3. 5 Characteristics of Population
1. Geographic Distribution
2. Density
3. Dispersion
4. Growth Rate
5. Age Structure
4. Geographic Distribution
The range of the population
Describes the area that is inhabited
by the population
Such as:
The mold on a piece of bread
The migration area of whales
5.
6. Population Density
The number of individuals per unit area
# of individuals
Area (units2)
Variation in density depends on:
The species
The ecosystem
= population density
7. Practice Problem
If scientists sampling a population of
deer counted 200 individuals in an
area of 10 square kilometers, what is
the density of this deer population per
square kilometer?
A: 20 deer per square kilometer
8. 2000 U.S. population
density in persons
per sq. mile
(contiguous U.S.
only). Averaged on
a per-county basis.
Legend, light to dark
(white to dark blue):
0-1 (white)
1-4 (yellow)
5-9 (yellow-green)
10-24 (green)
25-49 (teal)
50-99 (dark teal)
100-249 (blue)
250-66,995 (violet)
9. Dispersion
The spatial distribution of individuals
within the population
Three types:
Clumped Dispersion
Even Dispersion
Random Dispersion
10. Clumped Dispersion
Individuals are clustered together
Occurs:
When resources (food, water, living
spaces) are clumped together
Species have a certain social behavior
For example: herding animals, flocks of
birds, schools of fish, hives of bees
11. Even Dispersion (a.k.a Uniform Dispersion)
Individuals are separated by a fairly
even distance.
Occurs:
As a result of social interaction
Individuals trying to get as far
away from each other as possible.
Limited resources, competition,
nesting
12. Random Dispersion
Location of one individual is
independent of the location of the
other individuals
Examples:
Seed dispersal by the wind or animals
13. Growth Rate
The amount by which a population’s size
changes in a given time.
A measure of the speed of reproduction
14. Factors affecting population size
1. The number of births.
2. The number of deaths.
3. Migration
The movement of individuals into
and out of a population
Immigration
Emigration
16. Population Dynamics
Population are dynamic, meaning that they:
Change in size and composition over time!
Considerations:
1. Birth rate: the number of births occurring in a given
period of time
2. Death rate or mortality rate: the number of deaths in
a given period of time
3. Life expectancy: the length of time an individual is
expected to live
17. If more individuals are being born
than die in a given period of time,
the population size will ___________.
If birthrate is equal to death rate, the
population size will ______________.
If the death rate is greater than the
birthrate, the population will ______.
increase
remain stable
decrease
18. Studying Population Density
Questions to be answered:
Why is the birth rate unusually high
(or low)?
Why are more individuals dying than
normal?
Is there a reason for an unusually high
immigration or emigration?
20. Carrying Capacity
The actual size of the population is
usually higher or lower than the carrying
capacity
Below capacity
Birth rate increases
Above capacity
Population will die or starve
21. Factors Limiting Population
Limiting Factor – the resource that runs
out first
Helps to determine carrying capacity
Examples include:
1. Competition
2. Predation
3. Parasitism and disease
4. Drought and other climate extremes
5. Human disturbances
22. Types of Limiting Factors
1. Density-Dependent Factors
Only when the population density
reaches a certain level.
2. Density-Independent Factors
Unusual weather or natural disasters
Floods and fires
Human activities
Clear-cutting a forest or damning a
river
24. R-Strategists
Think “R” for “reproduction”
Population usually NOT near carrying capacity
J-curve growth (high growth rate)
Exponential Growth
Highly affected by abiotic factors like weather
Small body size and short life span
Have many offspring in a short time
27. K-Strategists
Think “K” for “carrying capacity”
Population lives near its carrying capacity
S-Curve Growth
Logistic Growth
Highly affected by biotic factors like
competition
Usually large body size
Have few offspring, but live a long time
30. Age-Structure Diagrams
The growth of a
population depends on:
how many people make
up the given population.
The future growth of a
population is predicted
using:
“age-structure diagrams.”
31. An “age-structure diagram” shows:
the population of a country broken down by gender
and age group.
Each bar in the diagram represents individuals within a 5-
year range. Males are shown to the left of the center line.
Females are shown to the right of the center line.
32. Look at the age structure of population A.
There are many more
_________ than ______
groups.
In each higher age
group, there are fewer
and fewer individuals.
It can reasonably be
predicted that population
A will experience:
rapid growth in the
future as the large
number of children reach
adulthood.
children older
33. Human Population Growth
For most of human
existence, the population
grew very slowly. There
were many limiting factors
that kept the human
population low:
1. Food was not always
readily available.
2. Diseases were rampant.
34. About 500 years ago, the human population began to
grow at a staggering rate. Reasons for this include:
1. The beginning of
agriculture and industry
made life much easier
and much safer.
2. Food is available on a
regular basis.
3. Goods can be shipped
around the world.
4. Improved sanitation and
living conditions
eliminated the high
levels of diseases.
5. Death rate dropped while
birth rate increased.
35. As a result, the human
population is experiencing
____________________.
The human population
________ continue to grow in
this manner.
The resources on Earth are
________.
exponential growth
cannot
limited
The questions to be answered are:
When will we reach the limit of these
resources?
How large will the population get?
Will the planet be able to support
this huge human population?
36. Demography is the scientific study:
of human populations.
Some countries today
have a much higher
growth rate than other
countries.
Birthrates, death rates,
and the age structure of
a population help
predict why some
countries have a higher
growth rate than other
countries.