This document provides an overview of ecosystems and ecology. It begins with definitions of ecology and ecosystem from various scholars. An ecosystem is defined as all the organisms in a given area interacting with the physical environment. Key components of ecosystems discussed include biotic and abiotic factors, producers and consumers, trophic levels, food chains and webs. Ecological concepts like pyramids of numbers, biomass and energy, primary and secondary productivity, and energy flow through ecosystems are also summarized. Diagrams illustrate these concepts and energy flows at the global, community and individual organism levels.

1. WELCOME
Shampa Bag
Assistant Professor
Ananda Mohan College
Kolkata

2. BASICS OF
ECOSYSTEM

3. HIERERCHY IN ECOLOGY

4. ECOSYSTEM
‘the study of an organism and its environment’
DEFINITION:
• The total relation of the animal to both its organic and its inorganic environment
(Ernst Haeckel ,1869)
• The study of the structure and function of ecosystems’ or ‘structure and function of
nature.’ (Eugene Odum 1963, 1969 and 1971)
• ecology is the scientific study of the relationships of living organisms with each
other and with their environments (Charles H. Southwick ,1976)
Any unit that includes all the organisms (the biotic community) in a given area
interacting with the physical environment so that a flow of energy leads to
clearly defined biotic structure and cycling of materials between living and
nonliving components is an ecological system or Ecosystem.
The term “Ecosystem “ was first proposed by A.G. Tansley (1935)

5. Ecosystem is the basic unit for ecological studies.
It is a conceptual unit, has both structure and
function but no size limit.
It is an ecological unit through which energy
flows and materials circulate. It is an open self
sustained and self regulated system.

6. BRANCHES OF ECOLOGY
ECOLOGY
AUTECOLOGY
(INDIVIDUAL)
SYNECOLOGY
(COMMUNITY)
AQUATIC ECOLOGY
MARINE
ECOLOGY
EUSTUARINE
ECOLOGY
FRESHWATE
R ECOLOGY
TERRESTRIAL
ECOLOGY
CROPLAND
ECOLOGY
FOREST
ECOLOGY
GRASSLAND
ECOLOGY
DESERT
ECOLOGY

7. STRUCTURE OF ECOSYSTEM
An ecosystem typically has two major components
A. Abiotic or Non-living Components
(1) Climatic condition and physical factors of the given region such as air, water,
soil, temperature, light (i.e., its duration and intensity), moisture (relative
humidity), pH, etc.
(2). Inorganic substances such as water, carbon (C), nitrogen (N), sulphur (S),
phosphorus (P) and so on, all of which are involved in cycling of materials in the
ecosystem (i.e., biogeochemical cycles).
(3). Organic substances such as proteins, carbohydrates, lipids, humic substances,
etc., present either in the biomass or in the environment,
B. Biotic or Living Components
1. Autotrophs: includes the producers or energy transducers which convert solar
energy into chemicalenergy-photoautotrophs & Chemoautotrophs
2. Heterotrophs also called consumers
(a) Macroconsumers. E.g. Herbivores(primary consumer),
Carnivores(secondary, tertiary, quaternary etc.)
b) Microconsumers. These are also called decomposers, reducers,
saprotrophs (sapro =decompose), osmotrophs .

8. FOOD CHAIN & FOOD WEB
• Biotic components of an ecosystem are linked in the patterns of ‘eat and being
eaten up’ , in its simplest forms result into a linear chain called food chain.
• In nature due to euryphagic nature of organisms various food chains are linked
together and intersect each other to form a complex network called food web.
Food Chain Food Web

9. 1.Grazing food chain.
(include predator and
parasitic food chain)
2. Detritus food chain.
Grazing & detritus food chain are
interconnected.
The proportion of energy flow
down the two pathways varies in
different kinds of ecosystem or
often varies seasonally or annually
in the same ecosystem e.g.
In grassland / heavily grazed
pasture >50% or more of the net
production may pass down the
grazing pathway whereas >90% of
the net production flows through
the detritus pathway in ocean,
forest, marshes, most natural
ecosystem etc.

