1. Population Dynamics Day 4

2. Population Characteristics
Population Density:
The number of organisms per unit area
Dispersion:
The pattern of spacing a population within an area
3 main types of dispersion
Clumped
Uniform
Random
Resource availability determines dispersion patterns

3. Population Limiting Factors
1) Density-independent factors
Factors that limit population size, regardless of population density.
usually abiotic
include natural phenomena
Ex. drought, flood, fire extreme temperature, tornadoes, etc.

4. Population Limiting Factors (cont.)
2) Density-dependent factors
Any environmental factor that depends on the density of the population
Usually biotic
For ex.
Predation
Disease
Parasites
Competition

5. Population Limiting Factors (cont.)
3) Population growth rate
How fast a 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

6. Understanding Exponentials
Put your pens down 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? 6

7. Understanding Exponentials
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?

8. Population Growth Models
1) 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?

9. Population Growth Models (cont.)
Limits to exponential growth
As population density increases, competition follows 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… 9

10. What population do you think this is?

11. 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?

12. Population Growth Models (cont.)
2) Logistical growth model
Often called the S-shaped growth curve
Growth slows or stops following exponential growth at the population’s carrying capacity
Populations stop increasing when:
Birth rate < Death rate
Emigration > Immigration
Carrying capacity can be raised or lowered. How?
Ex. 1: Artificial fertilizers have raised
Ex. 2: Decreased habitat can lower k 12

13. Community Dynamics
Day 5

14. Communities
Review:
A community is a group of interacting populations that occupy the same area at the same time.

15. Limiting Factors of Communities
Any abiotic or biotic factor that restricts the numbers, reproduction, or distribution of organisms.

16. Range of Tolerance
Upper and lower limit of conditions in which an organism can survive.
Ex. Temperature, Salinity, pH

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

18. Ecological Succession (cont.)
2 types:
10 Primary Succession
20 Secondary Succession

19. Primary Succession
In primary succession (10), the community establishes in an area of exposed rock (no soil)
It occurs very slowly at first

20. Primary Succession (cont.)
Pioneer species, or the first organisms to arrive, are usually lichens or mosses
They secrete acids that can break down rock, creating soil.

21. Primary Succession (cont.)
Small weedy plants and other organisms become established.
As they die, more soil is made

22. Primary Succession (cont.)
Animals, water and wind bring seeds that sprout
Eventually there is enough soil for shrubs and trees to grow.

23. Primary Succession (cont.)
The stable, mature community that eventually develops from bare rock is called a climax community.

24. Secondary (20) Succession
Disturbances (fire, flood, windstorms) can disrupt a community.
After a disturbance, new species of plants and animals might occupy the habitat.

25. Secondary Succession (cont.)
Pioneer species in 20 succession are usually plants that grow in disturbed area.
Much faster than 10 succession

26. Succession End point? Cannot be predicted
Different rates of growth & human involvement make it impossible to know if a true climax community has been reached.