ZOOLOGY Principles of Ecology
Introduction to the science of ecology Part 2
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Paper : 12 Principles of Ecology
Module : 02 Introduction to the science of ecology Part 2
Development Team
Paper Coordinator : Prof. D.K. Singh
Department of Zoology, University of Delhi
Principal Investigator : Prof. Neeta Sehgal
Department of Zoology, University of Delhi
Content Writer : Dr. Sudhida Gautam Parihar, Hansraj College, DU
Mr. Kiran Kumar Salam, Hindu College, DU
Content Reviewer : Prof. K.S. Rao
Department of Botany, University of Delhi
Co-Principal Investigator : Prof. D.K. Singh
Department of Zoology, University of Delhi
ZOOLOGY Principles of Ecology
Introduction to the science of ecology Part 2
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Description of Module
Subject Name ZOOLOGY
Paper Name Zool 12 Principles of Ecology
Module Name/Title Introduction to Ecology
Module Id M02 Introduction to the science of ecology Part 2
Keywords Trophic level, productivity, geo-chemical cycle, Ecological
pyramid, Succession, Homeostasis, human Impacts.
Contents
1. Learning outcomes
2. Introduction
3. Processes of an Ecosystem
3.1. Trophic level
3.2. Energy flow in an Ecosystem
3.3. Bio-geochemical Cycle
4. Factors of ecosystem
5. Relationship of Ecology with Different Subjects
6. Specialized Branches of Ecology
7. Ecological Relationships
8. Importance & Scope of Ecology
9. Mechanism of Ecosystem
9.1. Succession
9.2. Homeostasis: Maintaining the Balance
9.3. Human Impacts
10. Summary
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1. Learning outcomes
After reading this chapter you will be able to:
To understand the processes of ecosystem, intermingling of trophic levels in food
chain, food web and ecological pyramids.
Concepts of bioaccumulation, biomagnifications, energy flow and its impact on the
ecosystem.
Discuss the flow of energy and cycling of materials as fundamental to the ecosystem
functioning and indiscriminate intervention would lead to damage and disruption of
the environment.
Discus the environmental impact of human activities.
Importance of the study of ecology for man’s survival.
2. Introduction
Ecological studies mainly deal with the functioning of an ecosystem which depends on
energy flow and nutrient recycling. Energy flow takes place among organisms of various
trophic levels. Energy, water, nitrogen and soil minerals are the essential abiotic components
of an ecosystem which enters food chain primarily through Producers. Producers are the
main photosynthetic plants/ organisms which are at the base of food chain. They form the
food source for herbivores also consumers. Subsequently as we go up the trophic level
secondary consumer/Carnivore feeds on the consumer/herbivore. Interactions of the various
trophic levels give rise to a large number ecological relationships like, predation, mutualism,
ammensalism, neutralism etc. Complicated networks of food chains are referred to as the
food webs, comprising of two types namely; a grazing food web and detritus food web. As
we move up the trophic levels energy transfer is reduced whereas the pollutants are
accumulated due to increase in their concentrations.
The mineral nutrients are recycled endlessly within ecosystems, between their biotic and
abiotic components. Biochemical transformation of nutrients occurs within the bodies of
organisms and return back into the environment in the form of inorganic state. Various
internal and external factors are control the ecosystem components namely; climate,
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temperature, light, precipitation, topography, soil, biota etc. The study of an ecosystem
enables an ecologist to bring the information and skills from different and varied field of
sciences in a single field. Three main approaches used by an ecologist in their studies, namely
the descriptive, experimental, and theoretical. The study of ecosystem is highly important
because only a good knowledge and thorough understanding of ecology can preserve,
conserve and restore the delicate ecological balance. Ecological succession, positive-negative
feedback mechanism and human interference go hand in hand to maintain a healthy
ecological environment.
3. Processes of an Ecosystem
There are two main processes which help in the functioning of an ecosystem namely, energy
flows and ecosystem nutrient cycles. These two processes are closely linked, but they are not
quite the same.
