Good Morning Everyone!
1Env. 101
Introductory Environmental Science
The broad objective of the course is to provide basic theoretical knowledge on
Environmental Science.
The specific objectives of the course are as follows:
• To understand the concept of environmental science
• To acquaint with the society, culture and environment
• To familiarize with population, community and ecosystem dynamics
• To provide knowledge on environmental chemistry
• To provide knowledge on basic geology and atmospheric environment
2Course Content
• Unit 1: Introduction to Environmental Science (PP)
• Unit 2: Population and Community Analysis (PP)
• Unit 3: Ecosystem Dynamics (PW)
• Unit 4: Environmental Chemistry (PW)
• Unit 5: Atmospheric Environment (PW)
• Unit 6: Environmental Earth Science (PW + PP)
(*Lecture hour: 25 hours each unit; FM-100, PM-35)
3Population and Community Analysis
• Ecology: Concept, history, scope, types, ecological hierarchy;
Biosphere: Evolution, realms; Ecosystem: components and factors,
life supporting systems, concept of food chain, food web, trophic
structure, ecological pyramids; Concept of limiting factors; Liebig
Blackman law; Shelford‟s law of tolerance.
• Population characteristics: Size and density, pattern of dispersion,
age structure, natality, mortality, biotic potential; Population
dynamics and theory of population growth; Rate of natural increase;
Species interaction: Positive and negative; Regulation of population
size.
• Community characteristics: Classification and composition;
Characters used in community structure: Analytical and synthetics;
Concept of ecological dominance; Habitat and niche; Ecological
indicators; Keystone species; Ecotone and edge effect; Heterogeneity
and equitability; Adaptation: Origin and significance; Ecads;
Ecotypes; Ecocline; Speciation and extinction.
45
But first, What is Environment ? What are the Components of environment?
Environment is the total set of circumstances surrounding life.
The subject Environmental Science deals with the conditions and factors controlling
the habitat.• Ecology from Greek “oikos” meaning
“household” and “logos”” meaning
“study” .i.e., study of life at home
• The branch of science dealing with
interactions and relationships
between organisms and the
environment; the study of goods and
services provided by natural
ecosystems, including the integration
of these non market services with in
the economic market.
6Ecology…
• Ecology = Oikos + logos = household + study = life at home =
the study of the environmental house includes all the organisms in it
and all the functional process in that make the house habitable
• Ecology is the study of “life at home” with the emphasis on “the
totality or pattern of relations between organisms and their
environment”
• Because of its focus on the higher levels of the organization of life on
earth and on the interrelations between organisms and their
environment, ecology draws heavily on many other branches of
science, especially geology and geography, meteorology, pedology,
chemistry, and physics. Thus, ecology is said to be a holistic science.
7Environmental Interactions
• Ecology deals with organisms, populations, communities, ecosystems and the
biosphere.
• A lot of interactions between the life and the surrounding conditions and
among the organic world are expected to happen at all time. Several types of
interactions may happen between
o an organism & its place of living,
o an organism & its neighbor
o an organism & its own community,
o an organism & other communities,
o a group of organisms & an organism and
o a community to a community.
8History of Ecology
• The History of Ecology goes along with the History of Science.
• Ecology was first described as a separate discipline in 1886 by the German
Biologist Ernst Haeckel.
• It is a multidisciplinary science aimed to deal with many environmental
problems. In the History of Science, ecological thinking has been around for
several decades. Since it is related to life systems, the development was
contemporary to other biological disciplines.
• Literature sources indicate that, the first ecologists may have been
Aristotle or perhaps his student, Theophrastus, both of whom had interest in
many species of animals. Theophrastus described the interrelationships
between animals and between animals and their environment as early as the
4th century BC.
9History of Ecology…
• Modern ecology became a much more rigorous science in the late 19th century.
Evolutionary concepts relating to adaptation and natural selection became the
lead areas of study. In its early stages, the field was dominated by scientists
trained as botanists and zoologists.
1. The botanical geography and Alexander von Humboldt- "Idea for a Plant
Geography" (1805).
• The exposition on botanical geography by the German explorer , Alexander
von Humboldt, is another significant contribution to the growth of ecological
understanding.
10History of Ecology…
• The Other contributions came from many world expeditions to develop maritime
commerce with other countries, and to discover new natural resources, as well as
to catalog them. At the beginning of the 18th century, about twenty thousand
plant species were known, versus forty thousand at the beginning of the 19th
century, and almost 400,000 today.
• Due to this, Alexander von Humboldt is often considered to be the Father of
Ecology. He was the first to take on the study of the relationship between organisms
and their environment.. He exposed the existing relationships between observed
plant species and climate, and described vegetation zones using latitude and
altitude, a discipline now known as geobotany.
2. In 1825, the French naturalist, Adolphe Dureau de la Malle used the term societé
about an assemblage of plant individuals of different species.
11History of Ecology…
3. The notion of biocoenosis: Wallace and Möbius
Alfred Russel Wallace, a contemporary and competitor to Darwin, was first to
propose a "geography" of animal species.
• Several authors recognized at the time that species were not independent of each
other, and grouped them into plant species, animal species, and later into
communities of living beings or biocoenosis (the group of living creatures), . This
term was coined in 1877 by Karl Möbius.
4. Warming and the foundation of ecology as a discipline
Eugen Warming devised a new discipline that took abiotic factors, that is drought,
fire, salt,cold etc., as seriously as biotic factors in the assembly of biotic
communities. Warming gave the first university course in ecological plant geography
12History of Ecology…
5. Darwinism and the science of ecology
Towards 1850, there was a breakthrough in the field.
• The publishing of the work of Charles Darwin on The Origin of Species has made a
significant input in to the concepts of Ecology.
• From that time onwards, Ecology has passed out from a repetitive, mechanical
model to a biological, organic, and hence evolutionary model.
6. Early 20th century ~ Expansion of ecological thought
• By the 19th century, ecology blossomed due to new discoveries in chemistry by
Lavoisier and de Saussure, notably the nitrogen cycle. After observing the fact that
life developed only within strict limits of each compartment that makes up the
atmosphere, hydrosphere, and lithosphere, the Austrian geologist Eduard Suess
proposed the term biosphere in 1875..
13History of Ecology…
• Suess proposed the name biosphere for the conditions promoting life, such as
those found on Earth, which includes flora, fauna, minerals, matter cycles, etc
7. In the 1920s Vladimir I. Vernadsky, a Russian geologist, detailed the idea of the
biosphere in his work "The biosphere" (1926). It was he who described the
fundamental principles of the biogeochemical cycles. He thus redefined the
biosphere as the sum of all ecosystems
8. The Ecosystem: Arthur Tansley
• Over the 19th century, botanical geography and zoogeography combined to form
the basis of biogeography. This science, which deals with habitats of species,
seeks to explain the reasons for the presence of certain species in a given
location.
14History of Ecology…
• It was in 1935 that Arthur Tansley, the British ecologist, coined the term
ecosystem, the interactive system established between the biocoenosis
(the group of living creatures), and their biotope, the environment in
which they live.
• Ecology thus became the science of ecosystems.
• Since then, with the industrial revolution, more and more pressing
concerns have grown about the impact of human activity on the
environment.
• During the early 20th century, there was an expansion of ecological
thought.
• The term ecologist has been in use since the end of the 19th century.
• Tansley's concept of the ecosystem was adopted by the energetic and
influential biology educator Eugene Odum.
15History of Ecology…
9. Eugene Odum
• Tansley's concept of the ecosystem was adopted by the energetic and influential
biology educator Eugene Odum. Along with his brother, Howard Odum, Eugene P.
Odum wrote a textbook which (starting in 1953) educated more than one
generation of biologists and ecologists all over the world.
• Eugene Odum, published his popular ecology textbook in 1953. He became the
champion of the ecosystem concept. This ecosystem science dominated the
International Biological Program of the 1960s and 1970s, bringing both money
and prestige to ecology.
10. Ecological Succession - Henry Chandler Cowles
• At the turn of the 20th century, Henry Chandler Cowles was one of the founders
of the emerging study of "dynamic ecology", through his study of ecological
succession.
16History of Ecology…
11. Ecology's influence in the social sciences and humanities
• Human ecology has been a topic of interest for researchers, after 1920. Humans
greatly modify the environment through the development of the habitat (in
particular urban planning and growth), by intensive exploitation activities such
as logging and fishing, and as side effects of agriculture, mining, and industry.
• Besides ecology and biology, this discipline involved many other natural and
social sciences, such as anthropology and ethnology, economics, demography,
architecture and urban planning, medicine and psychology, and allied areas.
• The development of human ecology led to the increasing role of ecological
science in the design and management of cities.
17History of Ecology…
12. Ecology and global policy:
• Ecology became a central part of the World's politics as early as 1971,
UNESCO launched a research program called Man and Biosphere, with the
objective of increasing knowledge about the mutual relationship between
humans and nature.
• A few years later, it defined the concept of Biosphere Reserve.
• In 1972, the United Nations held the first international Conference on the
Human Environment in Stockholm, prepared by Rene Dubos and other
experts. This conference was the origin of the phrase "Think Globally, Act
Locally".
18Significance of Ecology
19
• Ecology is the scientific study of interaction between organisms and
their environment. It includes both biotic and abiotic factors.
• The level of organization of ecology is in such a way i.e., species,
population, community, ecosystem, biome, biosphere.
