Unit-2

Ecosystem
Ecosystem
Our environment provides us with a variety of goods and services necessary for
our day to day lives. These natural resources include, air, water, soil, minerals,
along with the climate and solar energy, which form the non-living or ‘abiotic’
part of nature. The ‘biotic’ or living parts of nature consists of plants and
animals, including microbes. Plants and animals can only survive as
communities of different organisms, all closely linked to each in their own
habitat, and requiring specific abiotic conditions. Thus, forests, grasslands,
deserts, mountains, rivers, lakes and the marine environment all form habitats
for specialised communities of plants and animals to live in.
• Interactions between the abiotic aspects of nature and specific living
organisms together form ecosystems of various types. Many of these
living organisms are used as our food resources. Others are linked to our
food less directly, such as pollinators and dispersers of plants.
History of our global environment:
About ten thousand years ago, when mankind changed from a hunter-gatherer,
living in wilderness areas such as forests and grasslands, into an agriculturalist
and pastoralist, we began to change the environment to suit our own
requirements. As our ability to grow food and use domestic animals grew, these
‘natural’ ecosystems were developed into agricultural land. Most traditional
agriculturists depended extensively on rain, streams and rivers for water. Later
they began to use wells to tap underground water sources and to impound water
and created irrigated land by building dams. Recently we began to use fertilizers
and pesticides to further boost the production of food from the same amount of
land.
However, we now realize that all this has led to several undesirable changes in
our environment. Mankind has been overusing and depleting natural resources.
The over-intensive use of land has been found to exhaust the capability of the
ecosystem to support the growing demands of more and more people, all
requiring more intensive use of resources. Industrial growth, urbanisation,
population growth and the enormous increase in the use of consumer goods,
have all put further stresses on the environment. They create great quantities of
solid waste. Pollution of air, water and soil have begun to seriously affect
human health.
Environment
The resources on which mankind is dependent are provided by various sources
or ‘spheres’.
1) Atmosphere
• Oxygen for human respiration (metabolic requirements).
• Oxygen for wild fauna in natural ecosystems and domestic animals used by
man as food.
• Oxygen as a part of carbon dioxide, used for the growth of plants (in turn are
used by man).
The atmosphere forms a protective shell over the earth. The lowest layer, the
troposphere, the only part warm enough for us to survive in, is only 12
kilometers thick. The stratosphere is 50 kilometers thick and contains a layer of
sulphates which is important for the formation of rain. It also contains a layer of
ozone, which absorbs ultra-violet light known to cause cancer and without
which, no life could exist on earth. The atmosphere is not uniformly warmed by
the sun. This leads to air flows and variations in climate, temperature and
rainfall in different parts of the earth. It is a complex dynamic system. If its
nature is disrupted it affects all mankind. Most air pollutants have both global
and regional effects. Living creatures cannot survive without air even for a span
of a few minutes. To continue to support life, air must be kept clean. Major
pollutants of air are created by industrial units that release various gases such as
carbon dioxide, carbon monoxide and toxic fumes into the air. Air is also
polluted by burning fossil fuels. The build-up of carbon dioxide which is known
as ‘greenhouse effect’ in the atmosphere is leading to current global warming.
2) Hydrosphere
• Clean water for drinking (a metabolic requirement for living processes).
• Water for washing and cooking.
• Water used in agriculture and industry.
• Food resources from the sea, including fish, crustacea, sea weed, etc.
• Food from fresh water sources, including fish, crustacea and aquatic plants.
