomposers – Bacteria and Fungi