Ecology and Ecosystem BBT654D

CONCEPT OF ECOLOGY AND ECOSYSTEM:

The term Ecology was coined by Earnst Haeckel in 1869. It is derived from the Greek words
Oikos- home + logos- study. So ecology deals with the study of organisms in their natural home
interacting with their surroundings. The surroundings or environment consists of other living
organisms (biotic) and physical (abiotic) components. Modern ecologists believe that an
adequate definition of ecology must specify some unit of study and one such basic unit
described by Tansley (1935) was ecosystem.
An ecosystem is a self-regulating group of biotic communities of species interacting with one
another and with their non-living environment exchanging energy and matter. Now ecology is
often defined as ‘‘the study of ecosystems’’. The ecosystem is a unit or a system which is
composed of a number of sub-units that are all directly or indirectly linked with each other.
They may be freely exchanging energy and matter from outside—an open ecosystem or may
be isolated from outside in term of exchange of matter—a closed ecosystem.
The ecosystem study is based on these two main factors:
I. Abiotic (Non-living things)
II. Biotic (Living Beings)
Structure of Ecosystem
It includes the substances or things that make the ecosystem. It consists of two types of
components:
1. Biotic Components
These are the living elements of the ecosystem. They can be subdivided into three main types.
Autotrophs (auto=self; troph=nutrition/nourishment)
They are the organisms that prepare their own food. They can also be called producers. They
are the first line in the food chain.
a. Photoautotrophs (Photo=light): The autotrophs that prepare their food by using sunlight
are called photoautotrophs. They do so via photosynthesis in the presence of sunlight, water,
and carbon dioxide. For eg, Green plants, Bacteria (Cyanobacteria), algae, etc.
Note: Photoautotrophs are often confused with photoheterotrophs which, although use light,
but instead Carbon dioxide, they use other organic materials as sources of carbon and cannot
prepare their own food.
b. Chemoautotrophs (Chemo=chemicals): They are generally bacteria that synthesize some
chemical components to produce their own food. For eg., nitrogen-fixing bacteria, iron-
oxidizing bacteria, etc.
Consumers
They are those organisms that cannot synthesize food on their own and just use the producers
or other organisms as food. They can be primary (feeding on producers directly), secondary
(feeding on primary consumers), and so on.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

a. Herbivore (Herb=plants; vore=kind of diet): They only consume grass or plants as a food
source. For e.g. Cows, Buffalo, deer, goats, etc.
b. Carnivore (Carni=meat): They solely depend on other animals’ flesh for their food. For
e.g., Lion, Tiger, etc.
c. Omnivore (Omni=everything): As the name suggests, they can consume anything no
matter it is plant or animal meat. For e.g. Cats, Dogs, Humans, etc.
Decomposers
These include those organisms that feed on dead and decayed organic matter. For e.g. microbes
such as bacteria and fungi.
2. Abiotic Components
These are the non-living components of the ecosystem.
Physical factors: These comprise the sunlight, temperature, humidity, etc.
Chemical factors: These comprise the chemicals such as air and water components.
Functions of the Ecosystem
It depicts the ways of interaction of the abiotic and biotic components. The main components
of the function are:
a. Physical (Energy Flow)
The energy which follows in the ecosystem is always fixed in one direction or unidirectional.
 It always flows from producers to consumers (herbivores to carnivores) and cannot be
vice-versa.
 The energy at each stage of transfer is lost in some amount. So if the energy produced
received by plants from sunlight is 100%, then they receive only a few amounts of it.
After consuming plants, the animals will receive maybe only 10% of the total energy,
not exactly all energy.
 The energy is lost during respiration, growth, movement, and other activities.
 This is why trophic levels can be up to four or five as the energy becomes minimal at
lower trophic levels, and the organism cannot survive with that amount.
 Different energy flow models depict the transfer of energy, such as the universal energy
flow model, single channel energy flow model, and double channel energy flow model.
b. Biological (Food, chain, Food web, and Ecological Pyramids)
Food Chain
It is a sequence or order in which one organism feeds on another. Every organism on this earth
is interconnected through the food chain i.e. each organism depends on others for its food
requirements. The main definition of the food chain is “it is the sequence of eating and being
eaten with the transfer of energy in every stage.” It represents the diet or feeding behavior of
organisms along with the flow of energy in the ecosystem. An example of a food chain is the

