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UNIT 2: ECOLOGY AND ECOSYSTEMS
•Concept of ecology and ecosystem, Structure and function of ecosystem; Energy flow in an
ecosystem; food chains, food webs; Basic concept of population and community ecology;
ecological succession.
•Characteristic features of the following:
a) Forest ecosystem b) Grassland ecosystem c) Desert ecosystem
d) Aquatic ecosystems (ponds, streams, lakes, wetlands, rivers, oceans, estuaries)
ECOLOGY: Ecology (from the Greek “oikos” meaning "house" or "dwelling", and “logos” meaning "to
study") is the study of the interactions of organisms with each other and their environment. The hierarchy
define each of the following.
species ~genus~ population ~ community ~ ecosystem ~ biosphere
AUTECOLOGY & SYNECOLOGY: Autecology & Synecology are two main branches of ecology.
Autecology is the study of individual organism or individual species. It is also known as population
ecology.
Synecology is the study of group of organisms of different species which are associated together as a
unit in form of a community.
Levels of Ecological Study
ORGANISMAL ECOLOGY - the study of individual organisms' behavior, physiology, morphology,
etc. in response to environmental challenges.
POPULATION ECOLOGY - the study of factors that affect and change the size and genetic
composition of populations of organisms.
COMMUNITY ECOLOGY - the study of how community structure and organization are changed by
interactions among living organisms
ECOSYSTEM ECOLOGY - the study of entire ecosystems, including the responses and changes in
the community in response to the abiotic components of the ecosystem. This field is concerned with
such large-scale topics as energy and nutrient cycling.
LANDSCAPE ECOLOGY – study of the exchanges of energy, materials, organisms and other
products of between ecosystems.
GLOBAL ECOLOGY - the study of the effects of regional change in energy and matter exchange on
the function and distribution of organisms across the biosphere.
ECOSYSTEM: An ecosystem is a large community of living organisms (plants, animals and microbes) in a
particular area. The living and physical components are linked together through nutrient cycles and energy
flows. Ecosystems are of any size, but usually they are in particular places.
STRUCTURE OF AN ECOSYSTEM:
An ecosystem consists of 2 components:
1. Abiotic components - The non living factors or the physical environment prevailing in an ecosystem
form the abiotic components. They have a strong influence on the structure, distribution, behaviour
and inter-relationship of organisms. Abiotic favtors are light, temperature, water, nutrients,
topography, etc.
Abiotic components are mainly of two types:
Climatic Factors: Which include rain, temperature, light, wind, humidity etc.
Edaphic Factors: Which include soil, pH, topography minerals etc.
SNC/KOUSIK GHOSH/2019 Page 1
2. Biotic Components: The living organisms including plants, animals and micro-organisms (Bacteria
and Fungi) that are present in an ecosystem form the biotic components.
On the basis of their role in the ecosystem the biotic components can be classified into three
main groups:
Producers
Consumers
Decomposers or Reducers.
Producers: The green plants have chlorophyll with the help of which they trap solar energy and
change it into chemical energy of carbohydrates using simple inorganic compounds namely water and
carbon dioxide. This process is known as photosynthesis. As the green plants manufacture their own
food they are known as Autotrophs (i.e. auto = self, trophos = feeder)
The chemical energy stored by the producers is utilised partly by the producers for their
own growth and survival and the remaining is stored in the plant parts for their future use.
Consumers: The animals lack chlorophyll and are unable to synthesise their own food. Therefore,
they depend on the producers for their food. They are known as heterotrophs (i.e. heteros = other,
trophos = feeder)
The consumers are of four types, namely:
Primary Consumers or First Order Consumers or Herbivores: These are the animals which
feed on plants or the producers. They are called herbivores. Examples are rabbit, deer, goat,
cattle etc.
Secondary Consumers or Second Order Consumers or Primary Carnivores: The animals
which feed on the herbivores are called the primary carnivores. Examples are cats, foxes,
snakes etc.
Tertiary Consumers or Third Order Consumers:These are the large carnivores which feed on
the secondary consumers. Example are Wolves.
Quaternary Consumers or Fourth Order Consumers or Omnivores:These are the largest
carnivores which feed on the tertiary consumers and are not eaten up by any other animal.
Examples are lions and tigers.
Decomposers or Reducers: Bacteria and fungi belong to this category. They breakdown the dead
organic materials of producers (plants) and consumers (animals) for their food and release to the
environment the simple inorganic and organic substances produced as by-products of their
metabolisms.