• Biomes are the environments that have characteristics of not
changing too much over time. There are few biomes in the world like:
Aquatic (rivers, streams, lakes, open sea zone, deep sea zone, neritic
zone) and Terrestrial (tundra, taiga, grass land, tropical rainforest, and
desert).
• The three basic approaches that conduct the ecological methods are
observing, experimenting and modelling. Significance of Ecology
• The energy that comes to the earth comes from sun that means sun
is the source of energy for the ecosystem.
• The feeding relationship in ecosystem is food chain and food web.
• To maintain the ecosystem many biochemical cycles are going on like
water, carbon, nitrogen, and phosphorus and limited nutrients.
• There are various studies related to ecology like bioecology i.e., the
study of ecology of both plants and animals whereas the study of
communities is synecology and the study of species is known as
autecology.
20Scope of Ecology
• Ecology is the study of organisms `at home' which is called as the `environment’.
• The Science of Ecology involves:
o the study of the relation of organisms or a group of organisms to their
environment and
o the study of the totality of man and his environment.
• Because of its focus on the higher levels of the organization of life on earth and
on the interrelations between organisms and their environment, ecology draws
heavily on many other branches of science, especially geology and geography,
meteorology, pedology, chemistry, and physics. Thus, ecology is said to be a
holistic science.
21Scope of Ecology…
22
As Ecology deals with…
• The spatial distribution of an abundance of organisms
• The temporal changes in the occurrence, abundance and activities of organisms
• The interrelations between organisms, communities and populations
• The structural adaptation and functional adjustments of organisms to the
change in environment,
• The behavior of organisms under natural environment, the productivity of
organisms
• Energy and other natural resources to mankind and
• The development of interactive models for analytical or predictive purposes.
…the scope of ecology is vast and varied.Scope of Ecology…
• The behavior of an organism in a given environment can be explained by
making use of data obtained from number of sources such as
morphology, taxonomy, genetics, soil science, physiology etc.
• Many practical applications of ecology have been used/ applied in
forestry, limnology, fishery, pest control, public health, toxicology etc.
• Moreover, ecology is directly connected with some ecological problems
like soil conservations, soil erosion, food control, deforestation, town
planning, pollution control, rapid human growth, urbanization etc.
• Workers in agricultural research whose problems are largely ecological
are dependent on ecology.
23Scope of Ecology…
• A knowledge of ecological principals help in discovering new sources of
food (Algal food, fungi etc), new non-polluting sources of energy such as
solar energy and new methods of pest controls such as biological
controls.
• By applying certain ecological techniques, ecologists are quite successful
in determining the cause of desertness of certain Australian deserts and
they investigated that these deserts lack certain trace elements desert.
Now they have cured their cured their ecological diseases and have
converted them into new agricultural lands
• The international problem of environmental pollution also needs
ecological assistance like huge plantation on highways, human settlement
areas and industrialized areas.
24Scope of Ecology…
• Ecology plays an important role in crop rotation, weed management
and conservation of natural resources.
• The destruction of forests result loss of valuable wild animals and
loss of valuable land due to soil erosion and all these can be checked
by applying the ecological techniques i.e, forestation , soil
management (to control soil erosion and land slides).
25Types of Ecology
In general, ecology is classified into two major divisions:
• Animal ecology : This branch deals with the animal population, its
changes, their behavior, and their relationships with the environment.
• Plant ecology : This branch deals with the relationships of plants to other
plants and their environment.
It is known that all animals mostly depend on plants for both food and
shelter. Hence, animal ecology deals with both animal and plant
communities. Due to these based on the organism and habitats, the
science of ecology is divided into
(a) synecology and ( b) autecology,
26Types of Ecology…
SYNECOLOGY:
• This branch deals with the study of
groups of organism which are
associated together as a unit in
form of a community.
• Also known as community ecology.
• This is a habitat based study.
• Example: if a study is concerned
with forest in which an oak or a
wood thrush lives, the approach
would be synecological
27
AUTECOLOGY
• This branch deals individual organism or
an individual species.
• This is also called as species ecology
• It is also known as population ecology.
• Life histories and behavior as means of
adaptation to the environment are
usually emphasized.
• Example: if a study is made of relation of
a white oak tree or a wood thrush to a
environment, the work would be
autecological in nature.Types of Ecology…
Synecology:
• This branch deals with the study of groups of organisms or the community.
• This is a habitat based study. A habitat is a place where an organism or species
population or a community thrives. There are two major habitats as :
1. terrestrial habitats and
2. aquatic habitats.
Examples:
• Aquatic habitats (water related) - Marine, Fresh water, Estuarine life.
The branches related are: Marine ecology, Estuarine ecology, Limnology, etc
• Terrestrial habitats (land based) - life in Forests, Grasslands, Deserts.
The branches related are: Forest ecology, Grassland ecology, etc.
28Types of Ecology…
• Synecology is divisible into population ecology and community ecology.
• A population emerges when individuals of the same species aggregate themselves to
function as a single unit. Much interactions occur when such populations inhabit an area.
• A community in-turn represents a group of populations. It denotes the co-habitation of
different species in a geographical region.
The Synecology includes the study of
• population characteristics,
• position of an individual in a population and its relationship (intraspecific),
• regulation of population,
• impact of population on the environment,
• community characteristics and their interrelationships (interspecific),
• successional changes and
• the impact of communities over an environment.
29Types of Ecology…
30
Autecology
• This branch deals with the study of species or the relationship of an organism to
one or more environmental conditions.
• This is also called as species ecology.
• It deals with the nutrition, growth, reproduction, development and life history of
individual species in an environment.
• Describing the type of habitat where in the organisms of a species live in.
•
Physical factors of the environment (air, temperature, light, water; oxygen,
chemicals) and their interaction with that particular environment and the
organism. Types of Ecology…
Autecology…
• The influence of various biotic factors (predation, parasitism, competition,
exploitation, etc) which have a bearing on the life and environment.
• The interaction of organisms with other organisms of different species. Life
and seasonal changes of the environment.
• Pattern of reproduction and dispersal of organisms.
31Some Other Branches (types) of Ecology
1. Population Ecology : Study of a population, its growth, competition,
means of dispersal etc.
2. Community Ecology : Study of distribution of animals in various
environments.
3. Ecosystem Ecology : Relation and interaction of plant and animal
communities with their total environment. It deals with the
formation of soil, chemical cycles, food and feeding relationship,
exchange of energy and productivity.
4. Evolution Ecology : Concerned with the manner in which all ecological
structure and functions have evolved.
5. Geographical Ecology : Deals with the distribution of organisms over
the world and the factors and forces brought out this distribution.
32Some Other Branches of Ecology…
6. Paleoecology : Deals with the organisms and their environment existed
in the distant geological past.
7. Applied Ecology : Deals with wild life management, forest
conservation, biological control, animal husbandry and pollution
control.
8. Oceanography : Study of marine habitat and organisms.
9. Limnology : Study of life in freshwater bodies.
10.Terrestrial Ecology : This is a major field including
a. Forest Ecology, b. Cropland Ecology and c. Grassland Ecology.
33Why it is Important to Study Ecology?
Existence in the world is made up of living and non living things. The two groups have to coexist
in order to share the resources that are available within the environmental ecosystem. To
understand about this mutual co relationship we need to study and understand ecology.
Survival of all organisms is actualized due to ecological balance. Various species survive
because favorable ecosystems were created. One core goal of ecology is to understand the
distribution and abundance of living things in the physical environment. Attainment of this goal
requires the integration of scientific disciplines inside and outside of biology, such as
biochemistry, physiology, evolution, biodiversity, molecular biology, geology, and climatology.
Some ecological research also applies many aspects of biology, geology, chemistry and physics,
and it frequently uses mathematical models. Ecologists study these relationships among
organisms and habitats of many different sizes, ranging from the study of microscopic bacteria
growing in a fish tank, to the complex interactions between the thousands of plant, animal, and
other communities found in a desert. Ecologists also study many kinds of environments. For
example, ecologists may study microbes living in the soil under your feet or animals and plants
in a rain forest or the ocean.
34Ecological Hierarchy
Hierarchy is :
(from Greek: ἱεραρχία, hierarkhia,
'rule of a high priest', from
hierarkhes, 'president of sacred
rites') is an arrangement of items
(objects, names, values,
categories, etc.) that are
represented as being "above",
"below", or "at the same level as"
one another.
Or simply,
“An arrangement into a graded
series”
35Ecological Hierarchy…
The arrangement of biological
organisms in relation to one another,
levels of ecological organization from
smallest to largest: individual,
population, species, community,
ecosystem, biosphere.
363738Ecological Hierarchy/Levels of Organizational Hierarchy
• At the simplest level of the hierarchy are individual organisms. At the individual
level, interactions with other organisms are not considered. Moving up the
hierarchy, ecologists have found more complex ways to describe the
relationships between organisms. These culminate in the biosphere, which
describes the totality of all living things on planet Earth.
• The first level of the ecological hierarchy is the individual organism. This level
of the hierarchy examines how one organism interacts with its environment.
Aspects of evolution are used extensively in studying this level. For example, the
individual-organism level allows a scientist to study why a giraffe has a very long
neck. He can infer that evolution has given the giraffe the long neck so it can
reach a food source high on a tree. Organismal ecology is concerned with the
biological, morphological and physiological development of individual organisms
in response to their natural environment.
