Ecosystem is a part of the pure subject Plant Physiology.

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Plant Physiology and Ecology: Ecosystem
Prepared By
Roksana Aftab Ruhi
Department of Agriculture
Noakhali Science and Technology University
Noakhali,Chittagong, Bangladesh.

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Introduction
An ecosystem comprises of all of the living things like plants, animals and organisms in a given
area constantly interacting with each other, and also with their non-living environments like,
weather, sun, soil, climate, and atmosphere etc. In an ecosystem, all living organisms have their
respective roles to play and within their own environment their depended on each other directly
or indirectly. Such dependence actually keeps ecological balance of the environment. An
example may clear the matter, in a puddle one may find lots of living organisms like aquatic and
non-aquatic flora and fauna, insects, amphibians like toad, tadpole, fishes and many more. These
living organisms are dependent on non-living things like sunlight, water, temperature, nutrients
in the flora and fauna, atmospheric pressure etc. These complex but very clear interactions
among living organisms or biotic factors and non-living things or abiotic factors help to preserve
the balance of carbon and nitrogen in the environment. Thus these interactions are the
foundations of ecosystem. Scarcity of any one of these ecological factor may disrupt the overall
balance of the system.
Definition of Ecosystem
The word "ecosystem" was coined first by Roy Clapham in 1930. However, it was the ecologist
Arthur Tansley that fully defined an ecosystem concept. In the classic article from 1935, Tansley
defined an ecosystem as:
"The whole system,including not only the organism-complex, but also the whole complex of
physical factors forming what we call the environment".
The ecosystem concept signalled a critical step in the study of ecology, as Tansely used the term
specifically to replace the previous "superorganism" concept, which stated that communities of
organisms comprised something like a higher-level and more complex organism - a mistaken
conception which formed a theoretical barrier for ecological scientific research. Though Tansely
with other ecologists used the ecosystem idea together with the now abandoned concept of an

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ecological "climax" (the "final“or "equilibrium" type of ecosystem or community arising under
some environmental conditions), the idea of ecosystem dynamics now replaces this. Eugene
Odum, the major figure for advancing the study of ecology, made the ecosystem concept into a
central part in the seminal textbook on ecology, by defining ecosystems as:
"Any unit that includes all of the organisms (ie: the "community") in a given area interacting
with the physical environment so that a flow of energy leads to clearly defined trophic structure,
biotic diversity, and material cycles (ie: exchange of materials between living and nonliving
parts) within the system is an ecosystem.
“The organisms and the physical features of the habitat form an ecological complex or more
briefly an ecosystem.” (Clarke, 1954).
According to Woodbury (1954), ecosystem is a complex in which habitat, plants and animals are
considered as one interesting unit, the materials and energy of one passing in and out of the
others.
Component of Ecosystem
An ecosystem has two basic components
i) Abiotic components ii) Biotic
components
The relationship between the abiotic components and the biotic components of the ecosystem is
termed 'holocoenosis'.
Abiotic Components
Those include the non-living or physico-chemical factors like air, soil, water and the basic
compounds and elements of the environment.
Abiotic factors are classified broadly under three categories:
a. Climatic factors, including the climatic regime with physical factors in the environment
such as light, atmospheric temperature, wind, humidity, etc;