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

grass that depends on sunlight and oxygen for food which is consumed by grasshopper feeding
on grass, which gets eaten by frogs and the frogs are taken as a diet by snakes which are eaten
by an eagle and as eagles die they are buried in the soil and decomposed by decomposers which
become minerals for plants to grow again.
Grass → Grasshopper → Frogs → Eagle → Dies and gets decomposed by
decomposers → Decomposed matters utilized by grass (Cycle continues).
The food chain can also be ordered at the trophic level. The energy moves from one trophic
level to another.
1. First Trophic Level: It includes producers which form the energy, such as green leafy
plants.
2. Second Trophic Level: The one which feeds directly on producers for energy comes in this
level. Such as the grasshopper in the above example.
3. Third Trophic Level: The one which feeds on organisms of the second trophic level comes
under this. For e.g. Frogs and Eagles.
The food chain is of two types:
1. Grazing Food Chain: It is the one that starts from sunlight. The energy from sunlight
is transferred to the producers and then to the consumers, to the decomposers, and again
to the producers.
2. Detritus Food Chain: It is the one that begins from dead organic matter. For instance,
dead leaves are eaten by insects which are further consumed by birds and so on.
Food Web
It is actually the interconnection or network between different food chains. It is an intricate
representation of different food chains that are interrelated. For e.g. grass can be eaten by
grasshoppers and goats; grasshoppers can be eaten by frogs, and frogs as well goats can be
eaten by one or more carnivores which can be interrelated on the basis of feeding.
Importance of the food chain and food web:
 Ecological Balance: It helps to predict the reason for the imbalance or ecological
disturbance in the ecosystem.
 Biomagnification: It is the process by which chemicals increase in concentration at
different trophic levels. It takes place through the food chain and can be predicted by
it. For, eg., the reason for the decrease in the number of vultures was predicted to be
the consumption of dead bodies of cattle which were injected with efficient chemicals
to boost their working stamina which then entered vultures and they started to die.
Ecological Pyramids
They are the representations of the number, biomass, and amount of energy at various trophic
levels of the food chain in the form of graphs or pyramids. The producers are kept at the bottom
of pyramids, and the consumers above, respectively, are based on their food chain. They can
be of different types and can be inverted or upright based on the type of ecosystem.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

 Pyramid of Numbers: It depicts the number of organisms at different trophic levels.

E.g., In an aquatic ecosystem, the number of plankton is numerous, and they are kept
at the bottom of the pyramid with broad bottoms, and the insects consuming that
plankton are lesser in number; the small fishes eating insects are lesser than insects, and
the large fishes are minimal in number that consume on those fishes, so they are kept
at the top with a narrow top. So the pyramid of the number of aquatic ecosystems is
upright.
 Pyramid of Biomass: It represents the dry weight of different organisms involved in a
food chain. For e.g. In an aquatic ecosystem, the dry mass of phytoplanktons is lesser
than those of small fishes, and the large fishes have a large dry mass. Hence the pyramid
formed is inverted.
 Pyramid of Energy: It represents the amount of energy at different levels of the food
chain. As energy flow is unidirectional and decreases at each step from producer to
consumer, so the pyramid of energy is always upright.
c. Biogeochemical cycle (Nutrient cycling)
The biogeochemical cycle is the phenomenon by which nutrients like carbon, nitrogen,
phosphorus, etc., are available from the atmosphere or surrounding to the plants and then to the
consumers in different forms such as carbohydrates, proteins, phosphates, etc., and get back to
the atmosphere in their original form. It is the transfer of nutrients from abiotic to biotic
components and vice-versa. The biogeochemical cycle is multi-directional in contrast to the
energy flow, which is uni-directional. It includes the water cycle, carbon cycle, nitrogen cycle,
etc.
Types of Ecosystem
Based on the location, the ecosystem can be divided into two types:
1. Terrestrial Ecosystem
It includes the ecosystem present on the land. It can be further divided into:
 Forest Ecosystem: These areas on land receive a very large amount of rainfall, which
is the reason for the diverse types of large trees and animals. Based on their distance
from the equator, forests can be of two types:
 Tropical Forest: The forests close to the equator are called tropical. It includes
tropical rainforest, tropical deciduous, and tropical scrub forest.
 Temperate Forest: The forests that are far from the equator are called
temperate forests. It includes temperate rainforest, temperate deciduous, and
coniferous forest.
 Grassland Ecosystem: If the terrestrial ecosystem receives a moderate amount of
rainfall that can be enough for the growth of grasses, then it is called a grassland
ecosystem. They can be of three types that include tropical grassland (e.g. Savanna
Grassland), temperate grassland (e.g. Pampas), and polar grassland.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

