HS Biology Notes

1. Population Ecology

2. What is Population?
A group of the same species
that lives in one area

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

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

15. Types of Migration
Immigration
The movement of individuals into an area
Emigration
The movement of individuals out of an area

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?

19. Factors affecting population
Carrying Capacity (K)
the maximum number of organisms a
given area can support

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

23. What limits population growth?

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

25. R-strategist make lots of babies!

26. Here’s what the graph looks like!

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

28. Kangaroos are K-Strategists!

29. Here’s what the graph looks like!

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.