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b. Edaphic factors, which relate to the composition and structure of the soil like its
chemical and physical properties – like the soil type, soil profile, organic matter,
minerals, soil water, and soil organisms.
c. Inorganic substances like water, carbon, sulphur, nitrogen, phosphorus and so on.
Organic substances like proteins, lipids, carbohydrates, humic substances etc.
Biotic Components
It consists of the living parts of the environment, including the association of a lot of interrelated
populations that belong to different species inhabiting a common environment. The populations
are those of the animal community, the plant community and the microbial community.
The biotic community is divided into:
a) Autotrophs (from Greek: auto - self, trophos - feeder) are called producers,
transducers or convertors, as well. Those are photosynthetic plants, normally
chlorophyll bearing, which synthesize a high-energy complex organic compound (or
food) from the inorganic raw materials utilizing the aid of the sunt, and this process is
called photosynthesis. Autortophs form the core of all biotic systems.
b) Heterotrophs (from Greek: heteros - other; trophs - feeder) are the consumers,
normally animals that feed on the other organisms. Consumers are also referred to as
phagotrophs (phago - to swallow or ingest) while macro-consumers are normally
herbivores and carnivores.
1. Herbivores are called First order or primary consumers, for they feed directly on green
plants. For example, Terrestrial ecosystem consumers are cattle, deer, grass hopper,
rabbit, etc. Aquatic ecosystem consumers are protozoans, crustaceans, etc.
2. Carnivores are animals that prey or feed on other animals. Second order consumers or
Primary carnivores include those animals that feed on herbivorous animals. For example,
fox, frog, smaller fishes, predatory birds, snakes, etc.
3. Third order consumers or Secondary carnivores are the animals that feed on primary
carnivores. For example, wolf, owl, peacock, etc. Some larger carnivores prey on
Secondary carnivores. Quaternary consumers or Tertiary carnivores include those
animals which feed upon secondary carnivores. For example, the lion, the tiger,etc. Those

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are not eated by any other animal. The larger carnivores which cannot be preyed on
further are also called the top carnivores.
c) Saprotrophs (from Greek again: sapros - rotten; trophos - feeder) are called the reducers
or decomposers. They break the complex organic compounds in dead matter down (dead
plants and animals). Decomposers don’t ingest the food. Instead they secrete a digestive
enzyme into the dead, decaying plant or animal remains and digest this organic material. The
enzymes act on the complex organic compounds in the dead matter. Decomposers absorb a
bit of the decomposition products to provide themselves with nourishment. The remaining
substance is added as minerals.
Types of Ecosystem
As we have seen there are many types of ecosystems and it would be impossible to classify them
all but there are some general classifications that can be used for their study: several main ways
of classifying ecosystems-
According to the Environment
1. Aquatic Ecosystem
They are made up of plants and animals that live in the water. These ecosystems differ in relation
to the geographic region where they exist (Antarctica, Subantarctic, tropical and subtropical) and
their proximity to the land (coastal, oceanic and estuarine ecosystems).
Aquatic (as well as terrestrial) ecosystems can vary widely in size from an ocean to a pool of
water. There are also aquatic ecosystems of salt and fresh water.
In this ecosystem the variations of temperatures are not very marked, reason why this does not
affect the survival of the alive beings. This ecosystem is the largest because they represent 75%.
According to different habitats of aquatic organism, aquatic ecosystem are various kinds and
divided into the following:

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a) Benthic: these are located at the bottom of aquatic ecosystems. In those that are not very
deep, the main inhabitants are algae. In the deeper ones, the majority are consumers.
b) Nectonic: these animals move freely, thanks to their means of locomotion can adapt to
water currents.
c) Planktonic: these living beings live floating in the terrestrial or marine water and are
dragged by the water currents, they do not move by their own movements.
d) Neustonic: these live on the surface of the water, floating.
According to the characteristics of landscapes aquatic ecosystem is the following:
– Wetland: is a zone of flat lands that has groundwater of shallow depth and that ascend to
the surface in determined periods, forming lagoons and marshes, until where they come to live
hundreds of species.
There are five classes of wetlands: marine, estuarine, lake, riparian and marshy.
– Mangrove: is a grouping of semi-submerged trees that have been flooded with water,
with high levels of salinity and therefore they develop and survive in coastal lands. The trees
grow on long roots, which like stilts raise the trunks above the level of the waters.
– Coral reef: it is one of the richest aquatic ecosystems of the planet, product of the great
amount of species that inhabit in them (fish, snails, corals and algae).They are found mainly in
tropical regions.
There are two types of coral: hard and soft.
2. Terrestrial Ecosystem
They are those zones or regions where organisms (animals, plants, etc.) live and develop in the
soil and in the air that surrounds a certain terrestrial space. In these places it is assumed that
living things that inhabit the ecosystem find everything they need to be able to survive.