3.1. Trophic level
In ecology, the ecosystem structure and dynamics is best described by the term food
chain which refers linear sequence of organisms through which nutrients and energy pass
from primary producers to higher-level consumers. Depending on their role, we can assign
species or groups of species into various trophic (Trophe = nourishment) levels with each
organism in a food chain occupying a specific trophic level.
Energy, water, nitrogen and soil minerals are the essential abiotic components of an
ecosystem which enters food chain primarily through producers. Producers such as
photosynthetic organisms (phytoplankton plants and/or) constitute the bottom of the food
chain in many ecosystems and are called Primary producer. Primary producers are eaten by
primary consumers such as herbivores. In this manner, higher-level consumers feed on the
subsequent lower tropic levels until it reaches the organisms at the top of the food chain
called the apex consumers.
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Fig 1: Pathways for energy transfer (a) Food chain (b) Food Web
(Source: Author and Departmental Artist)
However, food chain represents only a simple and isolated relationship and represents only a
part of the food or energy flow. In an ecosystem, several such food chains intercalate and
forms interconnected networks of feeding relationships that take the form of food webs
(Fig. 1). Hence, it is a holistic and non-linear graphical representation of primary producers,
primary consumers and higher level consumers which describe ecosystem structure and
dynamics and energy in an ecosystem (Fig. 2). The food webs can be divided into two
general types: A Grazing food web and a Detrital food web.
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Fig. 2: This conceptual model shows the flow of energy through a spring ecosystem in Silver Springs, Florida.
Notice that the energy decreases with each increase in trophic level.
Source: Author and Departmental Artist
Pollutants especially non-biodegradable ones in an ecosystem move through the various
trophic levels and cannot be metabolised by the living organisms. Consequently, we detect
higher concentration of such pollutants when we move from the lower trophic to higher
trophic level in an ecosystem. There can be two main processes for movement of such
pollutants:
Bio-accumulation: it refers to how pollutants enter the food chain in which there is an
increase in concentration of pollutants from the environment to the first organism.
Bio-magnification: It refers to the tendency of the pollutants to concentrate as they
move from one trophic level to the next.
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This phenomenon is of great concern as small concentration of chemicals in the environment
if enters the food chain can reach a high enough dosages to cause problem.
Diagrammatically, the steps of trophic levels can be expressed in a form of pyramid called
Ecological pyramid (Fig. 3). It can represent the number of individuals, biomass or energy
at each trophic level. The producer forms the base of the pyramid and the apex consumer
forms the tip. The ecological pyramids are of three categories (Fig. 4): (i) Pyramid of number
(ii) Pyramid of Biomass and (iii) Pyramid of energy.
Fig. 3: The relative energy in trophic levels in a Silver Springs, Florida, and ecosystem is shown. Each trophic
level has less energy available and supports fewer organisms at the next level
Source: Author and Departmental Artist
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Fig. 4: Ecological pyramids depict the (a) biomass, (b) number of organisms, and (c) energy in each trophic
level. (Source: http://cnx.org/contents/GFy_h8cu @9.66:y Wlgpmjv@8/Energy-Flow-through-Ecosystems)
3.2. Energy flow in an Ecosystem
The energy flows from the lower (producers) to higher (consumers) trophic level. It never
flows in reverse direction furthermore there is a loss of some energy in the form of unusable
heat in each trophic level. Hence energy level decreases from the first trophic level upward.
Sun is the main source of energy of our planet. So, the energy that flows through ecosystems
is also primarily obtained from the sun. Thus, light energy of sun or photon enter the
biological system and is transformed into chemical energy in organic molecules by cellular
processes like photosynthesis (a process that also captures carbon from the atmosphere) and
respiration (process that releases carbon back into the atmosphere) and ultimately is
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converted to heat energy (Fig: 5). Without this continued input of solar energy, biological
systems would quickly shut down. Therefore, earth is an open system with respect to energy.
