These slider covers: *Population Population Characters *Population Types =Population size =Population density =Dispersion patterns =Demographics =Survivorship curves =Population growth

1. SUBMITTED BY:SHERAZ AHMAD
DEPARTMENT:ZOOLOGY
SEMESTER:7TH
R.NO:9500
SUBJECT:ENVIRONMENTAL
BIOLOGY
TOPIC:POPULATION AND BASIC
POPULATION CHARACTERS
SUBMITTED TO: MR.IKRAM ULLAH

2. INTRODUCTION TO POPULATION:
The term population has its origin in the Latin word
populus, meaning people.Population can be defined differently by different Ecologist in which some are:
• Krebs (1972). A group of organisms of the same species occupying a particular space
at a particular time
• Cole (1957). A biological unit at the level of ecological integration where it is
meaningful to speak of birth rate, death rate, sex ratios, and age structure in
describing properties or parameters of the unit.
• Gotelli (1998) A group of plants, animals, or other organisms, all of the same species,
that live together and reproduce.

3. • Populations are dynamic entities. Populations consist all of the species living within a
specific area, and population fluctuate based on a number of factors: seasonal and yearly
changes in the environment, natural disasters such as forest fires and volcanic eruptions,
and competition for resources between and within species.
• Members of a population rely on the same resources, are influenced by similar
environmental factors, and have a high likelihood of interacting with and breeding with one
another
• Populations can evolve through natural selection acting on heritable variations among
individuals and changing the frequencies of various traits over time.

4. Types of Population
Some ecologists recognized following two types of
populations :
1. Monospecific population is the population of
individuals of only one species; and
2. Mixed or polyspecific population is the population of individuals of more than one
species. Often ecologists use the term community for polyspecific
population.

5. BASIC POPULATION CHARACTERES
Population have the following basic characters:
• Population size
• Population density
• Dispersion patterns
• Demographics
• Survivorship curves
• Population growth

6. POPULATION SIZE:
In population genetics and population ecology, population size (usually denoted N) is the
number of individual organisms in a population”.
Factors that Govern Population Size
1. Crude Birth Rate (CBR)
2. Crude Death Rate (CDR)
3. Immigration
4. Emigration

7. • Factors that increase population size
1. Natality is recruitment to a population through reproduction.
2. Immigration from external populations e.g. Bird migration.
• Factor reducing population size
1. Mortality which is the death rate from any source e.g. predation.
2. Emigration, where individuals leave the population for another habitat

8. • Natality
The birthrate, which is the ratio of total live births to total population in a particular area over
a specified period of time
• Mortality
The death rate, which is also the ratio of the total number of deaths to the total population.
• Immigration
The number of organisms moving into area occupied by the population is called immigration.
• Emigration
The number of organisms moving out of the area occupied by the population is called
emigration.

10. POPULATION DENSITY:
• Population density is a measurement of the number of people in an area. It is an average
number”.
• It is usually shown as the number of people per square kilometer.
• Density = Population/ Area

12. NEED TO ESTIMATE POPULATION DENSITY
• 1. How to quantify nature – ecologist role
• 2. Estimates are allows for comparisons between different populations in terms of space
and time measure
MEASUREMENT OF DENSITY
Density is measured by two methods.
1. Total count method
2. Sampling method

13. TOTAL COUNT METHOD:
• Direct counting of populations.
• Possible for few animals.
• Breeding colonies can be photographed then later counted.
• Examples
Human pop census
Trees in a given area

14. SAMPLING METHOD:
• Depends on the type of organism and its natural abundance and distribution.
• Two broad categories:
1. Plot-based (quadrant) methods
2. Capture-based methods

15. QUADRAT SAMLING METHOD:
• Widely used in plant studies
• Total population = Average number per quadrat × Total area/Area of quadrat

16. MARK RECAPTURE METHOD:
• Used for very mobile or elusive species
• First used in the 1890s by C. G. Peterson to estimate fish abundance

17. POPULATION DISPERSION:
• The dispersion of a population is the pattern of spacing among individuals within the
geographic boundaries.
• Population dispersion is of three types:
1.Clumped Dispersion
2.Uniform Dispersion
3.Random Dispersion

18. CLUMPED DISPERSION:
• Clumped is a pattern when individuals are aggregated in patches.
• Most frequent pattern of distribution in a population
Reasons:
• Some area of habitat are more suitable than others
• Heterogeneous environment with resources concentrated in patches
• Tendency of offspring to remain with parents
• Mating or social behavior of the individuals

