ORGANISM AND POPULATION || BIOLOGY || CLASS 12 ||

2. Ecology: Ecology is the branch of science that studies the
relationship between organisms and their physical & biological
environment.
ORGANISM
• Survival and Reproduction ; unit of Natural selection
POPULATION
• Population Dynamics; unit of Evolution
COMMUNITY
• Interactions among populations
ECOSYSTEM
• Energy flux and cycling of nutrients
BIOSPHERE
• Global Processes
Level of Organization in ecology:

3. Organisms : Organisms form the basic unit of study in ecology.
Species : Organisms with similar features and the potential to interbreed
among themselves and produce fertile offspring, constitute a species.
Populations : Population is a group of individuals of the same species,
inhabiting in a given area.
Biological Community : Biological community is constituted by an
assemblage of the populations of all different species that live in an area
and interact with each other. A biotic community has a distinct species
composition and structure.
Ecosystem : Is a biological system in nature and composed of a biotic
community integrated with its physical (abiotic) environment through the
exchange of energy and recycling of the nutrients.

4. Habitat : Habitat is the place where an organism lives.
Biomes : Biomes is a very large unit, constituting of a major vegetation
type and associate fauna found is a specialized zone.
Niche : The ecological niche of an organism represents the range of
conditions that it can tolerate the resources it utilizes and its functional
role in the ecological system. Each species occupies a distinct niche and
no two species occupy the same niche.
Biosphere : It is the sum total of all the biomes on the earth.
Environment : Environment is a sum total of all biotic and abiotic factors
that surround and potentially influence an organism. Temperature, water,
light and soil are the major abiotic factors.

5. BIOMES
• Large ecosystem are called Biome.
• Each Biome is identified by its climax community.
• Altitude and latitude determine the boundary of Biome.
• Annual variations in the intensity and duration of temperature and
precipitation are responsible for the formation of major biomes.

6. S. No. Biome Location Vegetation
1. TUNDRA Tundra region Lichen, Moss, Grass
2. NORTHERN
CONIFEROUS
South to tundra Pine, Deodar,
Cypress
3. TEMPERATE DECIDOUS Centrally located Oak
4. TROPICAL DECIDOUS Plains and low hilly areas Sal, Teak, Tendu
5. TROPICAL RAIN FOREST Equatorial region Hopea
6. MEDITERRANEAN
FOREST
Pacific coast of America
and Australia
Small trees and
Shrubs
7. TROPICAL SAVANNA South America and south
Australia
Coarse grasses.
Large trees
8. GRASS LAND
9. DESERT Asia, North Africa

7. Name of Grassland Place
Prairies North America
Pampas South America
Steppes Europe and Asia
Tussocks New Zealand
Veldts Africa
MAJOR GRASSLANDS

8. BIOTIC
FACTORS
PATHOGENS
PARASITES
PREDATORS
COMPETITORS
ABIOTIC
FACTORS
TEMPERATURE
WATER
LIGHT
SOIL
FACTORS EFFECTING ECOLOGY

9. ABIOTIC FACTORS
1. Temperature:
The physiological functions and geographical distribution of
organisms is governed by temperature.
Temperature affects the kinetics of enzymes, BMR (Basic Metabolic
Rate) and other physiological actions in organisms.
On the basis of temperature organisms are classified into 2 categories-
A. Eurythermal: A few organisms which can tolerate wide range of
temperatures are called eurythermal organisms.
B. Stenothermal: Many organisms which can tolerate narrow range
of temperatures are called stenothermal organisms.
C. Ectotherms / Poikilotherms / Cold blooded animals
D. Endotherms / Warm blooded animals

10. HOMEOSTASIS –
The process by which organism maintain constant internal
environment with respect to outside environment.
Temperature effect a no. of morphological characters in various
organism
A. Bergman rule – Birds and mammals attain greater body size in
colder regions and lesser in warmer regions.
B. Allen's rule – Animals from colder climate generally have shorter
ears and limbs to minimise heat loss.
C. Jorden’s rule – Fishes occurring in cold water have more vertebra
than those found in warmer water.

11. D. Gloger’s rule – Animals of tropic region are more darker in
colour and heavily pigmented than those in arctic region.
E. Rensch’s rule – Birds of colder region have narrow wings than
those found in warmer region.

12. THERMAL STRATIFICATION IN LAKES
3 layer on the basis of temperature.
1. Epi-limnion – Top most layer
exposed to solar radiation
2. Meta-limnion- transition zone;
max temp. change
3. Hypo-limnion- basal region ; low
temperature

13. 2. Soil:
Nature and properties of soil depends on climate, weathering process.
The process of soil formation by breaking of rocks is called
Peadogenesis
The physical and chemical properties of soil determine the type of
plants that can grow in a particular habitat.
The characteristics of the bottom sediments of aquatic environment
determine type of benthic animals that can live there.

