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Organisms and Populations
ORGANISMS AND POPULATIONS
Prerequisites
For better understanding this chapter, the following are the prerequisites you need to know before
starting this chapter.
What is Diversity in organisms and how they are interacting?
How Human beings are interacting with other animals in real life?
How we as Humans are depending on other organisms for our survival?
What is the population of India and what are its affects on our life style?
How parasites are affecting our health and life style?
Learning Objectives
The following are the objectives for this lesson:
Organisms and Factors affecting it.
Major Biomes in India.
Adaptations and kinds of adaptations.
Populations and Population Attributes.
Population Dispersal and Growth Models.
Population Interactions.
Parasitism and Types of Parasites.
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Organisms and Populations
Introduction
Nature itself is a combination of living and non living components. The living component of the
nature is highly complex and more diversified. The complexity of living world or living component
shows various levels of hierarchy or organisations, starting from molecules to biomes. In the levels
of organisations, organisms and populations are one level of organisations.
ORGANISMS
It is the one level of organisation in the nature.
They perform various types of activities in the
nature. When we observe every activity of the
organism, we can understand the mechanism and
significance of the activity.
For e.g. when we consider the bird male crow, this
bird during spring season gives a sweet melodious
voice to the nature. The bird gives such voice due
to the presence of voice box and vibrating bone.
This voice is used to attract & communicate the
Male and Female crows
female crow to perform sexual reproduction.
In this way when we want to study the every activity of an organism, with scientific approach, we
can easily understand the operation or mechanism of the activity.
The science ecology is basically concerned with four levels of biological organisations. They are
Organisms, Populations, Communities, and Biomes.
At present we can discuss about organisms and populations.
Organism and Its Environment
In the nature, different organisms adopted different
environments for their survival and reproduction.
Organisms in different Environments
In the nature, earth is moving around the sun, tilt on its axis causes annual variations in the intensity,
duration of temperature, resulting in the formation of different seasons.
Solar system
Rainy season
Winter season
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Summer season
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These variations along with annual variations in precipitation account for the formation of major
biomes, such as deserts, rain forests, tundras. A wide variety of habitats are developed due to
regional and local variations within each biome. On planet earth, life exists on favorable places, and
also on extreme harsh habitats.
Desert
Tundras
Rain forests
Major biomes in India
Scorching Rajasthan desert,
Rain soaked Meghalaya forests,
Deep ocean trenches,
Permafrost polar regions,
High mountain tops,
Boiling thermal springs,
Shrinking compost pits.
Human intestine is a unique habitat for microbes.
Deep ocean trenches
Scorching
Rajasthan desert
Rain soaked
Meghalaya forests
High mountain
tops
Boiling
thermal springs
Permafrost polar
regions
The habitat or biomes are influenced by abiotic
& biotic components. The key elements that
bring so much variation in the physical, chemical
constituents of different habitats are temperature,
water, light and soil.
Water
Soil
The characteristics of a habitat are also influenced by biotic components like pathogens, predators,
parasitism, competitors etc.
In the nature, in course of time organisms through natural selection undergo changes; develop new
adaptations to optimise its survival and reproduction in its habitats.
Pathogens
Predators
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Parasitism
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MAJOR ABIOTIC FACTORS
TEMPERATURE
It is the most ecologically relevant environmental factor. Average temperature on land varies
seasonally. It decreases progressively from the equator towards the poles from plains to the
mountain tops.
It ranges from sub-zero levels in polar areas and
high altitudes to more than 50oC in tropical deserts
in summer.
In some unique habitats, average temperature
exceeds 100oCentigrade. E.g: thermal springs,
Deep sea
Thermal springs
deep sea hydrothermal vents.
hydrothermal vents
Organisms which grow in habitats with definite temperature cannot grow in other habitats with
different temperatures.
E.g: a) Mango trees do not & cannot grow in temperate countries like Canada, Germany.
b) Snow leopards are not found in Kerala forests.
c) Tuna fish are rarely caught beyond tropical latitudes in the ocean.
Mango trees
Snow leopards
Tuna fish
Temperature affects the kinetics of enzymes. Organisms tolerate at a specific rate of temperature.
Based on this, organisms are classified into two types, namely
EURTYTHERMAL - Organisms can tolerate and thrive in a wide range of temperatures.
STENOTHERMAL – Organisms can tolerate narrow range of temperatures.
The levels of thermal tolerance of organisms determine to a large extent their geographical
distribution. In recent years, there has been growing concern about the gradually increasing
average global temperatures. If this trend continues, the distributional range of some species to be
affected.
WATER
It is the second most important factor influencing
the life of organisms. Living organisms cannot
sustain without water. Life on earth originated in
water. In deserts, availability of water is so limited,
so plants develop special adaptations to survive in
deserts.
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Water
Desert
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Organisms and Populations
The productivity & distribution of plants is also heavily dependent on water.
The important factors for aquatic organisms for their survival in water are quality of water, salt
concentration of water. The salt concentration of water in which organisms grow is less than 5% in
inland water, 30-35% in the sea water, more than 100% in some hyper saline lagoons.
The tolerant capacity of organisms to the water is variable with one another. Based on this, organisms
are classified into two types.
EURYHALINE – organisms tolerant to a wide range of salinities.
STENOHALINE – organisms are restricted to a narrow range of salinities.
Many fresh water animals cannot live for long in sea water and vice versa, because of the osmotic
problems, they would face.
LIGHT
In the nature, Sun is the source of energy to all
living organisms.
Autotrophs are mainly depends by a process
called photosynthesis.
In dense forests, small plants (herbs & shrubs)
get low light intensity, because canopy is covered
by trees. So the rate of photosynthesis occurs at
optimum rate.
Sun
Dense forests
Autotrophs
Herbs and
Shrubs
Plants also depend on light for their flowering. Depending on the photoperiod required for their
flowering, plants are categorised into three groups, they are
Long day plants (LDP) – Plants which require more photoperiod or day length.