 Desert Ecosystem: If the terrestrial ecosystem receives a very low amount of rainfall,
then it is called a desert ecosystem. The components of this ecosystem are adaptive to
survive in those conditions. For eg., Camels have special pouches where they store
water for later consumption. Thorny plants such as cacti are present in this
ecosystem. They are two types:
 Hot Desert: The temperature is extremely high in this kind of desert. It includes
the tropical desert (Sahara), and temperate desert (Mojave Desert).
 Cold Desert: The temperature is relatively low in these deserts. One example
is the Gobi Desert.
2. Aquatic Ecosystem
It includes the ecosystem present in water. The food chain of the aquatic ecosystem comprises
plants or phytoplankton, insects, small fishes, large fishes, turtles, and other large aquatic
animals. It is further divided into two types based on the amount of salt content in the water:
Freshwater Ecosystem
The salt content is very low in comparison to the saltwater ecosystem. It can be subdivided into
two types:
Lentic water: Water is stationary. For eg. pond ecosystems and lake ecosystems. Based on the
availability of sunlight, the pond ecosystem can be divided into different zones:
 Littoral Zone: Plenty amount of sunlight is available in this zone. It is the top layer of
water, and generally, the plants survive in this zone.
 Limnetic Zone: Moderate amount of sunlight is available in this zone. It is the middle
layer of water. The food chain can operate quite efficiently in this zone.
 Profundal Zone: It includes the deep layer of water that receives minimal or no
sunlight where decomposers, such as bacteria, fungi, etc., survive.
Lotic water: Water is always moving or flowing. For, eg. the river ecosystem. It generally
originates from mountains, and the respective layer has a high amount of dissolved oxygen.
The middle layer has a lesser amount of dissolved oxygen and is warm. This layer flows
through a long distance and collects a lot of pollutants. The last segment is called the delta,
which finally leads to the deposition of water in oceans.
Saltwater Ecosystem
It has a very large amount of salt content. For eg. Seas and oceans. Its larger size and
connections with different landmasses, as well as freshwater ecosystems such as rivers, are the
reason for its wide range of biodiversity. On the basis of the availability of light, it can be
divided into the euphotic zone (a large amount of sunlight), an aphotic zone (less amount of
light), and an abyssal plain (totally dark).
It also includes estuaries where the river water meets the ocean water, and there is a higher
fluctuation of nutrients and temperature.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

Community Ecology:
The study of interactions between species in groups across a broad variety of temporal and
spatial scales, including distribution, population dynamics, structure, abundance, and
demography, is known as community ecology, or synecology. Community ecology is mainly
concerned with how certain genotypic and phenotypic features affect interactions within
populations. Studies of community ecology concentrate on the relationships and rivalry
between organisms that coexist in a certain ecological niche, such as a grassland, lake, or
forested area. Community ecology is the term suggested by Cornell professor Robert Whittaker
in 1975.
Types of Community
There are two main types of community:
1. Major Community
The smallest self-sustaining, self-regulating ecological unit is called a major community. These
communities typically exist in relative isolation from other communities, such as lakes, ponds,
forests, or grasslands. A major community is an amalgam of a microbiological community
(also known as "microbiocenosis"), a floral community (also known as "phytocenosis"), and a
faunal community (also known as "zoonenosis").
2. Minor Community
Smaller ecological entities that depend on interactions with other communities for survival,
minor communities, also known as merocenoses, are the building blocks of big communities.
An example of a minor community is the collection of organisms, which lives within a piece
of deadwood on the forest floor.
Examples of Community Ecology
Numerous diverse ecological interactions that are always changing are included in community
ecology. A forest community is made up of all the trees, the flora, fish in the Forest Rivers,
birds, deer, squirrels, foxes, mushrooms, insects, and other seasonal or local species. A coral
reef community is made up of different types of fish, algae, and coral. The biotic community
is significantly influenced by dispersion and abundance.
The interactions between different species that affect the health, growth, spread, and richness
of the ecological system are referred to as community ecology. At the communal level, species
often rely on each other. The majority of biological groups have multiple short food chains.
Characteristics of a Community Ecology
 Variability in Species: Every community consists of a variety of organisms, such
as bacteria, plants, and animals. They differ from one another in terms of taxonomy.
There may be a local or regional diversity of species.
 Growth Form and Organization: A community can be examined using primary
growth forms, such as trees, shrubs, and herbs. Each growth form found in trees may
contain a variety of plant species, including broadleaf trees, evergreen trees, etc. The
structure of a community is influenced by these many growth types.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