Fig. 5: Concept of open system (Source: Author and Departmental artist)
3.3. Bio-geochemical Cycle
Nutrients are recycled in global nutrient cycles. In these cycles, nutrients alternate between
organisms and the environment. Humans can disrupt nutrient cycles in many ways, with
profound impacts on ecosystems and our own future. Nutrients are found in four
compartments within the terrestrial ecosystem: in the atmosphere, in the pool of available
nutrients in the soil, in organic materials (biota and organic debris), and in soil and rock
mineral.
Biochemical transformation of nutrients occurs within the bodies of organisms and return
back into the environment in the form of inorganic state. Microorganisms such as bacteria
often complete this process of conversion which is termed as Decomposition or
Mineralization (Fig. 4). The mineral nutrients are recycled endlessly within ecosystems,
between their biotic and abiotic components. Hence the Earth is a closed system with respect
to materials or elements or nutrients (with the exception of a foreign space body entering the
system now and then.eg: meteorite (Fig. 6).
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Fig. 6: Nutrient relationships of a terrestrial ecosystem, showing sites of accumulation and major pathways.
Input and output may be composed of geologic, meteorologic, and biologic components, as described in the text.
Source: http://www.esf.edu/cue/documents/bormann-likens_nutrient-cycling_1967_000.pdf
Most nitrogen enters ecosystems through biological nitrogen fixation, is deposited through
precipitation, dust, gases or is applied as fertilizer as shown in the fig. 7 below.
Fig. 7: Nitrogen cycle (Source: Author and Departmental Artist)
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Other important nutrients include phosphorus, sulphur, calcium, potassium, magnesium and
manganese. Phosphorus, calcium, magnesium and manganese enter ecosystems through
weathering. Acid deposition is an important source of sulphur in many ecosystems.
Potassium is primarily cycled between living cells and soil organic matter, so is manganese
and magnesium.
4. Factors of ecosystem
All ecosystems are controlled by certain factors which are referred as internal factors and
external factors. The external factors are listed below:-
a) Climate- It is the most important external factor and determines the biome in which the
ecosystem is embedded.
b) Precipitation levels- The rainfall patterns undermine the availability of water in any
ecosystem.
c) Temperature- It affects the seasonality and the supply of energy (via. photosynthesis) in
the functional unit.
d) Parent material- It is the underlying geological material that gives rise to the type of
soils in the ecosystem and influences the nature of the soils present, along with their
nutrient mineral contents.
e) Topography- It controls the ecosystem processes by affecting things like microclimate,
soil development and the movement of water through a system. It has a major role in the
formation of habitats in an ecosystem. These external factors, also called as state factors,
control the overall structure of an ecosystem and the way things work within it, but are
not themselves influenced by the ecosystem.
Other external factors responsible for the invariable dynamic entity of an ecosystem, being
subject to periodic disturbances are:
Time – It plays a crucial role in the development of soil from bare rock and the recovery
of a community from disturbances.
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Potential Biota – It is the set of organisms potentially present in an area that can also
have a major impact on ecosystems. Non- native species, if introduced can too
substantially alter or shift the functioning of an ecosystem.
Resource inputs are generally controlled by external processes. Internal factors of ecosystems
not only control ecosystem processes, but are also controlled by them via feedback loops. The
availability of resources within the ecosystem is controlled by internal factors like
decomposition, root competition or shading. Apart from these, other internal factors are
disturbance, succession or the types of species present. Human activities are important in
almost all ecosystems and their cumulative effects are large enough to influence external
factors like climate.
5. Relationship of Ecology with Different Subjects
Ecology is one of the main divisions of biology. It is a multidisciplinary science related with
Zoology, Botany, Climatology, Chemistry, Biochemistry, Physics, Physiology, Biophysics,
Geology and Geography, which studies the interactions amongst organisms and their
environment (chemical and physical factors). An ecologist is concerned with the distribution,
behaviour, populations and communities in relation to the environment (ecosystems). The
evolution of adaptation and of species is of mutual interest to the ecologist and to the
geneticist; bio-meteorology is a connecting link between ecology and physiology; and system
analysis inter-relates ecology and mathematics. Ecology is also closely related to other
biological disciplines such as Evolution (study of how living beings evolved and how they
are expected to change in the future keeping in view the environmental changes) and
Epidemiology. Using statistics' help, the epidemiology study the development of epidemics
on the populations and support the Ecology. To fully understand an ecosystem, ecologists
also require some basic understanding of meteorology, oceanography, limnology, geology,
etc. And for understanding the living components, the knowledge of Thermodynamics and
Genomics also comes handy.