39Ecological Hierarchy…
• The second level involves populations. A population contains a group of
individuals -- belonging to one species and living in a specific geographic
area -- which interact with one another. Population ecology studies the
interactions among the individual members of a population.
• The third level of the ecological hierarchy describes communities of life.
The community level focuses on the relationship between different
species in a community. Predator and prey relationships play a large role
in community-level analyses. Parasitism and competition between
species are another important part of this ecological level.
40Ecological Hierarchy…
• The next level up is an ecosystem. A community is part of an ecosystem, but
does not comprise an entire ecosystem. Nonliving components in the
environment are included in an ecosystem. The living organisms in an ecosystem
interact with one another and with the nonliving factors in the environment.
Examples of an ecosystem include a single lake, a confined forest, a prairie or a
mountain summit.
• At the widest level of analysis, the biosphere represents the totality of all things
on Earth, including their interactions. The biosphere includes all ecosystems on
Earth and how they interact together. By default, the biosphere includes climate,
geology, the oceans and human pollution. This level of analysis can seem
abstract, but it frequently has practical applications. Global climate change, for
example, examines how the destruction of one ecosystem -- like the Amazon
rainforest -- can lead to a loss of global climate regulation, and affect life on a
part of Earth distant from the Amazon.
4142Biosphere: Evolution, realms
• The biosphere is that part of the Earth where living things thrive and
live. It is the portion of the planet that can sustain life.
43Biosphere…
• The biosphere:
(from Greek βίος bíos "life" and σφαῖρα sphaira "sphere"),
• Also known as the ecosphere is the worldwide sum of all ecosystems.
• Population of all different species occupying particular place make up
community i.e biological in particular complex interrelation of plants,
animal and micro-organism. And ecosystem is the community of
different species interacting with one another and with their non
living environment of matter and energy.
• All the earth ecosystems together make up biosphere. Major land
ecosystem such as forests, grassland and desert are called terrestrial
ecosystem or biome; major ecosystem found in hydrosphere are
called aquatic ecosystem.
44Biosphere…
• Large and small ecosystem, normally do not have distinct boundaries.
Each ecosystem blends into adjacent ones through transition zones that
contain many of the plants and animals and other characteristics found in
adjacent ecosystem (Edge Effects).
• Biosphere consists of the part of Earth’s atmosphere, hydrosphere, and
lithosphere (earth soil) in which all living thing exist and interact.
• Individuals at the base of pyramidal combination makes species, next lies
population then communities and exists under ecosystem.
• The aggregation of the entire ecosystem on the earth is sometimes
referred to as ecosphere or biosphere of the whole planet.
Shape may be pyramidal; structure may be tetrahedral in nature.
45Evolution of Biosphere…
• Questions about the origins and nature of Earth have long preoccupied human
thought and the scientific endeavor.
• Deciphering the planet’s history and processes could improve the ability to predict
catastrophes like earthquakes and volcanoes, to manage Earth’s resources, and to
anticipate changes in climate and geologic processes.
• Earth is an active place. Earth scientists have long been concerned with deciphering
the history—and predicting the future—of this active planet.
• Over the past four decades, Earth scientists have made great strides in
understanding Earth’s workings.
• Scientists have ever-improving tools to understand how Earth’s internal processes
shape the planet’s surface, how life can be sustained over billions of years, and
how geological, biological, atmospheric, and oceanic processes interact to produce
climate—and climatic change
46Evolution of Biosphere…
Long term evolution of ecosystem is shaped by;
1. Allogenic (outside) - forces such as geological and climatic changes
• As planets age and cool off, their internal and surface processes gradually
change. Manifestations of changes within Earth’s interior—such as the
development of mountains and volcanoes—have a huge influence on the
nature of Earth’s surface and atmosphere.
• plate tectonic theory explains many of Earth’s surface features.
• The geological record has revealed the history of the planet’s climate to be a
peculiar combination of both variability and stability. Global climate conditions
have been favorable for life and relatively stable for the past 10,000 years and
suitable for life for over 3 billion years.
• But geological evidence also shows that momentous changes in climate can
occur in periods as short as decades or centuries
.
47Evolution of Biosphere…
2. Autogenic (inside)
process resulting from activities of living components of ecosystem
• In The Origin of Species, Charles Darwin (1859) hypothesized that new species
arise by the modification of existing ones—that the raw material of life is life. But
somehow and somewhere, the tree of life had to take root from nonliving
precursors.
• Clues to shed light on these mysteries stem largely from investigations of Earth’s
ancient rocks and minerals—the only remaining evidence of the time when Earth’s
life first emerged.
• Scientists know that the composition of Earth’s atmosphere, especially its high
concentration of oxygen, is a consequence of the presence of life. At the
microscopic scale, life is an invisible but powerful chemical force: organisms
catalyze reactions that would not happen in their absence, and they accelerate or
slow down other reactions. These reactions, compounded over immense stretches
of time by a large biomass, can generate changes of global consequence
48Evolution of Biosphere…
• Scientists have ever-improving tools to understand how Earth’s internal processes shape the
planet’s surface, how life can be sustained over billions of years, and how geological,
biological, atmospheric, and oceanic processes interact to produce climate—and climatic
change
• Earth’s geologic evolution, as well as catastrophic events like meteorite impacts, has clearly
affected the evolution of life
• The first ecosystem, there billion years ago were populated by tiny anaerobic heterotrophs
that lived in an organic matter synthesized by abiotic process.
• Following the origin and population explosion of algal population which converted reducing
atmosphere into organic and inorganic oxygenic organisms have evolved through the long
geologic ages into increasing complex and diverse systems that:
1. Have achieved control of atmosphere
2. Are populated by longer and more highly organized multicellular species
• From this, evolutionary changes are said to be continued
4950Ecosystem
• The term `eco' refers to a part of the world and `system' refers to the co
ordinating units.
• The living organisms of a habitat and their surrounding environment
function together as a single unit. This ecological unit is called as an
`ecosystem’.
• An Ecosystem is a naturally occurring assemblage of life and the
environment.
The life is referred to the biotic community including the plants, animals
and other living organisms. This is denoted as biocoenosis. The
environment is the biotope encompassing the physical region of life.
• The term ecosystem first appeared in a publication by the British
ecologist Arthur Tansley, during 1935. An ecosystem may be of very
different size. It may be a whole forest, as well as a small pond
51Ecosystem…
• The term ecosystem first appeared in a publication by the British ecologist
Arthur Tansley, during 1935.
• An ecosystem may be of very different size. It may be a whole forest, as well
as a small pond.
• Different ecosystems are often separated by geographical barriers, like
deserts, mountains or oceans, or are isolated otherwise, like lakes or rivers.
• As these borders are never rigid, ecosystems tend to blend into each other.
As a result, the whole earth can be seen as a single ecosystem, or a lake can
be divided into several ecosystems, depending on the used scale.
• The ecosystem is an open system. It receives energy from an outside source
(the sun), as input, fixes and utilities the energy and ultimately dissipates the
heat into space as output.
52Ecosystem…
• An ecosystem has a physical environment, or factors, biological components and
interactions between them. And is characterized by a set of abiotic and biotic
factors, and functions.
• The organisms in an ecosystem are usually well balanced with each other and
with their environment. Within an ecosystem, all living things have a habitat or
the physical area in which they live.
• The habitat of an organism may include many different areas. For Example, a
mouse can be seen in a field, garden or even in a house. Animals that migrate
will have different habitats during different seasons. Some birds that live in a
place during summer spend the winter in some other place.
• Introduction of new environmental factors or new species can have disastrous
results, eventually leading to the collapse of an ecosystem and the death of
many of its native species.
53Macro and Microecosystems
• The dimension and spread of an ecosystem may vary. Depending upon
their existance and dimension, ecosystems are classified as
Macroecosystems and Microecosystems.
• Dimensionally larger systems such as a forest or a lake are called as
macroecosystems.
• Life scientists and environmental biologists who are interested to
evaluate the functional mechanisms of an ecosystem, may create an
experimental setup in the field or in the laboratory. Such setup are
considered to be microecosystems.
• Depending upon their matrix of research, it may be a terrestrial
microecosystem, or an aquatic microecosystem.
5455565758Components of Ecosystem
Biotic Components
• Includes all living organisms and
their products.
• This group includes all animals,
plants, bacteria, fungi and their
waste products like fallen leaves or
branches or excreta.
• Based on their activity, biotic
components are classified into four
categories as a) producers b)
consumers c) transformers and d)
decomposers.
59
Abiotic Components
• The non-living components of the
ecosystem.
• Some of the major non-living
factors of an ecosystem are:
Sunlight, Water, Temperature,
Oxygen, Soil and Air.
• They are of three categories
1. Climatic and physical factors
2. Inorganic substances
3. Organic compoundsAbiotic Components
1. Climatic and physical factors -air, water, soil and sunlight; rainfall,
temperature, humidity, soil texture and geomorphic conditions.
2. Inorganic substances- There are various nutrient elements and compounds,
such as carbon, nitrogen, sulfur, phosphorous, carbon-di-oxide, water, etc.
These are involve din the cycling of materials in the ecosystems.
3. Organic compounds- These are proteins, carbohydrates, lipids, humic
substances, etc. They largely form the living body and link the abiotic
compounds with the biotic factors.
