What is ecosystem?

• An ecosystem is a community of plants and animals interacting with each other in a

given area with their specific physical environment where energy flow leads to a
trophic (nutritional) structure and other material cycles within the system.
• Different regions that have different types of flora and fauna. The types of
organisms in an area are determined by various factors such as the climate,
temperature, rainfall, trophic structure etc.
• The size of ecosystems varies tremendously depending on its components (that
include plants, animals, and microorganisms; soil, rocks, and minerals; as well as
surrounding water sources and the local atmosphere).
 Producer
All green plants are the ‘producers’ in the ecosystem as they manufacture their food
by using energy from the sun.
In the forest these forms the communities of plant life. In the sea these include tiny
algal forms to large seaweed.
Consumers:
i) Primary consumers
The herbivorous animals are primary consumers as they live on the producers. In a
forest, these are the insects, amphibia, reptiles, birds and mammals. The herbivorous
animals include for example hare, deer and elephants that live on plant life. In grasslands,
there are herbivores such as the blackbuck that feed on grass. In the semiarid areas, there
are species such as the chinkara or Indian gazelle. In the sea, there are small fish that live on
algae and other plants.
ii) Secondary consumers
At a higher tropic level, there are carnivorous animals, or secondary consumers,
which live on herbivorous animals. In our forests, the carnivorous animals are tigers,
leopards, jackals, foxes and small wild cats. In the sea, carnivorous fish live on other fish
and marine animals. Animals that live in the sea range in size from microscopic forms to
giant mammals such as the whale.

Decomposers
Decomposers are a group of organisms consisting of small animals like worms,
insects, bacteria and fungi, which break down dead organic material into smaller particles
and finally into simpler substances that are used by plants as nutrition.
Decomposition thus is a vital function in nature, as without this, all the nutrients
would be tied up in dead matter and no new life could be produced.
 Non-living components (abiotic)
Physical component: Air, wind, terrain, soil and soil moisture, water current,
temp, light or energy from sun, etc.
Chemicals component: Water, gases, minerals, compounds, complex chemicals, etc.

Development of Ecosystem
• The development of ecological systems are based on the changes in the series of
biotic communities which occur on:
– an entirely new place and has never been colonized before (for example, a
newly raised land or quarried rock face or sand dunes),
– Or, which take place on a previously colonized area, but disturbed or extinct of
habitat over long periods (for example, after felling trees in a woodland, land
clearance or a fire).
• The gradual processes by which ecosystems are changing and developing over a
period of time are called ecological succession.
• Due to ecological succession nothing remains the same anywhere and habitats are
constantly changing everywhere of the world.

Processes of Ecological Succession

• The environment within an area always changing and gradually affect the area
through the processes of living, growing, reproducing and interaction among the
organisms.
• Each species is adapted to grow and compete against other species under a very
specific set of environmental conditions.
• If these conditions change, then the existing species will be outcompeted by a
different set of species which are better adapted to the new conditions.
• Change in the plant species present in an area is one of the driving forces behind
changes in animal species.
• This is because each plant species will have associated animal species (herbivore)
which feed on it.
The presence of these herbivore species will then dictate which particular carnivores,
omnivores or tertiary consumers will be present there.
Processes of Ecological Succession
• Changes in plant species also alter the fungal species present because many fungi are
associated with particular plants.
• Thus, if a forest is cleared or a new land is raised, it is initially colonized by a certain
group of species of plants and animals, which gradually change through an orderly
process of community development.
• So, one can predict that an opened up area will gradually be converted into
grassland, a shrub land and finally woodland and a forest if permitted to do so
without human interference.
Based on geographic position there are 2 Major classes of Ecosystem:
1) Aquatic Ecosystem
a. Freshwater
b. Marine
2) Terrestrial Ecosystem
a. Tundra
b. Desert
c. Grass Land
d. Coniferous Forest
e. Deciduous Forest
f. Tropical Forest
g. Rain Forest
What is ecology?
• The word "ecology" is a Greek origin (OIKOS & LOGOS), where, 'Oikos meaning
habitation (house), and logos meaning discourse or study, that implies a study of
the habitations of organisms.
• Ecology is the comprehensive study of the distribution and abundance of life in
nature (Earth) where biotic and abiotic components interact within their natural
environment.
• It helps scientists to develop methodology for understanding how the different
organisms grow and populate, how they interact with others and predators, how
the organisms die out as well as how they evolve or adapt to change climatic and
environmental situations.
• Ecologists are also concerned about the available natural resources scattered
throughout in environment.
• By studying ecology thus we learn how nature is works in the Earth.
 Atmosphere & its importance
• The atmosphere of Earth is a layer of gases surrounding the Earth planet that is
retained by Earth's gravity.
• The atmosphere protects life of earth by supplying oxygen, absorbing ultraviolet solar
radiation, warming the surface by heat retention (greenhouse effect), and reducing
temperature extremes between day and night (the diurnal temperature variation).
• In general, air pressure and density decrease in the atmosphere as height increases.
• The temperature behavior provides a useful metric to distinguish between
atmospheric layers.
• However, temperature has a more complicated profile with altitude, and may remain
relatively constant or even increase with altitude in some regions.
• Atmosphere also protect us from objects coming toward the earth from outer space.

