1. Scales of Ecological Organization
Biosphere
Ecosystem
Community
Population
Organism

2. Definition
Population ecology is the study of births, deaths, and the dynamics forces which regulate the number of individuals in a population.

3. Density and Dispersion
Is the number of individuals per unit area or volume
Dispersion
Is the pattern of spacing among individuals within the boundaries of the population

4. Population dispersion

5. Population dispersion
spatial patterns
spaced -- may indicate competing individuals
clumped -- may indicate social patterns or resource distribution

6. A random dispersion
Is one in which the position of each individual is independent of other individuals
(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

7. A uniform dispersion
Is one in which individuals are evenly distributed
May be influenced by social interactions such as territoriality
Figure 52.3b
(b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

8. A clumped dispersion Is one in which individuals aggregate in patches
May be influenced by resource availability and behavior
Figure 52.3a
(a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

9. Density is the result of a dynamic interplay between processes
Density is the result of a dynamic interplay between processes that add individuals to a population and those that remove individuals from it.
Births and immigration add individuals to a population.
Births
Immigration
PopuIation size
Emigration
Deaths
Deaths and emigration remove individuals from a population.

10. The life table of Belding’s ground squirrels
Reveals many things about this population

11. A survivorship curve
Is a graphic way of representing the data in a life table…
Figure 52.4
1000
100 10 1
Number of survivors (log scale) 2 4 6 8
Age (years)
Males
Females
The survivorship curve for Belding’s ground squirrels
Shows that the death rate is relatively constant

12. patterns in age structure
Population
patterns in age structure

17. r- vs K-selection r-selection K-selection
r is the rate of a population’s increase
K is a population’s carrying capacity
Disturbance Common, irregular Rarer, more regular
Mortality Variable, unpredictable Constant, predictable
Competition Low or variable High, constant
Pop. size Variable, below K Rel. constant, near K
Consequence High r Good competitors

18. Small size
Rapid growth
Early reproduction
Many, small offspring
Large size
Slow growth
Late reproduction
Few, large offspring

19. A. Body size and r
On average, small organisms have higher rates of per capita increase and more variable populations than large organisms.

20. K vs. r selection: extremes in parental care
Humpback whales
Sea urchins

21. K vs. r selection: extremes

22. When there are no limits, populations grow faster,
Population Growth Geometric growth vs. exponential growth vs logistic growth.
Bottom line:
When there are no limits, populations grow faster,
and FASTER
and FASTER!
Invasive Cordgrass (Spartina) in Willapa Bay

23. The Simple Case: Geometric Growth
Constant reproduction rate
Non-overlapping generations (like annual plants, insects)
Also, discrete breeding seasons (like birds, trees, bears)
Suppose the initial population size is 1 individual. This indivual reproduces once & dies, leaving 2 offspring. How many if this continues?

24. Exponential Growth
Assumes continuous breeding life history strategy and overlapping generations.

25. Human Population Growth

26. What happens if there ARE limits? (And eventually there ALWAYS are!)
Logistic Growth:
The sigmoidal curve--carrying capacity (K) plays a role in determining population growth.

30. patterns in age structure
Human population
patterns in age structure

31. Exponential growth model

32. Exponential growth