Population ecology examines how populations change over time based on birth, death, immigration, and emigration rates. Key concepts include: - Populations have a density that can be influenced by density-dependent and density-independent factors. - Natality is the birth rate and mortality is the death rate. These determine a population's growth rate. - Populations can exhibit exponential or logistic growth patterns depending on available resources/carrying capacity. - Reproductive strategies like r/K selection influence life history traits and population dynamics. - Competition between species occupying the same niche frequently leads to competitive exclusion of one species.

1. Population Ecology
By
Mr. K.C.More
Assistant Professor
Dept of Botany
SGBAU

2. Population ?

3. • Population:
–All the individuals of a species (or Collection of
individuals of same species) that live together in
an area ex. Tigers in Melghat, tigers in
Sundarban, Monkeys in Manas Sanctuary
(abhayarnya)
• Individuals in a population
– rely on the same resources,
– are influenced by the same environmental factors, and
– are likely to interact and breed with one another.

4. Demography:
The statistical study of populations,
allows predictions to be made about
how a population will change in future

5. Population Dynamics
• Key Features (Characteristics) of Populations
– Size (represented by Density)
– Density
– Growth rate =Natality, Mortality
– Migration =Immigration and Emigration
– Dispersion
– Age distribution

8. Crude density: It is the density in which number or biomass of the
individuals of the population is expressed per unit total space.
Specific or Ecological density: It is the density in which number or
biomass of the individuals is expressed per unit of habitat space i.e.
available area or the volume that can actually be colonised by the
population.
Density of the population can be divided into two main categories:

9. How Do You Affect Density?
1. Immigration: movement of individuals into a population
2. Emigration: movement of individuals out of a population
3. Density-dependent factors: Biotic factors in the
environment that have an increasing effect as population
size increases (disease, competition, parasites)
4. Density-independent factors: Abiotic factors in the
environment that affect populations regardless of their
density (temperature, weather)

12. It is simply a broader term covering the production of new
individuals of any organism.
These new individuals are born, hatched, germinated, arise
by division, etc.
In human population, natality rate is equivalent to the
‘birth rate’. Natality rate is the number of offspring
produced per female per unit time.
Natality

13.  Maximum or absolute or physiological natality:
It is the theoretical maximum production of new individuals
under ideal conditions. i. e. No ecological limiting factors,
reproduction being limited only by physiological factors. It is
constant for a given population. This is also called fecundity rate.
 Ecological or realized natality: It is a natality which refers
to population increase under an actual, existing specific
condition. It takes into account all the possible existing
environmental conditions. This is also designated as
fertility rate. Not constant but Vary with size and Age distribution
and Env conditions
Two types of natality:

14. It refers to death of individuals in the population. Mortality can be expressed as the
number of individuals dying in a given period (deaths per time), or as specific
rate in terms of units of the total population.
Mortality can be distinguished into two types:
Minimum mortality: 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 by their physiological longevity.
Ecological or realized mortality: It is the actual loss of individuals under a given
environmental condition. It is not a constant and varies with population and
environmental conditions.
After getting the knowledge of natality and mortality, let’s understand the term vital
index of population.
Vital Index
A percentage of birth to death ratio is called vital index.
Mortality (Death Rate)

16. A life table is an age-specific summary of the survival pattern of a population.
Information on natality and mortality in different ages and sexes can be
combined in the form of life tables. From these it is possible to estimate the
growth or decline of a population. In this, each table possesses different columns
for age of individuals; number surviving to each age group; the number dying in each
age group; the proportion dying from the previous age category; fertility rate and the
number of young born by each age group.
The best way to construct a life table is to follow the fate of a cohort, a group of
individuals of the same age, from birth throughout their lifetimes until all are dead. To
build a life table, we need to determine the number of individuals that die in each age
group and calculate the proportion of the cohort surviving from one age to the next.
The information obtained from these figures provides the net reproductive rate of the
population. i.e. offspring left by each individual. Similarly, life tables also provide the
information regarding mortality in a logarithmic form. These are then used to calculate
the rate of population growth.
Life Tables

17. Survivorship curves
A graphic way of representing the data in a life table is a Survivorship curve.
Survivorship Curves represent age-specific patterns of death (mortality) for a
given population in a given environment. Or it plot the number of surviving
individuals to a particular age