Ecologist brings the information and skills from different and varied field of sciences to bear
on the study of the ecosystem. They works on different fields of environment such as in land,
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sea, fresh water and others; as well as in different level such as the community level,
population level, and at the biome level. The ecologist usually uses three approaches in their
studies, namely the descriptive, experimental, and theoretical. Ecology and econometrics
share in similar math in their historical origins. Even Sociology and anthropology have its
active role in the study of ecology.
6. Specialized Branches of Ecology
Ecology is a broad biological science having numerous specialized branches listed below:
Organismal ecology - The study of individuals and species with focus on
physiological and behavioural aspects.
Habitat ecology - The study of different habitats on earth’s environment and their
effects on the organisms living there is called habitat ecology. Habitat ecology is sub-
divided into: marine ecology (oceanography), estuarine ecology, fresh water ecology
(limnology), and terrestrial ecology.
Terrestrial ecology is further classified into the following: forest ecology, cropland
ecology, grassland ecology, desert ecology, etc., according to the kinds of study of its
different habitats.
Population Ecology - It is also known as Demecology. It is the study of growth
mannerism, structure and regulation of populations of species.
Community Ecology - The study of the local distribution of organisms in different
habitats along with the identification and composition of community units, and their
succession.
Ecosystem Ecology - It is often referred as Ecological Dynamics. It is the study of the
processes of soil formation, nutrient cyclic energy flow, and productivity of
ecological levels.
Global ecology - The study of how all organisms interact and survive in their
planetary environment.
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Industrial Ecology - The study of industrial systems with the goal of finding ways to
lessen their environmental impact and help in the sustainability concept. It is the study
of material and energy flow through industrial systems.
Urban ecology - The study of ecosystems that include mankind inhabitation in urban
areas and cities. It is an emerging, interdisciplinary field that aims to understand how
human and ecological processes can coexist in human-dominated systems and thereby
help in city planning.
Landscape ecology - Landscape ecology is the study of the interactions between the
temporal and spatial aspects of a landscape and the organisms within a region of
interest (usually across large geographical areas), and how these interactions affect
ecological processes; especially the unique effects of spatial heterogeneity in a variety
of landscape scales and organizational levels of research and policy.
Cultural ecology - Cultural ecology is the study of human adaptations ( including
biological adaptations) to social and physical environments. It's an interdisciplinary
field of anthropology and ecology emphasising relationships between human cultures
and the environment that enable a population to survive and reproduce within a given
or changing environment.
Human ecology - Human ecology is the study of the relationship between humans and
their natural, social, and built environments. It is an interdisciplinary as well as trans
disciplinary subject amongst several social science, humanistic, and bioscience
disciplines.
Production ecology - In ecology, productivity or production refers to the rate of
generation of biomass in an ecosystem. Production ecology is usually expressed in
units of mass per unit surface (or volume) per unit time, for instance grams per square
metre per day (g m−2
d−1
). The mass unit may relate to dry matter or to the mass of
carbon generated
Applied ecology - Applied ecology is the study of ecological principles to solve real
world problems.
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Chemical ecology - Chemical ecology is the study of chemicals involved in the
interactions of living organisms. It focuses on the production of and response to
signalling molecules (i.e. semiochemicals) and toxins.
Physiological ecology - Physiological ecology is the study of the adaptations of an
organism's physiology to their constantly changing environmental conditions for their
successful reproduction and survival.
Medical ecology - Medical ecology is the study about the public’s health in lieu of
their environmental aspect.
Functional ecology - Functional ecology study about the species that play an important
role in the ecosystem.
Fire ecology - Fire ecology is the study about the role of fire in the environment of life
processes and its effect on ecological communities.