14. On the basis of agents involved in formation of soil it is of following
types :
1. Alluvial soil- make through water
2. Colluvial soil- make through gravity.
3. Galacial soil – make through ice.
4. Eolian – make through wind.

15. SOIL PROFILE
Vertical section of soil
representing its morphological
appearance.
Consist of 5 layers –
1. O-layer : humus content
2. A-layer : minerals particles
3. B-layer : big soil particles
4. C-layer : weathered rocks
5. R-layer : parental rocks

16. SOIL ORGANIC MATTER
The dead organic matter present in the soil is called humus which is
formed by the decomposition of plant and animal remains.
Freshly fallen plant and animal material is called Detritus or Litter
Partially decomposes litter is called Duff
Fully decomposed litter is called Humus.
Litter Duff Humus

17. Decomposition :
Breakdown of complex organic matter into simpler organic substances is
called decomposition.
Steps in Decomposition –
1. Fragmentation – Breakdown of detritus into smaller particles.
2. Leaching – movement of water soluble inorganic nutrients into the
soil.
3. Catabolism – degradation of detritus into simpler organic substance
with the help of bacterial and fungal enzymes.
4. Humification – accumulation of dark coloured substance called
humus.
5. Mineralisation – release of inorganic nutrients.

18. 3. Light:
It is a complex physical environmental factor.
light is important abiotic factor bec. the autotrophs prepares its food by
photosynthesis.
Sciophytes : Small herbaceous plants and some shrubs live under the
canopy forest trees are adapted to photosynthesis under very low light
intensities.
Animal use the seasonal variations in the light intensity and photoperiod
as cues for timing of forage, reproduction and migration.
The distribution of red, green and brown algae at difference depths of
water depends on the light, red algae can live in very deep water.

19. Solar constant – solar radiation before entering the atmosphere carries
energy at a constant rate of 2 cal 𝑐𝑚−2 𝑚𝑖𝑛−1 known as solar constant.
UV radiation is distinguished in
1. UV-C : 100-280 nm
2. UV-B : 280-320 nm
3. UV-A : 320-400 nm
AL-BIDO VALUE- The ability of a surface to reflect the incoming
radiation is called albido value.
It is 80% for fresh snow, 20-30% for sand and 5-10% for forest

20. 4. Water
Important factor influence the life of organisms.
The productivity and distribution depends on water.
For aquatic organisms, chemical composition , pH, salinity and
temperature of water are important.
Euryhaline: The organisms which can tolerate wide range of salinity are
called euryhaline organisms.
Stenohaline: The organisms which can tolerate narrow range of salinity
stenohaline organisms.

21. Response to Abiotic Factors
1. Regulators :
Some organisms are able to maintain homeostasis by physiological
(Some times behavioral) means which ensures body temperature,
constant osmotic concentration.
All birds and mammals, a very few lower vertebrates and invertebrates
are regulators (Thermoregulation and osmoregulation).
For example, human beings maintain their body temperature by
sweating in summer and shivering during winter season. Plants do not
have such mechanisms to maintain internal temperatures.

22. 2. Conformers :
Majority of animals and nearly all plants cannot maintain a constant
internal environment.
Their body temperature changes with the ambient temperature. In
aquatic animals the osmotic concentration of the body fluids change
with that of the ambient water and osmotic concentration.
Some species have evolved the ability to regulate, but only over a
limited range of environmental conditions, beyond which they simply
conform.
Thermoregulation is energy-expensive process. Heat loss or gain is a
function of surface area. Therefore small animals are not found in
polar region.

23. 3. Partial regulators :
Hairs on the body acts as heat insulator.
In smaller organisms the surface area is large as compared to the
volume. But in large animal this ratio is small. So, the larger animals
effectively controls the body temperature.
4. Migration :
The organisms can move away temporarily from the stressful habitat to
a more comfortable area and return when stressful period is over.
5. Suspension:
Organisms that cannot migrate , suspend their metabolic functions
during stressful period. It is called suspension.
E.g. Hibernation, aestivation, Diapause.

24. • Hibernation: Hibernation is a process by which the animals avoid
the stress and become inactive during winter.
Ex: Polar bear, Frogs, Lizards
• Aestivation: Aestivation is a process by which the animals avoid the
stress and summer related problems and become inactive during
summer.
Ex: snails and fishes
• Diapause: It is a stage of suspended development seen in many
zooplanktons to avoid unfavorable conditions.

