1. The Ecosystem
An Introduction

2. Ecosystem
 A community of interdependent organisms and
the interactions with the physical environment
in which they live.
 It can also be defined as the abiotic and biotic
factors and the interactions between them.
 The interaction between organisms and the
environment is the key!

3. Kind of ecosystems:
[1] Natural Ecosystem: this operates by themselves
Ex: Terrestrial Ecosystem: forest, grassland, desert
Aquatic Ecosystem: Fresh water, Marine water
[2] Artificial Ecosystem: These are man-made or
man-engineered.
Ex: Croplands, rice fields, gardens, aquarium etc.

4. Niche vs habitat
 A habitat is a place in which an organism lives.
The habitat must provide a source of food,
water and shelter for the organism.
 Niche: The role of the organism. This is
largely to do with the trophic level of the
organism.
 For example: plants produce food for the rest
of the food chain. Tigers keep herbivore
populations under control.

5. Abiotic and Biotic factors
Abiotic factor: A non-living, physical factor that
may influence an organism or a system
[1] Climatic conditions:
Ex: water, soil, light, temperature, pH etc.
[2] Inorganic substances:
Ex: H2O, C, N, S, P
[3] Organic substances:
Ex: proteins, carbohydrates, lipids etc.

6. Biotic Factor: A living, biological factor that may
influence an organism or a system.
[1] Autotrophic component (Producers):
(i) Photoautotrophs: convert solar energy into
chemical energy. Ex: Trees, grass
(ii) Chemoautotrophs: energy generated by redox
reaction. Ex: Sulphur bacteria
[2] Heterotrophic component (consumers): they
consumes matter built by producers.

7.  (i) Macroconsumers/ Phagotrophs:
Herbivores, Carnivores
 (ii) Microconsumers/decomposers/saprophytes:
Decompose organic compounds of dead or
living protoplasm & release inorganic nutrients in
the environment.
Ex: micro-organisms such as bacteria, fungi etc.

8. Function:
1. Means how much sunlight is trapped by
plants in a year.
2. How much plant material is eaten by
herbivores.
3. How many herbivores are eaten by
carnivores.
4. Energy flow in a ecosystem is non-cyclic
(unidirectional) whereas minerals keep in
moving in a cyclic manner.

9. Limiting factors
 An abiotic factor can limit the population size if there
is too much or too little of it. Even if there is the
right amount of other factors
 Examples to consider:
Sunlight
Precipitation
Salinity
Nutrients in the soil

10. Trophic levels
 Ecosystems are often broken up and described
according to feeding relationships.
Trophic level:
 Number of links by which it is separated from
the producer, or as nth position of the organisms.
 The position of an organism in a food chain.
 The pattern of eating and being eaten forms a
linear chain called food chain.
 A group of organisms that occupy the same place
in a food chain

11. Trophic levels in food chains
 Primary producers (autotrophs)
 Primary consumers (herbivores)
 Secondary consumers(carnivores)
 Tertiary consumers (top carnivores)
 Decomposers
 Detrivores

12. Energy flow and material cycling

13. Food Chains

14. Types of food chain:
[1] Grazing Food Chain:
Autotrophic energy capture & movement of energy to
herbivores.
Solar radiation Herbivores Primary
carnivore secondary carnivore

15. [2] Detritus food chain:
• Organic wastes & dead matter derived from the grazing food
chain are termed as detritus.
• Energy of detritus is serve as energy for a group of organisms
(detritivores) that are separate from grazing food chain.
• Organism: Algae, Bacteria, Molluscs, Rotifer, Mites etc.
Grazing food chain
Dead & Excretory material soil organisms consumed by
carnivores in the grazing food chain
Decomposer organisms soil animals which consume
other living organisms
Organic material permanently incorporated into sediments, soil &

16. Significance:
1. It helps us to understand the feeding relationship and
interactions between organisms in any ecosystem.
2. Energy flow mechanisms & matter circulations.
3. Movement of toxic substances & process of
biomagnification.

17. Food webs
 In a given ecosystem various food chains are
linked together & intersect each other to form a
complex network called food web
 Show energy flow through an ecosystem

18. Food
webs

19. Ecological Pyramids:
It represent the trophic structure & also trophic
function of the ecosystem.
It may be of three types:
(1) Pyramid of number
(2) Pyramid of biomass
(3) Pyramid of energy

20. Pyramid of Number, Energy

21. Pyramid of biomass

22. Primary productivity
Primary productivity is the rate of energy capture
by producers.
= the amount of new biomass of producers, per
unit time and space

23.  Gross primary production (GPP)
= total amount of energy captured
 Net primary production (NPP)= GPP - respiration
 Net primary production is thus the amount of
energy stored by the producers and potentially
available to consumers and decomposers.

24. Secondary Productivity
 Secondary productivity is the rate of production of
new biomass by consumers, i.e., the rate at which
consumers convert organic material into new
biomass of consumers.
 Secondary production simply involves the
repackaging of energy previously captured by
producers--no additional energy is introduced into
the food chain.

