1. Population Ecology

3. Definitions in population ecology
Individuals of a species within a given area
constitute a Population
Population density: the number of individuals of a species per unit of area (or volume)
Population dynamics: change in population
density through time and space
Demography: study of birth, death, and
movement rates that give rise to population
dynamics

4. Population Size Size can affect the populations ability to survive
Too big?? – issues
Too small?? - issues
Q – What are some challenges that populations have to face in order to survive?
Competition for food, shelter, mates, water!

5. Q – What is the advantage of a large population over a small population?

6. Growth rates Growth occurs when: Populations are steady when:
births outnumber deaths
Immigration (into an area) is greater than emigration (out of an area)
Populations are steady when:
births = deaths
Immigration = emigration
Decline in populations occur when:
deaths outnumber births.
emigration is greater than immigration

7. Exponential Growth Population size increases steadily
Example: bacteria
1 cell can divide every 30 minutes = 1 million bacteria in just 10 hours

8. Growth is limited
Q – Specifically, what do you think can limit a populations growth? What can cause growth to slow down?
Predators
Disease
Availability of resources

9. Resources
When resources (food, water, shelter) become limited, growth will slow down.
Density-dependent factors-
-the rate at which resources are gone, depends on the size/density of the population

10. Determine…
Name 1 density-dependent factor that could affect the following populations:
Deer -
Coyotes -
Rabbits -
Butterflies -

11. Density-dependent factors stabilize the population
Per capita birth and death rates fluctuate in response to population density
- e.g., dense population may deplete food supply, reducing the amount of food each individual gets.
Poor nutrition may increase death rates and decrease birth rates
-e.g., diseases, which may increase death rates, spread more easily in dense populations than in sparse populations

12. Logistic Growth
Because these factors affect the size of populations, they can be shown as a Logistic Growth Model
“logical”

13. Carrying Capacity (K) The population size an environment can sustain
NOTE: when below carrying capacity, growth occurs rapidly (exponentially). Once resources are limiting (due to the growth) rate slows down.

14. Q- Explain the relationship between density-dependant factors and competition?
These factors are what organisms must compete for in order to survive
– water, shelter, mates, etc.

15. Density-independent factors
Factors that affect birth and death rates in a population independent of its density
(aka no matter how many there are)
i.e. - a severely cold winter may kill large
numbers of a population regardless of its density.
Any other larger natural disaster (fire, hurricane, etc)

16. Show me your fingers!!
Hold up the appropriate number of fingers for the number answer you think is correct

17. Which number shows exponential growth?1 3 4 2
Population Growth Over Time

18. Population Growth Over Time
Which number would represent the death rate increasing and the birth rate decreasing? 1 2 3 4
Population Growth Over Time

19. Which number shows the growth, if resources were NOT limited?1 4 2 3
Population Growth Over Time

20. Which number best represents about the same birth and death rates?3 1 2 4
Population Growth Over Time

21. “Strategists”
Remember, animals can not “plan” or “strategize” their life. We say “strategists” meaning their pattern of living
TWO main types:
- r-strategists
- K-strategists

22. r-strategists-
grow exponentially when the environment allows them to
Examples:
a. mosquitos – breed like crazy in the summer months, populations decrease in the winter

23. K- strategists
Organisms that grow slowly and have small population sizes.
Bears, whales, etc.

24. In summary
1) There are many ways for the size of populations to be affected (density-dependant and independent factors)
2) There are many things populations must compete for (food, shelter, water, mates)
3) There are TWO main ways to model population growth (exponentially and logistically)
4) Depending on strategy, can either be an r-strategist or K-strategist (breed a LOT and fast OR slow and steady)