Sociology - Sociology is a behavioural science which does a systematic study about
the human social relationships and institutions, using various methods of empirical
investigation and critical analysis to develop a body of knowledge about social order,
disorder, and change for proper functioning of human society.
Palaeoecology - Palaeoecology is the study of the environmental relationships of
organisms in the geological past using fossil deposits of animals and plants for
investigations regarding ancient life forms and their habitats.
Genocology (Ecological genetics) - Genocology the study of genetics in natural
populations, which integrates ecological and genetics mechanism of speciation.
Pedology - Pedology is the study of soils in their natural environment. It is one of two
main branches of soil science, the other being Edaphology.
Space ecology - It is involved in the study of solutions for sustainable life in deep
space, especially on the problem of how to establish a quasi-closed ecological system
on Mars for use in human habitation.
Ecogeography (geographic ecology) - It is the study of large-scale patterns of the
distribution and diversity of organisms and ecological processes.
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Ethology - Ethology is a branch of zoology concerned with scientific and objective
study of animal (human too) behaviour, usually with a focus on behaviour under
natural conditions, and viewing behaviour as an evolutionarily adaptive trait.
Radiation ecology - Radiation ecology is the study of the effects of radioactive
materials on living systems and on the pathways by which they are dispersed through
various ecosystems, including their dispersal through the abiotic environment.
Systems ecology - Systems ecology is an interdisciplinary field of ecology, that takes a
holistic approach to the study of ecological systems, specifically the performance of
an ecosystem as an integrated whole and how it coheres as a unit. It is essentially a
branch of ecosystem ecology.
Microbial ecology - Microbial Ecology is the study of the microscopic organisms and
their community such as bacteria, fungi, protozoa, etc in order to understand their
contribution and influence upon the larger ecosystems.
*Bio-ecology - Animal ecology and Plant ecology are given equal emphasis in understanding
ecological dynamics and are together referred as Bio-ecology.
7. Ecological Relationships
An ecological relationship is the relationship between an organism or population of
organisms in the habitat of their respective ecosystem, depending upon the way the particular
organism gets adapted to its environmental pressures on evolutionary basis. The web of
relationships is interdependent and complex as all organisms in any and every ecosystem are
connected and every interaction is dependent on the one before it. So, the ecological
relationship an organism has depends on the way the organism adapted to its environmental
pressures on evolutionary basis. The oppositional relationships are predation and competition.
The symbiotic relationships are mutualism, commensalism, amensalism, neutralism,
cooperation and parasitism (Fig. 8). The interaction among organisms within or between
overlapping niches can be characterized into various types of ecological relationships given
below:
i) Mutualism - It is an obligatory symbiotic relationship in which both the organisms are
beneficially affected. E.g.: For example, some anemones share a mutualistic relationship with
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Boxer crabs, Lybia tesselata. The Boxer crab holds the anemone in its claws to use its
stinging tentacles to fend off predators. In turn, the anemone consumes the crab's leftovers.
ii) Commensalism - It is a symbiotic interaction amongst organisms, where one species
benefits and the other is unaffected i.e., where one species provides protection for another
less mobile or more vulnerable species. Eg. relationship between sea anemone and clown
fish.
iii) Ammensalism - The ecological interaction in which an individual harms another without
obtaining benefit. A classic example is the release of chemical toxins by plants that can
inhibit the growth of other plant species. For instance: black walnut (Juglans nigra), which
secretes juglone, a substance that destroys many herbaceous plants within its root zone.
iv) Cooperation - It is an interaction among groups of organisms working or acting together
for common or mutual benefit, as opposed to working in competition for selfish benefit. Eg.:
working of ants.
v) Proto-cooperation is an ecological interaction in which both participants benefit but
which is not obligatory for their survival. Eg: the spur-winged plover, which eats residues
from crocodile teeth by using its beak.
vi) Neutralism - In this symbiosis relationship between two species, both species interact but
do not affect each other in any way. Eg: interaction between a rainbow trout and dandelion in
a mountain valley.
vii) Parasitism - When one species benefits and the other is harmed it is defined as
Parasitism. It too is a form of symbiotic ecological relationship. Eg: ectoparasites and
endoparasites.