20. First is Highly convex curve. It is characteristic of the species in which the
population mortality rate is low until near the end of life span. Thus,
such species tend to live throughout their life span, with low mortality. Many
species of large animals as deer, mountain sheep and man, etc. show such
curves. (Iteroparous = reproduce many time during life).
Third is Highly concave curve. It is characteristic of such species where
mortality rate is high during the young stages. Oysters, shell fish, oak trees,
etc. show this type of survivorship. (Semelparous= reproduce once in life)
Second is Diagonal curve. If age-specific survival is more nearly constant,
the curve approaches a diagonal straight line as shown in the curve.. It thus
shows a constant proportion of organisms dying per unit time. Probably, no
population in the real world has a constant age-specific survival rate
throughout the whole life span. Thus, a slightly concave or sigmoid curve B3
as shown in the figure is characteristic of many birds, mice and rabbits. In
this, the mortality rate is high in the young but lower and more nearly
constant in the adult. Still, in some insects such as butterflies, there is
expected generally a ‘stair shape’ type of curve as shown in curve B1.

22. • Dispersion: describes the spacing of
organisms relative to each other (or spatial
and temporal distribution of individual in
population)
– Clumped
– Uniform
– Random
Dispersion

23. Dispersion

26. Population Dispersion

27. Age Distribution
• Distribution of males and females in each age
group of a population
• Used to predict future population growth

34. Population growth
• Growth Rate:
– Birth Rate (natality) - Death Rate (mortality)
– How many individuals are born vs. how many die
– Birth rate (b) − death rate (d) = rate of natural
increase (r)
Change in the numbers of individuals in a population with time

35. Factors affecting change in population Size

37. Types of growth pattern

39. Figure 35.3A
Exponential Growth Curve

41. Carrying Capacity
• Carrying Capacity (k):
– The maximum population size that can be supported by
the available resources
– There can only be as many organisms as the
environmental resources can support

42. Measurement of Growth rate

43. Difference between Exponential and Logistic growth

45. Difference between Exponential and Logistic growth

50. Metapopulation
Set of local populations connected by dispersing individuals
known as Metapopulation

54. Reproductive Strategies
• R Strategists
(Opportunist)
 Short life span
 Small body size
 Reproduce quickly
 Have many young
 Little parental care
 Ex: cockroaches,
weeds, bacteria
annual plants,
Algae and rodents

55. Reproductive Strategies
• K Strategists
(competitors)
(Under constant/ stable Env
reach to carrying capacity)
 Long life span
 Large body size
 Reproduce slowly
 Have few young
 Provides parental care
 Ex: humans, elephants

57. Position of r and k species on the sigmoid population growth curve

58. Factors Limiting Growth Rate
• Declining birth rate or increasing death rate are
caused by several factors including:
– Limited food supply
– The buildup of toxic wastes
– Increased disease
– Predation

59. Human Population Growth
• J curve growth
• Grows at a rate of about 80 million yearly
– r =1.3%
• Why doesn’t environmental resistance take effect?
– Altering their environment
– Technological advances
• The cultural revolution
• The agricultural revolution
• The industrial-medical revolution

60. The Human Population
• Doubled three times in the last three centuries
• About 6.1 billion and may reach 9.3 billion by
the year 2050
• Improved health and technology have lowered
death rates

61. History of the Human Population

64. When two different species overlap in the same biological niche, they are
a . unaffected by one another.
b . dependent on one another.
c . in co-operation with one another.
d . in competition with one another.
e . dependent on different food supplies.

65. Competitive exclusion is most likely to occur between two
(A) closely related species occupying different niches
(B) closely related species occupying the same niche
(C) related species occupying different habitats
(D) unrelated species occupying different niches
(E) populations of the same species
Competition for food would probably be most severe between two
(A) closely related species in different niches
(B) closely related species in similar niches
(C) unrelated species in different communities
(D) unrelated species in the same community occupying different niches
(E) ecological equivalents in different niches

66. An overlap in the niches of two species will most frequently result in
(A) interspecific cooperation
(B) a hybridization of species
(C) a mutualistic symbiotic relationship
(D) an increase in the biomass
(E) interspecific competition
Which of the following best explains why many different species can live
together within an ecosystem with limited resources?
(A) Each species lives in a slightly different habitat.
(B) Each species occupies a different niche.
(C) Each species inhabits a different biome.
(D) Each species makes up a different population.
(E) Each species functions at a different trophic level.

70. Thank You!