• Water flowing down from mountain ranges harnessed to generate electricity in
hydroelectric projects. The hydrosphere covers three quarters of the earth’s
surface. A major part of the hydrosphere is the marine ecosystem in the ocean,
while only a small part occurs in fresh water. Fresh water in rivers, lakes and
glaciers, is perpetually being renewed by a process of evaporation and rainfall.
Some of this fresh water lies in underground aquifers. Human activities such as
deforestation create serious changes in the hydrosphere. Once land is denuded
of vegetation, the rain erodes the soil which is washed into the sea
3) Lithosphere
• Soil, the basis for agriculture to provide us with food.
• Stone, sand and gravel, used for construction.
• Micronutrients in soil, essential for plant growth.
• Microscopic flora, small soil fauna and fungi in soil, important living
organisms of the lithosphere, which break down plant litter as well as animal
wastes to provide nutrients for plants.
• A large number of minerals on which our industries are based.
• Oil, coal and gas, extracted from underground sources.
It provides power for vehicles, agricultural machinery, industry, and for our
homes. The lithosphere began as a hot ball of matter which formed the earth
about 4.6 billion years ago. About 3.2 billion years ago, the earth cooled down
considerably and a very special event took place - life began on our planet. The
crust of the earth is 6 or 7 kilometers thick and lies under the continents. Of the
92 elements in the lithosphere only eight are common constituents of crustal
rocks. Of these constituents, 47% is oxygen, 28% is silicon, 8% is aluminium,
5% is iron, while sodium, magnesium, potassium and calcium constitute 4%
each. Together, these elements form about 200 common mineral compounds.
Rocks, when broken down, form soil on which man is dependent for his
agriculture. Their minerals are also the raw material used in various industries
4) Biosphere
• Food, from crops and domestic animals, providing human metabolic
requirements.
• Food, for all forms of life which live as interdependent species in a community
and form food chains in nature on which man is dependent.
• Energy needs: Biomass fuel wood collected from forests and plantations,
along with other forms of organic matter, used as a source of energy.
• Timber and other construction materials. This is the relatively thin layer on the
earth in which life can exist.
Within it the air, water, rocks and soil and the living creatures, form structural
and functional ecological units, which together can be considered as one giant
global living system, that of our Earth itself. Within this framework, those
characterised by broadly similar geography and climate, as well as communities
of plant and animal life can be divided for convenience into different
biogeographical realms. These occur on different continents. Within these,
smaller biogeographical units can be identified on the basis of structural
differences and functional aspects into distinctive recognizable ecosystems,
which give a distinctive character to a landscape or waterscape. Their easily
visible and identifiable characteristics can be described at different scales such
as those of a country, a state, a district or even an individual valley, hill range,
river or lake. The simplest of these ecosystems to understand is a pond. It can be
used as a model to understand the nature of any other ecosystem and to
appreciate the changes over time that are seen in any ecosystem. The structural
features of a pond include its size, depth and the quality of its water. The
periphery, the shallow part and the deep part of the pond, each provide specific
conditions for different plant and animal communities. Functionally, a variety of
cycles
Ecosystem: Definition
• An ecosystem is a structural and functional unit of ecology where the
living organisms interact with each other and the surrounding
environment. In other words, an ecosystem is a chain of interactions
between organisms and their environment. The term “Ecosystem” was
first coined by A.G.Tansley, an English botanist, in 1935.