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Fig. 8: Patterns of population interactions) (Source: Author and Departmental Artist)
viii) Predation - Predation is a positive-negative ecological relationship which is an essential
natural mechanism of population control, where one organism hunts (predator) and consumes
the other hunted organism (prey).Here, one individual mutilates or kills another to get food.
Solar energy received by the prey is then transferred to the predator. A predator is usually a
carnivore that hunts, kills and eats other animals. For example: snake eating a mouse or a
hawk eating a snake, pitcher plant or venus fly trap are carnivorous plants.
ix) Cannibalism is the most grade form of predation, where in a particular population the
individuals start eating each other due to scarcity of food resources.eg: frogs (Lurdes Isufaj)
x) Competition - In this ecological interaction neither species is benefited as the individuals
explore the same ecological niche or their ecological niches partially coincide. It is further
sub- divided into intraspecies (within similar species) competition, interspecies ( within
dissimilar species) competition and competitive exclusion principle (two species that compete
for the exact same resources cannot stably coexist).
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xi) Symbiosis is a close ecological relationship between the individuals of two (or more)
different species that dwell together. This mechanism helps some organisms adapt to
conditions by helping each other survive.
xii) Mimicry is an ecological relationship, where one species mimics another; typically using
colour or pattern. For example, the harmless banded snake eel may imitate a more dangerous
sea snake.
xiii) Camouflage is another form of mimicry and can be seen in seahorses and scorpionfish.
An inharmonious or negative, ecological interaction is when at least of the participating
organisms is harmed.eg: interspecific competition, parasitism, predation and ammensalism.
And harmonious, or positive, ecological interaction is when none of the participating
organisms is harmed.eg: commensalism, mutualism, cooperation.
8. Importance & Scope of Ecology
The study of the ecosystem and the environment can be traced way back in the time of
Theophrastus in around 372-287 B.C in the ancient Greece. Since 1960’s, the study of
Ecology has grown in leaps and bounds responding to the increasing environmental problems
throughout the world. The scientific study of ecology is important to protect and conserve
nature in general and prevent the extinction of species in particular by step by step analysis.
With the advent of modern civilization; the detrimental effects of population explosion,
pollution, deforestation, and many other problems have altered the delicate balance of nature
for amicable existence of all species. Only a good knowledge and thorough understanding of
ecology can preserve, conserve and restore the delicate ecological balance. Furthermore, it
allows us to forecast predictable picture of how human activities which affect environment
over time.
The scope of ecology is boundless as its study determines the distribution and abundance of
organisms with the ever changing phenomenon of the abiotic and biotic factors, thereby
keeping the role of an ecologist quite challenging. Ecologists seek to explain:
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All life processes and their interactions
Adaptations of flora and fauna and natural selection
The every flow and movement of materials within ecosystems
Study of bio-geochemical cycles
The successional development of living communities
Sustainability of life-supporting functions of dynamically different ecosystems
The abundance and distribution of organisms in habitats and in ecological hierarchy.
Also the biodiversity in the context of our planet’s environment.
Ways to preserve this biodiversity from human activities without hampering either
one.
The ecologist usually uses three approaches in their studies, namely the descriptive,
experimental, and theoretical.
The ecologist usually uses three approaches in their studies, namely the descriptive,
experimental, and theoretical. Descriptive approach involves a detailed field observation.
The experimental approach seeks information on how the specific ecosystem works. The
theoretical approach deals with the theories or principles that govern the nature of the
ecosystem.
Ecology can also be called as human science, in lieu of the many practical applications of
ecology in biology, wetland management, agroecology, agriculture, forestry, agroforestry,
fisheries, city planning , community health, economics, basic and applied science, and human
social interaction. The enormous branching of ecological study has expanded the scope of
this interdisciplinary field by many folds.
Thus, the scope of ecology contains a wide array of interacting levels of organization
spanning micro-level (e.g., cells) to a planetary scale (e.g., biosphere) phenomena.