Short day plants (SDP) – Plants which require short photoperiod or day length.
Day neutral plants (DNP) – Plants which require average day length or photoperiod.
Long day plants
Short day plants
Day neutral plants
Animals also influenced by light intensity in their foraging, reproduction and migratory activities.
Intensity of light is variable when diurnal & seasonal variations exists.
Sun is the source of energy and temperature to the nature. So the availability of light on land is
closely linked with that of temperature.
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In deep ocean (>500 meters) the environment is
perpetually dark. The habitat of these regions is
not aware of the existence of solar energy. The
spectral quality of solar radiation is also important
Deep ocean
for life.
The UV component of the spectrum is harmful to many organisms while not all the colour components
of the visible spectrum are available for marine plants living at different depths of the oceans.
Depth of oceans
SOIL
The nature and properties of soil differ from one
another in different habitats or environments.
The nature & properties of soils are depends upon
the climate, the weathering process, formation of
soils, development of soils etc.
Soil
The soil characteristics like soil composition, grain size, aggregation determine the percolation and
water holding capacity of the soils.
These characters along with PH, mineral composition and topography determine to a large extent
the vegetation in any area. This is in turn dictates the type of animals that can be supported.
In the aquatic environments, the sediment characteristics often determine the type of benthic
animals that can thrive there.
RESPONSE TO ABIOTIC FACTORS
In the nature, abiotic factors are variable from time to time and area to area.
These abiotic conditions influence the external and internal environment of living beings. Generally
internal environment is stable in most of the organisms. It is called HOMEOSTASIS.
E.g: Maintenance of optimum temperature & osmotic concentration of body.
Internal environment of the living organisms is maintained by physiological & biochemical activities
of the organisms.
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External environment of the organisms is severally influenced by the habitat state.
A person is able to form his/her best when the temp is 25oC and wishes to maintain it so, even when
it is scorchingly hot or freezingly cold outside.
Human beings
Heater
Conditioner
It could be achieved at home/in the car while travelling/at work place, by using air conditioner in
summer and heater in winter.
Then his/her performance would be always maximal regardless of the weather around him/her.
In these conditions homeostasis of the organisms is maintained by artificial methods.
Living organisms core with the situations by means of various possibilities like Regulate, Conform,
Migrate, and Suspend.
REGULATE
It is one of the important activities of organisms to survive in any external environment. Organisms
are regulated in any type of environment by various activities.
Some organisms regulate the homeostasis or internal environment by physiological conditions like
regulation of the body temperature, constant osmotic concentration of body fluids, etc.
All birds, mammals, and a very low vertebrates and invertebrates’ species are indeed capable
of such regulations.
E.g: Thermoregulation & Osmoregulation.
Bird
Mammal
Vertebrate
Invertebrate
According to evolutionary biologists, the fitness of mammals is largely due to their ability to maintain
a constant body temperature, and thrive to maintain or live in Antarctica or in the Sahara desert.
Mammals
Antarctica
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Sahara desert
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The mechanism used by most mammals to regulate the body temperature is similar to the ones
used by human beings.
Human beings maintain constant body temperature 37o centigrade. In summer, the body
temperature is maintained by profuse sweating, because outside temperature is more than that of
inside temperature.
Similarly in winter also body temperature is maintained by shivering, because external temperature
is less than that of internal temperature. Shivering is a type of exercise which generates heat and
raises the body temperature.
Plants do not have such mechanism to maintain internal temperature.
CONFORM
Organisms which can change their internal
environment, according to the ambient environment
are called Conformers and the process is called
Conform.
In majority of animals and nearly all plants
body temperature changes with the ambient
temperature.
In aquatic animals, the osmotic concentration of
the body fluids changes with that of ambient water
osmotic concentration.
Aquatic Animals
Organisms maintain constant internal environment cannot act as conformers. Conformers also act
as regulators.
In majority of conformers thermoregulation is energetically expensive process. It is based on heat
loss/heat gain of surface area.
The small animals like Shrew and Humming birds
have a larger surface area relative to their volume.
They tend to lose body heat very fast when it is
cold outside.
They have to spend much energy to generate body
heat through metabolism. Due to this reason, very
small animals are rarely found in Polar Regions.
Shrew
Humming bird
During the course of evolution, the costs and benefits of maintaining a constant internal environment
are taken into consideration.
Some species have evolved the ability to regulate, but only over a limited range of environment
conditions, beyond which they simply conform.
If the stressful external conditions are localised or remain only for a short duration, the organisms
has two other alternatives. They are Migrate and Suspend.
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MIGRATE
The movement of organisms temporarily form
the stressful habitat to a more hospitable area
and return when stressful period is over is called
Migration.
In terms of human analogy, during summer human
beings move from Delhi to Shimla (hot place to
cool place).
Eg: Siberian Cranes – These birds migrate every
winter season from Siberia to Keolado National
Park, Bharatpur, Rajasthan, to avoid extreme
cold.
Siberian Cranes
SUSPEND
Temporary withstanding of organisms in different forms during stressful/unfavourable conditions is
called Suspend.
Bacteria, fungi, lower plants produce various types of thick walled spores to survive during
unfavourable conditions. These spores germinate during favourable conditions.
Higher plants survive during unfavourable conditions in the form of seeds & vegetative reproductive
structures. These parts by reducing their metabolic activity survive during unfavourable conditions.
It is called Dormancy.
When favourable conditions prevailed, they germinate and develop into new plants. Higher plants
also exhibit dispersal to avoid unfavourable conditions.
Animals avoid/escape unfavourable conditions by escaping in time.
Bear – These animals going into hibernation during winter.
Snails & Fishes – these animals going into aestivation to avoid summer (heat & desiccation).
Zooplanktons – these animals enter into diapause – a stage of suspended development.
Bear
Snail
Fish
Zooplanktons
ADAPTATIONS
Any attribute of the organisms that enables the organism to survive, reproduce in its habitat are
called Adaptations.