 Dominion: Within a community, species vary in importance. A community's traits are

determined by a chosen few species. A few numbers of species regulate and rule over
the community.
 Self-Reliance: There are many different heterotrophic and autotrophic organisms in
every group. Plants that are autotrophic can endure on their own.
 Relative Abundance: The idea of relative abundance states that many populations
coexist in a community in relative amounts.
 Trophic Structure: The trophic organisation of each ecosystem regulates the flow of
food and energy from plants to herbivores and then to carnivores.
Importance of Community Ecology
The community ecology is important because:
 It helps in the understanding of community structure and evolution by scientists. It also
helps in understanding the causes, effects, and maintenance of species variety.
 The interactions and competition between organisms that coexist in a certain ecological
niche are the main focus of community ecology.
 This is particularly important for invasive species, which, if they can fill certain niches
held by native species, may be able to establish themselves in particular groups.
 Abiotic variables that affect species interactions or distributions are also taken into
consideration in community ecology. For example, the soil pH or the annual
temperature.
Population Ecology:
Population ecology is the study of how various factors impact population growth, rates of
survival and reproduction, and risk of extinction. Population ecology has its most profound
historical roots and development in the study of population growth, regulation, dynamics, or
demography. The population can be open or closed population.
Closed Population
A closed population is not able to exchange with other people after a while. The population
can grow through the birth of new people. This circumstance is usually seen on islands as a
population might be laid out during a storm or any other influence but no additional members
will be added over time. When a brief period of time is over, a population is bound to be closed.
A storm event where more turtles are added during a single year than 100 years is less likely
to happen on an island. Animals will not be able to cross the river during a normal year if the
river stays at its full level. The population can grow through birth and decline through death,
making it easier to project growth rates. The growth rate is not determined by the number of
organisms or the rate of reproduction.
The population will be diminished by the death rate. Population growth can be influenced:
 space
 hereditary qualities

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

 age of individuals
 resources
Open Population
An open population can acquire and lose different populations over time. The population isn’t
geographically isolated. The longer the period of time, the more probable it is that the
population will open. The typical changes in an environmental system are the reason for this.
Characteristics of Population Ecology
Ecologists use diverse terms while understanding and examining populations of organisms. A
population is all of one sort of species living in a particular location. Population size describes
the total number of individuals in a habitat. Population density refers to how many individuals
live in a specific area.
Population size is represented by the letter N, which refers to the total number of individual
organisms in a population. The bigger a population is, the greater its generic variation and thus
its potential for long-term survival. Increased population size can, however, lead to further
issues, such as overuse of resources leading to a population crash.
Population Density refers to the number of individual organisms in a particular area. A low-
density region would have more organisms spread out. High-density regions would have more
individuals residing closer together, leading to greater resource competition.
Population Dispersion: Hauls helpful information regarding how species interact with each
other. Researchers can discover more about populations by studying how they are distributed
or dispersed.
Population distribution describes how individual organisms of a species are spread out, whether
they live close or far apart or massed into groups.
 Uniform dispersion means the organisms that live in a distinct territory. One example
would be penguins. Penguins live in parts; within those territories, the birds space
themselves reasonably uniformly.
 Random dispersion means the spread of individual organisms, such as wind-dispersed
seeds, which fall randomly after transiting.
 Clustered or clumped dispersion means a drop of seeds straight to the ground, instead
of being carried, to groups of animals living together, such as herds or schools. Schools
of the fish show this manner of dispersion.
Ecological Succession:
It is the gradual process of change in the species composition of an ecosystem over time.
It occurs as a result of natural disturbances like fires, floods, or human activities such as farming
or deforestation. In the initial stages of succession, pioneer species, like mosses and lichens,
colonize barren environments, gradually paving the way for more complex communities of
plants and animals.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