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Depending on the abiotic factors of each ecosystem, there are different types of terrestrial
habitats:
a. Deserts
b. Grasslands
c. Forests.
Terrestrial ecosystems are part of other larger ecosystems, called biomass or ecological regions.
This ecosystem develops on the surface of the Earth called Biosphere.
The most-wide individuals in this ecosystem are insects, of which there are 900,000 species. The
birds would occupy the second place, with about 8,500 species. Third, mammals of which there
are 4,100 species.
Tropical forests: These are tropical forests that receive an average rainfall of 80 per 400 inches
annually. The forests are characterized by dense vegetation comprising tall trees at different
heights.
– Tropical forests: They have a high biodiversity in plants and animals; also one of the oldest
ecosystems of the planet and they are below the 1200 meters of height; The temperature and
light remain constant throughout the year.
– Temperate forest: Those who have a good number of trees like mosses and ferns are for them.
Temperate forests exist in regions where the climate changes significantly from summer to
winter
-Swamp: Situated just before the Arctic regions, swamp is defined by evergreen conifers. The
temperature is below zero degrees for almost half a year, the rest of the months, is full of
migratory birds and insects.
– Tundra: It has an extremely cold climate.Its rainfall is very low, so it reduces the growth of
living organisms. There are no large trees, only small plants (mosses, lichens and other tree
species).

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– Desert: Occupy about 17% of all the land on our planet. Due to the high temperatures, low
availability of water and intense sunlight, the fauna and flora are scarce and underdeveloped.
– Savanna: They support a large number of predators and herbivores.
– Grassland: The temperate of grassland are completely devoid of large shrubs and trees.
Grasslands could be categorized as mixed grass, tall grass and grassy meadows.
– Mountain: Offers a dispersed and diverse matrix of habitats where large numbers of animals
and plants can be found. In the higher areas, the harsh environmental conditions that normally
prevail, and where only the alpine vegetation without trees can survive. The animals that live
there have thick fur coats for preventing cold and hibernation in the winter months.
3. Ocean Ecosystems
Ocean ecosystems are relatively contained, although they, like freshwater ecosystems, also
include certain birds that hunt for fish and insects close to the ocean’s surface. There are
different sorts of ocean ecosystems:
• Shallow water – Some tiny fish and coral only live in the shallow waters close to land.
• Deep water – Big and even gigantic creatures can live deep in the waters of the oceans.
Some of the strangest creatures in the world live right at the bottom of the sea.
• Warm water – Warmer waters, such as those of the Pacific Ocean, contain some of the
most impressive and intricate ecosystems in the world.
• Cold water – Less diverse, cold waters still support relatively complex ecosystems.
Plankton usually form the base of the food chain, following by small fish that are either
eaten by bigger fish or by other creatures such as seals or penguins.
Ocean ecosystems are amongst some of the most interesting in the world, especially in warm
waters such as those of the Pacific Ocean. This is not least because around 75% of the Earth is

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covered by the sea, which means that there is lots of space for all sorts of different creatures to
live and thrive.
There are actually three different types of oceanic ecosystems: shallow waters, deep waters and
the deep ocean surface. In two of these the very base of the food chain is plankton, just as it is in
freshwater ecosystems. These plankton and other plants that grow in the ocean close to the
surface are responsible for 40% of all photosynthesis that occurs on Earth.
According to the Degree of Human Intervention
1. Natural Ecosystems: Man has not intervened in their formation, such as forests, lakes,
deserts.
2. Artificial Ecosystems: Man actively participates in its formation, such as dams, parks,
gardens.
According to Size
– Micro-Ecosystems: As tiny as a drop of water, a vase with water, a pot, etc.
– Macro-Ecosystems: As big as the lake of Maracaibo, the Caribbean Sea, the mountain range of
the Andes, etc.
Ecosystem Processes
There are four ecosystem processes that are fundamental to all terrestrial ecosystems:
1 The Water Cycle
2 The Nutrient Cycle
3 Plant and Animal Succession
4 Energy Flow