Many adaptations have evolved over a long evolutionary time and are genetically fixed. These
adaptations are in morphological, physiological and behavioural.
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MORPHOLOGICAL ADAPTATIONS
XEROPHYTES: These plants have a thick cuticle
on their leaf surfaces and have their stomata
arranged in deep pits to minimise water loss
through transpirations.
They also have a special photosynthetic pathway
(CAM) that enables their stomata to remain closed
during day time.
Xerophytes
Opuntia – Leaves are reduced to spines,
stems are modified into phylloclade to perform
photosynthesis.
Mammals – Mammals from colder climates
generally have shorter ears and limbs to minimise
heat loss (Allen’s rule).
AQUATIC MAMMALS – SEALS – These animals
have a thick layer of fat (bubber) below their skin
that act as insulator and reduces the loss of body
heat.
Opuntia
Seals
PHYSIOLOGICAL ADAPTATIONS
Some organisms exhibit physiological adaptations to tide over unfavourable conditions.
ALTITUDE SICKNESS
It is the most important adaptation experienced by
the people who move to the high altitudes.
When the people move to the high altitudes (more
than 3,500 meters) like Rohtang pass near
Manali, Manasarovar, in China occupied Tibet.
Rohtang pass
Manasarovar
In the high altitudes low atmospheric pressure exists. So body does not get enough oxygen. The
symptoms like Nausea, Fatigue, heart palpitations develop.
But these symptoms gradually decrease and the organism gets acclimatised to the conditions,
finally altitude sickness stops.
The body compensates the low availability of oxygen by increasing RBC production, decreasing the
binding capacity of haemoglobin and by increasing breathing rate.
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ANIMALS – In majority of animals, all metabolic reactions/physiological functions proceed optimally
in a narrow temporary range.
ARCHAEBACTERIA – They flourish in hot water springs, deep sea hydrothermal vents, and
temperature exceeds 100oC.
FISHES – Many fishes thrive in Antarctic water, temperature below zero.
MARINE INVERTEBRATES- FISHES – These organisms live at great depth in the ocean where
the pressure could be >100 times the normal atmospheric pressure that we experience. These
organisms show a fascinating array of biochemical adaptations.
Fig 13.61 Animals
Fig 13.62 Archaebacteria
Fig 13.63 Fishes
Fig 13.64 Marine
Invertebrates Fishes
BEHAVIOURAL ADAPTATIONS
Some organisms show behavioural responses to cope with variations in their environment.
DESERT LIZARD – These organisms maintain the
constant body temperature by behavioural means.
They bask in the Sun & absorb heat when their
body temperature drops below the comfort zone,
but move into shade when the ambient temperature
starts increasing.
Some species are capable of burrowing into the
soil to hide & escape from the above ground heat.
Desert lizard
Populations
A group of organisms of similar species belongs to same locality is called Population.
Every population is confined to a well defined area, share or compete for similar responses,
potentially interbred or reproduce by vegetative & sexual methods.
LOCAL POPULATIONS or DEME – A group of interbreeding individuals of a species found in a
space or geographical area at a particular time is called Local populations or Deme.
METAPOPULATIONS – A complex of local populations connected by dispersing individuals is
called Metapopulations. Population gives various meanings in different areas of study. They are
HUMAN DEMOGRAPHY – According to human demography population means number of human
beings in a given area (School, Village, Town etc.)
GENETICS – According to Genetics, Population is a group of interbreeding individuals of the same
species which live in semi isolation from other such groups.
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ECOLOGY – According the Ecology, population is a group of individuals of the same species living
in the same area which functions as a unit of biotic community.
The parameters used for describing a population are
a) Total number of individuals or population size.
b) Kind and ratio of individuals like male and female and pre-reproductive and post-reproductive.
c) Space or area.
d) Time.
Natural selection plays an important role to produce the desired traits in populations.
Population ecology, an important area of ecology because it links ecology to population genetics &
evolution.
POPULATION ATTRIBUTES
Every population expresses certain attributes to survive in the environment. They are
1) Birth & Death rate.
2) Sex ratio.
3) Age of the organisms.
4) Population size/ Population density.
Birth And death rate
In a population birth and death rates refer to per capita birth & deaths respectively.
These rates hence are expressed is change in numbers with respect to members of populations.
Eg: In a pond 20 Lotus plants are present in last year, by reproduction 8 new plants are added.
Current population reaches 28.
Example of Birth Rate
Then the birth rate is 8/20 = 0.4 that means 0.4 off-springs per Lotus plants per year are added.
If 4 individuals in laboratory populations of 40 fruit flies are died during a specified time interval
(week), the death rate in the population during that period is 4/40=0.1 individuals per fruit fly per
week.
Died
40
4
40
0.1
Example of Death Rate
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SEX RATIO
It is the number of individuals of a particular sex out of total populations.
60
60
40
40
Females
males
Images showing Sex ratio
Eg: In a population 60 females and 40 males are present. That means 60% of females, 40% males
are present.
AGE DISTRIBUTION
Ecologically a population has three age groups. They are pre-reproductive, reproductive and postreproductive.
Their comparative abundance determines the reproductive status of population.
A population having larger number of young individuals will show rapid increase. It will have a slow
increase or become static in various age groups are evenly balanced.
A population with larger number of post-reproductive or older individuals and less number of pre
reproductive individuals will show a negative growth etc.
The graphic representation of different age groups
found in a population with pre-reproductive groups
at the base, reproductive ones in the middle and
post-reproductive groups at the top is called Age
pyramid.
A population at any given time is composed of
individuals of different ages.
A graph is made by plotting number of individuals
in a population on one axis and their age is on
another axis, the resulting graph/structure is called
AGE PYRAMID.
For human population, the age pyramid generally
show age distribution of males & females in a
combined diagram.