26. Adaptation
Adaptation is any changes of the organism (morphological,
physiological, and behavioral) that enables it to survive and reproduce
in its habitat.
Adaptations have evolved over a long period of time and are
genetically controlled.
Examples:
Desert Plants: have thick cuticle on leaf surface.
• Sunken stomata.
• leaves modified into spines.
• Due to CAM pathway photosynthesis the stomata remain
closed during the day.
• Ex: Opuntia, cactus etc.

27. Aquatic Plants: Have evolved aerenchyma for buoyancy and floating.
leaves have waxy covering.
Desert animal: Kangaroo rat living in the desert of North America
never drink water. The water requirement is by internal fat oxidation (in
which water is the by product).
It is also able to concentrate its urine so that the minimal volume of
water is lost during excretion

28. || POPULATIONS ECOLOGY ||

29. Population Attributes
Population is a group of individual living in a particular geographical
area.
A population has certain attributes that an individual does not possesses.
Important characteristics of a population are :
1. Population density :
Population density of a species is the number of individuals of a species
per unit area or volume
Population density =
Number of individual in a region (N)
Number of unit area in a region (S)

30. 2. Birth rate or Natality Rate :
It is expressed as the number of births per thousand individuals of a
population per year.
3. Death rate or Mortality rate :
It is expressed as the number of deaths per thousand individual of a
populations during a given period.
4. Sex ratio :
It is expressed as the number of females per 1000 males of a population
in given time.

31. Age pyramid
A population at any given time is composed of individuals of different
age group.-
1. Pre-reproductive (0-14 years)
2. Reproductive (14-44 Years)
3. Post- reproductive (45 and above)
If the age distribution is plotted for the population, the resulting
structure is called as age pyramid.
For human population, the age pyramids show the age distribution of
males and females in a combined diagram.
The shape of pyramids reflects the growth status of the population i.e.
an expanding/ growing population, a stable population, a declining
population.

33. Population Growth
The size of population keeps changes with the time, depending on the
factors like:
1. Food available
2. Weather
3. predator pressure
4. Competition.
The density of a population in a given habitat during a given period
changes due to four basic - Natality (N), Mortality (M), Immigration (I)
and Emigration (E).
Immigration : Number of individuals of the same species that have
come into the habitat from elsewhere during a given period.
Emigration : Number of individuals of the population who have left the
habitat and gone elsewhere during a given time period.

34. The natality and immigration contribute to increase in the size and
density of a population.
Mortality and emigration contribute to a decrease in population.
If ‘N’ is the population density at time t’ then, the equation for the
population growth is:
Nt = N0+[(B+I)- (D+E)]
• Nt = Population density at time.
• N0 = Population in beginning.
• B = Birth rate.
• I = Immigration.
• D = death rate.
• E = emigration.

36. Population Growth Models
1. Exponential Growth Model
When the resources availability is unlimited in the habitat, the
population grows in an exponential or geometric fashion,
Exponential Growth Equation is 𝑵 𝒕 = 𝑵 𝟎 𝒆 𝒓𝒕
Where,
𝑁𝑡 = Population density after time t
𝑁0 = Population density at time zero
r = intrinsic rate of natural increase
e = the base of natural logarithms (2.71828)
Exponential growth : ‘J’shape curve is obtained.
• When resources are not limiting the growth.
• Any species growth exponentially under unlimited resources
conditions can reach enormous population densities in a short time.
• Growth is not so realistic

37. 2. Logistic growth model
A population growing in a habitat with limited resources (food and
space) shows logistic growth :
Verhulst-Pearl Logistic Growth is described by the following equations
:
dN/dt = rN (K-N / K)
Where, N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity
• Logistic Growth (Sigmoid curve is obtained)
• When resources are limiting the Growth.
• Resources for growth for most animal populations are finite and
become limiting.
• The logistic growth model is a more realistic one.

39. Population Interactions
Living organisms interact in various ways to form biological
communities.
Interspecific interactions: It is the interactions of population of two
different species.
Intraspecific interactions: It is the interactions of individuals of the
same species.
Interaction are of following types –
• Predation
• Competition
• Parasitism
• Commensalism
• Ammensalism.
• Mutualism.

40. 1. Predation :
• Interaction between species involving killing and consumption of
prey is called predation.
• The species which eats the other is called the predator and the one
consumed is termed as the prey.
• The predator keeps check on prey population. The reduction in
predator population may lead to increase in prey population.
• Predators play important roles in ecosystem :
(a) Transfer of energy across trophic levels.
(b) Keep prey population under control : The invasive prickly pear
cactus was brought under control by introduction of a cactus-feeding
predator (moth) in Australia.
• Biological pest control methods : Used in agricultural are based on
the ability of predator to regulate prey population.