20. UNIFORM DISPERSION:
• Evenly spaced distributions, in which members of the population maintain a minimum
distance from one another.
• In plants due to competition for water, sunlight, or available nutrients
Example Creosote bushes in the Mojave desert
• In animals due to strong territoriality
Example The desert lizard Uta sp

22. RANDOM DISPERSION:
• It is a spacing pattern based on total unpredictability.
• Least common pattern of distribution
Reasons
• Members of a species do not frequently interact with one another
• Not heavily influenced by the microenvironments within their habitat

24. FACTORS AFFECTING DISTRIBUTION:
Density Independent
* Floods *Hurricanes
*Unseasonable Weather *Fire
*Clear Cutting *Pesticide Spraying
Density dependent
*Competition for Resources *Predation
* Parasitism *Infectious Disease

25. DEMOGRAPHY:
• Demography is the study of the vital statistics of a population
and how they change over time
• Two statistics that are of particular import are a population's
age structure and a population's sex ratio

26. SEX RATIO:
• It is the ratio of males to females in a population.
• Primary sex ratio
• Secondary sex ratio
• Tertiary sex ratio
• The human sex ratio is of particular interest to anthropologists and demographers

27. AGE STRUCTURE
• The age structure describes the number of individuals in each age class as a ratio of one
class to another.
• Age classes can be specific categories, such as people in the same age range

28. POPULATION PYRAMID
• Age structure diagram
• Graphical illustration that shows the distribution of various age groups & sex ratio in a
population.
• Three age categories:
1. Prereproductive (ages 0-14)
2. Reproductive (ages 15-44)
3. Postreproductive (ages 45 and up)

29. SURVIVORSHIP CURVE:
• Graph showing the number or proportion of individuals surviving at each age for a given
species or group (e.g. males/females).
• Constructed for a given cohort (a group of individuals of roughly the same age) based on
a life table.
• Three types
1. Type I
2. Type II
3. Type III

31. • Type I survivorship curves are characterized by high survival in early and middle life,
followed a rapid decline in survivorship in later life.
• Example: Humans
• Type II curves are an intermediate between Type I and III, where roughly constant mortality
rate is experienced regardless of age.
• Example: Some birds
In Type III curves, the greatest mortality is experienced early on in life, with relatively low
rates of death for those surviving this bottleneck.
Example: Octopus

32. POPULATION GROWTH:
• Refers to how the number of individuals in a population
increases (or decreases) with time.
• Controlled by the rate at which new individuals are added to
the population -- the birth rate, and the rate at which
individuals leave the population -- the death rate

33. EXPONENTIAL GROWTH:
• If a population has a constant birth rate through time and is never limited by
food or disease, it has what is known as exponential growth.
• With exponential growth the birth rate alone controls how fast (or slow) the
population grows
• Continuouspopulation growth in an unlimited environment can be modeled
exponentially.
dN / dt = rmax N
• As population size (N) increases, rate of population increase (dN/dt) gets
larger

34. • For an exponentially growing population, size at any time can be calculated as: Nt = N⁰ert
• Nt = number individuals at time t.
• N0 = initial number of individuals.
• e = base of natural logarithms.
• r (rmax ) = per capita rate of increase.
• t = number of time intervals

37. LOGISTIC POPULATION GROWTH:
• As resources are depleted, population growth rate slows and eventually stops: logistic
population growth.
• Sigmoid (S-shaped) curve
• Carryingcapacity (K) is the number of individuals of a population the environment can
support.
• Finite amount of resources can only support a finite number of individuals.

38. • dN/dt = rmaxN(1-N/K)
• rmax= Maximum per capita rate of increase under ideal conditions.
• When N nears K, the right side of the equation nears zero.
• As population size increases, logistic growth rate becomes a small fraction of growth rate.
• Highest when N=K/2

41. • LIMIT TO POPULATION GROWTH:
Environment limits population growth by altering birth and death rates.
Density-dependent factors
• Disease, Parasites, Resource Competition
• Populations do not show continuous geometric increase
• When density increases other organisms reduces the fertility and longevity of the
individuals in the population
• This reduces the rate of increase of the pop until eventually the pop ceases to grow
• The growth curve is defined as the sigmoid curve, S – shaped
• K = carrying capacity (upper asymptote or maximum value) – the maximum number
of individuals that environment can support
Density-independent factors
Natural disasters
Climate

45. Referances:
• Campbell/Reece Biology, 7th Edition, Pearson Education, Inc. 52-1.
• Ecology and Environment, P.D.Sharma, 10th edition
• Cell biology,Genetics,Molecular Biology,Evolution And Ecology,PS.Verma
and VK Agarawal
• https://www.slideshare.net/gurya87/population-ecology-11685161