The shape of the age reflects the growth status of
the population. They are
a) Growing/Expanding b) Stable and C) Declining
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Age Groups
AGE PYRAMID
Post
reproduction
Reproduction
Pre-reproduction
Population
Age Pyramid
Graphic Representation of Different age
groups in a population
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TYPES OF AGE PYRAMIDS
Post-reproduction
Reproduction
Pre-reproduction
negative growth
Triangular
Bell shaped
Turn shaped
Types of Age Pyramid
TRIANGULAR AGE PYRAMID
In this, the number of pre-reproductive individuals is very large. The Number of reproductive
individuals is moderate. The number of post-reproductive individuals is less.
Population growth depends upon the comparative size of pre-reproductive population.
BELL SHAPED AGE PYRAMID
In this, the number of pre-reproductive and reproductive individuals is almost equal.
Post reproductive individuals are comparatively fewer. The population size remains stable.
TURN SHAPED AGE PYRAMID
The proportion of reproductive age group is higher than individuals in pre-reproductive age group.
The number of post–reproductive individuals is also sizeable. Population shows negative growth.
POPULATION SIZE (OR) DENSITY
The number of individuals confined to a particular
habitat is called Population size.
Population size is more technically described as
population density. It is designated as D.
Population Density =
(Number of Individuals (N)
or
Space (S)
D=
N
S
Population size
It always indicates the nature or status of the habitat. The population size/density of a habitat
depends upon the outcome of the various ecological processes or associations like competition,
predation, mutualism etc.
In the nature, size could be as low as less than
10 (Siberian Cranes at Bharatpur wetlands in any
year) or go into millions (Chlamydomonas in a
pond).
Siberian Cranes
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Chlamydomonas
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Generally population density can be calculated by knowing the total number of individuals of a
particular area irrespective of their role in that area. In some cases it is meaningful and difficult to
estimate.
For eg: In an area 200 Parthenium plants and one
Banyan tree is present. As per our observations,
population density of Banyan tree is less than that
of Parthenium plants.
In such cases, the percent cover of biomass is a
more meaningful measure of the population size.
The contribution/rate of Banyan tree in that area is
more than that of Parthenium plants.
Parthenium plants
Banyan tree
When the population is huge and counting is impossible and time taking, then total number is again
not an adoptable measure.
Culture media
Fishes
For eg: culture media in a petridish is completely filled with bacteria. The total number of bacteria
in the culture cannot be countable. In such cases relation densities serve the purpose equally well
than absolute population densities.
For instance, the population density of fish in a lake is determined by number of fish caught per
trap.
It is better to understand the population density/size of a habitat or area indirectly without actually
counting them/ seeing them.
For eg: the tiger census in our national parks & tiger reserves is often based upon on pug marks &
faecal pellets.
In case of aquatic habitat, the space is measured in three dimensions, while the space in terrestrial
habitat is measured in two dimensions.
Unit of area depends upon the size and number of individuals.
For plants and animals, density is known by counting individuals in sampling units of predetermined
sizes randomly in an area.
Density of a population may vary from time to time and area to area. Eg: Density of small plants in
rainy season and dry season.
Population density is also depends upon availability of nutrients and other resources for it.
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POPULATION GROWTH
The population growth in any area is based on population density.
Population growth is not a static parameter. It keeps on changing in time, depending on various
factors including food availability, predation pressure and reduced weather.
The population density in a given habitat during a given period fluctuates due to changes in four
basic processes, in which two processes contribute an increase in populations, they are natality &
immigration. The remaining two processes contribute in declining the population number, they are
mortality & emigration.
Immigration
Nalality
Population
density(N)
Mortality
Emigration
NATALITY (B)
It refers to the number of births during a given period in the population that are added to the initial
density or the rate of production of new individuals per unit of population per unit time through birth,
hatching, germination or vegetative propagation.
Biotic potential – The maximum natality or birth rate achieved under ideal conditions is called
Biotic potential.
It can be realised only when environmental resources are non-limiting and conditions favour for
minimum mortality.
Realised natality – The actual birth rate found under existing conditions is termed as realised
natality.
In Human beings, natality is calculated per thousand per year.
Natality
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MORTALITY (D)
It refers to the number of deaths in the population during a given period or it is the rate of loss of
individuals per unit time due to death.
Maximum mortality occurs in egg/larval/seeding and old age.
Specific mortality – it is the theoretical, minimum death rate that occurs under ideal conditions due
to natural processes or senescence.
Realised mortality – The actual rate of death occurring in a unit population due to environmental
changes, nutritional deficiency, disease, competition, predation etc. is called realised mortality.
Mortality
VITAL INDEX
The percent ratio of natality in relation to mortality. It indicates the normal rate of growth of
population.
Vitality index= n/m x 100
IMMIGRATION(I)
It refers to the number of individuals of the same species that have come into the habitat from
elsewhere during the time period under consideration.
Immigration
EMIGRATION(E)
It refers to the number of individuals of the population who left the habitat and gone elsewhere
during the time period under consideration.
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Emigration
If N is the population density at time (t), then its density at a given time (t+1) is
Nt+1 = Nt + [(B+I) – (D+E)]
Then Nt+1 = population density at a given time
Nt= Population density at a time ‘t’
B = Natality
I = Immigration
D = Mortality
E = Emigration
From the above equation, population density increases, if number of births plus number of immigrants
is more than the number of deaths and number of emigrants. Otherwise it will decrease.
Under normal conditions, for an existing habitat, the most important factors, influence the population
density are Natality & Mortality, where as Immigration & Emigration are special factors, which
influence the population density.
For instance, for a newly formed habitat immigration may contribute more significantly to the
population growth than other factors.
POPULATION DISPERSAL
It is the movement of individuals or propagules into or out of population for preventing overcrowding,
obtaining food, avoiding predators and other adverse conditions is called population dispersal.
It affects the size of the population.
Emigration, Immigration, Migration together called Population dispersal.