Troposphere
The troposphere is the lowest layer of the atmosphere and extends from the Earth's surface
to about 7 km high at the north and south poles and 17 km high at the equator.
• This is where we live.
• All of our weather occurs in the troposphere.
• As the density of the air in this layer decrease with height, the air temperature in
the troposphere also decreases with height. The temperature drops from about 14
to 15 °C at the surface to about -45 °C at the top of the troposphere.
• The troposphere contains about 80% of the total mass of the atmosphere and 50%
percent of the total mass of the atmosphere is located in the lowest 5 to 6
kilometers of the troposphere.
• As one go higher into the atmosphere, there's less air pressure and therefore less
oxygen.
• The cruising altitude of commercial airliners is usually about 9 to 10 kilometers
which is close to the top of the troposphere.
 Hydrosphere:
Hydrosphere is the discontinuous layer of water that are found on, under, and over the
surface of the Earth.
It includes all liquid and frozen surface waters, groundwater, water held in soil and rock,
and atmospheric water as vapor.
Distribution of Water on our planet:
 Oceans 96.60  Ground Water 0.50 %
%  Surface Water 0.02 %
 Ice Sheets & Glaciers 1.87 %  Soil Moisture etc 0.01 %
 Biosphere:
• The biosphere is the global sum of all ecosystems.
• It is integrating all living beings and their relationships, including their interaction
with the elements of the lithosphere, hydrosphere, and atmosphere.
• It can also be called the zone of life on Earth.
• Most of the planet's life is found from three meters below the ground to thirty
meters above it.
• The actual thickness of the biosphere of the Earth is difficult to measure. As,
some of living organisms are found at the height of 41 km and 5 km beneath the
Earth’s crust.

