1. Population Ecology
Items that are BOLD, underlined, or a different color are MOST important to write down

2. Population Characteristics
Population Ecology: Population Characteristics
Population Characteristics
Population Density:
The number of organisms per unit area
Spatial Distribution:
Dispersion: The pattern of spacing a population within an area
3 main types of dispersion
Clumped
Uniform
Random
The primary cause of dispersion is resource availability

3. Measuring density of populations is a difficult task.
We can count individuals; we can estimate population numbers.
Unfortunately, it is usually impractical to attempt to count individuals in a population.
One sampling technique that researchers use is known as the mark-recapture method.
Individuals are trapped, captured, tagged, recorded, and then released.
After a period of time individuals are recaptured.
This information allows estimates of population changes to be made
Fig. 52.1
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4. Population Limiting Factors
Population Ecology: Population Characteristics
Population Limiting Factors
Population growth rate
How fast a given population grows
Factors that influence this are:
Natality (____ rate)
Mortality (_____ rate)
Emigration (the number of individuals moving _________ a population)
Immigration (the number of individuals _________ a population)
birth
death
away from
moving to

5. How they effect size or density of a population:
Immigration
Birth
Population (N)
Death
Emigration
Figure 1. The size of a population is determined by a balance between births, immigration, deaths and emigration

6. Review What is an… Organism Population Community Ecosystem Biome
What do we know so far that affects populations?

7. Lets say we constructed a table with data about the lives of ground squirrels. Looks confusing…
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. A graphic way of representing the data is a survivorship curve.
A Type I curve shows a low death rate early in life (humans).
The Type II curve shows death rate constant over lifespan(squirrels).
Type III curve shows a high death rate early in life (oysters).

9. Survivorship Curve
This is a plot of the number of individuals in an area still alive at each age.

10. Population Limiting Factors
Population Ecology: Density-independent factors
Population Limiting Factors
Density-independent factors
Factors that limit population size, regardless of population density.
These are usually abiotic factors
They include natural phenomena, such as weather events
Drought, flooding, extreme heat or cold, tornadoes, hurricanes, fires, etc.

11. Population Limiting Factors
Population Ecology: Density-dependent factors
Population Limiting Factors
Density-dependent factors
Any factor in the environment that depends on the number of members in a population per unit area
Usually biotic factors
These include
Predation
Disease
Parasites
Competition

12. Review Look at your scales… What is a… Survivorship Curve
Are you a 1 or a 2?
means you can list factors the influence population growth, know what exponential and logistic growth is, and can state types of succession
Can classify factors as density dependent or independent/ predict affect of resources on carrying capacity
What is a…
Survivorship Curve
Density-Independent factor
Density-Dependent factor

13. Understanding Exponentials
Population Ecology: Population Growth Rate
Understanding Exponentials
Put your pens down (DO NOT WRITE) for a minute & think about this:
An employer offers you two equal jobs for one hour each day for fourteen days.
The first pays $10 an hour.
The second pays only 1 cent a day, but the rate doubles each day.
Which job will you accept? 13

14. Understanding Exponentials
Population Ecology: Population Growth Rate
Understanding Exponentials
Dollars an hour
Now, how much would your employer owe you if you stayed at this job for another 2 weeks?
Job 2 lags for a long time before exponential growth kicks in!
What would happen if this type of growth took place within a population?
Days at work

15. Population growth models
Exponential growth model
Also called geometric growth or J-shaped growth.
First growth phase is slow and called the lag phase
Second growth phase is rapid and called the exponential growth phase
Bacteria can grow at this rate, so why aren’t we up to our ears in bacterial cells?

16. Limits to exponential growth
Competition - as nutrients and resources are used up
The limit to population size that a particular environment can support is called carrying capacity (k)
When you’re done writing, put your pens down…

17. Population Ecology: Population Growth Rate
What population do you think this is? Look at the dates and number of individuals
Plants?
Animals?
Insects?
Humans?

18. So, what do you think is going to happen to the human population?
We will probably reach our carrying capacity.
Our growth rate will start to look like most organisms, which is the Logistic Growth Model
Carrying Capacity (k)
What letter does this curve kind of look like?

19. Logistic Growth Model S-shaped growth curve
population’s growth slows or stops following exponential growth
stops at the population’s carrying capacity
Populations stop increasing when:
Birth rate is less than death rate (Birth rate < Death rate)
Emigration exceeds Immigration (Emigration > Immigration)

20. Ecological Succession
The change in an ecosystem that happens when one community replaces another as a result of changing biotic and abiotic factors

21. Ecological Succession
Community Ecology: Ecological Succession
Ecological Succession
Consists of 2 types:
Primary Succession
Secondary Succession

22. Ecological Succession: Primary
Community Ecology: Ecological Succession: Primary Succession
Ecological Succession: Primary
The establishment of a community in an area of exposed rock that does not have topsoil is called Primary Succession.
It occurs very slowly at first

23. Community Ecology: Ecological Succession: Primary Succession
The first organisms to arrive are usually lichens or mosses, which are called pioneer species.
They secrete acids that can break down rock
Their dead, decaying organic materials, along with bits of sediment from the rock make up soil.

24. Community Ecology: Ecological Succession: Primary Succession
Small weedy plants and other organisms become established.
As these organisms die, additional soil is created

25. Community Ecology: Ecological Succession: Primary Succession
Seeds brought in by animals, water and wind begin to grow in the soil.
Eventually enough soil is present for shrubs and trees to grow.

26. Ecological Succession: Secondary
Community Ecology: Ecological Succession: Secondary Succession
Ecological Succession: Secondary
Disturbances (fire, flood, windstorms) can disrupt a community.
After a disturbance, new species of plants and animals might occupy the habitat.
Think Lion King 

27. Community Ecology: Ecological Succession: Secondary Succession
Pioneer species in secondary succession are usually plants that begin to grow in the disturbed area.
This is much faster than primary succession