1. Question for Thought
How would you describe the population of elephants below to a classmate? What kinds of information would you use?

2. Population ecology is the study of how and why populations change
A population is a group of individuals of a single species that occupy the same general area.
Individuals in a population
rely on the same resources,
are influenced by the same environmental factors, and
are likely to interact and breed with one another.
© 2012 Pearson Education, Inc. 2

3. What do population ecologist look at?
Population ecology is concerned with
the changes in population size and
factors that regulate populations over time.
Populations
increase through birth and immigration to an area and
decrease through death and emigration out of an area.
© 2012 Pearson Education, Inc. 3

4. Population Density and Dispersion
Population density is the number of individuals of a species per unit area or volume.
Examples of population density include the
number of oak trees per square kilometer in a forest or
number of earthworms per cubic meter in forest soil.
The dispersion pattern of a population refers to the way individuals are spaced within their area.
© 2012 Pearson Education, Inc. 4

5. 3 Different Dispersion Patterns
In a clumped pattern
resources are often unequally distributed and
individuals are grouped in patches.
In a uniform pattern, individuals are
most likely interacting and
equally spaced in the environment.
In a random pattern of dispersion, the individuals in a population are spaced in an unpredictable way.
© 2012 Pearson Education, Inc. 5

6. 3 Different Dispersion Patterns
Clumped
Uniform
Random
Figure 36.UN05 Testing Your Knowledge, question 12 6

7. Population size (N) Time (months) 500 450 400 350 300 250 200 150 100
Figure 36.4A
500
450
400
350
Population size (N)
300
250
200
Figure 36.4A Exponential growth of rabbits
150
100 50 1 2 3 4 5 6 7 8 9 10 11 12
Time (months) 7

8. Breeding male fur seals
Figure 36.4B 10 8
Breeding male fur seals
(thousands)
Figure 36.4B Growth of a population of fur seals 6 4 2
1915
1925
1935
1945
Year 8

9. Carrying Capacity
Most populations follow the logistic curve because eventually the carrying capacity is reached.
The carrying capacity is the largest size of a population that the environment can sustain.
Carrying capacity is represented by K.
Once reached, it will usually stay there.
© 2012 Pearson Education, Inc. 9

10. Most species fall between these two extremes.
R vs K Selection Theory
r-selected species
produce many offspring and have little or no parental care
grow rapidly in unpredictable environments.
K-selected species
raise fewer offspring and a lot of parental care
maintain relatively stable populations.
Most species fall between these two extremes.
© 2012 Pearson Education, Inc. 10

11. Some populations have “boom-and-bust” cycles
Some populations fluctuate in density with regularity.
Boom-and-bust cycles may be due to
food shortages or
predator-prey interactions.
© 2012 Pearson Education, Inc. 11

12. There are three main types of survivorship curves.
Survivorship curves plot survivorship as the proportion of individuals from an initial population that are alive at each age.
There are three main types of survivorship curves.
Type I
Type II
Type III
© 2012 Pearson Education, Inc. 12

13. Percentage of survivors (log scale)
Figure 36.3
100 I 10
Percentage of survivors (log scale) II 1
III
Figure 36.3 Three types of survivorship curves
0.1 50
100
Percentage of maximum life span 13

14. Analyzing the Age of Individuals in a Population
The age structure of a population
is the proportion of individuals in different age groups and
affects the future growth of the population.
© 2012 Pearson Education, Inc. 14

15. Analyzing the Age of Individuals in a Population