The inorganic substances like nitrates, carbonates and phosphates occur either
freely or in the form of compounds dissolved in water and soil. Some of them are
recycled by micro-organisms on the dead bodies of plants and animals.
60Abiotic Components…
The abiotic factors determine the type of organisms that can successfully live in a particular
area. Some of the major non-living factors of an ecosystem are:
• Sunlight is necessary for photosynthesis; it influences organisms and their environment;
it has a profound effect on the growth and development of life.
• Water is the elixir of life; all living things require water for their survival, but some can
live with lesser amounts
• Temperature - all living things have a range of temperatures in which they can survive;
beyond those limits it will be difficult for them to live.
• Oxygen - many living things require oxygen; it is necessary for cellular respiration, a
process used to obtain energy from food; others are actually killed by the presence of
oxygen (certain bacteria)
• Soil - the type of soil, pH, amount of water it holds, available nutrients, etc determine
what type of organism can successfully live in or on the soil; for example, cacti live in
sand, cattails in soil saturated with water.
61Biotic Components
• Biotic components - include all living organisms and their products. Based
on their activity, biotic components are classified into four categories as
a) producers b) consumers c) transformers and d) decomposers.
• Producers or autotrophs make their own food. Producers, such as plants,
make food through a process called photosynthesis. This food is used by
the plant for its own energy or may be eaten by consumers.
• Consumers or heterotrophs need to eat food that autotrophs have
produced. There are different types of consumers. Herbivores eat plants.
Carnivores eat animals. Omnivores eat both plants and animals.
• Decomposers or saprotrophs are heterotrophs that break down the dead
tissue and waste products. They play a very important role in the
ecosystem because they recycle the nutrients. Bacteria and fungi are the
main decomposers.
6263Biotic Components…
Producers are called energy transducers.
• They convert solar energy into chemical energy, with the help of organic
and inorganic substances.
• The producers are called as autotrophic
(auto = self; troph = nourishing) organisms.
• They are capable of synthesizing food from non-living inorganic
compounds.
• They are largely represented by green plants on land (trees, grasses,
crops) and phytoplanktons on water.
64Biotic Components…
Consumers are the organisms, whose food requirement are met by feeding
on other organisms.
• They consume the food materials prepared by the producers (autotrophs).
Hence, consumers are called as heterotrophic organisms.
• Animals belong to this category.
• Depending upon their food habits, consumers are classified into primary,
secondary and tertiary consumers.
65Biotic Components…
• The Primary Consumers are solely feed on plants.
Herbivores are plant eaters - grasshopper, rabit, goat, sheep are primary
consumers.
• The Secondary Consumers feed on some primary consumers.
Carnivores-are flesh eaters. Eg. - Hawks ,Tiger and Lion.
Omnivores (Biophages ) - eat both vegetables and flesh
( cockroaches, fox, humans). Secondary consumers are those which
predate on primary consumers. Eg. several species of insects and fishes.
• Tertiary Consumers are the predators of predators.
They are mostly larger animals
66Biotic Components…
• Transformers are certain types of bacteria .
They attack on materials excreted by other living organisms (even dead
plants and animals ).
They transform the above into either organic or inorganic substances.
These substances are suitable for the nutrition of green plants.
• Transformers help in recycling the nutrients which came as waste
already.
67Biotic Components…
Decomposers :
• They are also called as microconsumers.
• They depend on dead organic matter for their food .
• They are chiefly micro organisms like bacteria and fungi.
• They break the complex organic matter found in plant and animal bodies,
and release simple substances .
• These substances will be used by autotrophs once again. Some
invertebrate animals like protozoa and earthworms use these dead
organic matter for their food. They are called as secondary decomposers.
6869Functions Of An Ecosystem
A system is an organization that functions in a particular method.
The functions of an ecosystem include
1) Flow of energy through the medium of living organisms and their
activities
2) Food chains
3) Biodiversity and biomass
4) Circulation and transformation of elements and nutrients
5) Development and evolution and
6) Control.
70Functions Of An Ecosystem…
• Energy is also consumed by the autotrophs at cellular level for the
reactions related to:
(1). growth
(2). development
(3). maintenance and
(4). reproduction.
• The specific functional processes of an ecosystem include:
(a) photosynthesis, (b) decomposition, (c) predator - prey relations
(herbivory, carnivory, parasitism and (d) symbiois.
• Directly or indirectly the ecosystem's functional concept is useful in the
management of renewable resources such as forests, watersheds,
fisheries, wildlife and agricultural crops and stock.
71The Internal Process
• Photosynthesis (Ps) and respiration (Rp) are the two major processes
involved in the production and transformation of energy.
• The rate of photosynthesis increases by an increase of temperature.
• Many other factors influence the process of photosynthesis. However,
it is involved
-(1) in the intake of radiant energy and C02 and
(2) release of oxygen.
• Respiration is involved in the uptake of oxygen and release of CO2 and
energy.
• In the absence of light, Ps is arrested but Rp continues. In the presence
of light Ps and Rp work together. The total synthesis of organic matter
resulting from the exposure of light can give the Gross Primary
Production.
72The Internal Process…
• The amount of organic matter stored after expenditure (in terms of
respiration) is called as the Net Primary Production. Hence, Primary
Production is the amount of organic carbon and Primary Productivity
is the rate of production.
• The net primary productivity is also called as apparent photosynthesis
or net assimilation. The grain, straw, stalks, roots, etc harvested from a
paddy field ( after a growing. season) comprise the net primary
production.
• It is well known that animals are not capable of synthesizing their food.
So, they have to rely upon other plants and animals for their food.
There are two biological processes involved in animal life.
They are (1). Metabolism and (2). Growth.
73The Internal Process…
• They (animals) require energy which is obtained from the ingestion of
food. The food, which is in excess of the metabolic needs, is used to
produce animal tissue. This process is known as secondary production.
• It is estimated by measuring the increase in weight or size of the animals
over a period of time.
• So, secondary productivity is the amount of new organic matter stored
by the consumers or the heterotrophs. It is a function of the amount of
primary production in an ecosystem. The total quantity of organic matter
present at any given time in an ecosystem, is called as the biomass.
• Life in Ecosystems need a continuous supply of energy for survival.
• Almost all the energy available to us on earth comes from the sun. The
radiation gives heat and light. The uneven heat develops the wind to
blow. The radiation evaporates water into the air and the evaporated
molecules arc returned back as rain.
74The Internal Process…
• Plants are fundamental to all life on earth.
Because, plants have the ability to trap solar energy falling over them
and use this energy to build living tissues. This process is called
photosynthesis.
• During this process, the inorganic energy - poor molecules (C02 and
water) are converted into organic -rich food molecules (sugars). In this
way, plants do not need to depend on other organisms.
Hence, they are treated as self nourishers or autotrophs.
• Animals can not use the sun in this way. So, they are dependent,
directly (or) indirectly, on plants for food.
Hence, animals are treated as other nourishers or heterotrophs.
75The Internal Process…
• The energy used during photosynthesis by plants is not lost. Sugar is a
product of photosynthesis. This sugar contains stored chemical energy and
can be burnt to produce heat.
• Now, in this process, C02 and water are released as by-products. Sugar
combines with oxygen inside the living cells and produce some output,
under a slow rate.
This process is called as respiration.
• It releases the 'energy in the form of complex molecules for use in
maintaining the cell functions.
• Plants are engaged in both photosynthesis and respiration.
• Animals can not make their own food. They must eat other organisms to
obtain the energy rich molecules for survival. Therefore, they are the major
consumers. Animals are technically called as heterotrophs ( other -
nourishing ).
76Why to Preserve the ecosystem?
An ecosystem (example- forest) is a living world for organisms and plants.
Due to some events, a change in the setup may occur which will ultimately
affect the ecosystem. For example, cutting the trees in a forest is
considered to be a habitat destruction: This activity,
a) destroys the homes of some animals,
b) increases the amount of light that reaches the forest floor,
c) reduces the amount of food for organisms that depend on those trees,
d) reduces the amount of carbon dioxide taken from the air and oxygen
released into it.
As a result of this habitat destruction, some organisms may become
threatened, endangered and eventually extinct.
Hence, it is necessary to preserve the ecosystems.
777879Ecosystem: concept of food chain
The transfer of food energy
from the producers, through
series of organism (herbivore to
carnivore to decomposers) with
repeat eating and being eaten
is called food chain.
In nature, they are generally
distributed into two groups:
• Grazing Food Chain
• Detritus Food Chain
80Food Chain…
• Grazing Food Chain: starts from the living green plants to grazing
herbivores (that feed on living plants materials with their predator) and
on carnivores. Ecosystem with such type of food chain are directly
dependent on the influx of solar radiation. Examples:
*Phytoplankton → Zooplanktons → Fish (sequence)
*Grass → rabbit → fox (sequence)
• Detritus Food Chain: goes from dead organic matter into
microorganisms and then to organism feeding on detritus and their
predators. Such system is thus less dependent on direct solar energy,
but depends chiefly on the influx of organic matter produced in another
system.
Examples: a fallen leaf in the pond (affected by saprophytes fungi,
bacteria, protozoa etc and colonized mainly by phytoplankton and
benthic algae) are eaten and re-eaten by the key group of small
animals. These animals includes crobes, insect larvae, nematodes,
bivale, molluscans etc. The animals are detritus consumers
8182Ecosystem: concept of Food Web
• Food chain in natural conditions never operate but
are interconnected with each other forming some
sort of interlocking patterns, which is referred to as
food web.