As these communities develop, they change the environmental conditions which make it more
suitable for different species to thrive. This process continues until a stable climax community
is reached. It is characterized by a range of species which are well adapted to the prevailing
environmental conditions.
Types of ecological succession: Primary and Secondary Succession.
Primary Succession
It is a gradual process of change by which a barren area is transformed into a thriving
ecosystem. This types of ecological succession starts in places with no plants or animals, like
bare land or new volcanic rocks. Over time, microorganisms break down these rocks and create
soil in a process called soil erosion.
Then, plants start to grow in the soil. It takes several hundred to 1,000 years for a full
community of plants and animals to develop, depending on the area and climate. These plants
support different animals, and the ecosystem evolves from simple to more complex. If the
ecosystem is disturbed, like by a fire or human activity, secondary succession begins.

Secondary Succession
Secondary ecological succession occurs in areas where an existing ecosystem has been
disturbed, but not completely destroyed.
Examples of disturbances include forest fires, floods, landslides, or human activities like
farming or logging. Unlike primary succession, secondary succession starts with some
remaining and left over fertile soil and organisms (seeds, spores, etc.) from the previous
community. This allows for faster recolonization by plants and animals.
Process of Recolonization
The process of recolonization in secondary ecological succession involves:
 Following the disturbance, small, fast-growing plants like weeds and grasses are the
first to establish themselves. They benefit from the increased sunlight penetration and
readily available nutrients.
 Over time, these pioneer species are gradually replaced by larger plants and shrubs, as
the environment becomes more shaded and soil conditions change.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

 Through continued succession, the ecosystem progresses towards a stable climax

community. This is a self-sustaining ecosystem characteristic of the region’s climate
and geography. The climax community represents a mature stage with a complex web
of plant and animal life.

Stages of Ecological Succession

The process of ecological succession involves five stages, which are:
1. Nudation
This is the development of a vacant area with no life. It can be caused by events like volcanic
eruptions, landslides, floods, erosion, earthquakes, forest fires, or the spread of disease.
2. Invasion or Intrusion
This stage involves the establishment of species in a barren area. The seeds or spores of various
species arrive in the new or exposed area through air, water, etc., a process called migration.
These species then adapt to the conditions, known as ecesis, and multiply, which is
called aggregation.
3. Competition and coaction
As species increase in number, they compete with each other for food, space, and other
resources. This competition can be within the same species (intraspecific) or between different
species (interspecific), along with interactions with the environment. New species of plants and
animals continue to invade.
4. Reaction
In this phase, living organisms alter the environment through their activities, which is
called reaction.
5. Stabilization
This final stage occurs when the ecosystem becomes stable and balanced for a longer period,
resulting in a climax community that is well adapted to the specific environment.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College
Ecology and Ecosystem BBT654D

Ecological Succession Causes:

The reasons for environmental progression are fundamentally three types. These are the
following:
 Initial Causes: These include both biotic and climatic factors, such as erosion, wind,
fire, and natural disasters. These events significantly impact the population in an area.
 Ecesis or Continuing Causes: Also known as ongoing causes, these factors help the
population adapt to environmental conditions. They include accumulation, competition,
and migration.
 Climatic Causes: These involve factors like the local climate, soil fertility, and the
availability of minerals.
Examples of Ecological Succession
The examples of ecological succession are as follows:
 Coral Reefs: Small coral formations settle on rocks. These corals grow and divide to
form larger colonies. The coral reefs attract small fish and shellfish, which then become
food for bigger fish, creating a fully functioning coral reef ecosystem.
 Tropical Forests: Tropical forests are examples of secondary succession where forests
were cleared for lumber and farming. The forest regrowth happened at different rates,
and it took several years for the community to be fully restored.
 Acadia National Park: This Park experienced a devastating wildfire. Nature was
allowed to restore the forest. In the first few years, only small plants grew on the burned
soil. Over time, the forest developed a variety of tree species. Before the fire, the trees
were mostly evergreen, but after the fire, deciduous trees became more common.

Bilwashri H, Asst. Prof,

Dept. of BT, BIET College