Population Dispersal
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GROWTH MODELS
In the nature, the growth of a population with time
show specific & predictable pattern of population
growth.
When plotting of population growth against time in
the form of graph, the resulting structure/graph is
called growth model.
Growth models are useful to understand the growth
pattern of the organisms and the application of
controlling factors.
Population
(bn)
1.5
1.4
1.3
1.2
1.1
2000 10
20 30
40
Time
Graph Showing growth of population with time
There are two types of growth models explained below to understand the population growth. They
are
1) EXPONENTIAL GROWTH
2) LOGISTIC GROWTH
The growth of population is unlimited when the
resource availability is unlimited. The graph which
shows this type of growth is called Exponential
growth.
When resources in the habitat are unlimited, each
species has the ability to release fully its innate
potential to grow in number as Darwin observed
while developing his theory of natural selection.
Then the population grows in an exponential or
geometric fashion.
Population
EXPONENTIAL GROWTH
Exponential growth
Time
Graph Showing Exponential growth
In a population of size N, the birth rates are represented as b and death rates are represented as d,
then the increase or decrease in population size (N) during unit
time period t(dN) will be
(dt)
dN = (b-d) x N
dt
Let (b-d) = r then dN
= rN
dt
r = Intrinsic rate of natural increase.
r is an important parameter chosen for assessing impacts of any biotic or abiotic factors on population
growth.
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The above equation describes the exponential or geometric growth pattern of population growth,
and results in J-shaped curve. When we plot N in relation to time, the magnitude of r value is
variable between the organisms.
For eg: r value of Norway is 0.015
Flour beetle is 0.12
Human beings in 1981 is 0.025.
The integral form of exponential growth equation can be derived by using calculus
Nt = N0 ert
Nt = population density after time t.
N0 = Population density at time zero.
r = Intrinsic rate of natural increase.
e = the base of natural logarithm (2.71828)
Under unlimited resource conditions, any species
grown exponentially and it can reach enormous
population densities in a short time.
Darwin showed how even a slow growing animal
like elephant could reach enormous number in the
absence of checks.
Darwin
Population growth in which the growth rate
decreases with increasing number of individuals
until it becomes zero when the population reaches
a maximum state.
When
the
population
density
increases
exponentially, competition develops between the
organisms. Finally fittest individual will survive &
reproduce.
Population
LOGISTIC GROWTH
Logistic growth
Exponential growth
Time
Graph Showing Logistic growth
In the nature in a given habitat every species shows carrying capacity.
CARRYING CAPACITY (K) – A species with maximum limited number of individuals in a given
habitat, which has enough resources to support them, is called carrying capacity (K) for that species
in that habitat.
The maximum number of individuals of a population which can be provided with all the necessary
resources for their healthy living in a habitat/locality/environment is called carrying capacity.
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Organisms and Populations
Carrying capacity(K)
dN = rN (K-N)
dt
K
Population
When carrying capacity of habitat/locality/
environment is exceeds the limit, the size of the
population begins to decrease due to lower natality,
higher mortality and emigration.
A population growing in a habitat with limited
resources show initially lag phase, followed by
phases of acceleration and deceleration and finally
an asymptote when the population density reaches
the carrying capacity.
Logistic growth
Exponential growth
Time
Graph Showing Carrying Capacity
A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called
VERHULST – PEARL LOGISTIC GROWTH. This is described by the following equation
dN
(K-N)
= rN
dt
K
Where N= population density at time t,
e = Intrinsic rate of natural increase,
K = carrying capacity.
Since growth resources for most of the animal populations are limited and becoming limiting factor
gradually, the logistic model is considered as more realistic one.
ENVIRONMENTAL RESISTANCE
The sum of abiotic and biotic factors which checks the rise in population size and prevents the
species to realise its biotic potential is called Environmental resistance.
It is inversely related to difference between carrying capacity (K) and number of existing population
(N).
Environmental resistance rises as the population size approaches the carrying capacity of the
habitat. It helps in limiting population size to below the carrying capacity.
Carrying capacity(K)
Population
Environmental resistance
rN
Logistic growth
(K-N)
K
Exponential growth
Time
Graph Showing Environment Resistance
The effect of environmental resistance on biotic potential is denoted by the following formula.
Where r is reproductive rate and N is the population.
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LIFE HISTORY VARIATIONS
The life history of an organism depends upon the abiotic & biotic factors available in that particular
habitat. It is variable from one species to another species.
Life history of an organism mainly depends on reproductive fitness of that organism. It is also called
DARWINIAN FITNESS.
Reproductive fitness of an organism depends on the nature of habitat in which they live.
In a particular habitat, organisms evolve towards the most efficient reproductive strategy under a
particular set of selection pressures.
According to reproductive strategy of the organism, some organisms breed only once in their life
time.
Eg: Pacific fish, Bamboo, while some other organisms breed many times during their life time.
Eg: most of the birds and mammals.
Pacific fish
Mammals
Birds
Some produce a large number of small sized
offsprings (Oysters, Perlagic fishes) while others
produce a small number of large sized offsprings
(Birds, mammals).
Oysters
Perlagic fishes
Ecologists suggest that life history traits of the organism have evolved in relation to the constraints
imposed by the abiotic & biotic components of the habitat in which they live.
Evolution of life history traits in different species is currently an important area of research being
conducted by ecologists.
POPULATION INTERACTIONS
In the nature, in any natural habitat, a group of
different species or populations exists together.
When they exist together, they interact with one
another in various ways and form into a biological
community.
Biological community
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Even in minimal communities, many interactive
linkages exist, although all may not be readily
apparent.
For example, when we observe plants regularly
interacting with microbes and animals, microbes
involve in breakdown of complex organic materials
into simpler ones. Plants absorb these simple
inorganic substances to prepare biomolecules.
Simultaneously animals also interact with plants
for pollination, dispersal of fruits and seeds.
microbes
Pollination
In every biological community, interactions arise
among the different species or populations. These
are called Interspecific interactions.