• Under natural conditions the linear arrangement of
food chains hardly occurs and these remains indeed
interconnected with each other through different
types of different trophic levels.
• A balanced system is essential for the survival of all
living organisms of the system. For instance had
primary consumers not being in nature, the
producers could have perished due to over –
crowding and competition
• Similarly, the survival of primary consumers and so
on. Thus each species of an ecosystem is indeed
kept under some sorts of the natural check so that
system may remain balanced.
83Shorter the food chain, greater the energy availability
848586Trophic Structure …
• The interaction of the food chain phenomena (energy loss at each
transfer) and the size metabolism relationship results in communities
having a definite trophic structure, which is often characteristic of a
particular type of ecosystem (lake, forest, coral reef, pasture, etc), is
trophic structure, is referred as trophic structure.
• Trophic structure may be measured and described either in terms of
the standing crop per unit area or in terms of fixed per unit area per
time at successive trophic levels.
• Trophic structure and also trophic function may be shown graphically
by means of ecological pyramids in which the first producer level
forms the base and successive levels the tiers which make up the apex.
• Because of such universality, trophic levels enable us to compare the
role of vastly different species in vastly different systems.
87Ecosystem: Trophic Structure…
• The basic abstraction of the food chain or
food web is the trophic level.
• After each energy exchange between
organisms, the energy is said to have passed
to a higher trophic level.
• Ecological food chains are typically short,
consisting of not more than four or five
trophic levels. This is usually explained by a
reduction in the energy which is available to
successive links in the food chain
• we believe that the number of trophic levels
is constrained by population dynamics and
not by ecological energetics
8889
A trophic level is each of the sequential, hierarchical levels in a food chain which is comprised
of organisms that share the same function in the food chain and the same nutritional
relationship to the primary sources of energy:
o Primary producer (green plants) trophic level
o Primary consumer (herbivores) trophic level
o Secondary consumer (predators) trophic level
o Tertiary consumer (apex predator) trophic levelEcosystem: Ecological Pyramids
• An ecological pyramid is a graphical representation showing the relationship between
different organisms in an ecosystem. It shows the flow of energy at different trophic levels in
an ecosystem.
• These pyramids are in the shape of actual pyramids with the base being the broadest, which
is covered by the lowest trophic level, i.e., producers. The next level is occupied by the next
trophic level, i.e., the primary consumers and so on.
• They show the feeding of different organisms in different ecosystems.
• It shows the efficiency of energy transfer.
• The condition of the ecosystem can be monitored, and any further damage can be
prevented.
• Trophic level pyramids [or Ecological Pyramids] are of three types
o Pyramid of number,
o Pyramid of biomass, and
o Pyramid of energy
90Ecological Pyramids of Number, Biomass and Energy
91Pyramid of Number
• A pyramid of numbers shows the
relative number of individual
organism at each trophic level.
• As we move to higher trophic
levels, we see larger animals. And
yet, moving to higher trophic
levels, these larger animals need
to live on smaller energy
production from the next trophic
level down. As a result, there will
usually be fewer animals at higher
trophic levels.
92Pyramid of Number…
• Actually the pyramids of number do not give actual picture of food
chain as they aren’t very functional.
• They do not indicate the relative effect of the geometry, food chain,
and size factors of the organisms.
• They generally vary with different communities with different types of
food chain in the same environment.
• It becomes sometimes very difficult represent the whole community
on the same numerical scale (as in forest ecosystem).
93Pyramid of Biomass • (number of animals) Total biomass = × (weight of each
animal, at each trophic level
• The number of animals tends to decrease as
trophic level increases, while the weight of
each animal tends to increase.
• in aquatic systems, very small organisms at
low trophic levels have very rapid rates of
biomass turnover and can be grazed to
quite low levels, one frequently (but not
always), “inverted pyramids” of biomass,
with more biomass at higher trophic levels.
• Terrestrial systems typically (though by no
means always) display pyramids of biomass,
with less biomass at higher trophic levels.
94Pyramid of Biomass…
• Pyramid of Biomass are comparatively more fundamental, as they
instead of geometric factor, show qualitative relationships of the
standing crops.
• In grassland and forests, there is generally a decrease in biomass of
organism at successive levels from the producers to carnivores. The
pyramids are upright.
• However, in pond, the producers are small organisms, their biomass is
least and this value gradually shows an increase towards the apex of
the pyramid, thus made the pyramids inverted.
95Pyramid of Energy
• Of the three types of ecological pyramids,
the pyramid of energy give the best
picture of overall nature of the
ecosystem.
• Here, number and weight of organisms at
any level does not depend on the amount
of fixed energy any one time in the level
just below but rather on the rate at which
food is being produced.
• The pyramid of energy is a picture of the
rates of passage of food mass through the
food chain.
• In shape, it is always a gradual decrease in
the energy content at successive tropics
levels from the producer to various
consumers
96Pyramid of Energy…
• The species structure includes not only the number and kinds of
species but also diversity of species i.e., the relation between species
number and individuals or biomass and the dispersion / spatial
arrangement of individual of each species present in the community.
9798Limiting Factors
• A limiting factor is anything that constrains a population's size and slows or stops it from
growing. Some examples of limiting factors are:
– Biotic : food, mates, and competition with other organisms for resources.
– Abiotic: space, temperature, altitude, and amount of sunlight available in an
environment.
• Limiting factors are usually expressed as a lack of a particular resource.
– For example, if there are not enough prey animals in a forest to feed a large population
of predators, then food becomes a limiting factor.
– Likewise, if there is not enough space in a pond for a large number of fish, then space
becomes a limiting factor.
• There can be many different limiting factors at work in a single habitat, and the same
limiting factors can affect the populations of both plant and animal species.
• Ultimately, limiting factors determine a habitat's carrying capacity, which is the maximum
size of the population it can support.
99Limiting Factors…
• A rabbit can raise up to seven litters a year.
So why are we not overrun with rabbits?
In nature, limiting factors act on populations to keep
them in check.
• All living animals within their residing ecosystem have
a range of tolerance for every environmental factors
like temperature , light , humidity , water etc.
• Any environmental factor that by its presence, absence, amount (increase or
decrease ) influence the metabolic activities and overall growth of organisms and
populations also.
• If an environmental factor exceeds the maximum tolerable level or it goes below
the minimum tolerance in an given area, it becomes a limiting factor preventing
the distribution of the particular organism or population in that particular
ecosystem.
• In another word, any factor that tends to slow down potential growth in an
ecosystem is a limiting factor
100101Limiting Factors (Liebig-Blackman law)…
Concept of Limiting Factors: The Liebig Law of the Minimum
• The success of an organism, a group of organisms, or a whole biotic community
depends on a complex of conditions. Any condition that approaches or exceeds
the limits of tolerance is said to be a limiting condition or a limiting factor.
• Under stable conditions, the essential constituent available in amounts most
closely approaching the need tends to be the limiting one, a concept termed
the Liebig law of the minimum. The concept is less applicable under transient
state conditions, when the amounts, and hence the effects, of any constituents
are rapidly changing.
• The idea that an organism is no stronger than the weakest link in its ecological
chain of requirements was first clearly expressed by Baron Justus von Liebig in
1840, Liebig was a pioneer in studying the effect of various factors on the
growth of plants, especially domestic crops.
102(Liebig-Blackman law)…
• He found (as do agriculturists today) that the yield of crops was often limited not by
nutrients needed in large quantities, such as carbon dioxide and water, because these
were often abundant in the environment, but by some raw material (such as zinc)
needed in minute quantities but very scarce in the soil. His statement that the
"growth of a plant is dependent on the amount of foodstuff which is presented to it
in minimum quantity" has come to be known as Liebig's law.
• The scientific application of “law of minimum” are extended to ecosystem models or
population. The organism or plant growth depends on many factors (organic or
inorganic /abiotic or biotic factors). At any given time, these factors are available in
different levels and one among all different factors are present in minimum levels,
thus limiting than others factors.
• This law is now incorporated with a law of limiting factors originated by a plant
physiologist) F.F. Blackman (1905).
• Blackman while studying the factors affecting the rate of photosynthesis discovered
that rate of photosynthesis is governed by the levels of the factors that is operating at
a limiting intensity
103(Liebig-Blackman law)…
• Later work on limiting factor added two subsidiary principles to this concept.
These are,
– A constraint that the Liebig’s law is strictly applicable only under steady-state
conditions i.e., when inflows balance outflows of energy and materials. For
example, CO2 was the major limited factor in a lake/pond and the productivity
was in equilibrium with the rate of supply of CO2 coming from the decay of
organic matters. It is assumed that the light , nitrogen ,phosphorous etc. were
available in excess in this steady state equilibrium. If more CO2 is added by any
means in water bodies the rate of production would change and be dependent
upon others factors as well .While the rate is changing, there is no steady state
and no minimum constituents. The rate of production would change rapidly as
various constituents were used up until some constituents perhaps CO2 again,
became limiting and the water body system would once be operating at the rate
controlled by the law of minimum.
104(Liebig-Blackman law)…
– The second important principle is factor interaction. Higher concentration of
some substances other than the minimum one may modify the rate of utilization
of the latter. Sometimes organism are able to substitute at least partly , a
chemically closely related substances for one that is deficient in environment,
mollusks are able to substitute this for calcium to partial extent in their shells.