25. Energy flow in ecosystems:
• Energy flow is the movement of energy through
an ecosystem : from the external environment
through organisms and back to the external
environment.
• Energy flow can be explained by various energy
flow models.

26. [1] Single Channel Energy Flow
Model:
• Unidirectional flow of energy.
• In each trophic level, there occurs progressive
decrease in energy

27. [2] Y-Shaped or double channel energy flow model:
• Given by H.T. Odum in 1956.
• Shows a common boundary, light and heat flows as well as the
import, export & storage of organic matter.
• Decomposers are placed in separate box.
• Explain stratified structure of ecosystems.
• Separates the food chain.

28. [3] Universal Energy Flow model:
• Given by E.P. Odum.
• Energy was lose at each energy level, thereby resulting in less
energy available at next trophic level as indicated by narrow
pipes (energy flow) & smaller boxes (stores energy in
biomass).

29. Energy transfer in a food chain:
First law of thermodynamics

30. Ecological Succession
• The development of the community by the action of
vegetation on the environment leading to the establishment of
new species is termed succession.
• Final & stable community is termed as climax community.
• Traditional community is called sere or seral stage. Its
directional change in vegetation.

31. Causes
1. Initiating Causes: climatic (erosion, deposits, wind,
wire etc.), Biotic
2. Ecesis or continuing causes: migration, competition,
reaction etc.
3. Stabilizing causes: climate of area which stabilize the
community.

32. Changes during succession
1. Continuous change occurs in the kinds of plants & animals.
2. Increase in diversity of species takes place.
3. Progressive increase in the amount of living biomass & dead.
4. Green pigment go on increasing during primary succession.
5. Food chain become more complex.
6. Role of detritus becomes progressively more & more important.
7. Quality of the habitat gets modified.
8. Life cycle of mature community species are longer & complex.

33. Types of succession
1. Primary: its an area in any of the basic environments is
colonized by organisms for the first time.
2. Secondary: if the area under colonization has been cleared
by an agency as burning, grazing, clearing, sudden change in
climatic factor etc. of the previous plants
3. Autogenic: community itself modifies its own environment
and, thus, causing its own replacement by new community.

34. 4. Allogenic: replacement of one community by another is largely
due to force other than the effects of communities on the
environment.
5. Autotrophic: its characterized by early & continued dominance
of autotrophic organisms such as green plants.
6. Heterotrophic: it is characterized by early dominance of
heterotrophic organisms as bacteria, fungi & animals.

35. 7. Induced: activities such as overgrazing, frequent scrapping,
shifting cultivation or industrial pollution may cause
deterioration of an ecosystem.
8. Retrogressive: return to simpler & less dense or even
improvised form of community from an advanced or climax
community causes are allogenic.
9. Cyclic: repeated occurrence of certain stages of succession
whenever there is an open condition created within a large
community.

36. Process of succession
1. Nudation: development of a bare area without any form of
life.
It may occur due to landslides, erosion, deposition.
Three types are there:
(a) Topographic: soil erosion by gravity, water or wind causes
disappearance of existing community.
(b) Climatic: Glaciers, dry period etc. may destroy community.
(c) Biotic: man-made destruction of forest, grasslands for
housing, industry, agriculture etc. disease epidemics caused
by fungi, bacteria, virus etc.

37. 2. Invasion: Successful establishment of a species in a
bare area.
(a) Migration (Disposal): seeds, spores etc. may reach to
bare area by air, water etc.
(b) Ecesis (Establishment): After reaching new areas, the
process of successful establishment of the species
means adjustment with condition there. For ex: seeds-
---------germinate---------grow---------adult start to
reproduce
(c) Aggregation: colonization by successive offsprings &
new migrants help increase the population. Number
of individuals of the species increases in number.

38. 3. Competition and coaction:
Due to aggregation of a large number of individuals of the
species at the limited place, there develops competition (i.e.
interspecific & intraspecific) for space & nutrition.
Individuals of a species affect each other’s life in various ways
this is called coaction.
The species which fail to compete with other species are
discarded.

39. 4. Reaction:
 It includes mechanisms of the modification of the
environment through the influence of living organisms on
it.
 As a result of reaction, the environment is modified &
become unusable for existing community which sooner or
later replaced by another community.
 Whole sequence of communities that replaces one another
in the given area called sere and different communities
constituting the sere are called seral stages or development
stages.

40. 5. Stabilization (Climax):
 Finally, there occur a stage in the process, when the final
community become more & less established for a longer period
of time & it can maintain itself with climate.
 The final community is not replace & known as climax
community & stage is climax stage.

41. Primary succession-

42. Secondary succession-
 Ex:
 A fire levels
portions of a
forest

43. Secondary succession-
 Ex:
 A farmer
plows his
field

44. Secondary succession-