41. Examples :
(i) Biological control methods to control pests
(ii) Carnivorous animals like tiger eating deers, snake eating frog
(iii) Insectivorous plants like Nepenthes, Drosera, Utricularia
Prey species have evolved various defence mechanisms to reduce the
impact of predation –
• Certain insect species and frogs have camouflage (Cryptic
coloration).
• Monarch Butterfly is very distasteful to its prey bird. It has a special
chemical in its body. This chemical is produced during its caterpillar
stage by feeding on poisonous weeds.
• The problem of predation is more severe for plants than animals as
they cannot move.
• Plants have developed certain morphological and chemical defense
mechanism against herbivores.

42. 2. Competition:
• Competition is an interaction among the individuals of same species
(Intraspecific ) or between individuals of different species (Interspecific).
• Competition between the individuals of same species is for same
resources that are limited.
• In some case, resources need not be limiting for competition to occur,
the feeding efficiency of one species might be reduced due to the
interfering of the other species.
E.g. Abingdon tortoise in Galapagos Island became extinct within a
decade after goats were introduced into the island.
It was due to the fact that the goats had greater browsing efficiency than
the tortoise.

43. • Unrelated species also compete for same resources.
Ex:- flamingo & fish compete for zooplankton
Competitive release:
• "A species, whose distribution is restricted to a small geographical
area because of the presence of a competitively superior species is
called competitive release.
• These species is found to expand its distributional range dramatically
when the competing species is experimentally removed.
Gause’s Competitive Exclusion Principle :
It states, ‘that two closely related species competing for the same
resources cannot exist together and the competitively inferior will be
eliminated by superior’.

44. Resource Partitioning:
It is the mechanism meant for coexistence of species to face
competition .
According to this, if two species compete for the same resource, they
could avoid competition by choosing different times for feeding or
different foraging patterns.
Ex. MacArthur showed that five closely related species of Warbles
living on the same tree were able to coexist and avoid competition by
having behavioral differences in their foraging( hunting) activities.

45. 3. Parasitism:
• Parasitism is the interspecific interaction where one of the species
(Parasite) depends the other species (Host)for food and shelter.
• Host gets harmed and parasite gets benefitted.
• Parasites are host-specific and parasite and its host tend to co-evolve.
Co-evolve: It means that if the host evolves a special mechanism to
reject or resist the parasite, the parasite has to evolve the mechanisms to
neutralize them.
Parasitism also involves shelter, in addition to food obtained by a
parasite.
Parasites may be ectoparasites or endoparasites. Ectoparasites live on
the surface of their host while endoparasites live inside the body of the
host.

46. Parasites adaptations:
• Parasite tends to co-evolve.
• It may loss of sense organs.
• Presence of suckers or hooks.
• Loss of digestive system.
• High reproductive capacity.
Examples
(i) Cuscuta growing on shoe Flower plant
(ii) Head lice and humans
(iii) Ascaris, Taenia, Plasmodium causing diseases in humans
Example of Brood parasitism
(i) Koel laying its eggs in crow’s nest.

47. 4. Commensalism:
• It is the interspecific interaction in which one species benefits and the
other is neither harmed nor benefitted.
Ex:
• Epiphytes i.e Orchids growing on a tree branch.
• Barnacles growing on the back of whales.
• Association between Egret and grazing cattle. Egrets always forage
close to cattle are grazing because they easily get insects.
• The Clown fish living along with sea anemones. Clown fish get
protection from predators.
• Sucker fish on the back of shark
• Sea anemone on the shell of hermit crab

48. 5. Mutualism:
It is the interspecific interaction in which Both the species interact gets
benefit.
E.g.
• Lichens are relationship between Fungus and Algae/ Cyanobacteria.
• Mycorrhiza – an association of Fungus with roots of higher plants.
Fungi help to absorb nutrients from the rocks and plants provide
energy yielding carbohydrates to fungi.
• Plants depend on insects for pollination and in return they give them
nectar or pollens to eat.
• Animals help the plants in seed dispersal and in return they give fruits
to animals as food.
• fig tree and pollinator species of wasp. Fig species can be pollinated by
its partner wasp only.
• Rhizobium in root nodules of legumes

49. 6. Amensalism:
It is the interspecific interaction in which one is harmed and the other is
neither benefited nor harmed.
• E.g: Penicillium secretes chemical penicillin kills bacteria.

50. Interaction Species A Species B
Predation + -
Competition - -
Parasitism + -
Commensalism + 0
Ammensalism - 0
Mutualism + +
Population Interactions

51. • THANK YOU •