Population Ecology Fundamentals and types

Fundamentals of population Ecology

1. Fundamentals of
population ecology
Presented By :
➢Shahnaz 5025
➢SalihaAfzaal5011
➢GhaziaBatool 5001
➢Noor Fatima 5016
➢Mehrunnisa5006

2. POPULATION ECOLOGY:
1.Population ecology is the study of populations in relation to the
environment. It includes environmental influences on population density
and distribution, age structure, and variations in population size.
❖CHARACTERISTICS OF POPULATION:
●Population size
●Population density
●Dispersion patterns
●Demographics
●Survivorship curves
●Population growth
Ghazia5001

3. 1.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

4. 1.POPCULATION SIZE:
The death rate, which is
also the ratio of the total
number of deaths to the
total population.
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:
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.
1
3
2
4

5. 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.
Population Change calculation:
Population Change = (births + immigration) -(deaths + emigration)

6. 2.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
There are two types of density
-■Crude density-It is the density per unit total space.
■Specific (ecological) density-It is the density per unit of
habitat space.
Shahnaz 5025

7. Methods of calculation:
1.Total Count
Method:
•Usually population size
is estimated by counting
all the individuals from a
small sample area then
calculated for large area.
The Mark-Recapture:
●MarkRecapturetechnique
isusedtoestimatethe
sizeofapopulationwhere
itisimpracticaltocount
everyindividual.
•Thebasicideaisthatyou
captureasmallnumber
ofindividuals,puta
harmlessmarkonthem,
andreleasethemback
intothepopulation.
Quardratsampling
method:
●In this method, the window
containing the point
pattern is divided into a
grid of rectangular tiles or
‘quadrats’.
1 2
3

8. The Mark-
Recapture:
Where a small random sample of the
population is captured, marked, then
release to disperse within the general
population .
The marked individuals mix with the
unmarked individuals within a period
of time are randomly mix.
The population was resampled and
the number of marked and unmarked
individuals is recorded . And it was
considered as second sample taken
in the same ratio as first one.

9. We can use a simple formula for estimating total population size
(N):
Total individual mark in first sample *size of second sample
Number of marked individual re captures in second sample
N =

10. 1.CLUMPED DISPERSION:
3.POPULATION DISPERSION:
The dispersion of a population is the pattern of spacing among individuals
within the geographic boundaries.
Clumped is a pattern when individuals are aggregated in patches.
Most frequent pattern of distribution in a population.
Reasons:
1.immigrationarea of habitat are more suitable than others.
2.Heterogeneous environment with resources concentrated in
patches.
3.Tendency of offspring to remain with parents.
4.Mating or social behavior of the individuals.
Saleha 5011

11. 2.UNIFORM DISPERSION:
Evenly spaced distributions, in which members of the population maintain a minimum
distance from one another.
Reasons:
In plants due to competition for water, sunlight, or available nutrients.
Creosote bushes in the Mojave desert.
In animals due to strong territoriality.
3.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 microenvironments within their habitat.

12. FACTORS AFFECTING DISTRIBUTION:
●Floods
●Hurricanes
●Unseasonable
●Predation
●Weather
●Parasitism
●Fire
●Infectious Disease
●Clear Cutting
●Pesticide Spraying

13. 4.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.
1.Sex ratio:
●It is the ratio of males to females in a population:
1.Primary sex ratio
2.Secondary sex ratio
3.Tertiary sex ratio.
●The human sex ratio is of particular interest to anthropologists and demographers.
2.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.
Noor Fatima
5016

14. 3.Population Pyramid:
●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).
4.Life Table:
A life table (mortality table) is a table which shows, for each age, what the probability is that a person of that
age will die before his or her next birthday.
From this starting point, a number of inferences can be derived.
●The probability of surviving any particular year of age
●Remaining life expectancy for people at different ages
Separately for men and for women because of their substantially different mortality rates.

15. 5.POPULATION GROWTH:
Population growth refers to the increase in the number of individuals in a population over time. It's influenced by
factors like births, deaths, immigration, and emigration. There are two main types of population growth:
exponential growth and logistic growth.
1.Exponential Growth:
●In exponential growth, the population size increases at a constant rate over time.
●This type of growth occurs when resources are unlimited, and there are no limiting factors to population
increase.
●The growth rate remains the same regardless of the population size.
●It's represented by a J-shaped curve on a graph.
2. Logistic Growth:
●Logistic growth occurs when a population's growth slows and then stops, following a period of exponential
growth.
●This type of growth occurs when environmental factors limit population size, such as limited resources or
space.
Mehrunisa5006

16. Thankyou