• It is a set of all living species and abiotic components existing and

interacting in a given area. There is an interaction with both living and
nonliving components of the environment.

• Ecosystems can generally be classified into two classes such as natural and
artificial. Artificial ecosystems are natural regions affected by man’s
interferences. They are artificial lakes, reservoirs, townships, and
cities. Natural ecosystems are basically classified into two major types.
They are aquatic ecosystem and terrestrial ecosystem.

Types of Natural Ecosystem

An ecosystem is a self-contained unit of living things and their non-living

environment. The following chart shows the types of Natural Ecosystem −
Biotic (Living Components)
Biotic components in ecosystems include organisms such as plants, animals, and
microorganisms. The biotic components of ecosystem comprise −
• Producers or Autotrophs
• Consumers or Heterotrophs
• Decomposers or Detritus
Abiotic (Non-living Components)
Abiotic components consist of climate or factors of climate such as temperature,
light, humidity, precipitation, gases, wind, water, soil, salinity, substratum,
mineral, topography, and habitat. The flow of energy and the cycling of water and
nutrients are critical to each ecosystem on the earth. Non-living components set
the stage for ecosystem operation.

Aquatic Ecosystem

An ecosystem which is located in a body of water is known as an aquatic

ecosystem. The nature and characteristics of the communities of living or biotic
organisms and non-living or abiotic factors which interact with and interrelate to
one another are determined by the aquatic surroundings of their environment they
are dependent upon.
Aquatic ecosystem can be broadly classified into Marine Ecosystem and
Freshwater Ecosystem.
Marine Ecosystem
These ecosystems are the biggest of all ecosystems as all oceans and their parts
are included in them. They contain salt marshes, intertidal zones, estuaries,
lagoons, mangroves, coral reefs, the deep sea, and the sea floor.
Marine ecosystem has a unique flora and fauna, and supports a vast kingdom of
species. These ecosystems are essential for the overall health of both marine and
terrestrial environments.
Salt marshes, seagrass meadows, and mangrove forests are among the most
productive ecosystem. Coral reef provides food and shelter to the highest number
of marine inhabitants in the world. Marine ecosystem has a large biodiversity.
Freshwater Ecosystem
Freshwater ecosystem includes lakes, rivers, streams, and ponds. Lakes are large
bodies of freshwater surrounded by land.
Plants and algae are important to freshwater ecosystem because they provide
oxygen through photosynthesis and food for animals in this ecosystem. Estuaries
house plant life with the unique adaptation of being able to survive in fresh and
salty environments. Mangroves and pickle weed are examples of estuarine plants.
Many animals live in freshwater ecosystem. Freshwater ecosystem is very
important for people as they provide them water for drinking, energy and
transportation, recreation, etc.

Terrestrial Ecosystem

Terrestrial ecosystems are those ecosystems that exist on land. Water may be
present in a terrestrial ecosystem but these ecosystems are primarily situated on
land. These ecosystems are of different types such as forest ecosystem, desert
ecosystem, grassland and mountain ecosystems.
Terrestrial ecosystems are distinguished from aquatic ecosystems by the lower
availability of water and the consequent importance of water as a limiting factor.
These are characterized by greater temperature fluctuations on both diurnal and
seasonal basis, than in aquatic ecosystems in similar climates.

Structure of the Ecosystem

The structure of an ecosystem is characterised by the organisation of both biotic
and abiotic components. This includes the distribution of energy in our
environment. It also includes the climatic conditions prevailing in that particular
environment.
The structure of an ecosystem can be split into two main components, namely:
 • Biotic Components
• Abiotic Components
The biotic and abiotic components are interrelated in an ecosystem. It is an open
system where the energy and components can flow throughout the boundaries.

Biotic Components
Biotic components refer to all living components in an ecosystem. Based on
nutrition, biotic components can be categorised into autotrophs, heterotrophs
and saprotrophs (or decomposers).

• Producers include all autotrophs such as plants. They are called

autotrophs as they can produce food through the process of
photosynthesis. Consequently, all other organisms higher up on the food
chain rely on producers for food.
• Consumers or heterotrophs are organisms that depend on other organisms
for food. Consumers are further classified into primary consumers,
secondary consumers and tertiary consumers.
• Primary consumers are always herbivores as they rely on producers
for food.
• Secondary consumers depend on primary consumers for energy.
They can either be carnivores or omnivores.
• Tertiary consumers are organisms that depend on secondary
consumers for food. Tertiary consumers can also be carnivores or
omnivores.
 • Quaternary consumers are present in some food chains. These
organisms prey on tertiary consumers for energy. Furthermore, they
are usually at the top of a food chain as they have no natural
predators.
• Decomposers include saprophytes such as fungi and bacteria. They
directly thrive on the dead and decaying organic matter. Decomposers
are essential for the ecosystem as they help in recycling nutrients to be
reused by plants.

Abiotic Components
Abiotic components are the non-living component of an ecosystem. It includes
air, water, soil, minerals, sunlight, temperature, nutrients, wind, altitude,
turbidity, etc.