Interspecific interactions
These interactions are either beneficial or detrimental or neutral.
Beneficial interactions are designated as +
Detrimental interactions are designated as –
Neutral interactions are designated as 0 (Zero)
Different types of population interactions are explained below
Beneficial (+ve) Interactions are mutualism, Detrimental (-ve) interactions are Competition,
Predation, Parasitism and Neutral interactions are commensalism, amensalism.
PREDATION
The association, in which one organism kills the
other organism, is called Predation.
The organism which killed the other organism is
called Predator and other organism is called Prey.
These are carnivorous organisms.
It is a mechanism of biological control that helps
in keeping the population of various organisms
under check.
Predation is one of the nature’s ways of transferring
energy from higher trophic level to lower trophic
level. So predators act as ‘conducts’ for every
transfer across trophic levels.
E.g: Herbivores eating the plants.
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Predation
Predation
Herbivores eating
the plants
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Predators plays an important role in the nature. Predator keeps prey population under control.
Without predators, prey species could achieve very high population densities and cause ecosystem
instability.
When certain exotic species are introduced into a geographical area, they become invasive and
start spreading fast because the invaded land does not have its natural resources.
In the early 1920’s a prickly pear cactus
is introduced into Australia. It causes havoc
by spreading rapidly into million hectares of
rangeland.
Biological control methods adopted in agriculture
pest control based on the ability of the predator to
regulate prey population.
Prickly pear cactus
The invasive prickly pear cactus in Australia was
brought under control only after a cactus feeding
predator (a moth) from its natural habitats into the
country.
Predators also help in maintaining species
diversity in a community, by reducing the intensity
of competition among competing prey species.
feeding predator
In the rocky intertidal communities of the American
pacific coast, the star fish Piaster is an important
predator.
In a field experiment, when all the Starfish were
removed from an enclosed intertidal area, more the
10 species of invertebrates become extinct within
a year, because of interspecific competition.
star fish Piaster
If a predator is too efficient and over its prey, then the prey might become extinct and following it,
the predator will also become extinct for the lack of food. This is the reason why predators in nature
are prudent. Some species of insects and frogs are cryptically coloured to avoid being detected
easily by the predator. Some are poisonous and therefore avoided by the predators.
The monarch butterfly is highly distasteful to its
predator (bird) because of a special chemical
present it its body. Interestingly, the butterfly
acquires this chemical during its caterpillar stage
by feeding on a poisonous weed.
butterfly
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caterpillar
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Herbivores are the predators for plants. Nearly 25% of the all insects are known to be phytophagous.
The problem is particularly severe for plants, because unlike animals, they cannot run away from
their predators. Therefore plants have an astonishing variety of morphological and chemical
defences against herbivores.
E.g: Thorns are the most common morphological means of defence
Many plants produce & store chemicals that make the herbivore sick when they are eaten, inhibit
feeding/digestion, disrupt its reproduction or even kill it.
CALOTROPIS – This is mostly growing in abandoned fields. The plant produces highly poisonous
cardiac glycosides. Due to this reason cattle or goats will not eat this plant.
Thorns
cattle
goats
A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine,
caffeine, quinine, strychnine, opium, etc.) are produced by them actually as defences against
grazes & browsers.
nicotine
caffeine
quinine
strychnine
opium
A rise in predator population will reduce prey population, which in turn will cause reduction in the
population of predators due to starvation and emigration. A rise in herbivore population will result in
overgrazing, shortage of herbage and ultimately reduction in herbivore population.
Eg: Insectivorous plants – Drosera, Nepenthes, Utricularia.
Drosera
Nepenthes
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Utricularia
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COMPETITION
Charles Darwin was first convinced that
interspecific competition is a potent force in
organic evolution. Competition exists between
either related or unrelated species for the same
resource.
Eg: Flamingos & resident fishes present in some
shallow South American lakes compete for their
common food, the zooplankton in the lake.
Charles Darwin
Flamingos
Interference is another important factor in competition of different species, which compete for the
same resource of food. It is called Interference competition.
In the inference competition, the feeding efficiency of one species might be reduced due to
interference & inhibitory presence of the other species, even if the resources are abundant. So
competition is best defined as a process in which the fitness of one species is significantly lower in
the presence of another species.
Gause & other experimental ecologists demonstrated in laboratory experiments that when
resources are limited the competitively superior species will eventually eliminate the other species,
but evidence for such competition exclusion occurs in nature is not always conclusive.
Strong & Persuasive circumstantial evidence does exist however in some cases. Competitive
release is another important evidence for the occurrence of competition in nature. A species, whose
distribution is restricted to a small geographical area because of the presence of competitively
superior species, is found to expand its distributional range dramatically when the competing
species is experimentally removed.
Connell’s elegant field experiment showed that the larger and competitively superior barnacle
Balanus dominates the intertidal area and excludes the smaller Barnacle chathamalus from that
zone.
In general, herbivores are plants appear to be more adversely affected by competition than
carnivores.
GAUSE’S COMPETITION EXCLUSION PRINCIPLE
It states that two closely related species competing
for the same resources cannot co-exist indefinitely
and the competitively inferior one will be eliminated
eventually. This may be true if resources are
limiting, but not otherwise.
These generalizations are not supporting
competition completely. It is called RESOURCE
PARTITIONING.
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Resource Partitioning
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Many ecologists in more recent studies observed that in the inter-specific competition when species
facing competition they might evolve mechanisms that promote co-existence rather that exclusion.
RESOURCE PARTITIONING
If two species compete for the same resource, they could avoid competition by choosing, different
times for feeding or different foraging patterns.
McArthur showed that five closely related species
of Warblers living on the same tree were able to
avoid competition and co-exists due to behavioural
differences in their foraging activities
PARASITISM
Warblers
The association, in which one organism obtains nourishment from another organism, is called
Parasitism. The organism which obtains food is called Parasite and the organism which supply
food is called Host.