Difference between Ecology, Ecosystem and Environment

An environment is the surrounding condition of an organism or a group of
organism that influences the growth, progress, and survival of that organism or a group
of organisms.
An ecosystem is the place where community of plants and animals interacting
with each other in a given area with their specific physical environment where energy
flow leads to a trophic (nutritional) structure and material cycles within the system.
Different regions that have different types of flora and fauna.
Ecology is the comprehensive study of the distribution and abundance of life in
nature where biotic and abiotic components interact within their natural environment.
Climate and vegetation of Bangladesh
• Bangladesh has a subtropical monsoon climate characterized by wide seasonal
variations in rainfall, moderately warm temperatures, and high humidity.
• Maximum summer temperatures range between 32°C and 38°C.
• January is the coldest month, when the average temperature for most of the
country is 10°C.
• Most parts of the country receive at least 200 centimeters of rainfall per year. Dry
western region of Rajshahi, where the annual rainfall is about 160 centimeters.
• Sylhet in northeastern Bangladesh receives the greatest average precipitation
ranged between 328 and 478 centimeters per year.
• About 80 percent of rain falls receives during the monsoon season.
• Generally, average daily humidity ranged between 45 and 71 percent from
November to February and rest of month it ranged between 84 and 92 percent.
• The flora of Bangladesh is made up of broadleaf evergreen vegetation in the hilly
regions and deciduous trees, and fruit trees and other broad leaf tree in plains
areas. In mangrove areas sundari, gewa, sal and garyan are main plant.
 Structure and Functions of an Ecosystem
Structural parameters of an ecosystem:
Structural parameters are the composition of both biological community & and
the abiotic materials. Examples of them are:
1) Inorganic materials – C, N, CO2, H2O, etc.
2) Organic compounds – Protein, Carbohydrates,
Lipids, etc.
3) Climatic regimes – Temperature, Moisture,
Light, Topography, etc.
4) Producers – Plants.
5) Macro consumers – Lion, Tiger, Human etc.
6) Micro consumers – Insects, snakes, etc
7) Decomposer – microorganisms
Functional parameters of an ecosystem:
Ecosystem is functioning by the sum of all natural processes and activities that
keep a system working continually. All the activities, processes or properties of
ecosystems are influenced by its biota. The functional parameters are:
1) Energy cycles.
2) Food chains.
3) Diversity-inter-linkages between organisms.
4) Nutrient cycles-biogeochemical cycles.
5) Evolution.
How does an ecosystem operate?
The fundamental steps for the operation of the ecosystem are:
 Reception of energy
 Production of organic materials by producers
 Consumption of these materials by consumers and its further elaboration.
 Decomposition to inorganic compounds and transformation to forms suitable for
the nutrition of the producers.
 Recycle processes
Functioning the Ecosystem
 All the functions of the ecosystem are in some way related to the growth and
regeneration of its plant and animal species.
 These processes depend on:
 - Energy from sunlight. During photosynthesis carbon dioxide
 is taken up by plants and oxygen is released.
 - All living things depend on this oxygen for their respiration.
 - The water cycle depends on the rainfall, which is necessary
 for plants and animals to live.
 - The energy cycle recycles nutrients into the soil on which
 plant life grows.
  - All organisms are in the food chain, and most of them get energy by eating
food, either from plant or animal.
 - Herbivores eat the plants and get their energy from them.
 - Then carnivores eat the herbivores and get their energy from them.
 - Every ecosystem is controlled by these cycles.
The Energy Cycle
• In the ecosystem, the energy is cycled through a flow of energy in terms of food
chains from one to another.
• Energy from sunlight is converted to chemical energy which is then used by
plants themselves for growing new plant material which includes leaves, flowers,
fruit, branches, trunks and roots of plants.
• These plant materials are used by herbivorous animals as food, which gives them
energy.
• The carnivores in turn depend on herbivorous animals on which they feed.
• Thus the different plant and animal species are linked to one another through
food chains.
• A large part of this energy is used up for day to day functions of these animals
such as breathing, digesting food, supporting growth of tissue, maintaining blood
flow and body temperature. Energy is also used for activities such as looking for
food, finding shelter, breeding and bringing up young ones.
• When plants and animals die, this material is again returned to the soil after
being broken down into simpler substances by decomposers such as insects,
worms, bacteria and fungi.
Photosynthesis:
• The name photosynthesis comes from the Greek word phōs, means "light" and
synthesis means, "putting together". Photosynthesis is a process where plants
and producer convert light energy, from the sun, into chemical energy that can
be used as fuel for the organisms' activities.
• Light energy is absorbed by protein (RuBP) of chloroplast of chlorophyll and
converted it to chemical energy which is stored in ATP (adenosine triphosphate)
and NADPH (nicotinamide adenine dinucleotide phosphate) present in leaf cell. In
presence of water, ATP and NADPH capture CO2 and produce sugar through a
series of chemical reactions.
• The overall chemical reaction involved in photosynthesis is:
6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2.
Thus, by photosynthesis carbohydrates, such as sugars, are synthesized from carbon
dioxide and water. Oxygen is released, mostly as a by-product.
• The process always begins when light energy from the Sun is absorbed by
proteins (ribulose bisphosphate (RuBP) of green chlorophyll pigments.
• In plants, these proteins are held inside the chloroplasts of chlorophyll, which are
most abundant in leaf cells, while in bacteria they are embedded in the plasma
membrane.
NUTRIENT CYCLE / BIOGEOCHEMICAL CYCLES
Nutrient cycling is one of the most important processes that occur in an ecosystem.
Valuable elements such as carbon, oxygen, hydrogen, phosphorus, and nitrogen are
essential to life and must be recycled in order for organisms to exist.
These elements are recycled through abiotic environments including the atmosphere,
water, and soil, hence, also known as biogeochemical cycles
The Carbon cycle
• Carbon is a building block of both plant and animal tissues. In the atmosphere,
carbon occurs as carbon dioxide (CO2).
• In the presence of sunlight, plants take up carbon dioxide from the atmosphere
through their leaves. In the presence of sunlight they are able to form carbohydrates
through the process of photosynthesis.
• Both plants and animals release carbon dioxide during respiration. They also return
fixed carbon to the soil from the waste they excrete.
• When plants and animals die they also return their carbon to the soil.
• These processes complete the carbon cycle that help in regulating and monitoring
the percentage of Carbon dioxide in the earth’s atmosphere.
• Due to anthropogenic activity, excess CO2 is accumulated in air.

The Nitrogen Cycle

Nitrogen is necessary for all known forms of life on Earth. It is a component in all amino
acids, as incorporated into proteins, and is also present in nucleic acids such as RNA and
DNA and in chlorophyll molecules.
Nitrogen gas (N2) is the largest constituent of the Earth's atmosphere, but this form is
relatively non-reactive and unusable by plants.
Chemical processing or natural fixation (through processes such as bacterial conversion
by rhizobium) are necessary to convert gaseous nitrogen into compounds such as
nitrate or ammonia which can be used by plants.
The nitrogen cycle is the process by which nitrogen is converted and transformed
to its various chemical forms. This transformation can be carried out through both
biological and physical processes.
Important processes in the nitrogen cycle include fixation, ammonification, nitrification,
and denitrification. The abundance or scarcity of this "fixed" nitrogen (also known as
reactive nitrogen) frequently limits plant growth in both managed and wild
environments.
The nitrogen cycle, like the carbon cycle, is an important part of every ecosystem.
 1) Aquatic ecosystems
There are two types of Aquatic ecosystems
a. Freshwater
b. Marine
a. Freshwater (i.e. ponds, rivers and lakes)
• Relatively small in area ~ 1.8% of earth's surface
• Support many species of life including fish, amphibians,
insects and plants.
• Base of food-web is found in freshwater Plankton (small
microscopic organisms)
b. Marine (i.e. oceans and estuaries):
• Very large amount of Earth is covered by ocean (~97%)
• 40% of all photosynthesis occurs in oceans.
Aquatic ecosystems cover about 75% of the earth’s surface. Within aquatic
ecosystem, the sub- ecosystems are:
- Wetlands
- Lakes
- Rivers, streams
- Intertidal zones
- Oceanic pelagic biome
- Benthos
- Coral reefs