Ecological System Concept
(Concept of Ecosystem)
Ecosystem is the basic structural andEcosystem is the basic structural and
functional unit of ecology.functional unit of ecology.
“Ecosystems are the basic units of
on the face of the earth”.
An ecosystem is an ecological unit, or a
subdivision of the landscape, or a geographic area that
is relatively homogeneous and reasonably distinct from
J.W. Marr, 1961
Ecosystem – another view
• Ecosystem is a spatial functional structure
• The space may be geographically large or
• Largest ecosystem. e.g., Planet earth
• Smallest ecosystem (microcosm):
• e.g. a handful of soil and moss in a sealed
Components of an Ecosystem
(geographical, climatic,(geographical, climatic,
physicochemical characteristics)physicochemical characteristics)
(Plants, animals, microbes)(Plants, animals, microbes)
Mountain ecosystem – Removal of forest cover
Evergreen forests – Over exploitation of forest resources
Coral reefs – Human interference, Dynamite fishing
River ecosystem – Pollution
Land ecosystem – Dumping solid wastes
Specific influence of human
beings on sensitive Ecosystems
Properties of Ecological
1. Networks –Interdependence, diversity,
2. Boundaries- Scale and limits
3. Cycles – Recycling of resources and
4. Flow –through – Energy and resources
5. Development – Succession and co-evolution
6. Dynamic balance- Self – organization,
flexibility, stability, sustainability
A Cybernetic system of
Plant Cow Man
Output - Input
Output - input
Series open system components
System X Y Z
Open system with components
Features of an open systemFeatures of an open system
Open systems process inputs and produce
The amount of output produced is directly
related to the amount of input received.
Features of Complex systems
• Complex systems are composed of many
interconnected and interacting subunits.
• They are capable of adaptation and self-
All living systems are open systems.
A cell is an open system because it
constantly acquires food from outside
itself and eliminates wastes.
It gives off heat as it carries on
chemical processes (respiration).
Biological SystemsBiological Systems
Hierarchical SystemHierarchical System
Dynamics of ecosystems
Plants → animals
Biogeochemical cycles and population
– Evolution spiral
The earth as a single system
Solar energy is converted to chemical energy
Chemical energy is used to do work
Degraded Waste Energy
Energy flow in an Ecosystem
Pyramid of numbers:
No of individuals at each trophic level
Graphic representation of tropic structure and
function of an ecosystem.
Parasites (Lice, bugs)
Pyramid of biomass:
Total biomass (dry matter) at each tropic level
Pyramid of energy:
Amount of energy present at each trophic level.
At every trophic level there is 90% loss of energy (respiration, activity).
Only 10% energy is transferred from one trophic level to the other.
There is one-way flow of energy.
Nutrients like C, N, S, O, H, P etc.
Move in circular paths.
Energy flow in an ecosystem
The sequence of feeding relationships in
an ecosystem is called food chain.
Each organism in the ecosystem is
assigned a feed level or trophic level.
Simple food web model
Producer : Pond grass
Herbivore : Water insects
Carnivore : Large fish
Herbivore : Small fish
Carnivore : Duck
Top Carnivore : Man
Simple Food – Chain Model
Kinds of food chain
1. Grazing food chain – Starts with green plants and ends with
Grass → Rabbit→ Fox
2. Detritus food chain – Starts with dead organic matter and
ends with predators.
Leaf litter →Saprotrophs / detritivores (crabs) →Small carnivorous fish →
Large Carnivorous fish
- a complex inter connected network of food chains
at different trophic levels.
Significance of food chain
1.Food chains maintain energy flow and nutrient cycling.
2.Food chains maintain ecological balance by regulating
3.Food chains biologically magnify toxicity of some
Kinds of Ecosystems
e.g. Forest, Desert
e.g. Agricultural land use,
Urban / industrial land use
Coastal lagoon ecosystems
Coral reef ecosystems
Sandy beach ecosystems
Threats from Agricultural
Ecological simplicity – large
High degree of biological
uniformity (minimum genetic
Widespread disease outbreaks or
Depletion of fertilizers
(nutrients) and energy (fossil
Elimination of other crop species
and other ecosystems.