1. Population Ecology

2. Characteristics of Populations
A group of individuals of the same species that live in the same area at the same time.
These are the important characteristics of a population:
1. Geographic distribution
2. Density
3. Dispersion
4. Growth rate
5. Age structure

3. Geographic distribution is the range of the population.
This term describes:
the area that is inhabited by the population.
The range can vary in ______. It may be just a few centimeters, such as the mold on a piece of bread. Or the range may be huge, such as the migration area of whales.
size

4. Population Density Population density is:
the number of individuals per unit area.
Density is one of the main characteristics that describes a population. There is tremendous variation in density depending on the _________ and the _____________. Some populations have _____ densities, while other populations have ______ densities.
species
ecosystem
low
high

5. Do Now
1. What is the population density of China? _____________ people per square mile
Population: 1,321,851,888
Area: 5,795,162 square miles
2. What is the population density of the U.S.? _____________ people per square mile
Population: 301,139,947
Area: 5,692,955 square miles
3. What is the population density of Canada? _____________ people per square mile
Population: 33,056,500
Area: 3,854,085 square miles

6. Clumped Dispersion Random Dispersion Even Dispersion Dispersion is….
…. the spatial distribution of individuals within the population.
The three types of dispersion are:
Clumped Dispersion
Random Dispersion
Even
Dispersion

7. Clumped Dispersion
a) In clumped dispersion the individuals are clustered together.
Clumped distributions often occur when:
resources such as food, water, or living spaces are clumped together.
Clumped distributions may also occur because a species has:
a certain social behavior, such as herding animals, flocks of birds, schools of fish or hives of bees.

8. Even Dispersion a) In an even dispersion, individuals are:
These penguins exhibit even dispersion because of aggressive interactions that occur between neighbors.
a) In an even dispersion, individuals are:
separated by a fairly even distance.
Even distributions are usually the result of _____________________, but the interaction results in the individuals trying to:
get as far away from each other as possible.
social interactions

9. Random Dispersion
a) In random dispersion, the location of one individual is independent of the location of the other individuals.
b) Random dispersal may result from seed dispersal:
by the wind or animals.
c) A forest or a field of wildflowers results from the random dispersal of seeds.

10. All populations are dynamic, meaning that they:
Population Dynamics
All populations are dynamic, meaning that they:
change in size and composition over time.
To understand the changes that are taking place in a population, the following must be considered:
Birth rate:
the number of births occurring in a given period of time.
Death rate or mortality rate:
the number of deaths in a given period of time.
Life expectancy:
the length of time an individual is expected to live.

11. Patterns of Mortality
The mortality rate of the individuals in the population generally follows one of the following patterns.
These are called __________________________ because they show the likelihood of ___________ at different _____ throughout the lifetime of the organism.
Number of survivors
survivorship curves
Age (years)
survival
ages

12. It drops steeply near the end indicating:
Type I Survivorship Curve:
This curve is:
flat at the start, indicating a low death rate in the early and middle stages of life.
It drops steeply near the end indicating:
a high death rate as the organisms become older.
An example is large mammals that produce very _____ offspring, but provide them with _______________.
few
good care

13. Type III Survivorship Curve:
a) This curve drops sharply at the start, indicating:
a high death rate among the young.
It flattens out as death rates:
decline for the few that do survive the early die-off.
c) This would include organisms that produce:
large numbers of offspring, but provide them with little or no care.
d) Examples include:
fishes, many plants, and most marine invertebrates.

14. Type II Survivorship Curve:
a) This curve is:
intermediate to the above 2 curves.
b) There is a constant death rate over the organism’s life span.
c) This may occur in rodents and lizards.

15. Population Growth
A population may remain very stable over time, or there can be fluctuations in population size.
At any given time a population may experience ___________________, or ______________.
tremendous growth
rapid decline

16. The amount by which a population’s size changes in a given time.
There are three factors that can greatly increase or decrease the size of a population.
1. The number of births.
2. The number of deaths.
3. The number of individuals that enter or leave the population.
Growth Rate:
The amount by which a population’s size changes in a given time.

17. increase stable decline
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 will remain ________ in size.
If the death rate is greater than the birthrate, the population will ________.
increase
stable
decline

18. …the movement of individuals into and out of a population.
Migration is…
…the movement of individuals into and out of a population.
Immigration:
The movement of individuals into an area.
Emigration: The movement of individuals out of an area.
Immigration would _________ the size of the population while emigration would cause the population to __________ in size.
increase
decrease

19. Two processes decrease the size of the population:
Two processes increase the size of the population:
birth rate and immigration.
Two processes decrease the size of the population:
death rate and emigration.