Some plants require less zinc when growing in the shade than when growing in full
sunlight ;therefore a given amount of zinc in the soil would be less limiting to
plants in shade than under the same conditions in full sunlight.
• The law of minimum has been restated by Taylor (1934) in broad ecological terms.
• The functioning of an organism is controlled or limited by that essential
environmental factor or combination of factors present in the least favorable amount.
• The factors may not be continuously effective but only at some critical period during
the year or perhaps only during some critical year in a climatic cycle.
105106Limiting Factors - Limits of Tolerance Concept
• Not only may too little of something be a limiting factor, as proposed by Liebig (1840)
but also too much of such fac tors as heat, light, and water acts as limiting factors.
• Thus, organisms have an ecological minimum and maximum; the range in between
represents the limits of tolerance.
• The concept of the limiting effect of maximum as well as minimum constituents was
incorporated into the Shelford law of tolerance (Shelford 1913).
• Since then, much work has been done in "stress ecology," so that the limits of
tolerance within which various plants and animals can exist are well known. Especially
useful are what can be termed stress tests, carried out in the laboratory or in the field,
in which organisms are subjected to an experimental range of conditions. Such a
physiological approach has helped ecologists to understand the distribution of
organisms in nature; however, it is only part of the story.
• All physical requirements may be well within the limits of tolerance for an organism,
but the organism may still fail because of biological interrelations, such as competition
or predation
107Shelford law of tolerance …
Some subsidiary principles to the law of tolerance may be stated as follows:
• Organisms may have a wide range of tolerance for one factor and a narrow range
for another.
• Organisms with wide ranges of tolerance for limiting factors are likely to be most
widely distributed.
• When conditions are not optimal for a species with respect to one ecological
factor, the limits of tolerance may be reduced for other ecological factors.
– For example, when soil nitrogen is limiting, the resistance of grass to drought
is reduced (more water is required to prevent wilting at low nitrogen levels
than at high levels)
108Shelford law of tolerance …
• Frequently, organisms in nature are not actually living at the optimum range (as
determined experimentally) of a particular physical factor. In such cases, some
other factor or factors are found to have greater importance.
For example, cord grass (Spartina alterniflora),
which dominates East Coast salt marshes, actually
grows better in freshwater than in salt water,
but in nature it is found only in salt water,
apparently because it can extrude the salt from
its leaves better than other rooted marsh plants
(that is, because this mechanism enables cord
grass to out compete its competitors).
109Shelford law of tolerance …
• Reproduction is usually a critical period when environmental factors
are most likely to be limiting. The limits of tolerance for reproductive
individuals, seeds, eggs, embryos, seedlings, and larvae are usually
narrower than for non-reproducing adult plants or animals. Examples:
-> An adult cypress tree will grow continually sub merged in water or on
dry upland, but it cannot reproduce unless there is moist, unflooded
ground for seedling development.
-> Adult blue crabs and many other marine animals can tolerate brackish
water or freshwater that has a high chloride content and, thus, are often
found for some distance up rivers. The larvae, however, cannot live in
such waters; therefore, the species cannot reproduce in the riverine
environment and never becomes established permanently.
-> The geographical range of game birds is often determined by the
impact of climate on eggs or young rather than on adults.
-> One could cite hundreds of other examples
110Shelford law of tolerance …
For the relative degree of tolerance, a series of terms have come into general use in ecology
that use the prefixes steno-, meaning "narrow," and eury-, meaning "wide”. Thus,
• Stenothermal-eurythermal ( refers to narrow and wide tolerance, respectively, of
temperature)
• Stenohydric –euryhydric (refers to narrow and wide tolerance, respectively, of water)
• Stenohaline -euryhaline (refers to narrow and wide tolerance, respectively, of salinity)
• Stenophagic - euryphagic (refers to narrow and wide tolerance, respectively, of food)
• Stenoecious-euryecious (refers to narrow and wide tolerance, respectively, of habitat
selection)
(These terms apply not only to the organism level but equally well
to the community and ecosystem levels. For example, coral reefs
are very stenothermal, in that they prosper only within a very
narrow range of temperature. A prolonged 2° C temperature drop
is stressful, causing "bleaching" or loss of the symbiotic algae that
make it possible for corals to prosper in very low-nutrient waters.)
111The concept of limiting factors is valuable because it gives the ecologist
an "entering wedge into the study of complex ecosystems. Environmental relations of
organisms are complex, but fortunately, all possible factors are not equally important
in a given situation for a particular organism. Studying a particular situation, the
ecologist can usually discover the probable weak links and focus attention, initially at
least, on those environmental conditions most likely to be critical or limiting. If an
organism has a wide limit of tolerance for a relatively constant factor present in
moderate quantity in the environment, that factor is not likely to be limiting.
Conversely, if an organism is known to have definite limits of tolerance for a factor
that is also variable in the environment, then that factor merits careful study, because
it might be limiting. For example, oxygen is so abundant, constant, and readily
available in above ground terrestrial environments that it is rarely limiting to land
organisms, except in parasites or organisms living in soil or at high altitudes. On the
other hand, oxygen is relatively scarce and often extremely variable in water and,
thus, is often an important limiting factor to aquatic organisms, especially animals.
112Population characteristics:
113Population
• A collective group of organisms of the same species (or other groups within
which individuals may exchange genetic information) occupying particular
space, has various characteristics which, although expressed as statistical
functions, are the unique possession of group and are not characteristics of
the individual in the group.
• Some of the properties are density, natality (birth rate), mortality (death
rate), age distribution, biotic potential, dispersion, growth form.
• Populations also possess genetic characteristics directly related to their
ecology, namely, adaptiveness, reproductive (Darwinism) fitness and
persistence (probability of leaving descendants over long period of time).
114Population
The population is a collective group of organism of the species occupying a
particular space has the following characteristics.
Population size and density,
Population dispersion
Natality (birth rate),
Mortality (death rate),
Age distribution / Age structure,
Biotic potential,
Life table,
Growth rate.
115Size and density
• Two important measures of a population are population size, the number
of individuals, and population density, the number of individuals per unit
area or volume.
• Population density is the population size in relation to some unit of space.
• Generally assayed and expressed as the number of individuals, or the
population biomass:
– 200 trees per acre
– 5 diatoms per cubic meter
– 200 pounds of fish per acre of water surface
• The number of individual of population biomass per unit area (or volume)
of environment is called population density.
• Larger organisms as trees may be expressed as 500 trees per hectare, where
as smaller ones like phytoplankton’s as 2million cells per cubic meter of
water.
116Size and density…
Population Density are of two types: Crude and Ecological Density.
• Crude Density is a density of number (or biomass) per unit total space.
e.g. the number of Rhinoceros living in the Kaziranga National Park; 1000
fish in a pond
• Ecological Density is the density (number or biomass) per unit of habitat
space i.e. available area or volume that can actually be colonized by a
population.
E.g. 1000 fish in the volume of water in the pond
The density calculated considering the total area or volume would be the
raw (or Crude) density, whereas the density that considers only the area
where an individual species e.g. a plant species actually grow would be the
ecological density
117Pattern Of Dispersion
• Species dispersion patterns—or distribution patterns—refer to how the
individuals in a population are distributed in space at a given time.
• The individual organisms that make up a population can be more or less
equally spaced, dispersed randomly with no predictable pattern, or
clustered in groups. These are known as uniform (or regular), random, and
clumped dispersion patterns, respectively.
118Pattern Of Dispersion…
• Dispersion is the spatial pattern of individual in a population relative to one
another.
• Population dispersion is the movement of individuals or their disseminates or
propagules (seeds, spores, larvae etc)
• It is the means by which new or depopulated area are colonized and equilibrium
is established
• An important component in gene flow and the process of speciation.
119Pattern Of Dispersion…
1. Uniform Dispersion or Regular Dispersion
• In uniform dispersion, individuals of a population
are spaced more or less evenly.
• One example of uniform dispersion comes from
plants that secrete toxins to inhibit growth of
nearby individuals—a phenomenon called
allelopathy.
• We can also find uniform dispersion in animal
species where individuals stake out and defend
territories.
• Uniform distribution may occur where competition
between individuals is severe or where there is
positive antagonism which promotes spacing.
120Pattern Of Dispersion…
2. Random Dispersion:
• In random dispersion, individuals are distributed
randomly, without a predictable pattern.
• An example of random dispersion comes from
dandelions and other plants that have wind
dispersed seeds. The seeds spread widely and
sprout where they happen to fall, as long as the
environment is favorable—has enough soil,
water, nutrients, and light.
• Such distribution is relatively rare in nature,
occurring where the environment is very uniform
and there is no tendency to aggregate.
121Pattern Of Dispersion…
3. Clumped Dispersion.
• In a clumped dispersion, individuals are
clustered in groups.
• Individuals are distributed in groups or patches.
• Also known as aggregated distribution.
• A clumped dispersion may be seen in plants
that drop their seeds straight to the ground—
such as oak trees—or animals that live in
groups—schools of fish or herds of elephants.
• Clumped dispersions also happen in habitats
that are patchy, with only some patches
suitable to live in.
122Age Structure
• In most populations, individuals are of different ages. The portion of individuals
in each group is called age structure of the population.