Functions of Ecosystem
The functions of the ecosystem are as follows:
1. It regulates the essential ecological processes, supports life systems
and renders stability.
2. It is also responsible for the cycling of nutrients between biotic and
abiotic components.
3. It maintains a balance among the various trophic levels in the
ecosystem.
4. It cycles the minerals through the biosphere.
5. The abiotic components help in the synthesis of organic
components that involve the exchange of energy.
So the functional units of an ecosystem or functional components that work
together in an ecosystem are:

• Productivity – It refers to the rate of biomass production.

• Energy flow – It is the sequential process through which energy flows
from one trophic level to another. The energy captured from the sun flows
from producers to consumers and then to decomposers and finally back to
the environment.
• Decomposition – It is the process of breakdown of dead organic material.
The top-soil is the major site for decomposition.
• Nutrient cycling – In an ecosystem nutrients are consumed and recycled
back in various forms for the utilisation by various organisms.
Ecology and level of Organization
Ecology is the scientific study of the distribution and abundance of life along
with the interactions between different organisms and their natural environment.
It is the branch of biology, and the name Ecology was derived from the Greek
word, which refers to the house or the environment. here are five Levels of
Organization, and all levels are listed according to their size in increasing order
– from small to large.

Level of Organization

Organism
It is the lowest level of organization, which includes both unicellular
and multicellular organisms. All the living species in this level exhibit all the
characteristics required for the existence of life.

Population
A population is a group of individuals of a single species living together within
a particular geographic area. They interbreed and compete with each other for
resources.

Community
It refers to the several populations that interact and inhabit a common
environment and are interdependent.

Types of Community

Communities can be classified into two groups based on their size and degree of
relative independence:

Major Community

• These are huge, well-organized, and self-sufficient organizations. They

rely solely on solar energy from the outside and are unaffected by the
inputs and outputs of neighboring communities.
• For instance, tropical evergreen forest in the North-East.

Minor Community

• These are often referred to as societies because they are reliant on

adjacent communities.
 • They are secondary aggregations within a larger community, and so are
not totally self-contained in terms of energy and nutrient dynamics.
• A lichen mat on a cow dung pad, for instance.

Ecosystem

• The living organisms (all populations) in a certain area, as well as

the non-living features of the environment, make up an ecosystem.
• Nutrient cycles and energy flows bind these biotic and abiotic
components together.
• Photosynthesis brings energy into the system, which is absorbed into
plant tissue.

Ecosystem

Biome

• The biosphere's terrestrial portion is divided into vast sections known as

biomes.
• Biomes are defined by climate, flora, animal life, and general soil
type.
• There are no two biomes that are alike.
• The biome boundaries and the abundance of plants and animals found in
each one are determined by the climate.
• Temperature and precipitation are the most important climatic elements.
 • Tundra, Boreal Forests, Grasslands, Deserts, Temperate Forests, Tropical
Rain Forests, Tropical Deciduous Forests and Savannah are all biomes.

Biosphere

• The biosphere refers to the portion of the planet that

contains living beings.
• The biosphere encompasses the majority of the Earth's surface, as well as
a portion of the oceans and atmosphere.
• In other words, the biosphere encompasses the sum of all living
organisms and their surroundings.
• Thus the atmosphere, lithosphere and hydrosphere are all included in the
biosphere.

BIOGEOCHEMICAL CYCLES
Biogeochemical cycles mainly refer to the movement of nutrients and other
elements between biotic and abiotic factors.”
The term biogeochemical is derived
from “bio” meaning biosphere, “geo” meaning the geological components and
“chemical” meaning the elements that move through a cycle.
The matter on Earth is conserved and present in the form of atoms. Since matter
can neither be created nor destroyed, it is recycled in the earth’s system in various
forms.
The earth obtains energy from the sun which is radiated back as heat, rest all other
elements are present in a closed system. The major elements include:

• Carbon
• Hydrogen
• Nitrogen
• Oxygen

• Phosphorus
• Sulphur
These elements are recycled through the biotic and abiotic components of
the ecosystem. The atmosphere, hydrosphere and lithosphere are the abiotic
components of the ecosystem.