20. Under what conditions would rapid growth occur in a population?
There would have to be plenty of space and an abundance of food.
There could be no predators or disease.
If all factors for reproduction and growth are ideal, the population might grow ______________.
Exponential Growth
exponentially

21. Exponential growth describes a population that is increasing __________. The ________ the population gets, the ________ it grows.
rapidly
larger
faster

22. For example: A single bacterium can reproduce by dividing into two cells every 20 minutes.
At the end of the first 20 minutes, there would be two bacterial cells.
At the end of 40 minutes, four cells will have been produced, and by the end of the first hour, there would be eight cells.
This growth doesn’t seem too impressive at first.
But, if the number of cells doubles every 20 minutes, then at the end of one day the colony would contain 4.72 x 1021 cells (4,720,000,000,000,000,000,000 cells!)

23. Exponential Growth:
This occurs when the members of the population are reproducing at a constant rate.
ideal
Under _______
conditions, with ___________ resources, a population will grow exponentially.
At first, the population seems to be growing _______, but over time, the power of exponential growth can produce a population of extremely ______ size.
unlimited
slowly
large

24. When exponential growth is viewed on a graph, the pattern of growth is a ______ curve.
J-shaped
cannot
In reality, populations ______ continue to grow exponentially for very long.
Resources will become ______ and ______ will accumulate, ______ growth.
In addition, competition for the limited resources will intensify as the population grows.
scarce
wastes
limiting

25. Exponential growth does ________________ in natural populations for very long.
NOT continue
Carrying Capacity
At first a population may appear to be experiencing exponential growth, but as resources become ______________, the growth of the population will ____________.
less available
slow or stop

26. How will resources be limited during the growth of the population?
Food will become:
more and more scarce.
There may be:
water shortages.
c) A ________ might be introduced into the population.
The population will:
run out of space.
e) Additional __________ may be attracted to the rising ______ population.
disease
f) There will be increased _____________ between the members of the group.
g) The accumulation of:
wastes could lead to an increase in diseases and poor health.
competition
predators
prey

27. Eventually a growing population will reach the carrying capacity of the environment.
The carrying capacity is:
the number of individuals the environment can support over a long period of time.

28. The ___________ in the graph to the right indicates that the population has exceeded the _________________ of the environment.
Many members of the population will ______________, causing the population size to ____________ the carrying capacity.
overshoot
carrying capacity
The size of the population will fluctuate _________________ the carrying capacity of the environment.
die or starve
above and below
drop below

29. Logistic Growth Logistic Growth: letter “S”
A model of population growth in which growth slows or stops following a period of exponential growth.
A graph of logistic growth looks like a stretched out __________.
letter “S”

30. Logistic Growth
When the population size is ______, birth rates are ______ and death rates are _____, causing the population to grow nearly _______________.
small
high
low
When the population is at the carrying capacity:
the birth rate equals the death rate, and growth stops.
exponentially
As the population reaches the carrying capacity, the growth rate _______.
slows

31. Limits to Growth Limiting Factors:
No population can undergo exponential growth forever.
There are…
…limits to how fast and how big a population can grow.
Examples of limiting factors include:
1. Competition
2. Predation
3. Parasitism and disease
4. Drought and other climate extremes
5. Human disturbances
Limiting Factors:
A limiting factor is a factor that causes population growth to decrease.

32. Density-Dependent Factors
1. A limiting factor that depends on population size is called a density-dependent limiting factor.
Density-Dependent Factors
This means that the limiting factor only becomes “_________” when:
the population density reaches a certain level.
limiting

33. Population density refers to the: number of organisms per unit area.
Density-dependent limiting factors include:
competition
predation
parasitism and disease
shortages of food
shortage of nesting sites.

34. food, water, sunlight, space to grow, and nesting sites.
As a population becomes more and more crowded, organisms will have to compete with one another for:
food, water, sunlight, space to grow, and nesting sites.
Competition is a density-dependent factor.
The more individuals that live in the population:
the sooner they will use up the available resources.
The greater the population size becomes, the more intense the competition for resources.
Competition may also occur between populations consisting of separate species.

35. Density-Independent Factors
The density-independent factors affect:
all populations in similar ways, regardless of the size of the population.
Density-Independent Factors
Examples of density-independent factors include:
a) Unusual weather or natural disasters such as floods and fires.
b) Certain human activities, such as the damning of a river, or clear-cutting a forest.