population ecology presentation

1. Populations
BIOL 1407 – Fall 2017 - Ebeling

2. Objectives – Populations
By the end of this course successful students should be able to:
• Describe the factors that affect the size of a population
• Distinguish among the different forms of population distribution
• Describe how birth and death rates influence a population.
• Compare and contrast the three types of survivorship curves.
• Use the exponential and logistic growth equations to measure
changes in a population.
• Define carrying capacity and understand how it can affect
population size.
• Compare and contrast density-dependent and density
independent growth.
• Compare and contrast r-selected and K-selected life history
adaptations.

3. What is a population?

5. Section 37.1
A habitat is the physical
location where the members of
a population live.
Population density is the
number of individuals of a
species per unit area or unit
volume of a habitat.
Figure 39.14
©Ed Reschke

6. Population Distribution

8. Estimating population size
Section 37.1
Estimating population size also
interests many ecologists.
Consider this population of
wildebeest. How can the
number of individuals be
determined?
• Aerial photos
• Sampling small subset
• Mark-recapture
Figure 39.12
©Arthur Morris/Corbis

9. Births and deaths affect population size

10. Factors that increase population size
Section 37.2
Birth rate is the number of
individuals produced per
unit of time.
Immigration is the
movement of individuals
into a population.
Table 37.1
T A B L E 37.1 Factors Affecting Population Growth: A Summary
Factor Affected by…
Additions
Births • Number of reproductive episodes per lifetime
• Number of offspring per reproductive episode
• Age at first reproduction
• Population age structure (proportion at
reproductive age)
Immigration • Availability of dispersal mechanism
• Availability of suitable habitat
Subtractions
Deaths • Availability of nutrients
• Predation
• Accidents
• Genetic/infectious disease
Emigration • Availability of dispersal mechanism

11. Factors that decrease population size
Section 37.2
Death rate is the number of
deaths per unit of time.
Emigration is the movement
of individuals out of a
population.
Table 37.1
T A B L E 37.1 Factors Affecting Population Growth: A Summary
Factor Affected by…
Additions
Births • Number of reproductive episodes per lifetime
• Number of offspring per reproductive episode
• Age at first reproduction
• Population age structure (proportion at
reproductive age)
Immigration • Availability of dispersal mechanism
• Availability of suitable habitat
Subtractions
Deaths • Availability of nutrients
• Predation
• Accidents
• Genetic/infectious disease
Emigration • Availability of dispersal mechanism

12. Survivorship Curves

13. Three types of survivorship curves
Section 37.2
Survivorship curves
follow predictable
patterns.
Figure 37.5

14. Type I survivorship curve
Section 37.2
A type I survivorship
curve is representative
of species that invest
much energy caring for
young and have low
death rates early in life.
Most individuals survive
to reproduce.
Figure 37.5

15. Type II survivorship curve
Section 37.2
Type II species have an
approximately equal
probability of dying at
any age.
Figure 37.5

16. Type III survivorship curve
Section 37.2
A type III survivorship
curve is representative of
species that invest little
energy raising their
young and have high
death rates among
offspring. Few individuals
survive to reproductive
age.
Figure 37.5

17. Calculating Population Change
r = per capita rate of change

20. A population growth experiment
Section 37.3
A population is growing exponentially if the number of new individuals is
proportional to the size of the population.
Researchers put 100 rotifers in an environment with abundant
resources and no predators. The population grew exponentially.
Figure 37.6

21. Day 5 of the experiment
Section 37.4
By day 5, the growth rate was 49 individuals per day.
Time
(days)
r N G = rN
Total Population at
End of Day
1 0.22 100 22 122
2 0.22 122 27 149
3 0.22 149 33 182
4 0.22 182 40 222
5 0.22 222 49 271
6 0.22 271 60 331
7 0.22 331 73 404
8 0.22 404 89 493
9 0.22 493 108 601
10 0.22 601 132 733
11 0.22 733 161 894
12 0.22 894 197 1091
13 0.22 1091 240 1331
14 0.22 1331 293 1624
15 0.22 1624 357 1981
16 0.22 1981 436 2417
17 0.22 2417 532 2949
18 0.22 2949 649 3598
19 0.22 3598 792 4390
20 0.22 4390 966 5356
r = Per capita rate of increase
N = Number of individuals at start of time interval
G = Growth rate (number of individuals added per unit time)
Figure 37.6