Types of Biogeochemical Cycles

Biogeochemical cycles are basically divided into two types:

• Gaseous cycles – Includes Carbon, Oxygen, Nitrogen, and the Water

cycle.
• Sedimentary cycles – Includes Sulphur, Phosphorus, Rock cycle, etc.

NICHE

An ecological niche refers to the interrelationship of a species with all

the biotic and abiotic factors affecting it. Despite the varying definitions of
niche, it is now generally considered to pertain to how an organism or
a population responds to, as well as alters, competition and the distribution of
resources. It particularly describes the relational position of an organism or a
population in a particular ecosystem.

A niche may be influenced by biotic and abiotic factors of an ecosystem.

However, the niche of a species in a particular ecosystem will help set the
features of its environment as these features will be crucial to its survival.
Niche is defined in a general sense as a cavity, hollow, or recess, especially in a
wall. However, in biology and ecology, a niche pertains to any of the following:

• The specific area where an organism inhabits

• The role or function of an organism or species in an ecosystem
• The interrelationship of a species with all the biotic and abiotic factors
affecting it

Niche vs. Habitat

In ecology, a habitat is a place where an organism or a biological population

normally (or is adapted to) live(s), reside(s), or occur(s). It may be a forest, a
river, a mountain, or a dessert. While habitat is a geographical place a niche is
the relationship of a species with the components of an ecosystem. The niche of
an organism depicts how it lives and is able to survive in its environment. Thus,
a habitat may consist of many niches and could support various species at a
given time. Niche is all about a single species as a part of the habitat with all its
biological activities as influenced by biotic and abiotic factors. The niche of
organisms could, therefore, be defined by living factors
(e.g. predators, competitors, parasites, commensals, etc.) and non-living factors.

Niche Formation

Both abiotic and biotic factors help shape the niche of an ecosystem. Abiotic
factors, such as temperature, climate, and soil type, of an ecosystem will help
form the niches while natural selection works to set which niches would be
favored and not. Through time, the species eventually develop special features
that help them adapt to their environment. If they fit in, they could thrive and
survive in surroundings that match their features.

• A fundamental niche is defined as the niche of a species in the absence of

competition. Conversely, a realized niche is the niche that a species
occupies due to pressures, e.g. the arrival of a competing species to its
habitat. (1)
• Niche overlap is defined as that when two organisms use the same
resources or other environmental variables. Often, niches overlap only
partially as the resources are shared. (2)
• A vacant niche is a niche that is yet to be occupied in an environment.
However, the existence of a vacant niche is still a matter of debate.
Nevertheless, possible causes of vacant niches are presumed to be habitat
disturbances (e.g. forest fires and droughts) and evolutionary eventualities
(i.e. when species failed to evolve).

ECOTONE
 • An ecotone is a zone of junction or a transition area between two biomes
(diverse ecosystems).
• Ecotone is the zone where two communities meet and integrate.
• For e.g. the mangrove forests represent an ecotone between marine and
terrestrial ecosystem.
• Other examples are grassland (between forest and
desert), estuary (between fresh water and salt water) and riverbank or
marshland (between dry and wet).

Characteristics of Ecotone
• It may be narrow (between grassland and forest) or wide (between forest
and desert).
 • It has conditions intermediate to the adjacent ecosystems. Hence it is
a zone of tension.
• Usually, the number and the population density of the species of an
outgoing community decreases as we move away from the community
or ecosystem.
• A well-developed ecotone contains some organisms which are entirely
different from that of the adjoining communities.
Ecocline
• Ecocline is a zone of gradual but continuous change from one ecosystem
to another when there is no sharp boundary between the two in terms of
species composition.
•
Edge Effect – Edge Species
• Edge effect refers to the changes in population or community structures
that occur at the boundary of two habitats (ecotone).
• Sometimes the number of species and the population density of some of
the species in the ecotone is much greater than either community. This is
called edge effect.
• The organisms which occur primarily or most abundantly in this zone are
known as edge species.
• In the terrestrial ecosystems edge effect is especially applicable to birds.
• For example, the density of birds is greater in the ecotone between the
forest and the desert.