9. Mechanism of Ecosystem
Ecosystems are complex system with many interacting components which are regularly
exposed to various changes or disturbances in the environment. Many disturbances are
caused by natural processes but recently human activities have been one of the main factors
in disturbing this environment.
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9.1. Succession
Progressive change in biotic communities is a part of their normal development. The orderly
change or replacement of one community in an area by another in specific period of time is
called ecological succession. Depending on the force of change, succession can be of two
types:
Autogenic succession: succession is the result of the organisms themselves.
Allogenic succession: due to external force mainly physical forces such as, storm,
fire, earthquake, human interference etc.
Often succession is the result of both autogenic and allogenic factors even though it may be
triggered by either one of them. In 1916 F.E. Clement described the ‘Theory of Succession’
and involves the following steps:
Nudation: development of bare site.
Migration: arrivals of propagules
Ecesis: establishment and initial growth of vegetation.
Competition: species compete for space, light and nutrition.
Reaction: replacement of one community by another.
Stabilization: development of climax community.
Ecological succession can broadly be divided into two types:
Each succession consists of series of sequential stage known as a sere and each sere is made
up of a sequence of seral communities (seral stages). Seres are classified according to the
environment like halosere develops in salt marshes while hydrosere in aquatic environment.
Primary Succession:
Is the process where succession starts on barren ground where no community had existed
before forming a mature community. The example is the invasion and colonisation of
bare rock on a recently created volcanic island. The first (pioneer) community in
primary succession is mainly lichen which invades the area through various dispersal
methods. The tenacious and water-seeking nature of fungus is suitable in forming the
pioneer community. It secretes weak acids that gradually erode the rock surface
promoting for other communities to succeed.
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Secondary Succession:
It is the process of succession, in which a mature community is formed in area which has
been previously destroyed by either natural calamities or human interventions. It is a
long term repair process and occurs more rapidly than primary succession. The example
is the reclamation of previously burned forest or an area after limestone mining.
Biotic and abiotic components change during succession. The pioneer and intermediate
communities modify the condition so that it favors the growth of new communities which
eventually replace the previous one. The most important result of succession is the increase
in species diversity and ecosystem stability.
9.2. Homeostasis: Maintaining the Balance
The whole universe can be isolated into different systems for the purpose of observation and
study. But in reality these systems have close interaction with each other. The capacity and
state of a system to self-regulate itself to maintain internal consistency is called Homeostasis.
The word homeostasis is derived from two Greek words, homeo, which means ‘same’ and
stasis meaning ‘standing’. Hence ‘staying the same’ is the literal translation of homeostasis.
Ecologists believe that earth is in a state of equilibrium of many self-regulating living
systems. Feedback mechanism keeps the system in fairly constant state. Nonetheless if we
push it too far in one direction, the self-regulating mechanism will break down resulting in
radical changes.
i. Feedback Loops: Biological systems in an ecosystem have a variety of regulatory circuits
called feedback loop. Feedback loop can be described as sequence of events or
interactions in which a change in some original rate alters the rate and direction of
further change. It is divided into two types i.e. negative feedback and positive feedback.
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Fig. 9: Positive And Negative feedback Mechanism. (Source: Author and Departmental Artist)
In negative feedback the stimulus results in response that inhibits or reverses any change
from the original state bringing the system back to the set point. A classic illustration of
negative feedback is ‘population regulation’ which restrains the population within the limit
of support of ecosystem (Fig. 9). On the other hand, positive feedback leads to further change
in the same direction taking it away from the set point and causes damage to the system.
Positive feedback causes exponential growth (increase rapidly)in population when there is a
surplus of resources .In short homeostasis controls an organism’s internal physical and
chemical condition within limits essential for the organism’s survival.
9.3. Human Impacts:
We are all a part of the ecosystem and human beings too are dependent on it for their
survival. The biotic (plants, animals, microorganisms, man, etc.) and abiotic (temperature,
atmosphere, earth, sunlight, precipitation, etc.) components are closely linked together
through nutrient cycles and energy flows. An ecosystem is said to be in equilibrium when all
these components are in steady state. The capacity of an ecosystem to continue at equilibrium
in spite of being disturbed is called Resistance. The speed with which an ecosystem restores
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after being disturbed is called Resilience. The damage can be such a degree that an ecosystem
lose its resilience entirely leading to complete annihilation and irreparable lose to the
ecosystem. Human beings have often cause disturbances intentionally or unintentionally,
disrupting the delicate balance of ecosystem.
