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

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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.