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Water Cycle;The constant process of precipitation, transpiration, evaporation, and surface and
ground water flow is called the water cycle. The effectiveness of the water cycle and its overall
functioning are directly influenced by land management practices.
Nutrient Cycle;The nutrient cycle may also be referred to as the nutrient cycle. Nutrients follow
cyclical patterns as they are used and re-used by all living organisms. Physical processes such as
oxidation, photo-decay, mechanical breakage, fire, and actions of wind and water are
nonbiological facets of the mineral cycle. The manner and rate at which nutrients are cycled play
a critical role in rangeland health and are directly influenced by land management practices.
Plant and Animal Succession (Community Dynamics); The process of change is the only
constant in all ecosystems. Populations of plants and animals change continually in response to
all sorts of environmental pressures. As resource managers, we have learned to manipulate
succession through a variety of means, sometimes successfully, and sometimes not. We have
many tools at our disposal that may be used to advance, arrest, or reverse succession.
Energy Flow; This flow of energy in our ecosystems is sometimes referred to as the carbon
cycle because carbon is involved in all energy storage and transfer. Energy flow is closely related
to the other ecosystem processes water cycling, mineral cycling, and succession. It in fact drives
these activities and makes them possible. Energy flow is a critical process on rangelands and is
directly influenced by land management practices.
Function of Ecosystem
Ecosystem function is the capacity of natural processes and components to provide goods and
services that satisfy human needs, either directly or indirectly (de Groot et al 2002).
An ecosystem is a discrete structural, functional and life sustaining environmental system. The
environmental system consists of biotic and abiotic components in a habitat. Biotic component of
the ecosystem includes the living organisms; plants, animals and microbes whereas the abiotic
component includes inorganic matter and energy.

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Abiotic components provide the matrix for the synthesis and perpetuation of organic components
(protoplasm). The synthesis and perpetuation processes involve energy exchange and this energy
comes from the sun in the form of light or solar energy.
In an ecosystem there are two processes proceeding simultaneously:
1) Energy flow and 2) Biogeochemical cycle
1] Energy Flow Function
The energy flow is in a single direction and is non-cyclic whereas Bio-geochemical flow is cyclic
(Any mineral cycle).
Food chains, food web and energy flow are the functional properties of ecosystems which make
them dynamic.
Food Chain
The unidirectional transfer of food energy from the producers, through a series of organisms
(herbivores to carnivores to decomposers) with repeated eating and being eaten, is known as
food chain. It is the movement of organic matter and energy from the producer level through
various consumer levels.
Types of Food Chains • Grazing Food Chain
Grazing food chain (GFC) is the most common food chain. It is also called predator food chain
as predation occurs at every step. This food chain is consists of producers, consumers and
decomposers. Consumers are often of 3 to 5 types: first order (primary), second order
(secondary), third order (tertiary), fourth order (quarternary) consumers. Grasses
Grasshopper Frog Snake Hawk/Eagle
• Detritus Food Chain
Detritus food chain (DFC) begins with detritus or dead organic matter. The food energy present
in detritus passes into detrivores and decomposers who feed over it. Detrivores and decomposers
are consumed by smaller carnivores which in turn become food for larger carnivores and so on.
A common detritus food chain with earthworm as detrivores is:

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Detritus _____ Earthworm _____ Sparrow _____ Falcon
• Parasitic Food Chain
Parasitic food chain also called auxiliary food chain; it begins with host and usually ends in
parasite.
Food Web
Simple food chains are very rare in nature because each organism may obtain food from more
than one trophic level. Thus in an ecosystem, the various food chains are interconnected to each
other to form a network called food web. A food web illustrates all possible transfers of energy
and nutrients among the organisms in an ecosystem, whereas a food chain traces only one
pathway of the food. Food webs are very important in maintaining the stability of an ecosystem.
Difference of Food Chain and Food Web
Ecological Pyramids
Ecological pyramid Ecological pyramids are the graphic representations of trophic levels in an
ecosystem.
There are three types of Ecological Pyramids