These simple substances are reused by the producers resulting in a cyclic exchange of materials
between the biotic community and the abiotic environment of the ecosystem. The decomposers are
known as Saprotrophs (i.e., sapros = rotten, trophos = feeder)
Ecosystem
Abiotic components Biotic components
Climatic Factors Edaphic Factors Producers Consumers Decomposers
(Autotrophs) (Heterotrophs) (Saprotrophs)
Rain Soil Primary
Light pH Secondary
Wind Minerals Tertiary
Temperature Topography Quaternary
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FUNCTIONS OF AN ECOSYSTEM: In the ecosystem, biotic components and other materials like N,
C, H O Circulated within and outside of the system.
2
The energy is transferred from one tropic level to the other in the form of a chain called as food chain.
The important source of energy is the sun.
Some factors which are responsible for high productivity. for example high temperature and rainfall
accelerate weathering and decomposition of dead organic matter.
Climatic changes is the functioning of ecosystem
Effects of local and regional shifts of energy, materials and populations on ecosystems and economic
of rational use of ecosystem.
Production, consumption and decomposition are important functions of ecosystem.
Production:
"Conservancy of solar energy into potential energy"
Every year about 100 billion tones of organic matter is produced on the earth by "Photosynthetic
organisms".
Photosynthesis by Green plants
The plants capture the solar energy and converted into carbohydrate through the process of photosynthesis
Chlorophyll
6 CO 12 H O C H O 6O 6H O
2 + 2 6 12 6 + 2 + 2
The Presence of chlorophyll in the plants absorbs sun light, CO and water to prepare carbohydrate and
2
liberate oxygen.
Composition (Consumption): It is the process of transfer of material and transformation of energy from one
tropic level to another through the process of eating and being eaten.
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Decomposition: It is a process in which complex compounds are broken into simpler compounds. The simple
compounds can be utilizes for plants growth. This process is done by bacteria and fungi. In ecosystem dead bodies
are decomposes by bacterial action.
ENERGY FLOW IN AN ECOSYSTEM
An ecosystem comprises biotic and abiotic components which interact extensively with each other. Based on their
ecological roles, the biotic components of an ecosystem can be classified as:
Producer: they are the green plants which absorb solar energy to synthesize complex organic compounds from
simple inorganic substances by photosynthesis, they act as the ultimate food source to all the heterotrophs. The
other producers are green algae and blue green algae, they are mainly found in aquatic habitat, such as freshwater
and marine water, they are the most important producers in earth (as 70% of the earth surface is covered with
water).
Consumer: they are heterotrophs which ingest other organisms or organic particles, they are mainly animals
primary consumer : they are the herbivores which feed on plants e. g. pond snail, insect larva and
zooplanktons
secondary consumer : they are the carnivores which feed on primary consumers e. g. water beetles, tigers,
etc.
tertiary consumer : they are large carnivores which feed on the secondary and primary consumers as
well as producers, e. g. man
detritus consumer : they are detritivores ( detritus feeder / scavengers) which feed on detritus that refer to
the particulate organic matter involved in the decomposition of dead organisms, e. g. earthworm and crab
etc.
Decomposer: they are mainly bacteria, fungi and some flagellates, by means of their saprophytic activities; they
decompose the eliminated products of animals and the dead bodies of the organisms into simple compounds, these
compounds are absorbed as nutrients by the green plants again they enable the nutrients to be used continuously in
a cyclic form in the ecosystem. They are most abundant in the soil or water bottom where the dead bodies of plant
and animals accumulate when the temperature conditions are favourable, decomposition occurs rapidly
Energy and essential materials are therefore transferred from producers to consumers through the feeding
processes. Eventually, decomposers break down the organic matter and release inorganic materials back to the
environment. These inorganic materials are used by the producers as nutrients again.
Food chain: the transfer of food energy from producers through a series of organisms with repeated eating and
being eaten
Ecosystem Producer Primary Secondary Tertiary
consumer consumer consumer
freshwater pond green algae protozoa mosquito larva fish
rocky pond weeds molluscs starfish sea birds
Grassland grass grasshopper lizard snake
Woodland green plants caterpillars sparrow hawk
Food web: In general, the food chains in an ecosystem are not isolated, but are interconnected
with one another; i. e. an herbivore may feed on several species of plants, and/ or be consumed by
many consumers and so on, such a number of interconnected food chains is known as food web.
Trophic level: organisms in a food chain occupy different trophic levels, which indicate their place in the energy
flow through the community; organisms whose food is obtained from plants by the same number of
steps in the food chain belong to the same trophic level
Producers- first trophic level
Primary consumers - second trophic level
SNC/KOUSIK GHOSH/2019 Page 4
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