• Age group is important as it influence both natality (birth rate) and mortality
(death rate) of the population.
• The ratio of various age groups in a population determines the current
reproductive status of the population.
• From ecological point of view, there are three major ecological ages (age groups
in any population). These are:
1. Pre-reproductive
2. Reproductive
3. Post reproductive
123Age Structure…
• The relative duration of these ages group in proportion to the life span varies
greatly with different organism.
• In man, three age relatively equal in length.
• Many plants and animals have a very long pre-reproductive period. Some
animals particularly have long pre-reproductive periods, a very short
reproductive period and no reproductive period.
124Age Structure…
Model representing geometrically the proportions of different ages in the
population of any organism is called age pyramid. These are of 3 types:
1. A pyramid with broad base indicating a high percentage of young individuals.
In rapid grieving young population birth rate is high and population growth may
be in yeast, housefly, paramecium etc.
2. A bell shaped polygon indicating moderate proportion of young to old. As the
growth becomes slow and stable i.e. the pre-reproductive and reproductive age
groups becomes more or less equal in size. Post reproduction group remaining
as the smallest, there results a bell shaped structure.
3. An urn shaped figure indicating a low percentage age of young individuals. If
the birth rate is reduced, the pre-reproductive groups dwindles (haraunu) in
proportion to the other two groups and it results an urn shaped figure.
125Natality
• Natality is the inherent ability of a population to increase.
• Natality rate is equivalent to the birth rate in terminology of human population
study (demography).
• It is simply a broader term covering the production of new individuals ore born,
hatched, germinated, arise by division etc.
• It is theoretical maximum production of new individuals under ideal conditions
(i.e. no ecological limiting factors, reproduction being limited only by
physiological factors).
• Natality refers to population increase under an actual or specific environmental
condition. It is not a constant for population but may vary with size and
composition of population and the physical environmental conditions.
126Natality…
• Natality generally expressed as a rate determined by dividing the number of new
individuals produced by time.
Or as the number of new individuals per unit of time per unit of population
• Natality rate usually increases during the period of maturity and then falls again
as the organism gets older.
• Natality patterns differ in tropical and temperate populations.
• Breeding time and clutch size are two important criteria.
• In tropical area with dry periods, breeding is at least as seasonal as in temperate
areas,
• Clutch size in tropical environment is smaller than in temperate zone. Many
birds, some plants, some insects and some small mammals exhibit this trend.
127Mortality
• Mortality refers to death of individuals in the population.
• It is more or less antithesis of natality with some parallel sub-concepts.
• Mortality rate is equivalent to “death rate” in human demography. It is also
called specific or potential mortality.
• It represents the theoretical minimum loss under ideal or non-limiting
conditions.
• It is a constant for a population. Thus even under the best conditions individuals
would die of “old age” determined their physiological longevity (long life)
• Often it is the survival rate that is greater than the death rate.
128Life Table
• Information on natality and mortality in different ages and sexes can be
combined in the form of life tables.
• To estimate the growth or decline of a population.
• As survivorships curves, life tables are standardized to follow the progress
of a cohort (a group of people/population with a shared characteristic).
• In each table there are columns for age of individuals, number surviving to
each age, the number dying in each age group, the preparation dying from
the previous age category, fertility rate and the number of young born by
each age group. These information provides net reproductive rate of the
population i.e. offspring’s left by each individual.
• Similarly from life table, mortality in logarithmic form is also obtained.
These are then used to calculate the rate of population growth.
• Life table shows the probability that an individual of that age will or might
die in certain time frame.
129Life Table…
From this starting point, a number of inferences can be derived, like,
• The probability of surviving any particular year of age.
• The remaining life expectancy for people / species at different ages.
There are two types of life tables:
– Period or static life tables show the current probability of death (for people of
different ages, in the current year)
– Cohort life tables show the probability of death of people from a given cohort
(especially birth year) over the course of their lifetime.
– Multi-state life tables (also known as increment-decrements life tables) are based on
transition rates in and out of the different states and to death
– Prevalence-based life tables (also known as the Sullivan method) are based on
external information on the proportion in each state. Life tables can also be extended
to show life expectancies in different labor force states or marital status states.
130Biotic Potential
• Biotic potential is defined as the maximum number of individuals a species
can produce.
• As with other organisms, this is and always has been a survival strategy against
food deprivation, predation, and parasitism.
• Under natural conditions, animals that overproduce have their population
reduced by inadequate food supplies, parasitism, and predation. Since food
supplies have been adequate (for the most part in industrialized countries) for
a thriving human population, contemporary humans do not have predators to
keep their populations in check (other than themselves), and parasites have
been eliminated or severely cut back in many parts of the developed world, the
human population is increasing almost at an exponential rate and growing to a
dangerous level
131Biotic Potential…
• Biotic potential represents the maximum reproductive capacity of a population under
optimum environmental conditions.
• Thus, a species fulfilling its biotic potential would exhibit maximal exponential
population growth, thereby augmenting the possibilities of transmission of the species.
• A wide range of factors affects the biotic potential of each species, and among the
external factors, temperature clearly influences the life cycles of most parasitic species.
132Biotic Potential…
• Significant differences in biotic potential exist between species – many large mammals,
like humans or elephants, will only produce one offspring per year and some small
organisms, like insects, will produce thousands of offspring per year.
• Organisms do not tend to fulfill their biotic potential because most species do not live
under ideal environmental conditions. At some point, population growth will be
hindered by predators, disease, changes in environment, a lack of available food, or a
combination of these factors.
• The maximum number of a given species that can be sustained by resources in a given
environment is the species’ carrying capacity. When a population is nearing its carrying
capacity, the amount of resources used is equal to the amount of resources being
produced. It is at this time individuals start competing; some may die and others may
not reproduce because of the lack of resources. Conditions are no longer ideal and as a
result, these individuals cannot reach their full biotic potential.
133Population dynamics and theory of population growth
• The study of population dynamics can be defined as the analysis of the
factors that affect the increase, stability and decrease of populations over
time.
• Population dynamics is one of the fundamental areas of ecology, forming
both the basis for the study of more complex communities and of many
applied questions.
• Understanding population dynamics is the key to understanding the
relative importance of competition for resources and predation in
structuring ecological communities, which is a central question in ecology.
134Population dynamics and theory of population growth…
Population ecology is the study of how populations — of plants, animals,
and other organisms — change over time and space and interact with their
environment. Populations are groups of organisms of the same species
living in the same area at the same time. They are described by
characteristics that include:
– population size: the number of individuals in the population
– population density: how many individuals are in a particular area
– population growth: how the size of the population is changing over
time.
135Population Growth and Growth Curves…
• Growth is one of the dynamic features of a population size increases in
characteristics manner.
• When the number of individual of a species plotted on the y-axis and the
time on the x-axis, a curve is obtained that indicates the trend in growth
of population size in the given area. So obtained curve of population
through the time is known as population curve.
• There are two types of growth curve
– S-shaped growth curve,
or logistic curve, or Sigmoid Curve
– J – shaped growth curve,
or geometric growth curve
or exponential curve
136Population Growth and Growth Curves…
S – shaped growth curve
• In logistic growth curve, the initial growth is slow and is
known as lag and then positive acceleration phase. This
is followed by rapid growth continuous up to certain
point after which there is steady decrease in the
growth take negatively. The level beyond which is no
major increase occurs is known as saturation level or
carrying capacity.
• Thus, there is almost equal number of organisms dying
and taking birth, so that equilibrium is established
between natality and environment resistance and
maintaining maximum number of population density
for long period. Sigmoid curve is obtained in this way.
• The sigmoid curve is common in population ecology.
137S – Shaped Growth Curve…
S – shaped growth form can be represented as
dN/dt = r.N (K-N)/K
Where,
dN/dt = rate of population growth per unit time
N= starting population
K = maximum population size (constant) or carrying capacity of the
environment
r= rate of increase (intrinsic rate of increase)
138Population Growth and Growth Curves…
J – shaped growth curve
• Such curve involve geometric ratio of
increase up to a certain point after which
there is an abrupt growth in population.
• But after sometime change in
environmental factors makes the sudden
decline, also due to less food supply in the
habitat limited which alternately results in
decrease in population size.
• The growth curve obtained in this
progression more or less J – shaped.
• This type of growth is common in nature
but found when favourable condition
meets individual species needs.
139J – Shaped Growth Curves…
J – shaped growth form can be represented as
dN/ dt = r. N
where,
dN= rate of population growth
dt = time interval
r = rate of geometric increase
N = population size
Integral equation is
This is widely used for calculating growth
N
T
= N.e^(r.t)
where,
N
T
= Number of individuals at time “t”
r = intrinsic rate
t = time taken
140Rate of Natural Increase
The rate of natural increase (RNI) is a measure of how quickly a population is
growing or declining. However, the RNI does not factor in population change
resulting from immigration or emigration – it is determined solely by the
difference between birth and death rates in a region.
Logistic growth & Exponential growth
k-selected species & r-selected species
141Rate of Natural Increase…
The r – k scale of reproductive strategy: Balancing Egg Output versus parental care.
Oysters are an example of a very r – strategy. They produce 500 million
fertilized eggs a year and provide no parental care. The great apes are an
example of a very k – strategy. They produce one infant every five or six years
and provide extensive parental care.