Fig. 10: Human impact analysis model
(Source: Recreated from ‘Environmental Science’, 8th edition by Daniel D. Chiras)
The model shows how human activities have impacted both biotic and abiotic components of
an ecosystem resulting in its own destruction (Fig. 10).The basic knowledge and
understanding of environment is outpaced by technology. Restoring the natural system will
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not only save species but also ensure adequate supply of food for all. Realising its
importance, scientist Ed Garbisch and the others gave rise to a new field of ecology called
restoration ecology which is one branch of science called conservation biology.
10. Summary
There are two main processes which help in the functioning of an ecosystem namely,
energy flows and ecosystem nutrient cycles which take place among various
trophic/nourishment levels. Producers such as photosynthetic organisms (phytoplankton
plants and/or) constitute the bottom of the food chain in many ecosystems and are called
Primary producer. Primary producers are eaten by primary consumers such as herbivores.
Herbivores are fed upon by the carnivores. In this manner, higher-level consumers feed on
the subsequent lower tropic levels until it reaches the organisms at the top of the food
chain called the apex consumers. Complicated networks of food chains are the food webs.
Pollutants especially non-biodegradable ones in an ecosystem move through the various
trophic levels by two main processes namely; Bioaccumulation: it refers to how pollutants
enter the food chain in which there is an increase in concentration of pollutants from the
environment to the first organism and Biomagnification: It refers to the tendency of the
pollutants to concentrate as they move from one trophic level to the next.
Digrammatic representation of the trophic levels is referred to as food pyramids which are
of three types; (i) Pyramid of number (ii) Pyramid of Biomass and (iii) Pyramid of energy.
Flow of energy in the ecosystem is always unidirectional from producers to apex
consumers. Sun is the main source of energy of our planet. Without this continued input of
solar energy, biological systems would quickly shut down. Therefore, earth is an open
system with respect to energy.
Bio-geochemical Cycle helps in recycling the mineral nutrients endlessly within
ecosystems through Decomposition and Mineralisation among its biotic and abiotic
components. Hence the Earth is a closed system with respect to materials or elements or
nutrients.
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Ecology is a multidisciplinary science related with Zoology, Botany, Climatology,
Chemistry, Biochemistry, Physics, Physiology, Biophysics, Geology and Geography,
which studies the interactions amongst organisms and their environment (chemical and
physical factors). An ecologist is concerned with the distribution, behaviour, populations
and communities in relation to the environment (ecosystems). The ecologist usually uses
three approaches in their studies, namely the descriptive, experimental, and theoretical.
Ecology and econometrics share in similar math in their historical origins.
The webs of relationships are interdependent and complex as all organisms in any and
every ecosystem are connected and every interaction is dependent on the one before it.
The oppositional relationships are predation and competition. The symbiotic relationships
are mutualism, commensalism, amensalism, neutralism , cooperation and parasitism
With the advent of modern civilization; the detrimental effects of population explosion,
pollution, deforestation, and many other problems have altered the delicate balance of
nature for amicable existence of all species. Only a good knowledge and thorough
understanding of ecology can preserve, conserve and restore the delicate ecological
balance.
The orderly replacement of one community in an area by another in specific period of time
is called ecological succession. It takes place on its own (Autogenic succession) or due to
external factors (Allogenic succession). The most important result of succession is the
increase in species diversity and ecosystem stability.
We are all a part of the ecosystem and human beings too are dependent on it for their
survival. The basic knowledge and understanding of environment is outpaced by
technology. Restoring the natural system will not only save species but also ensure
adequate supply of food for all. Realizing its importance, scientist Ed Garbisch and the
others gave rise to a new field of ecology called restoration ecology which is one branch of
science called conservation biology.