In this association, parasites also obtain shelter from their host.
In this association, host becomes weak with reduced life cycle and reduced reproduction often
leading to sterility. Parasites reach the host through contact with infected hosts, contaminated food
and water, animal bites and direct entry.
Parasites reach the host by developing different
types of adaptations. They are
a) Holdfast, Haustoria, Suckers (ectoparasites)
b) Suckers, hooks and spines (endoparasites)
ectoparasites
endoparasites
c) Resistant covering, resistant eggs or cysts, formation of antienzymes, anaerobic respiration,
degeneration of unwanted organs.
Parasitic mode of life ensures free lodging and meals of a person in a host family.
Parasitism has evolved in so many taxonomic groups from plants to higher vertebrates.
Many parasites have evolved to be host specific in such a way that both host & parasitic tend to
co-evolve, that is if the host evolves special mechanisms for rejecting or resisting the parasite, the
parasite has to evolve mechanisms to counteract & neutralise them in order to be successful with
the same host species.
In accordance with their life styles, parasites evolved special adaptations such as the loss of
unnecessary sense organs, presence of adhesive organs or suckers to clings on to the host, loss
of digestive system & high reproductive capacity.
The life cycles of parasites are often complex, involving one or two intermediate host or vectors to
facilitate parasitisation of its primary host.
Eg: The human lever fluke (a trematode parasite) depends on two intermediate host (a snail and
a fish) to complete its life cycle.
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The human lever fluke
host
The malaria parasite needs a vector, to spread to other hosts.
Majority of parasites harm the host. They reduce the survival growth and reproduction of the host,
reduce its population density. They might render the host more vulnerable to predation by making
it physically weak.
host
malaria parasite
TYPES OF PARASITES
a) Non pathogenic – eg: Entamoeba coli
b) Pathogenic – eg: Entamoeba histolytica, Taenia solium, Ascaris, Vibrio cholrae
c) Temporary parasites – eg: Female mosquito, Leech, bed bugs
d) Permanent parasites – eg: Entamoeba, Ascaris
Entamoebacoli
Entamoebahistolytica
Female mosquito
Taenia solium
Leech
Vibrio cholrae
bed bugs
Ascaris
Entamoeba
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e) ECTOPARAISTES - Parasites that feed on the external surface of the host organism are called
ectoparasites. They attach to skin, hair and other surface features of the host. They have suckers,
camps adhesive surface, cutting, biting or sucking mouth parts or root. Lice, ticks, mites, leeches,
mosquitoes feed on body fluids
Example: Lice on humans, Ticks on Dogs, Copepods on marine fish, Cuscuta on Hedge
plants.
Female mosquito is not considered as parasite, but it needs our blood for reproduction.
Lice
Ticks on Dogs
tick
mite
leeche
Copepods on marine fish
mosquitoe
Cuscuta on Hedge plants
f) ENDOPARASITES- Parasites that live inside the host body at different sites (liver, kidney, lungs,
RBC, etc. are called endoparasites.
The lifecycles of these parasites are more complex because of their extreme specialization. Their
morphological & anatomical features are greatly simplified while emphasising their reproductive
potential.
eg: Intracellular Plasmodium, Tissue parasite - Trichinella,Body fluid parasite Trypanosoma,Gut parasite - Taenia
liver
kidney
lungs
RBC
Intracellular
Plasmodium
Trichinella
Trypanosoma
Taenia
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g) Holoparasite – These are also called complete parasites
eg: Animal parasite, Cuscuta, Rafflesia
h) Semi parasite – These are also called Incomplete parasites
eg: Visum, Loranthus
i)Hyperparasite – Parasite over parasite.
Cicinnobolus cesatii on Powdery mildew.
Animal
parasite
Cuscuta
Rafflesia
Loranthus
BROOD PARASITISM
It is fascinating examples of parasitism in which
the parasitic bird lays its eggs in the nest of its
host and lets the host incubate them. It is called
Brood parasitism.
During the course of evolution, the eggs of the
parasitic bird have evolved to resemble the host’s
egg in size & colour to reduce the chances of the
host bird detecting the foreign egg and ejecting
them from the nest.
Example: Cuckoo (Koel) and Crown relation.
Cuckoo
Crown relation
COMMENSALISM
In this type of interaction, one species benefits and the other is neither harmed nor benefited. It is
of two types: a) periodic contact and b) continuous contact.
Periodic contact
a) Fierasfer in Cloaca of Cucumaria is able to obtain shelter and food.
b) Polynox in the burrow of Chatopterus is able to obtain shelter and food.
c) Clone fish is able to protect itself by living in the company of Sea Anemones.
d) Naucrates, Remora (Pilot fish) accompanies shark without getting attached to the shark.
Fierasfer
Polynox
Clone fish
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Remora
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e) Echeneis (Sucker fish) has a holdfast or
sucker which is a modified dorsal fin. It attaches
to the underside of shark and therefore remains
protected. The fish obtain food from small pieces
of left over when shark is feeding on its prey.
f) Jackal and Hyena accompany Tiger or Lion for
eating over small bits of prey.
Echeneis
Jackal and Hyena
Continuous contact
a) Barnacles are often attached to the surface of whales for shelter and obtaining more food.
b) Escherichia coli in human intestine.
c) Climbers and twiners over other plants for exposing their foliage.
d) Epiphytes perched on other plants for space only
e) Adamsia pallicata (Sea Anemone) is commensal over Eupagurus prideauxi (Hermit crab). The
latter gets protection in a small shell.
Barnacles
Epiphytes perched
Escherichia
Adamsia pallicata
Sea Anemone attaches to the surface of shell. Hermit crab carries it from place to place. This
provides otherwise sedentary Sea Anemone with food.
MUTUALISM
It is an interaction in which both species get
benefited with one another.
Eg: Lichens, Mycorrhizae, Plant-animal
associations.
