1. Population Biology
BCOR 012
Chapter 53

2. Note:
The Tri-Beta honors society will be having its regular
intro bio tutoring sessions Monday and Tuesday after
break, 6 - 8pm in Rowell 244.
This is in addition to the regular Sunday sessions in
Living and Learning.

3. Ecology - the study of the interaction between organisms and their environment

4. Ecology and evolutionary biology are closely related disciplines: events that occur in ecological time affect life on the scale of evolutionary time.
Put another way, an important cause of evolutionary change is the interaction of organisms with their environment.

5. occurs at many different scales.
Organismal
ecology
The focus of
ecological studies
occurs at many different
scales.
Population
ecology
Community
ecology
Ecosystem
ecology
Figure 52.2 The scope of ecological research
Landscape
ecology
Global
ecology

6. Population Ecology
Chapter 53
I. Characteristics of Populations
A. Introduction
B. Two important characteristics of populations are density and the
spacing of individuals (= dispersion)
C. Demography
II. Life Histories
A. Natural selection favors strategies that maximize and individual’s fitness.
B. Reproductive strategies
C. Trade-offs between reproduction and survival

7. Population ecology is concerned with:
measuring changes in population size and composition
identifying the ecological causes of such fluctuations

8. From Chapter 23:
So what is a population?
A population is a set of individuals of the same species that live close enough together to interbreed.
in a particular geographic area.

9. Aerial census of African water buffalo in the Serengeti
Density – the number of individuals per unit area
Aerial census of African water buffalo in the Serengeti

10. Dispersion – the spacing among individuals within the population boundaries

11. Demography
Study of the vital statistics of populations and how they change over time
~ Birth and Death rates

12. A life table follows fate of a cohort from birth to death

13. Idealized survivorship curves
Type I
Few offspring with good care (mammals)
Death rate low until older ages
Type II
Intermediate (rodents, annual plants)
Death rate constant
Type III
Many offspring with little care (marine invertebrates, long-lived plants)
Initial death rate high, then low

14. Population Ecology
Chapter 53
I. Characteristics of Populations
A. Introduction
B. Two important characteristics of populations are density and the
spacing of individuals (= dispersion)
C. Demography
II. Life Histories
A. Natural selection favors strategies that maximize an individual’s fitness.
B. Reproductive strategies
C. Trade-offs between reproduction and survival

15. Life history - the set of traits related to reproduction, including
frequency of reproduction, number of offspring, investment in
parental care, etc.

16. Fitness involves both individual survival and the production of viable offspring that will live to reproduce themselves.
Therefore, why not a life history strategy that involves early
reproductive maturity, frequent reproduction, and many offspring
per brood?

17. Survivorship vs. brood size in European kestrel
A. Trade-offs between reproduction and survival:
Survivorship vs. brood size in European kestrel

18. Population Ecology
Chapter 53
III. Population Growth
A. Exponential Growth
B. Logistical Growth
IV. Population Limiting Factors
A. Density dependence
B. Population fluctuations
C. .
V. Human Population Growth
A. Earth’s carrying capacity
B. What can you do?

19. Growth rate results from processes that add and remove individuals
Population Growth
Growth rate results from processes that add and remove individuals
+ Births
− Deaths
+ Immigration
− Emigration
Therefore r = (b+i) - (d+e)

20. r is the per capita growth
rate, r = b - d, where b is
the per capita birth rate and
d is the per capita death rate

21. Clicker Question What is r? 0.02 22 r = (b+i) - (d+e) 44 2
 Kingfish, Louisiana, had a population of 1,100 individuals. They had a birth rate of 12/100, a death rate of 8/100, and an emigration (individuals leaving the population) rate of 2/100. How many people were added to Kingfish's population in one year?
What is r?
0.02 22 44 2
Not enough information given
r = (b+i) - (d+e)
r = ( ) = 0.02
rN=(0.02)(1,100) = 22
good job!

22. As b decreases and/or d increases, r, the per capita growth rate, decreases.

23. The carrying capacity (K) of an environment
is the maximum population size that the
environment can sustain with no degradation
of the habitat.

24. As the population size (N) approaches carrying capacity (K), the
population growth rate approaches zero.

25. The Logistical Growth Equation
K - N
 K  dN dt
= rmaxN
By multiplying the exponential rate of increase rmaxN by
(K - N)/K, we reduce the actual growth rate of the population
as N increases.

27. The logistic model of population growth produces a sigmoid (S-shaped)
curve when N is plotted over time.

28. How well do actual populations fit the logistical model?
This laboratory population
of Paramecium grew according
a logistical model.
This laboratory population of
Daphnia overshot carrying capacity.
And this natural
population of song
sparrows fluctuated
considerably in
response to environ-
mental stresses.

29. Population Ecology
Chapter 53
III. Population Growth
A. Exponential Growth
B. Logistical Growth
IV. Population Limiting Factors
A. Density dependence
B. Population fluctuations
V. Human Population Growth
A. Earth’s carrying capacity
B. What can you do?

30. Density-dependent factors limiting population growth
Plants: light, nutrients, water
Animals: food, water, nesting/breeding sites
Increased predation
Accumulation of waste in the environment
Increased transmission of disease
Stress

31. Fluctuation in a moose population on Isle Royale,
Lake Superior

32. Population Ecology
Chapter 53
III. Population Growth
A. Exponential Growth
B. Logistical Growth
IV. Population Limiting Factors
A. Density dependence
B. Population fluctuations
V. Human Population Growth
A. Earth’s carrying capacity
B. What can you do?

33. The human population has been growing exponentially, though the rate has slowed in recent decades
Where is K???

34. In the U.S., our ecological footprint is large

35. So what can you do about it?
Live sustainably
Use resources wisely
Eat more vegetable protein and less meat
Support global family planning efforts
Work for peace and justice

36. Two's company ...
6,600,000,000 is a crowd!