10. TROPHIC LEVEL:
The producers and the consumers can be arranged into several feeding
groups called as TROPHIC LEVEL .Each trophic level contains at any time a
certain amount of living matter(standing crop), which can be expressed as
no. per unit area or as ‘biomass’(total mass of living matter expressed in
fresh weight, dry weight or energy per unit area or volume)

11. ECOLOGICAL PYRAMID
Graphical representation of the relationships between numbers, biomass and energy
flow of the various trphic levels at th biotic community level is known as ecological
pyramid
a. Pyramid of numbers
b. Pyramid of Biomass
c. Pyramid of Energy
Numbers overemphasizes
small and biomass
Overemphasizes large animals,
Energy flow is the most
suitable index for comparing
any or all components of
ecosystem

12. CONCEPT OF PRODUCTIVITY
The fixing of energy at any trophic level is known as Production. It can be of two types- PRIMARY
PRODUCTION (production by autotrophs) and SECONDARY PRODUCTION(production by heterotrophs)
Approximately 1 to 5% of the solar energy that falls on a plant is converted to the chemical bonds of organic
material.
Rate of production is called as PRODUCTIVITY i.e., the amount of organic matter
Accumulated in any unit time.
1. Primary production or primary productivity are terms used to describe the amount of
organic matter produced from solar energy in a given area during a given period of
time. It is defined as the rate at which radiant energy is stored by photosynthetic and chemosynthetic
activity of producers. Primary productivity is of following types:
(i) Gross primary productivity (GPP) is the total organic matter produced, including that used by the
photosynthetic organism for respiration. It refers to the total rate of photosynthesis including the
organic matter used up in respiration during the measurement period. GPP depends on the chlorophyll
content. The rate of primary productivity are estimated in terms of either chlorophyll content as chl/g
dry weight/unit area or photosynthetic number, i.e., amount of CO2 fixed/g chl/hour.

13. Concept of production
(ii) Net primary productivity(NPP). It is the rate of storage of
organic matter in plant tissues in excess of the respiratory
utilization by plants during the measurement period.
therefore, is a measure of the amount of organic matter
produced in a community in a given time that is available for
heterotrophs.
It equals the gross primary productivity minus the amount of
energy expended by the metabolic activities of the
Photosynthetic organisms. Mathematically,
NPP=GPP-R
The net weight of all of the organisms living in an ecosystem,
its biomass, increases as a result of its net production.

14. Global Terrestrial Ecosystem Productivity Per Year

15. SECONDARY PRODUCTION:Production by heterotrophs
The rate of production by heterotrophs is called
Secondary productivity. Because herbivores and
carnivores cannot carry out photosynthesis, they
do not manufacture biomolecules Directly from
CO2. instead, they obtain them by eating plants
or other heterotrophs.
So, secondary productivity is not divided into ‘gross’
and ‘net’ amounts. The rate of storage of organic
matter not used by the heterotrophs or
consumers, i.e., equivalent to net primary
production minus consumption by the
heterotrophs during the unit period as a season
or year, etc. is called as Net Productivity.
Mathematically,
I=P+R+E
Thus, P=I-R-E
I=Ingestion
P=Secondary Production
R=Respiratory Energy
E=Excretory Energy

16. Secondary Production in African Elephant
Data studied by Petrides and Swank(1966) modified by Krebs(1985)
The data clearly shows that only a very small fraction of I (Ingestion) is
actually converted into P(Production)
TYPE OF ENERGY AMOUNT(Kcal/m2/Year)
Net Primary Productivity 747.0
Ingestion(I) 71.5
Faecal Energy Loss(F) 40.2
Maintenance Metabolism(R) 31.0
Growth(P) 0.34

17. Energy Flow through the
Ecosystem(Models)

18. Energy Flow through the
Ecosystem(Models)

19. Ecological Efficiency
Ratio between energy flow at different points along the food chain expressed
in percentage is called ecological efficiency. Various types of efficiencies are:

20. THANK YOU