It is considered to be obligatory.
Lichens
Mycorrhizae
a) Association between an alga and fungus in lichen
b) Rhizobium and root in nodular roots of leguminous plants
c) Fungus and root in mycorrhiza.
d) Bacteria present in the stomach of ruminants help in the digestion of cellulose.
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e) Trichonympha (cellulose digesting flagellate) in intestine of Termite.
f) Coelentarates and alga in coral reefs. Hydra and zoochlorellae.
g) Insects obtain nectar and perform pollination in flowers
h) Some ants take shelter and food from fruit trees. They protect the trees from other animals. This
phenomenon is called Myrmecophily.
lichen
Trichonympha
Rhizobium
mycorrhiza
Bacteria
Hydra
Insects
ants
PLANT – ANIMAL ASSOCIATION
It is a classical example of mutualism.
Eg: Ficus – Wasp association
Ficus
Ficus – Wasp association
In this type of interaction plants need the help of
animals for pollinating their flowers and dispersing
their seeds. Plants reciprocate to the animals by
offering the rewards in the form of pollen, nectar or
juicy nutritious fruits. This system should also safe
guard against ‘cheaters’.
Ficus – Wasp
Plant animal interactions often involve co-evolution of the mutualist, that is the evolution of the
flower and pollinating agent.
In Ficus trees, there is a tight one to one relationship with plant & pollinator agent WASP. This
relationship explains that for very Ficus tree, the pollinating agent is WASP only, no other insect
involve in it.
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The female WASP uses the fruit not only as an opposition site but uses the developing seeds within
the fruit for nourishing its larvae.
The WASP pollinates the Ficus inflorescence while searching for suitable egg laying sites. In return,
for the flavour of pollination, the Ficus offer the WASP some of its developing seeds as food for the
developing WASP larvae.
ORCHID- HONEY BEE ASSOCIATION
Orchids show bewildering diversity of floral patterns, which are meant for attraction of suitable
pollinating agent and ensure guaranteed pollination by them. They are Bees & Bumble bees. In this
relation, only few orchids offer rewards, not all.
The Mediterranean Orchid Ophrys employs sexual deceit, to get pollination by the Bee species.
In the plant, one petal of its flower resembles the
female bees, in its size, colour and markings.
The male bee is attracted by this petal during
reproduction by perceiving as a female bee. The
male bee pseudo copulates with the flower. During
this process, pollen of this flower falls on male bee
body.
male bee
pollen
When the same male bee wants to pseudocopulate with another flower, pollen is transfered to the
stigma of that flower. It leads to the occurrence of pollination. Here we can observe the co-evolution
of partners. If the female bee’s colour pattern changes for any reason during evolution, pollination
success rate will be reduced unless the orchid flower co-evolve to maintain the resemblances of its
petal to the female bee.
PROTOCOOPERATION
It is non-obligatory mutually beneficial relationship which develops when two different organisms
get associated.
a) Bubalcus ibis (Cattle Egret) feeds on lice and ticks of cattle.
b) Buphagus(Ox pecker) on skin parasites of Rhino.
c) Pluvianis (Crocodile Bird) rids Crocodile of leeches sticking inside its mouth while Shrimp eats
up the parasites on the body of fish.
Bubalcus ibis
Buphagus
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Pluvianis
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AMENSALISM
It is the association in which one inhibits the growth of other by secreting chemicals. This phenomenon
is called ANTIBIOSIS.
The process of preventing growth of other organisms through secretion of toxic chemicals is called
ALLOPATHY.
a) Smoother crops do not allow weeds to grow.
Eg: Sorghum, Sunflower, Barley, Sacred Basil does not allow other plants to flourish nearby.
Convolvulus arvensis inhibits the germination of wheat seeds.
Sorghum
Barley
Sunflower
Sacred Basil
Trichoderma checks the growth of Aspergillus, Chlorella inhibits the growth of Nitzschia frustrulum.
Tagetus kills soil nematodes.
Juglans regia (Walnut) produces allochemic juglone for preventing growth of Apple, Tomato, Alfa
alfa, etc.
Chlorella
Nitzschia frustrulum
Juglans regia
AUTOPATHY
The process of inhibition of their own organisms
by an oraganism is called Autopathy.
Eg: Grevillea robusta (Silver oak) does not allow
its own seeds to germinate.
Grevillea robusta (Silver oak)
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SUMMARY
1. In the nature, different organisms adopted different environments for their survival and
reproduction.
2. MAJOR ABIOTIC FACTORS: TEMPERATURE, WATER, LIGHT and SOIL.
3. Generally internal environment is stable in most of the organisms. It is called HOMEOSTASIS.
4. Homeostasis of the organisms is maintained by artificial methods. Living organisms core with
the situations by means of various possibilities like Regulate, Conform, Migrate, and Suspend.
5. Adaptations are in morphological, physiological and behavioural in nature.
6. XEROPHYTES: These plants have a thick cuticle on their leaf surfaces and have their stomata
arranged in deep pits to minimise water loss through transpirations.
7. ALTITUDE SICKNESS - It is the most important adaptation experienced by the people who
move to the high altitudes.
8. DESERT LIZARD – These organisms maintain the constant body temperature by behavioural
means. They bask in the Sun & absorb heat when their body temperature drops below the
comfort zone, but move into shade when the ambient temperature starts increasing.
9. A group of organisms of similar species belongs to same locality is called Population.
10.Every population expresses certain attributes to survive in the environment. They are: Birth &
Death rate, Sex ratio, Age of the organisms and Population size/ Population density.
11. The number of individuals confined to a particular habitat is called Population size.
12.In the nature, the growth of a population with time show specific & predictable pattern of
population growth.
13.The sum of abiotic and biotic factors which checks the rise in population size and prevents the
species to realise its biotic potential is called Environmental resistance.
14.The life history of an organism depends upon the abiotic & biotic factors available in that
particular habitat. It is variable from one species to another species.
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