1. 1. To describe and understand population characteristics
POPULATION ECOLOGY Ch. 53
Lecture Objectives
1. To describe and understand population characteristics

2. What is population ecology?
Population ecology explores how biotic and abiotic factors influence density, distribution, size, and age structure of populations
Loggerhead Turtle (Caretta caretta)

3. Biological Processes influence population size & Density
A population is a group of individuals of a single species living in the same general area
Populations are described by their boundaries and size

4. Population characteristics Size & density
Size - # of organisms that contribute to a population’s gene pool
Changes in size with BR, DR, and migration
Density - # of individuals per unit of area or volume
Determined by sampling techniques
Count
Plot & Estimate
Indicator
Mark & Recapture

5. Size & density con’t. Hector’s Dolphins Mark & Recapture
Capture, tag, and release random sample of individuals (s)
Mix back into population
Capture 2nd sampling (n) & note how many marked (x)
Population size (N) 
N = sn x

6. Population characteristics size & density  demographics
Demography = study of the vital statistics of populations and how they change over time.
BR & DR
Survivorship curves
a graphic way of representing the average lifespan of a species

7. Survivorship curves I survivors II # III % of maximum life span
Type I: Low death rates during early and middle life and an increase in death rates among older age groups
Type II: A constant death rate over the organism’s life span
Type III: High death rates for the young and a lower death rate for survivors
Many species are intermediate to these curves
III
% of maximum life span

8. Population characteristics age structure
relative number of individuals at each age
can predict a population’s growth trends
They can illuminate social conditions and help us plan for the future

9. Rapid growth Slow growth No growth Afghanistan United States Italy
Figure 53.24
Rapid growth
Slow growth
No growth
Afghanistan
United States
Italy
Male
Female
Age
Male
Female
Age
Male
Female
85+
85+
80–84
80–84
75–79
75–79
70–74
70–74
65–69
65–69
60–64
60–64
55–59
55–59
50–54
50–54
45–49
45–49
40–44
40–44
35–39
35–39
30–34
30–34
25–29
25–29
20–24
20–24
15–19
15–19
Figure Age-structure pyramids for the human population of three countries (data as of 2010)
10–14
10–14
5–9
5–9
0–4
0–4 10 8 6 4 2 2 4 6 8 10 5 4 3 2 1 1 2 3 4 5 5 4 3 2 1 1 2 3 4 5
Percent of population
Percent of population
Percent of population

10. Population characteristics distribution
the pattern of spacing among individuals within the boundaries of the population
Uniform
Random
Clumped

11. Population characteristics population growth models
Exponential growth
population increase under idealized conditions
rate of increase is at its maximum & constant
results in a J-shaped curve
Logistic growth
Starts with exponential models but rate of increase declines as carrying capacity is reached
Carrying capacity (K) = maximum population size the environment can support
varies with the abundance of limiting resources
sigmoid (S-shaped) curve

12. Population growth begins slowing here. 500
Exponential growth
2,000 dN
= 1.0N dt
1,500
K = 1,500
Logistic growth
Population size (N) dN
1,500 − N
= 1.0N dt
1,500
1,000
Population growth begins slowing here.
500
Figure Population growth predicted by the logistic model 5 10 15
Number of generations
Figure 53.10

13. Number of Paramecium/mL
Figure 53.11
1,000
180
150
800
120
Number of Daphnia/50 mL
Number of Paramecium/mL
600 90
400 60
200 30 5 10 15 20 40 60 80
100
120
140
160
Figure How well do these populations fit the logistic growth model?
Time (days)
Time (days)
(a) A Paramecium population in the lab
(b) A Daphnia population in the lab

14. Figure 53.9
8,000
6,000
Elephant population
4,000
2,000
Figure 53.9 Exponential growth in the African elephant population of Kruger National Part, South Africa
Year

15. Human population (billions)
Figure 53.22 7 6 5
Human population (billions) 4 3 2
Figure Human population growth (data as of 2012)
Population ecologists predict a global population of 8.1–10.6 billion people in 2050
Our carrying capacity could potentially be limited by food, space, nonrenewable resources, or buildup of wastes
Unlike other organisms, we can regulate our population growth through social changes 1
8000
BCE
4000
BCE
3000
BCE
2000
BCE
1000
BCE
1000 CE
2000 CE

16. Annual percent increase
Figure 53.23
2.2
2.0
1.8
1.6
1.4
2011
Annual percent increase
1.2
Projected
data
1.0
0.8
0.6
Figure Annual percent increase in the global human population (data as of 2011)
0.4
0.2
1950
1975
2000
2025
2050
Year

17. Competition for resources Disease Predation
Figure 53.18
Competition for resources
Disease
Predation
Figure Exploring mechanisms of density-dependent regulation
competition for resources and results in a lower birth rate
pathogens can spread more rapidly
prey population builds up, predators may feed preferentially on that species
intrinsic (physiological) factors appear to regulate population size
5 µm
Territoriality
Intrinsic factors
Toxic wastes