22. Days 15 and 20 of the experiment
Section 37.4
After 15 days, the growth
rate had increased to 357
individuals per day.
At the end of the monitoring
period, the growth rate was
966 individuals per day!
But exponential growth
cannot continue indefinitely.
Time
(days)
r N G = rN
Total Population at End
of Day
1 0.22 100 22 122
2 0.22 122 27 149
3 0.22 149 33 182
4 0.22 182 40 222
5 0.22 222 49 271
6 0.22 271 60 331
7 0.22 331 73 404
8 0.22 404 89 493
9 0.22 493 108 601
10 0.22 601 132 733
11 0.22 733 161 894
12 0.22 894 197 1091
13 0.22 1091 240 1331
14 0.22 1331 293 1624
15 0.22 1624 357 1981
16 0.22 1981 436 2417
17 0.22 2417 532 2949
18 0.22 2949 649 3598
19 0.22 3598 792 4390
20 0.22 4390 966 5356
r = Per capita rate of increase
N = Number of individuals at start of time interval
G = Growth rate (number of individuals added per unit time)
Figure 37.6

23. Population growth eventually slows
Section 37.4
When resources become limited (or when any factor happens
that increases death rate or reduces birth rate), population
growth levels off.
Figure 37.8

24. Carrying Capacity (K)

27. Day 26 of the experiment
Section 37.4
At 26 days, the population size is near carrying capacity.
The growth rate has slowed to 30 individuals per day.
Figure 37.8

28. The logistic growth equation
Section 37.4
The following equation is used to calculate the growth rate at any population
size.
Notice that this equation is similar to the one for exponential growth, except
for the following addition.
𝐺 = 𝑟𝑁
𝐾 − 𝑁
𝐾
The boxed portion of
the equation
approaches zero as
population size gets
close to the carrying
capacity. Growth rate
therefore also
approaches zero.
G is the growth rate, r is the per capita rate of increase, N is the initial
population size, and K is the carrying capacity.

32. Life History Adaptations

34. A summary of life histories
Section 37.5 Figure 37.20
Opportunistic life history
• High reproduction rate
• Many offspring
• Each offspring receives little
parental care
• Low survival rate for juveniles
• Early reproductive maturity
• Type III survivorship curve:
Equilibrium life history
• Low reproduction rate
• Few offspring
• Each offspring receives
extensive parental care
• High survival rate for juveniles
• Late reproductive maturity
• Type I survivorship curve:

35. Human Population Growth

37. Human population growth is unsustainable
Section 37.5 Figure 37.17
The human population cannot
continue to grow exponentially.
Humans overexploit resources.
This diagram shows how much
land area each country needs
to support its current lifestyle.
Many countries have a large
ecological footprint, which
means they require more land
than is available.

38. Investigating life:
A toxic compromise
Section 37.6
Species face life history
trade-offs when living in a
challenging environment.
Fish called Atlantic mollies
sometimes live in toxic, dark
caves.
However, other Atlantic mollies
of the same species (but of
different subpopulations) live in
less challenging environments:
• Nontoxic cave
• Toxic surface water
• Nontoxic surface water
Figure 37.18
©Stephen Alvarez/National Geographic Creative/Getty Images

39. Investigating life:
Toxic vs. nontoxic
Section 37.6
Scientists studied Atlantic mollies
to learn how the environment
affects life history traits.
Mollies in dark, toxic caves
produce fewer, larger offspring
(high parental investment).
In contrast, mollies inhabiting
nontoxic surface water produce
many small offspring (lower
parental investment).
Figure 37.19

40. Investigating life:
How does toxicity relate to parental investment?
Section 37.6
Why is birthing larger offspring
adaptive in a dark, toxic
environment? Researchers
speculate that large offspring
are better swimmers that can
more easily find food in the
dark and survive in the toxic
water.
Figure 37.19

41. Investigating life:
Habitat differentiation may lead to speciation
Section 37.6
Because of these
differences in life history
traits, subpopulations of
Atlantic mollies seldom
interbreed. They may
eventually become
unique species.
Figure 37.18
©Stephen Alvarez/National Geographic Creative/Getty Images