142Rate of Natural Increase…
R – selected species (Opportunists)
• Each species has a characteristics mode of reproduction.
• At one extreme, one species reproduce early and put most of their energy into
reproduction. They have:
– Many (usually small) off springs each time they reproduce
– Reach reproductive age rapidly
– Have short generation time
– Give offspring little or no time for parental care or protection to help them
survive
– Short lived (usually) with a life span of less than a year
• Species with such a capacity for high intrinsic rate of increase (r) are called
r-selected species
143R – selected species …
• Examples: algae, bacteria, rodents, annual plants
(such as dandelion) and most of the insects
• These species tend to be opportunistic and they
reproduce and produce rapidly under favorable
condition, even in a disturb environment.
• But competition amongst opportunists makes more or
less unfavorable condition. Therefore mostly r
selected species go through irregular unstable boom
cycles of the growth in their population growth.
• To survive opportunist must continually invade new
areas to compensate for being displaced by more
competitive species.
144Rate of Natural Increase…
K – selected species (Competitive) These species:
– Put fairly little energy in reproduction.
– Tend to produce late in life.
– Have few offs prings with long generation time.
– Are cared for or protected by one or both
parents. Until they reach reproductive age.
The result creates little individual competition for
resources and reproduces a few young to begin the
cycle again. Such species are called k-selected
species, because they tend to do well in competitive
condition when their population size is near the
carrying capacity of the environment.
145K – selected species…
These follow logistic population growth. Examples are;
– Most large mammals (such as elephant, whale, human etc.)
– Birds, prey animals etc.
– Large plant such as oak trees, cactus, redwood tree and most tropical
forest trees.
k- Selected species with long generation time posses low reproductive rate
such as elephant, rhinoceros and sharks.
• So in practice, k-selected species forms the best ecosystem in agriculture.
R-selected species experienced habitat, forest, grassland raising crop.
146Rate of Natural Increase…
• So concept of carrying capacity is based on
environmental resistance which consist of
all the factors affecting to limit the growth
of population, in a given space and time
determined by the individual biotic
potential. Hence, together biotic potential
and environmental resistance determine
the carrying capacity. The number of
individuals of a species can be sustained
indefinitely in a given space (area or
volume).
147Species Interaction…
Species is the basic unit i.e. taxon of
classification. It is the group of
individuals which are
morphologically alike, have
descended from a common
ancestor and can freely interbreed.
Examples Triticum aestivum,
Triticum vulgare are the species of
genus Triticum.
Most ecosystems contain
population of several taxonomically
different species plant, microbes,
animals which interact in several
ways to maintain the ecosystem.
148Species Interaction…
• These interactions bring changes in the population characteristics of the
species involved. Several terms are proposed time to time, among them the
term "symbiosis" is in favor of which means living together in broad sense.
Odum recently (1971) used the term symbiosis in its broader sense and prefer
to group all symbiotic interactions into two major group i.e. positive and
negative interactions.
• Each group of organism has to adapt itself during evolution not only with
environment but also to the environment itself surround it. There is a struggle
which we called interaction in nature for survival between individuals and
species.
• When the species or individual group near by i.e. in a closed spatial (different
habitat) condition, they exist or rises a competition for the nutritive source,
space, water, CO₂ or any other resources for their survival.
149Species Interaction…
• Such sharing of the common resources creates a
wide varieties of interaction categorized as:
– Positive Interaction
the population helps one another, the
interaction being one way or both. This includes
mutualism, commensalisms and co operation.
– Negative interaction
the population harms one another, the
interaction being one way or both. This includes
ammensalism, predation, exploitation,
competition.
• These interactions tend to regulate the population
of a species and can help them survive, with the
changes with the environmental condition.
150151
Positive Interactions:
- Mutualism
- Commensalism
- Proto- cooperation
Negative Interactions:
- Ammensalism
- Parasitism
- Predation
- Cannibalism
- CompetitionSpecies Interaction (Positive interaction)…
• Commensalism: In this situation one population benefits while other remains
unaffected. It generally occurs when one population on its normal growth and metabolism
changes the environment or system which becomes favorable to other population. The
facultative aerobic microorganism use oxygen and create favorable environment for
anaerobic (obligatory) microorganism. The obligate aerobe benefits from facultative
anaerobes but aerobic microorganism are also not badly affected. Some fungi produce
extracellular fungi which decompose cellulose materials and produce glucose from which
other microbes may get benefited. (e.g: Barnacles catch a ride with whales for food and
protection)
• Proto cooperation (synotrophism): It is the relationship between two populations in
which both are benefited but it is not obligatory relationship. Here two populations
supply each others requirements. Synotrophism is the relationship between two
populations in which the populations are capable to synthesize the materials which can't
be synthesized alone. Examples. usually thousands of pathogens are required to cause
disease as a single pathogen is rarely become host defense. (e.g., crocodiles and birds)
152Species Interaction (Positive interaction)…
• Mutualism: In mutualism there is an intimate or obligate relationship between
two populations. Lichens are good examples in which fungus and algal species are
mutually associated for complete metabolism. The algal thalli perform
photosynthesis while fungal part absorbs the water and other nutrients.
(e.g: Flowers depends on bees for pollination and bees use flowers for necter)
• Neutralism: Organisms living together may have dissimilar requirements for
nutrient or other factor. In this case, they do not interact and consider as neutral.
So, neutralism actually represents a lack of interaction between two populations
i.e. doesn't affect other directly. Neutralism is usually a rare case but it can takes
place between the populations. This type of interaction is temporary but not
permanent.
153Species Interaction (Negative interaction)…
• Ammensalism: It is a kind of negative interaction in which one population is
inhibited and the other is not affected. It is just temporary interaction. Micro
organism that produces substance toxic to competing population will naturally
have competitive advantages once an organism establishes itself within a
habitat, it may prevent other population from surviving in the habitat.
Examples. E-coline cannot grow alone in rumen because of presence of
volatile fatty acids produced by heterotrophic microbial population. Acid
produced by microbial population in vaginal tract are responsible for
preventing from infection of pathogens such as Canadida albicans.
Example: Algal bloom leads to death of many aquatic species (fish) however
algae do not benefit from the deaths of these individuals
154Species Interaction (Negative interaction)…
• Predation: It is one of the negative interaction in which one population is prey and
other is predator. Examples. the ciliates, flagellates and amoeboid population prey
upon bacterial population. This relationship is responsible for the maintenance of
bacterial population in balance in soil and aquatic systems. (e.g: Snake and rat)
• Exploitation: Here one species harm the other by making its direct or indirect use
for support shelter or food. The exploitation may be in respect of shelter or food.
The various relationships in respect of may be parasitism or predation. Parasite is
the organism which lives on the body of another organisms and feeds on the animal
and live in its body but do not kill but in the case of predation the animal is killed
for food. (e.g: Mosquitoes biting humans for blood)
• Competition: competition occurs when individual try to obtain a resource i.e.
inadequate to support all the individuals harm one another in trying to obtain it.
In competition species of same population may involve as well as interacting
population of different species. Competition is done for raw material such as light,
inorganic nutrients, water, space to grow nest, hide from predator etc.
155Regulation Of Population Size
• The logistic model of population growth, while valid in many natural populations and a useful
model, is a simplification of real-world population dynamics. Implicit in the model is that the
carrying capacity of the environment does not change, which is not the case.
• The carrying capacity varies annually. For example, some summers are hot and dry whereas
others are cold and wet; in many areas, the carrying capacity during the winter is much lower
than it is during the summer. Also, natural events such as earthquakes, volcanoes, and fires
can alter an environment and hence its carrying capacity. Additionally, populations do not
usually exist in isolation. They share the environment with other species, competing with
them for the same resources (interspecific competition). These factors are also important to
understanding how a specific population will grow.
• Population growth is regulated in a variety of ways. These are grouped into density
dependent factors, in which the density of the population affects growth rate and mortality,
and density-independent factors, which cause mortality in a population regardless of
population density. Wildlife biologists, in particular, want to understand both types because
this helps them manage populations and prevent extinction or overpopulation.
156Density-dependent Regulation
• Most density-dependent factors are biological in nature and include
predation, inter- and intraspecific competition, and parasites.
• Usually, the denser a population is, the greater its mortality rate.
For example, during intra- and interspecific competition, the reproductive
rates of the species will usually be lower, reducing their populations’ rate of
growth.
• In addition, low prey density increases the mortality of its predator because
it has more difficulty locating its food source.
• Also, when the population is denser, diseases spread more rapidly among
the members of the population, which affect the mortality rate.
157Density-independent Regulation
• Many factors that are typically physical in nature cause mortality of a
population regardless of its density.
• These factors include weather, natural disasters, and pollution.
• An individual deer will be killed in a forest fire regardless of how many deer
happen to be in that area.
• Its chances of survival are the same whether the population density is high
or low. The same holds true for cold winter weather.
158Regulation Of Population Size…
This graph shows the age-specific mortality
rates for wild donkeys from high- and low
density populations. The juvenile mortality
is much higher in the high-density
population because of maternal
malnutrition caused by a shortage of high
quality food.
159Regulation Of Population Size…
• In real-life situations, population regulation is very complicated and density
dependent and independent factors can interact. A dense population that
suffers mortality from a density-independent cause will be able to recover
differently than a sparse population. For example, a population of deer
affected by a harsh winter will recover faster if there are more deer
remaining to reproduce.
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