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a) Pyramid of energy; the pyramid of energy or the energy pyramid describes the overall
nature of the ecosystem. During the flow of energy from organism to other, there is considerable
loss of energy in the form of heat.
b) Pyramid of Numbers; it is a graphic representation of the number of individuals per unit
area of various trophic levels stepwise with producers being kept at the base and top carnivores
kept at the tip.
c) Pyramid of biomass; the pyramid of biomass is more fundamental, they represent the
quantitative relationships of the standing crops. In this pyramid there is a gradual decrease in the
biomass from the producers to the higher trophic levels.
2] Biogeochemical cycles
Organic materials synthesized by the producers are eaten and assimilated by the consumers .The
cyclic flow of nutrients between non-living environment (soil, rocks, air, water) and living
organisms is known as biogeochemical cycle. The major nutrient element i.e. carbon, hydrogen,
oxygen and nitrogen, which form about 95% mass of the living organism, are circulated again
and again between living and non-living components of the ecosystem.
Carbon cycle
The atmosphere contains a pool of CO2. CO2 is removed from the pool by the photosynthetic
activities of plants. It is released back into the environment by respiration which is carried out by
all organisms including those micro-organisms (decomposing bacteria) responsible for the decay
of dead plants and animals. Not all dead material decays. Sometimes dead plants and animals
form fossil fuels such as peat, coal, petroleum and petroleum-based gases. Man uses these
materials as sources of energy.

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Nitrogen Cycle
The nitrogen cycle is complex as it depends on the activities of various bacteria. Nitrate in the
soil is built up by plants into protein which is then passed on to animals, which eat the plants.
The nitrogen from the protein is returned to the environment as ammonia (ammonification),
either from excretory matter or through the action of decomposing bacteria on dead bodies.
Various nitrifying bacteria convert the ammonia back to nitrate (nitrification).
Ecosystem Stability
Most ecologists describe ecosystem stability as the ability of an ecosystem to maintain its
structure and function over long periods of time and despite disturbances. Ecosystems that show
a high degree of stability may have different combinations of resistance and resilience.
Research has shown that species diversity is often the key to both ecosystem resistance and
resilience. An ecosystem rich in biodiversity will likely be more stable than one whose
biodiversity is low.
Environmental change affect Ecosystem Stability
Communities respond to environmental change in ways that reflect the responses of the species
and populations in the community. Changing environmental conditions can cause the decline of
local biodiversity. If this happens, an ecosystem’s resistance and/or resilience may decline. The
end result is that the ecosystem loses stability.
Ecosystems that are less stable may not be able to respond to a normal environmental
disturbance, which may damage ecosystem structure, ecosystem function, or both.

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Human actions affect Ecosystem Stability
Humans affect ecosystem stability in many ways, including habitat loss, introduction of
nonnative species, releases of pollution into food webs, and contribution to climate change.
Ecosystems are frequently destroyed for agricultural activity and urban development.
Clearing patches of habitat can split ecosystems into pieces, a process called habitat
fragmentation. Remaining pieces of habitat become habitat “islands” surrounded by a different
habitat. A keystone species is one that has a strong and/or wide-reaching impact on a
community’s stability. If a keystone species declines in number, the ecosystem becomes much
less stable.
Conclusion
Ecosystems provide a number of goods such as food, timber, medicines, genetic resources, etc.
Ecosystems also serve a number of functions; ecological, economic, recreational/aesthetic, as well as
educational. Major ecological functions of ecosystems include: meeting the habitat (shelter), food, water,
air as well as breeding demands of not just humans but also of the various other organisms; providing
ecological services—clean air, water, waste absorption to the organisms living in it; regulating climate,
flood control ,coastline stabilization, carbon appropriation, waste treatment, biodiversity conservation,
soil generation, disease regulation, and the provision of aesthetic and cultural benefits.
Thus, an ecosystem provides both products as well as services (the ecological functions) to humans. Each
ecosystem has a unique set of environmental services provided and goods that it provides (for example,
grasslands are usually the fodder source for browsers and grazer.
Ecosystems contribute to human well-being via the provision of goods and services where the benefits are
direct, such as in the production of food and raw materials, and indirect as is the case in the regulation of
water quality and supply. For example, a healthy wetland that contains a biologically diverse array of
producers and consumers purifies water, making freshwater available for irrigated agricultural production,

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which in turn provides food for human consumption. Making the link between function and service also
enables us to identify threats to ecosystem services from unsustainable management practices.
Appendixes
Ecosystem

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Components of Ecosystem
Types of Ecosystem

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Aquatic Ecosystem

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Terrestial Ecosystem
Ocean/Marine Ecosystem

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Ecosystem Processes

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Bio-geochemical flow of ecosystem function
Energy flow of Ecosystem

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Functions of Ecosystem

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Carbon and Nitrogen Cycles